Merge branch 'bug6816_squashed_nowarn' of git://git.torproject.org/nickm/tor

36 files changed, 10581 insertions, 2253 deletions

diff --git a/src/or/Makefile.nmake b/src/or/Makefile.nmake
index 3181e79c2..677618e74 100644
--- a/src/or/Makefile.nmake
+++ b/src/or/Makefile.nmake
@@ -8,15 +8,15 @@ LIBS = ..\..\..\build-alpha\lib\libevent.a \
  ..\..\..\build-alpha\lib\libz.a \
  ws2_32.lib advapi32.lib shell32.lib
 
-LIBTOR_OBJECTS = buffers.obj circuitbuild.obj circuitlist.obj circuituse.obj \
+LIBTOR_OBJECTS = buffers.obj channel.obj channeltls.obj circuitbuild.obj \
+	circuitlist.obj circuitmux.obj circuitmux_ewma.obj circuituse.obj \
 	command.obj config.obj connection.obj connection_edge.obj \
 	connection_or.obj control.obj cpuworker.obj directory.obj \
-	dirserv.obj dirvote.obj dns.obj dnsserv.obj geoip.obj \
-	hibernate.obj main.obj microdesc.obj networkstatus.obj \
-	nodelist.obj onion.obj policies.obj reasons.obj relay.obj \
-	rendclient.obj rendcommon.obj rendmid.obj rendservice.obj \
-	rephist.obj router.obj routerlist.obj routerparse.obj status.obj \
-	config_codedigest.obj ntmain.obj
+	dirserv.obj dirvote.obj dns.obj dnsserv.obj geoip.obj hibernate.obj \
+	main.obj microdesc.obj networkstatus.obj nodelist.obj onion.obj \
+	policies.obj reasons.obj relay.obj rendclient.obj rendcommon.obj \
+	rendmid.obj rendservice.obj rephist.obj router.obj routerlist.obj \
+	routerparse.obj status.obj config_codedigest.obj ntmain.obj
 
 libtor.lib: $(LIBTOR_OBJECTS)
 	lib $(LIBTOR_OBJECTS) /out:libtor.lib
diff --git a/src/or/channel.c b/src/or/channel.c
new file mode 100644
index 000000000..b52db405e
--- /dev/null
+++ b/src/or/channel.c
@@ -0,0 +1,4086 @@
+/* * Copyright (c) 2012, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file channel.c
+ * \brief OR-to-OR channel abstraction layer
+ **/
+
+/*
+ * Define this so channel.h gives us things only channel_t subclasses
+ * should touch.
+ */
+
+#define _TOR_CHANNEL_INTERNAL
+
+#include "or.h"
+#include "channel.h"
+#include "channeltls.h"
+#include "circuitbuild.h"
+#include "circuitlist.h"
+#include "connection_or.h" /* For var_cell_free() */
+#include "circuitmux.h"
+#include "geoip.h"
+#include "nodelist.h"
+#include "relay.h"
+#include "rephist.h"
+#include "router.h"
+#include "routerlist.h"
+
+/* Cell queue structure */
+
+typedef struct cell_queue_entry_s cell_queue_entry_t;
+struct cell_queue_entry_s {
+  enum {
+    CELL_QUEUE_FIXED,
+    CELL_QUEUE_VAR,
+    CELL_QUEUE_PACKED
+  } type;
+  union {
+    struct {
+      cell_t *cell;
+    } fixed;
+    struct {
+      var_cell_t *var_cell;
+    } var;
+    struct {
+      packed_cell_t *packed_cell;
+    } packed;
+  } u;
+};
+
+/* Global lists of channels */
+
+/* All channel_t instances */
+static smartlist_t *all_channels = NULL;
+
+/* All channel_t instances not in ERROR or CLOSED states */
+static smartlist_t *active_channels = NULL;
+
+/* All channel_t instances in ERROR or CLOSED states */
+static smartlist_t *finished_channels = NULL;
+
+/* All channel_listener_t instances */
+static smartlist_t *all_listeners = NULL;
+
+/* All channel_listener_t instances in LISTENING state */
+static smartlist_t *active_listeners = NULL;
+
+/* All channel_listener_t instances in LISTENING state */
+static smartlist_t *finished_listeners = NULL;
+
+/* Counter for ID numbers */
+static uint64_t n_channels_allocated = 0;
+
+/* Digest->channel map
+ *
+ * Similar to the one used in connection_or.c, this maps from the identity
+ * digest of a remote endpoint to a channel_t to that endpoint.  Channels
+ * should be placed here when registered and removed when they close or error.
+ * If more than one channel exists, follow the next_with_same_id pointer
+ * as a linked list.
+ */
+static digestmap_t *channel_identity_map = NULL;
+
+static cell_queue_entry_t * cell_queue_entry_dup(cell_queue_entry_t *q);
+static void cell_queue_entry_free(cell_queue_entry_t *q, int handed_off);
+static int cell_queue_entry_is_padding(cell_queue_entry_t *q);
+static cell_queue_entry_t *
+cell_queue_entry_new_fixed(cell_t *cell);
+static cell_queue_entry_t *
+cell_queue_entry_new_var(var_cell_t *var_cell);
+
+/* Functions to maintain the digest map */
+static void channel_add_to_digest_map(channel_t *chan);
+static void channel_remove_from_digest_map(channel_t *chan);
+
+/*
+ * Flush cells from just the outgoing queue without trying to get them
+ * from circuits; used internall by channel_flush_some_cells().
+ */
+static ssize_t
+channel_flush_some_cells_from_outgoing_queue(channel_t *chan,
+                                             ssize_t num_cells);
+static void channel_force_free(channel_t *chan);
+static void
+channel_free_list(smartlist_t *channels, int mark_for_close);
+static void
+channel_listener_free_list(smartlist_t *channels, int mark_for_close);
+static void channel_listener_force_free(channel_listener_t *chan_l);
+static void
+channel_write_cell_queue_entry(channel_t *chan, cell_queue_entry_t *q);
+
+/***********************************
+ * Channel state utility functions *
+ **********************************/
+
+/**
+ * Indicate whether a given channel state is valid
+ */
+
+int
+channel_state_is_valid(channel_state_t state)
+{
+  int is_valid;
+
+  switch (state) {
+    case CHANNEL_STATE_CLOSED:
+    case CHANNEL_STATE_CLOSING:
+    case CHANNEL_STATE_ERROR:
+    case CHANNEL_STATE_MAINT:
+    case CHANNEL_STATE_OPENING:
+    case CHANNEL_STATE_OPEN:
+      is_valid = 1;
+      break;
+    case CHANNEL_STATE_LAST:
+    default:
+      is_valid = 0;
+  }
+
+  return is_valid;
+}
+
+/**
+ * Indicate whether a given channel listener state is valid
+ */
+
+int
+channel_listener_state_is_valid(channel_listener_state_t state)
+{
+  int is_valid;
+
+  switch (state) {
+    case CHANNEL_LISTENER_STATE_CLOSED:
+    case CHANNEL_LISTENER_STATE_LISTENING:
+    case CHANNEL_LISTENER_STATE_CLOSING:
+    case CHANNEL_LISTENER_STATE_ERROR:
+      is_valid = 1;
+      break;
+    case CHANNEL_LISTENER_STATE_LAST:
+    default:
+      is_valid = 0;
+  }
+
+  return is_valid;
+}
+
+/**
+ * Indicate whether a channel state transition is valid
+ *
+ * This function takes two channel states and indicates whether a
+ * transition between them is permitted (see the state definitions and
+ * transition table in or.h at the channel_state_t typedef).
+ */
+
+int
+channel_state_can_transition(channel_state_t from, channel_state_t to)
+{
+  int is_valid;
+
+  switch (from) {
+    case CHANNEL_STATE_CLOSED:
+      is_valid = (to == CHANNEL_STATE_OPENING);
+      break;
+    case CHANNEL_STATE_CLOSING:
+      is_valid = (to == CHANNEL_STATE_CLOSED ||
+                  to == CHANNEL_STATE_ERROR);
+      break;
+    case CHANNEL_STATE_ERROR:
+      is_valid = 0;
+      break;
+    case CHANNEL_STATE_MAINT:
+      is_valid = (to == CHANNEL_STATE_CLOSING ||
+                  to == CHANNEL_STATE_ERROR ||
+                  to == CHANNEL_STATE_OPEN);
+      break;
+    case CHANNEL_STATE_OPENING:
+      is_valid = (to == CHANNEL_STATE_CLOSING ||
+                  to == CHANNEL_STATE_ERROR ||
+                  to == CHANNEL_STATE_OPEN);
+      break;
+    case CHANNEL_STATE_OPEN:
+      is_valid = (to == CHANNEL_STATE_CLOSING ||
+                  to == CHANNEL_STATE_ERROR ||
+                  to == CHANNEL_STATE_MAINT);
+      break;
+    case CHANNEL_STATE_LAST:
+    default:
+      is_valid = 0;
+  }
+
+  return is_valid;
+}
+
+/**
+ * Indicate whether a channel listener state transition is valid
+ *
+ * This function takes two channel listener states and indicates whether a
+ * transition between them is permitted (see the state definitions and
+ * transition table in or.h at the channel_listener_state_t typedef).
+ */
+
+int
+channel_listener_state_can_transition(channel_listener_state_t from,
+                                      channel_listener_state_t to)
+{
+  int is_valid;
+
+  switch (from) {
+    case CHANNEL_LISTENER_STATE_CLOSED:
+      is_valid = (to == CHANNEL_LISTENER_STATE_LISTENING);
+      break;
+    case CHANNEL_LISTENER_STATE_CLOSING:
+      is_valid = (to == CHANNEL_LISTENER_STATE_CLOSED ||
+                  to == CHANNEL_LISTENER_STATE_ERROR);
+      break;
+    case CHANNEL_LISTENER_STATE_ERROR:
+      is_valid = 0;
+      break;
+    case CHANNEL_LISTENER_STATE_LISTENING:
+      is_valid = (to == CHANNEL_LISTENER_STATE_CLOSING ||
+                  to == CHANNEL_LISTENER_STATE_ERROR);
+      break;
+    case CHANNEL_LISTENER_STATE_LAST:
+    default:
+      is_valid = 0;
+  }
+
+  return is_valid;
+}
+
+/**
+ * Return a human-readable description for a channel state
+ */
+
+const char *
+channel_state_to_string(channel_state_t state)
+{
+  const char *descr;
+
+  switch (state) {
+    case CHANNEL_STATE_CLOSED:
+      descr = "closed";
+      break;
+    case CHANNEL_STATE_CLOSING:
+      descr = "closing";
+      break;
+    case CHANNEL_STATE_ERROR:
+      descr = "channel error";
+      break;
+    case CHANNEL_STATE_MAINT:
+      descr = "temporarily suspended for maintenance";
+      break;
+    case CHANNEL_STATE_OPENING:
+      descr = "opening";
+      break;
+    case CHANNEL_STATE_OPEN:
+      descr = "open";
+      break;
+    case CHANNEL_STATE_LAST:
+    default:
+      descr = "unknown or invalid channel state";
+  }
+
+  return descr;
+}
+
+/**
+ * Return a human-readable description for a channel listenier state
+ */
+
+const char *
+channel_listener_state_to_string(channel_listener_state_t state)
+{
+  const char *descr;
+
+  switch (state) {
+    case CHANNEL_LISTENER_STATE_CLOSED:
+      descr = "closed";
+      break;
+    case CHANNEL_LISTENER_STATE_CLOSING:
+      descr = "closing";
+      break;
+    case CHANNEL_LISTENER_STATE_ERROR:
+      descr = "channel listener error";
+      break;
+    case CHANNEL_LISTENER_STATE_LISTENING:
+      descr = "listening";
+      break;
+    case CHANNEL_LISTENER_STATE_LAST:
+    default:
+      descr = "unknown or invalid channel listener state";
+  }
+
+  return descr;
+}
+
+/***************************************
+ * Channel registration/unregistration *
+ ***************************************/
+
+/**
+ * Register a channel
+ *
+ * This function registers a newly created channel in the global lists/maps
+ * of active channels.
+ */
+
+void
+channel_register(channel_t *chan)
+{
+  tor_assert(chan);
+
+  /* No-op if already registered */
+  if (chan->registered) return;
+
+  log_debug(LD_CHANNEL,
+            "Registering channel %p (ID " U64_FORMAT ") "
+            "in state %s (%d) with digest %s",
+            chan, U64_PRINTF_ARG(chan->global_identifier),
+            channel_state_to_string(chan->state), chan->state,
+            hex_str(chan->identity_digest, DIGEST_LEN));
+
+  /* Make sure we have all_channels, then add it */
+  if (!all_channels) all_channels = smartlist_new();
+  smartlist_add(all_channels, chan);
+
+  /* Is it finished? */
+  if (chan->state == CHANNEL_STATE_CLOSED ||
+      chan->state == CHANNEL_STATE_ERROR) {
+    /* Put it in the finished list, creating it if necessary */
+    if (!finished_channels) finished_channels = smartlist_new();
+    smartlist_add(finished_channels, chan);
+  } else {
+    /* Put it in the active list, creating it if necessary */
+    if (!active_channels) active_channels = smartlist_new();
+    smartlist_add(active_channels, chan);
+
+    if (chan->state != CHANNEL_STATE_CLOSING) {
+      /* It should have a digest set */
+      if (!tor_digest_is_zero(chan->identity_digest)) {
+        /* Yeah, we're good, add it to the map */
+        channel_add_to_digest_map(chan);
+      } else {
+        log_info(LD_CHANNEL,
+                "Channel %p (global ID " U64_FORMAT ") "
+                "in state %s (%d) registered with no identity digest",
+                chan, U64_PRINTF_ARG(chan->global_identifier),
+                channel_state_to_string(chan->state), chan->state);
+      }
+    }
+  }
+
+  /* Mark it as registered */
+  chan->registered = 1;
+}
+
+/**
+ * Unregister a channel
+ *
+ * This function removes a channel from the global lists and maps and is used
+ * when freeing a closed/errored channel.
+ */
+
+void
+channel_unregister(channel_t *chan)
+{
+  tor_assert(chan);
+
+  /* No-op if not registered */
+  if (!(chan->registered)) return;
+
+  /* Is it finished? */
+  if (chan->state == CHANNEL_STATE_CLOSED ||
+      chan->state == CHANNEL_STATE_ERROR) {
+    /* Get it out of the finished list */
+    if (finished_channels) smartlist_remove(finished_channels, chan);
+  } else {
+    /* Get it out of the active list */
+    if (active_channels) smartlist_remove(active_channels, chan);
+  }
+
+  /* Get it out of all_channels */
+ if (all_channels) smartlist_remove(all_channels, chan);
+
+  /* Mark it as unregistered */
+  chan->registered = 0;
+
+  /* Should it be in the digest map? */
+  if (!tor_digest_is_zero(chan->identity_digest) &&
+      !(chan->state == CHANNEL_STATE_CLOSING ||
+        chan->state == CHANNEL_STATE_CLOSED ||
+        chan->state == CHANNEL_STATE_ERROR)) {
+    /* Remove it */
+    channel_remove_from_digest_map(chan);
+  }
+}
+
+/**
+ * Register a channel listener
+ *
+ * This function registers a newly created channel listner in the global
+ * lists/maps of active channel listeners.
+ */
+
+void
+channel_listener_register(channel_listener_t *chan_l)
+{
+  tor_assert(chan_l);
+
+  /* No-op if already registered */
+  if (chan_l->registered) return;
+
+  log_debug(LD_CHANNEL,
+            "Registering channel listener %p (ID " U64_FORMAT ") "
+            "in state %s (%d)",
+            chan_l, U64_PRINTF_ARG(chan_l->global_identifier),
+            channel_listener_state_to_string(chan_l->state),
+            chan_l->state);
+
+  /* Make sure we have all_channels, then add it */
+  if (!all_listeners) all_listeners = smartlist_new();
+  smartlist_add(all_listeners, chan_l);
+
+  /* Is it finished? */
+  if (chan_l->state == CHANNEL_LISTENER_STATE_CLOSED ||
+      chan_l->state == CHANNEL_LISTENER_STATE_ERROR) {
+    /* Put it in the finished list, creating it if necessary */
+    if (!finished_listeners) finished_listeners = smartlist_new();
+    smartlist_add(finished_listeners, chan_l);
+  } else {
+    /* Put it in the active list, creating it if necessary */
+    if (!active_listeners) active_listeners = smartlist_new();
+    smartlist_add(active_listeners, chan_l);
+  }
+
+  /* Mark it as registered */
+  chan_l->registered = 1;
+}
+
+/**
+ * Unregister a channel listener
+ *
+ * This function removes a channel listener from the global lists and maps
+ * and is used when freeing a closed/errored channel listener.
+ */
+
+void
+channel_listener_unregister(channel_listener_t *chan_l)
+{
+  tor_assert(chan_l);
+
+  /* No-op if not registered */
+  if (!(chan_l->registered)) return;
+
+  /* Is it finished? */
+  if (chan_l->state == CHANNEL_LISTENER_STATE_CLOSED ||
+      chan_l->state == CHANNEL_LISTENER_STATE_ERROR) {
+    /* Get it out of the finished list */
+    if (finished_listeners) smartlist_remove(finished_listeners, chan_l);
+  } else {
+    /* Get it out of the active list */
+    if (active_listeners) smartlist_remove(active_listeners, chan_l);
+  }
+
+  /* Get it out of all_channels */
+ if (all_listeners) smartlist_remove(all_listeners, chan_l);
+
+  /* Mark it as unregistered */
+  chan_l->registered = 0;
+}
+
+/*********************************
+ * Channel digest map maintenance
+ *********************************/
+
+/**
+ * Add a channel to the digest map
+ *
+ * This function adds a channel to the digest map and inserts it into the
+ * correct linked list if channels with that remote endpoint identity digest
+ * already exist.
+ */
+
+static void
+channel_add_to_digest_map(channel_t *chan)
+{
+  channel_t *tmp;
+
+  tor_assert(chan);
+
+  /* Assert that the state makes sense */
+  tor_assert(!(chan->state == CHANNEL_STATE_CLOSING ||
+               chan->state == CHANNEL_STATE_CLOSED ||
+               chan->state == CHANNEL_STATE_ERROR));
+
+  /* Assert that there is a digest */
+  tor_assert(!tor_digest_is_zero(chan->identity_digest));
+
+  /* Allocate the identity map if we have to */
+  if (!channel_identity_map) channel_identity_map = digestmap_new();
+
+  /* Insert it */
+  tmp = digestmap_set(channel_identity_map,
+                      chan->identity_digest,
+                      chan);
+  if (tmp) {
+    /* There already was one, this goes at the head of the list */
+    chan->next_with_same_id = tmp;
+    chan->prev_with_same_id = NULL;
+    tmp->prev_with_same_id = chan;
+  } else {
+    /* First with this digest */
+    chan->next_with_same_id = NULL;
+    chan->prev_with_same_id = NULL;
+  }
+
+  log_debug(LD_CHANNEL,
+            "Added channel %p (global ID " U64_FORMAT ") "
+            "to identity map in state %s (%d) with digest %s",
+            chan, U64_PRINTF_ARG(chan->global_identifier),
+            channel_state_to_string(chan->state), chan->state,
+            hex_str(chan->identity_digest, DIGEST_LEN));
+}
+
+/**
+ * Remove a channel from the digest map
+ *
+ * This function removes a channel from the digest map and the linked list of
+ * channels for that digest if more than one exists.
+ */
+
+static void
+channel_remove_from_digest_map(channel_t *chan)
+{
+  channel_t *tmp;
+
+  tor_assert(chan);
+
+  /* Assert that there is a digest */
+  tor_assert(!tor_digest_is_zero(chan->identity_digest));
+
+  /* Make sure we have a map */
+  if (!channel_identity_map) {
+    /*
+     * No identity map, so we can't find it by definition.  This
+     * case is similar to digestmap_get() failing below.
+     */
+    log_warn(LD_BUG,
+             "Trying to remove channel %p (global ID " U64_FORMAT ") "
+             "with digest %s from identity map, but didn't have any identity "
+             "map",
+             chan, U64_PRINTF_ARG(chan->global_identifier),
+             hex_str(chan->identity_digest, DIGEST_LEN));
+    /* Clear out its next/prev pointers */
+    if (chan->next_with_same_id) {
+      chan->next_with_same_id->prev_with_same_id = chan->prev_with_same_id;
+    }
+    if (chan->prev_with_same_id) {
+      chan->prev_with_same_id->next_with_same_id = chan->next_with_same_id;
+    }
+    chan->next_with_same_id = NULL;
+    chan->prev_with_same_id = NULL;
+
+    return;
+  }
+
+  /* Look for it in the map */
+  tmp = digestmap_get(channel_identity_map, chan->identity_digest);
+  if (tmp) {
+    /* Okay, it's here */
+    /* Look for this channel */
+    while (tmp && tmp != chan) {
+      tmp = tmp->next_with_same_id;
+    }
+
+    if (tmp == chan) {
+      /* Found it, good */
+      if (chan->next_with_same_id) {
+        chan->next_with_same_id->prev_with_same_id = chan->prev_with_same_id;
+      }
+      /* else we're the tail of the list */
+      if (chan->prev_with_same_id) {
+        /* We're not the head of the list, so we can *just* unlink */
+        chan->prev_with_same_id->next_with_same_id = chan->next_with_same_id;
+      } else {
+        /* We're the head, so we have to point the digest map entry at our
+         * next if we have one, or remove it if we're also the tail */
+        if (chan->next_with_same_id) {
+          digestmap_set(channel_identity_map,
+                        chan->identity_digest,
+                        chan->next_with_same_id);
+        } else {
+          digestmap_remove(channel_identity_map,
+                           chan->identity_digest);
+        }
+      }
+
+      /* NULL out its next/prev pointers, and we're finished */
+      chan->next_with_same_id = NULL;
+      chan->prev_with_same_id = NULL;
+
+      log_debug(LD_CHANNEL,
+                "Removed channel %p (global ID " U64_FORMAT ") from "
+                "identity map in state %s (%d) with digest %s",
+                chan, U64_PRINTF_ARG(chan->global_identifier),
+                channel_state_to_string(chan->state), chan->state,
+                hex_str(chan->identity_digest, DIGEST_LEN));
+    } else {
+      /* This is not good */
+      log_warn(LD_BUG,
+               "Trying to remove channel %p (global ID " U64_FORMAT ") "
+               "with digest %s from identity map, but couldn't find it in "
+               "the list for that digest",
+               chan, U64_PRINTF_ARG(chan->global_identifier),
+               hex_str(chan->identity_digest, DIGEST_LEN));
+      /* Unlink it and hope for the best */
+      if (chan->next_with_same_id) {
+        chan->next_with_same_id->prev_with_same_id = chan->prev_with_same_id;
+      }
+      if (chan->prev_with_same_id) {
+        chan->prev_with_same_id->next_with_same_id = chan->next_with_same_id;
+      }
+      chan->next_with_same_id = NULL;
+      chan->prev_with_same_id = NULL;
+    }
+  } else {
+    /* Shouldn't happen */
+    log_warn(LD_BUG,
+             "Trying to remove channel %p (global ID " U64_FORMAT ") with "
+             "digest %s from identity map, but couldn't find any with "
+             "that digest",
+             chan, U64_PRINTF_ARG(chan->global_identifier),
+             hex_str(chan->identity_digest, DIGEST_LEN));
+    /* Clear out its next/prev pointers */
+    if (chan->next_with_same_id) {
+      chan->next_with_same_id->prev_with_same_id = chan->prev_with_same_id;
+    }
+    if (chan->prev_with_same_id) {
+      chan->prev_with_same_id->next_with_same_id = chan->next_with_same_id;
+    }
+    chan->next_with_same_id = NULL;
+    chan->prev_with_same_id = NULL;
+  }
+}
+
+/****************************
+ * Channel lookup functions *
+ ***************************/
+
+/**
+ * Find channel by global ID
+ *
+ * This function searches for a channel by the global_identifier assigned
+ * at initialization time.  This identifier is unique for the lifetime of the
+ * Tor process.
+ */
+
+channel_t *
+channel_find_by_global_id(uint64_t global_identifier)
+{
+  channel_t *rv = NULL;
+
+  if (all_channels && smartlist_len(all_channels) > 0) {
+    SMARTLIST_FOREACH_BEGIN(all_channels, channel_t *, curr) {
+      if (curr->global_identifier == global_identifier) {
+        rv = curr;
+        break;
+      }
+    } SMARTLIST_FOREACH_END(curr);
+  }
+
+  return rv;
+}
+
+/**
+ * Find channel by digest of the remote endpoint
+ *
+ * This function looks up a channel by the digest of its remote endpoint in
+ * the channel digest map.  It's possible that more than one channel to a
+ * given endpoint exists.  Use channel_next_with_digest() and
+ * channel_prev_with_digest() to walk the list.
+ */
+
+channel_t *
+channel_find_by_remote_digest(const char *identity_digest)
+{
+  channel_t *rv = NULL;
+
+  tor_assert(identity_digest);
+
+  /* Search for it in the identity map */
+  if (channel_identity_map) {
+    rv = digestmap_get(channel_identity_map, identity_digest);
+  }
+
+  return rv;
+}
+
+/**
+ * Get next channel with digest
+ *
+ * This function takes a channel and finds the next channel in the list
+ * with the same digest.
+ */
+
+channel_t *
+channel_next_with_digest(channel_t *chan)
+{
+  tor_assert(chan);
+
+  return chan->next_with_same_id;
+}
+
+/**
+ * Get previous channel with digest
+ *
+ * This function takes a channel and finds the previos channel in the list
+ * with the same digest.
+ */
+
+channel_t *
+channel_prev_with_digest(channel_t *chan)
+{
+  tor_assert(chan);
+
+  return chan->prev_with_same_id;
+}
+
+/**
+ * Initialize a channel
+ *
+ * This function should be called by subclasses to set up some per-channel
+ * variables.  I.e., this is the superclass constructor.  Before this, the
+ * channel should be allocated with tor_malloc_zero().
+ */
+
+void
+channel_init(channel_t *chan)
+{
+  tor_assert(chan);
+
+  /* Assign an ID and bump the counter */
+  chan->global_identifier = n_channels_allocated++;
+
+  /* Init timestamp */
+  chan->timestamp_last_added_nonpadding = time(NULL);
+
+  /* Init next_circ_id */
+  chan->next_circ_id = crypto_rand_int(1 << 15);
+
+  /* Timestamp it */
+  channel_timestamp_created(chan);
+}
+
+/**
+ * Initialize a channel listener
+ *
+ * This function should be called by subclasses to set up some per-channel
+ * variables.  I.e., this is the superclass constructor.  Before this, the
+ * channel listener should be allocated with tor_malloc_zero().
+ */
+
+void
+channel_init_listener(channel_listener_t *chan_l)
+{
+  tor_assert(chan_l);
+
+  /* Assign an ID and bump the counter */
+  chan_l->global_identifier = n_channels_allocated++;
+
+  /* Timestamp it */
+  channel_listener_timestamp_created(chan_l);
+}
+
+/**
+ * Free a channel; nothing outside of channel.c and subclasses should call
+ * this - it frees channels after they have closed and been unregistered.
+ */
+
+void
+channel_free(channel_t *chan)
+{
+  if (!chan) return;
+
+  /* It must be closed or errored */
+  tor_assert(chan->state == CHANNEL_STATE_CLOSED ||
+             chan->state == CHANNEL_STATE_ERROR);
+  /* It must be deregistered */
+  tor_assert(!(chan->registered));
+
+  /* Call a free method if there is one */
+  if (chan->free) chan->free(chan);
+
+  channel_clear_remote_end(chan);
+
+  if (chan->cmux) {
+    circuitmux_detach_all_circuits(chan->cmux);
+    circuitmux_free(chan->cmux);
+    chan->cmux = NULL;
+  }
+
+  /* We're in CLOSED or ERROR, so the cell queue is already empty */
+
+  tor_free(chan);
+}
+
+/**
+ * Free a channel listener; nothing outside of channel.c and subclasses
+ * should call this - it frees channel listeners after they have closed and
+ * been unregistered.
+ */
+
+void
+channel_listener_free(channel_listener_t *chan_l)
+{
+  if (!chan_l) return;
+
+  /* It must be closed or errored */
+  tor_assert(chan_l->state == CHANNEL_LISTENER_STATE_CLOSED ||
+             chan_l->state == CHANNEL_LISTENER_STATE_ERROR);
+  /* It must be deregistered */
+  tor_assert(!(chan_l->registered));
+
+  /* Call a free method if there is one */
+  if (chan_l->free) chan_l->free(chan_l);
+
+  /*
+   * We're in CLOSED or ERROR, so the incoming channel queue is already
+   * empty.
+   */
+
+  tor_free(chan_l);
+}
+
+/**
+ * Free a channel and skip the state/registration asserts; this internal-
+ * use-only function should be called only from channel_free_all() when
+ * shutting down the Tor process.
+ */
+
+static void
+channel_force_free(channel_t *chan)
+{
+  tor_assert(chan);
+
+  /* Call a free method if there is one */
+  if (chan->free) chan->free(chan);
+
+  channel_clear_remote_end(chan);
+
+  /* We might still have a cell queue; kill it */
+  if (chan->incoming_queue) {
+    SMARTLIST_FOREACH_BEGIN(chan->incoming_queue,
+                            cell_queue_entry_t *, q) {
+      cell_queue_entry_free(q, 0);
+    } SMARTLIST_FOREACH_END(q);
+
+    smartlist_free(chan->incoming_queue);
+    chan->incoming_queue = NULL;
+  }
+
+  /* Outgoing cell queue is similar, but we can have to free packed cells */
+  if (chan->outgoing_queue) {
+    SMARTLIST_FOREACH_BEGIN(chan->outgoing_queue,
+                            cell_queue_entry_t *, q) {
+      cell_queue_entry_free(q, 0);
+    } SMARTLIST_FOREACH_END(q);
+
+    smartlist_free(chan->outgoing_queue);
+    chan->outgoing_queue = NULL;
+  }
+
+  tor_free(chan);
+}
+
+/**
+ * Free a channel listener and skip the state/reigstration asserts; this
+ * internal-use-only function should be called only from channel_free_all()
+ * when shutting down the Tor process.
+ */
+
+static void
+channel_listener_force_free(channel_listener_t *chan_l)
+{
+  tor_assert(chan_l);
+
+  /* Call a free method if there is one */
+  if (chan_l->free) chan_l->free(chan_l);
+
+  /*
+   * The incoming list just gets emptied and freed; we request close on
+   * any channels we find there, but since we got called while shutting
+   * down they will get deregistered and freed elsewhere anyway.
+   */
+  if (chan_l->incoming_list) {
+    SMARTLIST_FOREACH_BEGIN(chan_l->incoming_list,
+                            channel_t *, qchan) {
+      channel_mark_for_close(qchan);
+    } SMARTLIST_FOREACH_END(qchan);
+
+    smartlist_free(chan_l->incoming_list);
+    chan_l->incoming_list = NULL;
+  }
+
+  tor_free(chan_l);
+}
+
+/**
+ * Return the current registered listener for a channel listener
+ *
+ * This function returns a function pointer to the current registered
+ * handler for new incoming channels on a channel listener.
+ */
+
+channel_listener_fn_ptr
+channel_listener_get_listener_fn(channel_listener_t *chan_l)
+{
+  tor_assert(chan_l);
+
+  if (chan_l->state == CHANNEL_LISTENER_STATE_LISTENING)
+    return chan_l->listener;
+
+  return NULL;
+}
+
+/**
+ * Set the listener for a channel listener
+ *
+ * This function sets the handler for new incoming channels on a channel
+ * listener.
+ */
+
+void
+channel_listener_set_listener_fn(channel_listener_t *chan_l,
+                                channel_listener_fn_ptr listener)
+{
+  tor_assert(chan_l);
+  tor_assert(chan_l->state == CHANNEL_LISTENER_STATE_LISTENING);
+
+  log_debug(LD_CHANNEL,
+           "Setting listener callback for channel listener %p "
+           "(global ID " U64_FORMAT ") to %p",
+           chan_l, U64_PRINTF_ARG(chan_l->global_identifier),
+           listener);
+
+  chan_l->listener = listener;
+  if (chan_l->listener) channel_listener_process_incoming(chan_l);
+}
+
+/**
+ * Return the fixed-length cell handler for a channel
+ *
+ * This function gets the handler for incoming fixed-length cells installed
+ * on a channel.
+ */
+
+channel_cell_handler_fn_ptr
+channel_get_cell_handler(channel_t *chan)
+{
+  tor_assert(chan);
+
+  if (chan->state == CHANNEL_STATE_OPENING ||
+      chan->state == CHANNEL_STATE_OPEN ||
+      chan->state == CHANNEL_STATE_MAINT)
+    return chan->cell_handler;
+
+  return NULL;
+}
+
+/**
+ * Return the variable-length cell handler for a channel
+ *
+ * This function gets the handler for incoming variable-length cells
+ * installed on a channel.
+ */
+
+channel_var_cell_handler_fn_ptr
+channel_get_var_cell_handler(channel_t *chan)
+{
+  tor_assert(chan);
+
+  if (chan->state == CHANNEL_STATE_OPENING ||
+      chan->state == CHANNEL_STATE_OPEN ||
+      chan->state == CHANNEL_STATE_MAINT)
+    return chan->var_cell_handler;
+
+  return NULL;
+}
+
+/**
+ * Set both cell handlers for a channel
+ *
+ * This function sets both the fixed-length and variable length cell handlers
+ * for a channel and processes any incoming cells that had been blocked in the
+ * queue because none were available.
+ */
+
+void
+channel_set_cell_handlers(channel_t *chan,
+                          channel_cell_handler_fn_ptr cell_handler,
+                          channel_var_cell_handler_fn_ptr
+                            var_cell_handler)
+{
+  int try_again = 0;
+
+  tor_assert(chan);
+  tor_assert(chan->state == CHANNEL_STATE_OPENING ||
+             chan->state == CHANNEL_STATE_OPEN ||
+             chan->state == CHANNEL_STATE_MAINT);
+
+  log_debug(LD_CHANNEL,
+           "Setting cell_handler callback for channel %p to %p",
+           chan, cell_handler);
+  log_debug(LD_CHANNEL,
+           "Setting var_cell_handler callback for channel %p to %p",
+           chan, var_cell_handler);
+
+  /* Should we try the queue? */
+  if (cell_handler &&
+      cell_handler != chan->cell_handler) try_again = 1;
+  if (var_cell_handler &&
+      var_cell_handler != chan->var_cell_handler) try_again = 1;
+
+  /* Change them */
+  chan->cell_handler = cell_handler;
+  chan->var_cell_handler = var_cell_handler;
+
+  /* Re-run the queue if we have one and there's any reason to */
+  if (chan->incoming_queue &&
+      (smartlist_len(chan->incoming_queue) > 0) &&
+      try_again &&
+      (chan->cell_handler ||
+       chan->var_cell_handler)) channel_process_cells(chan);
+}
+
+/**
+ * Mark a channel for closure
+ *
+ * This function tries to close a channel_t; it will go into the CLOSING
+ * state, and eventually the lower layer should put it into the CLOSED or
+ * ERROR state.  Then, channel_run_cleanup() will eventually free it.
+ */
+
+void
+channel_mark_for_close(channel_t *chan)
+{
+  tor_assert(chan != NULL);
+  tor_assert(chan->close != NULL);
+
+  /* If it's already in CLOSING, CLOSED or ERROR, this is a no-op */
+  if (chan->state == CHANNEL_STATE_CLOSING ||
+      chan->state == CHANNEL_STATE_CLOSED ||
+      chan->state == CHANNEL_STATE_ERROR) return;
+
+  log_debug(LD_CHANNEL,
+            "Closing channel %p (global ID " U64_FORMAT ") "
+            "by request",
+            chan, U64_PRINTF_ARG(chan->global_identifier));
+
+  /* Note closing by request from above */
+  chan->reason_for_closing = CHANNEL_CLOSE_REQUESTED;
+
+  /* Change state to CLOSING */
+  channel_change_state(chan, CHANNEL_STATE_CLOSING);
+
+  /* Tell the lower layer */
+  chan->close(chan);
+
+  /*
+   * It's up to the lower layer to change state to CLOSED or ERROR when we're
+   * ready; we'll try to free channels that are in the finished list from
+   * channel_run_cleanup().  The lower layer should do this by calling
+   * channel_closed().
+   */
+}
+
+/**
+ * Mark a channel listener for closure
+ *
+ * This function tries to close a channel_listener_t; it will go into the
+ * CLOSING state, and eventually the lower layer should put it into the CLOSED
+ * or ERROR state.  Then, channel_run_cleanup() will eventually free it.
+ */
+
+void
+channel_listener_mark_for_close(channel_listener_t *chan_l)
+{
+  tor_assert(chan_l != NULL);
+  tor_assert(chan_l->close != NULL);
+
+  /* If it's already in CLOSING, CLOSED or ERROR, this is a no-op */
+  if (chan_l->state == CHANNEL_LISTENER_STATE_CLOSING ||
+      chan_l->state == CHANNEL_LISTENER_STATE_CLOSED ||
+      chan_l->state == CHANNEL_LISTENER_STATE_ERROR) return;
+
+  log_debug(LD_CHANNEL,
+            "Closing channel listener %p (global ID " U64_FORMAT ") "
+            "by request",
+            chan_l, U64_PRINTF_ARG(chan_l->global_identifier));
+
+  /* Note closing by request from above */
+  chan_l->reason_for_closing = CHANNEL_LISTENER_CLOSE_REQUESTED;
+
+  /* Change state to CLOSING */
+  channel_listener_change_state(chan_l, CHANNEL_LISTENER_STATE_CLOSING);
+
+  /* Tell the lower layer */
+  chan_l->close(chan_l);
+
+  /*
+   * It's up to the lower layer to change state to CLOSED or ERROR when we're
+   * ready; we'll try to free channels that are in the finished list from
+   * channel_run_cleanup().  The lower layer should do this by calling
+   * channel_listener_closed().
+   */
+}
+
+/**
+ * Close a channel from the lower layer
+ *
+ * Notify the channel code that the channel is being closed due to a non-error
+ * condition in the lower layer.  This does not call the close() method, since
+ * the lower layer already knows.
+ */
+
+void
+channel_close_from_lower_layer(channel_t *chan)
+{
+  tor_assert(chan != NULL);
+
+  /* If it's already in CLOSING, CLOSED or ERROR, this is a no-op */
+  if (chan->state == CHANNEL_STATE_CLOSING ||
+      chan->state == CHANNEL_STATE_CLOSED ||
+      chan->state == CHANNEL_STATE_ERROR) return;
+
+  log_debug(LD_CHANNEL,
+            "Closing channel %p (global ID " U64_FORMAT ") "
+            "due to lower-layer event",
+            chan, U64_PRINTF_ARG(chan->global_identifier));
+
+  /* Note closing by event from below */
+  chan->reason_for_closing = CHANNEL_CLOSE_FROM_BELOW;
+
+  /* Change state to CLOSING */
+  channel_change_state(chan, CHANNEL_STATE_CLOSING);
+}
+
+/**
+ * Close a channel listener from the lower layer
+ *
+ * Notify the channel code that the channel listener is being closed due to a
+ * non-error condition in the lower layer.  This does not call the close()
+ * method, since the lower layer already knows.
+ */
+
+void
+channel_listener_close_from_lower_layer(channel_listener_t *chan_l)
+{
+  tor_assert(chan_l != NULL);
+
+  /* If it's already in CLOSING, CLOSED or ERROR, this is a no-op */
+  if (chan_l->state == CHANNEL_LISTENER_STATE_CLOSING ||
+      chan_l->state == CHANNEL_LISTENER_STATE_CLOSED ||
+      chan_l->state == CHANNEL_LISTENER_STATE_ERROR) return;
+
+  log_debug(LD_CHANNEL,
+            "Closing channel listener %p (global ID " U64_FORMAT ") "
+            "due to lower-layer event",
+            chan_l, U64_PRINTF_ARG(chan_l->global_identifier));
+
+  /* Note closing by event from below */
+  chan_l->reason_for_closing = CHANNEL_LISTENER_CLOSE_FROM_BELOW;
+
+  /* Change state to CLOSING */
+  channel_listener_change_state(chan_l, CHANNEL_LISTENER_STATE_CLOSING);
+}
+
+/**
+ * Notify that the channel is being closed due to an error condition
+ *
+ * This function is called by the lower layer implementing the transport
+ * when a channel must be closed due to an error condition.  This does not
+ * call the channel's close method, since the lower layer already knows.
+ */
+
+void
+channel_close_for_error(channel_t *chan)
+{
+  tor_assert(chan != NULL);
+
+  /* If it's already in CLOSING, CLOSED or ERROR, this is a no-op */
+  if (chan->state == CHANNEL_STATE_CLOSING ||
+      chan->state == CHANNEL_STATE_CLOSED ||
+      chan->state == CHANNEL_STATE_ERROR) return;
+
+  log_debug(LD_CHANNEL,
+            "Closing channel %p due to lower-layer error",
+            chan);
+
+  /* Note closing by event from below */
+  chan->reason_for_closing = CHANNEL_CLOSE_FOR_ERROR;
+
+  /* Change state to CLOSING */
+  channel_change_state(chan, CHANNEL_STATE_CLOSING);
+}
+
+/**
+ * Notify that the channel listener is being closed due to an error condition
+ *
+ * This function is called by the lower layer implementing the transport
+ * when a channel listener must be closed due to an error condition.  This
+ * does not call the channel listener's close method, since the lower layer
+ * already knows.
+ */
+
+void
+channel_listener_close_for_error(channel_listener_t *chan_l)
+{
+  tor_assert(chan_l != NULL);
+
+  /* If it's already in CLOSING, CLOSED or ERROR, this is a no-op */
+  if (chan_l->state == CHANNEL_LISTENER_STATE_CLOSING ||
+      chan_l->state == CHANNEL_LISTENER_STATE_CLOSED ||
+      chan_l->state == CHANNEL_LISTENER_STATE_ERROR) return;
+
+  log_debug(LD_CHANNEL,
+            "Closing channel listener %p (global ID " U64_FORMAT ") "
+            "due to lower-layer error",
+            chan_l, U64_PRINTF_ARG(chan_l->global_identifier));
+
+  /* Note closing by event from below */
+  chan_l->reason_for_closing = CHANNEL_LISTENER_CLOSE_FOR_ERROR;
+
+  /* Change state to CLOSING */
+  channel_listener_change_state(chan_l, CHANNEL_LISTENER_STATE_CLOSING);
+}
+
+/**
+ * Notify that the lower layer is finished closing the channel
+ *
+ * This function should be called by the lower layer when a channel
+ * is finished closing and it should be regarded as inactive and
+ * freed by the channel code.
+ */
+
+void
+channel_closed(channel_t *chan)
+{
+  tor_assert(chan);
+  tor_assert(chan->state == CHANNEL_STATE_CLOSING ||
+             chan->state == CHANNEL_STATE_CLOSED ||
+             chan->state == CHANNEL_STATE_ERROR);
+
+  /* No-op if already inactive */
+  if (chan->state == CHANNEL_STATE_CLOSED ||
+      chan->state == CHANNEL_STATE_ERROR) return;
+
+  if (chan->reason_for_closing == CHANNEL_CLOSE_FOR_ERROR) {
+    /* Inform any pending (not attached) circs that they should
+     * give up. */
+    circuit_n_chan_done(chan, 0);
+  }
+  /* Now close all the attached circuits on it. */
+  circuit_unlink_all_from_channel(chan, END_CIRC_REASON_CHANNEL_CLOSED);
+
+  if (chan->reason_for_closing != CHANNEL_CLOSE_FOR_ERROR) {
+    channel_change_state(chan, CHANNEL_STATE_CLOSED);
+  } else {
+    channel_change_state(chan, CHANNEL_STATE_ERROR);
+  }
+}
+
+/**
+ * Notify that the lower layer is finished closing the channel listener
+ *
+ * This function should be called by the lower layer when a channel listener
+ * is finished closing and it should be regarded as inactive and
+ * freed by the channel code.
+ */
+
+void
+channel_listener_closed(channel_listener_t *chan_l)
+{
+  tor_assert(chan_l);
+  tor_assert(chan_l->state == CHANNEL_LISTENER_STATE_CLOSING ||
+             chan_l->state == CHANNEL_LISTENER_STATE_CLOSED ||
+             chan_l->state == CHANNEL_LISTENER_STATE_ERROR);
+
+  /* No-op if already inactive */
+  if (chan_l->state == CHANNEL_LISTENER_STATE_CLOSED ||
+      chan_l->state == CHANNEL_LISTENER_STATE_ERROR) return;
+
+  if (chan_l->reason_for_closing != CHANNEL_LISTENER_CLOSE_FOR_ERROR) {
+    channel_listener_change_state(chan_l, CHANNEL_LISTENER_STATE_CLOSED);
+  } else {
+    channel_listener_change_state(chan_l, CHANNEL_LISTENER_STATE_ERROR);
+  }
+}
+
+/**
+ * Clear the identity_digest of a channel
+ *
+ * This function clears the identity digest of the remote endpoint for a
+ * channel; this is intended for use by the lower layer.
+ */
+
+void
+channel_clear_identity_digest(channel_t *chan)
+{
+  int state_not_in_map;
+
+  tor_assert(chan);
+
+  log_debug(LD_CHANNEL,
+            "Clearing remote endpoint digest on channel %p with "
+            "global ID " U64_FORMAT,
+            chan, U64_PRINTF_ARG(chan->global_identifier));
+
+  state_not_in_map =
+    (chan->state == CHANNEL_STATE_CLOSING ||
+     chan->state == CHANNEL_STATE_CLOSED ||
+     chan->state == CHANNEL_STATE_ERROR);
+
+  if (!state_not_in_map && chan->registered &&
+      !tor_digest_is_zero(chan->identity_digest))
+    /* if it's registered get it out of the digest map */
+    channel_remove_from_digest_map(chan);
+
+  memset(chan->identity_digest, 0,
+         sizeof(chan->identity_digest));
+}
+
+/**
+ * Set the identity_digest of a channel
+ *
+ * This function sets the identity digest of the remote endpoint for a
+ * channel; this is intended for use by the lower layer.
+ */
+
+void
+channel_set_identity_digest(channel_t *chan,
+                            const char *identity_digest)
+{
+  int was_in_digest_map, should_be_in_digest_map, state_not_in_map;
+
+  tor_assert(chan);
+
+  log_debug(LD_CHANNEL,
+            "Setting remote endpoint digest on channel %p with "
+            "global ID " U64_FORMAT " to digest %s",
+            chan, U64_PRINTF_ARG(chan->global_identifier),
+            identity_digest ?
+              hex_str(identity_digest, DIGEST_LEN) : "(null)");
+
+  state_not_in_map =
+    (chan->state == CHANNEL_STATE_CLOSING ||
+     chan->state == CHANNEL_STATE_CLOSED ||
+     chan->state == CHANNEL_STATE_ERROR);
+  was_in_digest_map =
+    !state_not_in_map &&
+    chan->registered &&
+    !tor_digest_is_zero(chan->identity_digest);
+  should_be_in_digest_map =
+    !state_not_in_map &&
+    chan->registered &&
+    (identity_digest &&
+     !tor_digest_is_zero(identity_digest));
+
+  if (was_in_digest_map)
+    /* We should always remove it; we'll add it back if we're writing
+     * in a new digest.
+     */
+    channel_remove_from_digest_map(chan);
+
+  if (identity_digest) {
+    memcpy(chan->identity_digest,
+           identity_digest,
+           sizeof(chan->identity_digest));
+  } else {
+    memset(chan->identity_digest, 0,
+           sizeof(chan->identity_digest));
+  }
+
+  /* Put it in the digest map if we should */
+  if (should_be_in_digest_map)
+    channel_add_to_digest_map(chan);
+}
+
+/**
+ * Clear the remote end metadata (identity_digest/nickname) of a channel
+ *
+ * This function clears all the remote end info from a channel; this is
+ * intended for use by the lower layer.
+ */
+
+void
+channel_clear_remote_end(channel_t *chan)
+{
+  int state_not_in_map;
+
+  tor_assert(chan);
+
+  log_debug(LD_CHANNEL,
+            "Clearing remote endpoint identity on channel %p with "
+            "global ID " U64_FORMAT,
+            chan, U64_PRINTF_ARG(chan->global_identifier));
+
+  state_not_in_map =
+    (chan->state == CHANNEL_STATE_CLOSING ||
+     chan->state == CHANNEL_STATE_CLOSED ||
+     chan->state == CHANNEL_STATE_ERROR);
+
+  if (!state_not_in_map && chan->registered &&
+      !tor_digest_is_zero(chan->identity_digest))
+    /* if it's registered get it out of the digest map */
+    channel_remove_from_digest_map(chan);
+
+  memset(chan->identity_digest, 0,
+         sizeof(chan->identity_digest));
+  tor_free(chan->nickname);
+}
+
+/**
+ * Set the remote end metadata (identity_digest/nickname) of a channel
+ *
+ * This function sets new remote end info on a channel; this is intended
+ * for use by the lower layer.
+ */
+
+void
+channel_set_remote_end(channel_t *chan,
+                       const char *identity_digest,
+                       const char *nickname)
+{
+  int was_in_digest_map, should_be_in_digest_map, state_not_in_map;
+
+  tor_assert(chan);
+
+  log_debug(LD_CHANNEL,
+            "Setting remote endpoint identity on channel %p with "
+            "global ID " U64_FORMAT " to nickname %s, digest %s",
+            chan, U64_PRINTF_ARG(chan->global_identifier),
+            nickname ? nickname : "(null)",
+            identity_digest ?
+              hex_str(identity_digest, DIGEST_LEN) : "(null)");
+
+  state_not_in_map =
+    (chan->state == CHANNEL_STATE_CLOSING ||
+     chan->state == CHANNEL_STATE_CLOSED ||
+     chan->state == CHANNEL_STATE_ERROR);
+  was_in_digest_map =
+    !state_not_in_map &&
+    chan->registered &&
+    !tor_digest_is_zero(chan->identity_digest);
+  should_be_in_digest_map =
+    !state_not_in_map &&
+    chan->registered &&
+    (identity_digest &&
+     !tor_digest_is_zero(identity_digest));
+
+  if (was_in_digest_map)
+    /* We should always remove it; we'll add it back if we're writing
+     * in a new digest.
+     */
+    channel_remove_from_digest_map(chan);
+
+  if (identity_digest) {
+    memcpy(chan->identity_digest,
+           identity_digest,
+           sizeof(chan->identity_digest));
+
+  } else {
+    memset(chan->identity_digest, 0,
+           sizeof(chan->identity_digest));
+  }
+
+  tor_free(chan->nickname);
+  if (nickname)
+    chan->nickname = tor_strdup(nickname);
+
+  /* Put it in the digest map if we should */
+  if (should_be_in_digest_map)
+    channel_add_to_digest_map(chan);
+}
+
+/**
+ * Duplicate a cell queue entry; this is a shallow copy intended for use
+ * in channel_write_cell_queue_entry().
+ */
+
+static cell_queue_entry_t *
+cell_queue_entry_dup(cell_queue_entry_t *q)
+{
+  cell_queue_entry_t *rv = NULL;
+
+  tor_assert(q);
+
+  rv = tor_malloc(sizeof(*rv));
+  memcpy(rv, q, sizeof(*rv));
+
+  return rv;
+}
+
+/**
+ * Free a cell_queue_entry_t; the handed_off parameter indicates whether
+ * the contents were passed to the lower layer (it is responsible for
+ * them) or not (we should free).
+ */
+
+static void
+cell_queue_entry_free(cell_queue_entry_t *q, int handed_off)
+{
+  if (!q) return;
+
+  if (!handed_off) {
+    /*
+     * If we handed it off, the recipient becomes responsible (or
+     * with packed cells the channel_t subclass calls packed_cell
+     * free after writing out its contents; see, e.g.,
+     * channel_tls_write_packed_cell_method().  Otherwise, we have
+     * to take care of it here if possible.
+     */
+    switch (q->type) {
+      case CELL_QUEUE_FIXED:
+        if (q->u.fixed.cell) {
+          /*
+           * There doesn't seem to be a cell_free() function anywhere in the
+           * pre-channel code; just use tor_free()
+           */
+          tor_free(q->u.fixed.cell);
+        }
+        break;
+      case CELL_QUEUE_PACKED:
+        if (q->u.packed.packed_cell) {
+          packed_cell_free(q->u.packed.packed_cell);
+        }
+        break;
+      case CELL_QUEUE_VAR:
+        if (q->u.var.var_cell) {
+          /*
+           * This one's in connection_or.c; it'd be nice to figure out the
+           * whole flow of cells from one end to the other and factor the
+           * cell memory management functions like this out of the specific
+           * TLS lower layer.
+           */
+          var_cell_free(q->u.var.var_cell);
+        }
+        break;
+      default:
+        /*
+         * Nothing we can do if we don't know the type; this will
+         * have been warned about elsewhere.
+         */
+        break;
+    }
+  }
+  tor_free(q);
+}
+
+/**
+ * Check whether a cell queue entry is padding; this is a helper function
+ * for channel_write_cell_queue_entry()
+ */
+
+static int
+cell_queue_entry_is_padding(cell_queue_entry_t *q)
+{
+  tor_assert(q);
+
+  if (q->type == CELL_QUEUE_FIXED) {
+    if (q->u.fixed.cell) {
+      if (q->u.fixed.cell->command == CELL_PADDING ||
+          q->u.fixed.cell->command == CELL_VPADDING) {
+        return 1;
+      }
+    }
+  } else if (q->type == CELL_QUEUE_VAR) {
+    if (q->u.var.var_cell) {
+      if (q->u.var.var_cell->command == CELL_PADDING ||
+          q->u.var.var_cell->command == CELL_VPADDING) {
+        return 1;
+      }
+    }
+  }
+
+  return 0;
+}
+
+/**
+ * Allocate a new cell queue entry for a fixed-size cell
+ */
+
+static cell_queue_entry_t *
+cell_queue_entry_new_fixed(cell_t *cell)
+{
+  cell_queue_entry_t *q = NULL;
+
+  tor_assert(cell);
+
+  q = tor_malloc(sizeof(*q));
+  q->type = CELL_QUEUE_FIXED;
+  q->u.fixed.cell = cell;
+
+  return q;
+}
+
+/**
+ * Allocate a new cell queue entry for a variable-size cell
+ */
+
+static cell_queue_entry_t *
+cell_queue_entry_new_var(var_cell_t *var_cell)
+{
+  cell_queue_entry_t *q = NULL;
+
+  tor_assert(var_cell);
+
+  q = tor_malloc(sizeof(*q));
+  q->type = CELL_QUEUE_VAR;
+  q->u.var.var_cell = var_cell;
+
+  return q;
+}
+
+/**
+ * Write to a channel based on a cell_queue_entry_t
+ *
+ * Given a cell_queue_entry_t filled out by the caller, try to send the cell
+ * and queue it if we can't.
+ */
+
+static void
+channel_write_cell_queue_entry(channel_t *chan, cell_queue_entry_t *q)
+{
+  int result = 0, sent = 0;
+  cell_queue_entry_t *tmp = NULL;
+
+  tor_assert(chan);
+  tor_assert(q);
+
+  /* Assert that the state makes sense for a cell write */
+  tor_assert(chan->state == CHANNEL_STATE_OPENING ||
+             chan->state == CHANNEL_STATE_OPEN ||
+             chan->state == CHANNEL_STATE_MAINT);
+
+  /* Increment the timestamp unless it's padding */
+  if (!cell_queue_entry_is_padding(q)) {
+    chan->timestamp_last_added_nonpadding = approx_time();
+  }
+
+  /* Can we send it right out?  If so, try */
+  if (!(chan->outgoing_queue &&
+        (smartlist_len(chan->outgoing_queue) > 0)) &&
+       chan->state == CHANNEL_STATE_OPEN) {
+    /* Pick the right write function for this cell type and save the result */
+    switch (q->type) {
+      case CELL_QUEUE_FIXED:
+        tor_assert(chan->write_cell);
+        tor_assert(q->u.fixed.cell);
+        result = chan->write_cell(chan, q->u.fixed.cell);
+        break;
+      case CELL_QUEUE_PACKED:
+        tor_assert(chan->write_packed_cell);
+        tor_assert(q->u.packed.packed_cell);
+        result = chan->write_packed_cell(chan, q->u.packed.packed_cell);
+        break;
+      case CELL_QUEUE_VAR:
+        tor_assert(chan->write_var_cell);
+        tor_assert(q->u.var.var_cell);
+        result = chan->write_var_cell(chan, q->u.var.var_cell);
+        break;
+      default:
+        tor_assert(1);
+    }
+
+    /* Check if we got it out */
+    if (result > 0) {
+      sent = 1;
+      /* Timestamp for transmission */
+      channel_timestamp_xmit(chan);
+      /* If we're here the queue is empty, so it's drained too */
+      channel_timestamp_drained(chan);
+      /* Update the counter */
+      ++(chan->n_cells_xmitted);
+    }
+  }
+
+  if (!sent) {
+    /* Not sent, queue it */
+    if (!(chan->outgoing_queue))
+      chan->outgoing_queue = smartlist_new();
+    /*
+     * We have to copy the queue entry passed in, since the caller probably
+     * used the stack.
+     */
+    tmp = cell_queue_entry_dup(q);
+    smartlist_add(chan->outgoing_queue, tmp);
+    /* Try to process the queue? */
+    if (chan->state == CHANNEL_STATE_OPEN) channel_flush_cells(chan);
+  }
+}
+
+/**
+ * Write a cell to a channel
+ *
+ * Write a fixed-length cell to a channel using the write_cell() method.
+ * This is equivalent to the pre-channels connection_or_write_cell_to_buf();
+ * it is called by the transport-independent code to deliver a cell to a
+ * channel for transmission.
+ */
+
+void
+channel_write_cell(channel_t *chan, cell_t *cell)
+{
+  cell_queue_entry_t q;
+
+  tor_assert(chan);
+  tor_assert(cell);
+
+  log_debug(LD_CHANNEL,
+            "Writing cell_t %p to channel %p with global ID "
+            U64_FORMAT,
+            cell, chan, U64_PRINTF_ARG(chan->global_identifier));
+
+  q.type = CELL_QUEUE_FIXED;
+  q.u.fixed.cell = cell;
+  channel_write_cell_queue_entry(chan, &q);
+}
+
+/**
+ * Write a packed cell to a channel
+ *
+ * Write a packed cell to a channel using the write_cell() method.  This is
+ * called by the transport-independent code to deliver a packed cell to a
+ * channel for transmission.
+ */
+
+void
+channel_write_packed_cell(channel_t *chan, packed_cell_t *packed_cell)
+{
+  cell_queue_entry_t q;
+
+  tor_assert(chan);
+  tor_assert(packed_cell);
+
+  log_debug(LD_CHANNEL,
+            "Writing packed_cell_t %p to channel %p with global ID "
+            U64_FORMAT,
+            packed_cell, chan,
+            U64_PRINTF_ARG(chan->global_identifier));
+
+  q.type = CELL_QUEUE_PACKED;
+  q.u.packed.packed_cell = packed_cell;
+  channel_write_cell_queue_entry(chan, &q);
+}
+
+/**
+ * Write a variable-length cell to a channel
+ *
+ * Write a variable-length cell to a channel using the write_cell() method.
+ * This is equivalent to the pre-channels
+ * connection_or_write_var_cell_to_buf(); it's called by the transport-
+ * independent code to deliver a var_cell to a channel for transmission.
+ */
+
+void
+channel_write_var_cell(channel_t *chan, var_cell_t *var_cell)
+{
+  cell_queue_entry_t q;
+
+  tor_assert(chan);
+  tor_assert(var_cell);
+
+  log_debug(LD_CHANNEL,
+            "Writing var_cell_t %p to channel %p with global ID "
+            U64_FORMAT,
+            var_cell, chan,
+            U64_PRINTF_ARG(chan->global_identifier));
+
+  q.type = CELL_QUEUE_VAR;
+  q.u.var.var_cell = var_cell;
+  channel_write_cell_queue_entry(chan, &q);
+}
+
+/**
+ * Change channel state
+ *
+ * This internal and subclass use only function is used to change channel
+ * state, performing all transition validity checks and whatever actions
+ * are appropriate to the state transition in question.
+ */
+
+void
+channel_change_state(channel_t *chan, channel_state_t to_state)
+{
+  channel_state_t from_state;
+  unsigned char was_active, is_active;
+  unsigned char was_in_id_map, is_in_id_map;
+
+  tor_assert(chan);
+  from_state = chan->state;
+
+  tor_assert(channel_state_is_valid(from_state));
+  tor_assert(channel_state_is_valid(to_state));
+  tor_assert(channel_state_can_transition(chan->state, to_state));
+
+  /* Check for no-op transitions */
+  if (from_state == to_state) {
+    log_debug(LD_CHANNEL,
+              "Got no-op transition from \"%s\" to itself on channel %p"
+              "(global ID " U64_FORMAT ")",
+              channel_state_to_string(to_state),
+              chan, U64_PRINTF_ARG(chan->global_identifier));
+    return;
+  }
+
+  /* If we're going to a closing or closed state, we must have a reason set */
+  if (to_state == CHANNEL_STATE_CLOSING ||
+      to_state == CHANNEL_STATE_CLOSED ||
+      to_state == CHANNEL_STATE_ERROR) {
+    tor_assert(chan->reason_for_closing != CHANNEL_NOT_CLOSING);
+  }
+
+  /*
+   * We need to maintain the queues here for some transitions:
+   * when we enter CHANNEL_STATE_OPEN (especially from CHANNEL_STATE_MAINT)
+   * we may have a backlog of cells to transmit, so drain the queues in
+   * that case, and when going to CHANNEL_STATE_CLOSED the subclass
+   * should have made sure to finish sending things (or gone to
+   * CHANNEL_STATE_ERROR if not possible), so we assert for that here.
+   */
+
+  log_debug(LD_CHANNEL,
+            "Changing state of channel %p (global ID " U64_FORMAT
+            ") from \"%s\" to \"%s\"",
+            chan,
+            U64_PRINTF_ARG(chan->global_identifier),
+            channel_state_to_string(chan->state),
+            channel_state_to_string(to_state));
+
+  chan->state = to_state;
+
+  /* Need to add to the right lists if the channel is registered */
+  if (chan->registered) {
+    was_active = !(from_state == CHANNEL_STATE_CLOSED ||
+                   from_state == CHANNEL_STATE_ERROR);
+    is_active = !(to_state == CHANNEL_STATE_CLOSED ||
+                  to_state == CHANNEL_STATE_ERROR);
+
+    /* Need to take off active list and put on finished list? */
+    if (was_active && !is_active) {
+      if (active_channels) smartlist_remove(active_channels, chan);
+      if (!finished_channels) finished_channels = smartlist_new();
+      smartlist_add(finished_channels, chan);
+    }
+    /* Need to put on active list? */
+    else if (!was_active && is_active) {
+      if (finished_channels) smartlist_remove(finished_channels, chan);
+      if (!active_channels) active_channels = smartlist_new();
+      smartlist_add(active_channels, chan);
+    }
+
+    if (!tor_digest_is_zero(chan->identity_digest)) {
+      /* Now we need to handle the identity map */
+      was_in_id_map = !(from_state == CHANNEL_STATE_CLOSING ||
+                        from_state == CHANNEL_STATE_CLOSED ||
+                        from_state == CHANNEL_STATE_ERROR);
+      is_in_id_map = !(to_state == CHANNEL_STATE_CLOSING ||
+                       to_state == CHANNEL_STATE_CLOSED ||
+                       to_state == CHANNEL_STATE_ERROR);
+
+      if (!was_in_id_map && is_in_id_map) channel_add_to_digest_map(chan);
+      else if (was_in_id_map && !is_in_id_map)
+        channel_remove_from_digest_map(chan);
+    }
+  }
+
+  /* Tell circuits if we opened and stuff */
+  if (to_state == CHANNEL_STATE_OPEN) {
+    channel_do_open_actions(chan);
+
+    /* Check for queued cells to process */
+    if (chan->incoming_queue &&
+        smartlist_len(chan->incoming_queue) > 0)
+      channel_process_cells(chan);
+    if (chan->outgoing_queue &&
+        smartlist_len(chan->outgoing_queue) > 0)
+      channel_flush_cells(chan);
+  } else if (to_state == CHANNEL_STATE_CLOSED ||
+             to_state == CHANNEL_STATE_ERROR) {
+    /* Assert that all queues are empty */
+    tor_assert(!(chan->incoming_queue) ||
+                smartlist_len(chan->incoming_queue) == 0);
+    tor_assert(!(chan->outgoing_queue) ||
+                smartlist_len(chan->outgoing_queue) == 0);
+  }
+}
+
+/**
+ * Change channel listener state
+ *
+ * This internal and subclass use only function is used to change channel
+ * listener state, performing all transition validity checks and whatever
+ * actions are appropriate to the state transition in question.
+ */
+
+void
+channel_listener_change_state(channel_listener_t *chan_l,
+                              channel_listener_state_t to_state)
+{
+  channel_listener_state_t from_state;
+  unsigned char was_active, is_active;
+
+  tor_assert(chan_l);
+  from_state = chan_l->state;
+
+  tor_assert(channel_listener_state_is_valid(from_state));
+  tor_assert(channel_listener_state_is_valid(to_state));
+  tor_assert(channel_listener_state_can_transition(chan_l->state, to_state));
+
+  /* Check for no-op transitions */
+  if (from_state == to_state) {
+    log_debug(LD_CHANNEL,
+              "Got no-op transition from \"%s\" to itself on channel "
+              "listener %p (global ID " U64_FORMAT ")",
+              channel_listener_state_to_string(to_state),
+              chan_l, U64_PRINTF_ARG(chan_l->global_identifier));
+    return;
+  }
+
+  /* If we're going to a closing or closed state, we must have a reason set */
+  if (to_state == CHANNEL_LISTENER_STATE_CLOSING ||
+      to_state == CHANNEL_LISTENER_STATE_CLOSED ||
+      to_state == CHANNEL_LISTENER_STATE_ERROR) {
+    tor_assert(chan_l->reason_for_closing != CHANNEL_LISTENER_NOT_CLOSING);
+  }
+
+  /*
+   * We need to maintain the queues here for some transitions:
+   * when we enter CHANNEL_STATE_OPEN (especially from CHANNEL_STATE_MAINT)
+   * we may have a backlog of cells to transmit, so drain the queues in
+   * that case, and when going to CHANNEL_STATE_CLOSED the subclass
+   * should have made sure to finish sending things (or gone to
+   * CHANNEL_STATE_ERROR if not possible), so we assert for that here.
+   */
+
+  log_debug(LD_CHANNEL,
+            "Changing state of channel listener %p (global ID " U64_FORMAT
+            "from \"%s\" to \"%s\"",
+            chan_l, U64_PRINTF_ARG(chan_l->global_identifier),
+            channel_listener_state_to_string(chan_l->state),
+            channel_listener_state_to_string(to_state));
+
+  chan_l->state = to_state;
+
+  /* Need to add to the right lists if the channel listener is registered */
+  if (chan_l->registered) {
+    was_active = !(from_state == CHANNEL_LISTENER_STATE_CLOSED ||
+                   from_state == CHANNEL_LISTENER_STATE_ERROR);
+    is_active = !(to_state == CHANNEL_LISTENER_STATE_CLOSED ||
+                  to_state == CHANNEL_LISTENER_STATE_ERROR);
+
+    /* Need to take off active list and put on finished list? */
+    if (was_active && !is_active) {
+      if (active_listeners) smartlist_remove(active_listeners, chan_l);
+      if (!finished_listeners) finished_listeners = smartlist_new();
+      smartlist_add(finished_listeners, chan_l);
+    }
+    /* Need to put on active list? */
+    else if (!was_active && is_active) {
+      if (finished_listeners) smartlist_remove(finished_listeners, chan_l);
+      if (!active_listeners) active_listeners = smartlist_new();
+      smartlist_add(active_listeners, chan_l);
+    }
+  }
+
+  if (to_state == CHANNEL_LISTENER_STATE_CLOSED ||
+      to_state == CHANNEL_LISTENER_STATE_ERROR) {
+    /* Assert that the queue is empty */
+    tor_assert(!(chan_l->incoming_list) ||
+                smartlist_len(chan_l->incoming_list) == 0);
+  }
+}
+
+/**
+ * Try to flush cells to the lower layer
+ *
+ * this is called by the lower layer to indicate that it wants more cells;
+ * it will try to write up to num_cells cells from the channel's cell queue or
+ * from circuits active on that channel, or as many as it has available if
+ * num_cells == -1.
+ */
+
+#define MAX_CELLS_TO_GET_FROM_CIRCUITS_FOR_UNLIMITED 256
+
+ssize_t
+channel_flush_some_cells(channel_t *chan, ssize_t num_cells)
+{
+  unsigned int unlimited = 0;
+  ssize_t flushed = 0;
+  int num_cells_from_circs, clamped_num_cells;
+
+  tor_assert(chan);
+
+  if (num_cells < 0) unlimited = 1;
+  if (!unlimited && num_cells <= flushed) goto done;
+
+  /* If we aren't in CHANNEL_STATE_OPEN, nothing goes through */
+  if (chan->state == CHANNEL_STATE_OPEN) {
+    /* Try to flush as much as we can that's already queued */
+    flushed += channel_flush_some_cells_from_outgoing_queue(chan,
+        (unlimited ? -1 : num_cells - flushed));
+    if (!unlimited && num_cells <= flushed) goto done;
+
+    if (circuitmux_num_cells(chan->cmux) > 0) {
+      /* Calculate number of cells, including clamp */
+      if (unlimited) {
+        clamped_num_cells = MAX_CELLS_TO_GET_FROM_CIRCUITS_FOR_UNLIMITED;
+      } else {
+        if (num_cells - flushed >
+            MAX_CELLS_TO_GET_FROM_CIRCUITS_FOR_UNLIMITED) {
+          clamped_num_cells = MAX_CELLS_TO_GET_FROM_CIRCUITS_FOR_UNLIMITED;
+        } else {
+          clamped_num_cells = (int)(num_cells - flushed);
+        }
+      }
+      /* Try to get more cells from any active circuits */
+      num_cells_from_circs = channel_flush_from_first_active_circuit(
+          chan, clamped_num_cells);
+
+      /* If it claims we got some, process the queue again */
+      if (num_cells_from_circs > 0) {
+        flushed += channel_flush_some_cells_from_outgoing_queue(chan,
+          (unlimited ? -1 : num_cells - flushed));
+      }
+    }
+  }
+
+ done:
+  return flushed;
+}
+
+/**
+ * Flush cells from just the channel's outgoing cell queue
+ *
+ * This gets called from channel_flush_some_cells() above to flush cells
+ * just from the queue without trying for active_circuits.
+ */
+
+static ssize_t
+channel_flush_some_cells_from_outgoing_queue(channel_t *chan,
+                                             ssize_t num_cells)
+{
+  unsigned int unlimited = 0;
+  ssize_t flushed = 0;
+  cell_queue_entry_t *q = NULL;
+
+  tor_assert(chan);
+  tor_assert(chan->write_cell);
+  tor_assert(chan->write_packed_cell);
+  tor_assert(chan->write_var_cell);
+
+  if (num_cells < 0) unlimited = 1;
+  if (!unlimited && num_cells <= flushed) return 0;
+
+  /* If we aren't in CHANNEL_STATE_OPEN, nothing goes through */
+  if (chan->state == CHANNEL_STATE_OPEN) {
+    while ((unlimited || num_cells > flushed) &&
+           (chan->outgoing_queue &&
+            (smartlist_len(chan->outgoing_queue) > 0))) {
+      /*
+       * Ewww, smartlist_del_keeporder() is O(n) in list length; maybe a
+       * a linked list would make more sense for the queue.
+       */
+
+      /* Get the head of the queue */
+      q = smartlist_get(chan->outgoing_queue, 0);
+      if (q) {
+        /*
+         * Okay, we have a good queue entry, try to give it to the lower
+         * layer.
+         */
+        switch (q->type) {
+          case CELL_QUEUE_FIXED:
+            if (q->u.fixed.cell) {
+              if (chan->write_cell(chan,
+                    q->u.fixed.cell)) {
+                ++flushed;
+                channel_timestamp_xmit(chan);
+                ++(chan->n_cells_xmitted);
+                cell_queue_entry_free(q, 1);
+                q = NULL;
+              }
+              /* Else couldn't write it; leave it on the queue */
+            } else {
+              /* This shouldn't happen */
+              log_info(LD_CHANNEL,
+                       "Saw broken cell queue entry of type CELL_QUEUE_FIXED "
+                       "with no cell on channel %p "
+                       "(global ID " U64_FORMAT ").",
+                       chan, U64_PRINTF_ARG(chan->global_identifier));
+              /* Throw it away */
+              cell_queue_entry_free(q, 0);
+              q = NULL;
+            }
+            break;
+         case CELL_QUEUE_PACKED:
+            if (q->u.packed.packed_cell) {
+              if (chan->write_packed_cell(chan,
+                    q->u.packed.packed_cell)) {
+                ++flushed;
+                channel_timestamp_xmit(chan);
+                ++(chan->n_cells_xmitted);
+                cell_queue_entry_free(q, 1);
+                q = NULL;
+              }
+              /* Else couldn't write it; leave it on the queue */
+            } else {
+              /* This shouldn't happen */
+              log_info(LD_CHANNEL,
+                       "Saw broken cell queue entry of type CELL_QUEUE_PACKED "
+                       "with no cell on channel %p "
+                       "(global ID " U64_FORMAT ").",
+                       chan, U64_PRINTF_ARG(chan->global_identifier));
+              /* Throw it away */
+              cell_queue_entry_free(q, 0);
+              q = NULL;
+            }
+            break;
+         case CELL_QUEUE_VAR:
+            if (q->u.var.var_cell) {
+              if (chan->write_var_cell(chan,
+                    q->u.var.var_cell)) {
+                ++flushed;
+                channel_timestamp_xmit(chan);
+                ++(chan->n_cells_xmitted);
+                cell_queue_entry_free(q, 1);
+                q = NULL;
+              }
+              /* Else couldn't write it; leave it on the queue */
+            } else {
+              /* This shouldn't happen */
+              log_info(LD_CHANNEL,
+                       "Saw broken cell queue entry of type CELL_QUEUE_VAR "
+                       "with no cell on channel %p "
+                       "(global ID " U64_FORMAT ").",
+                       chan, U64_PRINTF_ARG(chan->global_identifier));
+              /* Throw it away */
+              cell_queue_entry_free(q, 0);
+              q = NULL;
+            }
+            break;
+          default:
+            /* Unknown type, log and free it */
+            log_info(LD_CHANNEL,
+                     "Saw an unknown cell queue entry type %d on channel %p "
+                     "(global ID " U64_FORMAT "; ignoring it."
+                     "  Someone should fix this.",
+                     q->type, chan, U64_PRINTF_ARG(chan->global_identifier));
+            cell_queue_entry_free(q, 0);
+            q = NULL;
+        }
+      } else {
+        /* This shouldn't happen; log and throw it away */
+        log_info(LD_CHANNEL,
+                 "Saw a NULL entry in the outgoing cell queue on channel %p "
+                 "(global ID " U64_FORMAT "); this is definitely a bug.",
+                 chan, U64_PRINTF_ARG(chan->global_identifier));
+        /* q is already NULL, so we know to delete that queue entry */
+      }
+
+      /* if q got NULLed out, we used it and should remove the queue entry */
+      if (!q) smartlist_del_keeporder(chan->outgoing_queue, 0);
+      /* No cell removed from list, so we can't go on any further */
+      else break;
+    }
+  }
+
+  /* Did we drain the queue? */
+  if (!(chan->outgoing_queue) ||
+      smartlist_len(chan->outgoing_queue) == 0) {
+    /* Timestamp it */
+    channel_timestamp_drained(chan);
+  }
+
+  return flushed;
+}
+
+/**
+ * Flush as many cells as we possibly can from the queue
+ *
+ * This tries to flush as many cells from the queue as the lower layer
+ * will take.  It just calls channel_flush_some_cells_from_outgoing_queue()
+ * in unlimited mode.
+ */
+
+void
+channel_flush_cells(channel_t *chan)
+{
+  channel_flush_some_cells_from_outgoing_queue(chan, -1);
+}
+
+/**
+ * Check if any cells are available
+ *
+ * This gets used from the lower layer to check if any more cells are
+ * available.
+ */
+
+int
+channel_more_to_flush(channel_t *chan)
+{
+  tor_assert(chan);
+
+  /* Check if we have any queued */
+  if (chan->incoming_queue &&
+      smartlist_len(chan->incoming_queue) > 0) return 1;
+
+  /* Check if any circuits would like to queue some */
+  if (circuitmux_num_cells(chan->cmux) > 0) return 1;
+
+  /* Else no */
+  return 0;
+}
+
+/**
+ * Notify the channel we're done flushing the output in the lower layer
+ *
+ * Connection.c will call this when we've flushed the output; there's some
+ * dirreq-related maintenance to do.
+ */
+
+void
+channel_notify_flushed(channel_t *chan)
+{
+  tor_assert(chan);
+
+  if (chan->dirreq_id != 0)
+    geoip_change_dirreq_state(chan->dirreq_id,
+                              DIRREQ_TUNNELED,
+                              DIRREQ_CHANNEL_BUFFER_FLUSHED);
+}
+
+/**
+ * Process the queue of incoming channels on a listener
+ *
+ * Use a listener's registered callback to process as many entries in the
+ * queue of incoming channels as possible.
+ */
+
+void
+channel_listener_process_incoming(channel_listener_t *listener)
+{
+  tor_assert(listener);
+
+  /*
+   * CHANNEL_LISTENER_STATE_CLOSING permitted because we drain the queue
+   * while closing a listener.
+   */
+  tor_assert(listener->state == CHANNEL_LISTENER_STATE_LISTENING ||
+             listener->state == CHANNEL_LISTENER_STATE_CLOSING);
+  tor_assert(listener->listener);
+
+  log_debug(LD_CHANNEL,
+            "Processing queue of incoming connections for channel "
+            "listener %p (global ID " U64_FORMAT ")",
+            listener, U64_PRINTF_ARG(listener->global_identifier));
+
+  if (!(listener->incoming_list)) return;
+
+  SMARTLIST_FOREACH_BEGIN(listener->incoming_list,
+                          channel_t *, chan) {
+    tor_assert(chan);
+
+    log_debug(LD_CHANNEL,
+              "Handling incoming channel %p (" U64_FORMAT ") "
+              "for listener %p (" U64_FORMAT ")",
+              chan,
+              U64_PRINTF_ARG(chan->global_identifier),
+              listener,
+              U64_PRINTF_ARG(listener->global_identifier));
+    /* Make sure this is set correctly */
+    channel_mark_incoming(chan);
+    listener->listener(listener, chan);
+  } SMARTLIST_FOREACH_END(chan);
+
+  smartlist_free(listener->incoming_list);
+  listener->incoming_list = NULL;
+}
+
+/**
+ * Take actions required when a channel becomes open
+ *
+ * Handle actions we should do when we know a channel is open; a lot of
+ * this comes from the old connection_or_set_state_open() of connection_or.c.
+ *
+ * Because of this mechanism, future channel_t subclasses should take care
+ * not to change a channel to from CHANNEL_STATE_OPENING to CHANNEL_STATE_OPEN
+ * until there is positive confirmation that the network is operational.
+ * In particular, anything UDP-based should not make this transition until a
+ * packet is received from the other side.
+ */
+
+void
+channel_do_open_actions(channel_t *chan)
+{
+  tor_addr_t remote_addr;
+  int started_here, not_using = 0;
+  time_t now = time(NULL);
+
+  tor_assert(chan);
+
+  started_here = channel_is_outgoing(chan);
+
+  if (started_here) {
+    circuit_build_times_network_is_live(&circ_times);
+    rep_hist_note_connect_succeeded(chan->identity_digest, now);
+    if (entry_guard_register_connect_status(
+          chan->identity_digest, 1, 0, now) < 0) {
+      /* Close any circuits pending on this channel. We leave it in state
+       * 'open' though, because it didn't actually *fail* -- we just
+       * chose not to use it. */
+      log_debug(LD_OR,
+                "New entry guard was reachable, but closing this "
+                "connection so we can retry the earlier entry guards.");
+      circuit_n_chan_done(chan, 0);
+      not_using = 1;
+    }
+    router_set_status(chan->identity_digest, 1);
+  } else {
+    /* only report it to the geoip module if it's not a known router */
+    if (!router_get_by_id_digest(chan->identity_digest)) {
+      if (channel_get_addr_if_possible(chan, &remote_addr)) {
+        geoip_note_client_seen(GEOIP_CLIENT_CONNECT, &remote_addr,
+                               now);
+      }
+      /* Otherwise the underlying transport can't tell us this, so skip it */
+    }
+  }
+
+  if (!not_using) circuit_n_chan_done(chan, 1);
+}
+
+/**
+ * Queue an incoming channel on a listener
+ *
+ * Internal and subclass use only function to queue an incoming channel from
+ * a listener.  A subclass of channel_listener_t should call this when a new
+ * incoming channel is created.
+ */
+
+void
+channel_listener_queue_incoming(channel_listener_t *listener,
+                                channel_t *incoming)
+{
+  int need_to_queue = 0;
+
+  tor_assert(listener);
+  tor_assert(listener->state == CHANNEL_LISTENER_STATE_LISTENING);
+  tor_assert(incoming);
+
+  log_debug(LD_CHANNEL,
+            "Queueing incoming channel %p (global ID " U64_FORMAT ") on "
+            "channel listener %p (global ID " U64_FORMAT ")",
+            incoming, U64_PRINTF_ARG(incoming->global_identifier),
+            listener, U64_PRINTF_ARG(listener->global_identifier));
+
+  /* Do we need to queue it, or can we just call the listener right away? */
+  if (!(listener->listener)) need_to_queue = 1;
+  if (listener->incoming_list &&
+      (smartlist_len(listener->incoming_list) > 0))
+    need_to_queue = 1;
+
+  /* If we need to queue and have no queue, create one */
+  if (need_to_queue && !(listener->incoming_list)) {
+    listener->incoming_list = smartlist_new();
+  }
+
+  /* Bump the counter and timestamp it */
+  channel_listener_timestamp_active(listener);
+  channel_listener_timestamp_accepted(listener);
+  ++(listener->n_accepted);
+
+  /* If we don't need to queue, process it right away */
+  if (!need_to_queue) {
+    tor_assert(listener->listener);
+    listener->listener(listener, incoming);
+  }
+  /*
+   * Otherwise, we need to queue; queue and then process the queue if
+   * we can.
+   */
+  else {
+    tor_assert(listener->incoming_list);
+    smartlist_add(listener->incoming_list, incoming);
+    if (listener->listener) channel_listener_process_incoming(listener);
+  }
+}
+
+/**
+ * Process queued incoming cells
+ *
+ * Process as many queued cells as we can from the incoming
+ * cell queue.
+ */
+
+void
+channel_process_cells(channel_t *chan)
+{
+  tor_assert(chan);
+  tor_assert(chan->state == CHANNEL_STATE_CLOSING ||
+             chan->state == CHANNEL_STATE_MAINT ||
+             chan->state == CHANNEL_STATE_OPEN);
+
+  log_debug(LD_CHANNEL,
+            "Processing as many incoming cells as we can for channel %p",
+            chan);
+
+  /* Nothing we can do if we have no registered cell handlers */
+  if (!(chan->cell_handler ||
+        chan->var_cell_handler)) return;
+  /* Nothing we can do if we have no cells */
+  if (!(chan->incoming_queue)) return;
+
+  /*
+   * Process cells until we're done or find one we have no current handler
+   * for.
+   */
+  SMARTLIST_FOREACH_BEGIN(chan->incoming_queue,
+                          cell_queue_entry_t *, q) {
+    tor_assert(q);
+    tor_assert(q->type == CELL_QUEUE_FIXED ||
+               q->type == CELL_QUEUE_VAR);
+
+    if (q->type == CELL_QUEUE_FIXED &&
+        chan->cell_handler) {
+      /* Handle a fixed-length cell */
+      tor_assert(q->u.fixed.cell);
+      log_debug(LD_CHANNEL,
+                "Processing incoming cell_t %p for channel %p (global ID "
+                U64_FORMAT ")",
+                q->u.fixed.cell, chan,
+                U64_PRINTF_ARG(chan->global_identifier));
+      chan->cell_handler(chan, q->u.fixed.cell);
+      SMARTLIST_DEL_CURRENT(chan->incoming_queue, q);
+      tor_free(q);
+    } else if (q->type == CELL_QUEUE_VAR &&
+               chan->var_cell_handler) {
+      /* Handle a variable-length cell */
+      tor_assert(q->u.var.var_cell);
+      log_debug(LD_CHANNEL,
+                "Processing incoming var_cell_t %p for channel %p (global ID "
+                U64_FORMAT ")",
+                q->u.var.var_cell, chan,
+                U64_PRINTF_ARG(chan->global_identifier));
+      chan->var_cell_handler(chan, q->u.var.var_cell);
+      SMARTLIST_DEL_CURRENT(chan->incoming_queue, q);
+      tor_free(q);
+    } else {
+      /* Can't handle this one */
+      break;
+    }
+  } SMARTLIST_FOREACH_END(q);
+
+  /* If the list is empty, free it */
+  if (smartlist_len(chan->incoming_queue) == 0 ) {
+    smartlist_free(chan->incoming_queue);
+    chan->incoming_queue = NULL;
+  }
+}
+
+/**
+ * Queue incoming cell
+ *
+ * This should be called by a channel_t subclass to queue an incoming fixed-
+ * length cell for processing, and process it if possible.
+ */
+
+void
+channel_queue_cell(channel_t *chan, cell_t *cell)
+{
+  int need_to_queue = 0;
+  cell_queue_entry_t *q;
+
+  tor_assert(chan);
+  tor_assert(cell);
+  tor_assert(chan->state == CHANNEL_STATE_OPEN);
+
+  /* Do we need to queue it, or can we just call the handler right away? */
+  if (!(chan->cell_handler)) need_to_queue = 1;
+  if (chan->incoming_queue &&
+      (smartlist_len(chan->incoming_queue) > 0))
+    need_to_queue = 1;
+
+  /* If we need to queue and have no queue, create one */
+  if (need_to_queue && !(chan->incoming_queue)) {
+    chan->incoming_queue = smartlist_new();
+  }
+
+  /* Timestamp for receiving */
+  channel_timestamp_recv(chan);
+
+  /* Update the counter */
+  ++(chan->n_cells_recved);
+
+  /* If we don't need to queue we can just call cell_handler */
+  if (!need_to_queue) {
+    tor_assert(chan->cell_handler);
+    log_debug(LD_CHANNEL,
+              "Directly handling incoming cell_t %p for channel %p "
+              "(global ID " U64_FORMAT ")",
+              cell, chan,
+              U64_PRINTF_ARG(chan->global_identifier));
+    chan->cell_handler(chan, cell);
+  } else {
+    /* Otherwise queue it and then process the queue if possible. */
+    tor_assert(chan->incoming_queue);
+    q = cell_queue_entry_new_fixed(cell);
+    log_debug(LD_CHANNEL,
+              "Queueing incoming cell_t %p for channel %p "
+              "(global ID " U64_FORMAT ")",
+              cell, chan,
+              U64_PRINTF_ARG(chan->global_identifier));
+    smartlist_add(chan->incoming_queue, q);
+    if (chan->cell_handler ||
+        chan->var_cell_handler) {
+      channel_process_cells(chan);
+    }
+  }
+}
+
+/**
+ * Queue incoming variable-length cell
+ *
+ * This should be called by a channel_t subclass to queue an incoming
+ * variable-length cell for processing, and process it if possible.
+ */
+
+void
+channel_queue_var_cell(channel_t *chan, var_cell_t *var_cell)
+{
+  int need_to_queue = 0;
+  cell_queue_entry_t *q;
+
+  tor_assert(chan);
+  tor_assert(var_cell);
+  tor_assert(chan->state == CHANNEL_STATE_OPEN);
+
+  /* Do we need to queue it, or can we just call the handler right away? */
+  if (!(chan->var_cell_handler)) need_to_queue = 1;
+  if (chan->incoming_queue &&
+      (smartlist_len(chan->incoming_queue) > 0))
+    need_to_queue = 1;
+
+  /* If we need to queue and have no queue, create one */
+  if (need_to_queue && !(chan->incoming_queue)) {
+    chan->incoming_queue = smartlist_new();
+  }
+
+  /* Timestamp for receiving */
+  channel_timestamp_recv(chan);
+
+  /* Update the counter */
+  ++(chan->n_cells_recved);
+
+  /* If we don't need to queue we can just call cell_handler */
+  if (!need_to_queue) {
+    tor_assert(chan->var_cell_handler);
+    log_debug(LD_CHANNEL,
+              "Directly handling incoming var_cell_t %p for channel %p "
+              "(global ID " U64_FORMAT ")",
+              var_cell, chan,
+              U64_PRINTF_ARG(chan->global_identifier));
+    chan->var_cell_handler(chan, var_cell);
+  } else {
+    /* Otherwise queue it and then process the queue if possible. */
+    tor_assert(chan->incoming_queue);
+    q = cell_queue_entry_new_var(var_cell);
+    log_debug(LD_CHANNEL,
+              "Queueing incoming var_cell_t %p for channel %p "
+              "(global ID " U64_FORMAT ")",
+              var_cell, chan,
+              U64_PRINTF_ARG(chan->global_identifier));
+    smartlist_add(chan->incoming_queue, q);
+    if (chan->cell_handler ||
+        chan->var_cell_handler) {
+      channel_process_cells(chan);
+    }
+  }
+}
+
+/**
+ * Send destroy cell on a channel
+ *
+ * Write a destroy cell with circ ID <b>circ_id</b> and reason <b>reason</b>
+ * onto channel <b>chan</b>.  Don't perform range-checking on reason:
+ * we may want to propagate reasons from other cells.
+ */
+
+int
+channel_send_destroy(circid_t circ_id, channel_t *chan, int reason)
+{
+  cell_t cell;
+
+  tor_assert(chan);
+
+  memset(&cell, 0, sizeof(cell_t));
+  cell.circ_id = circ_id;
+  cell.command = CELL_DESTROY;
+  cell.payload[0] = (uint8_t) reason;
+  log_debug(LD_OR,
+            "Sending destroy (circID %d) on channel %p "
+            "(global ID " U64_FORMAT ")",
+            circ_id, chan,
+            U64_PRINTF_ARG(chan->global_identifier));
+
+  channel_write_cell(chan, &cell);
+
+  return 0;
+}
+
+/**
+ * Dump channel statistics to the log
+ *
+ * This is called from dumpstats() in main.c and spams the log with
+ * statistics on channels.
+ */
+
+void
+channel_dumpstats(int severity)
+{
+  if (all_channels && smartlist_len(all_channels) > 0) {
+    log(severity, LD_GENERAL,
+        "Dumping statistics about %d channels:",
+        smartlist_len(all_channels));
+    log(severity, LD_GENERAL,
+        "%d are active, and %d are done and waiting for cleanup",
+        (active_channels != NULL) ?
+          smartlist_len(active_channels) : 0,
+        (finished_channels != NULL) ?
+          smartlist_len(finished_channels) : 0);
+
+    SMARTLIST_FOREACH(all_channels, channel_t *, chan,
+                      channel_dump_statistics(chan, severity));
+
+    log(severity, LD_GENERAL,
+        "Done spamming about channels now");
+  } else {
+    log(severity, LD_GENERAL,
+        "No channels to dump");
+  }
+}
+
+/**
+ * Dump channel listener statistics to the log
+ *
+ * This is called from dumpstats() in main.c and spams the log with
+ * statistics on channel listeners.
+ */
+
+void
+channel_listener_dumpstats(int severity)
+{
+  if (all_listeners && smartlist_len(all_listeners) > 0) {
+    log(severity, LD_GENERAL,
+        "Dumping statistics about %d channel listeners:",
+        smartlist_len(all_listeners));
+    log(severity, LD_GENERAL,
+        "%d are active and %d are done and waiting for cleanup",
+        (active_listeners != NULL) ?
+          smartlist_len(active_listeners) : 0,
+        (finished_listeners != NULL) ?
+          smartlist_len(finished_listeners) : 0);
+
+    SMARTLIST_FOREACH(all_listeners, channel_listener_t *, chan_l,
+                      channel_listener_dump_statistics(chan_l, severity));
+
+    log(severity, LD_GENERAL,
+        "Done spamming about channel listeners now");
+  } else {
+    log(severity, LD_GENERAL,
+        "No channel listeners to dump");
+  }
+}
+
+/**
+ * Set the cmux policy on all active channels
+ */
+
+void
+channel_set_cmux_policy_everywhere(circuitmux_policy_t *pol)
+{
+  if (!active_channels) return;
+
+  SMARTLIST_FOREACH_BEGIN(active_channels, channel_t *, curr) {
+    if (curr->cmux) {
+      circuitmux_set_policy(curr->cmux, pol);
+    }
+  } SMARTLIST_FOREACH_END(curr);
+}
+
+/**
+ * Clean up channels
+ *
+ * This gets called periodically from run_scheduled_events() in main.c;
+ * it cleans up after closed channels.
+ */
+
+void
+channel_run_cleanup(void)
+{
+  channel_t *tmp = NULL;
+
+  /* Check if we need to do anything */
+  if (!finished_channels || smartlist_len(finished_channels) == 0) return;
+
+  /* Iterate through finished_channels and get rid of them */
+  SMARTLIST_FOREACH_BEGIN(finished_channels, channel_t *, curr) {
+    tmp = curr;
+    /* Remove it from the list */
+    SMARTLIST_DEL_CURRENT(finished_channels, curr);
+    /* Also unregister it */
+    channel_unregister(tmp);
+    /* ... and free it */
+    channel_free(tmp);
+  } SMARTLIST_FOREACH_END(curr);
+}
+
+/**
+ * Clean up channel listeners
+ *
+ * This gets called periodically from run_scheduled_events() in main.c;
+ * it cleans up after closed channel listeners.
+ */
+
+void
+channel_listener_run_cleanup(void)
+{
+  channel_listener_t *tmp = NULL;
+
+  /* Check if we need to do anything */
+  if (!finished_listeners || smartlist_len(finished_listeners) == 0) return;
+
+  /* Iterate through finished_channels and get rid of them */
+  SMARTLIST_FOREACH_BEGIN(finished_listeners, channel_listener_t *, curr) {
+    tmp = curr;
+    /* Remove it from the list */
+    SMARTLIST_DEL_CURRENT(finished_listeners, curr);
+    /* Also unregister it */
+    channel_listener_unregister(tmp);
+    /* ... and free it */
+    channel_listener_free(tmp);
+  } SMARTLIST_FOREACH_END(curr);
+}
+
+/**
+ * Free a list of channels for channel_free_all()
+ */
+
+static void
+channel_free_list(smartlist_t *channels, int mark_for_close)
+{
+  if (!channels) return;
+
+  SMARTLIST_FOREACH_BEGIN(channels, channel_t *, curr) {
+    /* Deregister and free it */
+    tor_assert(curr);
+    log_debug(LD_CHANNEL,
+              "Cleaning up channel %p (global ID " U64_FORMAT ") "
+              "in state %s (%d)",
+              curr, U64_PRINTF_ARG(curr->global_identifier),
+              channel_state_to_string(curr->state), curr->state);
+    /* Detach circuits early so they can find the channel */
+    if (curr->cmux) {
+      circuitmux_detach_all_circuits(curr->cmux);
+    }
+    channel_unregister(curr);
+    if (mark_for_close) {
+      if (!(curr->state == CHANNEL_STATE_CLOSING ||
+            curr->state == CHANNEL_STATE_CLOSED ||
+            curr->state == CHANNEL_STATE_ERROR)) {
+        channel_mark_for_close(curr);
+      }
+      channel_force_free(curr);
+    } else channel_free(curr);
+  } SMARTLIST_FOREACH_END(curr);
+}
+
+/**
+ * Free a list of channel listeners for channel_free_all()
+ */
+
+static void
+channel_listener_free_list(smartlist_t *listeners, int mark_for_close)
+{
+  if (!listeners) return;
+
+  SMARTLIST_FOREACH_BEGIN(listeners, channel_listener_t *, curr) {
+    /* Deregister and free it */
+    tor_assert(curr);
+    log_debug(LD_CHANNEL,
+              "Cleaning up channel listener %p (global ID " U64_FORMAT ") "
+              "in state %s (%d)",
+              curr, U64_PRINTF_ARG(curr->global_identifier),
+              channel_listener_state_to_string(curr->state), curr->state);
+    channel_listener_unregister(curr);
+    if (mark_for_close) {
+      if (!(curr->state == CHANNEL_LISTENER_STATE_CLOSING ||
+            curr->state == CHANNEL_LISTENER_STATE_CLOSED ||
+            curr->state == CHANNEL_LISTENER_STATE_ERROR)) {
+        channel_listener_mark_for_close(curr);
+      }
+      channel_listener_force_free(curr);
+    } else channel_listener_free(curr);
+  } SMARTLIST_FOREACH_END(curr);
+}
+
+/**
+ * Close all channels and free everything
+ *
+ * This gets called from tor_free_all() in main.c to clean up on exit.
+ * It will close all registered channels and free associated storage,
+ * then free the all_channels, active_channels, listening_channels and
+ * finished_channels lists and also channel_identity_map.
+ */
+
+void
+channel_free_all(void)
+{
+  log_debug(LD_CHANNEL,
+            "Shutting down channels...");
+
+  /* First, let's go for finished channels */
+  if (finished_channels) {
+    channel_free_list(finished_channels, 0);
+    smartlist_free(finished_channels);
+    finished_channels = NULL;
+  }
+
+  /* Now the finished listeners */
+  if (finished_listeners) {
+    channel_listener_free_list(finished_listeners, 0);
+    smartlist_free(finished_listeners);
+    finished_listeners = NULL;
+  }
+
+  /* Now all active channels */
+  if (active_channels) {
+    channel_free_list(active_channels, 1);
+    smartlist_free(active_channels);
+    active_channels = NULL;
+  }
+
+  /* Now all active listeners */
+  if (active_listeners) {
+    channel_listener_free_list(active_listeners, 1);
+    smartlist_free(active_listeners);
+    active_listeners = NULL;
+  }
+
+  /* Now all channels, in case any are left over */
+  if (all_channels) {
+    channel_free_list(all_channels, 1);
+    smartlist_free(all_channels);
+    all_channels = NULL;
+  }
+
+  /* Now all listeners, in case any are left over */
+  if (all_listeners) {
+    channel_listener_free_list(all_listeners, 1);
+    smartlist_free(all_listeners);
+    all_listeners = NULL;
+  }
+
+  /* Now free channel_identity_map */
+  if (channel_identity_map) {
+    log_debug(LD_CHANNEL,
+              "Freeing channel_identity_map");
+    /* Geez, anything still left over just won't die ... let it leak then */
+    digestmap_free(channel_identity_map, NULL);
+    channel_identity_map = NULL;
+  }
+
+  log_debug(LD_CHANNEL,
+            "Done cleaning up after channels");
+}
+
+/**
+ * Connect to a given addr/port/digest
+ *
+ * This sets up a new outgoing channel; in the future if multiple
+ * channel_t subclasses are available, this is where the selection policy
+ * should go.  It may also be desirable to fold port into tor_addr_t
+ * or make a new type including a tor_addr_t and port, so we have a
+ * single abstract object encapsulating all the protocol details of
+ * how to contact an OR.
+ */
+
+channel_t *
+channel_connect(const tor_addr_t *addr, uint16_t port,
+                const char *id_digest)
+{
+  return channel_tls_connect(addr, port, id_digest);
+}
+
+/**
+ * Decide which of two channels to prefer for extending a circuit
+ *
+ * This function is called while extending a circuit and returns true iff
+ * a is 'better' than b.  The most important criterion here is that a
+ * canonical channel is always better than a non-canonical one, but the
+ * number of circuits and the age are used as tie-breakers.
+ *
+ * This is based on the former connection_or_is_better() of connection_or.c
+ */
+
+int
+channel_is_better(time_t now, channel_t *a, channel_t *b,
+                  int forgive_new_connections)
+{
+  int a_grace, b_grace;
+  int a_is_canonical, b_is_canonical;
+  int a_has_circs, b_has_circs;
+
+  /*
+   * Do not definitively deprecate a new channel with no circuits on it
+   * until this much time has passed.
+   */
+#define NEW_CHAN_GRACE_PERIOD (15*60)
+
+  tor_assert(a);
+  tor_assert(b);
+
+  /* Check if one is canonical and the other isn't first */
+  a_is_canonical = channel_is_canonical(a);
+  b_is_canonical = channel_is_canonical(b);
+
+  if (a_is_canonical && !b_is_canonical) return 1;
+  if (!a_is_canonical && b_is_canonical) return 0;
+
+  /*
+   * Okay, if we're here they tied on canonicity. Next we check if
+   * they have any circuits, and if one does and the other doesn't,
+   * we prefer the one that does, unless we are forgiving and the
+   * one that has no circuits is in its grace period.
+   */
+
+  a_has_circs = (channel_num_circuits(a) > 0);
+  b_has_circs = (channel_num_circuits(b) > 0);
+  a_grace = (forgive_new_connections &&
+             (now < channel_when_created(a) + NEW_CHAN_GRACE_PERIOD));
+  b_grace = (forgive_new_connections &&
+             (now < channel_when_created(b) + NEW_CHAN_GRACE_PERIOD));
+
+  if (a_has_circs && !b_has_circs && !b_grace) return 1;
+  if (!a_has_circs && b_has_circs && !a_grace) return 0;
+
+  /* They tied on circuits too; just prefer whichever is newer */
+
+  if (channel_when_created(a) > channel_when_created(b)) return 1;
+  else return 0;
+}
+
+/**
+ * Get a channel to extend a circuit
+ *
+ * Pick a suitable channel to extend a circuit to given the desired digest
+ * the address we believe is correct for that digest; this tries to see
+ * if we already have one for the requested endpoint, but if there is no good
+ * channel, set *msg_out to a message describing the channel's state
+ * and our next action, and set *launch_out to a boolean indicated whether
+ * the caller should try to launch a new channel with channel_connect().
+ */
+
+channel_t *
+channel_get_for_extend(const char *digest,
+                       const tor_addr_t *target_addr,
+                       const char **msg_out,
+                       int *launch_out)
+{
+  channel_t *chan, *best = NULL;
+  int n_inprogress_goodaddr = 0, n_old = 0;
+  int n_noncanonical = 0, n_possible = 0;
+  time_t now = approx_time();
+
+  tor_assert(msg_out);
+  tor_assert(launch_out);
+
+  if (!channel_identity_map) {
+    *msg_out = "Router not connected (nothing is).  Connecting.";
+    *launch_out = 1;
+    return NULL;
+  }
+
+  chan = channel_find_by_remote_digest(digest);
+
+  /* Walk the list, unrefing the old one and refing the new at each
+   * iteration.
+   */
+  for (; chan; chan = channel_next_with_digest(chan)) {
+    tor_assert(tor_memeq(chan->identity_digest,
+                         digest, DIGEST_LEN));
+
+    if (chan->state == CHANNEL_STATE_CLOSING ||
+        chan->state == CHANNEL_STATE_CLOSED ||
+        chan->state == CHANNEL_STATE_ERROR)
+      continue;
+
+    /* Never return a channel on which the other end appears to be
+     * a client. */
+    if (channel_is_client(chan)) {
+      continue;
+    }
+
+    /* Never return a non-open connection. */
+    if (chan->state != CHANNEL_STATE_OPEN) {
+      /* If the address matches, don't launch a new connection for this
+       * circuit. */
+      if (!channel_matches_target_addr_for_extend(chan, target_addr))
+        ++n_inprogress_goodaddr;
+      continue;
+    }
+
+    /* Never return a connection that shouldn't be used for circs. */
+    if (channel_is_bad_for_new_circs(chan)) {
+      ++n_old;
+      continue;
+    }
+
+    /* Never return a non-canonical connection using a recent link protocol
+     * if the address is not what we wanted.
+     *
+     * The channel_is_canonical_is_reliable() function asks the lower layer
+     * if we should trust channel_is_canonical().  The below is from the
+     * comments of the old circuit_or_get_for_extend() and applies when
+     * the lower-layer transport is channel_tls_t.
+     *
+     * (For old link protocols, we can't rely on is_canonical getting
+     * set properly if we're talking to the right address, since we might
+     * have an out-of-date descriptor, and we will get no NETINFO cell to
+     * tell us about the right address.)
+     */
+    if (!channel_is_canonical(chan) &&
+         channel_is_canonical_is_reliable(chan) &&
+        !channel_matches_target_addr_for_extend(chan, target_addr)) {
+      ++n_noncanonical;
+      continue;
+    }
+
+    ++n_possible;
+
+    if (!best) {
+      best = chan; /* If we have no 'best' so far, this one is good enough. */
+      continue;
+    }
+
+    if (channel_is_better(now, chan, best, 0))
+      best = chan;
+  }
+
+  if (best) {
+    *msg_out = "Connection is fine; using it.";
+    *launch_out = 0;
+    return best;
+  } else if (n_inprogress_goodaddr) {
+    *msg_out = "Connection in progress; waiting.";
+    *launch_out = 0;
+    return NULL;
+  } else if (n_old || n_noncanonical) {
+    *msg_out = "Connections all too old, or too non-canonical. "
+               " Launching a new one.";
+    *launch_out = 1;
+    return NULL;
+  } else {
+    *msg_out = "Not connected. Connecting.";
+    *launch_out = 1;
+    return NULL;
+  }
+}
+
+/**
+ * Describe the transport subclass for a channel
+ *
+ * Invoke a method to get a string description of the lower-layer
+ * transport for this channel.
+ */
+
+const char *
+channel_describe_transport(channel_t *chan)
+{
+  tor_assert(chan);
+  tor_assert(chan->describe_transport);
+
+  return chan->describe_transport(chan);
+}
+
+/**
+ * Describe the transport subclass for a channel listener
+ *
+ * Invoke a method to get a string description of the lower-layer
+ * transport for this channel listener.
+ */
+
+const char *
+channel_listener_describe_transport(channel_listener_t *chan_l)
+{
+  tor_assert(chan_l);
+  tor_assert(chan_l->describe_transport);
+
+  return chan_l->describe_transport(chan_l);
+}
+
+/**
+ * Dump channel statistics
+ *
+ * Dump statistics for one channel to the log
+ */
+
+void
+channel_dump_statistics(channel_t *chan, int severity)
+{
+  double avg, interval, age;
+  time_t now = time(NULL);
+  tor_addr_t remote_addr;
+  int have_remote_addr;
+  char *remote_addr_str;
+
+  tor_assert(chan);
+
+  age = (double)(now - chan->timestamp_created);
+
+  log(severity, LD_GENERAL,
+      "Channel " U64_FORMAT " (at %p) with transport %s is in state "
+      "%s (%d)",
+      U64_PRINTF_ARG(chan->global_identifier), chan,
+      channel_describe_transport(chan),
+      channel_state_to_string(chan->state), chan->state);
+  log(severity, LD_GENERAL,
+      " * Channel " U64_FORMAT " was created at " U64_FORMAT
+      " (" U64_FORMAT " seconds ago) "
+      "and last active at " U64_FORMAT " (" U64_FORMAT " seconds ago)",
+      U64_PRINTF_ARG(chan->global_identifier),
+      U64_PRINTF_ARG(chan->timestamp_created),
+      U64_PRINTF_ARG(now - chan->timestamp_created),
+      U64_PRINTF_ARG(chan->timestamp_active),
+      U64_PRINTF_ARG(now - chan->timestamp_active));
+
+  /* Handle digest and nickname */
+  if (!tor_digest_is_zero(chan->identity_digest)) {
+    if (chan->nickname) {
+      log(severity, LD_GENERAL,
+          " * Channel " U64_FORMAT " says it is connected "
+          "to an OR with digest %s and nickname %s",
+          U64_PRINTF_ARG(chan->global_identifier),
+          hex_str(chan->identity_digest, DIGEST_LEN),
+          chan->nickname);
+    } else {
+      log(severity, LD_GENERAL,
+          " * Channel " U64_FORMAT " says it is connected "
+          "to an OR with digest %s and no known nickname",
+          U64_PRINTF_ARG(chan->global_identifier),
+          hex_str(chan->identity_digest, DIGEST_LEN));
+    }
+  } else {
+    if (chan->nickname) {
+      log(severity, LD_GENERAL,
+          " * Channel " U64_FORMAT " does not know the digest"
+          " of the OR it is connected to, but reports its nickname is %s",
+          U64_PRINTF_ARG(chan->global_identifier),
+          chan->nickname);
+    } else {
+      log(severity, LD_GENERAL,
+          " * Channel " U64_FORMAT " does not know the digest"
+          " or the nickname of the OR it is connected to",
+          U64_PRINTF_ARG(chan->global_identifier));
+    }
+  }
+
+  /* Handle remote address and descriptions */
+  have_remote_addr = channel_get_addr_if_possible(chan, &remote_addr);
+  if (have_remote_addr) {
+    remote_addr_str = tor_dup_addr(&remote_addr);
+    log(severity, LD_GENERAL,
+        " * Channel " U64_FORMAT " says its remote address"
+        " is %s, and gives a canonical description of \"%s\" and an "
+        "actual description of \"%s\"",
+        U64_PRINTF_ARG(chan->global_identifier),
+        remote_addr_str,
+        channel_get_canonical_remote_descr(chan),
+        channel_get_actual_remote_descr(chan));
+    tor_free(remote_addr_str);
+  } else {
+    log(severity, LD_GENERAL,
+        " * Channel " U64_FORMAT " does not know its remote "
+        "address, but gives a canonical description of \"%s\" and an "
+        "actual description of \"%s\"",
+        U64_PRINTF_ARG(chan->global_identifier),
+        channel_get_canonical_remote_descr(chan),
+        channel_get_actual_remote_descr(chan));
+  }
+
+  /* Handle marks */
+  log(severity, LD_GENERAL,
+      " * Channel " U64_FORMAT " has these marks: %s %s %s "
+      "%s %s %s",
+      U64_PRINTF_ARG(chan->global_identifier),
+      channel_is_bad_for_new_circs(chan) ?
+        "bad_for_new_circs" : "!bad_for_new_circs",
+      channel_is_canonical(chan) ?
+        "canonical" : "!canonical",
+      channel_is_canonical_is_reliable(chan) ?
+        "is_canonical_is_reliable" :
+        "!is_canonical_is_reliable",
+      channel_is_client(chan) ?
+        "client" : "!client",
+      channel_is_local(chan) ?
+        "local" : "!local",
+      channel_is_incoming(chan) ?
+        "incoming" : "outgoing");
+
+  /* Describe queues */
+  log(severity, LD_GENERAL,
+      " * Channel " U64_FORMAT " has %d queued incoming cells"
+      " and %d queued outgoing cells",
+      U64_PRINTF_ARG(chan->global_identifier),
+      (chan->incoming_queue != NULL) ?
+        smartlist_len(chan->incoming_queue) : 0,
+      (chan->outgoing_queue != NULL) ?
+        smartlist_len(chan->outgoing_queue) : 0);
+
+  /* Describe circuits */
+  log(severity, LD_GENERAL,
+      " * Channel " U64_FORMAT " has %d active circuits out of"
+      " %d in total",
+      U64_PRINTF_ARG(chan->global_identifier),
+      (chan->cmux != NULL) ?
+         circuitmux_num_active_circuits(chan->cmux) : 0,
+      (chan->cmux != NULL) ?
+         circuitmux_num_circuits(chan->cmux) : 0);
+
+  /* Describe timestamps */
+  log(severity, LD_GENERAL,
+      " * Channel " U64_FORMAT " was last used by a "
+      "client at " U64_FORMAT " (" U64_FORMAT " seconds ago)",
+      U64_PRINTF_ARG(chan->global_identifier),
+      U64_PRINTF_ARG(chan->timestamp_client),
+      U64_PRINTF_ARG(now - chan->timestamp_client));
+  log(severity, LD_GENERAL,
+      " * Channel " U64_FORMAT " was last drained at "
+      U64_FORMAT " (" U64_FORMAT " seconds ago)",
+      U64_PRINTF_ARG(chan->global_identifier),
+      U64_PRINTF_ARG(chan->timestamp_drained),
+      U64_PRINTF_ARG(now - chan->timestamp_drained));
+  log(severity, LD_GENERAL,
+      " * Channel " U64_FORMAT " last received a cell "
+      "at " U64_FORMAT " (" U64_FORMAT " seconds ago)",
+      U64_PRINTF_ARG(chan->global_identifier),
+      U64_PRINTF_ARG(chan->timestamp_recv),
+      U64_PRINTF_ARG(now - chan->timestamp_recv));
+  log(severity, LD_GENERAL,
+      " * Channel " U64_FORMAT " last trasmitted a cell "
+      "at " U64_FORMAT " (" U64_FORMAT " seconds ago)",
+      U64_PRINTF_ARG(chan->global_identifier),
+      U64_PRINTF_ARG(chan->timestamp_xmit),
+      U64_PRINTF_ARG(now - chan->timestamp_xmit));
+
+  /* Describe counters and rates */
+  log(severity, LD_GENERAL,
+      " * Channel " U64_FORMAT " has received "
+      U64_FORMAT " cells and transmitted " U64_FORMAT,
+      U64_PRINTF_ARG(chan->global_identifier),
+      U64_PRINTF_ARG(chan->n_cells_recved),
+      U64_PRINTF_ARG(chan->n_cells_xmitted));
+  if (now > chan->timestamp_created &&
+      chan->timestamp_created > 0) {
+    if (chan->n_cells_recved > 0) {
+      avg = (double)(chan->n_cells_recved) / age;
+      if (avg >= 1.0) {
+        log(severity, LD_GENERAL,
+            " * Channel " U64_FORMAT " has averaged %f "
+            "cells received per second",
+            U64_PRINTF_ARG(chan->global_identifier), avg);
+      } else if (avg >= 0.0) {
+        interval = 1.0 / avg;
+        log(severity, LD_GENERAL,
+            " * Channel " U64_FORMAT " has averaged %f "
+            "seconds between received cells",
+            U64_PRINTF_ARG(chan->global_identifier), interval);
+      }
+    }
+    if (chan->n_cells_xmitted > 0) {
+      avg = (double)(chan->n_cells_xmitted) / age;
+      if (avg >= 1.0) {
+        log(severity, LD_GENERAL,
+            " * Channel " U64_FORMAT " has averaged %f "
+            "cells transmitted per second",
+            U64_PRINTF_ARG(chan->global_identifier), avg);
+      } else if (avg >= 0.0) {
+        interval = 1.0 / avg;
+        log(severity, LD_GENERAL,
+            " * Channel " U64_FORMAT " has averaged %f "
+            "seconds between transmitted cells",
+            U64_PRINTF_ARG(chan->global_identifier), interval);
+      }
+    }
+  }
+
+  /* Dump anything the lower layer has to say */
+  channel_dump_transport_statistics(chan, severity);
+}
+
+/**
+ * Dump channel listener statistics
+ *
+ * Dump statistics for one channel listener to the log
+ */
+
+void
+channel_listener_dump_statistics(channel_listener_t *chan_l, int severity)
+{
+  double avg, interval, age;
+  time_t now = time(NULL);
+
+  tor_assert(chan_l);
+
+  age = (double)(now - chan_l->timestamp_created);
+
+  log(severity, LD_GENERAL,
+      "Channel listener " U64_FORMAT " (at %p) with transport %s is in "
+      "state %s (%d)",
+      U64_PRINTF_ARG(chan_l->global_identifier), chan_l,
+      channel_listener_describe_transport(chan_l),
+      channel_listener_state_to_string(chan_l->state), chan_l->state);
+  log(severity, LD_GENERAL,
+      " * Channel listener " U64_FORMAT " was created at " U64_FORMAT
+      " (" U64_FORMAT " seconds ago) "
+      "and last active at " U64_FORMAT " (" U64_FORMAT " seconds ago)",
+      U64_PRINTF_ARG(chan_l->global_identifier),
+      U64_PRINTF_ARG(chan_l->timestamp_created),
+      U64_PRINTF_ARG(now - chan_l->timestamp_created),
+      U64_PRINTF_ARG(chan_l->timestamp_active),
+      U64_PRINTF_ARG(now - chan_l->timestamp_active));
+
+  log(severity, LD_GENERAL,
+      " * Channel listener " U64_FORMAT " last accepted an incoming "
+        "channel at " U64_FORMAT " (" U64_FORMAT " seconds ago) "
+        "and has accepted " U64_FORMAT " channels in total",
+        U64_PRINTF_ARG(chan_l->global_identifier),
+        U64_PRINTF_ARG(chan_l->timestamp_accepted),
+        U64_PRINTF_ARG(now - chan_l->timestamp_accepted),
+        U64_PRINTF_ARG(chan_l->n_accepted));
+
+  /*
+   * If it's sensible to do so, get the rate of incoming channels on this
+   * listener
+   */
+  if (now > chan_l->timestamp_created &&
+      chan_l->timestamp_created > 0 &&
+      chan_l->n_accepted > 0) {
+    avg = (double)(chan_l->n_accepted) / age;
+    if (avg >= 1.0) {
+      log(severity, LD_GENERAL,
+          " * Channel listener " U64_FORMAT " has averaged %f incoming "
+          "channels per second",
+          U64_PRINTF_ARG(chan_l->global_identifier), avg);
+    } else if (avg >= 0.0) {
+      interval = 1.0 / avg;
+      log(severity, LD_GENERAL,
+          " * Channel listener " U64_FORMAT " has averaged %f seconds "
+          "between incoming channels",
+          U64_PRINTF_ARG(chan_l->global_identifier), interval);
+    }
+  }
+
+  /* Dump anything the lower layer has to say */
+  channel_listener_dump_transport_statistics(chan_l, severity);
+}
+
+/**
+ * Invoke transport-specific stats dump for channel
+ *
+ * If there is a lower-layer statistics dump method, invoke it
+ */
+
+void
+channel_dump_transport_statistics(channel_t *chan, int severity)
+{
+  tor_assert(chan);
+
+  if (chan->dumpstats) chan->dumpstats(chan, severity);
+}
+
+/**
+ * Invoke transport-specific stats dump for channel listener
+ *
+ * If there is a lower-layer statistics dump method, invoke it
+ */
+
+void
+channel_listener_dump_transport_statistics(channel_listener_t *chan_l,
+                                           int severity)
+{
+  tor_assert(chan_l);
+
+  if (chan_l->dumpstats) chan_l->dumpstats(chan_l, severity);
+}
+
+/**
+ * Return text description of the remote endpoint
+ *
+ * This function return a test provided by the lower layer of the remote
+ * endpoint for this channel; it should specify the actual address connected
+ * to/from.
+ */
+
+const char *
+channel_get_actual_remote_descr(channel_t *chan)
+{
+  tor_assert(chan);
+  tor_assert(chan->get_remote_descr);
+
+  /* Param 1 indicates the actual description */
+  return chan->get_remote_descr(chan, 1);
+}
+
+/**
+ * Return text description of the remote endpoint canonical address
+ *
+ * This function return a test provided by the lower layer of the remote
+ * endpoint for this channel; it should use the known canonical address for
+ * this OR's identity digest if possible.
+ */
+
+const char *
+channel_get_canonical_remote_descr(channel_t *chan)
+{
+  tor_assert(chan);
+  tor_assert(chan->get_remote_descr);
+
+  /* Param 0 indicates the canonicalized description */
+  return chan->get_remote_descr(chan, 0);
+}
+
+/**
+ * Get remote address if possible
+ *
+ * Write the remote address out to a tor_addr_t if the underlying transport
+ * supports this operation.
+ */
+
+int
+channel_get_addr_if_possible(channel_t *chan, tor_addr_t *addr_out)
+{
+  tor_assert(chan);
+  tor_assert(addr_out);
+
+  if (chan->get_remote_addr)
+    return chan->get_remote_addr(chan, addr_out);
+  /* Else no support, method not implemented */
+  else return 0;
+}
+
+/**
+ * Check if there are outgoing queue writes on this channel
+ *
+ * Indicate if either we have queued cells, or if not, whether the underlying
+ * lower-layer transport thinks it has an output queue.
+ */
+
+int
+channel_has_queued_writes(channel_t *chan)
+{
+  int has_writes = 0;
+
+  tor_assert(chan);
+  tor_assert(chan->has_queued_writes);
+
+  if (chan->outgoing_queue &&
+      smartlist_len(chan->outgoing_queue) > 0) {
+    has_writes = 1;
+  } else {
+    /* Check with the lower layer */
+    has_writes = chan->has_queued_writes(chan);
+  }
+
+  return has_writes;
+}
+
+/**
+ * Check the is_bad_for_new_circs flag
+ *
+ * This function returns the is_bad_for_new_circs flag of the specified
+ * channel.
+ */
+
+int
+channel_is_bad_for_new_circs(channel_t *chan)
+{
+  tor_assert(chan);
+
+  return chan->is_bad_for_new_circs;
+}
+
+/**
+ * Mark a channel as bad for new circuits
+ *
+ * Set the is_bad_for_new_circs_flag on chan.
+ */
+
+void
+channel_mark_bad_for_new_circs(channel_t *chan)
+{
+  tor_assert(chan);
+
+  chan->is_bad_for_new_circs = 1;
+}
+
+/**
+ * Get the client flag
+ *
+ * This returns the client flag of a channel, which will be set if
+ * command_process_create_cell() in command.c thinks this is a connection
+ * from a client.
+ */
+
+int
+channel_is_client(channel_t *chan)
+{
+  tor_assert(chan);
+
+  return chan->is_client;
+}
+
+/**
+ * Set the client flag
+ *
+ * Mark a channel as being from a client
+ */
+
+void
+channel_mark_client(channel_t *chan)
+{
+  tor_assert(chan);
+
+  chan->is_client = 1;
+}
+
+/**
+ * Get the canonical flag for a channel
+ *
+ * This returns the is_canonical for a channel; this flag is determined by
+ * the lower layer and can't be set in a transport-independent way.
+ */
+
+int
+channel_is_canonical(channel_t *chan)
+{
+  tor_assert(chan);
+  tor_assert(chan->is_canonical);
+
+  return chan->is_canonical(chan, 0);
+}
+
+/**
+ * Test if the canonical flag is reliable
+ *
+ * This function asks if the lower layer thinks it's safe to trust the
+ * result of channel_is_canonical()
+ */
+
+int
+channel_is_canonical_is_reliable(channel_t *chan)
+{
+  tor_assert(chan);
+  tor_assert(chan->is_canonical);
+
+  return chan->is_canonical(chan, 1);
+}
+
+/**
+ * Test incoming flag
+ *
+ * This function gets the incoming flag; this is set when a listener spawns
+ * a channel.  If this returns true the channel was remotely initiated.
+ */
+
+int
+channel_is_incoming(channel_t *chan)
+{
+  tor_assert(chan);
+
+  return chan->is_incoming;
+}
+
+/**
+ * Set the incoming flag
+ *
+ * This function is called when a channel arrives on a listening channel
+ * to mark it as incoming.
+ */
+
+void
+channel_mark_incoming(channel_t *chan)
+{
+  tor_assert(chan);
+
+  chan->is_incoming = 1;
+}
+
+/**
+ * Test local flag
+ *
+ * This function gets the local flag; the lower layer should set this when
+ * setting up the channel if is_local_addr() is true for all of the
+ * destinations it will communicate with on behalf of this channel.  It's
+ * used to decide whether to declare the network reachable when seeing incoming
+ * traffic on the channel.
+ */
+
+int
+channel_is_local(channel_t *chan)
+{
+  tor_assert(chan);
+
+  return chan->is_local;
+}
+
+/**
+ * Set the local flag
+ *
+ * This internal-only function should be called by the lower layer if the
+ * channel is to a local address.  See channel_is_local() above or the
+ * description of the is_local bit in channel.h
+ */
+
+void
+channel_mark_local(channel_t *chan)
+{
+  tor_assert(chan);
+
+  chan->is_local = 1;
+}
+
+/**
+ * Test outgoing flag
+ *
+ * This function gets the outgoing flag; this is the inverse of the incoming
+ * bit set when a listener spawns a channel.  If this returns true the channel
+ * was locally initiated.
+ */
+
+int
+channel_is_outgoing(channel_t *chan)
+{
+  tor_assert(chan);
+
+  return !(chan->is_incoming);
+}
+
+/**
+ * Mark a channel as outgoing
+ *
+ * This function clears the incoming flag and thus marks a channel as
+ * outgoing.
+ */
+
+void
+channel_mark_outgoing(channel_t *chan)
+{
+  tor_assert(chan);
+
+  chan->is_incoming = 0;
+}
+
+/*********************
+ * Timestamp updates *
+ ********************/
+
+/**
+ * Update the created timestamp for a channel
+ *
+ * This updates the channel's created timestamp and should only be called
+ * from channel_init().
+ */
+
+void
+channel_timestamp_created(channel_t *chan)
+{
+  time_t now = time(NULL);
+
+  tor_assert(chan);
+
+  chan->timestamp_created = now;
+}
+
+/**
+ * Update the created timestamp for a channel listener
+ *
+ * This updates the channel listener's created timestamp and should only be
+ * called from channel_init_listener().
+ */
+
+void
+channel_listener_timestamp_created(channel_listener_t *chan_l)
+{
+  time_t now = time(NULL);
+
+  tor_assert(chan_l);
+
+  chan_l->timestamp_created = now;
+}
+
+/**
+ * Update the last active timestamp for a channel
+ *
+ * This function updates the channel's last active timestamp; it should be
+ * called by the lower layer whenever there is activity on the channel which
+ * does not lead to a cell being transmitted or received; the active timestamp
+ * is also updated from channel_timestamp_recv() and channel_timestamp_xmit(),
+ * but it should be updated for things like the v3 handshake and stuff that
+ * produce activity only visible to the lower layer.
+ */
+
+void
+channel_timestamp_active(channel_t *chan)
+{
+  time_t now = time(NULL);
+
+  tor_assert(chan);
+
+  chan->timestamp_active = now;
+}
+
+/**
+ * Update the last active timestamp for a channel listener
+ */
+
+void
+channel_listener_timestamp_active(channel_listener_t *chan_l)
+{
+  time_t now = time(NULL);
+
+  tor_assert(chan_l);
+
+  chan_l->timestamp_active = now;
+}
+
+/**
+ * Update the last accepted timestamp.
+ *
+ * This function updates the channel listener's last accepted timestamp; it
+ * should be called whenever a new incoming channel is accepted on a
+ * listener.
+ */
+
+void
+channel_listener_timestamp_accepted(channel_listener_t *chan_l)
+{
+  time_t now = time(NULL);
+
+  tor_assert(chan_l);
+
+  chan_l->timestamp_active = now;
+  chan_l->timestamp_accepted = now;
+}
+
+/**
+ * Update client timestamp
+ *
+ * This function is called by relay.c to timestamp a channel that appears to
+ * be used as a client.
+ */
+
+void
+channel_timestamp_client(channel_t *chan)
+{
+  time_t now = time(NULL);
+
+  tor_assert(chan);
+
+  chan->timestamp_client = now;
+}
+
+/**
+ * Update the last drained timestamp
+ *
+ * This is called whenever we transmit a cell which leaves the outgoing cell
+ * queue completely empty.  It also updates the xmit time and the active time.
+ */
+
+void
+channel_timestamp_drained(channel_t *chan)
+{
+  time_t now = time(NULL);
+
+  tor_assert(chan);
+
+  chan->timestamp_active = now;
+  chan->timestamp_drained = now;
+  chan->timestamp_xmit = now;
+}
+
+/**
+ * Update the recv timestamp
+ *
+ * This is called whenever we get an incoming cell from the lower layer.
+ * This also updates the active timestamp.
+ */
+
+void
+channel_timestamp_recv(channel_t *chan)
+{
+  time_t now = time(NULL);
+
+  tor_assert(chan);
+
+  chan->timestamp_active = now;
+  chan->timestamp_recv = now;
+}
+
+/**
+ * Update the xmit timestamp
+ * This is called whenever we pass an outgoing cell to the lower layer.  This
+ * also updates the active timestamp.
+ */
+
+void
+channel_timestamp_xmit(channel_t *chan)
+{
+  time_t now = time(NULL);
+
+  tor_assert(chan);
+
+  chan->timestamp_active = now;
+  chan->timestamp_xmit = now;
+}
+
+/***************************************************************
+ * Timestamp queries - see above for definitions of timestamps *
+ **************************************************************/
+
+/**
+ * Query created timestamp for a channel
+ */
+
+time_t
+channel_when_created(channel_t *chan)
+{
+  tor_assert(chan);
+
+  return chan->timestamp_created;
+}
+
+/**
+ * Query created timestamp for a channel listener
+ */
+
+time_t
+channel_listener_when_created(channel_listener_t *chan_l)
+{
+  tor_assert(chan_l);
+
+  return chan_l->timestamp_created;
+}
+
+/**
+ * Query last active timestamp for a channel
+ */
+
+time_t
+channel_when_last_active(channel_t *chan)
+{
+  tor_assert(chan);
+
+  return chan->timestamp_active;
+}
+
+/**
+ * Query last active timestamp for a channel listener
+ */
+
+time_t
+channel_listener_when_last_active(channel_listener_t *chan_l)
+{
+  tor_assert(chan_l);
+
+  return chan_l->timestamp_active;
+}
+
+/**
+ * Query last accepted timestamp for a channel listener
+ */
+
+time_t
+channel_listener_when_last_accepted(channel_listener_t *chan_l)
+{
+  tor_assert(chan_l);
+
+  return chan_l->timestamp_accepted;
+}
+
+/**
+ * Query client timestamp
+ */
+
+time_t
+channel_when_last_client(channel_t *chan)
+{
+  tor_assert(chan);
+
+  return chan->timestamp_client;
+}
+
+/**
+ * Query drained timestamp
+ */
+
+time_t
+channel_when_last_drained(channel_t *chan)
+{
+  tor_assert(chan);
+
+  return chan->timestamp_drained;
+}
+
+/**
+ * Query recv timestamp
+ */
+
+time_t
+channel_when_last_recv(channel_t *chan)
+{
+  tor_assert(chan);
+
+  return chan->timestamp_recv;
+}
+
+/**
+ * Query xmit timestamp
+ */
+
+time_t
+channel_when_last_xmit(channel_t *chan)
+{
+  tor_assert(chan);
+
+  return chan->timestamp_xmit;
+}
+
+/**
+ * Query accepted counter
+ */
+
+uint64_t
+channel_listener_count_accepted(channel_listener_t *chan_l)
+{
+  tor_assert(chan_l);
+
+  return chan_l->n_accepted;
+}
+
+/**
+ * Query received cell counter
+ */
+
+uint64_t
+channel_count_recved(channel_t *chan)
+{
+  tor_assert(chan);
+
+  return chan->n_cells_recved;
+}
+
+/**
+ * Query transmitted cell counter
+ */
+
+uint64_t
+channel_count_xmitted(channel_t *chan)
+{
+  tor_assert(chan);
+
+  return chan->n_cells_xmitted;
+}
+
+/**
+ * Check if a channel matches an extend_info_t
+ *
+ * This function calls the lower layer and asks if this channel matches a
+ * given extend_info_t.
+ */
+
+int
+channel_matches_extend_info(channel_t *chan, extend_info_t *extend_info)
+{
+  tor_assert(chan);
+  tor_assert(chan->matches_extend_info);
+  tor_assert(extend_info);
+
+  return chan->matches_extend_info(chan, extend_info);
+}
+
+/**
+ * Check if a channel matches a given target address
+ *
+ * This function calls into the lower layer and asks if this channel thinks
+ * it matches a given target address for circuit extension purposes.
+ */
+
+int
+channel_matches_target_addr_for_extend(channel_t *chan,
+                                       const tor_addr_t *target)
+{
+  tor_assert(chan);
+  tor_assert(chan->matches_target);
+  tor_assert(target);
+
+  return chan->matches_target(chan, target);
+}
+
+/**
+ * Return the total number of circuits used by a channel
+ *
+ * @param chan Channel to query
+ * @return Number of circuits using this as n_chan or p_chan
+ */
+
+unsigned int
+channel_num_circuits(channel_t *chan)
+{
+  tor_assert(chan);
+
+  return chan->num_n_circuits +
+         chan->num_p_circuits;
+}
+
+/**
+ * Set up circuit ID generation
+ *
+ * This is called when setting up a channel and replaces the old
+ * connection_or_set_circid_type()
+ */
+
+void
+channel_set_circid_type(channel_t *chan, crypto_pk_t *identity_rcvd)
+{
+  int started_here;
+  crypto_pk_t *our_identity;
+
+  tor_assert(chan);
+
+  started_here = channel_is_outgoing(chan);
+  our_identity = started_here ?
+    get_tlsclient_identity_key() : get_server_identity_key();
+
+  if (identity_rcvd) {
+    if (crypto_pk_cmp_keys(our_identity, identity_rcvd) < 0) {
+      chan->circ_id_type = CIRC_ID_TYPE_LOWER;
+    } else {
+      chan->circ_id_type = CIRC_ID_TYPE_HIGHER;
+    }
+  } else {
+    chan->circ_id_type = CIRC_ID_TYPE_NEITHER;
+  }
+}
+
diff --git a/src/or/channel.h b/src/or/channel.h
new file mode 100644
index 000000000..cb9835a9f
--- /dev/null
+++ b/src/or/channel.h
@@ -0,0 +1,471 @@
+/* * Copyright (c) 2012, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file channel.h
+ * \brief Header file for channel.c
+ **/
+
+#ifndef _TOR_CHANNEL_H
+#define _TOR_CHANNEL_H
+
+#include "or.h"
+#include "circuitmux.h"
+
+/* Channel handler function pointer typedefs */
+typedef void (*channel_listener_fn_ptr)(channel_listener_t *, channel_t *);
+typedef void (*channel_cell_handler_fn_ptr)(channel_t *, cell_t *);
+typedef void (*channel_var_cell_handler_fn_ptr)(channel_t *, var_cell_t *);
+
+/*
+ * Channel struct; see the channel_t typedef in or.h.  A channel is an
+ * abstract interface for the OR-to-OR connection, similar to connection_or_t,
+ * but without the strong coupling to the underlying TLS implementation.  They
+ * are constructed by calling a protocol-specific function to open a channel
+ * to a particular node, and once constructed support the abstract operations
+ * defined below.
+ */
+
+struct channel_s {
+  /* Magic number for type-checking cast macros */
+  uint32_t magic;
+
+  /* Current channel state */
+  channel_state_t state;
+
+  /* Globally unique ID number for a channel over the lifetime of a Tor
+   * process.
+   */
+  uint64_t global_identifier;
+
+  /* Should we expect to see this channel in the channel lists? */
+  unsigned char registered:1;
+
+  /** Why did we close?
+   */
+  enum {
+    CHANNEL_NOT_CLOSING = 0,
+    CHANNEL_CLOSE_REQUESTED,
+    CHANNEL_CLOSE_FROM_BELOW,
+    CHANNEL_CLOSE_FOR_ERROR
+  } reason_for_closing;
+
+  /* Timestamps for both cell channels and listeners */
+  time_t timestamp_created; /* Channel created */
+  time_t timestamp_active; /* Any activity */
+
+  /* Methods implemented by the lower layer */
+
+  /* Free a channel */
+  void (*free)(channel_t *);
+  /* Close an open channel */
+  void (*close)(channel_t *);
+  /* Describe the transport subclass for this channel */
+  const char * (*describe_transport)(channel_t *);
+  /* Optional method to dump transport-specific statistics on the channel */
+  void (*dumpstats)(channel_t *, int);
+
+  /* Registered handlers for incoming cells */
+  channel_cell_handler_fn_ptr cell_handler;
+  channel_var_cell_handler_fn_ptr var_cell_handler;
+
+  /* Methods implemented by the lower layer */
+
+  /*
+   * Ask the underlying transport what the remote endpoint address is, in
+   * a tor_addr_t.  This is optional and subclasses may leave this NULL.
+   * If they implement it, they should write the address out to the
+   * provided tor_addr_t *, and return 1 if successful or 0 if no address
+   * available.
+   */
+  int (*get_remote_addr)(channel_t *, tor_addr_t *);
+  /*
+   * Get a text description of the remote endpoint; canonicalized if the
+   * arg is 0, or the one we originally connected to/received from if it's
+   * 1.
+   */
+  const char * (*get_remote_descr)(channel_t *, int);
+  /* Check if the lower layer has queued writes */
+  int (*has_queued_writes)(channel_t *);
+  /*
+   * If the second param is zero, ask the lower layer if this is
+   * 'canonical', for a transport-specific definition of canonical; if
+   * it is 1, ask if the answer to the preceding query is safe to rely
+   * on.
+   */
+  int (*is_canonical)(channel_t *, int);
+  /* Check if this channel matches a specified extend_info_t */
+  int (*matches_extend_info)(channel_t *, extend_info_t *);
+  /* Check if this channel matches a target address when extending */
+  int (*matches_target)(channel_t *, const tor_addr_t *);
+  /* Write a cell to an open channel */
+  int (*write_cell)(channel_t *, cell_t *);
+   /* Write a packed cell to an open channel */
+  int (*write_packed_cell)(channel_t *, packed_cell_t *);
+  /* Write a variable-length cell to an open channel */
+  int (*write_var_cell)(channel_t *, var_cell_t *);
+
+  /*
+   * Hash of the public RSA key for the other side's identity key, or
+   * zeroes if the other side hasn't shown us a valid identity key.
+   */
+  char identity_digest[DIGEST_LEN];
+  /* Nickname of the OR on the other side, or NULL if none. */
+  char *nickname;
+
+  /*
+   * Linked list of channels with the same identity digest, for the
+   * digest->channel map
+   */
+  channel_t *next_with_same_id, *prev_with_same_id;
+
+  /* List of incoming cells to handle */
+  smartlist_t *incoming_queue;
+
+  /* List of queued outgoing cells */
+  smartlist_t *outgoing_queue;
+
+  /* Circuit mux for circuits sending on this channel */
+  circuitmux_t *cmux;
+
+  /* Circuit ID generation stuff for use by circuitbuild.c */
+
+  /*
+   * When we send CREATE cells along this connection, which half of the
+   * space should we use?
+   */
+  circ_id_type_t circ_id_type:2;
+  /*
+   * Which circ_id do we try to use next on this connection?  This is
+   * always in the range 0..1<<15-1.
+   */
+  circid_t next_circ_id;
+
+  /* For how many circuits are we n_chan?  What about p_chan? */
+  unsigned int num_n_circuits, num_p_circuits;
+
+  /*
+   * True iff this channel shouldn't get any new circs attached to it,
+   * because the connection is too old, or because there's a better one.
+   * More generally, this flag is used to note an unhealthy connection;
+   * for example, if a bad connection fails we shouldn't assume that the
+   * router itself has a problem.
+   */
+  unsigned int is_bad_for_new_circs:1;
+
+  /** True iff we have decided that the other end of this connection
+   * is a client.  Channels with this flag set should never be used
+   * to satisfy an EXTEND request.  */
+  unsigned int is_client:1;
+
+  /** Set if the channel was initiated remotely (came from a listener) */
+  unsigned int is_incoming:1;
+
+  /** Set by lower layer if this is local; i.e., everything it communicates
+   * with for this channel returns true for is_local_addr().  This is used
+   * to decide whether to declare reachability when we receive something on
+   * this channel in circuitbuild.c
+   */
+  unsigned int is_local:1;
+
+  /** Channel timestamps for cell channels */
+  time_t timestamp_client; /* Client used this, according to relay.c */
+  time_t timestamp_drained; /* Output queue empty */
+  time_t timestamp_recv; /* Cell received from lower layer */
+  time_t timestamp_xmit; /* Cell sent to lower layer */
+
+  /* Timestamp for relay.c */
+  time_t timestamp_last_added_nonpadding;
+
+  /** Unique ID for measuring direct network status requests;vtunneled ones
+   * come over a circuit_t, which has a dirreq_id field as well, but is a
+   * distinct namespace. */
+  uint64_t dirreq_id;
+
+  /** Channel counters for cell channels */
+  uint64_t n_cells_recved;
+  uint64_t n_cells_xmitted;
+};
+
+struct channel_listener_s {
+  /* Current channel listener state */
+  channel_listener_state_t state;
+
+  /* Globally unique ID number for a channel over the lifetime of a Tor
+   * process.
+   */
+  uint64_t global_identifier;
+
+  /* Should we expect to see this channel in the channel lists? */
+  unsigned char registered:1;
+
+  /** Why did we close?
+   */
+  enum {
+    CHANNEL_LISTENER_NOT_CLOSING = 0,
+    CHANNEL_LISTENER_CLOSE_REQUESTED,
+    CHANNEL_LISTENER_CLOSE_FROM_BELOW,
+    CHANNEL_LISTENER_CLOSE_FOR_ERROR
+  } reason_for_closing;
+
+  /* Timestamps for both cell channels and listeners */
+  time_t timestamp_created; /* Channel created */
+  time_t timestamp_active; /* Any activity */
+
+  /* Methods implemented by the lower layer */
+
+  /* Free a channel */
+  void (*free)(channel_listener_t *);
+  /* Close an open channel */
+  void (*close)(channel_listener_t *);
+  /* Describe the transport subclass for this channel */
+  const char * (*describe_transport)(channel_listener_t *);
+  /* Optional method to dump transport-specific statistics on the channel */
+  void (*dumpstats)(channel_listener_t *, int);
+
+  /* Registered listen handler to call on incoming connection */
+  channel_listener_fn_ptr listener;
+
+  /* List of pending incoming connections */
+  smartlist_t *incoming_list;
+
+  /* Timestamps for listeners */
+  time_t timestamp_accepted;
+
+  /* Counters for listeners */
+  uint64_t n_accepted;
+};
+
+/* Channel state manipulations */
+
+int channel_state_is_valid(channel_state_t state);
+int channel_listener_state_is_valid(channel_listener_state_t state);
+
+int channel_state_can_transition(channel_state_t from, channel_state_t to);
+int channel_listener_state_can_transition(channel_listener_state_t from,
+                                          channel_listener_state_t to);
+
+const char * channel_state_to_string(channel_state_t state);
+const char *
+channel_listener_state_to_string(channel_listener_state_t state);
+
+/* Abstract channel operations */
+
+void channel_mark_for_close(channel_t *chan);
+void channel_write_cell(channel_t *chan, cell_t *cell);
+void channel_write_packed_cell(channel_t *chan, packed_cell_t *cell);
+void channel_write_var_cell(channel_t *chan, var_cell_t *cell);
+
+void channel_listener_mark_for_close(channel_listener_t *chan_l);
+
+/* Channel callback registrations */
+
+/* Listener callback */
+channel_listener_fn_ptr
+channel_listener_get_listener_fn(channel_listener_t *chan);
+
+void channel_listener_set_listener_fn(channel_listener_t *chan,
+                                      channel_listener_fn_ptr listener);
+
+/* Incoming cell callbacks */
+channel_cell_handler_fn_ptr channel_get_cell_handler(channel_t *chan);
+
+channel_var_cell_handler_fn_ptr
+channel_get_var_cell_handler(channel_t *chan);
+
+void channel_set_cell_handlers(channel_t *chan,
+                               channel_cell_handler_fn_ptr cell_handler,
+                               channel_var_cell_handler_fn_ptr
+                                 var_cell_handler);
+
+/* Clean up closed channels and channel listeners periodically; these are
+ * called from run_scheduled_events() in main.c.
+ */
+void channel_run_cleanup(void);
+void channel_listener_run_cleanup(void);
+
+/* Close all channels and deallocate everything */
+void channel_free_all(void);
+
+/* Dump some statistics in the log */
+void channel_dumpstats(int severity);
+void channel_listener_dumpstats(int severity);
+
+/* Set the cmux policy on all active channels */
+void channel_set_cmux_policy_everywhere(circuitmux_policy_t *pol);
+
+#ifdef _TOR_CHANNEL_INTERNAL
+
+/* Channel operations for subclasses and internal use only */
+
+/* Initialize a newly allocated channel - do this first in subclass
+ * constructors.
+ */
+
+void channel_init(channel_t *chan);
+void channel_init_listener(channel_listener_t *chan);
+
+/* Channel registration/unregistration */
+void channel_register(channel_t *chan);
+void channel_unregister(channel_t *chan);
+
+/* Channel listener registration/unregistration */
+void channel_listener_register(channel_listener_t *chan_l);
+void channel_listener_unregister(channel_listener_t *chan_l);
+
+/* Close from below */
+void channel_close_from_lower_layer(channel_t *chan);
+void channel_close_for_error(channel_t *chan);
+void channel_closed(channel_t *chan);
+
+void channel_listener_close_from_lower_layer(channel_listener_t *chan_l);
+void channel_listener_close_for_error(channel_listener_t *chan_l);
+void channel_listener_closed(channel_listener_t *chan_l);
+
+/* Free a channel */
+void channel_free(channel_t *chan);
+void channel_listener_free(channel_listener_t *chan_l);
+
+/* State/metadata setters */
+
+void channel_change_state(channel_t *chan, channel_state_t to_state);
+void channel_clear_identity_digest(channel_t *chan);
+void channel_clear_remote_end(channel_t *chan);
+void channel_mark_local(channel_t *chan);
+void channel_mark_incoming(channel_t *chan);
+void channel_mark_outgoing(channel_t *chan);
+void channel_set_identity_digest(channel_t *chan,
+                                 const char *identity_digest);
+void channel_set_remote_end(channel_t *chan,
+                            const char *identity_digest,
+                            const char *nickname);
+
+void channel_listener_change_state(channel_listener_t *chan_l,
+                                   channel_listener_state_t to_state);
+
+/* Timestamp updates */
+void channel_timestamp_created(channel_t *chan);
+void channel_timestamp_active(channel_t *chan);
+void channel_timestamp_drained(channel_t *chan);
+void channel_timestamp_recv(channel_t *chan);
+void channel_timestamp_xmit(channel_t *chan);
+
+void channel_listener_timestamp_created(channel_listener_t *chan_l);
+void channel_listener_timestamp_active(channel_listener_t *chan_l);
+void channel_listener_timestamp_accepted(channel_listener_t *chan_l);
+
+/* Incoming channel handling */
+void channel_listener_process_incoming(channel_listener_t *listener);
+void channel_listener_queue_incoming(channel_listener_t *listener,
+                                     channel_t *incoming);
+
+/* Incoming cell handling */
+void channel_process_cells(channel_t *chan);
+void channel_queue_cell(channel_t *chan, cell_t *cell);
+void channel_queue_var_cell(channel_t *chan, var_cell_t *var_cell);
+
+/* Outgoing cell handling */
+void channel_flush_cells(channel_t *chan);
+
+/* Request from lower layer for more cells if available */
+ssize_t channel_flush_some_cells(channel_t *chan, ssize_t num_cells);
+
+/* Query if data available on this channel */
+int channel_more_to_flush(channel_t *chan);
+
+/* Notify flushed outgoing for dirreq handling */
+void channel_notify_flushed(channel_t *chan);
+
+/* Handle stuff we need to do on open like notifying circuits */
+void channel_do_open_actions(channel_t *chan);
+
+#endif
+
+/* Helper functions to perform operations on channels */
+
+int channel_send_destroy(circid_t circ_id, channel_t *chan,
+                         int reason);
+
+/*
+ * Outside abstract interfaces that should eventually get turned into
+ * something transport/address format independent.
+ */
+
+channel_t * channel_connect(const tor_addr_t *addr, uint16_t port,
+                            const char *id_digest);
+
+channel_t * channel_get_for_extend(const char *digest,
+                                   const tor_addr_t *target_addr,
+                                   const char **msg_out,
+                                   int *launch_out);
+
+/* Ask which of two channels is better for circuit-extension purposes */
+int channel_is_better(time_t now,
+                      channel_t *a, channel_t *b,
+                      int forgive_new_connections);
+
+/** Channel lookups
+ */
+
+channel_t * channel_find_by_global_id(uint64_t global_identifier);
+channel_t * channel_find_by_remote_digest(const char *identity_digest);
+
+/** For things returned by channel_find_by_remote_digest(), walk the list.
+ */
+
+channel_t * channel_next_with_digest(channel_t *chan);
+channel_t * channel_prev_with_digest(channel_t *chan);
+
+/*
+ * Metadata queries/updates
+ */
+
+const char * channel_describe_transport(channel_t *chan);
+void channel_dump_statistics(channel_t *chan, int severity);
+void channel_dump_transport_statistics(channel_t *chan, int severity);
+const char * channel_get_actual_remote_descr(channel_t *chan);
+int channel_get_addr_if_possible(channel_t *chan, tor_addr_t *addr_out);
+const char * channel_get_canonical_remote_descr(channel_t *chan);
+int channel_has_queued_writes(channel_t *chan);
+int channel_is_bad_for_new_circs(channel_t *chan);
+void channel_mark_bad_for_new_circs(channel_t *chan);
+int channel_is_canonical(channel_t *chan);
+int channel_is_canonical_is_reliable(channel_t *chan);
+int channel_is_client(channel_t *chan);
+int channel_is_local(channel_t *chan);
+int channel_is_incoming(channel_t *chan);
+int channel_is_outgoing(channel_t *chan);
+void channel_mark_client(channel_t *chan);
+int channel_matches_extend_info(channel_t *chan, extend_info_t *extend_info);
+int channel_matches_target_addr_for_extend(channel_t *chan,
+                                           const tor_addr_t *target);
+unsigned int channel_num_circuits(channel_t *chan);
+void channel_set_circid_type(channel_t *chan, crypto_pk_t *identity_rcvd);
+void channel_timestamp_client(channel_t *chan);
+
+const char * channel_listener_describe_transport(channel_listener_t *chan_l);
+void channel_listener_dump_statistics(channel_listener_t *chan_l,
+                                      int severity);
+void channel_listener_dump_transport_statistics(channel_listener_t *chan_l,
+                                                int severity);
+
+/* Timestamp queries */
+time_t channel_when_created(channel_t *chan);
+time_t channel_when_last_active(channel_t *chan);
+time_t channel_when_last_client(channel_t *chan);
+time_t channel_when_last_drained(channel_t *chan);
+time_t channel_when_last_recv(channel_t *chan);
+time_t channel_when_last_xmit(channel_t *chan);
+
+time_t channel_listener_when_created(channel_listener_t *chan_l);
+time_t channel_listener_when_last_active(channel_listener_t *chan_l);
+time_t channel_listener_when_last_accepted(channel_listener_t *chan_l);
+
+/* Counter queries */
+uint64_t channel_count_recved(channel_t *chan);
+uint64_t channel_count_xmitted(channel_t *chan);
+
+uint64_t channel_listener_count_accepted(channel_listener_t *chan_l);
+
+#endif
+
diff --git a/src/or/channeltls.c b/src/or/channeltls.c
new file mode 100644
index 000000000..1a2956b75
--- /dev/null
+++ b/src/or/channeltls.c
@@ -0,0 +1,1894 @@
+/* * Copyright (c) 2012, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file channeltls.c
+ * \brief channel_t concrete subclass using or_connection_t
+ **/
+
+/*
+ * Define this so channel.h gives us things only channel_t subclasses
+ * should touch.
+ */
+
+#define _TOR_CHANNEL_INTERNAL
+
+#include "or.h"
+#include "channel.h"
+#include "channeltls.h"
+#include "circuitmux.h"
+#include "circuitmux_ewma.h"
+#include "config.h"
+#include "connection.h"
+#include "connection_or.h"
+#include "control.h"
+#include "relay.h"
+#include "router.h"
+#include "routerlist.h"
+
+/** How many CELL_PADDING cells have we received, ever? */
+uint64_t stats_n_padding_cells_processed = 0;
+/** How many CELL_VERSIONS cells have we received, ever? */
+uint64_t stats_n_versions_cells_processed = 0;
+/** How many CELL_NETINFO cells have we received, ever? */
+uint64_t stats_n_netinfo_cells_processed = 0;
+/** How many CELL_VPADDING cells have we received, ever? */
+uint64_t stats_n_vpadding_cells_processed = 0;
+/** How many CELL_CERTS cells have we received, ever? */
+uint64_t stats_n_certs_cells_processed = 0;
+/** How many CELL_AUTH_CHALLENGE cells have we received, ever? */
+uint64_t stats_n_auth_challenge_cells_processed = 0;
+/** How many CELL_AUTHENTICATE cells have we received, ever? */
+uint64_t stats_n_authenticate_cells_processed = 0;
+/** How many CELL_AUTHORIZE cells have we received, ever? */
+uint64_t stats_n_authorize_cells_processed = 0;
+
+/** Active listener, if any */
+channel_listener_t *channel_tls_listener = NULL;
+
+/* channel_tls_t method declarations */
+
+static void channel_tls_close_method(channel_t *chan);
+static const char * channel_tls_describe_transport_method(channel_t *chan);
+static int
+channel_tls_get_remote_addr_method(channel_t *chan, tor_addr_t *addr_out);
+static const char *
+channel_tls_get_remote_descr_method(channel_t *chan, int req);
+static int channel_tls_has_queued_writes_method(channel_t *chan);
+static int channel_tls_is_canonical_method(channel_t *chan, int req);
+static int
+channel_tls_matches_extend_info_method(channel_t *chan,
+                                       extend_info_t *extend_info);
+static int channel_tls_matches_target_method(channel_t *chan,
+                                             const tor_addr_t *target);
+static int channel_tls_write_cell_method(channel_t *chan,
+                                         cell_t *cell);
+static int channel_tls_write_packed_cell_method(channel_t *chan,
+                                                packed_cell_t *packed_cell);
+static int channel_tls_write_var_cell_method(channel_t *chan,
+                                             var_cell_t *var_cell);
+
+/* channel_listener_tls_t method declarations */
+
+static void channel_tls_listener_close_method(channel_listener_t *chan_l);
+static const char *
+channel_tls_listener_describe_transport_method(channel_listener_t *chan_l);
+
+/** Handle incoming cells for the handshake stuff here rather than
+ * passing them on up. */
+
+static void channel_tls_process_versions_cell(var_cell_t *cell,
+                                              channel_tls_t *tlschan);
+static void channel_tls_process_netinfo_cell(cell_t *cell,
+                                             channel_tls_t *tlschan);
+static void channel_tls_process_certs_cell(var_cell_t *cell,
+                                           channel_tls_t *tlschan);
+static void channel_tls_process_auth_challenge_cell(var_cell_t *cell,
+                                                    channel_tls_t *tlschan);
+static void channel_tls_process_authenticate_cell(var_cell_t *cell,
+                                                  channel_tls_t *tlschan);
+static int command_allowed_before_handshake(uint8_t command);
+static int enter_v3_handshake_with_cell(var_cell_t *cell,
+                                        channel_tls_t *tlschan);
+
+/**
+ * Start a new TLS channel
+ *
+ * Launch a new OR connection to <b>addr</b>:<b>port</b> and expect to
+ * handshake with an OR with identity digest <b>id_digest</b>, and wrap
+ * it in a channel_tls_t.
+ */
+
+channel_t *
+channel_tls_connect(const tor_addr_t *addr, uint16_t port,
+                    const char *id_digest)
+{
+  channel_tls_t *tlschan = tor_malloc_zero(sizeof(*tlschan));
+  channel_t *chan = &(tlschan->_base);
+  channel_init(chan);
+  chan->magic = TLS_CHAN_MAGIC;
+  chan->state = CHANNEL_STATE_OPENING;
+  chan->close = channel_tls_close_method;
+  chan->describe_transport = channel_tls_describe_transport_method;
+  chan->get_remote_addr = channel_tls_get_remote_addr_method;
+  chan->get_remote_descr = channel_tls_get_remote_descr_method;
+  chan->has_queued_writes = channel_tls_has_queued_writes_method;
+  chan->is_canonical = channel_tls_is_canonical_method;
+  chan->matches_extend_info = channel_tls_matches_extend_info_method;
+  chan->matches_target = channel_tls_matches_target_method;
+  chan->write_cell = channel_tls_write_cell_method;
+  chan->write_packed_cell = channel_tls_write_packed_cell_method;
+  chan->write_var_cell = channel_tls_write_var_cell_method;
+
+  log_debug(LD_CHANNEL,
+            "In channel_tls_connect() for channel %p "
+            "(global id " U64_FORMAT ")",
+            tlschan,
+            U64_PRINTF_ARG(chan->global_identifier));
+
+  if (is_local_addr(addr)) channel_mark_local(chan);
+  channel_mark_outgoing(chan);
+
+  chan->cmux = circuitmux_alloc();
+  if (cell_ewma_enabled()) {
+    circuitmux_set_policy(chan->cmux, &ewma_policy);
+  }
+
+  /* Set up or_connection stuff */
+  tlschan->conn = connection_or_connect(addr, port, id_digest, tlschan);
+  /* connection_or_connect() will fill in tlschan->conn */
+  if (!(tlschan->conn)) {
+    chan->reason_for_closing = CHANNEL_CLOSE_FOR_ERROR;
+    channel_change_state(chan, CHANNEL_STATE_ERROR);
+    goto err;
+  }
+
+  log_debug(LD_CHANNEL,
+            "Got orconn %p for channel with global id " U64_FORMAT,
+            tlschan->conn, U64_PRINTF_ARG(chan->global_identifier));
+
+  goto done;
+
+ err:
+  circuitmux_free(chan->cmux);
+  tor_free(tlschan);
+  chan = NULL;
+
+ done:
+  /* If we got one, we should register it */
+  if (chan) channel_register(chan);
+
+  return chan;
+}
+
+/**
+ * Return the current channel_tls_t listener
+ *
+ * Returns the current channel listener for incoming TLS connections, or
+ * NULL if none has been established
+ */
+
+channel_listener_t *
+channel_tls_get_listener(void)
+{
+  return channel_tls_listener;
+}
+
+/**
+ * Start a channel_tls_t listener if necessary
+ *
+ * Return the current channel_tls_t listener, or start one if we haven't yet,
+ * and return that.
+ */
+
+channel_listener_t *
+channel_tls_start_listener(void)
+{
+  channel_listener_t *listener;
+
+  if (!channel_tls_listener) {
+    listener = tor_malloc_zero(sizeof(*listener));
+    channel_init_listener(listener);
+    listener->state = CHANNEL_LISTENER_STATE_LISTENING;
+    listener->close = channel_tls_listener_close_method;
+    listener->describe_transport =
+      channel_tls_listener_describe_transport_method;
+
+    channel_tls_listener = listener;
+
+    log_debug(LD_CHANNEL,
+              "Starting TLS channel listener %p with global id " U64_FORMAT,
+              listener, U64_PRINTF_ARG(listener->global_identifier));
+
+    channel_listener_register(listener);
+  } else listener = channel_tls_listener;
+
+  return listener;
+}
+
+/**
+ * Free everything on shutdown
+ *
+ * Not much to do here, since channel_free_all() takes care of a lot, but let's
+ * get rid of the listener.
+ */
+
+void
+channel_tls_free_all(void)
+{
+  log_debug(LD_CHANNEL,
+            "Shutting down TLS channels...");
+
+  if (channel_tls_listener) {
+    channel_listener_unregister(channel_tls_listener);
+    channel_listener_mark_for_close(channel_tls_listener);
+    channel_listener_free(channel_tls_listener);
+    channel_tls_listener = NULL;
+  }
+
+  log_debug(LD_CHANNEL,
+            "Done shutting down TLS channels");
+}
+
+/**
+ * Create a new channel around an incoming or_connection_t
+ */
+
+channel_t *
+channel_tls_handle_incoming(or_connection_t *orconn)
+{
+  channel_tls_t *tlschan = tor_malloc_zero(sizeof(*tlschan));
+  channel_t *chan = &(tlschan->_base);
+
+  tor_assert(orconn);
+  tor_assert(!(orconn->chan));
+
+  channel_init(chan);
+  chan->magic = TLS_CHAN_MAGIC;
+  chan->state = CHANNEL_STATE_OPENING;
+  chan->close = channel_tls_close_method;
+  chan->describe_transport = channel_tls_describe_transport_method;
+  chan->get_remote_descr = channel_tls_get_remote_descr_method;
+  chan->has_queued_writes = channel_tls_has_queued_writes_method;
+  chan->is_canonical = channel_tls_is_canonical_method;
+  chan->matches_extend_info = channel_tls_matches_extend_info_method;
+  chan->matches_target = channel_tls_matches_target_method;
+  chan->write_cell = channel_tls_write_cell_method;
+  chan->write_packed_cell = channel_tls_write_packed_cell_method;
+  chan->write_var_cell = channel_tls_write_var_cell_method;
+
+  /* Link the channel and orconn to each other */
+  tlschan->conn = orconn;
+  orconn->chan = tlschan;
+
+  if (is_local_addr(&(TO_CONN(orconn)->addr))) channel_mark_local(chan);
+  channel_mark_incoming(chan);
+
+  chan->cmux = circuitmux_alloc();
+  if (cell_ewma_enabled()) {
+    circuitmux_set_policy(chan->cmux, &ewma_policy);
+  }
+
+  /* If we got one, we should register it */
+  if (chan) channel_register(chan);
+
+  return chan;
+}
+
+/*********
+ * Casts *
+ ********/
+
+/**
+ * Cast a channel_tls_t to a channel_t.
+ */
+
+channel_t *
+channel_tls_to_base(channel_tls_t *tlschan)
+{
+  if (!tlschan) return NULL;
+
+  return &(tlschan->_base);
+}
+
+/**
+ * Cast a channel_t to a channel_tls_t, with appropriate type-checking
+ * asserts.
+ */
+
+channel_tls_t *
+channel_tls_from_base(channel_t *chan)
+{
+  if (!chan) return NULL;
+
+  tor_assert(chan->magic == TLS_CHAN_MAGIC);
+
+  return (channel_tls_t *)(chan);
+}
+
+/********************************************
+ * Method implementations for channel_tls_t *
+ *******************************************/
+
+/**
+ * Close a channel_tls_t
+ *
+ * This implements the close method for channel_tls_t
+ */
+
+static void
+channel_tls_close_method(channel_t *chan)
+{
+  channel_tls_t *tlschan = BASE_CHAN_TO_TLS(chan);
+
+  tor_assert(tlschan);
+
+  if (tlschan->conn) connection_or_close_normally(tlschan->conn, 1);
+  else {
+    /* Weird - we'll have to change the state ourselves, I guess */
+    log_info(LD_CHANNEL,
+             "Tried to close channel_tls_t %p with NULL conn",
+             tlschan);
+    channel_change_state(chan, CHANNEL_STATE_ERROR);
+  }
+}
+
+/**
+ * Describe the transport for a channel_tls_t
+ *
+ * This returns the string "TLS channel on connection <id>" to the upper
+ * layer.
+ */
+
+static const char *
+channel_tls_describe_transport_method(channel_t *chan)
+{
+  static char *buf = NULL;
+  uint64_t id;
+  channel_tls_t *tlschan;
+  const char *rv = NULL;
+
+  tor_assert(chan);
+
+   tlschan = BASE_CHAN_TO_TLS(chan);
+
+  if (tlschan->conn) {
+    id = TO_CONN(tlschan->conn)->global_identifier;
+
+    if (buf) tor_free(buf);
+    tor_asprintf(&buf,
+                 "TLS channel (connection " U64_FORMAT ")",
+                 U64_PRINTF_ARG(id));
+
+    rv = buf;
+  } else {
+    rv = "TLS channel (no connection)";
+  }
+
+  return rv;
+}
+
+/**
+ * Get the remote address of a channel_tls_t
+ *
+ * This implements the get_remote_addr method for channel_tls_t; copy the
+ * remote endpoint of the channel to addr_out and return 1 (always
+ * succeeds for this transport).
+ */
+
+static int
+channel_tls_get_remote_addr_method(channel_t *chan, tor_addr_t *addr_out)
+{
+  channel_tls_t *tlschan = BASE_CHAN_TO_TLS(chan);
+
+  tor_assert(tlschan);
+  tor_assert(addr_out);
+  tor_assert(tlschan->conn);
+
+  tor_addr_copy(addr_out, &(TO_CONN(tlschan->conn)->addr));
+
+  return 1;
+}
+
+/**
+ * Get endpoint description of a channel_tls_t
+ *
+ * This implements the get_remote_descr method for channel_tls_t; it returns
+ * a text description of the remote endpoint of the channel suitable for use
+ * in log messages.  The req parameter is 0 for the canonical address or 1 for
+ * the actual address seen.
+ */
+
+static const char *
+channel_tls_get_remote_descr_method(channel_t *chan, int req)
+{
+#define MAX_DESCR_LEN 32
+
+  static char buf[MAX_DESCR_LEN + 1];
+  channel_tls_t *tlschan = BASE_CHAN_TO_TLS(chan);
+  connection_t *conn;
+  const char *answer = NULL;
+  char *addr_str;
+
+  tor_assert(tlschan);
+  tor_assert(tlschan->conn);
+
+  conn = TO_CONN(tlschan->conn);
+
+  switch (req) {
+    case 0:
+      /* Canonical address */
+      tor_snprintf(buf, MAX_DESCR_LEN + 1,
+                   "%s:%u", conn->address, conn->port);
+      answer = buf;
+      break;
+    case 1:
+      /* Actual address */
+      addr_str = tor_dup_addr(&(tlschan->conn->real_addr));
+      tor_snprintf(buf, MAX_DESCR_LEN + 1,
+                   "%s:%u", addr_str, conn->port);
+      tor_free(addr_str);
+      answer = buf;
+      break;
+    default:
+      /* Something's broken in channel.c */
+      tor_assert(1);
+  }
+
+  return answer;
+}
+
+/**
+ * Tell the upper layer if we have queued writes
+ *
+ * This implements the has_queued_writes method for channel_tls _t; it returns
+ * 1 iff we have queued writes on the outbuf of the underlying or_connection_t.
+ */
+
+static int
+channel_tls_has_queued_writes_method(channel_t *chan)
+{
+  size_t outbuf_len;
+  channel_tls_t *tlschan = BASE_CHAN_TO_TLS(chan);
+
+  tor_assert(tlschan);
+  tor_assert(tlschan->conn);
+
+  outbuf_len = connection_get_outbuf_len(TO_CONN(tlschan->conn));
+
+  return (outbuf_len > 0);
+}
+
+/**
+ * Tell the upper layer if we're canonical
+ *
+ * This implements the is_canonical method for channel_tls_t; if req is zero,
+ * it returns whether this is a canonical channel, and if it is one it returns
+ * whether that can be relied upon.
+ */
+
+static int
+channel_tls_is_canonical_method(channel_t *chan, int req)
+{
+  int answer = 0;
+  channel_tls_t *tlschan = BASE_CHAN_TO_TLS(chan);
+
+  tor_assert(tlschan);
+  tor_assert(tlschan->conn);
+
+  switch (req) {
+    case 0:
+      answer = tlschan->conn->is_canonical;
+      break;
+    case 1:
+      /*
+       * Is the is_canonical bit reliable?  In protocols version 2 and up
+       * we get the canonical address from a NETINFO cell, but in older
+       * versions it might be based on an obsolete descriptor.
+       */
+      answer = (tlschan->conn->link_proto >= 2);
+      break;
+    default:
+      /* This shouldn't happen; channel.c is broken if it does */
+      tor_assert(1);
+  }
+
+  return answer;
+}
+
+/**
+ * Check if we match an extend_info_t
+ *
+ * This implements the matches_extend_info method for channel_tls_t; the upper
+ * layer wants to know if this channel matches an extend_info_t.
+ */
+
+static int
+channel_tls_matches_extend_info_method(channel_t *chan,
+                                       extend_info_t *extend_info)
+{
+  channel_tls_t *tlschan = BASE_CHAN_TO_TLS(chan);
+
+  tor_assert(tlschan);
+  tor_assert(extend_info);
+
+  return (tor_addr_eq(&(extend_info->addr),
+                      &(TO_CONN(tlschan->conn)->addr)) &&
+         (extend_info->port == TO_CONN(tlschan->conn)->port));
+}
+
+/**
+ * Check if we match a target address
+ *
+ * This implements the matches_target method for channel_tls _t; the upper
+ * layer wants to know if this channel matches a target address when extending
+ * a circuit.
+ */
+
+static int
+channel_tls_matches_target_method(channel_t *chan,
+                                  const tor_addr_t *target)
+{
+  channel_tls_t *tlschan = BASE_CHAN_TO_TLS(chan);
+
+  tor_assert(tlschan);
+  tor_assert(target);
+  tor_assert(tlschan->conn);
+
+  return tor_addr_compare(&(tlschan->conn->real_addr),
+                          target, CMP_EXACT);
+}
+
+/**
+ * Write a cell to a channel_tls_t
+ *
+ * This implements the write_cell method for channel_tls_t; given a
+ * channel_tls_t and a cell_t, transmit the cell_t.
+ */
+
+static int
+channel_tls_write_cell_method(channel_t *chan, cell_t *cell)
+{
+  channel_tls_t *tlschan = BASE_CHAN_TO_TLS(chan);
+
+  tor_assert(tlschan);
+  tor_assert(cell);
+  tor_assert(tlschan->conn);
+
+  connection_or_write_cell_to_buf(cell, tlschan->conn);
+
+  return 1;
+}
+
+/**
+ * Write a packed cell to a channel_tls_t
+ *
+ * This implements the write_packed_cell method for channel_tls_t; given a
+ * channel_tls_t and a packed_cell_t, transmit the packed_cell_t.
+ */
+
+static int
+channel_tls_write_packed_cell_method(channel_t *chan,
+                                     packed_cell_t *packed_cell)
+{
+  channel_tls_t *tlschan = BASE_CHAN_TO_TLS(chan);
+
+  tor_assert(tlschan);
+  tor_assert(packed_cell);
+  tor_assert(tlschan->conn);
+
+  connection_write_to_buf(packed_cell->body, CELL_NETWORK_SIZE,
+                          TO_CONN(tlschan->conn));
+
+  /* This is where the cell is finished; used to be done from relay.c */
+  packed_cell_free(packed_cell);
+
+  return 1;
+}
+
+/**
+ * Write a variable-length cell to a channel_tls_t
+ *
+ * This implements the write_var_cell method for channel_tls_t; given a
+ * channel_tls_t and a var_cell_t, transmit the var_cell_t.
+ */
+
+static int
+channel_tls_write_var_cell_method(channel_t *chan, var_cell_t *var_cell)
+{
+  channel_tls_t *tlschan = BASE_CHAN_TO_TLS(chan);
+
+  tor_assert(tlschan);
+  tor_assert(var_cell);
+  tor_assert(tlschan->conn);
+
+  connection_or_write_var_cell_to_buf(var_cell, tlschan->conn);
+
+  return 1;
+}
+
+/*************************************************
+ * Method implementations for channel_listener_t *
+ ************************************************/
+
+/**
+ * Close a channel_listener_t
+ *
+ * This implements the close method for channel_listener_t
+ */
+
+static void
+channel_tls_listener_close_method(channel_listener_t *chan_l)
+{
+  tor_assert(chan_l);
+
+  /*
+   * Listeners we just go ahead and change state through to CLOSED, but
+   * make sure to check if they're channel_tls_listener to NULL it out.
+   */
+  if (chan_l == channel_tls_listener)
+    channel_tls_listener = NULL;
+
+  if (!(chan_l->state == CHANNEL_LISTENER_STATE_CLOSING ||
+        chan_l->state == CHANNEL_LISTENER_STATE_CLOSED ||
+        chan_l->state == CHANNEL_LISTENER_STATE_ERROR)) {
+    channel_listener_change_state(chan_l, CHANNEL_LISTENER_STATE_CLOSING);
+  }
+
+  if (chan_l->incoming_list) {
+    SMARTLIST_FOREACH_BEGIN(chan_l->incoming_list,
+                            channel_t *, ichan) {
+      channel_mark_for_close(ichan);
+    } SMARTLIST_FOREACH_END(ichan);
+
+    smartlist_free(chan_l->incoming_list);
+    chan_l->incoming_list = NULL;
+  }
+
+  if (!(chan_l->state == CHANNEL_LISTENER_STATE_CLOSED ||
+        chan_l->state == CHANNEL_LISTENER_STATE_ERROR)) {
+    channel_listener_change_state(chan_l, CHANNEL_LISTENER_STATE_CLOSED);
+  }
+}
+
+/**
+ * Describe the transport for a channel_listener_t
+ *
+ * This returns the string "TLS channel (listening)" to the upper
+ * layer.
+ */
+
+static const char *
+channel_tls_listener_describe_transport_method(channel_listener_t *chan_l)
+{
+  tor_assert(chan_l);
+
+  return "TLS channel (listening)";
+}
+
+/*******************************************************
+ * Functions for handling events on an or_connection_t *
+ ******************************************************/
+
+/**
+ * Handle an orconn state change
+ *
+ * This function will be called by connection_or.c when the or_connection_t
+ * associated with this channel_tls_t changes state.
+ */
+
+void
+channel_tls_handle_state_change_on_orconn(channel_tls_t *chan,
+                                          or_connection_t *conn,
+                                          uint8_t old_state,
+                                          uint8_t state)
+{
+  channel_t *base_chan;
+
+  tor_assert(chan);
+  tor_assert(conn);
+  tor_assert(conn->chan == chan);
+  tor_assert(chan->conn == conn);
+  /* -Werror appeasement */
+  tor_assert(old_state == old_state);
+
+  base_chan = TLS_CHAN_TO_BASE(chan);
+
+  /* Make sure the base connection state makes sense - shouldn't be error,
+   * closed or listening. */
+
+  tor_assert(base_chan->state == CHANNEL_STATE_OPENING ||
+             base_chan->state == CHANNEL_STATE_OPEN ||
+             base_chan->state == CHANNEL_STATE_MAINT ||
+             base_chan->state == CHANNEL_STATE_CLOSING);
+
+  /* Did we just go to state open? */
+  if (state == OR_CONN_STATE_OPEN) {
+    /*
+     * We can go to CHANNEL_STATE_OPEN from CHANNEL_STATE_OPENING or
+     * CHANNEL_STATE_MAINT on this.
+     */
+    channel_change_state(base_chan, CHANNEL_STATE_OPEN);
+  } else {
+    /*
+     * Not open, so from CHANNEL_STATE_OPEN we go to CHANNEL_STATE_MAINT,
+     * otherwise no change.
+     */
+    if (base_chan->state == CHANNEL_STATE_OPEN) {
+      channel_change_state(base_chan, CHANNEL_STATE_MAINT);
+    }
+  }
+}
+
+/**
+ * Flush cells from a channel_tls_t
+ *
+ * Try to flush up to about num_cells cells, and return how many we flushed.
+ */
+
+ssize_t
+channel_tls_flush_some_cells(channel_tls_t *chan, ssize_t num_cells)
+{
+  ssize_t flushed = 0;
+
+  tor_assert(chan);
+
+  if (flushed >= num_cells) goto done;
+
+  /*
+   * If channel_tls_t ever buffers anything below the channel_t layer, flush
+   * that first here.
+   */
+
+  flushed += channel_flush_some_cells(TLS_CHAN_TO_BASE(chan),
+                                      num_cells - flushed);
+
+  /*
+   * If channel_tls_t ever buffers anything below the channel_t layer, check
+   * how much we actually got and push it on down here.
+   */
+
+ done:
+  return flushed;
+}
+
+/**
+ * Check if a channel_tls_t has anything to flush
+ *
+ * Return true if there is any more to flush on this channel (cells in queue
+ * or active circuits).
+ */
+
+int
+channel_tls_more_to_flush(channel_tls_t *chan)
+{
+  tor_assert(chan);
+
+  /*
+   * If channel_tls_t ever buffers anything below channel_t, the
+   * check for that should go here first.
+   */
+
+  return channel_more_to_flush(TLS_CHAN_TO_BASE(chan));
+}
+
+#ifdef KEEP_TIMING_STATS
+
+/**
+ * Timing states wrapper
+ *
+ * This is a wrapper function around the actual function that processes the
+ * <b>cell</b> that just arrived on <b>chan</b>. Increment <b>*time</b>
+ * by the number of microseconds used by the call to <b>*func(cell, chan)</b>.
+ */
+
+static void
+channel_tls_time_process_cell(cell_t *cell, channel_tls_t *chan, int *time,
+                              void (*func)(cell_t *, channel_tls_t *))
+{
+  struct timeval start, end;
+  long time_passed;
+
+  tor_gettimeofday(&start);
+
+  (*func)(cell, chan);
+
+  tor_gettimeofday(&end);
+  time_passed = tv_udiff(&start, &end) ;
+
+  if (time_passed > 10000) { /* more than 10ms */
+    log_debug(LD_OR,"That call just took %ld ms.",time_passed/1000);
+  }
+
+  if (time_passed < 0) {
+    log_info(LD_GENERAL,"That call took us back in time!");
+    time_passed = 0;
+  }
+
+  *time += time_passed;
+}
+#endif
+
+/**
+ * Handle an incoming cell on a channel_tls_t
+ *
+ * This is called from connection_or.c to handle an arriving cell; it checks
+ * for cell types specific to the handshake for this transport protocol and
+ * handles them, and queues all other cells to the channel_t layer, which
+ * eventually will hand them off to command.c.
+ */
+
+void
+channel_tls_handle_cell(cell_t *cell, or_connection_t *conn)
+{
+  channel_tls_t *chan;
+  int handshaking;
+
+#ifdef KEEP_TIMING_STATS
+#define PROCESS_CELL(tp, cl, cn) STMT_BEGIN {                   \
+    ++num ## tp;                                                \
+    channel_tls_time_process_cell(cl, cn, & tp ## time ,            \
+                             channel_tls_process_ ## tp ## _cell);  \
+    } STMT_END
+#else
+#define PROCESS_CELL(tp, cl, cn) channel_tls_process_ ## tp ## _cell(cl, cn)
+#endif
+
+  tor_assert(cell);
+  tor_assert(conn);
+
+  chan = conn->chan;
+
+ if (!chan) {
+   log_warn(LD_CHANNEL,
+            "Got a cell_t on an OR connection with no channel");
+   return;
+  }
+
+  handshaking = (TO_CONN(conn)->state != OR_CONN_STATE_OPEN);
+
+  if (conn->_base.marked_for_close)
+    return;
+
+  /* Reject all but VERSIONS and NETINFO when handshaking. */
+  /* (VERSIONS should actually be impossible; it's variable-length.) */
+  if (handshaking && cell->command != CELL_VERSIONS &&
+      cell->command != CELL_NETINFO) {
+    log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
+           "Received unexpected cell command %d in chan state %s / "
+           "conn state %s; closing the connection.",
+           (int)cell->command,
+           channel_state_to_string(TLS_CHAN_TO_BASE(chan)->state),
+           conn_state_to_string(CONN_TYPE_OR, TO_CONN(conn)->state));
+    connection_or_close_for_error(conn, 0);
+    return;
+  }
+
+  if (conn->_base.state == OR_CONN_STATE_OR_HANDSHAKING_V3)
+    or_handshake_state_record_cell(conn->handshake_state, cell, 1);
+
+  switch (cell->command) {
+    case CELL_PADDING:
+      ++stats_n_padding_cells_processed;
+      /* do nothing */
+      break;
+    case CELL_VERSIONS:
+      tor_fragile_assert();
+      break;
+    case CELL_NETINFO:
+      ++stats_n_netinfo_cells_processed;
+      PROCESS_CELL(netinfo, cell, chan);
+      break;
+    case CELL_CREATE:
+    case CELL_CREATE_FAST:
+    case CELL_CREATED:
+    case CELL_CREATED_FAST:
+    case CELL_RELAY:
+    case CELL_RELAY_EARLY:
+    case CELL_DESTROY:
+      /*
+       * These are all transport independent and we pass them up through the
+       * channel_t mechanism.  They are ultimately handled in command.c.
+       */
+      channel_queue_cell(TLS_CHAN_TO_BASE(chan), cell);
+      break;
+    default:
+      log_fn(LOG_INFO, LD_PROTOCOL,
+             "Cell of unknown type (%d) received in channeltls.c.  "
+             "Dropping.",
+             cell->command);
+             break;
+  }
+}
+
+/**
+ * Handle an incoming variable-length cell on a channel_tls_t
+ *
+ * Process a <b>var_cell</b> that was just received on <b>conn</b>. Keep
+ * internal statistics about how many of each cell we've processed so far
+ * this second, and the total number of microseconds it took to
+ * process each type of cell.  All the var_cell commands are handshake-
+ * related and live below the channel_t layer, so no variable-length
+ * cells ever get delivered in the current implementation, but I've left
+ * the mechanism in place for future use.
+ */
+
+void
+channel_tls_handle_var_cell(var_cell_t *var_cell, or_connection_t *conn)
+{
+  channel_tls_t *chan;
+
+#ifdef KEEP_TIMING_STATS
+  /* how many of each cell have we seen so far this second? needs better
+   * name. */
+  static int num_versions = 0, num_certs = 0;
+  static time_t current_second = 0; /* from previous calls to time */
+  time_t now = time(NULL);
+
+  if (current_second == 0) current_second = now;
+  if (now > current_second) { /* the second has rolled over */
+    /* print stats */
+    log_info(LD_OR,
+             "At end of second: %d versions (%d ms), %d certs (%d ms)",
+             num_versions, versions_time / ((now - current_second) * 1000),
+             num_certs, certs_time / ((now - current_second) * 1000));
+
+    num_versions = num_certs = 0;
+    versions_time = certs_time = 0;
+
+    /* remember which second it is, for next time */
+    current_second = now;
+  }
+#endif
+
+  tor_assert(var_cell);
+  tor_assert(conn);
+
+  chan = conn->chan;
+
+  if (!chan) {
+    log_warn(LD_CHANNEL,
+             "Got a var_cell_t on an OR connection with no channel");
+    return;
+  }
+
+  if (TO_CONN(conn)->marked_for_close)
+    return;
+
+  switch (TO_CONN(conn)->state) {
+    case OR_CONN_STATE_OR_HANDSHAKING_V2:
+      if (var_cell->command != CELL_VERSIONS) {
+        log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
+               "Received a cell with command %d in unexpected "
+               "orconn state \"%s\" [%d], channel state \"%s\" [%d]; "
+               "closing the connection.",
+               (int)(var_cell->command),
+               conn_state_to_string(CONN_TYPE_OR, TO_CONN(conn)->state),
+               TO_CONN(conn)->state,
+               channel_state_to_string(TLS_CHAN_TO_BASE(chan)->state),
+               (int)(TLS_CHAN_TO_BASE(chan)->state));
+        /*
+         * The code in connection_or.c will tell channel_t to close for
+         * error; it will go to CHANNEL_STATE_CLOSING, and then to
+         * CHANNEL_STATE_ERROR when conn is closed.
+         */
+        connection_or_close_for_error(conn, 0);
+        return;
+      }
+      break;
+    case OR_CONN_STATE_TLS_HANDSHAKING:
+      /* If we're using bufferevents, it's entirely possible for us to
+       * notice "hey, data arrived!" before we notice "hey, the handshake
+       * finished!" And we need to be accepting both at once to handle both
+       * the v2 and v3 handshakes. */
+
+      /* fall through */
+    case OR_CONN_STATE_TLS_SERVER_RENEGOTIATING:
+      if (!(command_allowed_before_handshake(var_cell->command))) {
+        log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
+               "Received a cell with command %d in unexpected "
+               "orconn state \"%s\" [%d], channel state \"%s\" [%d]; "
+               "closing the connection.",
+               (int)(var_cell->command),
+               conn_state_to_string(CONN_TYPE_OR, TO_CONN(conn)->state),
+               (int)(TO_CONN(conn)->state),
+               channel_state_to_string(TLS_CHAN_TO_BASE(chan)->state),
+               (int)(TLS_CHAN_TO_BASE(chan)->state));
+        /* see above comment about CHANNEL_STATE_ERROR */
+        connection_or_close_for_error(conn, 0);
+        return;
+      } else {
+        if (enter_v3_handshake_with_cell(var_cell, chan) < 0)
+          return;
+      }
+      break;
+    case OR_CONN_STATE_OR_HANDSHAKING_V3:
+      if (var_cell->command != CELL_AUTHENTICATE)
+        or_handshake_state_record_var_cell(conn->handshake_state, var_cell, 1);
+      break; /* Everything is allowed */
+    case OR_CONN_STATE_OPEN:
+      if (conn->link_proto < 3) {
+        log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
+               "Received a variable-length cell with command %d in orconn "
+               "state %s [%d], channel state %s [%d] with link protocol %d; "
+               "ignoring it.",
+               (int)(var_cell->command),
+               conn_state_to_string(CONN_TYPE_OR, TO_CONN(conn)->state),
+               (int)(TO_CONN(conn)->state),
+               channel_state_to_string(TLS_CHAN_TO_BASE(chan)->state),
+               (int)(TLS_CHAN_TO_BASE(chan)->state),
+               (int)(conn->link_proto));
+        return;
+      }
+      break;
+    default:
+      log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
+             "Received var-length cell with command %d in unexpected "
+             "orconn state \"%s\" [%d], channel state \"%s\" [%d]; "
+             "ignoring it.",
+             (int)(var_cell->command),
+             conn_state_to_string(CONN_TYPE_OR, TO_CONN(conn)->state),
+             (int)(TO_CONN(conn)->state),
+             channel_state_to_string(TLS_CHAN_TO_BASE(chan)->state),
+             (int)(TLS_CHAN_TO_BASE(chan)->state));
+      return;
+  }
+
+  /* Now handle the cell */
+
+  switch (var_cell->command) {
+    case CELL_VERSIONS:
+      ++stats_n_versions_cells_processed;
+      PROCESS_CELL(versions, var_cell, chan);
+      break;
+    case CELL_VPADDING:
+      ++stats_n_vpadding_cells_processed;
+      /* Do nothing */
+      break;
+    case CELL_CERTS:
+      ++stats_n_certs_cells_processed;
+      PROCESS_CELL(certs, var_cell, chan);
+      break;
+    case CELL_AUTH_CHALLENGE:
+      ++stats_n_auth_challenge_cells_processed;
+      PROCESS_CELL(auth_challenge, var_cell, chan);
+      break;
+    case CELL_AUTHENTICATE:
+      ++stats_n_authenticate_cells_processed;
+      PROCESS_CELL(authenticate, var_cell, chan);
+      break;
+    case CELL_AUTHORIZE:
+      ++stats_n_authorize_cells_processed;
+      /* Ignored so far. */
+      break;
+    default:
+      log_fn(LOG_INFO, LD_PROTOCOL,
+             "Variable-length cell of unknown type (%d) received.",
+             (int)(var_cell->command));
+      break;
+  }
+}
+
+/**
+ * Check if this cell type is allowed before the handshake is finished
+ *
+ * Return true if <b>command</b> is a cell command that's allowed to start a
+ * V3 handshake.
+ */
+
+static int
+command_allowed_before_handshake(uint8_t command)
+{
+  switch (command) {
+    case CELL_VERSIONS:
+    case CELL_VPADDING:
+    case CELL_AUTHORIZE:
+      return 1;
+    default:
+      return 0;
+  }
+}
+
+/**
+ * Start a V3 handshake on an incoming connection
+ *
+ * Called when we as a server receive an appropriate cell while waiting
+ * either for a cell or a TLS handshake.  Set the connection's state to
+ * "handshaking_v3', initializes the or_handshake_state field as needed,
+ * and add the cell to the hash of incoming cells.)
+ */
+
+static int
+enter_v3_handshake_with_cell(var_cell_t *cell, channel_tls_t *chan)
+{
+  int started_here = 0;
+
+  tor_assert(cell);
+  tor_assert(chan);
+  tor_assert(chan->conn);
+
+  started_here = connection_or_nonopen_was_started_here(chan->conn);
+
+  tor_assert(TO_CONN(chan->conn)->state == OR_CONN_STATE_TLS_HANDSHAKING ||
+             TO_CONN(chan->conn)->state ==
+               OR_CONN_STATE_TLS_SERVER_RENEGOTIATING);
+
+  if (started_here) {
+    log_fn(LOG_PROTOCOL_WARN, LD_OR,
+           "Received a cell while TLS-handshaking, not in "
+           "OR_HANDSHAKING_V3, on a connection we originated.");
+  }
+  chan->conn->_base.state = OR_CONN_STATE_OR_HANDSHAKING_V3;
+  if (connection_init_or_handshake_state(chan->conn, started_here) < 0) {
+    connection_or_close_for_error(chan->conn, 0);
+    return -1;
+  }
+  or_handshake_state_record_var_cell(chan->conn->handshake_state, cell, 1);
+  return 0;
+}
+
+/**
+ * Process a 'versions' cell.
+ *
+ * This function is called to handle an incoming VERSIONS cell; the current
+ * link protocol version must be 0 to indicate that no version has yet been
+ * negotiated.  We compare the versions in the cell to the list of versions
+ * we support, pick the highest version we have in common, and continue the
+ * negotiation from there.
+ */
+
+static void
+channel_tls_process_versions_cell(var_cell_t *cell, channel_tls_t *chan)
+{
+  int highest_supported_version = 0;
+  const uint8_t *cp, *end;
+  int started_here = 0;
+
+  tor_assert(cell);
+  tor_assert(chan);
+  tor_assert(chan->conn);
+
+  started_here = connection_or_nonopen_was_started_here(chan->conn);
+
+  if (chan->conn->link_proto != 0 ||
+      (chan->conn->handshake_state &&
+       chan->conn->handshake_state->received_versions)) {
+    log_fn(LOG_PROTOCOL_WARN, LD_OR,
+           "Received a VERSIONS cell on a connection with its version "
+           "already set to %d; dropping",
+           (int)(chan->conn->link_proto));
+    return;
+  }
+  switch (chan->conn->_base.state)
+    {
+    case OR_CONN_STATE_OR_HANDSHAKING_V2:
+    case OR_CONN_STATE_OR_HANDSHAKING_V3:
+      break;
+    case OR_CONN_STATE_TLS_HANDSHAKING:
+    case OR_CONN_STATE_TLS_SERVER_RENEGOTIATING:
+    default:
+      log_fn(LOG_PROTOCOL_WARN, LD_OR,
+             "VERSIONS cell while in unexpected state");
+      return;
+  }
+
+  tor_assert(chan->conn->handshake_state);
+  end = cell->payload + cell->payload_len;
+  for (cp = cell->payload; cp+1 < end; ++cp) {
+    uint16_t v = ntohs(get_uint16(cp));
+    if (is_or_protocol_version_known(v) && v > highest_supported_version)
+      highest_supported_version = v;
+  }
+  if (!highest_supported_version) {
+    log_fn(LOG_PROTOCOL_WARN, LD_OR,
+           "Couldn't find a version in common between my version list and the "
+           "list in the VERSIONS cell; closing connection.");
+    connection_or_close_for_error(chan->conn, 0);
+    return;
+  } else if (highest_supported_version == 1) {
+    /* Negotiating version 1 makes no sense, since version 1 has no VERSIONS
+     * cells. */
+    log_fn(LOG_PROTOCOL_WARN, LD_OR,
+           "Used version negotiation protocol to negotiate a v1 connection. "
+           "That's crazily non-compliant. Closing connection.");
+    connection_or_close_for_error(chan->conn, 0);
+    return;
+  } else if (highest_supported_version < 3 &&
+             chan->conn->_base.state ==  OR_CONN_STATE_OR_HANDSHAKING_V3) {
+    log_fn(LOG_PROTOCOL_WARN, LD_OR,
+           "Negotiated link protocol 2 or lower after doing a v3 TLS "
+           "handshake. Closing connection.");
+    connection_or_close_for_error(chan->conn, 0);
+    return;
+  }
+
+  chan->conn->link_proto = highest_supported_version;
+  chan->conn->handshake_state->received_versions = 1;
+
+  if (chan->conn->link_proto == 2) {
+    log_info(LD_OR,
+             "Negotiated version %d with %s:%d; sending NETINFO.",
+             highest_supported_version,
+             safe_str_client(chan->conn->_base.address),
+             chan->conn->_base.port);
+
+    if (connection_or_send_netinfo(chan->conn) < 0) {
+      connection_or_close_for_error(chan->conn, 0);
+      return;
+    }
+  } else {
+    const int send_versions = !started_here;
+    /* If we want to authenticate, send a CERTS cell */
+    const int send_certs = !started_here || public_server_mode(get_options());
+    /* If we're a relay that got a connection, ask for authentication. */
+    const int send_chall = !started_here && public_server_mode(get_options());
+    /* If our certs cell will authenticate us, we can send a netinfo cell
+     * right now. */
+    const int send_netinfo = !started_here;
+    const int send_any =
+      send_versions || send_certs || send_chall || send_netinfo;
+    tor_assert(chan->conn->link_proto >= 3);
+
+    log_info(LD_OR,
+             "Negotiated version %d with %s:%d; %s%s%s%s%s",
+             highest_supported_version,
+             safe_str_client(chan->conn->_base.address),
+             chan->conn->_base.port,
+             send_any ? "Sending cells:" : "Waiting for CERTS cell",
+             send_versions ? " VERSIONS" : "",
+             send_certs ? " CERTS" : "",
+             send_chall ? " AUTH_CHALLENGE" : "",
+             send_netinfo ? " NETINFO" : "");
+
+#ifdef DISABLE_V3_LINKPROTO_SERVERSIDE
+    if (1) {
+      connection_or_close_normally(chan->conn, 1);
+      return;
+    }
+#endif
+
+    if (send_versions) {
+      if (connection_or_send_versions(chan->conn, 1) < 0) {
+        log_warn(LD_OR, "Couldn't send versions cell");
+        connection_or_close_for_error(chan->conn, 0);
+        return;
+      }
+    }
+    if (send_certs) {
+      if (connection_or_send_certs_cell(chan->conn) < 0) {
+        log_warn(LD_OR, "Couldn't send certs cell");
+        connection_or_close_for_error(chan->conn, 0);
+        return;
+      }
+    }
+    if (send_chall) {
+      if (connection_or_send_auth_challenge_cell(chan->conn) < 0) {
+        log_warn(LD_OR, "Couldn't send auth_challenge cell");
+        connection_or_close_for_error(chan->conn, 0);
+        return;
+      }
+    }
+    if (send_netinfo) {
+      if (connection_or_send_netinfo(chan->conn) < 0) {
+        log_warn(LD_OR, "Couldn't send netinfo cell");
+        connection_or_close_for_error(chan->conn, 0);
+        return;
+      }
+    }
+  }
+}
+
+/**
+ * Process a 'netinfo' cell
+ *
+ * This function is called to handle an incoming NETINFO cell; read and act
+ * on its contents, and set the connection state to "open".
+ */
+
+static void
+channel_tls_process_netinfo_cell(cell_t *cell, channel_tls_t *chan)
+{
+  time_t timestamp;
+  uint8_t my_addr_type;
+  uint8_t my_addr_len;
+  const uint8_t *my_addr_ptr;
+  const uint8_t *cp, *end;
+  uint8_t n_other_addrs;
+  time_t now = time(NULL);
+
+  long apparent_skew = 0;
+  tor_addr_t my_apparent_addr = TOR_ADDR_NULL;
+
+  tor_assert(cell);
+  tor_assert(chan);
+  tor_assert(chan->conn);
+
+  if (chan->conn->link_proto < 2) {
+    log_fn(LOG_PROTOCOL_WARN, LD_OR,
+           "Received a NETINFO cell on %s connection; dropping.",
+           chan->conn->link_proto == 0 ? "non-versioned" : "a v1");
+    return;
+  }
+  if (chan->conn->_base.state != OR_CONN_STATE_OR_HANDSHAKING_V2 &&
+      chan->conn->_base.state != OR_CONN_STATE_OR_HANDSHAKING_V3) {
+    log_fn(LOG_PROTOCOL_WARN, LD_OR,
+           "Received a NETINFO cell on non-handshaking connection; dropping.");
+    return;
+  }
+  tor_assert(chan->conn->handshake_state &&
+             chan->conn->handshake_state->received_versions);
+
+  if (chan->conn->_base.state == OR_CONN_STATE_OR_HANDSHAKING_V3) {
+    tor_assert(chan->conn->link_proto >= 3);
+    if (chan->conn->handshake_state->started_here) {
+      if (!(chan->conn->handshake_state->authenticated)) {
+        log_fn(LOG_PROTOCOL_WARN, LD_OR,
+               "Got a NETINFO cell from server, "
+               "but no authentication.  Closing the connection.");
+        connection_or_close_for_error(chan->conn, 0);
+        return;
+      }
+    } else {
+      /* we're the server.  If the client never authenticated, we have
+         some housekeeping to do.*/
+      if (!(chan->conn->handshake_state->authenticated)) {
+        tor_assert(tor_digest_is_zero(
+                  (const char*)(chan->conn->handshake_state->
+                      authenticated_peer_id)));
+        channel_set_circid_type(TLS_CHAN_TO_BASE(chan), NULL);
+
+        connection_or_init_conn_from_address(chan->conn,
+                  &(chan->conn->_base.addr),
+                  chan->conn->_base.port,
+                  (const char*)(chan->conn->handshake_state->
+                   authenticated_peer_id),
+                  0);
+      }
+    }
+  }
+
+  /* Decode the cell. */
+  timestamp = ntohl(get_uint32(cell->payload));
+  if (labs(now - chan->conn->handshake_state->sent_versions_at) < 180) {
+    apparent_skew = now - timestamp;
+  }
+
+  my_addr_type = (uint8_t) cell->payload[4];
+  my_addr_len = (uint8_t) cell->payload[5];
+  my_addr_ptr = (uint8_t*) cell->payload + 6;
+  end = cell->payload + CELL_PAYLOAD_SIZE;
+  cp = cell->payload + 6 + my_addr_len;
+  if (cp >= end) {
+    log_fn(LOG_PROTOCOL_WARN, LD_OR,
+           "Addresses too long in netinfo cell; closing connection.");
+    connection_or_close_for_error(chan->conn, 0);
+    return;
+  } else if (my_addr_type == RESOLVED_TYPE_IPV4 && my_addr_len == 4) {
+    tor_addr_from_ipv4n(&my_apparent_addr, get_uint32(my_addr_ptr));
+  } else if (my_addr_type == RESOLVED_TYPE_IPV6 && my_addr_len == 16) {
+    tor_addr_from_ipv6_bytes(&my_apparent_addr, (const char *) my_addr_ptr);
+  }
+
+  n_other_addrs = (uint8_t) *cp++;
+  while (n_other_addrs && cp < end-2) {
+    /* Consider all the other addresses; if any matches, this connection is
+     * "canonical." */
+    tor_addr_t addr;
+    const uint8_t *next =
+      decode_address_from_payload(&addr, cp, (int)(end-cp));
+    if (next == NULL) {
+      log_fn(LOG_PROTOCOL_WARN,  LD_OR,
+             "Bad address in netinfo cell; closing connection.");
+      connection_or_close_for_error(chan->conn, 0);
+      return;
+    }
+    if (tor_addr_eq(&addr, &(chan->conn->real_addr))) {
+      chan->conn->is_canonical = 1;
+      break;
+    }
+    cp = next;
+    --n_other_addrs;
+  }
+
+  /* Act on apparent skew. */
+  /** Warn when we get a netinfo skew with at least this value. */
+#define NETINFO_NOTICE_SKEW 3600
+  if (labs(apparent_skew) > NETINFO_NOTICE_SKEW &&
+      router_get_by_id_digest(chan->conn->identity_digest)) {
+    char dbuf[64];
+    int severity;
+    /*XXXX be smarter about when everybody says we are skewed. */
+    if (router_digest_is_trusted_dir(chan->conn->identity_digest))
+      severity = LOG_WARN;
+    else
+      severity = LOG_INFO;
+    format_time_interval(dbuf, sizeof(dbuf), apparent_skew);
+    log_fn(severity, LD_GENERAL,
+           "Received NETINFO cell with skewed time from "
+           "server at %s:%d.  It seems that our clock is %s by %s, or "
+           "that theirs is %s. Tor requires an accurate clock to work: "
+           "please check your time and date settings.",
+           chan->conn->_base.address,
+           (int)(chan->conn->_base.port),
+           apparent_skew > 0 ? "ahead" : "behind",
+           dbuf,
+           apparent_skew > 0 ? "behind" : "ahead");
+    if (severity == LOG_WARN) /* only tell the controller if an authority */
+      control_event_general_status(LOG_WARN,
+                          "CLOCK_SKEW SKEW=%ld SOURCE=OR:%s:%d",
+                          apparent_skew,
+                          chan->conn->_base.address,
+                          chan->conn->_base.port);
+  }
+
+  /* XXX maybe act on my_apparent_addr, if the source is sufficiently
+   * trustworthy. */
+
+  if (connection_or_set_state_open(chan->conn) < 0) {
+    log_fn(LOG_PROTOCOL_WARN, LD_OR,
+           "Got good NETINFO cell from %s:%d; but "
+           "was unable to make the OR connection become open.",
+           safe_str_client(chan->conn->_base.address),
+           chan->conn->_base.port);
+    connection_or_close_for_error(chan->conn, 0);
+  } else {
+    log_info(LD_OR,
+             "Got good NETINFO cell from %s:%d; OR connection is now "
+             "open, using protocol version %d. Its ID digest is %s. "
+             "Our address is apparently %s.",
+             safe_str_client(chan->conn->_base.address),
+             chan->conn->_base.port,
+             (int)(chan->conn->link_proto),
+             hex_str(TLS_CHAN_TO_BASE(chan)->identity_digest,
+                     DIGEST_LEN),
+             tor_addr_is_null(&my_apparent_addr) ?
+             "<none>" : fmt_and_decorate_addr(&my_apparent_addr));
+  }
+  assert_connection_ok(TO_CONN(chan->conn),time(NULL));
+}
+
+/**
+ * Process a CERTS cell from a channel.
+ *
+ * This function is called to process an incoming CERTS cell on a
+ * channel_tls_t:
+ *
+ * If the other side should not have sent us a CERTS cell, or the cell is
+ * malformed, or it is supposed to authenticate the TLS key but it doesn't,
+ * then mark the connection.
+ *
+ * If the cell has a good cert chain and we're doing a v3 handshake, then
+ * store the certificates in or_handshake_state.  If this is the client side
+ * of the connection, we then authenticate the server or mark the connection.
+ * If it's the server side, wait for an AUTHENTICATE cell.
+ */
+
+static void
+channel_tls_process_certs_cell(var_cell_t *cell, channel_tls_t *chan)
+{
+  tor_cert_t *link_cert = NULL;
+  tor_cert_t *id_cert = NULL;
+  tor_cert_t *auth_cert = NULL;
+  uint8_t *ptr;
+  int n_certs, i;
+  int send_netinfo = 0;
+
+  tor_assert(cell);
+  tor_assert(chan);
+  tor_assert(chan->conn);
+
+#define ERR(s)                                                  \
+  do {                                                          \
+    log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,                      \
+           "Received a bad CERTS cell from %s:%d: %s",          \
+           safe_str(chan->conn->_base.address),                 \
+           chan->conn->_base.port, (s));                        \
+    connection_or_close_for_error(chan->conn, 0);               \
+    return;                                                     \
+  } while (0)
+
+  if (chan->conn->_base.state != OR_CONN_STATE_OR_HANDSHAKING_V3)
+    ERR("We're not doing a v3 handshake!");
+  if (chan->conn->link_proto < 3)
+    ERR("We're not using link protocol >= 3");
+  if (chan->conn->handshake_state->received_certs_cell)
+    ERR("We already got one");
+  if (chan->conn->handshake_state->authenticated) {
+    /* Should be unreachable, but let's make sure. */
+    ERR("We're already authenticated!");
+  }
+  if (cell->payload_len < 1)
+    ERR("It had no body");
+  if (cell->circ_id)
+    ERR("It had a nonzero circuit ID");
+
+  n_certs = cell->payload[0];
+  ptr = cell->payload + 1;
+  for (i = 0; i < n_certs; ++i) {
+    uint8_t cert_type;
+    uint16_t cert_len;
+    if (ptr + 3 > cell->payload + cell->payload_len) {
+      goto truncated;
+    }
+    cert_type = *ptr;
+    cert_len = ntohs(get_uint16(ptr+1));
+    if (ptr + 3 + cert_len > cell->payload + cell->payload_len) {
+      goto truncated;
+    }
+    if (cert_type == OR_CERT_TYPE_TLS_LINK ||
+        cert_type == OR_CERT_TYPE_ID_1024 ||
+        cert_type == OR_CERT_TYPE_AUTH_1024) {
+      tor_cert_t *cert = tor_cert_decode(ptr + 3, cert_len);
+      if (!cert) {
+        log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
+               "Received undecodable certificate in CERTS cell from %s:%d",
+               safe_str(chan->conn->_base.address),
+               chan->conn->_base.port);
+      } else {
+        if (cert_type == OR_CERT_TYPE_TLS_LINK) {
+          if (link_cert) {
+            tor_cert_free(cert);
+            ERR("Too many TLS_LINK certificates");
+          }
+          link_cert = cert;
+        } else if (cert_type == OR_CERT_TYPE_ID_1024) {
+          if (id_cert) {
+            tor_cert_free(cert);
+            ERR("Too many ID_1024 certificates");
+          }
+          id_cert = cert;
+        } else if (cert_type == OR_CERT_TYPE_AUTH_1024) {
+          if (auth_cert) {
+            tor_cert_free(cert);
+            ERR("Too many AUTH_1024 certificates");
+          }
+          auth_cert = cert;
+        } else {
+          tor_cert_free(cert);
+        }
+      }
+    }
+    ptr += 3 + cert_len;
+    continue;
+
+  truncated:
+    ERR("It ends in the middle of a certificate");
+  }
+
+  if (chan->conn->handshake_state->started_here) {
+    int severity;
+    if (! (id_cert && link_cert))
+      ERR("The certs we wanted were missing");
+    /* Okay. We should be able to check the certificates now. */
+    if (! tor_tls_cert_matches_key(chan->conn->tls, link_cert)) {
+      ERR("The link certificate didn't match the TLS public key");
+    }
+    /* Note that this warns more loudly about time and validity if we were
+    * _trying_ to connect to an authority, not necessarily if we _did_ connect
+    * to one. */
+    if (router_digest_is_trusted_dir(
+          TLS_CHAN_TO_BASE(chan)->identity_digest))
+      severity = LOG_WARN;
+    else
+      severity = LOG_PROTOCOL_WARN;
+
+    if (! tor_tls_cert_is_valid(severity, link_cert, id_cert, 0))
+      ERR("The link certificate was not valid");
+    if (! tor_tls_cert_is_valid(severity, id_cert, id_cert, 1))
+      ERR("The ID certificate was not valid");
+
+    chan->conn->handshake_state->authenticated = 1;
+    {
+      const digests_t *id_digests = tor_cert_get_id_digests(id_cert);
+      crypto_pk_t *identity_rcvd;
+      if (!id_digests)
+        ERR("Couldn't compute digests for key in ID cert");
+
+      identity_rcvd = tor_tls_cert_get_key(id_cert);
+      if (!identity_rcvd)
+        ERR("Internal error: Couldn't get RSA key from ID cert.");
+      memcpy(chan->conn->handshake_state->authenticated_peer_id,
+             id_digests->d[DIGEST_SHA1], DIGEST_LEN);
+      channel_set_circid_type(TLS_CHAN_TO_BASE(chan), identity_rcvd);
+      crypto_pk_free(identity_rcvd);
+    }
+
+    if (connection_or_client_learned_peer_id(chan->conn,
+            chan->conn->handshake_state->authenticated_peer_id) < 0)
+      ERR("Problem setting or checking peer id");
+
+    log_info(LD_OR,
+             "Got some good certificates from %s:%d: Authenticated it.",
+             safe_str(chan->conn->_base.address), chan->conn->_base.port);
+
+    chan->conn->handshake_state->id_cert = id_cert;
+    id_cert = NULL;
+
+    if (!public_server_mode(get_options())) {
+      /* If we initiated the connection and we are not a public server, we
+       * aren't planning to authenticate at all.  At this point we know who we
+       * are talking to, so we can just send a netinfo now. */
+      send_netinfo = 1;
+    }
+  } else {
+    if (! (id_cert && auth_cert))
+      ERR("The certs we wanted were missing");
+
+    /* Remember these certificates so we can check an AUTHENTICATE cell */
+    if (! tor_tls_cert_is_valid(LOG_PROTOCOL_WARN, auth_cert, id_cert, 1))
+      ERR("The authentication certificate was not valid");
+    if (! tor_tls_cert_is_valid(LOG_PROTOCOL_WARN, id_cert, id_cert, 1))
+      ERR("The ID certificate was not valid");
+
+    log_info(LD_OR,
+             "Got some good certificates from %s:%d: "
+             "Waiting for AUTHENTICATE.",
+             safe_str(chan->conn->_base.address),
+             chan->conn->_base.port);
+    /* XXXX check more stuff? */
+
+    chan->conn->handshake_state->id_cert = id_cert;
+    chan->conn->handshake_state->auth_cert = auth_cert;
+    id_cert = auth_cert = NULL;
+  }
+
+  chan->conn->handshake_state->received_certs_cell = 1;
+
+  if (send_netinfo) {
+    if (connection_or_send_netinfo(chan->conn) < 0) {
+      log_warn(LD_OR, "Couldn't send netinfo cell");
+      connection_or_close_for_error(chan->conn, 0);
+      goto err;
+    }
+  }
+
+ err:
+  tor_cert_free(id_cert);
+  tor_cert_free(link_cert);
+  tor_cert_free(auth_cert);
+#undef ERR
+}
+
+/**
+ * Process an AUTH_CHALLENGE cell from a channel_tls_t
+ *
+ * This function is called to handle an incoming AUTH_CHALLENGE cell on a
+ * channel_tls_t; if we weren't supposed to get one (for example, because we're
+ * not the originator of the channel), or it's ill-formed, or we aren't doing
+ * a v3 handshake, mark the channel.  If the cell is well-formed but we don't
+ * want to authenticate, just drop it.  If the cell is well-formed *and* we
+ * want to authenticate, send an AUTHENTICATE cell and then a NETINFO cell.
+ */
+
+static void
+channel_tls_process_auth_challenge_cell(var_cell_t *cell, channel_tls_t *chan)
+{
+  int n_types, i, use_type = -1;
+  uint8_t *cp;
+
+  tor_assert(cell);
+  tor_assert(chan);
+  tor_assert(chan->conn);
+
+#define ERR(s)                                                  \
+  do {                                                          \
+    log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,                      \
+           "Received a bad AUTH_CHALLENGE cell from %s:%d: %s", \
+           safe_str(chan->conn->_base.address),                 \
+           chan->conn->_base.port, (s));                        \
+    connection_or_close_for_error(chan->conn, 0);               \
+    return;                                                     \
+  } while (0)
+
+  if (chan->conn->_base.state != OR_CONN_STATE_OR_HANDSHAKING_V3)
+    ERR("We're not currently doing a v3 handshake");
+  if (chan->conn->link_proto < 3)
+    ERR("We're not using link protocol >= 3");
+  if (!(chan->conn->handshake_state->started_here))
+    ERR("We didn't originate this connection");
+  if (chan->conn->handshake_state->received_auth_challenge)
+    ERR("We already received one");
+  if (!(chan->conn->handshake_state->received_certs_cell))
+    ERR("We haven't gotten a CERTS cell yet");
+  if (cell->payload_len < OR_AUTH_CHALLENGE_LEN + 2)
+    ERR("It was too short");
+  if (cell->circ_id)
+    ERR("It had a nonzero circuit ID");
+
+  n_types = ntohs(get_uint16(cell->payload + OR_AUTH_CHALLENGE_LEN));
+  if (cell->payload_len < OR_AUTH_CHALLENGE_LEN + 2 + 2*n_types)
+    ERR("It looks truncated");
+
+  /* Now see if there is an authentication type we can use */
+  cp = cell->payload+OR_AUTH_CHALLENGE_LEN + 2;
+  for (i = 0; i < n_types; ++i, cp += 2) {
+    uint16_t authtype = ntohs(get_uint16(cp));
+    if (authtype == AUTHTYPE_RSA_SHA256_TLSSECRET)
+      use_type = authtype;
+  }
+
+  chan->conn->handshake_state->received_auth_challenge = 1;
+
+  if (! public_server_mode(get_options())) {
+    /* If we're not a public server then we don't want to authenticate on a
+       connection we originated, and we already sent a NETINFO cell when we
+       got the CERTS cell. We have nothing more to do. */
+    return;
+  }
+
+  if (use_type >= 0) {
+    log_info(LD_OR,
+             "Got an AUTH_CHALLENGE cell from %s:%d: Sending "
+             "authentication",
+             safe_str(chan->conn->_base.address),
+             chan->conn->_base.port);
+
+    if (connection_or_send_authenticate_cell(chan->conn, use_type) < 0) {
+      log_warn(LD_OR,
+               "Couldn't send authenticate cell");
+      connection_or_close_for_error(chan->conn, 0);
+      return;
+    }
+  } else {
+    log_info(LD_OR,
+             "Got an AUTH_CHALLENGE cell from %s:%d, but we don't "
+             "know any of its authentication types. Not authenticating.",
+             safe_str(chan->conn->_base.address),
+             chan->conn->_base.port);
+  }
+
+  if (connection_or_send_netinfo(chan->conn) < 0) {
+    log_warn(LD_OR, "Couldn't send netinfo cell");
+    connection_or_close_for_error(chan->conn, 0);
+    return;
+  }
+
+#undef ERR
+}
+
+/**
+ * Process an AUTHENTICATE cell from a channel_tls_t
+ *
+ * If it's ill-formed or we weren't supposed to get one or we're not doing a
+ * v3 handshake, then mark the connection.  If it does not authenticate the
+ * other side of the connection successfully (because it isn't signed right,
+ * we didn't get a CERTS cell, etc) mark the connection.  Otherwise, accept
+ * the identity of the router on the other side of the connection.
+ */
+
+static void
+channel_tls_process_authenticate_cell(var_cell_t *cell, channel_tls_t *chan)
+{
+  uint8_t expected[V3_AUTH_FIXED_PART_LEN];
+  const uint8_t *auth;
+  int authlen;
+
+  tor_assert(cell);
+  tor_assert(chan);
+  tor_assert(chan->conn);
+
+#define ERR(s)                                                  \
+  do {                                                          \
+    log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,                      \
+           "Received a bad AUTHENTICATE cell from %s:%d: %s",   \
+           safe_str(chan->conn->_base.address),                 \
+           chan->conn->_base.port, (s));                        \
+    connection_or_close_for_error(chan->conn, 0);               \
+    return;                                                     \
+  } while (0)
+
+  if (chan->conn->_base.state != OR_CONN_STATE_OR_HANDSHAKING_V3)
+    ERR("We're not doing a v3 handshake");
+  if (chan->conn->link_proto < 3)
+    ERR("We're not using link protocol >= 3");
+  if (chan->conn->handshake_state->started_here)
+    ERR("We originated this connection");
+  if (chan->conn->handshake_state->received_authenticate)
+    ERR("We already got one!");
+  if (chan->conn->handshake_state->authenticated) {
+    /* Should be impossible given other checks */
+    ERR("The peer is already authenticated");
+  }
+  if (!(chan->conn->handshake_state->received_certs_cell))
+    ERR("We never got a certs cell");
+  if (chan->conn->handshake_state->auth_cert == NULL)
+    ERR("We never got an authentication certificate");
+  if (chan->conn->handshake_state->id_cert == NULL)
+    ERR("We never got an identity certificate");
+  if (cell->payload_len < 4)
+    ERR("Cell was way too short");
+
+  auth = cell->payload;
+  {
+    uint16_t type = ntohs(get_uint16(auth));
+    uint16_t len = ntohs(get_uint16(auth+2));
+    if (4 + len > cell->payload_len)
+      ERR("Authenticator was truncated");
+
+    if (type != AUTHTYPE_RSA_SHA256_TLSSECRET)
+      ERR("Authenticator type was not recognized");
+
+    auth += 4;
+    authlen = len;
+  }
+
+  if (authlen < V3_AUTH_BODY_LEN + 1)
+    ERR("Authenticator was too short");
+
+  if (connection_or_compute_authenticate_cell_body(
+                        chan->conn, expected, sizeof(expected), NULL, 1) < 0)
+    ERR("Couldn't compute expected AUTHENTICATE cell body");
+
+  if (tor_memneq(expected, auth, sizeof(expected)))
+    ERR("Some field in the AUTHENTICATE cell body was not as expected");
+
+  {
+    crypto_pk_t *pk = tor_tls_cert_get_key(
+                                   chan->conn->handshake_state->auth_cert);
+    char d[DIGEST256_LEN];
+    char *signed_data;
+    size_t keysize;
+    int signed_len;
+
+    if (!pk)
+      ERR("Internal error: couldn't get RSA key from AUTH cert.");
+    crypto_digest256(d, (char*)auth, V3_AUTH_BODY_LEN, DIGEST_SHA256);
+
+    keysize = crypto_pk_keysize(pk);
+    signed_data = tor_malloc(keysize);
+    signed_len = crypto_pk_public_checksig(pk, signed_data, keysize,
+                                           (char*)auth + V3_AUTH_BODY_LEN,
+                                           authlen - V3_AUTH_BODY_LEN);
+    crypto_pk_free(pk);
+    if (signed_len < 0) {
+      tor_free(signed_data);
+      ERR("Signature wasn't valid");
+    }
+    if (signed_len < DIGEST256_LEN) {
+      tor_free(signed_data);
+      ERR("Not enough data was signed");
+    }
+    /* Note that we deliberately allow *more* than DIGEST256_LEN bytes here,
+     * in case they're later used to hold a SHA3 digest or something. */
+    if (tor_memneq(signed_data, d, DIGEST256_LEN)) {
+      tor_free(signed_data);
+      ERR("Signature did not match data to be signed.");
+    }
+    tor_free(signed_data);
+  }
+
+  /* Okay, we are authenticated. */
+  chan->conn->handshake_state->received_authenticate = 1;
+  chan->conn->handshake_state->authenticated = 1;
+  chan->conn->handshake_state->digest_received_data = 0;
+  {
+    crypto_pk_t *identity_rcvd =
+      tor_tls_cert_get_key(chan->conn->handshake_state->id_cert);
+    const digests_t *id_digests =
+      tor_cert_get_id_digests(chan->conn->handshake_state->id_cert);
+
+    /* This must exist; we checked key type when reading the cert. */
+    tor_assert(id_digests);
+
+    memcpy(chan->conn->handshake_state->authenticated_peer_id,
+           id_digests->d[DIGEST_SHA1], DIGEST_LEN);
+
+    channel_set_circid_type(TLS_CHAN_TO_BASE(chan), identity_rcvd);
+    crypto_pk_free(identity_rcvd);
+
+    connection_or_init_conn_from_address(chan->conn,
+                  &(chan->conn->_base.addr),
+                  chan->conn->_base.port,
+                  (const char*)(chan->conn->handshake_state->
+                    authenticated_peer_id),
+                  0);
+
+    log_info(LD_OR,
+             "Got an AUTHENTICATE cell from %s:%d: Looks good.",
+             safe_str(chan->conn->_base.address),
+             chan->conn->_base.port);
+  }
+
+#undef ERR
+}
+
diff --git a/src/or/channeltls.h b/src/or/channeltls.h
new file mode 100644
index 000000000..ca2fc8894
--- /dev/null
+++ b/src/or/channeltls.h
@@ -0,0 +1,57 @@
+/* * Copyright (c) 2012, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file channeltls.h
+ * \brief Header file for channeltls.c
+ **/
+
+#ifndef _TOR_CHANNEL_TLS_H
+#define _TOR_CHANNEL_TLS_H
+
+#include "or.h"
+#include "channel.h"
+
+#define BASE_CHAN_TO_TLS(c) (channel_tls_from_base((c)))
+#define TLS_CHAN_TO_BASE(c) (channel_tls_to_base((c)))
+
+#define TLS_CHAN_MAGIC 0x8a192427U
+
+#ifdef _TOR_CHANNEL_INTERNAL
+
+struct channel_tls_s {
+  /* Base channel_t struct */
+  channel_t _base;
+  /* or_connection_t pointer */
+  or_connection_t *conn;
+};
+
+#endif /* _TOR_CHANNEL_INTERNAL */
+
+channel_t * channel_tls_connect(const tor_addr_t *addr, uint16_t port,
+                                const char *id_digest);
+channel_listener_t * channel_tls_get_listener(void);
+channel_listener_t * channel_tls_start_listener(void);
+channel_t * channel_tls_handle_incoming(or_connection_t *orconn);
+
+/* Casts */
+
+channel_t * channel_tls_to_base(channel_tls_t *tlschan);
+channel_tls_t * channel_tls_from_base(channel_t *chan);
+
+/* Things for connection_or.c to call back into */
+ssize_t channel_tls_flush_some_cells(channel_tls_t *chan, ssize_t num_cells);
+int channel_tls_more_to_flush(channel_tls_t *chan);
+void channel_tls_handle_cell(cell_t *cell, or_connection_t *conn);
+void channel_tls_handle_state_change_on_orconn(channel_tls_t *chan,
+                                               or_connection_t *conn,
+                                               uint8_t old_state,
+                                               uint8_t state);
+void channel_tls_handle_var_cell(var_cell_t *var_cell,
+                                 or_connection_t *conn);
+
+/* Cleanup at shutdown */
+void channel_tls_free_all(void);
+
+#endif
+
diff --git a/src/or/circuitbuild.c b/src/or/circuitbuild.c
index 56c2c22d0..749985f90 100644
--- a/src/or/circuitbuild.c
+++ b/src/or/circuitbuild.c
@@ -12,9 +12,11 @@
 #define CIRCUIT_PRIVATE
 
 #include "or.h"
+#include "channel.h"
 #include "circuitbuild.h"
 #include "circuitlist.h"
 #include "circuituse.h"
+#include "command.h"
 #include "config.h"
 #include "confparse.h"
 #include "connection.h"
@@ -125,6 +127,9 @@ static int unit_tests = 0;
 
 /********* END VARIABLES ************/
 
+static channel_t * channel_connect_for_circuit(const tor_addr_t *addr,
+                                               uint16_t port,
+                                               const char *id_digest);
 static int circuit_deliver_create_cell(circuit_t *circ,
                                        uint8_t cell_type, const char *payload);
 static int onion_pick_cpath_exit(origin_circuit_t *circ, extend_info_t *exit);
@@ -141,6 +146,22 @@ static void bridge_free(bridge_info_t *bridge);
 static int entry_guard_inc_first_hop_count(entry_guard_t *guard);
 static void pathbias_count_success(origin_circuit_t *circ);
 
+/** This function tries to get a channel to the specified endpoint,
+ * and then calls command_setup_channel() to give it the right
+ * callbacks.
+ */
+static channel_t *
+channel_connect_for_circuit(const tor_addr_t *addr, uint16_t port,
+                            const char *id_digest)
+{
+  channel_t *chan;
+
+  chan = channel_connect(addr, port, id_digest);
+  if (chan) command_setup_channel(chan);
+
+  return chan;
+}
+
 /**
  * This function decides if CBT learning should be disabled. It returns
  * true if one or more of the following four conditions are met:
@@ -1683,26 +1704,29 @@ circuit_build_times_set_timeout(circuit_build_times_t *cbt)
  * Return it, or 0 if can't get a unique circ_id.
  */
 static circid_t
-get_unique_circ_id_by_conn(or_connection_t *conn)
+get_unique_circ_id_by_chan(channel_t *chan)
 {
   circid_t test_circ_id;
   circid_t attempts=0;
   circid_t high_bit;
 
-  tor_assert(conn);
-  if (conn->circ_id_type == CIRC_ID_TYPE_NEITHER) {
-    log_warn(LD_BUG, "Trying to pick a circuit ID for a connection from "
+  tor_assert(chan);
+
+  if (chan->circ_id_type == CIRC_ID_TYPE_NEITHER) {
+    log_warn(LD_BUG,
+             "Trying to pick a circuit ID for a connection from "
              "a client with no identity.");
     return 0;
   }
-  high_bit = (conn->circ_id_type == CIRC_ID_TYPE_HIGHER) ? 1<<15 : 0;
+  high_bit =
+    (chan->circ_id_type == CIRC_ID_TYPE_HIGHER) ? 1<<15 : 0;
   do {
     /* Sequentially iterate over test_circ_id=1...1<<15-1 until we find a
      * circID such that (high_bit|test_circ_id) is not already used. */
-    test_circ_id = conn->next_circ_id++;
+    test_circ_id = chan->next_circ_id++;
     if (test_circ_id == 0 || test_circ_id >= 1<<15) {
       test_circ_id = 1;
-      conn->next_circ_id = 2;
+      chan->next_circ_id = 2;
     }
     if (++attempts > 1<<15) {
       /* Make sure we don't loop forever if all circ_id's are used. This
@@ -1712,7 +1736,7 @@ get_unique_circ_id_by_conn(or_connection_t *conn)
       return 0;
     }
     test_circ_id |= high_bit;
-  } while (circuit_id_in_use_on_orconn(test_circ_id, conn));
+  } while (circuit_id_in_use_on_channel(test_circ_id, chan));
   return test_circ_id;
 }
 
@@ -1891,9 +1915,9 @@ onion_populate_cpath(origin_circuit_t *circ)
 origin_circuit_t *
 origin_circuit_init(uint8_t purpose, int flags)
 {
-  /* sets circ->p_circ_id and circ->p_conn */
+  /* sets circ->p_circ_id and circ->p_chan */
   origin_circuit_t *circ = origin_circuit_new();
-  circuit_set_state(TO_CIRCUIT(circ), CIRCUIT_STATE_OR_WAIT);
+  circuit_set_state(TO_CIRCUIT(circ), CIRCUIT_STATE_CHAN_WAIT);
   circ->build_state = tor_malloc_zero(sizeof(cpath_build_state_t));
   circ->build_state->onehop_tunnel =
     ((flags & CIRCLAUNCH_ONEHOP_TUNNEL) ? 1 : 0);
@@ -1945,7 +1969,7 @@ int
 circuit_handle_first_hop(origin_circuit_t *circ)
 {
   crypt_path_t *firsthop;
-  or_connection_t *n_conn;
+  channel_t *n_chan;
   int err_reason = 0;
   const char *msg = NULL;
   int should_launch = 0;
@@ -1959,12 +1983,12 @@ circuit_handle_first_hop(origin_circuit_t *circ)
             fmt_addr(&firsthop->extend_info->addr),
             firsthop->extend_info->port);
 
-  n_conn = connection_or_get_for_extend(firsthop->extend_info->identity_digest,
-                                        &firsthop->extend_info->addr,
-                                        &msg,
-                                        &should_launch);
+  n_chan = channel_get_for_extend(firsthop->extend_info->identity_digest,
+                                  &firsthop->extend_info->addr,
+                                  &msg,
+                                  &should_launch);
 
-  if (!n_conn) {
+  if (!n_chan) {
     /* not currently connected in a useful way. */
     log_info(LD_CIRC, "Next router is %s: %s",
              safe_str_client(extend_info_describe(firsthop->extend_info)),
@@ -1974,10 +1998,11 @@ circuit_handle_first_hop(origin_circuit_t *circ)
     if (should_launch) {
       if (circ->build_state->onehop_tunnel)
         control_event_bootstrap(BOOTSTRAP_STATUS_CONN_DIR, 0);
-      n_conn = connection_or_connect(&firsthop->extend_info->addr,
-                                     firsthop->extend_info->port,
-                                     firsthop->extend_info->identity_digest);
-      if (!n_conn) { /* connect failed, forget the whole thing */
+      n_chan = channel_connect_for_circuit(
+          &firsthop->extend_info->addr,
+          firsthop->extend_info->port,
+          firsthop->extend_info->identity_digest);
+      if (!n_chan) { /* connect failed, forget the whole thing */
         log_info(LD_CIRC,"connect to firsthop failed. Closing.");
         return -END_CIRC_REASON_CONNECTFAILED;
       }
@@ -1985,13 +2010,13 @@ circuit_handle_first_hop(origin_circuit_t *circ)
 
     log_debug(LD_CIRC,"connecting in progress (or finished). Good.");
     /* return success. The onion/circuit/etc will be taken care of
-     * automatically (may already have been) whenever n_conn reaches
+     * automatically (may already have been) whenever n_chan reaches
      * OR_CONN_STATE_OPEN.
      */
     return 0;
   } else { /* it's already open. use it. */
     tor_assert(!circ->_base.n_hop);
-    circ->_base.n_conn = n_conn;
+    circ->_base.n_chan = n_chan;
     log_debug(LD_CIRC,"Conn open. Delivering first onion skin.");
     if ((err_reason = circuit_send_next_onion_skin(circ)) < 0) {
       log_info(LD_CIRC,"circuit_send_next_onion_skin failed.");
@@ -2007,48 +2032,49 @@ circuit_handle_first_hop(origin_circuit_t *circ)
  * Status is 1 if connect succeeded, or 0 if connect failed.
  */
 void
-circuit_n_conn_done(or_connection_t *or_conn, int status)
+circuit_n_chan_done(channel_t *chan, int status)
 {
   smartlist_t *pending_circs;
   int err_reason = 0;
 
-  log_debug(LD_CIRC,"or_conn to %s/%s, status=%d",
-            or_conn->nickname ? or_conn->nickname : "NULL",
-            or_conn->_base.address, status);
+  tor_assert(chan);
+
+  log_debug(LD_CIRC,"chan to %s/%s, status=%d",
+            chan->nickname ? chan->nickname : "NULL",
+            channel_get_canonical_remote_descr(chan), status);
 
   pending_circs = smartlist_new();
-  circuit_get_all_pending_on_or_conn(pending_circs, or_conn);
+  circuit_get_all_pending_on_channel(pending_circs, chan);
 
   SMARTLIST_FOREACH_BEGIN(pending_circs, circuit_t *, circ)
     {
       /* These checks are redundant wrt get_all_pending_on_or_conn, but I'm
        * leaving them in in case it's possible for the status of a circuit to
        * change as we're going down the list. */
-      if (circ->marked_for_close || circ->n_conn || !circ->n_hop ||
-          circ->state != CIRCUIT_STATE_OR_WAIT)
+      if (circ->marked_for_close || circ->n_chan || !circ->n_hop ||
+          circ->state != CIRCUIT_STATE_CHAN_WAIT)
         continue;
 
       if (tor_digest_is_zero(circ->n_hop->identity_digest)) {
         /* Look at addr/port. This is an unkeyed connection. */
-        if (!tor_addr_eq(&circ->n_hop->addr, &or_conn->_base.addr) ||
-            circ->n_hop->port != or_conn->_base.port)
+        if (!channel_matches_extend_info(chan, circ->n_hop))
           continue;
       } else {
         /* We expected a key. See if it's the right one. */
-        if (tor_memneq(or_conn->identity_digest,
+        if (tor_memneq(chan->identity_digest,
                    circ->n_hop->identity_digest, DIGEST_LEN))
           continue;
       }
-      if (!status) { /* or_conn failed; close circ */
-        log_info(LD_CIRC,"or_conn failed. Closing circ.");
-        circuit_mark_for_close(circ, END_CIRC_REASON_OR_CONN_CLOSED);
+      if (!status) { /* chan failed; close circ */
+        log_info(LD_CIRC,"Channel failed; closing circ.");
+        circuit_mark_for_close(circ, END_CIRC_REASON_CHANNEL_CLOSED);
         continue;
       }
       log_debug(LD_CIRC, "Found circ, sending create cell.");
       /* circuit_deliver_create_cell will set n_circ_id and add us to
-       * orconn_circuid_circuit_map, so we don't need to call
-       * set_circid_orconn here. */
-      circ->n_conn = or_conn;
+       * chan_circuid_circuit_map, so we don't need to call
+       * set_circid_chan here. */
+      circ->n_chan = chan;
       extend_info_free(circ->n_hop);
       circ->n_hop = NULL;
 
@@ -2064,13 +2090,13 @@ circuit_n_conn_done(or_connection_t *or_conn, int status)
         }
       } else {
         /* pull the create cell out of circ->onionskin, and send it */
-        tor_assert(circ->n_conn_onionskin);
+        tor_assert(circ->n_chan_onionskin);
         if (circuit_deliver_create_cell(circ,CELL_CREATE,
-                                        circ->n_conn_onionskin)<0) {
+                                        circ->n_chan_onionskin)<0) {
           circuit_mark_for_close(circ, END_CIRC_REASON_RESOURCELIMIT);
           continue;
         }
-        tor_free(circ->n_conn_onionskin);
+        tor_free(circ->n_chan_onionskin);
         circuit_set_state(circ, CIRCUIT_STATE_OPEN);
       }
     }
@@ -2079,7 +2105,7 @@ circuit_n_conn_done(or_connection_t *or_conn, int status)
   smartlist_free(pending_circs);
 }
 
-/** Find a new circid that isn't currently in use on the circ->n_conn
+/** Find a new circid that isn't currently in use on the circ->n_chan
  * for the outgoing
  * circuit <b>circ</b>, and deliver a cell of type <b>cell_type</b>
  * (either CELL_CREATE or CELL_CREATE_FAST) with payload <b>payload</b>
@@ -2094,29 +2120,29 @@ circuit_deliver_create_cell(circuit_t *circ, uint8_t cell_type,
   circid_t id;
 
   tor_assert(circ);
-  tor_assert(circ->n_conn);
+  tor_assert(circ->n_chan);
   tor_assert(payload);
   tor_assert(cell_type == CELL_CREATE || cell_type == CELL_CREATE_FAST);
 
-  id = get_unique_circ_id_by_conn(circ->n_conn);
+  id = get_unique_circ_id_by_chan(circ->n_chan);
   if (!id) {
     log_warn(LD_CIRC,"failed to get unique circID.");
     return -1;
   }
   log_debug(LD_CIRC,"Chosen circID %u.", id);
-  circuit_set_n_circid_orconn(circ, id, circ->n_conn);
+  circuit_set_n_circid_chan(circ, id, circ->n_chan);
 
   memset(&cell, 0, sizeof(cell_t));
   cell.command = cell_type;
   cell.circ_id = circ->n_circ_id;
 
   memcpy(cell.payload, payload, ONIONSKIN_CHALLENGE_LEN);
-  append_cell_to_circuit_queue(circ, circ->n_conn, &cell,
+  append_cell_to_circuit_queue(circ, circ->n_chan, &cell,
                                CELL_DIRECTION_OUT, 0);
 
   if (CIRCUIT_IS_ORIGIN(circ)) {
     /* mark it so it gets better rate limiting treatment. */
-    circ->n_conn->client_used = time(NULL);
+    channel_timestamp_client(circ->n_chan);
   }
 
   return 0;
@@ -2218,7 +2244,7 @@ circuit_send_next_onion_skin(origin_circuit_t *circ)
     else
       control_event_bootstrap(BOOTSTRAP_STATUS_CIRCUIT_CREATE, 0);
 
-    node = node_get_by_id(circ->_base.n_conn->identity_digest);
+    node = node_get_by_id(circ->_base.n_chan->identity_digest);
     fast = should_use_create_fast_for_circuit(circ);
     if (!fast) {
       /* We are an OR and we know the right onion key: we should
@@ -2386,7 +2412,7 @@ circuit_note_clock_jumped(int seconds_elapsed)
 int
 circuit_extend(cell_t *cell, circuit_t *circ)
 {
-  or_connection_t *n_conn;
+  channel_t *n_chan;
   relay_header_t rh;
   char *onionskin;
   char *id_digest=NULL;
@@ -2396,9 +2422,9 @@ circuit_extend(cell_t *cell, circuit_t *circ)
   const char *msg = NULL;
   int should_launch = 0;
 
-  if (circ->n_conn) {
+  if (circ->n_chan) {
     log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
-           "n_conn already set. Bug/attack. Closing.");
+           "n_chan already set. Bug/attack. Closing.");
     return -1;
   }
   if (circ->n_hop) {
@@ -2457,19 +2483,20 @@ circuit_extend(cell_t *cell, circuit_t *circ)
   /* Next, check if we're being asked to connect to the hop that the
    * extend cell came from. There isn't any reason for that, and it can
    * assist circular-path attacks. */
-  if (tor_memeq(id_digest, TO_OR_CIRCUIT(circ)->p_conn->identity_digest,
-              DIGEST_LEN)) {
+  if (tor_memeq(id_digest,
+                TO_OR_CIRCUIT(circ)->p_chan->identity_digest,
+                DIGEST_LEN)) {
     log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
            "Client asked me to extend back to the previous hop.");
     return -1;
   }
 
-  n_conn = connection_or_get_for_extend(id_digest,
-                                        &n_addr,
-                                        &msg,
-                                        &should_launch);
+  n_chan = channel_get_for_extend(id_digest,
+                                  &n_addr,
+                                  &msg,
+                                  &should_launch);
 
-  if (!n_conn) {
+  if (!n_chan) {
     log_debug(LD_CIRC|LD_OR,"Next router (%s:%d): %s",
               fmt_addr(&n_addr), (int)n_port, msg?msg:"????");
 
@@ -2478,31 +2505,32 @@ circuit_extend(cell_t *cell, circuit_t *circ)
                                     NULL /*onion_key*/,
                                     &n_addr, n_port);
 
-    circ->n_conn_onionskin = tor_malloc(ONIONSKIN_CHALLENGE_LEN);
-    memcpy(circ->n_conn_onionskin, onionskin, ONIONSKIN_CHALLENGE_LEN);
-    circuit_set_state(circ, CIRCUIT_STATE_OR_WAIT);
+    circ->n_chan_onionskin = tor_malloc(ONIONSKIN_CHALLENGE_LEN);
+    memcpy(circ->n_chan_onionskin, onionskin, ONIONSKIN_CHALLENGE_LEN);
+    circuit_set_state(circ, CIRCUIT_STATE_CHAN_WAIT);
 
     if (should_launch) {
       /* we should try to open a connection */
-      n_conn = connection_or_connect(&n_addr, n_port, id_digest);
-      if (!n_conn) {
-        log_info(LD_CIRC,"Launching n_conn failed. Closing circuit.");
+      n_chan = channel_connect_for_circuit(&n_addr, n_port, id_digest);
+      if (!n_chan) {
+        log_info(LD_CIRC,"Launching n_chan failed. Closing circuit.");
         circuit_mark_for_close(circ, END_CIRC_REASON_CONNECTFAILED);
         return 0;
       }
       log_debug(LD_CIRC,"connecting in progress (or finished). Good.");
     }
     /* return success. The onion/circuit/etc will be taken care of
-     * automatically (may already have been) whenever n_conn reaches
+     * automatically (may already have been) whenever n_chan reaches
      * OR_CONN_STATE_OPEN.
      */
     return 0;
   }
 
   tor_assert(!circ->n_hop); /* Connection is already established. */
-  circ->n_conn = n_conn;
-  log_debug(LD_CIRC,"n_conn is %s:%u",
-            n_conn->_base.address,n_conn->_base.port);
+  circ->n_chan = n_chan;
+  log_debug(LD_CIRC,
+            "n_chan is %s",
+            channel_get_canonical_remote_descr(n_chan));
 
   if (circuit_deliver_create_cell(circ, CELL_CREATE, onionskin) < 0)
     return -1;
@@ -2699,8 +2727,8 @@ pathbias_count_first_hop(origin_circuit_t *circ)
     if (!circ->has_opened) {
       entry_guard_t *guard;
 
-      guard = entry_guard_get_by_id_digest(
-              circ->_base.n_conn->identity_digest);
+      guard =
+        entry_guard_get_by_id_digest(circ->_base.n_chan->identity_digest);
       if (guard) {
         if (circ->path_state == PATH_STATE_NEW_CIRC) {
           circ->path_state = PATH_STATE_DID_FIRST_HOP;
@@ -2770,6 +2798,7 @@ pathbias_count_success(origin_circuit_t *circ)
   static ratelim_t success_notice_limit =
     RATELIM_INIT(SUCCESS_NOTICE_INTERVAL);
   char *rate_msg = NULL;
+  entry_guard_t *guard = NULL;
 
   /* We can't do path bias accounting without entry guards.
    * Testing and controller circuits also have no guards. */
@@ -2804,8 +2833,8 @@ pathbias_count_success(origin_circuit_t *circ)
 
   /* Don't count cannibalized/reused circs for path bias */
   if (!circ->has_opened) {
-    entry_guard_t *guard =
-      entry_guard_get_by_id_digest(circ->_base.n_conn->identity_digest);
+    guard =
+      entry_guard_get_by_id_digest(circ->_base.n_chan->identity_digest);
 
     if (guard) {
       if (circ->path_state == PATH_STATE_DID_FIRST_HOP) {
@@ -3021,7 +3050,7 @@ circuit_truncated(origin_circuit_t *circ, crypt_path_t *layer, int reason)
    *     just give up.
    */
   circuit_mark_for_close(TO_CIRCUIT(circ),
-          END_CIRC_REASON_FLAG_REMOTE|reason);
+          END_CIRC_REASON_FLAG_REMOTE|END_CIRC_REASON_CHANNEL_CLOSED|reason);
   return 0;
 
 #if 0
@@ -3095,12 +3124,12 @@ onionskin_answer(or_circuit_t *circ, uint8_t cell_type, const char *payload,
   circ->is_first_hop = (cell_type == CELL_CREATED_FAST);
 
   append_cell_to_circuit_queue(TO_CIRCUIT(circ),
-                               circ->p_conn, &cell, CELL_DIRECTION_IN, 0);
+                               circ->p_chan, &cell, CELL_DIRECTION_IN, 0);
   log_debug(LD_CIRC,"Finished sending '%s' cell.",
             circ->is_first_hop ? "created_fast" : "created");
 
-  if (!is_local_addr(&circ->p_conn->_base.addr) &&
-      !connection_or_nonopen_was_started_here(circ->p_conn)) {
+  if (!channel_is_local(circ->p_chan) &&
+      !channel_is_outgoing(circ->p_chan)) {
     /* record that we could process create cells from a non-local conn
      * that we didn't initiate; presumably this means that create cells
      * can reach us too. */
diff --git a/src/or/circuitbuild.h b/src/or/circuitbuild.h
index 8ec48beb0..0abffc516 100644
--- a/src/or/circuitbuild.h
+++ b/src/or/circuitbuild.h
@@ -22,7 +22,7 @@ origin_circuit_t *circuit_establish_circuit(uint8_t purpose,
                                             extend_info_t *exit,
                                             int flags);
 int circuit_handle_first_hop(origin_circuit_t *circ);
-void circuit_n_conn_done(or_connection_t *or_conn, int status);
+void circuit_n_chan_done(channel_t *chan, int status);
 int inform_testing_reachability(void);
 int circuit_timeout_want_to_count_circ(origin_circuit_t *circ);
 int circuit_send_next_onion_skin(origin_circuit_t *circ);
diff --git a/src/or/circuitlist.c b/src/or/circuitlist.c
index d9b74bd4c..b73822635 100644
--- a/src/or/circuitlist.c
+++ b/src/or/circuitlist.c
@@ -10,6 +10,7 @@
  **/
 
 #include "or.h"
+#include "channel.h"
 #include "circuitbuild.h"
 #include "circuitlist.h"
 #include "circuituse.h"
@@ -34,8 +35,8 @@
 /** A global list of all circuits at this hop. */
 circuit_t *global_circuitlist=NULL;
 
-/** A list of all the circuits in CIRCUIT_STATE_OR_WAIT. */
-static smartlist_t *circuits_pending_or_conns=NULL;
+/** A list of all the circuits in CIRCUIT_STATE_CHAN_WAIT. */
+static smartlist_t *circuits_pending_chans = NULL;
 
 static void circuit_free(circuit_t *circ);
 static void circuit_free_cpath(crypt_path_t *cpath);
@@ -44,154 +45,190 @@ static void cpath_ref_decref(crypt_path_reference_t *cpath_ref);
 
 /********* END VARIABLES ************/
 
-/** A map from OR connection and circuit ID to circuit.  (Lookup performance is
+/** A map from channel and circuit ID to circuit.  (Lookup performance is
  * very important here, since we need to do it every time a cell arrives.) */
-typedef struct orconn_circid_circuit_map_t {
-  HT_ENTRY(orconn_circid_circuit_map_t) node;
-  or_connection_t *or_conn;
+typedef struct chan_circid_circuit_map_t {
+  HT_ENTRY(chan_circid_circuit_map_t) node;
+  channel_t *chan;
   circid_t circ_id;
   circuit_t *circuit;
-} orconn_circid_circuit_map_t;
+} chan_circid_circuit_map_t;
 
-/** Helper for hash tables: compare the OR connection and circuit ID for a and
+/** Helper for hash tables: compare the channel and circuit ID for a and
  * b, and return less than, equal to, or greater than zero appropriately.
  */
 static INLINE int
-_orconn_circid_entries_eq(orconn_circid_circuit_map_t *a,
-                          orconn_circid_circuit_map_t *b)
+_chan_circid_entries_eq(chan_circid_circuit_map_t *a,
+                        chan_circid_circuit_map_t *b)
 {
-  return a->or_conn == b->or_conn && a->circ_id == b->circ_id;
+  return a->chan == b->chan && a->circ_id == b->circ_id;
 }
 
 /** Helper: return a hash based on circuit ID and the pointer value of
- * or_conn in <b>a</b>. */
+ * chan in <b>a</b>. */
 static INLINE unsigned int
-_orconn_circid_entry_hash(orconn_circid_circuit_map_t *a)
+_chan_circid_entry_hash(chan_circid_circuit_map_t *a)
 {
-  return (((unsigned)a->circ_id)<<8) ^ (unsigned)(uintptr_t)(a->or_conn);
+  return (((unsigned)a->circ_id)<<8) ^ (unsigned)(uintptr_t)(a->chan);
 }
 
-/** Map from [orconn,circid] to circuit. */
-static HT_HEAD(orconn_circid_map, orconn_circid_circuit_map_t)
-     orconn_circid_circuit_map = HT_INITIALIZER();
-HT_PROTOTYPE(orconn_circid_map, orconn_circid_circuit_map_t, node,
-             _orconn_circid_entry_hash, _orconn_circid_entries_eq)
-HT_GENERATE(orconn_circid_map, orconn_circid_circuit_map_t, node,
-            _orconn_circid_entry_hash, _orconn_circid_entries_eq, 0.6,
+/** Map from [chan,circid] to circuit. */
+static HT_HEAD(chan_circid_map, chan_circid_circuit_map_t)
+     chan_circid_map = HT_INITIALIZER();
+HT_PROTOTYPE(chan_circid_map, chan_circid_circuit_map_t, node,
+             _chan_circid_entry_hash, _chan_circid_entries_eq)
+HT_GENERATE(chan_circid_map, chan_circid_circuit_map_t, node,
+            _chan_circid_entry_hash, _chan_circid_entries_eq, 0.6,
             malloc, realloc, free)
 
-/** The most recently returned entry from circuit_get_by_circid_orconn;
+/** The most recently returned entry from circuit_get_by_circid_chan;
  * used to improve performance when many cells arrive in a row from the
  * same circuit.
  */
-orconn_circid_circuit_map_t *_last_circid_orconn_ent = NULL;
+chan_circid_circuit_map_t *_last_circid_chan_ent = NULL;
 
-/** Implementation helper for circuit_set_{p,n}_circid_orconn: A circuit ID
- * and/or or_connection for circ has just changed from <b>old_conn, old_id</b>
- * to <b>conn, id</b>.  Adjust the conn,circid map as appropriate, removing
+/** Implementation helper for circuit_set_{p,n}_circid_channel: A circuit ID
+ * and/or channel for circ has just changed from <b>old_chan, old_id</b>
+ * to <b>chan, id</b>.  Adjust the chan,circid map as appropriate, removing
  * the old entry (if any) and adding a new one. */
 static void
-circuit_set_circid_orconn_helper(circuit_t *circ, int direction,
-                                 circid_t id,
-                                 or_connection_t *conn)
+circuit_set_circid_chan_helper(circuit_t *circ, int direction,
+                               circid_t id,
+                               channel_t *chan)
 {
-  orconn_circid_circuit_map_t search;
-  orconn_circid_circuit_map_t *found;
-  or_connection_t *old_conn, **conn_ptr;
+  chan_circid_circuit_map_t search;
+  chan_circid_circuit_map_t *found;
+  channel_t *old_chan, **chan_ptr;
   circid_t old_id, *circid_ptr;
-  int was_active, make_active;
+  int make_active, attached = 0;
 
   if (direction == CELL_DIRECTION_OUT) {
-    conn_ptr = &circ->n_conn;
+    chan_ptr = &circ->n_chan;
     circid_ptr = &circ->n_circ_id;
-    was_active = circ->next_active_on_n_conn != NULL;
-    make_active = circ->n_conn_cells.n > 0;
+    make_active = circ->n_chan_cells.n > 0;
   } else {
     or_circuit_t *c = TO_OR_CIRCUIT(circ);
-    conn_ptr = &c->p_conn;
+    chan_ptr = &c->p_chan;
     circid_ptr = &c->p_circ_id;
-    was_active = c->next_active_on_p_conn != NULL;
-    make_active = c->p_conn_cells.n > 0;
+    make_active = c->p_chan_cells.n > 0;
   }
-  old_conn = *conn_ptr;
+  old_chan = *chan_ptr;
   old_id = *circid_ptr;
 
-  if (id == old_id && conn == old_conn)
+  if (id == old_id && chan == old_chan)
     return;
 
-  if (_last_circid_orconn_ent &&
-      ((old_id == _last_circid_orconn_ent->circ_id &&
-        old_conn == _last_circid_orconn_ent->or_conn) ||
-       (id == _last_circid_orconn_ent->circ_id &&
-        conn == _last_circid_orconn_ent->or_conn))) {
-    _last_circid_orconn_ent = NULL;
+  if (_last_circid_chan_ent &&
+      ((old_id == _last_circid_chan_ent->circ_id &&
+        old_chan == _last_circid_chan_ent->chan) ||
+       (id == _last_circid_chan_ent->circ_id &&
+        chan == _last_circid_chan_ent->chan))) {
+    _last_circid_chan_ent = NULL;
   }
 
-  if (old_conn) { /* we may need to remove it from the conn-circid map */
-    tor_assert(old_conn->_base.magic == OR_CONNECTION_MAGIC);
+  if (old_chan) {
+    /*
+     * If we're changing channels or ID and had an old channel and a non
+     * zero old ID and weren't marked for close (i.e., we should have been
+     * attached), detach the circuit. ID changes require this because
+     * circuitmux hashes on (channel_id, circuit_id).
+     */
+    if (old_id != 0 && (old_chan != chan || old_id != id) &&
+        !(circ->marked_for_close)) {
+      tor_assert(old_chan->cmux);
+      circuitmux_detach_circuit(old_chan->cmux, circ);
+    }
+
+    /* we may need to remove it from the conn-circid map */
     search.circ_id = old_id;
-    search.or_conn = old_conn;
-    found = HT_REMOVE(orconn_circid_map, &orconn_circid_circuit_map, &search);
+    search.chan = old_chan;
+    found = HT_REMOVE(chan_circid_map, &chan_circid_map, &search);
     if (found) {
       tor_free(found);
-      --old_conn->n_circuits;
+      if (direction == CELL_DIRECTION_OUT) {
+        /* One fewer circuits use old_chan as n_chan */
+        --(old_chan->num_n_circuits);
+      } else {
+        /* One fewer circuits use old_chan as p_chan */
+        --(old_chan->num_p_circuits);
+      }
     }
-    if (was_active && old_conn != conn)
-      make_circuit_inactive_on_conn(circ,old_conn);
   }
 
   /* Change the values only after we have possibly made the circuit inactive
-   * on the previous conn. */
-  *conn_ptr = conn;
+   * on the previous chan. */
+  *chan_ptr = chan;
   *circid_ptr = id;
 
-  if (conn == NULL)
+  if (chan == NULL)
     return;
 
   /* now add the new one to the conn-circid map */
   search.circ_id = id;
-  search.or_conn = conn;
-  found = HT_FIND(orconn_circid_map, &orconn_circid_circuit_map, &search);
+  search.chan = chan;
+  found = HT_FIND(chan_circid_map, &chan_circid_map, &search);
   if (found) {
     found->circuit = circ;
   } else {
-    found = tor_malloc_zero(sizeof(orconn_circid_circuit_map_t));
+    found = tor_malloc_zero(sizeof(chan_circid_circuit_map_t));
     found->circ_id = id;
-    found->or_conn = conn;
+    found->chan = chan;
     found->circuit = circ;
-    HT_INSERT(orconn_circid_map, &orconn_circid_circuit_map, found);
+    HT_INSERT(chan_circid_map, &chan_circid_map, found);
   }
-  if (make_active && old_conn != conn)
-    make_circuit_active_on_conn(circ,conn);
 
-  ++conn->n_circuits;
+  /*
+   * Attach to the circuitmux if we're changing channels or IDs and
+   * have a new channel and ID to use and the circuit is not marked for
+   * close.
+   */
+  if (chan && id != 0 && (old_chan != chan || old_id != id) &&
+      !(circ->marked_for_close)) {
+    tor_assert(chan->cmux);
+    circuitmux_attach_circuit(chan->cmux, circ, direction);
+    attached = 1;
+  }
+
+  /*
+   * This is a no-op if we have no cells, but if we do it marks us active to
+   * the circuitmux
+   */
+  if (make_active && attached)
+    update_circuit_on_cmux(circ, direction);
+
+  /* Adjust circuit counts on new channel */
+  if (direction == CELL_DIRECTION_OUT) {
+    ++chan->num_n_circuits;
+  } else {
+    ++chan->num_p_circuits;
+  }
 }
 
 /** Set the p_conn field of a circuit <b>circ</b>, along
  * with the corresponding circuit ID, and add the circuit as appropriate
- * to the (orconn,id)-\>circuit map. */
+ * to the (chan,id)-\>circuit map. */
 void
-circuit_set_p_circid_orconn(or_circuit_t *circ, circid_t id,
-                            or_connection_t *conn)
+circuit_set_p_circid_chan(or_circuit_t *circ, circid_t id,
+                          channel_t *chan)
 {
-  circuit_set_circid_orconn_helper(TO_CIRCUIT(circ), CELL_DIRECTION_IN,
-                                   id, conn);
+  circuit_set_circid_chan_helper(TO_CIRCUIT(circ), CELL_DIRECTION_IN,
+                                 id, chan);
 
-  if (conn)
-    tor_assert(bool_eq(circ->p_conn_cells.n, circ->next_active_on_p_conn));
+  if (chan)
+    tor_assert(bool_eq(circ->p_chan_cells.n, circ->next_active_on_p_chan));
 }
 
 /** Set the n_conn field of a circuit <b>circ</b>, along
  * with the corresponding circuit ID, and add the circuit as appropriate
- * to the (orconn,id)-\>circuit map. */
+ * to the (chan,id)-\>circuit map. */
 void
-circuit_set_n_circid_orconn(circuit_t *circ, circid_t id,
-                            or_connection_t *conn)
+circuit_set_n_circid_chan(circuit_t *circ, circid_t id,
+                          channel_t *chan)
 {
-  circuit_set_circid_orconn_helper(circ, CELL_DIRECTION_OUT, id, conn);
+  circuit_set_circid_chan_helper(circ, CELL_DIRECTION_OUT, id, chan);
 
-  if (conn)
-    tor_assert(bool_eq(circ->n_conn_cells.n, circ->next_active_on_n_conn));
+  if (chan)
+    tor_assert(bool_eq(circ->n_chan_cells.n, circ->next_active_on_n_chan));
 }
 
 /** Change the state of <b>circ</b> to <b>state</b>, adding it to or removing
@@ -202,18 +239,18 @@ circuit_set_state(circuit_t *circ, uint8_t state)
   tor_assert(circ);
   if (state == circ->state)
     return;
-  if (!circuits_pending_or_conns)
-    circuits_pending_or_conns = smartlist_new();
-  if (circ->state == CIRCUIT_STATE_OR_WAIT) {
+  if (!circuits_pending_chans)
+    circuits_pending_chans = smartlist_new();
+  if (circ->state == CIRCUIT_STATE_CHAN_WAIT) {
     /* remove from waiting-circuit list. */
-    smartlist_remove(circuits_pending_or_conns, circ);
+    smartlist_remove(circuits_pending_chans, circ);
   }
-  if (state == CIRCUIT_STATE_OR_WAIT) {
+  if (state == CIRCUIT_STATE_CHAN_WAIT) {
     /* add to waiting-circuit list. */
-    smartlist_add(circuits_pending_or_conns, circ);
+    smartlist_add(circuits_pending_chans, circ);
   }
   if (state == CIRCUIT_STATE_OPEN)
-    tor_assert(!circ->n_conn_onionskin);
+    tor_assert(!circ->n_chan_onionskin);
   circ->state = state;
 }
 
@@ -232,51 +269,53 @@ circuit_add(circuit_t *circ)
   }
 }
 
-/** Append to <b>out</b> all circuits in state OR_WAIT waiting for
+/** Append to <b>out</b> all circuits in state CHAN_WAIT waiting for
  * the given connection. */
 void
-circuit_get_all_pending_on_or_conn(smartlist_t *out, or_connection_t *or_conn)
+circuit_get_all_pending_on_channel(smartlist_t *out, channel_t *chan)
 {
   tor_assert(out);
-  tor_assert(or_conn);
+  tor_assert(chan);
 
-  if (!circuits_pending_or_conns)
+  if (!circuits_pending_chans)
     return;
 
-  SMARTLIST_FOREACH_BEGIN(circuits_pending_or_conns, circuit_t *, circ) {
+  SMARTLIST_FOREACH_BEGIN(circuits_pending_chans, circuit_t *, circ) {
     if (circ->marked_for_close)
       continue;
     if (!circ->n_hop)
       continue;
-    tor_assert(circ->state == CIRCUIT_STATE_OR_WAIT);
+    tor_assert(circ->state == CIRCUIT_STATE_CHAN_WAIT);
     if (tor_digest_is_zero(circ->n_hop->identity_digest)) {
       /* Look at addr/port. This is an unkeyed connection. */
-      if (!tor_addr_eq(&circ->n_hop->addr, &or_conn->_base.addr) ||
-          circ->n_hop->port != or_conn->_base.port)
+      if (!channel_matches_extend_info(chan, circ->n_hop))
         continue;
     } else {
       /* We expected a key. See if it's the right one. */
-      if (tor_memneq(or_conn->identity_digest,
-                 circ->n_hop->identity_digest, DIGEST_LEN))
+      if (tor_memneq(chan->identity_digest,
+                     circ->n_hop->identity_digest, DIGEST_LEN))
         continue;
     }
     smartlist_add(out, circ);
   } SMARTLIST_FOREACH_END(circ);
 }
 
-/** Return the number of circuits in state OR_WAIT, waiting for the given
- * connection. */
+/** Return the number of circuits in state CHAN_WAIT, waiting for the given
+ * channel. */
 int
-circuit_count_pending_on_or_conn(or_connection_t *or_conn)
+circuit_count_pending_on_channel(channel_t *chan)
 {
   int cnt;
   smartlist_t *sl = smartlist_new();
-  circuit_get_all_pending_on_or_conn(sl, or_conn);
+
+  tor_assert(chan);
+
+  circuit_get_all_pending_on_channel(sl, chan);
   cnt = smartlist_len(sl);
   smartlist_free(sl);
   log_debug(LD_CIRC,"or_conn to %s at %s, %d pending circs",
-            or_conn->nickname ? or_conn->nickname : "NULL",
-            or_conn->_base.address,
+            chan->nickname ? chan->nickname : "NULL",
+            channel_get_canonical_remote_descr(chan),
             cnt);
   return cnt;
 }
@@ -324,7 +363,7 @@ circuit_state_to_string(int state)
   switch (state) {
     case CIRCUIT_STATE_BUILDING: return "doing handshakes";
     case CIRCUIT_STATE_ONIONSKIN_PENDING: return "processing the onion";
-    case CIRCUIT_STATE_OR_WAIT: return "connecting to server";
+    case CIRCUIT_STATE_CHAN_WAIT: return "connecting to server";
     case CIRCUIT_STATE_OPEN: return "open";
     default:
       log_warn(LD_BUG, "Unknown circuit state %d", state);
@@ -518,12 +557,6 @@ init_circuit_base(circuit_t *circ)
   circ->package_window = circuit_initial_package_window();
   circ->deliver_window = CIRCWINDOW_START;
 
-  /* Initialize the cell_ewma_t structure */
-  circ->n_cell_ewma.last_adjusted_tick = cell_ewma_get_tick();
-  circ->n_cell_ewma.cell_count = 0.0;
-  circ->n_cell_ewma.heap_index = -1;
-  circ->n_cell_ewma.is_for_p_conn = 0;
-
   circuit_add(circ);
 }
 
@@ -556,7 +589,7 @@ origin_circuit_new(void)
 /** Allocate a new or_circuit_t, connected to <b>p_conn</b> as
  * <b>p_circ_id</b>.  If <b>p_conn</b> is NULL, the circuit is unattached. */
 or_circuit_t *
-or_circuit_new(circid_t p_circ_id, or_connection_t *p_conn)
+or_circuit_new(circid_t p_circ_id, channel_t *p_chan)
 {
   /* CircIDs */
   or_circuit_t *circ;
@@ -564,23 +597,13 @@ or_circuit_new(circid_t p_circ_id, or_connection_t *p_conn)
   circ = tor_malloc_zero(sizeof(or_circuit_t));
   circ->_base.magic = OR_CIRCUIT_MAGIC;
 
-  if (p_conn)
-    circuit_set_p_circid_orconn(circ, p_circ_id, p_conn);
+  if (p_chan)
+    circuit_set_p_circid_chan(circ, p_circ_id, p_chan);
 
   circ->remaining_relay_early_cells = MAX_RELAY_EARLY_CELLS_PER_CIRCUIT;
 
   init_circuit_base(TO_CIRCUIT(circ));
 
-  /* Initialize the cell_ewma_t structure */
-
-  /* Initialize the cell counts to 0 */
-  circ->p_cell_ewma.cell_count = 0.0;
-  circ->p_cell_ewma.last_adjusted_tick = cell_ewma_get_tick();
-  circ->p_cell_ewma.is_for_p_conn = 1;
-
-  /* It's not in any heap yet. */
-  circ->p_cell_ewma.heap_index = -1;
-
   return circ;
 }
 
@@ -641,22 +664,22 @@ circuit_free(circuit_t *circ)
     }
 
     /* remove from map. */
-    circuit_set_p_circid_orconn(ocirc, 0, NULL);
+    circuit_set_p_circid_chan(ocirc, 0, NULL);
 
     /* Clear cell queue _after_ removing it from the map.  Otherwise our
      * "active" checks will be violated. */
-    cell_queue_clear(&ocirc->p_conn_cells);
+    cell_queue_clear(&ocirc->p_chan_cells);
   }
 
   extend_info_free(circ->n_hop);
-  tor_free(circ->n_conn_onionskin);
+  tor_free(circ->n_chan_onionskin);
 
   /* Remove from map. */
-  circuit_set_n_circid_orconn(circ, 0, NULL);
+  circuit_set_n_circid_chan(circ, 0, NULL);
 
   /* Clear cell queue _after_ removing it from the map.  Otherwise our
    * "active" checks will be violated. */
-  cell_queue_clear(&circ->n_conn_cells);
+  cell_queue_clear(&circ->n_chan_cells);
 
   memset(mem, 0xAA, memlen); /* poison memory */
   tor_free(mem);
@@ -702,10 +725,10 @@ circuit_free_all(void)
     global_circuitlist = next;
   }
 
-  smartlist_free(circuits_pending_or_conns);
-  circuits_pending_or_conns = NULL;
+  smartlist_free(circuits_pending_chans);
+  circuits_pending_chans = NULL;
 
-  HT_CLEAR(orconn_circid_map, &orconn_circid_circuit_map);
+  HT_CLEAR(chan_circid_map, &chan_circid_map);
 }
 
 /** Deallocate space associated with the cpath node <b>victim</b>. */
@@ -742,8 +765,12 @@ cpath_ref_decref(crypt_path_reference_t *cpath_ref)
  * of information about circuit <b>circ</b>.
  */
 static void
-circuit_dump_details(int severity, circuit_t *circ, int conn_array_index,
-                     const char *type, int this_circid, int other_circid)
+circuit_dump_conn_details(int severity,
+                          circuit_t *circ,
+                          int conn_array_index,
+                          const char *type,
+                          int this_circid,
+                          int other_circid)
 {
   log(severity, LD_CIRC, "Conn %d has %s circuit: circID %d (other side %d), "
       "state %d (%s), born %ld:",
@@ -764,50 +791,101 @@ circuit_dump_by_conn(connection_t *conn, int severity)
   circuit_t *circ;
   edge_connection_t *tmpconn;
 
-  for (circ=global_circuitlist;circ;circ = circ->next) {
+  for (circ = global_circuitlist; circ; circ = circ->next) {
     circid_t n_circ_id = circ->n_circ_id, p_circ_id = 0;
-    if (circ->marked_for_close)
+
+    if (circ->marked_for_close) {
       continue;
+    }
 
-    if (! CIRCUIT_IS_ORIGIN(circ))
+    if (!CIRCUIT_IS_ORIGIN(circ)) {
       p_circ_id = TO_OR_CIRCUIT(circ)->p_circ_id;
+    }
 
-    if (! CIRCUIT_IS_ORIGIN(circ) && TO_OR_CIRCUIT(circ)->p_conn &&
-        TO_CONN(TO_OR_CIRCUIT(circ)->p_conn) == conn)
-      circuit_dump_details(severity, circ, conn->conn_array_index, "App-ward",
-                           p_circ_id, n_circ_id);
     if (CIRCUIT_IS_ORIGIN(circ)) {
       for (tmpconn=TO_ORIGIN_CIRCUIT(circ)->p_streams; tmpconn;
            tmpconn=tmpconn->next_stream) {
         if (TO_CONN(tmpconn) == conn) {
-          circuit_dump_details(severity, circ, conn->conn_array_index,
-                               "App-ward", p_circ_id, n_circ_id);
+          circuit_dump_conn_details(severity, circ, conn->conn_array_index,
+                                    "App-ward", p_circ_id, n_circ_id);
         }
       }
     }
-    if (circ->n_conn && TO_CONN(circ->n_conn) == conn)
-      circuit_dump_details(severity, circ, conn->conn_array_index, "Exit-ward",
-                           n_circ_id, p_circ_id);
+
     if (! CIRCUIT_IS_ORIGIN(circ)) {
       for (tmpconn=TO_OR_CIRCUIT(circ)->n_streams; tmpconn;
            tmpconn=tmpconn->next_stream) {
         if (TO_CONN(tmpconn) == conn) {
-          circuit_dump_details(severity, circ, conn->conn_array_index,
-                               "Exit-ward", n_circ_id, p_circ_id);
+          circuit_dump_conn_details(severity, circ, conn->conn_array_index,
+                                    "Exit-ward", n_circ_id, p_circ_id);
         }
       }
     }
-    if (!circ->n_conn && circ->n_hop &&
-        tor_addr_eq(&circ->n_hop->addr, &conn->addr) &&
-        circ->n_hop->port == conn->port &&
-        conn->type == CONN_TYPE_OR &&
-        tor_memeq(TO_OR_CONN(conn)->identity_digest,
-                circ->n_hop->identity_digest, DIGEST_LEN)) {
-      circuit_dump_details(severity, circ, conn->conn_array_index,
-                           (circ->state == CIRCUIT_STATE_OPEN &&
-                            !CIRCUIT_IS_ORIGIN(circ)) ?
-                             "Endpoint" : "Pending",
-                           n_circ_id, p_circ_id);
+  }
+}
+
+/** A helper function for circuit_dump_by_chan() below. Log a bunch
+ * of information about circuit <b>circ</b>.
+ */
+static void
+circuit_dump_chan_details(int severity,
+                          circuit_t *circ,
+                          channel_t *chan,
+                          const char *type,
+                          int this_circid,
+                          int other_circid)
+{
+  log(severity, LD_CIRC, "Conn %p has %s circuit: circID %d (other side %d), "
+      "state %d (%s), born %ld:",
+      chan, type, this_circid, other_circid, circ->state,
+      circuit_state_to_string(circ->state),
+      (long)circ->timestamp_created.tv_sec);
+  if (CIRCUIT_IS_ORIGIN(circ)) { /* circ starts at this node */
+    circuit_log_path(severity, LD_CIRC, TO_ORIGIN_CIRCUIT(circ));
+  }
+}
+
+/** Log, at severity <b>severity</b>, information about each circuit
+ * that is connected to <b>chan</b>.
+ */
+void
+circuit_dump_by_chan(channel_t *chan, int severity)
+{
+  circuit_t *circ;
+
+  tor_assert(chan);
+
+  for (circ = global_circuitlist; circ; circ = circ->next) {
+    circid_t n_circ_id = circ->n_circ_id, p_circ_id = 0;
+
+    if (circ->marked_for_close) {
+      continue;
+    }
+
+    if (!CIRCUIT_IS_ORIGIN(circ)) {
+      p_circ_id = TO_OR_CIRCUIT(circ)->p_circ_id;
+    }
+
+    if (! CIRCUIT_IS_ORIGIN(circ) && TO_OR_CIRCUIT(circ)->p_chan &&
+        TO_OR_CIRCUIT(circ)->p_chan == chan) {
+      circuit_dump_chan_details(severity, circ, chan, "App-ward",
+                                p_circ_id, n_circ_id);
+    }
+
+    if (circ->n_chan && circ->n_chan == chan) {
+      circuit_dump_chan_details(severity, circ, chan, "Exit-ward",
+                                n_circ_id, p_circ_id);
+    }
+
+    if (!circ->n_chan && circ->n_hop &&
+        channel_matches_extend_info(chan, circ->n_hop) &&
+        tor_memeq(chan->identity_digest,
+                  circ->n_hop->identity_digest, DIGEST_LEN)) {
+      circuit_dump_chan_details(severity, circ, chan,
+                                (circ->state == CIRCUIT_STATE_OPEN &&
+                                 !CIRCUIT_IS_ORIGIN(circ)) ?
+                                "Endpoint" : "Pending",
+                                n_circ_id, p_circ_id);
     }
   }
 }
@@ -832,27 +910,39 @@ circuit_get_by_global_id(uint32_t id)
 
 /** Return a circ such that:
  *  - circ-\>n_circ_id or circ-\>p_circ_id is equal to <b>circ_id</b>, and
- *  - circ is attached to <b>conn</b>, either as p_conn or n_conn.
+ *  - circ is attached to <b>chan</b>, either as p_chan or n_chan.
  * Return NULL if no such circuit exists.
  */
 static INLINE circuit_t *
-circuit_get_by_circid_orconn_impl(circid_t circ_id, or_connection_t *conn)
+circuit_get_by_circid_channel_impl(circid_t circ_id, channel_t *chan)
 {
-  orconn_circid_circuit_map_t search;
-  orconn_circid_circuit_map_t *found;
+  chan_circid_circuit_map_t search;
+  chan_circid_circuit_map_t *found;
 
-  if (_last_circid_orconn_ent &&
-      circ_id == _last_circid_orconn_ent->circ_id &&
-      conn == _last_circid_orconn_ent->or_conn) {
-    found = _last_circid_orconn_ent;
+  if (_last_circid_chan_ent &&
+      circ_id == _last_circid_chan_ent->circ_id &&
+      chan == _last_circid_chan_ent->chan) {
+    found = _last_circid_chan_ent;
   } else {
     search.circ_id = circ_id;
-    search.or_conn = conn;
-    found = HT_FIND(orconn_circid_map, &orconn_circid_circuit_map, &search);
-    _last_circid_orconn_ent = found;
+    search.chan = chan;
+    found = HT_FIND(chan_circid_map, &chan_circid_map, &search);
+    _last_circid_chan_ent = found;
   }
-  if (found && found->circuit)
+  if (found && found->circuit) {
+    log_debug(LD_CIRC,
+              "circuit_get_by_circid_channel_impl() returning circuit %p for"
+              " circ_id %d, channel ID " U64_FORMAT " (%p)",
+              found->circuit, circ_id,
+              U64_PRINTF_ARG(chan->global_identifier), chan);
     return found->circuit;
+  }
+
+  log_debug(LD_CIRC,
+            "circuit_get_by_circid_channel_impl() found nothing for"
+            " circ_id %d, channel ID " U64_FORMAT " (%p)",
+            circ_id,
+            U64_PRINTF_ARG(chan->global_identifier), chan);
 
   return NULL;
   /* The rest of this checks for bugs. Disabled by default. */
@@ -862,15 +952,15 @@ circuit_get_by_circid_orconn_impl(circid_t circ_id, or_connection_t *conn)
     for (circ=global_circuitlist;circ;circ = circ->next) {
       if (! CIRCUIT_IS_ORIGIN(circ)) {
         or_circuit_t *or_circ = TO_OR_CIRCUIT(circ);
-        if (or_circ->p_conn == conn && or_circ->p_circ_id == circ_id) {
+        if (or_circ->p_chan == chan && or_circ->p_circ_id == circ_id) {
           log_warn(LD_BUG,
-                   "circuit matches p_conn, but not in hash table (Bug!)");
+                   "circuit matches p_chan, but not in hash table (Bug!)");
           return circ;
         }
       }
-      if (circ->n_conn == conn && circ->n_circ_id == circ_id) {
+      if (circ->n_chan == chan && circ->n_circ_id == circ_id) {
         log_warn(LD_BUG,
-                 "circuit matches n_conn, but not in hash table (Bug!)");
+                 "circuit matches n_chan, but not in hash table (Bug!)");
         return circ;
       }
     }
@@ -880,26 +970,38 @@ circuit_get_by_circid_orconn_impl(circid_t circ_id, or_connection_t *conn)
 
 /** Return a circ such that:
  *  - circ-\>n_circ_id or circ-\>p_circ_id is equal to <b>circ_id</b>, and
- *  - circ is attached to <b>conn</b>, either as p_conn or n_conn.
+ *  - circ is attached to <b>chan</b>, either as p_chan or n_chan.
  *  - circ is not marked for close.
  * Return NULL if no such circuit exists.
  */
 circuit_t *
-circuit_get_by_circid_orconn(circid_t circ_id, or_connection_t *conn)
+circuit_get_by_circid_channel(circid_t circ_id, channel_t *chan)
 {
-  circuit_t *circ = circuit_get_by_circid_orconn_impl(circ_id, conn);
+  circuit_t *circ = circuit_get_by_circid_channel_impl(circ_id, chan);
   if (!circ || circ->marked_for_close)
     return NULL;
   else
     return circ;
 }
 
+/** Return a circ such that:
+ *  - circ-\>n_circ_id or circ-\>p_circ_id is equal to <b>circ_id</b>, and
+ *  - circ is attached to <b>chan</b>, either as p_chan or n_chan.
+ * Return NULL if no such circuit exists.
+ */
+circuit_t *
+circuit_get_by_circid_channel_even_if_marked(circid_t circ_id,
+                                             channel_t *chan)
+{
+  return circuit_get_by_circid_channel_impl(circ_id, chan);
+}
+
 /** Return true iff the circuit ID <b>circ_id</b> is currently used by a
- * circuit, marked or not, on <b>conn</b>. */
+ * circuit, marked or not, on <b>chan</b>. */
 int
-circuit_id_in_use_on_orconn(circid_t circ_id, or_connection_t *conn)
+circuit_id_in_use_on_channel(circid_t circ_id, channel_t *chan)
 {
-  return circuit_get_by_circid_orconn_impl(circ_id, conn) != NULL;
+  return circuit_get_by_circid_channel_impl(circ_id, chan) != NULL;
 }
 
 /** Return the circuit that a given edge connection is using. */
@@ -916,27 +1018,27 @@ circuit_get_by_edge_conn(edge_connection_t *conn)
   return circ;
 }
 
-/** For each circuit that has <b>conn</b> as n_conn or p_conn, unlink the
- * circuit from the orconn,circid map, and mark it for close if it hasn't
+/** For each circuit that has <b>chan</b> as n_chan or p_chan, unlink the
+ * circuit from the chan,circid map, and mark it for close if it hasn't
  * been marked already.
  */
 void
-circuit_unlink_all_from_or_conn(or_connection_t *conn, int reason)
+circuit_unlink_all_from_channel(channel_t *chan, int reason)
 {
   circuit_t *circ;
 
-  connection_or_unlink_all_active_circs(conn);
+  channel_unlink_all_circuits(chan);
 
   for (circ = global_circuitlist; circ; circ = circ->next) {
     int mark = 0;
-    if (circ->n_conn == conn) {
-        circuit_set_n_circid_orconn(circ, 0, NULL);
+    if (circ->n_chan == chan) {
+        circuit_set_n_circid_chan(circ, 0, NULL);
         mark = 1;
     }
     if (! CIRCUIT_IS_ORIGIN(circ)) {
       or_circuit_t *or_circ = TO_OR_CIRCUIT(circ);
-      if (or_circ->p_conn == conn) {
-        circuit_set_p_circid_orconn(or_circ, 0, NULL);
+      if (or_circ->p_chan == chan) {
+        circuit_set_p_circid_chan(or_circ, 0, NULL);
         mark = 1;
       }
     }
@@ -1267,9 +1369,9 @@ _circuit_mark_for_close(circuit_t *circ, int reason, int line,
       circuit_rep_hist_note_result(ocirc);
     }
   }
-  if (circ->state == CIRCUIT_STATE_OR_WAIT) {
-    if (circuits_pending_or_conns)
-      smartlist_remove(circuits_pending_or_conns, circ);
+  if (circ->state == CIRCUIT_STATE_CHAN_WAIT) {
+    if (circuits_pending_chans)
+      smartlist_remove(circuits_pending_chans, circ);
   }
   if (CIRCUIT_IS_ORIGIN(circ)) {
     control_event_circuit_status(TO_ORIGIN_CIRCUIT(circ),
@@ -1306,9 +1408,10 @@ _circuit_mark_for_close(circuit_t *circ, int reason, int line,
                                              INTRO_POINT_FAILURE_UNREACHABLE);
     }
   }
-  if (circ->n_conn) {
-    circuit_clear_cell_queue(circ, circ->n_conn);
-    connection_or_send_destroy(circ->n_circ_id, circ->n_conn, reason);
+  if (circ->n_chan) {
+    circuit_clear_cell_queue(circ, circ->n_chan);
+    channel_send_destroy(circ->n_circ_id, circ->n_chan, reason);
+    circuitmux_detach_circuit(circ->n_chan->cmux, circ);
   }
 
   if (! CIRCUIT_IS_ORIGIN(circ)) {
@@ -1333,9 +1436,10 @@ _circuit_mark_for_close(circuit_t *circ, int reason, int line,
       conn->on_circuit = NULL;
     }
 
-    if (or_circ->p_conn) {
-      circuit_clear_cell_queue(circ, or_circ->p_conn);
-      connection_or_send_destroy(or_circ->p_circ_id, or_circ->p_conn, reason);
+    if (or_circ->p_chan) {
+      circuit_clear_cell_queue(circ, or_circ->p_chan);
+      channel_send_destroy(or_circ->p_circ_id, or_circ->p_chan, reason);
+      circuitmux_detach_circuit(or_circ->p_chan->cmux, circ);
     }
   } else {
     origin_circuit_t *ocirc = TO_ORIGIN_CIRCUIT(circ);
@@ -1438,22 +1542,22 @@ assert_circuit_ok(const circuit_t *c)
       or_circ = TO_OR_CIRCUIT(nonconst_circ);
   }
 
-  if (c->n_conn) {
+  if (c->n_chan) {
     tor_assert(!c->n_hop);
 
     if (c->n_circ_id) {
       /* We use the _impl variant here to make sure we don't fail on marked
        * circuits, which would not be returned by the regular function. */
-      circuit_t *c2 = circuit_get_by_circid_orconn_impl(c->n_circ_id,
-                                                        c->n_conn);
+      circuit_t *c2 = circuit_get_by_circid_channel_impl(c->n_circ_id,
+                                                         c->n_chan);
       tor_assert(c == c2);
     }
   }
-  if (or_circ && or_circ->p_conn) {
+  if (or_circ && or_circ->p_chan) {
     if (or_circ->p_circ_id) {
       /* ibid */
-      circuit_t *c2 = circuit_get_by_circid_orconn_impl(or_circ->p_circ_id,
-                                                        or_circ->p_conn);
+      circuit_t *c2 = circuit_get_by_circid_channel_impl(or_circ->p_circ_id,
+                                                         or_circ->p_chan);
       tor_assert(c == c2);
     }
   }
@@ -1464,7 +1568,7 @@ assert_circuit_ok(const circuit_t *c)
   tor_assert(c->deliver_window >= 0);
   tor_assert(c->package_window >= 0);
   if (c->state == CIRCUIT_STATE_OPEN) {
-    tor_assert(!c->n_conn_onionskin);
+    tor_assert(!c->n_chan_onionskin);
     if (or_circ) {
       tor_assert(or_circ->n_crypto);
       tor_assert(or_circ->p_crypto);
@@ -1472,12 +1576,12 @@ assert_circuit_ok(const circuit_t *c)
       tor_assert(or_circ->p_digest);
     }
   }
-  if (c->state == CIRCUIT_STATE_OR_WAIT && !c->marked_for_close) {
-    tor_assert(circuits_pending_or_conns &&
-               smartlist_isin(circuits_pending_or_conns, c));
+  if (c->state == CIRCUIT_STATE_CHAN_WAIT && !c->marked_for_close) {
+    tor_assert(circuits_pending_chans &&
+               smartlist_isin(circuits_pending_chans, c));
   } else {
-    tor_assert(!circuits_pending_or_conns ||
-               !smartlist_isin(circuits_pending_or_conns, c));
+    tor_assert(!circuits_pending_chans ||
+               !smartlist_isin(circuits_pending_chans, c));
   }
   if (origin_circ && origin_circ->cpath) {
     assert_cpath_ok(origin_circ->cpath);
diff --git a/src/or/circuitlist.h b/src/or/circuitlist.h
index 6e7735476..89e957c70 100644
--- a/src/or/circuitlist.h
+++ b/src/or/circuitlist.h
@@ -18,20 +18,24 @@ const char *circuit_purpose_to_controller_string(uint8_t purpose);
 const char *circuit_purpose_to_controller_hs_state_string(uint8_t purpose);
 const char *circuit_purpose_to_string(uint8_t purpose);
 void circuit_dump_by_conn(connection_t *conn, int severity);
-void circuit_set_p_circid_orconn(or_circuit_t *circ, circid_t id,
-                                 or_connection_t *conn);
-void circuit_set_n_circid_orconn(circuit_t *circ, circid_t id,
-                                 or_connection_t *conn);
+void circuit_dump_by_chan(channel_t *chan, int severity);
+void circuit_set_p_circid_chan(or_circuit_t *circ, circid_t id,
+                               channel_t *chan);
+void circuit_set_n_circid_chan(circuit_t *circ, circid_t id,
+                               channel_t *chan);
 void circuit_set_state(circuit_t *circ, uint8_t state);
 void circuit_close_all_marked(void);
 int32_t circuit_initial_package_window(void);
 origin_circuit_t *origin_circuit_new(void);
-or_circuit_t *or_circuit_new(circid_t p_circ_id, or_connection_t *p_conn);
-circuit_t *circuit_get_by_circid_orconn(circid_t circ_id,
-                                        or_connection_t *conn);
-int circuit_id_in_use_on_orconn(circid_t circ_id, or_connection_t *conn);
+or_circuit_t *or_circuit_new(circid_t p_circ_id, channel_t *p_chan);
+circuit_t *circuit_get_by_circid_channel(circid_t circ_id,
+                                         channel_t *chan);
+circuit_t *
+circuit_get_by_circid_channel_even_if_marked(circid_t circ_id,
+                                             channel_t *chan);
+int circuit_id_in_use_on_channel(circid_t circ_id, channel_t *chan);
 circuit_t *circuit_get_by_edge_conn(edge_connection_t *conn);
-void circuit_unlink_all_from_or_conn(or_connection_t *conn, int reason);
+void circuit_unlink_all_from_channel(channel_t *chan, int reason);
 origin_circuit_t *circuit_get_by_global_id(uint32_t id);
 origin_circuit_t *circuit_get_ready_rend_circ_by_rend_data(
   const rend_data_t *rend_data);
@@ -47,9 +51,9 @@ void _circuit_mark_for_close(circuit_t *circ, int reason,
                              int line, const char *file);
 int circuit_get_cpath_len(origin_circuit_t *circ);
 crypt_path_t *circuit_get_cpath_hop(origin_circuit_t *circ, int hopnum);
-void circuit_get_all_pending_on_or_conn(smartlist_t *out,
-                                        or_connection_t *or_conn);
-int circuit_count_pending_on_or_conn(or_connection_t *or_conn);
+void circuit_get_all_pending_on_channel(smartlist_t *out,
+                                        channel_t *chan);
+int circuit_count_pending_on_channel(channel_t *chan);
 
 #define circuit_mark_for_close(c, reason)                               \
   _circuit_mark_for_close((c), (reason), __LINE__, _SHORT_FILE_)
diff --git a/src/or/circuitmux.c b/src/or/circuitmux.c
new file mode 100644
index 000000000..f3b6b7cd7
--- /dev/null
+++ b/src/or/circuitmux.c
@@ -0,0 +1,1745 @@
+/* * Copyright (c) 2012, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file circuitmux.c
+ * \brief Circuit mux/cell selection abstraction
+ **/
+
+#include "or.h"
+#include "channel.h"
+#include "circuitlist.h"
+#include "circuitmux.h"
+
+/*
+ * Private typedefs for circuitmux.c
+ */
+
+/*
+ * Map of muxinfos for circuitmux_t to use; struct is defined below (name
+ * of struct must match HT_HEAD line).
+ */
+typedef struct chanid_circid_muxinfo_map chanid_circid_muxinfo_map_t;
+
+/*
+ * Hash table entry (yeah, calling it chanid_circid_muxinfo_s seems to
+ * break the hash table code).
+ */
+typedef struct chanid_circid_muxinfo_t chanid_circid_muxinfo_t;
+
+/*
+ * Anything the mux wants to store per-circuit in the map; right now just
+ * a count of queued cells.
+ */
+
+typedef struct circuit_muxinfo_s circuit_muxinfo_t;
+
+/*
+ * Structures for circuitmux.c
+ */
+
+/*
+ * A circuitmux is a collection of circuits; it tracks which subset
+ * of the attached circuits are 'active' (i.e., have cells available
+ * to transmit) and how many cells on each.  It expoes three distinct
+ * interfaces to other components:
+ *
+ * To channels, which each have a circuitmux_t, the supported operations
+ * are:
+ *
+ *   circuitmux_get_first_active_circuit():
+ *
+ *     Pick one of the circuitmux's active circuits to send cells from.
+ *
+ *   circuitmux_notify_xmit_cells():
+ *
+ *     Notify the circuitmux that cells have been sent on a circuit.
+ *
+ * To circuits, the exposed operations are:
+ *
+ *   circuitmux_attach_circuit():
+ *
+ *     Attach a circuit to the circuitmux; this will allocate any policy-
+ *     specific data wanted for this circuit and add it to the active
+ *     circuits list if it has queued cells.
+ *
+ *   circuitmux_detach_circuit():
+ *
+ *     Detach a circuit from the circuitmux, freeing associated structures.
+ *
+ *   circuitmux_clear_num_cells():
+ *
+ *     Clear the circuitmux's cell counter for this circuit.
+ *
+ *   circuitmux_set_num_cells():
+ *
+ *     Set the circuitmux's cell counter for this circuit.
+ *
+ * See circuitmux.h for the circuitmux_policy_t data structure, which contains
+ * a table of function pointers implementing a circuit selection policy, and
+ * circuitmux_ewma.c for an example of a circuitmux policy.  Circuitmux
+ * policies can be manipulated with:
+ *
+ *   circuitmux_get_policy():
+ *
+ *     Return the current policy for a circuitmux_t, if any.
+ *
+ *   circuitmux_clear_policy():
+ *
+ *     Remove a policy installed on a circuitmux_t, freeing all associated
+ *     data.  The circuitmux will revert to the built-in round-robin behavior.
+ *
+ *   circuitmux_set_policy():
+ *
+ *     Install a policy on a circuitmux_t; the appropriate callbacks will be
+ *     made to attach all existing circuits to the new policy.
+ *
+ */
+
+struct circuitmux_s {
+  /* Keep count of attached, active circuits */
+  unsigned int n_circuits, n_active_circuits;
+
+  /* Total number of queued cells on all circuits */
+  unsigned int n_cells;
+
+  /*
+   * Map from (channel ID, circuit ID) pairs to circuit_muxinfo_t
+   */
+  chanid_circid_muxinfo_map_t *chanid_circid_map;
+
+  /*
+   * Double-linked ring of circuits with queued cells waiting for room to
+   * free up on this connection's outbuf.  Every time we pull cells from
+   * a circuit, we advance this pointer to the next circuit in the ring.
+   */
+  struct circuit_t *active_circuits_head, *active_circuits_tail;
+
+  /*
+   * Circuitmux policy; if this is non-NULL, it can override the built-
+   * in round-robin active circuits behavior.  This is how EWMA works in
+   * the new circuitmux_t world.
+   */
+  const circuitmux_policy_t *policy;
+
+  /* Policy-specific data */
+  circuitmux_policy_data_t *policy_data;
+};
+
+/*
+ * This struct holds whatever we want to store per attached circuit on a
+ * circuitmux_t; right now, just the count of queued cells and the direction.
+ */
+
+struct circuit_muxinfo_s {
+  /* Count of cells on this circuit at last update */
+  unsigned int cell_count;
+  /* Direction of flow */
+  cell_direction_t direction;
+  /* Policy-specific data */
+  circuitmux_policy_circ_data_t *policy_data;
+  /* Mark bit for consistency checker */
+  unsigned int mark:1;
+};
+
+/*
+ * A map from channel ID and circuit ID to a circuit_muxinfo_t for that
+ * circuit.
+ */
+
+struct chanid_circid_muxinfo_t {
+  HT_ENTRY(chanid_circid_muxinfo_t) node;
+  uint64_t chan_id;
+  circid_t circ_id;
+  circuit_muxinfo_t muxinfo;
+};
+
+/*
+ * Internal-use #defines
+ */
+
+#ifdef CMUX_PARANOIA
+#define circuitmux_assert_okay_paranoid(cmux) \
+  circuitmux_assert_okay(cmux)
+#else
+#define circuitmux_assert_okay_paranoid(cmux)
+#endif
+
+/*
+ * Static function declarations
+ */
+
+static INLINE int
+chanid_circid_entries_eq(chanid_circid_muxinfo_t *a,
+                         chanid_circid_muxinfo_t *b);
+static INLINE unsigned int
+chanid_circid_entry_hash(chanid_circid_muxinfo_t *a);
+static chanid_circid_muxinfo_t *
+circuitmux_find_map_entry(circuitmux_t *cmux, circuit_t *circ);
+static void
+circuitmux_make_circuit_active(circuitmux_t *cmux, circuit_t *circ,
+                               cell_direction_t direction);
+static void
+circuitmux_make_circuit_inactive(circuitmux_t *cmux, circuit_t *circ,
+                                 cell_direction_t direction);
+static INLINE void
+circuitmux_move_active_circ_to_tail(circuitmux_t *cmux, circuit_t *circ,
+                                    cell_direction_t direction);
+static INLINE circuit_t **
+circuitmux_next_active_circ_p(circuitmux_t *cmux, circuit_t *circ);
+static INLINE circuit_t **
+circuitmux_prev_active_circ_p(circuitmux_t *cmux, circuit_t *circ);
+static void circuitmux_assert_okay_pass_one(circuitmux_t *cmux);
+static void circuitmux_assert_okay_pass_two(circuitmux_t *cmux);
+static void circuitmux_assert_okay_pass_three(circuitmux_t *cmux);
+
+/* Function definitions */
+
+/**
+ * Linked list helpers
+ */
+
+/**
+ * Move an active circuit to the tail of the cmux's active circuits list;
+ * used by circuitmux_notify_xmit_cells().
+ */
+
+static INLINE void
+circuitmux_move_active_circ_to_tail(circuitmux_t *cmux, circuit_t *circ,
+                                    cell_direction_t direction)
+{
+  circuit_t **next_p = NULL, **prev_p = NULL;
+  circuit_t **next_prev = NULL, **prev_next = NULL;
+  circuit_t **tail_next = NULL;
+  or_circuit_t *or_circ = NULL;
+
+  tor_assert(cmux);
+  tor_assert(circ);
+
+  circuitmux_assert_okay_paranoid(cmux);
+
+  /* Figure out our next_p and prev_p for this cmux/direction */
+  if (direction) {
+    if (direction == CELL_DIRECTION_OUT) {
+      tor_assert(circ->n_mux == cmux);
+      next_p = &(circ->next_active_on_n_chan);
+      prev_p = &(circ->prev_active_on_n_chan);
+    } else {
+      or_circ = TO_OR_CIRCUIT(circ);
+      tor_assert(or_circ->p_mux == cmux);
+      next_p = &(or_circ->next_active_on_p_chan);
+      prev_p = &(or_circ->prev_active_on_p_chan);
+    }
+  } else {
+    if (circ->n_mux == cmux) {
+      next_p = &(circ->next_active_on_n_chan);
+      prev_p = &(circ->prev_active_on_n_chan);
+      direction = CELL_DIRECTION_OUT;
+    } else {
+      or_circ = TO_OR_CIRCUIT(circ);
+      tor_assert(or_circ->p_mux == cmux);
+      next_p = &(or_circ->next_active_on_p_chan);
+      prev_p = &(or_circ->prev_active_on_p_chan);
+      direction = CELL_DIRECTION_IN;
+    }
+  }
+  tor_assert(next_p);
+  tor_assert(prev_p);
+
+  /* Check if this really is an active circuit */
+  if ((*next_p == NULL && *prev_p == NULL) &&
+      !(circ == cmux->active_circuits_head ||
+        circ == cmux->active_circuits_tail)) {
+    /* Not active, no-op */
+    return;
+  }
+
+  /* Check if this is already the tail */
+  if (circ == cmux->active_circuits_tail) return;
+
+  /* Okay, we have to move it; figure out next_prev and prev_next */
+  if (*next_p) next_prev = circuitmux_prev_active_circ_p(cmux, *next_p);
+  if (*prev_p) prev_next = circuitmux_next_active_circ_p(cmux, *prev_p);
+  /* Adjust the previous node's next pointer, if any */
+  if (prev_next) *prev_next = *next_p;
+  /* Otherwise, we were the head */
+  else cmux->active_circuits_head = *next_p;
+  /* Adjust the next node's previous pointer, if any */
+  if (next_prev) *next_prev = *prev_p;
+  /* We're out of the list; now re-attach at the tail */
+  /* Adjust our next and prev pointers */
+  *next_p = NULL;
+  *prev_p = cmux->active_circuits_tail;
+  /* Set the next pointer of the tail, or the head if none */
+  if (cmux->active_circuits_tail) {
+    tail_next = circuitmux_next_active_circ_p(cmux,
+                                              cmux->active_circuits_tail);
+    *tail_next = circ;
+  } else {
+    cmux->active_circuits_head = circ;
+  }
+  /* Set the tail to this circuit */
+  cmux->active_circuits_tail = circ;
+
+  circuitmux_assert_okay_paranoid(cmux);
+}
+
+static INLINE circuit_t **
+circuitmux_next_active_circ_p(circuitmux_t *cmux, circuit_t *circ)
+{
+  tor_assert(cmux);
+  tor_assert(circ);
+
+  if (circ->n_mux == cmux) return &(circ->next_active_on_n_chan);
+  else {
+    tor_assert(TO_OR_CIRCUIT(circ)->p_mux == cmux);
+    return &(TO_OR_CIRCUIT(circ)->next_active_on_p_chan);
+  }
+}
+
+static INLINE circuit_t **
+circuitmux_prev_active_circ_p(circuitmux_t *cmux, circuit_t *circ)
+{
+  tor_assert(cmux);
+  tor_assert(circ);
+
+  if (circ->n_mux == cmux) return &(circ->prev_active_on_n_chan);
+  else {
+    tor_assert(TO_OR_CIRCUIT(circ)->p_mux == cmux);
+    return &(TO_OR_CIRCUIT(circ)->prev_active_on_p_chan);
+  }
+}
+
+/**
+ * Helper for chanid_circid_cell_count_map_t hash table: compare the channel
+ * ID and circuit ID for a and b, and return less than, equal to, or greater
+ * than zero appropriately.
+ */
+
+static INLINE int
+chanid_circid_entries_eq(chanid_circid_muxinfo_t *a,
+                         chanid_circid_muxinfo_t *b)
+{
+    return a->chan_id == b->chan_id && a->circ_id == b->circ_id;
+}
+
+/**
+ * Helper: return a hash based on circuit ID and channel ID in a.
+ */
+
+static INLINE unsigned int
+chanid_circid_entry_hash(chanid_circid_muxinfo_t *a)
+{
+    return (((unsigned int)(a->circ_id) << 8) ^
+            ((unsigned int)((a->chan_id >> 32) & 0xffffffff)) ^
+            ((unsigned int)(a->chan_id & 0xffffffff)));
+}
+
+/* Declare the struct chanid_circid_muxinfo_map type */
+HT_HEAD(chanid_circid_muxinfo_map, chanid_circid_muxinfo_t);
+
+/* Emit a bunch of hash table stuff */
+HT_PROTOTYPE(chanid_circid_muxinfo_map, chanid_circid_muxinfo_t, node,
+             chanid_circid_entry_hash, chanid_circid_entries_eq);
+HT_GENERATE(chanid_circid_muxinfo_map, chanid_circid_muxinfo_t, node,
+            chanid_circid_entry_hash, chanid_circid_entries_eq, 0.6,
+            malloc, realloc, free);
+
+/*
+ * Circuitmux alloc/free functions
+ */
+
+/**
+ * Allocate a new circuitmux_t
+ */
+
+circuitmux_t *
+circuitmux_alloc(void)
+{
+  circuitmux_t *rv = NULL;
+
+  rv = tor_malloc_zero(sizeof(*rv));
+  rv->chanid_circid_map = tor_malloc_zero(sizeof(*( rv->chanid_circid_map)));
+  HT_INIT(chanid_circid_muxinfo_map, rv->chanid_circid_map);
+
+  return rv;
+}
+
+/**
+ * Detach all circuits from a circuitmux (use before circuitmux_free())
+ */
+
+void
+circuitmux_detach_all_circuits(circuitmux_t *cmux)
+{
+  chanid_circid_muxinfo_t **i = NULL, *to_remove;
+  channel_t *chan = NULL;
+  circuit_t *circ = NULL;
+
+  tor_assert(cmux);
+  /*
+   * Don't circuitmux_assert_okay_paranoid() here; this gets called when
+   * channels are being freed and have already been unregistered, so
+   * the channel ID lookups it does will fail.
+   */
+
+  i = HT_START(chanid_circid_muxinfo_map, cmux->chanid_circid_map);
+  while (i) {
+    to_remove = *i;
+    if (to_remove) {
+      /* Find a channel and circuit */
+      chan = channel_find_by_global_id(to_remove->chan_id);
+      if (chan) {
+        circ =
+          circuit_get_by_circid_channel_even_if_marked(to_remove->circ_id,
+                                                       chan);
+        if (circ) {
+          /* Clear the circuit's mux for this direction */
+          if (to_remove->muxinfo.direction == CELL_DIRECTION_OUT) {
+            /*
+             * Update active_circuits et al.; this does policy notifies, so
+             * comes before freeing policy data
+             */
+
+            if (to_remove->muxinfo.cell_count > 0) {
+              circuitmux_make_circuit_inactive(cmux, circ, CELL_DIRECTION_OUT);
+            }
+
+            /* Clear n_mux */
+            circ->n_mux = NULL;
+          } else if (circ->magic == OR_CIRCUIT_MAGIC) {
+            /*
+             * Update active_circuits et al.; this does policy notifies, so
+             * comes before freeing policy data
+             */
+
+            if (to_remove->muxinfo.cell_count > 0) {
+              circuitmux_make_circuit_inactive(cmux, circ, CELL_DIRECTION_IN);
+            }
+
+            /*
+             * It has a sensible p_chan and direction == CELL_DIRECTION_IN,
+             * so clear p_mux.
+             */
+            TO_OR_CIRCUIT(circ)->p_mux = NULL;
+          } else {
+            /* Complain and move on */
+            log_warn(LD_CIRC,
+                     "Circuit %d/channel " U64_FORMAT " had direction == "
+                     "CELL_DIRECTION_IN, but isn't an or_circuit_t",
+                     to_remove->circ_id,
+                     U64_PRINTF_ARG(to_remove->chan_id));
+          }
+
+          /* Free policy-specific data if we have it */
+          if (to_remove->muxinfo.policy_data) {
+            /*
+             * If we have policy data, assert that we have the means to
+             * free it
+             */
+            tor_assert(cmux->policy);
+            tor_assert(cmux->policy->free_circ_data);
+            /* Call free_circ_data() */
+            cmux->policy->free_circ_data(cmux,
+                                         cmux->policy_data,
+                                         circ,
+                                         to_remove->muxinfo.policy_data);
+            to_remove->muxinfo.policy_data = NULL;
+          }
+        } else {
+          /* Complain and move on */
+          log_warn(LD_CIRC,
+                   "Couldn't find circuit %d (for channel " U64_FORMAT ")",
+                   to_remove->circ_id,
+                   U64_PRINTF_ARG(to_remove->chan_id));
+        }
+      } else {
+        /* Complain and move on */
+        log_warn(LD_CIRC,
+                 "Couldn't find channel " U64_FORMAT " (for circuit id %d)",
+                 U64_PRINTF_ARG(to_remove->chan_id),
+                 to_remove->circ_id);
+      }
+
+      /* Assert that we don't have un-freed policy data for this circuit */
+      tor_assert(to_remove->muxinfo.policy_data == NULL);
+    }
+
+    i = HT_NEXT_RMV(chanid_circid_muxinfo_map, cmux->chanid_circid_map, i);
+
+    /* Free it */
+    tor_free(to_remove);
+  }
+
+  cmux->n_circuits = 0;
+  cmux->n_active_circuits = 0;
+  cmux->n_cells = 0;
+}
+
+/**
+ * Free a circuitmux_t; the circuits must be detached first with
+ * circuitmux_detach_all_circuits().
+ */
+
+void
+circuitmux_free(circuitmux_t *cmux)
+{
+  if (!cmux) return;
+
+  tor_assert(cmux->n_circuits == 0);
+  tor_assert(cmux->n_active_circuits == 0);
+
+  /*
+   * Free policy-specific data if we have any; we don't
+   * need to do circuitmux_set_policy(cmux, NULL) to cover
+   * the circuits because they would have been handled in
+   * circuitmux_detach_all_circuits() before this was
+   * called.
+   */
+  if (cmux->policy && cmux->policy->free_cmux_data) {
+    if (cmux->policy_data) {
+      cmux->policy->free_cmux_data(cmux, cmux->policy_data);
+      cmux->policy_data = NULL;
+    }
+  } else tor_assert(cmux->policy_data == NULL);
+
+  if (cmux->chanid_circid_map) {
+    HT_CLEAR(chanid_circid_muxinfo_map, cmux->chanid_circid_map);
+    tor_free(cmux->chanid_circid_map);
+  }
+
+  tor_free(cmux);
+}
+
+/*
+ * Circuitmux policy control functions
+ */
+
+/**
+ * Remove any policy installed on cmux; all policy data will be freed and
+ * cmux behavior will revert to the built-in round-robin active_circuits
+ * mechanism.
+ */
+
+void
+circuitmux_clear_policy(circuitmux_t *cmux)
+{
+  tor_assert(cmux);
+
+  /* Internally, this is just setting policy to NULL */
+  if (cmux->policy) {
+    circuitmux_set_policy(cmux, NULL);
+  }
+}
+
+/**
+ * Return the policy currently installed on a circuitmux_t
+ */
+
+const circuitmux_policy_t *
+circuitmux_get_policy(circuitmux_t *cmux)
+{
+  tor_assert(cmux);
+
+  return cmux->policy;
+}
+
+/**
+ * Set policy; allocate for new policy, detach all circuits from old policy
+ * if any, attach them to new policy, and free old policy data.
+ */
+
+void
+circuitmux_set_policy(circuitmux_t *cmux,
+                      const circuitmux_policy_t *pol)
+{
+  const circuitmux_policy_t *old_pol = NULL, *new_pol = NULL;
+  circuitmux_policy_data_t *old_pol_data = NULL, *new_pol_data = NULL;
+  chanid_circid_muxinfo_t **i = NULL;
+  channel_t *chan = NULL;
+  uint64_t last_chan_id_searched = 0;
+  circuit_t *circ = NULL;
+
+  tor_assert(cmux);
+
+  /* Set up variables */
+  old_pol = cmux->policy;
+  old_pol_data = cmux->policy_data;
+  new_pol = pol;
+
+  /* Check if this is the trivial case */
+  if (old_pol == new_pol) return;
+
+  /* Allocate data for new policy, if any */
+  if (new_pol && new_pol->alloc_cmux_data) {
+    /*
+     * If alloc_cmux_data is not null, then we expect to get some policy
+     * data.  Assert that we also have free_cmux_data so we can free it
+     * when the time comes, and allocate it.
+     */
+    tor_assert(new_pol->free_cmux_data);
+    new_pol_data = new_pol->alloc_cmux_data(cmux);
+    tor_assert(new_pol_data);
+  }
+
+  /* Install new policy and new policy data on cmux */
+  cmux->policy = new_pol;
+  cmux->policy_data = new_pol_data;
+
+  /* Iterate over all circuits, attaching/detaching each one */
+  i = HT_START(chanid_circid_muxinfo_map, cmux->chanid_circid_map);
+  while (i) {
+    /* Assert that this entry isn't NULL */
+    tor_assert(*i);
+
+    /*
+     * Get the channel; since normal case is all circuits on the mux share a
+     * channel, we cache last_chan_id_searched
+     */
+    if (!chan || last_chan_id_searched != (*i)->chan_id) {
+      chan = channel_find_by_global_id((*i)->chan_id);
+      last_chan_id_searched = (*i)->chan_id;
+    }
+    tor_assert(chan);
+
+    /* Get the circuit */
+    circ = circuit_get_by_circid_channel_even_if_marked((*i)->circ_id, chan);
+    tor_assert(circ);
+
+    /* Need to tell old policy it becomes inactive (i.e., it is active) ? */
+    if (old_pol && old_pol->notify_circ_inactive &&
+        (*i)->muxinfo.cell_count > 0) {
+      old_pol->notify_circ_inactive(cmux, old_pol_data, circ,
+                                    (*i)->muxinfo.policy_data);
+    }
+
+    /* Need to free old policy data? */
+    if ((*i)->muxinfo.policy_data) {
+      /* Assert that we have the means to free it if we have policy data */
+      tor_assert(old_pol);
+      tor_assert(old_pol->free_circ_data);
+      /* Free it */
+      old_pol->free_circ_data(cmux, old_pol_data, circ,
+                             (*i)->muxinfo.policy_data);
+      (*i)->muxinfo.policy_data = NULL;
+    }
+
+    /* Need to allocate new policy data? */
+    if (new_pol && new_pol->alloc_circ_data) {
+      /*
+       * If alloc_circ_data is not null, we expect to get some per-circuit
+       * policy data.  Assert that we also have free_circ_data so we can
+       * free it when the time comes, and allocate it.
+       */
+      tor_assert(new_pol->free_circ_data);
+      (*i)->muxinfo.policy_data =
+        new_pol->alloc_circ_data(cmux, new_pol_data, circ,
+                                 (*i)->muxinfo.direction,
+                                 (*i)->muxinfo.cell_count);
+    }
+
+    /* Need to make active on new policy? */
+    if (new_pol && new_pol->notify_circ_active &&
+        (*i)->muxinfo.cell_count > 0) {
+      new_pol->notify_circ_active(cmux, new_pol_data, circ,
+                                  (*i)->muxinfo.policy_data);
+    }
+
+    /* Advance to next circuit map entry */
+    i = HT_NEXT(chanid_circid_muxinfo_map, cmux->chanid_circid_map, i);
+  }
+
+  /* Free data for old policy, if any */
+  if (old_pol_data) {
+    /*
+     * If we had old policy data, we should have an old policy and a free
+     * function for it.
+     */
+    tor_assert(old_pol);
+    tor_assert(old_pol->free_cmux_data);
+    old_pol->free_cmux_data(cmux, old_pol_data);
+    old_pol_data = NULL;
+  }
+}
+
+/*
+ * Circuitmux/circuit attachment status inquiry functions
+ */
+
+/**
+ * Query the direction of an attached circuit
+ */
+
+cell_direction_t
+circuitmux_attached_circuit_direction(circuitmux_t *cmux, circuit_t *circ)
+{
+  chanid_circid_muxinfo_t *hashent = NULL;
+
+  /* Try to find a map entry */
+  hashent = circuitmux_find_map_entry(cmux, circ);
+
+  /*
+   * This function should only be called on attached circuits; assert that
+   * we had a map entry.
+   */
+  tor_assert(hashent);
+
+  /* Return the direction from the map entry */
+  return hashent->muxinfo.direction;
+}
+
+/**
+ * Find an entry in the cmux's map for this circuit or return NULL if there
+ * is none.
+ */
+
+static chanid_circid_muxinfo_t *
+circuitmux_find_map_entry(circuitmux_t *cmux, circuit_t *circ)
+{
+  chanid_circid_muxinfo_t search, *hashent = NULL;
+
+  /* Sanity-check parameters */
+  tor_assert(cmux);
+  tor_assert(cmux->chanid_circid_map);
+  tor_assert(circ);
+
+  /* Check if we have n_chan */
+  if (circ->n_chan) {
+    /* Okay, let's see if it's attached for n_chan/n_circ_id */
+    search.chan_id = circ->n_chan->global_identifier;
+    search.circ_id = circ->n_circ_id;
+
+    /* Query */
+    hashent = HT_FIND(chanid_circid_muxinfo_map, cmux->chanid_circid_map,
+                      &search);
+  }
+
+  /* Found something? */
+  if (hashent) {
+    /*
+     * Assert that the direction makes sense for a hashent we found by
+     * n_chan/n_circ_id before we return it.
+     */
+    tor_assert(hashent->muxinfo.direction == CELL_DIRECTION_OUT);
+  } else {
+    /* Not there, have we got a p_chan/p_circ_id to try? */
+    if (circ->magic == OR_CIRCUIT_MAGIC) {
+      search.circ_id = TO_OR_CIRCUIT(circ)->p_circ_id;
+      /* Check for p_chan */
+      if (TO_OR_CIRCUIT(circ)->p_chan) {
+        search.chan_id = TO_OR_CIRCUIT(circ)->p_chan->global_identifier;
+        /* Okay, search for that */
+        hashent = HT_FIND(chanid_circid_muxinfo_map, cmux->chanid_circid_map,
+                          &search);
+        /* Find anything? */
+        if (hashent) {
+          /* Assert that the direction makes sense before we return it */
+          tor_assert(hashent->muxinfo.direction == CELL_DIRECTION_IN);
+        }
+      }
+    }
+  }
+
+  /* Okay, hashent is it if it was there */
+  return hashent;
+}
+
+/**
+ * Query whether a circuit is attached to a circuitmux
+ */
+
+int
+circuitmux_is_circuit_attached(circuitmux_t *cmux, circuit_t *circ)
+{
+  chanid_circid_muxinfo_t *hashent = NULL;
+
+  /* Look if it's in the circuit map */
+  hashent = circuitmux_find_map_entry(cmux, circ);
+
+  return (hashent != NULL);
+}
+
+/**
+ * Query whether a circuit is active on a circuitmux
+ */
+
+int
+circuitmux_is_circuit_active(circuitmux_t *cmux, circuit_t *circ)
+{
+  chanid_circid_muxinfo_t *hashent = NULL;
+  int is_active = 0;
+
+  tor_assert(cmux);
+  tor_assert(circ);
+
+  /* Look if it's in the circuit map */
+  hashent = circuitmux_find_map_entry(cmux, circ);
+  if (hashent) {
+    /* Check the number of cells on this circuit */
+    is_active = (hashent->muxinfo.cell_count > 0);
+  }
+  /* else not attached, so not active */
+
+  return is_active;
+}
+
+/**
+ * Query number of available cells for a circuit on a circuitmux
+ */
+
+unsigned int
+circuitmux_num_cells_for_circuit(circuitmux_t *cmux, circuit_t *circ)
+{
+  chanid_circid_muxinfo_t *hashent = NULL;
+  unsigned int n_cells = 0;
+
+  tor_assert(cmux);
+  tor_assert(circ);
+
+  /* Look if it's in the circuit map */
+  hashent = circuitmux_find_map_entry(cmux, circ);
+  if (hashent) {
+    /* Just get the cell count for this circuit */
+    n_cells = hashent->muxinfo.cell_count;
+  }
+  /* else not attached, so 0 cells */
+
+  return n_cells;
+}
+
+/**
+ * Query total number of available cells on a circuitmux
+ */
+
+unsigned int
+circuitmux_num_cells(circuitmux_t *cmux)
+{
+  tor_assert(cmux);
+
+  return cmux->n_cells;
+}
+
+/**
+ * Query total number of circuits active on a circuitmux
+ */
+
+unsigned int
+circuitmux_num_active_circuits(circuitmux_t *cmux)
+{
+  tor_assert(cmux);
+
+  return cmux->n_active_circuits;
+}
+
+/**
+ * Query total number of circuits attached to a circuitmux
+ */
+
+unsigned int
+circuitmux_num_circuits(circuitmux_t *cmux)
+{
+  tor_assert(cmux);
+
+  return cmux->n_circuits;
+}
+
+/*
+ * Functions for circuit code to call to update circuit status
+ */
+
+/**
+ * Attach a circuit to a circuitmux, for the specified direction.
+ */
+
+void
+circuitmux_attach_circuit(circuitmux_t *cmux, circuit_t *circ,
+                          cell_direction_t direction)
+{
+  channel_t *chan = NULL;
+  uint64_t channel_id;
+  circid_t circ_id;
+  chanid_circid_muxinfo_t search, *hashent = NULL;
+  unsigned int cell_count;
+
+  tor_assert(cmux);
+  tor_assert(circ);
+  tor_assert(direction == CELL_DIRECTION_IN ||
+             direction == CELL_DIRECTION_OUT);
+  circuitmux_assert_okay_paranoid(cmux);
+
+  /*
+   * Figure out which channel we're using, and get the circuit's current
+   * cell count and circuit ID; assert that the circuit is not already
+   * attached to another mux.
+   */
+  if (direction == CELL_DIRECTION_OUT) {
+    /* It's n_chan */
+    chan = circ->n_chan;
+    cell_count = circ->n_chan_cells.n;
+    circ_id = circ->n_circ_id;
+  } else {
+    /* We want p_chan */
+    chan = TO_OR_CIRCUIT(circ)->p_chan;
+    cell_count = TO_OR_CIRCUIT(circ)->p_chan_cells.n;
+    circ_id = TO_OR_CIRCUIT(circ)->p_circ_id;
+  }
+  /* Assert that we did get a channel */
+  tor_assert(chan);
+  /* Assert that the circuit ID is sensible */
+  tor_assert(circ_id != 0);
+
+  /* Get the channel ID */
+  channel_id = chan->global_identifier;
+
+  /* See if we already have this one */
+  search.chan_id = channel_id;
+  search.circ_id = circ_id;
+  hashent = HT_FIND(chanid_circid_muxinfo_map, cmux->chanid_circid_map,
+                    &search);
+
+  if (hashent) {
+    /*
+     * This circuit was already attached to this cmux; make sure the
+     * directions match and update the cell count and active circuit count.
+     */
+    log_info(LD_CIRC,
+             "Circuit %u on channel " U64_FORMAT " was already attached to "
+             "cmux %p (trying to attach to %p)",
+             circ_id, U64_PRINTF_ARG(channel_id),
+             ((direction == CELL_DIRECTION_OUT) ?
+                circ->n_mux : TO_OR_CIRCUIT(circ)->p_mux),
+             cmux);
+
+    /*
+     * The mux pointer on this circuit and the direction in result should
+     * match; otherwise assert.
+     */
+    if (direction == CELL_DIRECTION_OUT) tor_assert(circ->n_mux == cmux);
+    else tor_assert(TO_OR_CIRCUIT(circ)->p_mux == cmux);
+    tor_assert(hashent->muxinfo.direction == direction);
+
+    /*
+     * Looks okay; just update the cell count and active circuits if we must
+     */
+    if (hashent->muxinfo.cell_count > 0 && cell_count == 0) {
+      --(cmux->n_active_circuits);
+      circuitmux_make_circuit_inactive(cmux, circ, direction);
+    } else if (hashent->muxinfo.cell_count == 0 && cell_count > 0) {
+      ++(cmux->n_active_circuits);
+      circuitmux_make_circuit_active(cmux, circ, direction);
+    }
+    cmux->n_cells -= hashent->muxinfo.cell_count;
+    cmux->n_cells += cell_count;
+    hashent->muxinfo.cell_count = cell_count;
+  } else {
+    /*
+     * New circuit; add an entry and update the circuit/active circuit
+     * counts.
+     */
+    log_debug(LD_CIRC,
+             "Attaching circuit %u on channel " U64_FORMAT " to cmux %p",
+             circ_id, U64_PRINTF_ARG(channel_id), cmux);
+
+    /*
+     * Assert that the circuit doesn't already have a mux for this
+     * direction.
+     */
+    if (direction == CELL_DIRECTION_OUT) tor_assert(circ->n_mux == NULL);
+    else tor_assert(TO_OR_CIRCUIT(circ)->p_mux == NULL);
+
+    /* Insert it in the map */
+    hashent = tor_malloc_zero(sizeof(*hashent));
+    hashent->chan_id = channel_id;
+    hashent->circ_id = circ_id;
+    hashent->muxinfo.cell_count = cell_count;
+    hashent->muxinfo.direction = direction;
+    /* Allocate policy specific circuit data if we need it */
+    if (cmux->policy && cmux->policy->alloc_circ_data) {
+      /* Assert that we have the means to free policy-specific data */
+      tor_assert(cmux->policy->free_circ_data);
+      /* Allocate it */
+      hashent->muxinfo.policy_data =
+        cmux->policy->alloc_circ_data(cmux,
+                                      cmux->policy_data,
+                                      circ,
+                                      direction,
+                                      cell_count);
+      /* If we wanted policy data, it's an error  not to get any */
+      tor_assert(hashent->muxinfo.policy_data);
+    }
+    HT_INSERT(chanid_circid_muxinfo_map, cmux->chanid_circid_map,
+              hashent);
+
+    /* Set the circuit's mux for this direction */
+    if (direction == CELL_DIRECTION_OUT) circ->n_mux = cmux;
+    else TO_OR_CIRCUIT(circ)->p_mux = cmux;
+
+    /* Make sure the next/prev pointers are NULL */
+    if (direction == CELL_DIRECTION_OUT) {
+      circ->next_active_on_n_chan = NULL;
+      circ->prev_active_on_n_chan = NULL;
+    } else {
+      TO_OR_CIRCUIT(circ)->next_active_on_p_chan = NULL;
+      TO_OR_CIRCUIT(circ)->prev_active_on_p_chan = NULL;
+    }
+
+    /* Update counters */
+    ++(cmux->n_circuits);
+    if (cell_count > 0) {
+      ++(cmux->n_active_circuits);
+      circuitmux_make_circuit_active(cmux, circ, direction);
+    }
+    cmux->n_cells += cell_count;
+  }
+
+  circuitmux_assert_okay_paranoid(cmux);
+}
+
+/**
+ * Detach a circuit from a circuitmux and update all counters as needed;
+ * no-op if not attached.
+ */
+
+void
+circuitmux_detach_circuit(circuitmux_t *cmux, circuit_t *circ)
+{
+  chanid_circid_muxinfo_t search, *hashent = NULL;
+  /*
+   * Use this to keep track of whether we found it for n_chan or
+   * p_chan for consistency checking.
+   */
+  cell_direction_t last_searched_direction;
+
+  tor_assert(cmux);
+  tor_assert(cmux->chanid_circid_map);
+  tor_assert(circ);
+  circuitmux_assert_okay_paranoid(cmux);
+
+  /* See if we have it for n_chan/n_circ_id */
+  if (circ->n_chan) {
+    search.chan_id = circ->n_chan->global_identifier;
+    search.circ_id = circ->n_circ_id;
+    hashent = HT_FIND(chanid_circid_muxinfo_map, cmux->chanid_circid_map,
+                        &search);
+    last_searched_direction = CELL_DIRECTION_OUT;
+  }
+
+  /* Got one? If not, see if it's an or_circuit_t and try p_chan/p_circ_id */
+  if (!hashent) {
+    if (circ->magic == OR_CIRCUIT_MAGIC) {
+      search.circ_id = TO_OR_CIRCUIT(circ)->p_circ_id;
+      if (TO_OR_CIRCUIT(circ)->p_chan) {
+        search.chan_id = TO_OR_CIRCUIT(circ)->p_chan->global_identifier;
+        hashent = HT_FIND(chanid_circid_muxinfo_map,
+                            cmux->chanid_circid_map,
+                            &search);
+        last_searched_direction = CELL_DIRECTION_IN;
+      }
+    }
+  }
+
+  /*
+   * If hashent isn't NULL, we have a circuit to detach; don't remove it from
+   * the map until later of circuitmux_make_circuit_inactive() breaks.
+   */
+  if (hashent) {
+    /* Update counters */
+    --(cmux->n_circuits);
+    if (hashent->muxinfo.cell_count > 0) {
+      --(cmux->n_active_circuits);
+      /* This does policy notifies, so comes before freeing policy data */
+      circuitmux_make_circuit_inactive(cmux, circ, last_searched_direction);
+    }
+    cmux->n_cells -= hashent->muxinfo.cell_count;
+
+    /* Free policy-specific data if we have it */
+    if (hashent->muxinfo.policy_data) {
+      /* If we have policy data, assert that we have the means to free it */
+      tor_assert(cmux->policy);
+      tor_assert(cmux->policy->free_circ_data);
+      /* Call free_circ_data() */
+      cmux->policy->free_circ_data(cmux,
+                                   cmux->policy_data,
+                                   circ,
+                                   hashent->muxinfo.policy_data);
+      hashent->muxinfo.policy_data = NULL;
+    }
+
+    /* Consistency check: the direction must match the direction searched */
+    tor_assert(last_searched_direction == hashent->muxinfo.direction);
+    /* Clear the circuit's mux for this direction */
+    if (last_searched_direction == CELL_DIRECTION_OUT) circ->n_mux = NULL;
+    else TO_OR_CIRCUIT(circ)->p_mux = NULL;
+
+    /* Now remove it from the map */
+    HT_REMOVE(chanid_circid_muxinfo_map, cmux->chanid_circid_map, hashent);
+
+    /* Free the hash entry */
+    tor_free(hashent);
+  }
+
+  circuitmux_assert_okay_paranoid(cmux);
+}
+
+/**
+ * Make a circuit active; update active list and policy-specific info, but
+ * we don't mess with the counters or hash table here.
+ */
+
+static void
+circuitmux_make_circuit_active(circuitmux_t *cmux, circuit_t *circ,
+                               cell_direction_t direction)
+{
+  circuit_t **next_active = NULL, **prev_active = NULL, **next_prev = NULL;
+  circuitmux_t *circuit_cmux = NULL;
+  chanid_circid_muxinfo_t *hashent = NULL;
+  channel_t *chan = NULL;
+  circid_t circ_id;
+  int already_active;
+
+  tor_assert(cmux);
+  tor_assert(circ);
+  tor_assert(direction == CELL_DIRECTION_OUT ||
+             direction == CELL_DIRECTION_IN);
+  /*
+   * Don't circuitmux_assert_okay_paranoid(cmux) here because the cell count
+   * already got changed and we have to update the list for it to be consistent
+   * again.
+   */
+
+  /* Get the right set of active list links for this direction */
+  if (direction == CELL_DIRECTION_OUT) {
+    next_active = &(circ->next_active_on_n_chan);
+    prev_active = &(circ->prev_active_on_n_chan);
+    circuit_cmux = circ->n_mux;
+    chan = circ->n_chan;
+    circ_id = circ->n_circ_id;
+  } else {
+    next_active = &(TO_OR_CIRCUIT(circ)->next_active_on_p_chan);
+    prev_active = &(TO_OR_CIRCUIT(circ)->prev_active_on_p_chan);
+    circuit_cmux = TO_OR_CIRCUIT(circ)->p_mux;
+    chan = TO_OR_CIRCUIT(circ)->p_chan;
+    circ_id = TO_OR_CIRCUIT(circ)->p_circ_id;
+  }
+
+  /* Assert that it is attached to this mux and a channel */
+  tor_assert(cmux == circuit_cmux);
+  tor_assert(chan != NULL);
+
+  /*
+   * Check if the circuit really was inactive; if it's active, at least one
+   * of the next_active and prev_active pointers will not be NULL, or this
+   * circuit will be either the head or tail of the list for this cmux.
+   */
+  already_active = (*prev_active != NULL || *next_active != NULL ||
+                    cmux->active_circuits_head == circ ||
+                    cmux->active_circuits_tail == circ);
+
+  /* If we're already active, log a warning and finish */
+  if (already_active) {
+    log_warn(LD_CIRC,
+             "Circuit %d on channel " U64_FORMAT " was already active",
+             circ_id, U64_PRINTF_ARG(chan->global_identifier));
+    return;
+  }
+
+  /*
+   * This is going at the head of the list; if the old head is not NULL,
+   * then its prev pointer should point to this.
+   */
+  *next_active = cmux->active_circuits_head; /* Next is old head */
+  *prev_active = NULL; /* Prev is NULL (this will be the head) */
+  if (cmux->active_circuits_head) {
+    /* The list had an old head; update its prev pointer */
+    next_prev =
+      circuitmux_prev_active_circ_p(cmux, cmux->active_circuits_head);
+    tor_assert(next_prev);
+    *next_prev = circ;
+  } else {
+    /* The list was empty; this becomes the tail as well */
+    cmux->active_circuits_tail = circ;
+  }
+  /* This becomes the new head of the list */
+  cmux->active_circuits_head = circ;
+
+  /* Policy-specific notification */
+  if (cmux->policy &&
+      cmux->policy->notify_circ_active) {
+    /* Okay, we need to check the circuit for policy data now */
+    hashent = circuitmux_find_map_entry(cmux, circ);
+    /* We should have found something */
+    tor_assert(hashent);
+    /* Notify */
+    cmux->policy->notify_circ_active(cmux, cmux->policy_data,
+                                     circ, hashent->muxinfo.policy_data);
+  }
+
+  circuitmux_assert_okay_paranoid(cmux);
+}
+
+/**
+ * Make a circuit inactive; update active list and policy-specific info, but
+ * we don't mess with the counters or hash table here.
+ */
+
+static void
+circuitmux_make_circuit_inactive(circuitmux_t *cmux, circuit_t *circ,
+                                 cell_direction_t direction)
+{
+  circuit_t **next_active = NULL, **prev_active = NULL;
+  circuit_t **next_prev = NULL, **prev_next = NULL;
+  circuitmux_t *circuit_cmux = NULL;
+  chanid_circid_muxinfo_t *hashent = NULL;
+  channel_t *chan = NULL;
+  circid_t circ_id;
+  int already_inactive;
+
+  tor_assert(cmux);
+  tor_assert(circ);
+  tor_assert(direction == CELL_DIRECTION_OUT ||
+             direction == CELL_DIRECTION_IN);
+  /*
+   * Don't circuitmux_assert_okay_paranoid(cmux) here because the cell count
+   * already got changed and we have to update the list for it to be consistent
+   * again.
+   */
+
+  /* Get the right set of active list links for this direction */
+  if (direction == CELL_DIRECTION_OUT) {
+    next_active = &(circ->next_active_on_n_chan);
+    prev_active = &(circ->prev_active_on_n_chan);
+    circuit_cmux = circ->n_mux;
+    chan = circ->n_chan;
+    circ_id = circ->n_circ_id;
+  } else {
+    next_active = &(TO_OR_CIRCUIT(circ)->next_active_on_p_chan);
+    prev_active = &(TO_OR_CIRCUIT(circ)->prev_active_on_p_chan);
+    circuit_cmux = TO_OR_CIRCUIT(circ)->p_mux;
+    chan = TO_OR_CIRCUIT(circ)->p_chan;
+    circ_id = TO_OR_CIRCUIT(circ)->p_circ_id;
+  }
+
+  /* Assert that it is attached to this mux and a channel */
+  tor_assert(cmux == circuit_cmux);
+  tor_assert(chan != NULL);
+
+  /*
+   * Check if the circuit really was active; if it's inactive, the
+   * next_active and prev_active pointers will be NULL and this circuit
+   * will not be the head or tail of the list for this cmux.
+   */
+  already_inactive = (*prev_active == NULL && *next_active == NULL &&
+                      cmux->active_circuits_head != circ &&
+                      cmux->active_circuits_tail != circ);
+
+  /* If we're already inactive, log a warning and finish */
+  if (already_inactive) {
+    log_warn(LD_CIRC,
+             "Circuit %d on channel " U64_FORMAT " was already inactive",
+             circ_id, U64_PRINTF_ARG(chan->global_identifier));
+    return;
+  }
+
+  /* Remove from the list; first get next_prev and prev_next */
+  if (*next_active) {
+    /*
+     * If there's a next circuit, its previous circuit becomes this
+     * circuit's previous circuit.
+     */
+    next_prev = circuitmux_prev_active_circ_p(cmux, *next_active);
+  } else {
+    /* Else, the tail becomes this circuit's previous circuit */
+    next_prev = &(cmux->active_circuits_tail);
+  }
+
+  /* Got next_prev, now prev_next */
+  if (*prev_active) {
+    /*
+     * If there's a previous circuit, its next circuit becomes this circuit's
+     * next circuit.
+     */
+    prev_next = circuitmux_next_active_circ_p(cmux, *prev_active);
+  } else {
+    /* Else, the head becomes this circuit's next circuit */
+    prev_next = &(cmux->active_circuits_head);
+  }
+
+  /* Assert that we got sensible values for the next/prev pointers */
+  tor_assert(next_prev != NULL);
+  tor_assert(prev_next != NULL);
+
+  /* Update the next/prev pointers - this removes circ from the list */
+  *next_prev = *prev_active;
+  *prev_next = *next_active;
+
+  /* Now null out prev_active/next_active */
+  *prev_active = NULL;
+  *next_active = NULL;
+
+  /* Policy-specific notification */
+  if (cmux->policy &&
+      cmux->policy->notify_circ_inactive) {
+    /* Okay, we need to check the circuit for policy data now */
+    hashent = circuitmux_find_map_entry(cmux, circ);
+    /* We should have found something */
+    tor_assert(hashent);
+    /* Notify */
+    cmux->policy->notify_circ_inactive(cmux, cmux->policy_data,
+                                       circ, hashent->muxinfo.policy_data);
+  }
+
+  circuitmux_assert_okay_paranoid(cmux);
+}
+
+/**
+ * Clear the cell counter for a circuit on a circuitmux
+ */
+
+void
+circuitmux_clear_num_cells(circuitmux_t *cmux, circuit_t *circ)
+{
+  /* This is the same as setting the cell count to zero */
+  circuitmux_set_num_cells(cmux, circ, 0);
+}
+
+/**
+ * Set the cell counter for a circuit on a circuitmux
+ */
+
+void
+circuitmux_set_num_cells(circuitmux_t *cmux, circuit_t *circ,
+                         unsigned int n_cells)
+{
+  chanid_circid_muxinfo_t *hashent = NULL;
+
+  tor_assert(cmux);
+  tor_assert(circ);
+
+  circuitmux_assert_okay_paranoid(cmux);
+
+  /* Search for this circuit's entry */
+  hashent = circuitmux_find_map_entry(cmux, circ);
+  /* Assert that we found one */
+  tor_assert(hashent);
+
+  /* Update cmux cell counter */
+  cmux->n_cells -= hashent->muxinfo.cell_count;
+  cmux->n_cells += n_cells;
+
+  /* Do we need to notify a cmux policy? */
+  if (cmux->policy && cmux->policy->notify_set_n_cells) {
+    /* Call notify_set_n_cells */
+    cmux->policy->notify_set_n_cells(cmux,
+                                     cmux->policy_data,
+                                     circ,
+                                     hashent->muxinfo.policy_data,
+                                     n_cells);
+  }
+
+  /*
+   * Update cmux active circuit counter: is the old cell count > 0 and the
+   * new cell count == 0 ?
+   */
+  if (hashent->muxinfo.cell_count > 0 && n_cells == 0) {
+    --(cmux->n_active_circuits);
+    hashent->muxinfo.cell_count = n_cells;
+    circuitmux_make_circuit_inactive(cmux, circ, hashent->muxinfo.direction);
+  /* Is the old cell count == 0 and the new cell count > 0 ? */
+  } else if (hashent->muxinfo.cell_count == 0 && n_cells > 0) {
+    ++(cmux->n_active_circuits);
+    hashent->muxinfo.cell_count = n_cells;
+    circuitmux_make_circuit_active(cmux, circ, hashent->muxinfo.direction);
+  } else {
+    /*
+     * Update the entry cell count like this so we can put a
+     * circuitmux_assert_okay_paranoid inside make_circuit_(in)active() too.
+     */
+    hashent->muxinfo.cell_count = n_cells;
+  }
+
+  circuitmux_assert_okay_paranoid(cmux);
+}
+
+/*
+ * Functions for channel code to call to get a circuit to transmit from or
+ * notify that cells have been transmitted.
+ */
+
+/**
+ * Pick a circuit to send from, using the active circuits list or a
+ * circuitmux policy if one is available.  This is called from channel.c.
+ */
+
+circuit_t *
+circuitmux_get_first_active_circuit(circuitmux_t *cmux)
+{
+  circuit_t *circ = NULL;
+
+  tor_assert(cmux);
+
+  if (cmux->n_active_circuits > 0) {
+    /* We also must have a cell available for this to be the case */
+    tor_assert(cmux->n_cells > 0);
+    /* Do we have a policy-provided circuit selector? */
+    if (cmux->policy && cmux->policy->pick_active_circuit) {
+      circ = cmux->policy->pick_active_circuit(cmux, cmux->policy_data);
+    }
+    /* Fall back on the head of the active circuits list */
+    if (!circ) {
+      tor_assert(cmux->active_circuits_head);
+      circ = cmux->active_circuits_head;
+    }
+  } else tor_assert(cmux->n_cells == 0);
+
+  return circ;
+}
+
+/**
+ * Notify the circuitmux that cells have been sent on a circuit; this
+ * is called from channel.c.
+ */
+
+void
+circuitmux_notify_xmit_cells(circuitmux_t *cmux, circuit_t *circ,
+                             unsigned int n_cells)
+{
+  chanid_circid_muxinfo_t *hashent = NULL;
+  int becomes_inactive = 0;
+
+  tor_assert(cmux);
+  tor_assert(circ);
+  circuitmux_assert_okay_paranoid(cmux);
+
+  if (n_cells == 0) return;
+
+  /*
+   * To handle this, we have to:
+   *
+   * 1.) Adjust the circuit's cell counter in the cmux hash table
+   * 2.) Move the circuit to the tail of the active_circuits linked list
+   *     for this cmux, or make the circuit inactive if the cell count
+   *     went to zero.
+   * 3.) Call cmux->policy->notify_xmit_cells(), if any
+   */
+
+  /* Find the hash entry */
+  hashent = circuitmux_find_map_entry(cmux, circ);
+  /* Assert that we found one */
+  tor_assert(hashent);
+
+  /* Adjust the cell counter and assert that we had that many cells to send */
+  tor_assert(n_cells <= hashent->muxinfo.cell_count);
+  hashent->muxinfo.cell_count -= n_cells;
+  /* Do we need to make the circuit inactive? */
+  if (hashent->muxinfo.cell_count == 0) becomes_inactive = 1;
+  /* Adjust the mux cell counter */
+  cmux->n_cells -= n_cells;
+
+  /* If we aren't making it inactive later, move it to the tail of the list */
+  if (!becomes_inactive) {
+    circuitmux_move_active_circ_to_tail(cmux, circ,
+                                        hashent->muxinfo.direction);
+  }
+
+  /*
+   * We call notify_xmit_cells() before making the circuit inactive if needed,
+   * so the policy can always count on this coming in on an active circuit.
+   */
+  if (cmux->policy && cmux->policy->notify_xmit_cells) {
+    cmux->policy->notify_xmit_cells(cmux, cmux->policy_data, circ,
+                                    hashent->muxinfo.policy_data,
+                                    n_cells);
+  }
+
+  /*
+   * Now make the circuit inactive if needed; this will call the policy's
+   * notify_circ_inactive() if present.
+   */
+  if (becomes_inactive) {
+    --(cmux->n_active_circuits);
+    circuitmux_make_circuit_inactive(cmux, circ, hashent->muxinfo.direction);
+  }
+
+  circuitmux_assert_okay_paranoid(cmux);
+}
+
+/*
+ * Circuitmux consistency checking assertions
+ */
+
+/**
+ * Check that circuitmux data structures are consistent and fail with an
+ * assert if not.
+ */
+
+void
+circuitmux_assert_okay(circuitmux_t *cmux)
+{
+  tor_assert(cmux);
+
+  /*
+   * Pass 1: iterate the hash table; for each entry:
+   *  a) Check that the circuit has this cmux for n_mux or p_mux
+   *  b) If the cell_count is > 0, set the mark bit; otherwise clear it
+   *  c) Also check activeness (cell_count > 0 should be active)
+   *  d) Count the number of circuits, active circuits and queued cells
+   *     and at the end check that they match the counters in the cmux.
+   *
+   * Pass 2: iterate the active circuits list; for each entry,
+   *         make sure the circuit is attached to this mux and appears
+   *         in the hash table.  Make sure the mark bit is 1, and clear
+   *         it in the hash table entry.  Consistency-check the linked
+   *         list pointers.
+   *
+   * Pass 3: iterate the hash table again; assert if any active circuits
+   *         (mark bit set to 1) are discovered that weren't cleared in pass 2
+   *         (don't appear in the linked list).
+   */
+
+  circuitmux_assert_okay_pass_one(cmux);
+  circuitmux_assert_okay_pass_two(cmux);
+  circuitmux_assert_okay_pass_three(cmux);
+}
+
+/**
+ * Do the first pass of circuitmux_assert_okay(); see the comment in that
+ * function.
+ */
+
+static void
+circuitmux_assert_okay_pass_one(circuitmux_t *cmux)
+{
+  chanid_circid_muxinfo_t **i = NULL;
+  uint64_t chan_id;
+  channel_t *chan;
+  circid_t circ_id;
+  circuit_t *circ;
+  or_circuit_t *or_circ;
+  unsigned int circ_is_active;
+  circuit_t **next_p, **prev_p;
+  unsigned int n_circuits, n_active_circuits, n_cells;
+
+  tor_assert(cmux);
+  tor_assert(cmux->chanid_circid_map);
+
+  /* Reset the counters */
+  n_circuits = n_active_circuits = n_cells = 0;
+  /* Start iterating the hash table */
+  i = HT_START(chanid_circid_muxinfo_map, cmux->chanid_circid_map);
+  while (i) {
+    /* Assert that the hash table entry isn't null */
+    tor_assert(*i);
+
+    /* Get the channel and circuit id */
+    chan_id = (*i)->chan_id;
+    circ_id = (*i)->circ_id;
+
+    /* Find the channel and circuit, assert that they exist */
+    chan = channel_find_by_global_id(chan_id);
+    tor_assert(chan);
+    circ = circuit_get_by_circid_channel_even_if_marked(circ_id, chan);
+    tor_assert(circ);
+    /* Clear the circ_is_active bit to start */
+    circ_is_active = 0;
+
+    /* Assert that we know which direction this is going */
+    tor_assert((*i)->muxinfo.direction == CELL_DIRECTION_OUT ||
+               (*i)->muxinfo.direction == CELL_DIRECTION_IN);
+
+    if ((*i)->muxinfo.direction == CELL_DIRECTION_OUT) {
+      /* We should be n_mux on this circuit */
+      tor_assert(cmux == circ->n_mux);
+      tor_assert(chan == circ->n_chan);
+      /* Get next and prev for next test */
+      next_p = &(circ->next_active_on_n_chan);
+      prev_p = &(circ->prev_active_on_n_chan);
+    } else {
+      /* This should be an or_circuit_t and we should be p_mux */
+      or_circ = TO_OR_CIRCUIT(circ);
+      tor_assert(cmux == or_circ->p_mux);
+      tor_assert(chan == or_circ->p_chan);
+      /* Get next and prev for next test */
+      next_p = &(or_circ->next_active_on_p_chan);
+      prev_p = &(or_circ->prev_active_on_p_chan);
+    }
+
+    /*
+     * Should this circuit be active?  I.e., does the mux know about > 0
+     * cells on it?
+     */
+    circ_is_active = ((*i)->muxinfo.cell_count > 0);
+
+    /* It should be in the linked list iff it's active */
+    if (circ_is_active) {
+      /* Either we have a next link or we are the tail */
+      tor_assert(*next_p || (circ == cmux->active_circuits_tail));
+      /* Either we have a prev link or we are the head */
+      tor_assert(*prev_p || (circ == cmux->active_circuits_head));
+      /* Increment the active circuits counter */
+      ++n_active_circuits;
+    } else {
+      /* Shouldn't be in list, so no next or prev link */
+      tor_assert(!(*next_p));
+      tor_assert(!(*prev_p));
+      /* And can't be head or tail */
+      tor_assert(circ != cmux->active_circuits_head);
+      tor_assert(circ != cmux->active_circuits_tail);
+    }
+
+    /* Increment the circuits counter */
+    ++n_circuits;
+    /* Adjust the cell counter */
+    n_cells += (*i)->muxinfo.cell_count;
+
+    /* Set the mark bit to circ_is_active */
+    (*i)->muxinfo.mark = circ_is_active;
+
+    /* Advance to the next entry */
+    i = HT_NEXT(chanid_circid_muxinfo_map, cmux->chanid_circid_map, i);
+  }
+
+  /* Now check the counters */
+  tor_assert(n_cells == cmux->n_cells);
+  tor_assert(n_circuits == cmux->n_circuits);
+  tor_assert(n_active_circuits == cmux->n_active_circuits);
+}
+
+/**
+ * Do the second pass of circuitmux_assert_okay(); see the comment in that
+ * function.
+ */
+
+static void
+circuitmux_assert_okay_pass_two(circuitmux_t *cmux)
+{
+  circuit_t *curr_circ, *prev_circ = NULL, *next_circ;
+  or_circuit_t *curr_or_circ;
+  uint64_t curr_chan_id;
+  circid_t curr_circ_id;
+  circuit_t **next_p, **prev_p;
+  channel_t *chan;
+  unsigned int n_active_circuits = 0;
+  cell_direction_t direction;
+  chanid_circid_muxinfo_t search, *hashent = NULL;
+
+  tor_assert(cmux);
+  tor_assert(cmux->chanid_circid_map);
+
+  /*
+   * Walk the linked list of active circuits in cmux; keep track of the
+   * previous circuit seen for consistency checking purposes.  Count them
+   * to make sure the number in the linked list matches
+   * cmux->n_active_circuits.
+   */
+  curr_circ = cmux->active_circuits_head;
+  while (curr_circ) {
+    /* Reset some things */
+    chan = NULL;
+    curr_or_circ = NULL;
+    next_circ = NULL;
+    next_p = prev_p = NULL;
+    direction = 0;
+
+    /* Figure out if this is n_mux or p_mux */
+    if (cmux == curr_circ->n_mux) {
+      /* Get next_p and prev_p */
+      next_p = &(curr_circ->next_active_on_n_chan);
+      prev_p = &(curr_circ->prev_active_on_n_chan);
+      /* Get the channel */
+      chan = curr_circ->n_chan;
+      /* Get the circuit id */
+      curr_circ_id = curr_circ->n_circ_id;
+      /* Remember the direction */
+      direction = CELL_DIRECTION_OUT;
+    } else {
+      /* We must be p_mux and this must be an or_circuit_t */
+      curr_or_circ = TO_OR_CIRCUIT(curr_circ);
+      tor_assert(cmux == curr_or_circ->p_mux);
+      /* Get next_p and prev_p */
+      next_p = &(curr_or_circ->next_active_on_p_chan);
+      prev_p = &(curr_or_circ->prev_active_on_p_chan);
+      /* Get the channel */
+      chan = curr_or_circ->p_chan;
+      /* Get the circuit id */
+      curr_circ_id = curr_or_circ->p_circ_id;
+      /* Remember the direction */
+      direction = CELL_DIRECTION_IN;
+    }
+
+    /* Assert that we got a channel and get the channel ID */
+    tor_assert(chan);
+    curr_chan_id = chan->global_identifier;
+
+    /* Assert that prev_p points to last circuit we saw */
+    tor_assert(*prev_p == prev_circ);
+    /* If that's NULL, assert that we are the head */
+    if (!(*prev_p)) tor_assert(curr_circ == cmux->active_circuits_head);
+
+    /* Get the next circuit */
+    next_circ = *next_p;
+    /* If it's NULL, assert that we are the tail */
+    if (!(*next_p)) tor_assert(curr_circ == cmux->active_circuits_tail);
+
+    /* Now find the hash table entry for this circuit */
+    search.chan_id = curr_chan_id;
+    search.circ_id = curr_circ_id;
+    hashent = HT_FIND(chanid_circid_muxinfo_map, cmux->chanid_circid_map,
+                      &search);
+
+    /* Assert that we have one */
+    tor_assert(hashent);
+
+    /* Assert that the direction matches */
+    tor_assert(direction == hashent->muxinfo.direction);
+
+    /* Assert that the hash entry got marked in pass one */
+    tor_assert(hashent->muxinfo.mark);
+
+    /* Clear the mark */
+    hashent->muxinfo.mark = 0;
+
+    /* Increment the counter */
+    ++n_active_circuits;
+
+    /* Advance to the next active circuit and update prev_circ */
+    prev_circ = curr_circ;
+    curr_circ = next_circ;
+  }
+
+  /* Assert that the counter matches the cmux */
+  tor_assert(n_active_circuits == cmux->n_active_circuits);
+}
+
+/**
+ * Do the third pass of circuitmux_assert_okay(); see the comment in that
+ * function.
+ */
+
+static void
+circuitmux_assert_okay_pass_three(circuitmux_t *cmux)
+{
+  chanid_circid_muxinfo_t **i = NULL;
+
+  tor_assert(cmux);
+  tor_assert(cmux->chanid_circid_map);
+
+  /* Start iterating the hash table */
+  i = HT_START(chanid_circid_muxinfo_map, cmux->chanid_circid_map);
+
+  /* Advance through each entry */
+  while (i) {
+    /* Assert that it isn't null */
+    tor_assert(*i);
+
+    /*
+     * Assert that this entry is not marked - i.e., that either we didn't
+     * think it should be active in pass one or we saw it in the active
+     * circuits linked list.
+     */
+    tor_assert(!((*i)->muxinfo.mark));
+
+    /* Advance to the next entry */
+    i = HT_NEXT(chanid_circid_muxinfo_map, cmux->chanid_circid_map, i);
+  }
+}
+
diff --git a/src/or/circuitmux.h b/src/or/circuitmux.h
new file mode 100644
index 000000000..a3eacaf7d
--- /dev/null
+++ b/src/or/circuitmux.h
@@ -0,0 +1,136 @@
+/* * Copyright (c) 2012, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file circuitmux.h
+ * \brief Header file for circuitmux.c
+ **/
+
+#ifndef _TOR_CIRCUITMUX_H
+#define _TOR_CIRCUITMUX_H
+
+#include "or.h"
+
+typedef struct circuitmux_policy_s circuitmux_policy_t;
+typedef struct circuitmux_policy_data_s circuitmux_policy_data_t;
+typedef struct circuitmux_policy_circ_data_s circuitmux_policy_circ_data_t;
+
+struct circuitmux_policy_s {
+  /* Allocate cmux-wide policy-specific data */
+  circuitmux_policy_data_t * (*alloc_cmux_data)(circuitmux_t *cmux);
+  /* Free cmux-wide policy-specific data */
+  void (*free_cmux_data)(circuitmux_t *cmux,
+                         circuitmux_policy_data_t *pol_data);
+  /* Allocate circuit policy-specific data for a newly attached circuit */
+  circuitmux_policy_circ_data_t *
+    (*alloc_circ_data)(circuitmux_t *cmux,
+                       circuitmux_policy_data_t *pol_data,
+                       circuit_t *circ,
+                       cell_direction_t direction,
+                       unsigned int cell_count);
+  /* Free circuit policy-specific data */
+  void (*free_circ_data)(circuitmux_t *cmux,
+                         circuitmux_policy_data_t *pol_data,
+                         circuit_t *circ,
+                         circuitmux_policy_circ_data_t *pol_circ_data);
+  /* Notify that a circuit has become active/inactive */
+  void (*notify_circ_active)(circuitmux_t *cmux,
+                             circuitmux_policy_data_t *pol_data,
+                             circuit_t *circ,
+                             circuitmux_policy_circ_data_t *pol_circ_data);
+  void (*notify_circ_inactive)(circuitmux_t *cmux,
+                               circuitmux_policy_data_t *pol_data,
+                               circuit_t *circ,
+                               circuitmux_policy_circ_data_t *pol_circ_data);
+  /* Notify of arriving/transmitted cells on a circuit */
+  void (*notify_set_n_cells)(circuitmux_t *cmux,
+                             circuitmux_policy_data_t *pol_data,
+                             circuit_t *circ,
+                             circuitmux_policy_circ_data_t *pol_circ_data,
+                             unsigned int n_cells);
+  void (*notify_xmit_cells)(circuitmux_t *cmux,
+                            circuitmux_policy_data_t *pol_data,
+                            circuit_t *circ,
+                            circuitmux_policy_circ_data_t *pol_circ_data,
+                            unsigned int n_cells);
+  /* Choose a circuit */
+  circuit_t * (*pick_active_circuit)(circuitmux_t *cmux,
+                                     circuitmux_policy_data_t *pol_data);
+};
+
+/*
+ * Circuitmux policy implementations can subclass this to store circuitmux-
+ * wide data; it just has the magic number in the base struct.
+ */
+
+struct circuitmux_policy_data_s {
+  uint32_t magic;
+};
+
+/*
+ * Circuitmux policy implementations can subclass this to store circuit-
+ * specific data; it just has the magic number in the base struct.
+ */
+
+struct circuitmux_policy_circ_data_s {
+  uint32_t magic;
+};
+
+/*
+ * Upcast #defines for the above types
+ */
+
+/**
+ * Convert a circuitmux_policy_data_t subtype to a circuitmux_policy_data_t.
+ */
+
+#define TO_CMUX_POL_DATA(x)  (&((x)->_base))
+
+/**
+ * Convert a circuitmux_policy_circ_data_t subtype to a
+ * circuitmux_policy_circ_data_t.
+ */
+
+#define TO_CMUX_POL_CIRC_DATA(x)  (&((x)->_base))
+
+/* Consistency check */
+void circuitmux_assert_okay(circuitmux_t *cmux);
+
+/* Create/destroy */
+circuitmux_t * circuitmux_alloc(void);
+void circuitmux_detach_all_circuits(circuitmux_t *cmux);
+void circuitmux_free(circuitmux_t *cmux);
+
+/* Policy control */
+void circuitmux_clear_policy(circuitmux_t *cmux);
+const circuitmux_policy_t * circuitmux_get_policy(circuitmux_t *cmux);
+void circuitmux_set_policy(circuitmux_t *cmux,
+                           const circuitmux_policy_t *pol);
+
+/* Status inquiries */
+cell_direction_t circuitmux_attached_circuit_direction(
+    circuitmux_t *cmux,
+    circuit_t *circ);
+int circuitmux_is_circuit_attached(circuitmux_t *cmux, circuit_t *circ);
+int circuitmux_is_circuit_active(circuitmux_t *cmux, circuit_t *circ);
+unsigned int circuitmux_num_cells_for_circuit(circuitmux_t *cmux,
+                                              circuit_t *circ);
+unsigned int circuitmux_num_cells(circuitmux_t *cmux);
+unsigned int circuitmux_num_circuits(circuitmux_t *cmux);
+unsigned int circuitmux_num_active_circuits(circuitmux_t *cmux);
+
+/* Channel interface */
+circuit_t * circuitmux_get_first_active_circuit(circuitmux_t *cmux);
+void circuitmux_notify_xmit_cells(circuitmux_t *cmux, circuit_t *circ,
+                                  unsigned int n_cells);
+
+/* Circuit interface */
+void circuitmux_attach_circuit(circuitmux_t *cmux, circuit_t *circ,
+                               cell_direction_t direction);
+void circuitmux_detach_circuit(circuitmux_t *cmux, circuit_t *circ);
+void circuitmux_clear_num_cells(circuitmux_t *cmux, circuit_t *circ);
+void circuitmux_set_num_cells(circuitmux_t *cmux, circuit_t *circ,
+                              unsigned int n_cells);
+
+#endif /* _TOR_CIRCUITMUX_H */
+
diff --git a/src/or/circuitmux_ewma.c b/src/or/circuitmux_ewma.c
new file mode 100644
index 000000000..c280bf4ab
--- /dev/null
+++ b/src/or/circuitmux_ewma.c
@@ -0,0 +1,683 @@
+/* * Copyright (c) 2012, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file circuitmux_ewma.c
+ * \brief EWMA circuit selection as a circuitmux_t policy
+ **/
+
+#define _TOR_CIRCUITMUX_EWMA_C
+
+#include <math.h>
+
+#include "or.h"
+#include "circuitmux.h"
+#include "circuitmux_ewma.h"
+#include "networkstatus.h"
+
+/*** EWMA parameter #defines ***/
+
+/** How long does a tick last (seconds)? */
+#define EWMA_TICK_LEN 10
+
+/** The default per-tick scale factor, if it hasn't been overridden by a
+ * consensus or a configuration setting.  zero means "disabled". */
+#define EWMA_DEFAULT_HALFLIFE 0.0
+
+/*** Some useful constant #defines ***/
+
+/*DOCDOC*/
+#define EPSILON 0.00001
+/*DOCDOC*/
+#define LOG_ONEHALF -0.69314718055994529
+
+/*** EWMA structures ***/
+
+typedef struct cell_ewma_s cell_ewma_t;
+typedef struct ewma_policy_data_s ewma_policy_data_t;
+typedef struct ewma_policy_circ_data_s ewma_policy_circ_data_t;
+
+/**
+ * The cell_ewma_t structure keeps track of how many cells a circuit has
+ * transferred recently.  It keeps an EWMA (exponentially weighted moving
+ * average) of the number of cells flushed from the circuit queue onto a
+ * connection in channel_flush_from_first_active_circuit().
+ */
+
+struct cell_ewma_s {
+  /** The last 'tick' at which we recalibrated cell_count.
+   *
+   * A cell sent at exactly the start of this tick has weight 1.0. Cells sent
+   * since the start of this tick have weight greater than 1.0; ones sent
+   * earlier have less weight. */
+  unsigned int last_adjusted_tick;
+  /** The EWMA of the cell count. */
+  double cell_count;
+  /** True iff this is the cell count for a circuit's previous
+   * channel. */
+  unsigned int is_for_p_chan : 1;
+  /** The position of the circuit within the OR connection's priority
+   * queue. */
+  int heap_index;
+};
+
+struct ewma_policy_data_s {
+  circuitmux_policy_data_t _base;
+
+  /**
+   * Priority queue of cell_ewma_t for circuits with queued cells waiting
+   * for room to free up on the channel that owns this circuitmux.  Kept
+   * in heap order according to EWMA.  This was formerly in channel_t, and
+   * in or_connection_t before that.
+   */
+  smartlist_t *active_circuit_pqueue;
+
+  /**
+   * The tick on which the cell_ewma_ts in active_circuit_pqueue last had
+   * their ewma values rescaled.  This was formerly in channel_t, and in
+   * or_connection_t before that.
+   */
+  unsigned int active_circuit_pqueue_last_recalibrated;
+};
+
+struct ewma_policy_circ_data_s {
+  circuitmux_policy_circ_data_t _base;
+
+  /**
+   * The EWMA count for the number of cells flushed from this circuit
+   * onto this circuitmux.  Used to determine which circuit to flush
+   * from next.  This was formerly in circuit_t and or_circuit_t.
+   */
+  cell_ewma_t cell_ewma;
+
+  /**
+   * Pointer back to the circuit_t this is for; since we're separating
+   * out circuit selection policy like this, we can't attach cell_ewma_t
+   * to the circuit_t any more, so we can't use SUBTYPE_P directly to a
+   * circuit_t like before; instead get it here.
+   */
+  circuit_t *circ;
+};
+
+#define EWMA_POL_DATA_MAGIC 0x2fd8b16aU
+#define EWMA_POL_CIRC_DATA_MAGIC 0x761e7747U
+
+/*** Downcasts for the above types ***/
+
+static ewma_policy_data_t *
+TO_EWMA_POL_DATA(circuitmux_policy_data_t *);
+
+static ewma_policy_circ_data_t *
+TO_EWMA_POL_CIRC_DATA(circuitmux_policy_circ_data_t *);
+
+/**
+ * Downcast a circuitmux_policy_data_t to an ewma_policy_data_t and assert
+ * if the cast is impossible.
+ */
+
+static INLINE ewma_policy_data_t *
+TO_EWMA_POL_DATA(circuitmux_policy_data_t *pol)
+{
+  if (!pol) return NULL;
+  else {
+    tor_assert(pol->magic == EWMA_POL_DATA_MAGIC);
+    return DOWNCAST(ewma_policy_data_t, pol);
+  }
+}
+
+/**
+ * Downcast a circuitmux_policy_circ_data_t to an ewma_policy_circ_data_t
+ * and assert if the cast is impossible.
+ */
+
+static INLINE ewma_policy_circ_data_t *
+TO_EWMA_POL_CIRC_DATA(circuitmux_policy_circ_data_t *pol)
+{
+  if (!pol) return NULL;
+  else {
+    tor_assert(pol->magic == EWMA_POL_CIRC_DATA_MAGIC);
+    return DOWNCAST(ewma_policy_circ_data_t, pol);
+  }
+}
+
+/*** Static declarations for circuitmux_ewma.c ***/
+
+static void add_cell_ewma(ewma_policy_data_t *pol, cell_ewma_t *ewma);
+static int compare_cell_ewma_counts(const void *p1, const void *p2);
+static unsigned cell_ewma_tick_from_timeval(const struct timeval *now,
+                                            double *remainder_out);
+static circuit_t * cell_ewma_to_circuit(cell_ewma_t *ewma);
+static INLINE double get_scale_factor(unsigned from_tick, unsigned to_tick);
+static cell_ewma_t * pop_first_cell_ewma(ewma_policy_data_t *pol);
+static void remove_cell_ewma(ewma_policy_data_t *pol, cell_ewma_t *ewma);
+static void scale_single_cell_ewma(cell_ewma_t *ewma, unsigned cur_tick);
+static void scale_active_circuits(ewma_policy_data_t *pol,
+                                  unsigned cur_tick);
+
+/*** Circuitmux policy methods ***/
+
+static circuitmux_policy_data_t * ewma_alloc_cmux_data(circuitmux_t *cmux);
+static void ewma_free_cmux_data(circuitmux_t *cmux,
+                                circuitmux_policy_data_t *pol_data);
+static circuitmux_policy_circ_data_t *
+ewma_alloc_circ_data(circuitmux_t *cmux, circuitmux_policy_data_t *pol_data,
+                     circuit_t *circ, cell_direction_t direction,
+                     unsigned int cell_count);
+static void
+ewma_free_circ_data(circuitmux_t *cmux,
+                    circuitmux_policy_data_t *pol_data,
+                    circuit_t *circ,
+                    circuitmux_policy_circ_data_t *pol_circ_data);
+static void
+ewma_notify_circ_active(circuitmux_t *cmux,
+                        circuitmux_policy_data_t *pol_data,
+                        circuit_t *circ,
+                        circuitmux_policy_circ_data_t *pol_circ_data);
+static void
+ewma_notify_circ_inactive(circuitmux_t *cmux,
+                          circuitmux_policy_data_t *pol_data,
+                          circuit_t *circ,
+                          circuitmux_policy_circ_data_t *pol_circ_data);
+static void
+ewma_notify_xmit_cells(circuitmux_t *cmux,
+                       circuitmux_policy_data_t *pol_data,
+                       circuit_t *circ,
+                       circuitmux_policy_circ_data_t *pol_circ_data,
+                       unsigned int n_cells);
+static circuit_t *
+ewma_pick_active_circuit(circuitmux_t *cmux,
+                         circuitmux_policy_data_t *pol_data);
+
+/*** EWMA global variables ***/
+
+/** The per-tick scale factor to be used when computing cell-count EWMA
+ * values.  (A cell sent N ticks before the start of the current tick
+ * has value ewma_scale_factor ** N.)
+ */
+static double ewma_scale_factor = 0.1;
+/* DOCDOC ewma_enabled */
+static int ewma_enabled = 0;
+
+/*** EWMA circuitmux_policy_t method table ***/
+
+circuitmux_policy_t ewma_policy = {  .alloc_cmux_data = ewma_alloc_cmux_data,
+  .free_cmux_data = ewma_free_cmux_data,
+  .alloc_circ_data = ewma_alloc_circ_data,
+  .free_circ_data = ewma_free_circ_data,
+  .notify_circ_active = ewma_notify_circ_active,
+  .notify_circ_inactive = ewma_notify_circ_inactive,
+  .notify_set_n_cells = NULL, /* EWMA doesn't need this */
+  .notify_xmit_cells = ewma_notify_xmit_cells,
+  .pick_active_circuit = ewma_pick_active_circuit
+};
+
+/*** EWMA method implementations using the below EWMA helper functions ***/
+
+/**
+ * Allocate an ewma_policy_data_t and upcast it to a circuitmux_policy_data_t;
+ * this is called when setting the policy on a circuitmux_t to ewma_policy.
+ */
+
+static circuitmux_policy_data_t *
+ewma_alloc_cmux_data(circuitmux_t *cmux)
+{
+  ewma_policy_data_t *pol = NULL;
+
+  tor_assert(cmux);
+
+  pol = tor_malloc_zero(sizeof(*pol));
+  pol->_base.magic = EWMA_POL_DATA_MAGIC;
+  pol->active_circuit_pqueue = smartlist_new();
+  pol->active_circuit_pqueue_last_recalibrated = cell_ewma_get_tick();
+
+  return TO_CMUX_POL_DATA(pol);
+}
+
+/**
+ * Free an ewma_policy_data_t allocated with ewma_alloc_cmux_data()
+ */
+
+static void
+ewma_free_cmux_data(circuitmux_t *cmux,
+                    circuitmux_policy_data_t *pol_data)
+{
+  ewma_policy_data_t *pol = NULL;
+
+  tor_assert(cmux);
+  if (!pol_data) return;
+
+  pol = TO_EWMA_POL_DATA(pol_data);
+
+  smartlist_free(pol->active_circuit_pqueue);
+  tor_free(pol);
+}
+
+/**
+ * Allocate an ewma_policy_circ_data_t and upcast it to a
+ * circuitmux_policy_data_t; this is called when attaching a circuit to a
+ * circuitmux_t with ewma_policy.
+ */
+
+static circuitmux_policy_circ_data_t *
+ewma_alloc_circ_data(circuitmux_t *cmux,
+                     circuitmux_policy_data_t *pol_data,
+                     circuit_t *circ,
+                     cell_direction_t direction,
+                     unsigned int cell_count)
+{
+  ewma_policy_circ_data_t *cdata = NULL;
+
+  tor_assert(cmux);
+  tor_assert(pol_data);
+  tor_assert(circ);
+  tor_assert(direction == CELL_DIRECTION_OUT ||
+             direction == CELL_DIRECTION_IN);
+  /* Shut the compiler up */
+  tor_assert(cell_count == cell_count);
+
+  cdata = tor_malloc_zero(sizeof(*cdata));
+  cdata->_base.magic = EWMA_POL_CIRC_DATA_MAGIC;
+  cdata->circ = circ;
+
+  /*
+   * Initialize the cell_ewma_t structure (formerly in
+   * init_circuit_base())
+   */
+  cdata->cell_ewma.last_adjusted_tick = cell_ewma_get_tick();
+  cdata->cell_ewma.cell_count = 0.0;
+  cdata->cell_ewma.heap_index = -1;
+  if (direction == CELL_DIRECTION_IN) {
+    cdata->cell_ewma.is_for_p_chan = 1;
+  } else {
+    cdata->cell_ewma.is_for_p_chan = 0;
+  }
+
+  return TO_CMUX_POL_CIRC_DATA(cdata);
+}
+
+/**
+ * Free an ewma_policy_circ_data_t allocated with ewma_alloc_circ_data()
+ */
+
+static void
+ewma_free_circ_data(circuitmux_t *cmux,
+                    circuitmux_policy_data_t *pol_data,
+                    circuit_t *circ,
+                    circuitmux_policy_circ_data_t *pol_circ_data)
+
+{
+  ewma_policy_circ_data_t *cdata = NULL;
+
+  tor_assert(cmux);
+  tor_assert(circ);
+  tor_assert(pol_data);
+
+  if (!pol_circ_data) return;
+
+  cdata = TO_EWMA_POL_CIRC_DATA(pol_circ_data);
+
+  tor_free(cdata);
+}
+
+/**
+ * Handle circuit activation; this inserts the circuit's cell_ewma into
+ * the active_circuits_pqueue.
+ */
+
+static void
+ewma_notify_circ_active(circuitmux_t *cmux,
+                        circuitmux_policy_data_t *pol_data,
+                        circuit_t *circ,
+                        circuitmux_policy_circ_data_t *pol_circ_data)
+{
+  ewma_policy_data_t *pol = NULL;
+  ewma_policy_circ_data_t *cdata = NULL;
+
+  tor_assert(cmux);
+  tor_assert(pol_data);
+  tor_assert(circ);
+  tor_assert(pol_circ_data);
+
+  pol = TO_EWMA_POL_DATA(pol_data);
+  cdata = TO_EWMA_POL_CIRC_DATA(pol_circ_data);
+
+  add_cell_ewma(pol, &(cdata->cell_ewma));
+}
+
+/**
+ * Handle circuit deactivation; this removes the circuit's cell_ewma from
+ * the active_circuits_pqueue.
+ */
+
+static void
+ewma_notify_circ_inactive(circuitmux_t *cmux,
+                          circuitmux_policy_data_t *pol_data,
+                          circuit_t *circ,
+                          circuitmux_policy_circ_data_t *pol_circ_data)
+{
+  ewma_policy_data_t *pol = NULL;
+  ewma_policy_circ_data_t *cdata = NULL;
+
+  tor_assert(cmux);
+  tor_assert(pol_data);
+  tor_assert(circ);
+  tor_assert(pol_circ_data);
+
+  pol = TO_EWMA_POL_DATA(pol_data);
+  cdata = TO_EWMA_POL_CIRC_DATA(pol_circ_data);
+
+  remove_cell_ewma(pol, &(cdata->cell_ewma));
+}
+
+/**
+ * Update cell_ewma for this circuit after we've sent some cells, and
+ * remove/reinsert it in the queue.  This used to be done (brokenly,
+ * see bug 6816) in channel_flush_from_first_active_circuit().
+ */
+
+static void
+ewma_notify_xmit_cells(circuitmux_t *cmux,
+                       circuitmux_policy_data_t *pol_data,
+                       circuit_t *circ,
+                       circuitmux_policy_circ_data_t *pol_circ_data,
+                       unsigned int n_cells)
+{
+  ewma_policy_data_t *pol = NULL;
+  ewma_policy_circ_data_t *cdata = NULL;
+  unsigned int tick;
+  double fractional_tick, ewma_increment;
+  /* The current (hi-res) time */
+  struct timeval now_hires;
+  cell_ewma_t *cell_ewma, *tmp;
+
+  tor_assert(cmux);
+  tor_assert(pol_data);
+  tor_assert(circ);
+  tor_assert(pol_circ_data);
+  tor_assert(n_cells > 0);
+
+  pol = TO_EWMA_POL_DATA(pol_data);
+  cdata = TO_EWMA_POL_CIRC_DATA(pol_circ_data);
+
+  /* Rescale the EWMAs if needed */
+  tor_gettimeofday_cached(&now_hires);
+  tick = cell_ewma_tick_from_timeval(&now_hires, &fractional_tick);
+
+  if (tick != pol->active_circuit_pqueue_last_recalibrated) {
+    scale_active_circuits(pol, tick);
+  }
+
+  /* How much do we adjust the cell count in cell_ewma by? */
+  ewma_increment =
+    ((double)(n_cells)) * pow(ewma_scale_factor, -fractional_tick);
+
+  /* Do the adjustment */
+  cell_ewma = &(cdata->cell_ewma);
+  cell_ewma->cell_count += ewma_increment;
+
+  /*
+   * Since we just sent on this circuit, it should be at the head of
+   * the queue.  Pop the head, assert that it matches, then re-add.
+   */
+  tmp = pop_first_cell_ewma(pol);
+  tor_assert(tmp == cell_ewma);
+  add_cell_ewma(pol, cell_ewma);
+}
+
+/**
+ * Pick the preferred circuit to send from; this will be the one with
+ * the lowest EWMA value in the priority queue.  This used to be done
+ * in channel_flush_from_first_active_circuit().
+ */
+
+static circuit_t *
+ewma_pick_active_circuit(circuitmux_t *cmux,
+                         circuitmux_policy_data_t *pol_data)
+{
+  ewma_policy_data_t *pol = NULL;
+  circuit_t *circ = NULL;
+  cell_ewma_t *cell_ewma = NULL;
+
+  tor_assert(cmux);
+  tor_assert(pol_data);
+
+  pol = TO_EWMA_POL_DATA(pol_data);
+
+  if (smartlist_len(pol->active_circuit_pqueue) > 0) {
+    /* Get the head of the queue */
+    cell_ewma = smartlist_get(pol->active_circuit_pqueue, 0);
+    circ = cell_ewma_to_circuit(cell_ewma);
+  }
+
+  return circ;
+}
+
+/** Helper for sorting cell_ewma_t values in their priority queue. */
+static int
+compare_cell_ewma_counts(const void *p1, const void *p2)
+{
+  const cell_ewma_t *e1 = p1, *e2 = p2;
+
+  if (e1->cell_count < e2->cell_count)
+    return -1;
+  else if (e1->cell_count > e2->cell_count)
+    return 1;
+  else
+    return 0;
+}
+
+/** Given a cell_ewma_t, return a pointer to the circuit containing it. */
+static circuit_t *
+cell_ewma_to_circuit(cell_ewma_t *ewma)
+{
+  ewma_policy_circ_data_t *cdata = NULL;
+
+  tor_assert(ewma);
+  cdata = SUBTYPE_P(ewma, ewma_policy_circ_data_t, cell_ewma);
+  tor_assert(cdata);
+
+  return cdata->circ;
+}
+
+/* ==== Functions for scaling cell_ewma_t ====
+
+   When choosing which cells to relay first, we favor circuits that have been
+   quiet recently.  This gives better latency on connections that aren't
+   pushing lots of data, and makes the network feel more interactive.
+
+   Conceptually, we take an exponentially weighted mean average of the number
+   of cells a circuit has sent, and allow active circuits (those with cells to
+   relay) to send cells in reverse order of their exponentially-weighted mean
+   average (EWMA) cell count.  [That is, a cell sent N seconds ago 'counts'
+   F^N times as much as a cell sent now, for 0<F<1.0, and we favor the
+   circuit that has sent the fewest cells]
+
+   If 'double' had infinite precision, we could do this simply by counting a
+   cell sent at startup as having weight 1.0, and a cell sent N seconds later
+   as having weight F^-N.  This way, we would never need to re-scale
+   any already-sent cells.
+
+   To prevent double from overflowing, we could count a cell sent now as
+   having weight 1.0 and a cell sent N seconds ago as having weight F^N.
+   This, however, would mean we'd need to re-scale *ALL* old circuits every
+   time we wanted to send a cell.
+
+   So as a compromise, we divide time into 'ticks' (currently, 10-second
+   increments) and say that a cell sent at the start of a current tick is
+   worth 1.0, a cell sent N seconds before the start of the current tick is
+   worth F^N, and a cell sent N seconds after the start of the current tick is
+   worth F^-N.  This way we don't overflow, and we don't need to constantly
+   rescale.
+ */
+
+/** Given a timeval <b>now</b>, compute the cell_ewma tick in which it occurs
+ * and the fraction of the tick that has elapsed between the start of the tick
+ * and <b>now</b>.  Return the former and store the latter in
+ * *<b>remainder_out</b>.
+ *
+ * These tick values are not meant to be shared between Tor instances, or used
+ * for other purposes. */
+
+static unsigned
+cell_ewma_tick_from_timeval(const struct timeval *now,
+                            double *remainder_out)
+{
+  unsigned res = (unsigned) (now->tv_sec / EWMA_TICK_LEN);
+  /* rem */
+  double rem = (now->tv_sec % EWMA_TICK_LEN) +
+    ((double)(now->tv_usec)) / 1.0e6;
+  *remainder_out = rem / EWMA_TICK_LEN;
+  return res;
+}
+
+/** Tell the caller whether ewma_enabled is set */
+int
+cell_ewma_enabled(void)
+{
+  return ewma_enabled;
+}
+
+/** Compute and return the current cell_ewma tick. */
+unsigned int
+cell_ewma_get_tick(void)
+{
+  return ((unsigned)approx_time() / EWMA_TICK_LEN);
+}
+
+/** Adjust the global cell scale factor based on <b>options</b> */
+void
+cell_ewma_set_scale_factor(const or_options_t *options,
+                           const networkstatus_t *consensus)
+{
+  int32_t halflife_ms;
+  double halflife;
+  const char *source;
+  if (options && options->CircuitPriorityHalflife >= -EPSILON) {
+    halflife = options->CircuitPriorityHalflife;
+    source = "CircuitPriorityHalflife in configuration";
+  } else if (consensus && (halflife_ms = networkstatus_get_param(
+                 consensus, "CircuitPriorityHalflifeMsec",
+                 -1, -1, INT32_MAX)) >= 0) {
+    halflife = ((double)halflife_ms)/1000.0;
+    source = "CircuitPriorityHalflifeMsec in consensus";
+  } else {
+    halflife = EWMA_DEFAULT_HALFLIFE;
+    source = "Default value";
+  }
+
+  if (halflife <= EPSILON) {
+    /* The cell EWMA algorithm is disabled. */
+    ewma_scale_factor = 0.1;
+    ewma_enabled = 0;
+    log_info(LD_OR,
+             "Disabled cell_ewma algorithm because of value in %s",
+             source);
+  } else {
+    /* convert halflife into halflife-per-tick. */
+    halflife /= EWMA_TICK_LEN;
+    /* compute per-tick scale factor. */
+    ewma_scale_factor = exp( LOG_ONEHALF / halflife );
+    ewma_enabled = 1;
+    log_info(LD_OR,
+             "Enabled cell_ewma algorithm because of value in %s; "
+             "scale factor is %f per %d seconds",
+             source, ewma_scale_factor, EWMA_TICK_LEN);
+  }
+}
+
+/** Return the multiplier necessary to convert the value of a cell sent in
+ * 'from_tick' to one sent in 'to_tick'. */
+static INLINE double
+get_scale_factor(unsigned from_tick, unsigned to_tick)
+{
+  /* This math can wrap around, but that's okay: unsigned overflow is
+     well-defined */
+  int diff = (int)(to_tick - from_tick);
+  return pow(ewma_scale_factor, diff);
+}
+
+/** Adjust the cell count of <b>ewma</b> so that it is scaled with respect to
+ * <b>cur_tick</b> */
+static void
+scale_single_cell_ewma(cell_ewma_t *ewma, unsigned cur_tick)
+{
+  double factor = get_scale_factor(ewma->last_adjusted_tick, cur_tick);
+  ewma->cell_count *= factor;
+  ewma->last_adjusted_tick = cur_tick;
+}
+
+/** Adjust the cell count of every active circuit on <b>chan</b> so
+ * that they are scaled with respect to <b>cur_tick</b> */
+static void
+scale_active_circuits(ewma_policy_data_t *pol, unsigned cur_tick)
+{
+  double factor;
+
+  tor_assert(pol);
+  tor_assert(pol->active_circuit_pqueue);
+
+  factor =
+    get_scale_factor(
+      pol->active_circuit_pqueue_last_recalibrated,
+      cur_tick);
+  /** Ordinarily it isn't okay to change the value of an element in a heap,
+   * but it's okay here, since we are preserving the order. */
+  SMARTLIST_FOREACH_BEGIN(
+      pol->active_circuit_pqueue,
+      cell_ewma_t *, e) {
+    tor_assert(e->last_adjusted_tick ==
+               pol->active_circuit_pqueue_last_recalibrated);
+    e->cell_count *= factor;
+    e->last_adjusted_tick = cur_tick;
+  } SMARTLIST_FOREACH_END(e);
+  pol->active_circuit_pqueue_last_recalibrated = cur_tick;
+}
+
+/** Rescale <b>ewma</b> to the same scale as <b>pol</b>, and add it to
+ * <b>pol</b>'s priority queue of active circuits */
+static void
+add_cell_ewma(ewma_policy_data_t *pol, cell_ewma_t *ewma)
+{
+  tor_assert(pol);
+  tor_assert(pol->active_circuit_pqueue);
+  tor_assert(ewma);
+  tor_assert(ewma->heap_index == -1);
+
+  scale_single_cell_ewma(
+      ewma,
+      pol->active_circuit_pqueue_last_recalibrated);
+
+  smartlist_pqueue_add(pol->active_circuit_pqueue,
+                       compare_cell_ewma_counts,
+                       STRUCT_OFFSET(cell_ewma_t, heap_index),
+                       ewma);
+}
+
+/** Remove <b>ewma</b> from <b>pol</b>'s priority queue of active circuits */
+static void
+remove_cell_ewma(ewma_policy_data_t *pol, cell_ewma_t *ewma)
+{
+  tor_assert(pol);
+  tor_assert(pol->active_circuit_pqueue);
+  tor_assert(ewma);
+  tor_assert(ewma->heap_index != -1);
+
+  smartlist_pqueue_remove(pol->active_circuit_pqueue,
+                          compare_cell_ewma_counts,
+                          STRUCT_OFFSET(cell_ewma_t, heap_index),
+                          ewma);
+}
+
+/** Remove and return the first cell_ewma_t from pol's priority queue of
+ * active circuits.  Requires that the priority queue is nonempty. */
+static cell_ewma_t *
+pop_first_cell_ewma(ewma_policy_data_t *pol)
+{
+  tor_assert(pol);
+  tor_assert(pol->active_circuit_pqueue);
+
+  return smartlist_pqueue_pop(pol->active_circuit_pqueue,
+                              compare_cell_ewma_counts,
+                              STRUCT_OFFSET(cell_ewma_t, heap_index));
+}
+
diff --git a/src/or/circuitmux_ewma.h b/src/or/circuitmux_ewma.h
new file mode 100644
index 000000000..eec16f372
--- /dev/null
+++ b/src/or/circuitmux_ewma.h
@@ -0,0 +1,29 @@
+/* * Copyright (c) 2012, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file circuitmux_ewma.h
+ * \brief Header file for circuitmux_ewma.c
+ **/
+
+#ifndef _TOR_CIRCUITMUX_EWMA_H
+#define _TOR_CIRCUITMUX_EWMA_H
+
+#include "or.h"
+#include "circuitmux.h"
+
+/* Everything but circuitmux_ewma.c should see this extern */
+#ifndef _TOR_CIRCUITMUX_EWMA_C
+
+extern circuitmux_policy_t ewma_policy;
+
+#endif /* !(_TOR_CIRCUITMUX_EWMA_C) */
+
+/* Externally visible EWMA functions */
+int cell_ewma_enabled(void);
+unsigned int cell_ewma_get_tick(void);
+void cell_ewma_set_scale_factor(const or_options_t *options,
+                                const networkstatus_t *consensus);
+
+#endif /* _TOR_CIRCUITMUX_EWMA_H */
+
diff --git a/src/or/circuituse.c b/src/or/circuituse.c
index 79e1ed0fb..be79b30bc 100644
--- a/src/or/circuituse.c
+++ b/src/or/circuituse.c
@@ -10,6 +10,7 @@
  **/
 
 #include "or.h"
+#include "channel.h"
 #include "circuitbuild.h"
 #include "circuitlist.h"
 #include "circuituse.h"
@@ -53,7 +54,7 @@ circuit_is_acceptable(const origin_circuit_t *origin_circ,
   tor_assert(conn);
   tor_assert(conn->socks_request);
 
-  if (must_be_open && (circ->state != CIRCUIT_STATE_OPEN || !circ->n_conn))
+  if (must_be_open && (circ->state != CIRCUIT_STATE_OPEN || !circ->n_chan))
     return 0; /* ignore non-open circs */
   if (circ->marked_for_close)
     return 0;
@@ -565,9 +566,9 @@ circuit_expire_building(void)
       continue;
     }
 
-    if (victim->n_conn)
-      log_info(LD_CIRC,"Abandoning circ %s:%d:%d (state %d:%s, purpose %d)",
-               victim->n_conn->_base.address, victim->n_conn->_base.port,
+    if (victim->n_chan)
+      log_info(LD_CIRC,"Abandoning circ %s:%d (state %d:%s, purpose %d)",
+               channel_get_canonical_remote_descr(victim->n_chan),
                victim->n_circ_id,
                victim->state, circuit_state_to_string(victim->state),
                victim->purpose);
@@ -977,13 +978,13 @@ circuit_expire_old_circuits_serverside(time_t now)
     /* If the circuit has been idle for too long, and there are no streams
      * on it, and it ends here, and it used a create_fast, mark it for close.
      */
-    if (or_circ->is_first_hop && !circ->n_conn &&
+    if (or_circ->is_first_hop && !circ->n_chan &&
         !or_circ->n_streams && !or_circ->resolving_streams &&
-        or_circ->p_conn &&
-        or_circ->p_conn->timestamp_last_added_nonpadding <= cutoff) {
+        or_circ->p_chan &&
+        channel_when_last_xmit(or_circ->p_chan) <= cutoff) {
       log_info(LD_CIRC, "Closing circ_id %d (empty %d secs ago)",
                or_circ->p_circ_id,
-               (int)(now - or_circ->p_conn->timestamp_last_added_nonpadding));
+               (int)(now - channel_when_last_xmit(or_circ->p_chan)));
       circuit_mark_for_close(circ, END_CIRC_REASON_FINISHED);
     }
   }
@@ -1163,6 +1164,7 @@ circuit_try_attaching_streams(origin_circuit_t *circ)
 void
 circuit_build_failed(origin_circuit_t *circ)
 {
+  channel_t *n_chan = NULL;
   /* we should examine circ and see if it failed because of
    * the last hop or an earlier hop. then use this info below.
    */
@@ -1179,11 +1181,12 @@ circuit_build_failed(origin_circuit_t *circ)
     /* We failed at the first hop. If there's an OR connection
      * to blame, blame it. Also, avoid this relay for a while, and
      * fail any one-hop directory fetches destined for it. */
-    const char *n_conn_id = circ->cpath->extend_info->identity_digest;
+    const char *n_chan_id = circ->cpath->extend_info->identity_digest;
     int already_marked = 0;
-    if (circ->_base.n_conn) {
-      or_connection_t *n_conn = circ->_base.n_conn;
-      if (n_conn->is_bad_for_new_circs) {
+    if (circ->_base.n_chan) {
+      n_chan = circ->_base.n_chan;
+
+      if (n_chan->is_bad_for_new_circs) {
         /* We only want to blame this router when a fresh healthy
          * connection fails. So don't mark this router as newly failed,
          * since maybe this was just an old circuit attempt that's
@@ -1195,18 +1198,18 @@ circuit_build_failed(origin_circuit_t *circ)
       }
       log_info(LD_OR,
                "Our circuit failed to get a response from the first hop "
-               "(%s:%d). I'm going to try to rotate to a better connection.",
-               n_conn->_base.address, n_conn->_base.port);
-      n_conn->is_bad_for_new_circs = 1;
+               "(%s). I'm going to try to rotate to a better connection.",
+               channel_get_canonical_remote_descr(n_chan));
+      n_chan->is_bad_for_new_circs = 1;
     } else {
       log_info(LD_OR,
                "Our circuit died before the first hop with no connection");
     }
-    if (n_conn_id && !already_marked) {
-      entry_guard_register_connect_status(n_conn_id, 0, 1, time(NULL));
+    if (n_chan_id && !already_marked) {
+      entry_guard_register_connect_status(n_chan_id, 0, 1, time(NULL));
       /* if there are any one-hop streams waiting on this circuit, fail
        * them now so they can retry elsewhere. */
-      connection_ap_fail_onehop(n_conn_id, circ->build_state);
+      connection_ap_fail_onehop(n_chan_id, circ->build_state);
     }
   }
 
diff --git a/src/or/command.c b/src/or/command.c
index d04509b3f..7ce134d62 100644
--- a/src/or/command.c
+++ b/src/or/command.c
@@ -12,10 +12,13 @@
 /* In-points to command.c:
  *
  * - command_process_cell(), called from
- *   connection_or_process_cells_from_inbuf() in connection_or.c
+ *   incoming cell handlers of channel_t instances;
+ *   callbacks registered in command_setup_channel(),
+ *   called when channels are created in circuitbuild.c
  */
 
 #include "or.h"
+#include "channel.h"
 #include "circuitbuild.h"
 #include "circuitlist.h"
 #include "command.h"
@@ -31,8 +34,6 @@
 #include "router.h"
 #include "routerlist.h"
 
-/** How many CELL_PADDING cells have we received, ever? */
-uint64_t stats_n_padding_cells_processed = 0;
 /** How many CELL_CREATE cells have we received, ever? */
 uint64_t stats_n_create_cells_processed = 0;
 /** How many CELL_CREATED cells have we received, ever? */
@@ -41,38 +42,16 @@ uint64_t stats_n_created_cells_processed = 0;
 uint64_t stats_n_relay_cells_processed = 0;
 /** How many CELL_DESTROY cells have we received, ever? */
 uint64_t stats_n_destroy_cells_processed = 0;
-/** How many CELL_VERSIONS cells have we received, ever? */
-uint64_t stats_n_versions_cells_processed = 0;
-/** How many CELL_NETINFO cells have we received, ever? */
-uint64_t stats_n_netinfo_cells_processed = 0;
 
-/** How many CELL_VPADDING cells have we received, ever? */
-uint64_t stats_n_vpadding_cells_processed = 0;
-/** How many CELL_CERTS cells have we received, ever? */
-uint64_t stats_n_certs_cells_processed = 0;
-/** How many CELL_AUTH_CHALLENGE cells have we received, ever? */
-uint64_t stats_n_auth_challenge_cells_processed = 0;
-/** How many CELL_AUTHENTICATE cells have we received, ever? */
-uint64_t stats_n_authenticate_cells_processed = 0;
-/** How many CELL_AUTHORIZE cells have we received, ever? */
-uint64_t stats_n_authorize_cells_processed = 0;
+/* Handle an incoming channel */
+static void command_handle_incoming_channel(channel_listener_t *listener,
+                                            channel_t *chan);
 
 /* These are the main functions for processing cells */
-static void command_process_create_cell(cell_t *cell, or_connection_t *conn);
-static void command_process_created_cell(cell_t *cell, or_connection_t *conn);
-static void command_process_relay_cell(cell_t *cell, or_connection_t *conn);
-static void command_process_destroy_cell(cell_t *cell, or_connection_t *conn);
-static void command_process_versions_cell(var_cell_t *cell,
-                                          or_connection_t *conn);
-static void command_process_netinfo_cell(cell_t *cell, or_connection_t *conn);
-static void command_process_certs_cell(var_cell_t *cell,
-                                      or_connection_t *conn);
-static void command_process_auth_challenge_cell(var_cell_t *cell,
-                                          or_connection_t *conn);
-static void command_process_authenticate_cell(var_cell_t *cell,
-                                          or_connection_t *conn);
-static int enter_v3_handshake_with_cell(var_cell_t *cell,
-                                        or_connection_t *conn);
+static void command_process_create_cell(cell_t *cell, channel_t *chan);
+static void command_process_created_cell(cell_t *cell, channel_t *chan);
+static void command_process_relay_cell(cell_t *cell, channel_t *chan);
+static void command_process_destroy_cell(cell_t *cell, channel_t *chan);
 
 #ifdef KEEP_TIMING_STATS
 /** This is a wrapper function around the actual function that processes the
@@ -80,15 +59,15 @@ static int enter_v3_handshake_with_cell(var_cell_t *cell,
  * by the number of microseconds used by the call to <b>*func(cell, conn)</b>.
  */
 static void
-command_time_process_cell(cell_t *cell, or_connection_t *conn, int *time,
-                               void (*func)(cell_t *, or_connection_t *))
+command_time_process_cell(cell_t *cell, channel_t *chan, int *time,
+                               void (*func)(cell_t *, channel_t *))
 {
   struct timeval start, end;
   long time_passed;
 
   tor_gettimeofday(&start);
 
-  (*func)(cell, conn);
+  (*func)(cell, chan);
 
   tor_gettimeofday(&end);
   time_passed = tv_udiff(&start, &end) ;
@@ -104,15 +83,14 @@ command_time_process_cell(cell_t *cell, or_connection_t *conn, int *time,
 }
 #endif
 
-/** Process a <b>cell</b> that was just received on <b>conn</b>. Keep internal
+/** Process a <b>cell</b> that was just received on <b>chan</b>. Keep internal
  * statistics about how many of each cell we've processed so far
  * this second, and the total number of microseconds it took to
  * process each type of cell.
  */
 void
-command_process_cell(cell_t *cell, or_connection_t *conn)
+command_process_cell(channel_t *chan, cell_t *cell)
 {
-  int handshaking = (conn->_base.state != OR_CONN_STATE_OPEN);
 #ifdef KEEP_TIMING_STATS
   /* how many of each cell have we seen so far this second? needs better
    * name. */
@@ -152,255 +130,115 @@ command_process_cell(cell_t *cell, or_connection_t *conn)
 #define PROCESS_CELL(tp, cl, cn) command_process_ ## tp ## _cell(cl, cn)
 #endif
 
-  if (conn->_base.marked_for_close)
-    return;
-
-  /* Reject all but VERSIONS and NETINFO when handshaking. */
-  /* (VERSIONS should actually be impossible; it's variable-length.) */
-  if (handshaking && cell->command != CELL_VERSIONS &&
-      cell->command != CELL_NETINFO) {
-    log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
-           "Received unexpected cell command %d in state %s; closing the "
-           "connection.",
-           (int)cell->command,
-           conn_state_to_string(CONN_TYPE_OR,conn->_base.state));
-    connection_mark_for_close(TO_CONN(conn));
-    return;
-  }
-
-  if (conn->_base.state == OR_CONN_STATE_OR_HANDSHAKING_V3)
-    or_handshake_state_record_cell(conn->handshake_state, cell, 1);
-
   switch (cell->command) {
-    case CELL_PADDING:
-      ++stats_n_padding_cells_processed;
-      /* do nothing */
-      break;
     case CELL_CREATE:
     case CELL_CREATE_FAST:
       ++stats_n_create_cells_processed;
-      PROCESS_CELL(create, cell, conn);
+      PROCESS_CELL(create, cell, chan);
       break;
     case CELL_CREATED:
     case CELL_CREATED_FAST:
       ++stats_n_created_cells_processed;
-      PROCESS_CELL(created, cell, conn);
+      PROCESS_CELL(created, cell, chan);
       break;
     case CELL_RELAY:
     case CELL_RELAY_EARLY:
       ++stats_n_relay_cells_processed;
-      PROCESS_CELL(relay, cell, conn);
+      PROCESS_CELL(relay, cell, chan);
       break;
     case CELL_DESTROY:
       ++stats_n_destroy_cells_processed;
-      PROCESS_CELL(destroy, cell, conn);
-      break;
-    case CELL_VERSIONS:
-      tor_fragile_assert();
-      break;
-    case CELL_NETINFO:
-      ++stats_n_netinfo_cells_processed;
-      PROCESS_CELL(netinfo, cell, conn);
+      PROCESS_CELL(destroy, cell, chan);
       break;
     default:
       log_fn(LOG_INFO, LD_PROTOCOL,
-             "Cell of unknown type (%d) received. Dropping.", cell->command);
+             "Cell of unknown or unexpected type (%d) received.  "
+             "Dropping.",
+             cell->command);
       break;
   }
 }
 
-/** Return true if <b>command</b> is a cell command that's allowed to start a
- * V3 handshake. */
-static int
-command_allowed_before_handshake(uint8_t command)
-{
-  switch (command) {
-    case CELL_VERSIONS:
-    case CELL_VPADDING:
-    case CELL_AUTHORIZE:
-      return 1;
-    default:
-      return 0;
-  }
-}
-
-/** Process a <b>cell</b> that was just received on <b>conn</b>. Keep internal
- * statistics about how many of each cell we've processed so far
- * this second, and the total number of microseconds it took to
- * process each type of cell.
+/** Process an incoming var_cell from a channel; in the current protocol all
+ * the var_cells are handshake-related and handles below the channel layer,
+ * so this just logs a warning and drops the cell.
  */
+
 void
-command_process_var_cell(var_cell_t *cell, or_connection_t *conn)
+command_process_var_cell(channel_t *chan, var_cell_t *var_cell)
 {
-#ifdef KEEP_TIMING_STATS
-  /* how many of each cell have we seen so far this second? needs better
-   * name. */
-  static int num_versions=0, num_certs=0;
-
-  time_t now = time(NULL);
-
-  if (now > current_second) { /* the second has rolled over */
-    /* print stats */
-    log_info(LD_OR,
-             "At end of second: %d versions (%d ms), %d certs (%d ms)",
-             num_versions, versions_time/1000,
-             num_certs, certs_time/1000);
-
-    num_versions = num_certs = 0;
-    versions_time = certs_time = 0;
+  tor_assert(chan);
+  tor_assert(var_cell);
 
-    /* remember which second it is, for next time */
-    current_second = now;
-  }
-#endif
-
-  if (conn->_base.marked_for_close)
-    return;
-
-  switch (conn->_base.state)
-  {
-    case OR_CONN_STATE_OR_HANDSHAKING_V2:
-      if (cell->command != CELL_VERSIONS) {
-        log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
-               "Received a cell with command %d in state %s; "
-               "closing the connection.",
-               (int)cell->command,
-               conn_state_to_string(CONN_TYPE_OR,conn->_base.state));
-        connection_mark_for_close(TO_CONN(conn));
-        return;
-      }
-      break;
-    case OR_CONN_STATE_TLS_HANDSHAKING:
-      /* If we're using bufferevents, it's entirely possible for us to
-       * notice "hey, data arrived!" before we notice "hey, the handshake
-       * finished!" And we need to be accepting both at once to handle both
-       * the v2 and v3 handshakes. */
-
-      /* fall through */
-    case OR_CONN_STATE_TLS_SERVER_RENEGOTIATING:
-      if (! command_allowed_before_handshake(cell->command)) {
-        log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
-               "Received a cell with command %d in state %s; "
-               "closing the connection.",
-               (int)cell->command,
-               conn_state_to_string(CONN_TYPE_OR,conn->_base.state));
-        connection_mark_for_close(TO_CONN(conn));
-        return;
-      } else {
-        if (enter_v3_handshake_with_cell(cell, conn)<0)
-          return;
-      }
-      break;
-    case OR_CONN_STATE_OR_HANDSHAKING_V3:
-      if (cell->command != CELL_AUTHENTICATE)
-        or_handshake_state_record_var_cell(conn->handshake_state, cell, 1);
-      break; /* Everything is allowed */
-    case OR_CONN_STATE_OPEN:
-      if (conn->link_proto < 3) {
-        log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
-               "Received a variable-length cell with command %d in state %s "
-               "with link protocol %d; ignoring it.",
-               (int)cell->command,
-               conn_state_to_string(CONN_TYPE_OR,conn->_base.state),
-               (int)conn->link_proto);
-        return;
-      }
-      break;
-    default:
-      log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
-             "Received var-length cell with command %d in unexpected state "
-             "%s [%d]; ignoring it.",
-             (int)cell->command,
-             conn_state_to_string(CONN_TYPE_OR,conn->_base.state),
-             (int)conn->_base.state);
-      return;
-  }
-
-  switch (cell->command) {
-    case CELL_VERSIONS:
-      ++stats_n_versions_cells_processed;
-      PROCESS_CELL(versions, cell, conn);
-      break;
-    case CELL_VPADDING:
-      ++stats_n_vpadding_cells_processed;
-      /* Do nothing */
-      break;
-    case CELL_CERTS:
-      ++stats_n_certs_cells_processed;
-      PROCESS_CELL(certs, cell, conn);
-      break;
-    case CELL_AUTH_CHALLENGE:
-      ++stats_n_auth_challenge_cells_processed;
-      PROCESS_CELL(auth_challenge, cell, conn);
-      break;
-    case CELL_AUTHENTICATE:
-      ++stats_n_authenticate_cells_processed;
-      PROCESS_CELL(authenticate, cell, conn);
-      break;
-    case CELL_AUTHORIZE:
-      ++stats_n_authorize_cells_processed;
-      /* Ignored so far. */
-      break;
-    default:
-      log_fn(LOG_INFO, LD_PROTOCOL,
-               "Variable-length cell of unknown type (%d) received.",
-               cell->command);
-      break;
-  }
+  log_info(LD_PROTOCOL,
+           "Received unexpected var_cell above the channel layer of type %d"
+           "; dropping it.",
+           var_cell->command);
 }
 
-/** Process a 'create' <b>cell</b> that just arrived from <b>conn</b>. Make a
+/** Process a 'create' <b>cell</b> that just arrived from <b>chan</b>. Make a
  * new circuit with the p_circ_id specified in cell. Put the circuit in state
  * onionskin_pending, and pass the onionskin to the cpuworker. Circ will get
  * picked up again when the cpuworker finishes decrypting it.
  */
 static void
-command_process_create_cell(cell_t *cell, or_connection_t *conn)
+command_process_create_cell(cell_t *cell, channel_t *chan)
 {
   or_circuit_t *circ;
   const or_options_t *options = get_options();
   int id_is_high;
 
+  tor_assert(cell);
+  tor_assert(chan);
+
+  log_debug(LD_OR,
+            "Got a CREATE cell for circ_id %d on channel " U64_FORMAT
+            " (%p)",
+            cell->circ_id,
+            U64_PRINTF_ARG(chan->global_identifier), chan);
+
   if (we_are_hibernating()) {
     log_info(LD_OR,
              "Received create cell but we're shutting down. Sending back "
              "destroy.");
-    connection_or_send_destroy(cell->circ_id, conn,
+    channel_send_destroy(cell->circ_id, chan,
                                END_CIRC_REASON_HIBERNATING);
     return;
   }
 
   if (!server_mode(options) ||
-      (!public_server_mode(options) && conn->is_outgoing)) {
+      (!public_server_mode(options) && channel_is_outgoing(chan))) {
     log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
-           "Received create cell (type %d) from %s:%d, but we're connected "
+           "Received create cell (type %d) from %s, but we're connected "
            "to it as a client. "
            "Sending back a destroy.",
-           (int)cell->command, conn->_base.address, conn->_base.port);
-    connection_or_send_destroy(cell->circ_id, conn,
-                               END_CIRC_REASON_TORPROTOCOL);
+           (int)cell->command, channel_get_canonical_remote_descr(chan));
+    channel_send_destroy(cell->circ_id, chan,
+                         END_CIRC_REASON_TORPROTOCOL);
     return;
   }
 
   /* If the high bit of the circuit ID is not as expected, close the
    * circ. */
   id_is_high = cell->circ_id & (1<<15);
-  if ((id_is_high && conn->circ_id_type == CIRC_ID_TYPE_HIGHER) ||
-      (!id_is_high && conn->circ_id_type == CIRC_ID_TYPE_LOWER)) {
+  if ((id_is_high &&
+       chan->circ_id_type == CIRC_ID_TYPE_HIGHER) ||
+      (!id_is_high &&
+       chan->circ_id_type == CIRC_ID_TYPE_LOWER)) {
     log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
            "Received create cell with unexpected circ_id %d. Closing.",
            cell->circ_id);
-    connection_or_send_destroy(cell->circ_id, conn,
-                               END_CIRC_REASON_TORPROTOCOL);
+    channel_send_destroy(cell->circ_id, chan,
+                         END_CIRC_REASON_TORPROTOCOL);
     return;
   }
 
-  if (circuit_id_in_use_on_orconn(cell->circ_id, conn)) {
-    const node_t *node = node_get_by_id(conn->identity_digest);
+  if (circuit_id_in_use_on_channel(cell->circ_id, chan)) {
+    const node_t *node = node_get_by_id(chan->identity_digest);
     log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
            "Received CREATE cell (circID %d) for known circ. "
            "Dropping (age %d).",
-           cell->circ_id, (int)(time(NULL) - conn->_base.timestamp_created));
+           cell->circ_id, (int)(time(NULL) - channel_when_created(chan)));
     if (node) {
       char *p = esc_for_log(node_get_platform(node));
       log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
@@ -411,7 +249,7 @@ command_process_create_cell(cell_t *cell, or_connection_t *conn)
     return;
   }
 
-  circ = or_circuit_new(cell->circ_id, conn);
+  circ = or_circuit_new(cell->circ_id, chan);
   circ->_base.purpose = CIRCUIT_PURPOSE_OR;
   circuit_set_state(TO_CIRCUIT(circ), CIRCUIT_STATE_ONIONSKIN_PENDING);
   if (cell->command == CELL_CREATE) {
@@ -435,7 +273,7 @@ command_process_create_cell(cell_t *cell, or_connection_t *conn)
 
     /* Make sure we never try to use the OR connection on which we
      * received this cell to satisfy an EXTEND request,  */
-    conn->is_connection_with_client = 1;
+    channel_mark_client(chan);
 
     if (fast_server_handshake(cell->payload, (uint8_t*)reply,
                               (uint8_t*)keys, sizeof(keys))<0) {
@@ -451,7 +289,7 @@ command_process_create_cell(cell_t *cell, or_connection_t *conn)
   }
 }
 
-/** Process a 'created' <b>cell</b> that just arrived from <b>conn</b>.
+/** Process a 'created' <b>cell</b> that just arrived from <b>chan</b>.
  * Find the circuit
  * that it's intended for. If we're not the origin of the circuit, package
  * the 'created' cell in an 'extended' relay cell and pass it back. If we
@@ -460,11 +298,11 @@ command_process_create_cell(cell_t *cell, or_connection_t *conn)
  * extend to the next hop in the circuit if necessary.
  */
 static void
-command_process_created_cell(cell_t *cell, or_connection_t *conn)
+command_process_created_cell(cell_t *cell, channel_t *chan)
 {
   circuit_t *circ;
 
-  circ = circuit_get_by_circid_orconn(cell->circ_id, conn);
+  circ = circuit_get_by_circid_channel(cell->circ_id, chan);
 
   if (!circ) {
     log_info(LD_OR,
@@ -511,17 +349,17 @@ command_process_created_cell(cell_t *cell, or_connection_t *conn)
  * circuit_receive_relay_cell() for actual processing.
  */
 static void
-command_process_relay_cell(cell_t *cell, or_connection_t *conn)
+command_process_relay_cell(cell_t *cell, channel_t *chan)
 {
   circuit_t *circ;
   int reason, direction;
 
-  circ = circuit_get_by_circid_orconn(cell->circ_id, conn);
+  circ = circuit_get_by_circid_channel(cell->circ_id, chan);
 
   if (!circ) {
     log_debug(LD_OR,
-              "unknown circuit %d on connection from %s:%d. Dropping.",
-              cell->circ_id, conn->_base.address, conn->_base.port);
+              "unknown circuit %d on connection from %s. Dropping.",
+              cell->circ_id, channel_get_canonical_remote_descr(chan));
     return;
   }
 
@@ -534,7 +372,7 @@ command_process_relay_cell(cell_t *cell, or_connection_t *conn)
   if (CIRCUIT_IS_ORIGIN(circ)) {
     /* if we're a relay and treating connections with recent local
      * traffic better, then this is one of them. */
-    conn->client_used = time(NULL);
+    channel_timestamp_client(chan);
   }
 
   if (!CIRCUIT_IS_ORIGIN(circ) &&
@@ -555,10 +393,10 @@ command_process_relay_cell(cell_t *cell, or_connection_t *conn)
       or_circuit_t *or_circ = TO_OR_CIRCUIT(circ);
       if (or_circ->remaining_relay_early_cells == 0) {
         log_fn(LOG_PROTOCOL_WARN, LD_OR,
-               "Received too many RELAY_EARLY cells on circ %d from %s:%d."
+               "Received too many RELAY_EARLY cells on circ %d from %s."
                "  Closing circuit.",
-               cell->circ_id, safe_str(conn->_base.address),
-               conn->_base.port);
+               cell->circ_id,
+               safe_str(channel_get_canonical_remote_descr(chan)));
         circuit_mark_for_close(circ, END_CIRC_REASON_TORPROTOCOL);
         return;
       }
@@ -575,7 +413,7 @@ command_process_relay_cell(cell_t *cell, or_connection_t *conn)
 }
 
 /** Process a 'destroy' <b>cell</b> that just arrived from
- * <b>conn</b>. Find the circ that it refers to (if any).
+ * <b>chan</b>. Find the circ that it refers to (if any).
  *
  * If the circ is in state
  * onionskin_pending, then call onion_pending_remove() to remove it
@@ -588,15 +426,15 @@ command_process_relay_cell(cell_t *cell, or_connection_t *conn)
  * and passes the destroy cell onward if necessary).
  */
 static void
-command_process_destroy_cell(cell_t *cell, or_connection_t *conn)
+command_process_destroy_cell(cell_t *cell, channel_t *chan)
 {
   circuit_t *circ;
   int reason;
 
-  circ = circuit_get_by_circid_orconn(cell->circ_id, conn);
+  circ = circuit_get_by_circid_channel(cell->circ_id, chan);
   if (!circ) {
-    log_info(LD_OR,"unknown circuit %d on connection from %s:%d. Dropping.",
-             cell->circ_id, conn->_base.address, conn->_base.port);
+    log_info(LD_OR,"unknown circuit %d on connection from %s. Dropping.",
+             cell->circ_id, channel_get_canonical_remote_descr(chan));
     return;
   }
   log_debug(LD_OR,"Received for circID %d.",cell->circ_id);
@@ -606,10 +444,10 @@ command_process_destroy_cell(cell_t *cell, or_connection_t *conn)
   if (!CIRCUIT_IS_ORIGIN(circ) &&
       cell->circ_id == TO_OR_CIRCUIT(circ)->p_circ_id) {
     /* the destroy came from behind */
-    circuit_set_p_circid_orconn(TO_OR_CIRCUIT(circ), 0, NULL);
+    circuit_set_p_circid_chan(TO_OR_CIRCUIT(circ), 0, NULL);
     circuit_mark_for_close(circ, reason|END_CIRC_REASON_FLAG_REMOTE);
   } else { /* the destroy came from ahead */
-    circuit_set_n_circid_orconn(circ, 0, NULL);
+    circuit_set_n_circid_chan(circ, 0, NULL);
     if (CIRCUIT_IS_ORIGIN(circ)) {
       circuit_mark_for_close(circ, reason|END_CIRC_REASON_FLAG_REMOTE);
     } else {
@@ -622,724 +460,43 @@ command_process_destroy_cell(cell_t *cell, or_connection_t *conn)
   }
 }
 
-/** Called when we as a server receive an appropriate cell while waiting
- * either for a cell or a TLS handshake.  Set the connection's state to
- * "handshaking_v3', initializes the or_handshake_state field as needed,
- * and add the cell to the hash of incoming cells.)
- *
- * Return 0 on success; return -1 and mark the connection on failure.
+/** Callback to handle a new channel; call command_setup_channel() to give
+ * it the right cell handlers.
  */
-static int
-enter_v3_handshake_with_cell(var_cell_t *cell, or_connection_t *conn)
-{
-  const int started_here = connection_or_nonopen_was_started_here(conn);
 
-  tor_assert(conn->_base.state == OR_CONN_STATE_TLS_HANDSHAKING ||
-             conn->_base.state == OR_CONN_STATE_TLS_SERVER_RENEGOTIATING);
-
-  if (started_here) {
-    log_fn(LOG_PROTOCOL_WARN, LD_OR,
-           "Received a cell while TLS-handshaking, not in "
-           "OR_HANDSHAKING_V3, on a connection we originated.");
-  }
-  conn->_base.state = OR_CONN_STATE_OR_HANDSHAKING_V3;
-  if (connection_init_or_handshake_state(conn, started_here) < 0) {
-    connection_mark_for_close(TO_CONN(conn));
-    return -1;
-  }
-  or_handshake_state_record_var_cell(conn->handshake_state, cell, 1);
-  return 0;
-}
-
-/** Process a 'versions' cell.  The current link protocol version must be 0
- * to indicate that no version has yet been negotiated.  We compare the
- * versions in the cell to the list of versions we support, pick the
- * highest version we have in common, and continue the negotiation from
- * there.
- */
 static void
-command_process_versions_cell(var_cell_t *cell, or_connection_t *conn)
+command_handle_incoming_channel(channel_listener_t *listener, channel_t *chan)
 {
-  int highest_supported_version = 0;
-  const uint8_t *cp, *end;
-  const int started_here = connection_or_nonopen_was_started_here(conn);
-  if (conn->link_proto != 0 ||
-      (conn->handshake_state && conn->handshake_state->received_versions)) {
-    log_fn(LOG_PROTOCOL_WARN, LD_OR,
-           "Received a VERSIONS cell on a connection with its version "
-           "already set to %d; dropping", (int) conn->link_proto);
-    return;
-  }
-  switch (conn->_base.state)
-    {
-    case OR_CONN_STATE_OR_HANDSHAKING_V2:
-    case OR_CONN_STATE_OR_HANDSHAKING_V3:
-      break;
-    case OR_CONN_STATE_TLS_HANDSHAKING:
-    case OR_CONN_STATE_TLS_SERVER_RENEGOTIATING:
-    default:
-      log_fn(LOG_PROTOCOL_WARN, LD_OR,
-             "VERSIONS cell while in unexpected state");
-      return;
-  }
-
-  tor_assert(conn->handshake_state);
-  end = cell->payload + cell->payload_len;
-  for (cp = cell->payload; cp+1 < end; ++cp) {
-    uint16_t v = ntohs(get_uint16(cp));
-    if (is_or_protocol_version_known(v) && v > highest_supported_version)
-      highest_supported_version = v;
-  }
-  if (!highest_supported_version) {
-    log_fn(LOG_PROTOCOL_WARN, LD_OR,
-           "Couldn't find a version in common between my version list and the "
-           "list in the VERSIONS cell; closing connection.");
-    connection_mark_for_close(TO_CONN(conn));
-    return;
-  } else if (highest_supported_version == 1) {
-    /* Negotiating version 1 makes no sense, since version 1 has no VERSIONS
-     * cells. */
-    log_fn(LOG_PROTOCOL_WARN, LD_OR,
-           "Used version negotiation protocol to negotiate a v1 connection. "
-           "That's crazily non-compliant. Closing connection.");
-    connection_mark_for_close(TO_CONN(conn));
-    return;
-  } else if (highest_supported_version < 3 &&
-             conn->_base.state ==  OR_CONN_STATE_OR_HANDSHAKING_V3) {
-    log_fn(LOG_PROTOCOL_WARN, LD_OR,
-           "Negotiated link protocol 2 or lower after doing a v3 TLS "
-           "handshake. Closing connection.");
-    connection_mark_for_close(TO_CONN(conn));
-    return;
-  }
-
-  conn->link_proto = highest_supported_version;
-  conn->handshake_state->received_versions = 1;
-
-  if (conn->link_proto == 2) {
-    log_info(LD_OR, "Negotiated version %d with %s:%d; sending NETINFO.",
-             highest_supported_version,
-             safe_str_client(conn->_base.address),
-             conn->_base.port);
-
-    if (connection_or_send_netinfo(conn) < 0) {
-      connection_mark_for_close(TO_CONN(conn));
-      return;
-    }
-  } else {
-    const int send_versions = !started_here;
-    /* If we want to authenticate, send a CERTS cell */
-    const int send_certs = !started_here || public_server_mode(get_options());
-    /* If we're a relay that got a connection, ask for authentication. */
-    const int send_chall = !started_here && public_server_mode(get_options());
-    /* If our certs cell will authenticate us, we can send a netinfo cell
-     * right now. */
-    const int send_netinfo = !started_here;
-    const int send_any =
-      send_versions || send_certs || send_chall || send_netinfo;
-    tor_assert(conn->link_proto >= 3);
-
-    log_info(LD_OR, "Negotiated version %d with %s:%d; %s%s%s%s%s",
-             highest_supported_version,
-             safe_str_client(conn->_base.address),
-             conn->_base.port,
-             send_any ? "Sending cells:" : "Waiting for CERTS cell",
-             send_versions ? " VERSIONS" : "",
-             send_certs ? " CERTS" : "",
-             send_chall ? " AUTH_CHALLENGE" : "",
-             send_netinfo ? " NETINFO" : "");
-
-#ifdef DISABLE_V3_LINKPROTO_SERVERSIDE
-    if (1) {
-      connection_mark_for_close(TO_CONN(conn));
-      return;
-    }
-#endif
-
-    if (send_versions) {
-      if (connection_or_send_versions(conn, 1) < 0) {
-        log_warn(LD_OR, "Couldn't send versions cell");
-        connection_mark_for_close(TO_CONN(conn));
-        return;
-      }
-    }
-    if (send_certs) {
-      if (connection_or_send_certs_cell(conn) < 0) {
-        log_warn(LD_OR, "Couldn't send certs cell");
-        connection_mark_for_close(TO_CONN(conn));
-        return;
-      }
-    }
-    if (send_chall) {
-      if (connection_or_send_auth_challenge_cell(conn) < 0) {
-        log_warn(LD_OR, "Couldn't send auth_challenge cell");
-        connection_mark_for_close(TO_CONN(conn));
-        return;
-      }
-    }
-    if (send_netinfo) {
-      if (connection_or_send_netinfo(conn) < 0) {
-        log_warn(LD_OR, "Couldn't send netinfo cell");
-        connection_mark_for_close(TO_CONN(conn));
-        return;
-      }
-    }
-  }
-}
-
-/** Process a 'netinfo' cell: read and act on its contents, and set the
- * connection state to "open". */
-static void
-command_process_netinfo_cell(cell_t *cell, or_connection_t *conn)
-{
-  time_t timestamp;
-  uint8_t my_addr_type;
-  uint8_t my_addr_len;
-  const uint8_t *my_addr_ptr;
-  const uint8_t *cp, *end;
-  uint8_t n_other_addrs;
-  time_t now = time(NULL);
-
-  long apparent_skew = 0;
-  tor_addr_t my_apparent_addr = TOR_ADDR_NULL;
+  tor_assert(listener);
+  tor_assert(chan);
 
-  if (conn->link_proto < 2) {
-    log_fn(LOG_PROTOCOL_WARN, LD_OR,
-           "Received a NETINFO cell on %s connection; dropping.",
-           conn->link_proto == 0 ? "non-versioned" : "a v1");
-    return;
-  }
-  if (conn->_base.state != OR_CONN_STATE_OR_HANDSHAKING_V2 &&
-      conn->_base.state != OR_CONN_STATE_OR_HANDSHAKING_V3) {
-    log_fn(LOG_PROTOCOL_WARN, LD_OR,
-           "Received a NETINFO cell on non-handshaking connection; dropping.");
-    return;
-  }
-  tor_assert(conn->handshake_state &&
-             conn->handshake_state->received_versions);
-
-  if (conn->_base.state == OR_CONN_STATE_OR_HANDSHAKING_V3) {
-    tor_assert(conn->link_proto >= 3);
-    if (conn->handshake_state->started_here) {
-      if (!conn->handshake_state->authenticated) {
-        log_fn(LOG_PROTOCOL_WARN, LD_OR, "Got a NETINFO cell from server, "
-               "but no authentication.  Closing the connection.");
-        connection_mark_for_close(TO_CONN(conn));
-        return;
-      }
-    } else {
-      /* we're the server.  If the client never authenticated, we have
-         some housekeeping to do.*/
-      if (!conn->handshake_state->authenticated) {
-        tor_assert(tor_digest_is_zero(
-                  (const char*)conn->handshake_state->authenticated_peer_id));
-        connection_or_set_circid_type(conn, NULL);
-
-        connection_or_init_conn_from_address(conn,
-                  &conn->_base.addr,
-                  conn->_base.port,
-                  (const char*)conn->handshake_state->authenticated_peer_id,
-                  0);
-      }
-    }
-  }
-
-  /* Decode the cell. */
-  timestamp = ntohl(get_uint32(cell->payload));
-  if (labs(now - conn->handshake_state->sent_versions_at) < 180) {
-    apparent_skew = now - timestamp;
-  }
-
-  my_addr_type = (uint8_t) cell->payload[4];
-  my_addr_len = (uint8_t) cell->payload[5];
-  my_addr_ptr = (uint8_t*) cell->payload + 6;
-  end = cell->payload + CELL_PAYLOAD_SIZE;
-  cp = cell->payload + 6 + my_addr_len;
-  if (cp >= end) {
-    log_fn(LOG_PROTOCOL_WARN, LD_OR,
-           "Addresses too long in netinfo cell; closing connection.");
-    connection_mark_for_close(TO_CONN(conn));
-    return;
-  } else if (my_addr_type == RESOLVED_TYPE_IPV4 && my_addr_len == 4) {
-    tor_addr_from_ipv4n(&my_apparent_addr, get_uint32(my_addr_ptr));
-  } else if (my_addr_type == RESOLVED_TYPE_IPV6 && my_addr_len == 16) {
-    tor_addr_from_ipv6_bytes(&my_apparent_addr, (const char *) my_addr_ptr);
-  }
-
-  n_other_addrs = (uint8_t) *cp++;
-  while (n_other_addrs && cp < end-2) {
-    /* Consider all the other addresses; if any matches, this connection is
-     * "canonical." */
-    tor_addr_t addr;
-    const uint8_t *next =
-      decode_address_from_payload(&addr, cp, (int)(end-cp));
-    if (next == NULL) {
-      log_fn(LOG_PROTOCOL_WARN,  LD_OR,
-             "Bad address in netinfo cell; closing connection.");
-      connection_mark_for_close(TO_CONN(conn));
-      return;
-    }
-    if (tor_addr_eq(&addr, &conn->real_addr)) {
-      conn->is_canonical = 1;
-      break;
-    }
-    cp = next;
-    --n_other_addrs;
-  }
-
-  /* Act on apparent skew. */
-  /** Warn when we get a netinfo skew with at least this value. */
-#define NETINFO_NOTICE_SKEW 3600
-  if (labs(apparent_skew) > NETINFO_NOTICE_SKEW &&
-      router_get_by_id_digest(conn->identity_digest)) {
-    char dbuf[64];
-    int severity;
-    /*XXXX be smarter about when everybody says we are skewed. */
-    if (router_digest_is_trusted_dir(conn->identity_digest))
-      severity = LOG_WARN;
-    else
-      severity = LOG_INFO;
-    format_time_interval(dbuf, sizeof(dbuf), apparent_skew);
-    log_fn(severity, LD_GENERAL, "Received NETINFO cell with skewed time from "
-           "server at %s:%d.  It seems that our clock is %s by %s, or "
-           "that theirs is %s. Tor requires an accurate clock to work: "
-           "please check your time and date settings.",
-           conn->_base.address, (int)conn->_base.port,
-           apparent_skew>0 ? "ahead" : "behind", dbuf,
-           apparent_skew>0 ? "behind" : "ahead");
-    if (severity == LOG_WARN) /* only tell the controller if an authority */
-      control_event_general_status(LOG_WARN,
-                          "CLOCK_SKEW SKEW=%ld SOURCE=OR:%s:%d",
-                          apparent_skew,
-                          conn->_base.address, conn->_base.port);
-  }
-
-  /* XXX maybe act on my_apparent_addr, if the source is sufficiently
-   * trustworthy. */
-
-  if (connection_or_set_state_open(conn)<0) {
-    log_fn(LOG_PROTOCOL_WARN, LD_OR, "Got good NETINFO cell from %s:%d; but "
-           "was unable to make the OR connection become open.",
-           safe_str_client(conn->_base.address),
-           conn->_base.port);
-    connection_mark_for_close(TO_CONN(conn));
-  } else {
-    log_info(LD_OR, "Got good NETINFO cell from %s:%d; OR connection is now "
-             "open, using protocol version %d. Its ID digest is %s. "
-             "Our address is apparently %s.",
-             safe_str_client(conn->_base.address),
-             conn->_base.port, (int)conn->link_proto,
-             hex_str(conn->identity_digest, DIGEST_LEN),
-             tor_addr_is_null(&my_apparent_addr) ?
-             "<none>" : fmt_and_decorate_addr(&my_apparent_addr));
-  }
-  assert_connection_ok(TO_CONN(conn),time(NULL));
+  command_setup_channel(chan);
 }
 
-/** Process a CERTS cell from an OR connection.
- *
- * If the other side should not have sent us a CERTS cell, or the cell is
- * malformed, or it is supposed to authenticate the TLS key but it doesn't,
- * then mark the connection.
- *
- * If the cell has a good cert chain and we're doing a v3 handshake, then
- * store the certificates in or_handshake_state.  If this is the client side
- * of the connection, we then authenticate the server or mark the connection.
- * If it's the server side, wait for an AUTHENTICATE cell.
+/** Given a channel, install the right handlers to process incoming
+ * cells on it.
  */
-static void
-command_process_certs_cell(var_cell_t *cell, or_connection_t *conn)
-{
-#define ERR(s)                                                  \
-  do {                                                          \
-    log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,                      \
-           "Received a bad CERTS cell from %s:%d: %s",          \
-           safe_str(conn->_base.address), conn->_base.port, (s)); \
-    connection_mark_for_close(TO_CONN(conn));                   \
-    goto err;                                                   \
-  } while (0)
-
-  tor_cert_t *link_cert = NULL;
-  tor_cert_t *id_cert = NULL;
-  tor_cert_t *auth_cert = NULL;
-
-  uint8_t *ptr;
-  int n_certs, i;
-  int send_netinfo = 0;
-
-  if (conn->_base.state != OR_CONN_STATE_OR_HANDSHAKING_V3)
-    ERR("We're not doing a v3 handshake!");
-  if (conn->link_proto < 3)
-    ERR("We're not using link protocol >= 3");
-  if (conn->handshake_state->received_certs_cell)
-    ERR("We already got one");
-  if (conn->handshake_state->authenticated) {
-    /* Should be unreachable, but let's make sure. */
-    ERR("We're already authenticated!");
-  }
-  if (cell->payload_len < 1)
-    ERR("It had no body");
-  if (cell->circ_id)
-    ERR("It had a nonzero circuit ID");
-
-  n_certs = cell->payload[0];
-  ptr = cell->payload + 1;
-  for (i = 0; i < n_certs; ++i) {
-    uint8_t cert_type;
-    uint16_t cert_len;
-    if (ptr + 3 > cell->payload + cell->payload_len) {
-      goto truncated;
-    }
-    cert_type = *ptr;
-    cert_len = ntohs(get_uint16(ptr+1));
-    if (ptr + 3 + cert_len > cell->payload + cell->payload_len) {
-      goto truncated;
-    }
-    if (cert_type == OR_CERT_TYPE_TLS_LINK ||
-        cert_type == OR_CERT_TYPE_ID_1024 ||
-        cert_type == OR_CERT_TYPE_AUTH_1024) {
-      tor_cert_t *cert = tor_cert_decode(ptr + 3, cert_len);
-      if (!cert) {
-        log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
-               "Received undecodable certificate in CERTS cell from %s:%d",
-               safe_str(conn->_base.address), conn->_base.port);
-      } else {
-        if (cert_type == OR_CERT_TYPE_TLS_LINK) {
-          if (link_cert) {
-            tor_cert_free(cert);
-            ERR("Too many TLS_LINK certificates");
-          }
-          link_cert = cert;
-        } else if (cert_type == OR_CERT_TYPE_ID_1024) {
-          if (id_cert) {
-            tor_cert_free(cert);
-            ERR("Too many ID_1024 certificates");
-          }
-          id_cert = cert;
-        } else if (cert_type == OR_CERT_TYPE_AUTH_1024) {
-          if (auth_cert) {
-            tor_cert_free(cert);
-            ERR("Too many AUTH_1024 certificates");
-          }
-          auth_cert = cert;
-        } else {
-          tor_cert_free(cert);
-        }
-      }
-    }
-    ptr += 3 + cert_len;
-    continue;
-
-  truncated:
-    ERR("It ends in the middle of a certificate");
-  }
-
-  if (conn->handshake_state->started_here) {
-    int severity;
-    if (! (id_cert && link_cert))
-      ERR("The certs we wanted were missing");
-    /* Okay. We should be able to check the certificates now. */
-    if (! tor_tls_cert_matches_key(conn->tls, link_cert)) {
-      ERR("The link certificate didn't match the TLS public key");
-    }
-    /* Note that this warns more loudly about time and validity if we were
-    * _trying_ to connect to an authority, not necessarily if we _did_ connect
-    * to one. */
-    if (router_digest_is_trusted_dir(conn->identity_digest))
-      severity = LOG_WARN;
-    else
-      severity = LOG_PROTOCOL_WARN;
-
-    if (! tor_tls_cert_is_valid(severity, link_cert, id_cert, 0))
-      ERR("The link certificate was not valid");
-    if (! tor_tls_cert_is_valid(severity, id_cert, id_cert, 1))
-      ERR("The ID certificate was not valid");
-
-    conn->handshake_state->authenticated = 1;
-    {
-      const digests_t *id_digests = tor_cert_get_id_digests(id_cert);
-      crypto_pk_t *identity_rcvd;
-      if (!id_digests)
-        ERR("Couldn't compute digests for key in ID cert");
-
-      identity_rcvd = tor_tls_cert_get_key(id_cert);
-      if (!identity_rcvd)
-        ERR("Internal error: Couldn't get RSA key from ID cert.");
-      memcpy(conn->handshake_state->authenticated_peer_id,
-             id_digests->d[DIGEST_SHA1], DIGEST_LEN);
-      connection_or_set_circid_type(conn, identity_rcvd);
-      crypto_pk_free(identity_rcvd);
-    }
-
-    if (connection_or_client_learned_peer_id(conn,
-                      conn->handshake_state->authenticated_peer_id) < 0)
-      ERR("Problem setting or checking peer id");
-
-    log_info(LD_OR, "Got some good certificates from %s:%d: Authenticated it.",
-             safe_str(conn->_base.address), conn->_base.port);
-
-    conn->handshake_state->id_cert = id_cert;
-    id_cert = NULL;
-
-    if (!public_server_mode(get_options())) {
-      /* If we initiated the connection and we are not a public server, we
-       * aren't planning to authenticate at all.  At this point we know who we
-       * are talking to, so we can just send a netinfo now. */
-      send_netinfo = 1;
-    }
-  } else {
-    if (! (id_cert && auth_cert))
-      ERR("The certs we wanted were missing");
-
-    /* Remember these certificates so we can check an AUTHENTICATE cell */
-    if (! tor_tls_cert_is_valid(LOG_PROTOCOL_WARN, auth_cert, id_cert, 1))
-      ERR("The authentication certificate was not valid");
-    if (! tor_tls_cert_is_valid(LOG_PROTOCOL_WARN, id_cert, id_cert, 1))
-      ERR("The ID certificate was not valid");
-
-    log_info(LD_OR, "Got some good certificates from %s:%d: "
-             "Waiting for AUTHENTICATE.",
-             safe_str(conn->_base.address), conn->_base.port);
-    /* XXXX check more stuff? */
 
-    conn->handshake_state->id_cert = id_cert;
-    conn->handshake_state->auth_cert = auth_cert;
-    id_cert = auth_cert = NULL;
-  }
-
-  conn->handshake_state->received_certs_cell = 1;
-
-  if (send_netinfo) {
-    if (connection_or_send_netinfo(conn) < 0) {
-      log_warn(LD_OR, "Couldn't send netinfo cell");
-      connection_mark_for_close(TO_CONN(conn));
-      goto err;
-    }
-  }
-
- err:
-  tor_cert_free(id_cert);
-  tor_cert_free(link_cert);
-  tor_cert_free(auth_cert);
-#undef ERR
-}
-
-/** Process an AUTH_CHALLENGE cell from an OR connection.
- *
- * If we weren't supposed to get one (for example, because we're not the
- * originator of the connection), or it's ill-formed, or we aren't doing a v3
- * handshake, mark the connection.  If the cell is well-formed but we don't
- * want to authenticate, just drop it.  If the cell is well-formed *and* we
- * want to authenticate, send an AUTHENTICATE cell and then a NETINFO cell. */
-static void
-command_process_auth_challenge_cell(var_cell_t *cell, or_connection_t *conn)
+void
+command_setup_channel(channel_t *chan)
 {
-  int n_types, i, use_type = -1;
-  uint8_t *cp;
-
-#define ERR(s)                                                  \
-  do {                                                          \
-    log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,                      \
-           "Received a bad AUTH_CHALLENGE cell from %s:%d: %s", \
-           safe_str(conn->_base.address), conn->_base.port, (s));       \
-    connection_mark_for_close(TO_CONN(conn));                   \
-    return;                                                     \
-  } while (0)
-
-  if (conn->_base.state != OR_CONN_STATE_OR_HANDSHAKING_V3)
-    ERR("We're not currently doing a v3 handshake");
-  if (conn->link_proto < 3)
-    ERR("We're not using link protocol >= 3");
-  if (! conn->handshake_state->started_here)
-    ERR("We didn't originate this connection");
-  if (conn->handshake_state->received_auth_challenge)
-    ERR("We already received one");
-  if (! conn->handshake_state->received_certs_cell)
-    ERR("We haven't gotten a CERTS cell yet");
-  if (cell->payload_len < OR_AUTH_CHALLENGE_LEN + 2)
-    ERR("It was too short");
-  if (cell->circ_id)
-    ERR("It had a nonzero circuit ID");
-
-  n_types = ntohs(get_uint16(cell->payload + OR_AUTH_CHALLENGE_LEN));
-  if (cell->payload_len < OR_AUTH_CHALLENGE_LEN + 2 + 2*n_types)
-    ERR("It looks truncated");
-
-  /* Now see if there is an authentication type we can use */
-  cp=cell->payload+OR_AUTH_CHALLENGE_LEN+2;
-  for (i=0; i < n_types; ++i, cp += 2) {
-    uint16_t authtype = ntohs(get_uint16(cp));
-    if (authtype == AUTHTYPE_RSA_SHA256_TLSSECRET)
-      use_type = authtype;
-  }
-
-  conn->handshake_state->received_auth_challenge = 1;
-
-  if (! public_server_mode(get_options())) {
-    /* If we're not a public server then we don't want to authenticate on a
-       connection we originated, and we already sent a NETINFO cell when we
-       got the CERTS cell. We have nothing more to do. */
-    return;
-  }
-
-  if (use_type >= 0) {
-    log_info(LD_OR, "Got an AUTH_CHALLENGE cell from %s:%d: Sending "
-             "authentication",
-             safe_str(conn->_base.address), conn->_base.port);
-
-    if (connection_or_send_authenticate_cell(conn, use_type) < 0) {
-      log_warn(LD_OR, "Couldn't send authenticate cell");
-      connection_mark_for_close(TO_CONN(conn));
-      return;
-    }
-  } else {
-    log_info(LD_OR, "Got an AUTH_CHALLENGE cell from %s:%d, but we don't "
-             "know any of its authentication types. Not authenticating.",
-             safe_str(conn->_base.address), conn->_base.port);
-  }
-
-  if (connection_or_send_netinfo(conn) < 0) {
-    log_warn(LD_OR, "Couldn't send netinfo cell");
-    connection_mark_for_close(TO_CONN(conn));
-    return;
-  }
+  tor_assert(chan);
 
-#undef ERR
+  channel_set_cell_handlers(chan,
+                            command_process_cell,
+                            command_process_var_cell);
 }
 
-/** Process an AUTHENTICATE cell from an OR connection.
- *
- * If it's ill-formed or we weren't supposed to get one or we're not doing a
- * v3 handshake, then mark the connection.  If it does not authenticate the
- * other side of the connection successfully (because it isn't signed right,
- * we didn't get a CERTS cell, etc) mark the connection.  Otherwise, accept
- * the identity of the router on the other side of the connection.
+/** Given a listener, install the right handler to process incoming
+ * channels on it.
  */
-static void
-command_process_authenticate_cell(var_cell_t *cell, or_connection_t *conn)
-{
-  uint8_t expected[V3_AUTH_FIXED_PART_LEN];
-  const uint8_t *auth;
-  int authlen;
-
-#define ERR(s)                                                  \
-  do {                                                          \
-    log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,                      \
-           "Received a bad AUTHENTICATE cell from %s:%d: %s",   \
-           safe_str(conn->_base.address), conn->_base.port, (s));       \
-    connection_mark_for_close(TO_CONN(conn));                   \
-    return;                                                     \
-  } while (0)
-
-  if (conn->_base.state != OR_CONN_STATE_OR_HANDSHAKING_V3)
-    ERR("We're not doing a v3 handshake");
-  if (conn->link_proto < 3)
-    ERR("We're not using link protocol >= 3");
-  if (conn->handshake_state->started_here)
-    ERR("We originated this connection");
-  if (conn->handshake_state->received_authenticate)
-    ERR("We already got one!");
-  if (conn->handshake_state->authenticated) {
-    /* Should be impossible given other checks */
-    ERR("The peer is already authenticated");
-  }
-  if (! conn->handshake_state->received_certs_cell)
-    ERR("We never got a certs cell");
-  if (conn->handshake_state->auth_cert == NULL)
-    ERR("We never got an authentication certificate");
-  if (conn->handshake_state->id_cert == NULL)
-    ERR("We never got an identity certificate");
-  if (cell->payload_len < 4)
-    ERR("Cell was way too short");
-
-  auth = cell->payload;
-  {
-    uint16_t type = ntohs(get_uint16(auth));
-    uint16_t len = ntohs(get_uint16(auth+2));
-    if (4 + len > cell->payload_len)
-      ERR("Authenticator was truncated");
-
-    if (type != AUTHTYPE_RSA_SHA256_TLSSECRET)
-      ERR("Authenticator type was not recognized");
-
-    auth += 4;
-    authlen = len;
-  }
-
-  if (authlen < V3_AUTH_BODY_LEN + 1)
-    ERR("Authenticator was too short");
-
-  if (connection_or_compute_authenticate_cell_body(
-                        conn, expected, sizeof(expected), NULL, 1) < 0)
-    ERR("Couldn't compute expected AUTHENTICATE cell body");
-
-  if (tor_memneq(expected, auth, sizeof(expected)))
-    ERR("Some field in the AUTHENTICATE cell body was not as expected");
-
-  {
-    crypto_pk_t *pk = tor_tls_cert_get_key(
-                                   conn->handshake_state->auth_cert);
-    char d[DIGEST256_LEN];
-    char *signed_data;
-    size_t keysize;
-    int signed_len;
 
-    if (!pk)
-      ERR("Internal error: couldn't get RSA key from AUTH cert.");
-    crypto_digest256(d, (char*)auth, V3_AUTH_BODY_LEN, DIGEST_SHA256);
-
-    keysize = crypto_pk_keysize(pk);
-    signed_data = tor_malloc(keysize);
-    signed_len = crypto_pk_public_checksig(pk, signed_data, keysize,
-                                           (char*)auth + V3_AUTH_BODY_LEN,
-                                           authlen - V3_AUTH_BODY_LEN);
-    crypto_pk_free(pk);
-    if (signed_len < 0) {
-      tor_free(signed_data);
-      ERR("Signature wasn't valid");
-    }
-    if (signed_len < DIGEST256_LEN) {
-      tor_free(signed_data);
-      ERR("Not enough data was signed");
-    }
-    /* Note that we deliberately allow *more* than DIGEST256_LEN bytes here,
-     * in case they're later used to hold a SHA3 digest or something. */
-    if (tor_memneq(signed_data, d, DIGEST256_LEN)) {
-      tor_free(signed_data);
-      ERR("Signature did not match data to be signed.");
-    }
-    tor_free(signed_data);
-  }
-
-  /* Okay, we are authenticated. */
-  conn->handshake_state->received_authenticate = 1;
-  conn->handshake_state->authenticated = 1;
-  conn->handshake_state->digest_received_data = 0;
-  {
-    crypto_pk_t *identity_rcvd =
-      tor_tls_cert_get_key(conn->handshake_state->id_cert);
-    const digests_t *id_digests =
-      tor_cert_get_id_digests(conn->handshake_state->id_cert);
-
-    /* This must exist; we checked key type when reading the cert. */
-    tor_assert(id_digests);
-
-    memcpy(conn->handshake_state->authenticated_peer_id,
-           id_digests->d[DIGEST_SHA1], DIGEST_LEN);
-
-    connection_or_set_circid_type(conn, identity_rcvd);
-    crypto_pk_free(identity_rcvd);
-
-    connection_or_init_conn_from_address(conn,
-                  &conn->_base.addr,
-                  conn->_base.port,
-                  (const char*)conn->handshake_state->authenticated_peer_id,
-                  0);
-
-    log_info(LD_OR, "Got an AUTHENTICATE cell from %s:%d: Looks good.",
-             safe_str(conn->_base.address), conn->_base.port);
-  }
+void
+command_setup_listener(channel_listener_t *listener)
+{
+  tor_assert(listener);
+  tor_assert(listener->state == CHANNEL_LISTENER_STATE_LISTENING);
 
-#undef ERR
+  channel_listener_set_listener_fn(listener, command_handle_incoming_channel);
 }
 
diff --git a/src/or/command.h b/src/or/command.h
index 078ccc9f5..f9a0ef20b 100644
--- a/src/or/command.h
+++ b/src/or/command.h
@@ -12,8 +12,12 @@
 #ifndef _TOR_COMMAND_H
 #define _TOR_COMMAND_H
 
-void command_process_cell(cell_t *cell, or_connection_t *conn);
-void command_process_var_cell(var_cell_t *cell, or_connection_t *conn);
+#include "channel.h"
+
+void command_process_cell(channel_t *chan, cell_t *cell);
+void command_process_var_cell(channel_t *chan, var_cell_t *cell);
+void command_setup_channel(channel_t *chan);
+void command_setup_listener(channel_listener_t *chan_l);
 
 extern uint64_t stats_n_padding_cells_processed;
 extern uint64_t stats_n_create_cells_processed;
diff --git a/src/or/config.c b/src/or/config.c
index bac2b2e64..3e92c4374 100644
--- a/src/or/config.c
+++ b/src/or/config.c
@@ -12,8 +12,11 @@
 #define CONFIG_PRIVATE
 
 #include "or.h"
+#include "channel.h"
 #include "circuitbuild.h"
 #include "circuitlist.h"
+#include "circuitmux.h"
+#include "circuitmux_ewma.h"
 #include "config.h"
 #include "connection.h"
 #include "connection_edge.h"
@@ -1167,6 +1170,7 @@ options_act(const or_options_t *old_options)
   char *msg=NULL;
   const int transition_affects_workers =
     old_options && options_transition_affects_workers(old_options, options);
+  int old_ewma_enabled;
 
   /* disable ptrace and later, other basic debugging techniques */
   {
@@ -1374,8 +1378,16 @@ options_act(const or_options_t *old_options)
     connection_bucket_init();
 #endif
 
+  old_ewma_enabled = cell_ewma_enabled();
   /* Change the cell EWMA settings */
   cell_ewma_set_scale_factor(options, networkstatus_get_latest_consensus());
+  /* If we just enabled ewma, set the cmux policy on all active channels */
+  if (cell_ewma_enabled() && !old_ewma_enabled) {
+    channel_set_cmux_policy_everywhere(&ewma_policy);
+  } else if (!cell_ewma_enabled() && old_ewma_enabled) {
+    /* Turn it off everywhere */
+    channel_set_cmux_policy_everywhere(NULL);
+  }
 
   /* Update the BridgePassword's hashed version as needed.  We store this as a
    * digest so that we can do side-channel-proof comparisons on it.
diff --git a/src/or/connection.c b/src/or/connection.c
index d64c676bf..db234f1cb 100644
--- a/src/or/connection.c
+++ b/src/or/connection.c
@@ -12,6 +12,13 @@
 
 #include "or.h"
 #include "buffers.h"
+/*
+ * Define this so we get channel internal functions, since we're implementing
+ * part of a subclass (channel_tls_t).
+ */
+#define _TOR_CHANNEL_INTERNAL
+#include "channel.h"
+#include "channeltls.h"
 #include "circuitbuild.h"
 #include "circuitlist.h"
 #include "circuituse.h"
@@ -257,10 +264,6 @@ or_connection_new(int socket_family)
   connection_init(now, TO_CONN(or_conn), CONN_TYPE_OR, socket_family);
 
   or_conn->timestamp_last_added_nonpadding = time(NULL);
-  or_conn->next_circ_id = crypto_rand_int(1<<15);
-
-  or_conn->active_circuit_pqueue = smartlist_new();
-  or_conn->active_circuit_pqueue_last_recalibrated = cell_ewma_get_tick();
 
   return or_conn;
 }
@@ -502,7 +505,6 @@ _connection_free(connection_t *conn)
     or_conn->tls = NULL;
     or_handshake_state_free(or_conn->handshake_state);
     or_conn->handshake_state = NULL;
-    smartlist_free(or_conn->active_circuit_pqueue);
     tor_free(or_conn->nickname);
   }
   if (conn->type == CONN_TYPE_AP) {
@@ -693,6 +695,16 @@ _connection_mark_for_close(connection_t *conn, int line, const char *file)
     return;
   }
 
+  if (conn->type == CONN_TYPE_OR) {
+    /*
+     * Bad news if this happens without telling the controlling channel; do
+     * this so we can find things that call this wrongly when the asserts hit.
+     */
+    log_debug(LD_CHANNEL,
+              "Calling connection_mark_for_close on an OR conn at %s:%d",
+              file, line);
+  }
+
   conn->marked_for_close = line;
   conn->marked_for_close_file = file;
   add_connection_to_closeable_list(conn);
@@ -1281,12 +1293,19 @@ static int
 connection_init_accepted_conn(connection_t *conn,
                               const listener_connection_t *listener)
 {
+  int rv;
+
   connection_start_reading(conn);
 
   switch (conn->type) {
     case CONN_TYPE_OR:
       control_event_or_conn_status(TO_OR_CONN(conn), OR_CONN_EVENT_NEW, 0);
-      return connection_tls_start_handshake(TO_OR_CONN(conn), 1);
+      rv = connection_tls_start_handshake(TO_OR_CONN(conn), 1);
+      if (rv < 0) {
+        connection_or_close_for_error(TO_OR_CONN(conn), 0);
+      }
+      return rv;
+      break;
     case CONN_TYPE_AP:
       TO_ENTRY_CONN(conn)->isolation_flags = listener->isolation_flags;
       TO_ENTRY_CONN(conn)->session_group = listener->session_group;
@@ -2091,7 +2110,8 @@ static int
 connection_counts_as_relayed_traffic(connection_t *conn, time_t now)
 {
   if (conn->type == CONN_TYPE_OR &&
-      TO_OR_CONN(conn)->client_used + CLIENT_IDLE_TIME_FOR_PRIORITY < now)
+      connection_or_client_used(TO_OR_CONN(conn)) +
+                                CLIENT_IDLE_TIME_FOR_PRIORITY < now)
     return 1;
   if (conn->type == CONN_TYPE_DIR && DIR_CONN_IS_SERVER(conn))
     return 1;
@@ -2688,11 +2708,14 @@ connection_handle_read_impl(connection_t *conn)
   before = buf_datalen(conn->inbuf);
   if (connection_read_to_buf(conn, &max_to_read, &socket_error) < 0) {
     /* There's a read error; kill the connection.*/
-    if (conn->type == CONN_TYPE_OR &&
-        conn->state == OR_CONN_STATE_CONNECTING) {
-      connection_or_connect_failed(TO_OR_CONN(conn),
-                                   errno_to_orconn_end_reason(socket_error),
-                                   tor_socket_strerror(socket_error));
+    if (conn->type == CONN_TYPE_OR) {
+      connection_or_notify_error(TO_OR_CONN(conn),
+                                 socket_error != 0 ?
+                                   errno_to_orconn_end_reason(socket_error) :
+                                   END_OR_CONN_REASON_CONNRESET,
+                                 socket_error != 0 ?
+                                   tor_socket_strerror(socket_error) :
+                                   "(unknown, errno was 0)");
     }
     if (CONN_IS_EDGE(conn)) {
       edge_connection_t *edge_conn = TO_EDGE_CONN(conn);
@@ -3214,9 +3237,9 @@ connection_handle_write_impl(connection_t *conn, int force)
         if (CONN_IS_EDGE(conn))
           connection_edge_end_errno(TO_EDGE_CONN(conn));
         if (conn->type == CONN_TYPE_OR)
-          connection_or_connect_failed(TO_OR_CONN(conn),
-                                       errno_to_orconn_end_reason(e),
-                                       tor_socket_strerror(e));
+          connection_or_notify_error(TO_OR_CONN(conn),
+                                     errno_to_orconn_end_reason(e),
+                                     tor_socket_strerror(e));
 
         connection_close_immediate(conn);
         connection_mark_for_close(conn);
@@ -3241,6 +3264,10 @@ connection_handle_write_impl(connection_t *conn, int force)
       connection_stop_writing(conn);
       if (connection_tls_continue_handshake(or_conn) < 0) {
         /* Don't flush; connection is dead. */
+        connection_or_notify_error(or_conn,
+                                   END_OR_CONN_REASON_MISC,
+                                   "TLS error in connection_tls_"
+                                   "continue_handshake()");
         connection_close_immediate(conn);
         connection_mark_for_close(conn);
         return -1;
@@ -3254,19 +3281,23 @@ connection_handle_write_impl(connection_t *conn, int force)
     result = flush_buf_tls(or_conn->tls, conn->outbuf,
                            max_to_write, &conn->outbuf_flushlen);
 
-    /* If we just flushed the last bytes, check if this tunneled dir
-     * request is done. */
+    /* If we just flushed the last bytes, tell the channel on the
+     * or_conn to check if it needs to geoip_change_dirreq_state() */
     /* XXXX move this to flushed_some or finished_flushing -NM */
-    if (buf_datalen(conn->outbuf) == 0 && conn->dirreq_id)
-      geoip_change_dirreq_state(conn->dirreq_id, DIRREQ_TUNNELED,
-                                DIRREQ_OR_CONN_BUFFER_FLUSHED);
+    if (buf_datalen(conn->outbuf) == 0 && or_conn->chan)
+      channel_notify_flushed(TLS_CHAN_TO_BASE(or_conn->chan));
 
     switch (result) {
       CASE_TOR_TLS_ERROR_ANY:
       case TOR_TLS_CLOSE:
-        log_info(LD_NET,result!=TOR_TLS_CLOSE?
+        log_info(LD_NET, result != TOR_TLS_CLOSE ?
                  "tls error. breaking.":"TLS connection closed on flush");
         /* Don't flush; connection is dead. */
+        connection_or_notify_error(or_conn,
+                                   END_OR_CONN_REASON_MISC,
+                                   result != TOR_TLS_CLOSE ?
+                                     "TLS error in during flush" :
+                                     "TLS closed during flush");
         connection_close_immediate(conn);
         connection_mark_for_close(conn);
         return -1;
@@ -3325,8 +3356,16 @@ connection_handle_write_impl(connection_t *conn, int force)
   if (result > 0) {
     /* If we wrote any bytes from our buffer, then call the appropriate
      * functions. */
-    if (connection_flushed_some(conn) < 0)
+    if (connection_flushed_some(conn) < 0) {
+      if (connection_speaks_cells(conn)) {
+        connection_or_notify_error(TO_OR_CONN(conn),
+                                   END_OR_CONN_REASON_MISC,
+                                   "Got error back from "
+                                   "connection_flushed_some()");
+      }
+
       connection_mark_for_close(conn);
+    }
   }
 
   if (!connection_wants_to_flush(conn)) { /* it's done flushing */
@@ -4125,7 +4164,6 @@ assert_connection_ok(connection_t *conn, time_t now)
     case CONN_TYPE_OR:
       tor_assert(conn->state >= _OR_CONN_STATE_MIN);
       tor_assert(conn->state <= _OR_CONN_STATE_MAX);
-      tor_assert(TO_OR_CONN(conn)->n_circuits >= 0);
       break;
     case CONN_TYPE_EXIT:
       tor_assert(conn->state >= _EXIT_CONN_STATE_MIN);
diff --git a/src/or/connection_edge.c b/src/or/connection_edge.c
index ade3b48df..45f3a06f3 100644
--- a/src/or/connection_edge.c
+++ b/src/or/connection_edge.c
@@ -11,6 +11,7 @@
 
 #include "or.h"
 #include "buffers.h"
+#include "channel.h"
 #include "circuitlist.h"
 #include "circuituse.h"
 #include "config.h"
@@ -3068,27 +3069,29 @@ connection_exit_begin_conn(cell_t *cell, circuit_t *circ)
       tor_free(address);
       return 0;
     }
-    if (or_circ && or_circ->p_conn && !options->AllowSingleHopExits &&
-        (or_circ->is_first_hop ||
-         (!connection_or_digest_is_known_relay(
-                                       or_circ->p_conn->identity_digest) &&
+    if (or_circ && or_circ->p_chan) {
+      if (!options->AllowSingleHopExits &&
+           (or_circ->is_first_hop ||
+            (!connection_or_digest_is_known_relay(
+                or_circ->p_chan->identity_digest) &&
           should_refuse_unknown_exits(options)))) {
-      /* Don't let clients use us as a single-hop proxy, unless the user
-       * has explicitly allowed that in the config. It attracts attackers
-       * and users who'd be better off with, well, single-hop proxies.
-       */
-      log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
-             "Attempt by %s to open a stream %s. Closing.",
-             safe_str(or_circ->p_conn->_base.address),
-             or_circ->is_first_hop ? "on first hop of circuit" :
-                                     "from unknown relay");
-      relay_send_end_cell_from_edge(rh.stream_id, circ,
-                                    or_circ->is_first_hop ?
-                                      END_STREAM_REASON_TORPROTOCOL :
-                                      END_STREAM_REASON_MISC,
-                                    NULL);
-      tor_free(address);
-      return 0;
+        /* Don't let clients use us as a single-hop proxy, unless the user
+         * has explicitly allowed that in the config. It attracts attackers
+         * and users who'd be better off with, well, single-hop proxies.
+         */
+        log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
+               "Attempt by %s to open a stream %s. Closing.",
+               safe_str(channel_get_canonical_remote_descr(or_circ->p_chan)),
+               or_circ->is_first_hop ? "on first hop of circuit" :
+                                       "from unknown relay");
+        relay_send_end_cell_from_edge(rh.stream_id, circ,
+                                      or_circ->is_first_hop ?
+                                        END_STREAM_REASON_TORPROTOCOL :
+                                        END_STREAM_REASON_MISC,
+                                      NULL);
+        tor_free(address);
+        return 0;
+      }
     }
   } else if (rh.command == RELAY_COMMAND_BEGIN_DIR) {
     if (!directory_permits_begindir_requests(options) ||
@@ -3101,8 +3104,8 @@ connection_exit_begin_conn(cell_t *cell, circuit_t *circ)
      * caller might want to know whether his IP address has changed, and
      * we might already have corrected _base.addr[ess] for the relay's
      * canonical IP address. */
-    if (or_circ && or_circ->p_conn)
-      address = tor_dup_addr(&or_circ->p_conn->real_addr);
+    if (or_circ && or_circ->p_chan)
+      address = tor_strdup(channel_get_actual_remote_descr(or_circ->p_chan));
     else
       address = tor_strdup("127.0.0.1");
     port = 1; /* XXXX This value is never actually used anywhere, and there
@@ -3120,7 +3123,7 @@ connection_exit_begin_conn(cell_t *cell, circuit_t *circ)
 
   /* Remember the tunneled request ID in the new edge connection, so that
    * we can measure download times. */
-  TO_CONN(n_stream)->dirreq_id = circ->dirreq_id;
+  n_stream->dirreq_id = circ->dirreq_id;
 
   n_stream->_base.purpose = EXIT_PURPOSE_CONNECT;
 
@@ -3178,8 +3181,6 @@ connection_exit_begin_conn(cell_t *cell, circuit_t *circ)
 
   if (rh.command == RELAY_COMMAND_BEGIN_DIR) {
     tor_assert(or_circ);
-    if (or_circ->p_conn && !tor_addr_is_null(&or_circ->p_conn->real_addr))
-      tor_addr_copy(&n_stream->_base.addr, &or_circ->p_conn->real_addr);
     return connection_exit_connect_dir(n_stream);
   }
 
@@ -3364,7 +3365,7 @@ connection_exit_connect_dir(edge_connection_t *exitconn)
 
   /* Note that the new dir conn belongs to the same tunneled request as
    * the edge conn, so that we can measure download times. */
-  TO_CONN(dirconn)->dirreq_id = TO_CONN(exitconn)->dirreq_id;
+  dirconn->dirreq_id = exitconn->dirreq_id;
 
   connection_link_connections(TO_CONN(dirconn), TO_CONN(exitconn));
 
diff --git a/src/or/connection_or.c b/src/or/connection_or.c
index dbd875766..f143e9b76 100644
--- a/src/or/connection_or.c
+++ b/src/or/connection_or.c
@@ -12,6 +12,13 @@
 
 #include "or.h"
 #include "buffers.h"
+/*
+ * Define this so we get channel internal functions, since we're implementing
+ * part of a subclass (channel_tls_t).
+ */
+#define _TOR_CHANNEL_INTERNAL
+#include "channel.h"
+#include "channeltls.h"
 #include "circuitbuild.h"
 #include "circuitlist.h"
 #include "command.h"
@@ -43,6 +50,17 @@ static int connection_or_check_valid_tls_handshake(or_connection_t *conn,
 
 static void connection_or_tls_renegotiated_cb(tor_tls_t *tls, void *_conn);
 
+static unsigned int
+connection_or_is_bad_for_new_circs(or_connection_t *or_conn);
+static void connection_or_mark_bad_for_new_circs(or_connection_t *or_conn);
+
+/*
+ * Call this when changing connection state, so notifications to the owning
+ * channel can be handled.
+ */
+
+static void connection_or_change_state(or_connection_t *conn, uint8_t state);
+
 #ifdef USE_BUFFEREVENTS
 static void connection_or_handle_event_cb(struct bufferevent *bufev,
                                           short event, void *arg);
@@ -127,8 +145,11 @@ connection_or_set_identity_digest(or_connection_t *conn, const char *digest)
     return;
 
   /* If the identity was set previously, remove the old mapping. */
-  if (! tor_digest_is_zero(conn->identity_digest))
+  if (! tor_digest_is_zero(conn->identity_digest)) {
     connection_or_remove_from_identity_map(conn);
+    if (conn->chan)
+      channel_clear_identity_digest(TLS_CHAN_TO_BASE(conn->chan));
+  }
 
   memcpy(conn->identity_digest, digest, DIGEST_LEN);
 
@@ -139,6 +160,10 @@ connection_or_set_identity_digest(or_connection_t *conn, const char *digest)
   tmp = digestmap_set(orconn_identity_map, digest, conn);
   conn->next_with_same_id = tmp;
 
+  /* Deal with channels */
+  if (conn->chan)
+    channel_set_identity_digest(TLS_CHAN_TO_BASE(conn->chan), digest);
+
 #if 1
   /* Testing code to check for bugs in representation. */
   for (; tmp; tmp = tmp->next_with_same_id) {
@@ -282,6 +307,39 @@ connection_or_report_broken_states(int severity, int domain)
   smartlist_free(items);
 }
 
+/** Call this to change or_connection_t states, so the owning channel_tls_t can
+ * be notified.
+ */
+
+static void
+connection_or_change_state(or_connection_t *conn, uint8_t state)
+{
+  uint8_t old_state;
+
+  tor_assert(conn);
+
+  old_state = conn->_base.state;
+  conn->_base.state = state;
+
+  if (conn->chan)
+    channel_tls_handle_state_change_on_orconn(conn->chan, conn,
+                                              old_state, state);
+}
+
+/** Return the number of circuits using an or_connection_t; this used to
+ * be an or_connection_t field, but it got moved to channel_t and we
+ * shouldn't maintain two copies. */
+
+int
+connection_or_get_num_circuits(or_connection_t *conn)
+{
+  tor_assert(conn);
+
+  if (conn->chan) {
+    return channel_num_circuits(TLS_CHAN_TO_BASE(conn->chan));
+  } else return 0;
+}
+
 /**************************************************************/
 
 /** Pack the cell_t host-order structure <b>src</b> into network-order
@@ -345,8 +403,11 @@ var_cell_free(var_cell_t *cell)
 int
 connection_or_reached_eof(or_connection_t *conn)
 {
+  tor_assert(conn);
+
   log_info(LD_OR,"OR connection reached EOF. Closing.");
-  connection_mark_for_close(TO_CONN(conn));
+  connection_or_close_normally(conn, 1);
+
   return 0;
 }
 
@@ -375,9 +436,12 @@ connection_or_process_inbuf(or_connection_t *conn)
         tor_assert(TO_CONN(conn)->proxy_state == PROXY_CONNECTED);
         if (connection_tls_start_handshake(conn, 0) < 0)
           ret = -1;
+        /* Touch the channel's active timestamp if there is one */
+        if (conn->chan)
+          channel_timestamp_active(TLS_CHAN_TO_BASE(conn->chan));
       }
       if (ret < 0) {
-        connection_mark_for_close(TO_CONN(conn));
+        connection_or_close_for_error(conn, 0);
       }
 
       return ret;
@@ -410,7 +474,7 @@ connection_or_process_inbuf(or_connection_t *conn)
            connection_or_nonopen_was_started_here(conn) ? "to" : "from",
            conn->_base.address, conn->_base.port,
            conn_state_to_string(conn->_base.type, conn->_base.state));
-    connection_mark_for_close(TO_CONN(conn));
+    connection_or_close_for_error(conn, 0);
     ret = -1;
   }
 
@@ -430,18 +494,31 @@ connection_or_process_inbuf(or_connection_t *conn)
 int
 connection_or_flushed_some(or_connection_t *conn)
 {
-  size_t datalen = connection_get_outbuf_len(TO_CONN(conn));
+  size_t datalen, temp;
+  ssize_t n, flushed;
+
   /* If we're under the low water mark, add cells until we're just over the
    * high water mark. */
+  datalen = connection_get_outbuf_len(TO_CONN(conn));
   if (datalen < OR_CONN_LOWWATER) {
-    ssize_t n = CEIL_DIV(OR_CONN_HIGHWATER - datalen, CELL_NETWORK_SIZE);
-    time_t now = approx_time();
-    while (conn->active_circuits && n > 0) {
-      int flushed;
-      flushed = connection_or_flush_from_first_active_circuit(conn, 1, now);
-      n -= flushed;
+    while ((conn->chan) && channel_tls_more_to_flush(conn->chan)) {
+      /* Compute how many more cells we want at most */
+      n = CEIL_DIV(OR_CONN_HIGHWATER - datalen, CELL_NETWORK_SIZE);
+      /* Bail out if we don't want any more */
+      if (n <= 0) break;
+      /* We're still here; try to flush some more cells */
+      flushed = channel_tls_flush_some_cells(conn->chan, n);
+      /* Bail out if it says it didn't flush anything */
+      if (flushed <= 0) break;
+      /* How much in the outbuf now? */
+      temp = connection_get_outbuf_len(TO_CONN(conn));
+      /* Bail out if we didn't actually increase the outbuf size */
+      if (temp <= datalen) break;
+      /* Update datalen for the next iteration */
+      datalen = temp;
     }
   }
+
   return 0;
 }
 
@@ -480,6 +557,7 @@ connection_or_finished_connecting(or_connection_t *or_conn)
 {
   const int proxy_type = or_conn->proxy_type;
   connection_t *conn;
+
   tor_assert(or_conn);
   conn = TO_CONN(or_conn);
   tor_assert(conn->state == OR_CONN_STATE_CONNECTING);
@@ -491,18 +569,18 @@ connection_or_finished_connecting(or_connection_t *or_conn)
   if (proxy_type != PROXY_NONE) {
     /* start proxy handshake */
     if (connection_proxy_connect(conn, proxy_type) < 0) {
-      connection_mark_for_close(conn);
+      connection_or_close_for_error(or_conn, 0);
       return -1;
     }
 
     connection_start_reading(conn);
-    conn->state = OR_CONN_STATE_PROXY_HANDSHAKING;
+    connection_or_change_state(or_conn, OR_CONN_STATE_PROXY_HANDSHAKING);
     return 0;
   }
 
   if (connection_tls_start_handshake(or_conn, 0) < 0) {
     /* TLS handshaking error of some kind. */
-    connection_mark_for_close(conn);
+    connection_or_close_for_error(or_conn, 0);
     return -1;
   }
   return 0;
@@ -516,11 +594,14 @@ connection_or_about_to_close(or_connection_t *or_conn)
   time_t now = time(NULL);
   connection_t *conn = TO_CONN(or_conn);
 
+  /* Tell the controlling channel we're closed */
+  if (or_conn->chan) {
+    channel_closed(TLS_CHAN_TO_BASE(or_conn->chan));
+    or_conn->chan = NULL;
+  }
+
   /* Remember why we're closing this connection. */
   if (conn->state != OR_CONN_STATE_OPEN) {
-    /* Inform any pending (not attached) circs that they should
-     * give up. */
-    circuit_n_conn_done(TO_OR_CONN(conn), 0);
     /* now mark things down as needed */
     if (connection_or_nonopen_was_started_here(or_conn)) {
       const or_options_t *options = get_options();
@@ -548,9 +629,6 @@ connection_or_about_to_close(or_connection_t *or_conn)
     control_event_or_conn_status(or_conn, OR_CONN_EVENT_CLOSED,
                 tls_error_to_orconn_end_reason(or_conn->tls_error));
   }
-  /* Now close all the attached circuits on it. */
-  circuit_unlink_all_from_or_conn(TO_OR_CONN(conn),
-                                  END_CIRC_REASON_OR_CONN_CLOSED);
 }
 
 /** Return 1 if identity digest <b>id_digest</b> is known to be a
@@ -708,152 +786,26 @@ connection_or_init_conn_from_address(or_connection_t *conn,
   }
 }
 
-/** Return true iff <b>a</b> is "better" than <b>b</b> for new circuits.
- *
- * A more canonical connection is always better than a less canonical
- * connection.  That aside, a connection is better if it has circuits and the
- * other does not, or if it was created more recently.
- *
- * Requires that both input connections are open; not is_bad_for_new_circs,
- * and not impossibly non-canonical.
- *
- * If <b>forgive_new_connections</b> is true, then we do not call
- * <b>a</b>better than <b>b</b> simply because b has no circuits,
- * unless b is also relatively old.
- */
-static int
-connection_or_is_better(time_t now,
-                        const or_connection_t *a,
-                        const or_connection_t *b,
-                        int forgive_new_connections)
-{
-  int newer;
-/** Do not definitively deprecate a new connection with no circuits on it
- * until this much time has passed. */
-#define NEW_CONN_GRACE_PERIOD (15*60)
-
-  if (b->is_canonical && !a->is_canonical)
-    return 0; /* A canonical connection is better than a non-canonical
-               * one, no matter how new it is or which has circuits. */
-
-  newer = b->_base.timestamp_created < a->_base.timestamp_created;
-
-  if (
-      /* We prefer canonical connections regardless of newness. */
-      (!b->is_canonical && a->is_canonical) ||
-      /* If both have circuits we prefer the newer: */
-      (b->n_circuits && a->n_circuits && newer) ||
-      /* If neither has circuits we prefer the newer: */
-      (!b->n_circuits && !a->n_circuits && newer))
-    return 1;
+/** These just pass all the is_bad_for_new_circs manipulation on to
+ * channel_t */
 
-  /* If one has no circuits and the other does... */
-  if (!b->n_circuits && a->n_circuits) {
-    /* Then it's bad, unless it's in its grace period and we're forgiving. */
-    if (forgive_new_connections &&
-        now < b->_base.timestamp_created + NEW_CONN_GRACE_PERIOD)
-      return 0;
-    else
-      return 1;
-  }
+static unsigned int
+connection_or_is_bad_for_new_circs(or_connection_t *or_conn)
+{
+  tor_assert(or_conn);
 
-  return 0;
+  if (or_conn->chan)
+    return channel_is_bad_for_new_circs(TLS_CHAN_TO_BASE(or_conn->chan));
+  else return 0;
 }
 
-/** Return the OR connection we should use to extend a circuit to the router
- * whose identity is <b>digest</b>, and whose address we believe (or have been
- * told in an extend cell) is <b>target_addr</b>.  If there is no good
- * connection, set *<b>msg_out</b> to a message describing the connection's
- * state and our next action, and set <b>launch_out</b> to a boolean for
- * whether we should launch a new connection or not.
- */
-or_connection_t *
-connection_or_get_for_extend(const char *digest,
-                             const tor_addr_t *target_addr,
-                             const char **msg_out,
-                             int *launch_out)
+static void
+connection_or_mark_bad_for_new_circs(or_connection_t *or_conn)
 {
-  or_connection_t *conn, *best=NULL;
-  int n_inprogress_goodaddr = 0, n_old = 0, n_noncanonical = 0, n_possible = 0;
-  time_t now = approx_time();
-
-  tor_assert(msg_out);
-  tor_assert(launch_out);
-
-  if (!orconn_identity_map) {
-    *msg_out = "Router not connected (nothing is).  Connecting.";
-    *launch_out = 1;
-    return NULL;
-  }
-
-  conn = digestmap_get(orconn_identity_map, digest);
-
-  for (; conn; conn = conn->next_with_same_id) {
-    tor_assert(conn->_base.magic == OR_CONNECTION_MAGIC);
-    tor_assert(conn->_base.type == CONN_TYPE_OR);
-    tor_assert(tor_memeq(conn->identity_digest, digest, DIGEST_LEN));
-    if (conn->_base.marked_for_close)
-      continue;
-    /* Never return a connection on which the other end appears to be
-     * a client. */
-    if (conn->is_connection_with_client) {
-      continue;
-    }
-    /* Never return a non-open connection. */
-    if (conn->_base.state != OR_CONN_STATE_OPEN) {
-      /* If the address matches, don't launch a new connection for this
-       * circuit. */
-      if (!tor_addr_compare(&conn->real_addr, target_addr, CMP_EXACT))
-        ++n_inprogress_goodaddr;
-      continue;
-    }
-    /* Never return a connection that shouldn't be used for circs. */
-    if (conn->is_bad_for_new_circs) {
-      ++n_old;
-      continue;
-    }
-    /* Never return a non-canonical connection using a recent link protocol
-     * if the address is not what we wanted.
-     *
-     * (For old link protocols, we can't rely on is_canonical getting
-     * set properly if we're talking to the right address, since we might
-     * have an out-of-date descriptor, and we will get no NETINFO cell to
-     * tell us about the right address.) */
-    if (!conn->is_canonical && conn->link_proto >= 2 &&
-        tor_addr_compare(&conn->real_addr, target_addr, CMP_EXACT)) {
-      ++n_noncanonical;
-      continue;
-    }
-
-    ++n_possible;
-
-    if (!best) {
-      best = conn; /* If we have no 'best' so far, this one is good enough. */
-      continue;
-    }
-
-    if (connection_or_is_better(now, conn, best, 0))
-      best = conn;
-  }
+  tor_assert(or_conn);
 
-  if (best) {
-    *msg_out = "Connection is fine; using it.";
-    *launch_out = 0;
-    return best;
-  } else if (n_inprogress_goodaddr) {
-    *msg_out = "Connection in progress; waiting.";
-    *launch_out = 0;
-    return NULL;
-  } else if (n_old || n_noncanonical) {
-    *msg_out = "Connections all too old, or too non-canonical. "
-      " Launching a new one.";
-    *launch_out = 1;
-    return NULL;
-  } else {
-    *msg_out = "Not connected. Connecting.";
-    *launch_out = 1;
-    return NULL;
-  }
+  if (or_conn->chan)
+    channel_mark_bad_for_new_circs(TLS_CHAN_TO_BASE(or_conn->chan));
 }
 
 /** How old do we let a connection to an OR get before deciding it's
@@ -874,8 +826,8 @@ connection_or_get_for_extend(const char *digest,
  *    - all open non-canonical connections for which a 'better' non-canonical
  *      connection exists to the same router at the same address.
  *
- * See connection_or_is_better() for our idea of what makes one OR connection
- * better than another.
+ * See channel_is_better() in channel.c for our idea of what makes one OR
+ * connection better than another.
  */
 static void
 connection_or_group_set_badness(or_connection_t *head, int force)
@@ -888,7 +840,7 @@ connection_or_group_set_badness(or_connection_t *head, int force)
    * everything else is. */
   for (or_conn = head; or_conn; or_conn = or_conn->next_with_same_id) {
     if (or_conn->_base.marked_for_close ||
-        or_conn->is_bad_for_new_circs)
+        connection_or_is_bad_for_new_circs(or_conn))
       continue;
     if (force ||
         or_conn->_base.timestamp_created + TIME_BEFORE_OR_CONN_IS_TOO_OLD
@@ -898,10 +850,10 @@ connection_or_group_set_badness(or_connection_t *head, int force)
                "(fd %d, %d secs old).",
                or_conn->_base.address, or_conn->_base.port, or_conn->_base.s,
                (int)(now - or_conn->_base.timestamp_created));
-      or_conn->is_bad_for_new_circs = 1;
+      connection_or_mark_bad_for_new_circs(or_conn);
     }
 
-    if (or_conn->is_bad_for_new_circs) {
+    if (connection_or_is_bad_for_new_circs(or_conn)) {
       ++n_old;
     } else if (or_conn->_base.state != OR_CONN_STATE_OPEN) {
       ++n_inprogress;
@@ -916,7 +868,7 @@ connection_or_group_set_badness(or_connection_t *head, int force)
    * expire everything that's worse, and find the very best if we can. */
   for (or_conn = head; or_conn; or_conn = or_conn->next_with_same_id) {
     if (or_conn->_base.marked_for_close ||
-        or_conn->is_bad_for_new_circs)
+        connection_or_is_bad_for_new_circs(or_conn))
       continue; /* This one doesn't need to be marked bad. */
     if (or_conn->_base.state != OR_CONN_STATE_OPEN)
       continue; /* Don't mark anything bad until we have seen what happens
@@ -930,12 +882,17 @@ connection_or_group_set_badness(or_connection_t *head, int force)
                "another connection to that OR that is.",
                or_conn->_base.address, or_conn->_base.port, or_conn->_base.s,
                (int)(now - or_conn->_base.timestamp_created));
-      or_conn->is_bad_for_new_circs = 1;
+      connection_or_mark_bad_for_new_circs(or_conn);
       continue;
     }
 
-    if (!best || connection_or_is_better(now, or_conn, best, 0))
+    if (!best ||
+        channel_is_better(now,
+                          TLS_CHAN_TO_BASE(or_conn->chan),
+                          TLS_CHAN_TO_BASE(best->chan),
+                          0)) {
       best = or_conn;
+    }
   }
 
   if (!best)
@@ -957,10 +914,13 @@ connection_or_group_set_badness(or_connection_t *head, int force)
    */
   for (or_conn = head; or_conn; or_conn = or_conn->next_with_same_id) {
     if (or_conn->_base.marked_for_close ||
-        or_conn->is_bad_for_new_circs ||
+        connection_or_is_bad_for_new_circs(or_conn) ||
         or_conn->_base.state != OR_CONN_STATE_OPEN)
       continue;
-    if (or_conn != best && connection_or_is_better(now, best, or_conn, 1)) {
+    if (or_conn != best &&
+        channel_is_better(now,
+                          TLS_CHAN_TO_BASE(best->chan),
+                          TLS_CHAN_TO_BASE(or_conn->chan), 1)) {
       /* This isn't the best conn, _and_ the best conn is better than it,
          even when we're being forgiving. */
       if (best->is_canonical) {
@@ -971,7 +931,7 @@ connection_or_group_set_badness(or_connection_t *head, int force)
                  or_conn->_base.address, or_conn->_base.port, or_conn->_base.s,
                  (int)(now - or_conn->_base.timestamp_created),
                  best->_base.s, (int)(now - best->_base.timestamp_created));
-        or_conn->is_bad_for_new_circs = 1;
+        connection_or_mark_bad_for_new_circs(or_conn);
       } else if (!tor_addr_compare(&or_conn->real_addr,
                                    &best->real_addr, CMP_EXACT)) {
         log_info(LD_OR,
@@ -981,7 +941,7 @@ connection_or_group_set_badness(or_connection_t *head, int force)
                  or_conn->_base.address, or_conn->_base.port, or_conn->_base.s,
                  (int)(now - or_conn->_base.timestamp_created),
                  best->_base.s, (int)(now - best->_base.timestamp_created));
-        or_conn->is_bad_for_new_circs = 1;
+        connection_or_mark_bad_for_new_circs(or_conn);
       }
     }
   }
@@ -1019,8 +979,41 @@ connection_or_connect_failed(or_connection_t *conn,
     control_event_bootstrap_problem(msg, reason);
 }
 
+/** <b>conn</b> got an error in connection_handle_read_impl() or
+ * connection_handle_write_impl() and is going to die soon.
+ *
+ * <b>reason</b> specifies the or_conn_end_reason for the failure;
+ * <b>msg</b> specifies the strerror-style error message.
+ */
+void
+connection_or_notify_error(or_connection_t *conn,
+                           int reason, const char *msg)
+{
+  channel_t *chan;
+
+  tor_assert(conn);
+
+  /* If we're connecting, call connect_failed() too */
+  if (TO_CONN(conn)->state == OR_CONN_STATE_CONNECTING)
+    connection_or_connect_failed(conn, reason, msg);
+
+  /* Tell the controlling channel if we have one */
+  if (conn->chan) {
+    chan = TLS_CHAN_TO_BASE(conn->chan);
+    /* Don't transition if we're already in closing, closed or error */
+    if (!(chan->state == CHANNEL_STATE_CLOSING ||
+          chan->state == CHANNEL_STATE_CLOSED ||
+          chan->state == CHANNEL_STATE_ERROR)) {
+      channel_close_for_error(chan);
+    }
+  }
+
+  /* No need to mark for error because connection.c is about to do that */
+}
+
 /** Launch a new OR connection to <b>addr</b>:<b>port</b> and expect to
- * handshake with an OR with identity digest <b>id_digest</b>.
+ * handshake with an OR with identity digest <b>id_digest</b>.  Optionally,
+ * pass in a pointer to a channel using this connection.
  *
  * If <b>id_digest</b> is me, do nothing. If we're already connected to it,
  * return that connection. If the connect() is in progress, set the
@@ -1035,7 +1028,8 @@ connection_or_connect_failed(or_connection_t *conn,
  */
 or_connection_t *
 connection_or_connect(const tor_addr_t *_addr, uint16_t port,
-                      const char *id_digest)
+                      const char *id_digest,
+                      channel_tls_t *chan)
 {
   or_connection_t *conn;
   const or_options_t *options = get_options();
@@ -1058,9 +1052,17 @@ connection_or_connect(const tor_addr_t *_addr, uint16_t port,
 
   conn = or_connection_new(tor_addr_family(&addr));
 
-  /* set up conn so it's got all the data we need to remember */
+  /*
+   * Set up conn so it's got all the data we need to remember for channels
+   *
+   * This stuff needs to happen before connection_or_init_conn_from_address()
+   * so connection_or_set_identity_digest() and such know where to look to
+   * keep the channel up to date.
+   */
+  conn->chan = chan;
+  chan->conn = conn;
   connection_or_init_conn_from_address(conn, &addr, port, id_digest, 1);
-  conn->_base.state = OR_CONN_STATE_CONNECTING;
+  connection_or_change_state(conn, OR_CONN_STATE_CONNECTING);
   control_event_or_conn_status(conn, OR_CONN_EVENT_LAUNCHED, 0);
 
   conn->is_outgoing = 1;
@@ -1129,6 +1131,52 @@ connection_or_connect(const tor_addr_t *_addr, uint16_t port,
   return conn;
 }
 
+/** Mark orconn for close and transition the associated channel, if any, to
+ * the closing state.
+ */
+
+void
+connection_or_close_normally(or_connection_t *orconn, int flush)
+{
+  channel_t *chan = NULL;
+
+  tor_assert(orconn);
+  if (flush) connection_mark_and_flush(TO_CONN(orconn));
+  else connection_mark_for_close(TO_CONN(orconn));
+  if (orconn->chan) {
+    chan = TLS_CHAN_TO_BASE(orconn->chan);
+    /* Don't transition if we're already in closing, closed or error */
+    if (!(chan->state == CHANNEL_STATE_CLOSING ||
+          chan->state == CHANNEL_STATE_CLOSED ||
+          chan->state == CHANNEL_STATE_ERROR)) {
+      channel_close_from_lower_layer(chan);
+    }
+  }
+}
+
+/** Mark orconn for close and transition the associated channel, if any, to
+ * the error state.
+ */
+
+void
+connection_or_close_for_error(or_connection_t *orconn, int flush)
+{
+  channel_t *chan = NULL;
+
+  tor_assert(orconn);
+  if (flush) connection_mark_and_flush(TO_CONN(orconn));
+  else connection_mark_for_close(TO_CONN(orconn));
+  if (orconn->chan) {
+    chan = TLS_CHAN_TO_BASE(orconn->chan);
+    /* Don't transition if we're already in closing, closed or error */
+    if (!(chan->state == CHANNEL_STATE_CLOSING ||
+          chan->state == CHANNEL_STATE_CLOSED ||
+          chan->state == CHANNEL_STATE_ERROR)) {
+      channel_close_for_error(chan);
+    }
+  }
+}
+
 /** Begin the tls handshake with <b>conn</b>. <b>receiving</b> is 0 if
  * we initiated the connection, else it's 1.
  *
@@ -1140,7 +1188,24 @@ connection_or_connect(const tor_addr_t *_addr, uint16_t port,
 int
 connection_tls_start_handshake(or_connection_t *conn, int receiving)
 {
-  conn->_base.state = OR_CONN_STATE_TLS_HANDSHAKING;
+  channel_listener_t *chan_listener;
+  channel_t *chan;
+
+  /* Incoming connections will need a new channel passed to the
+   * channel_tls_listener */
+  if (receiving) {
+    /* It shouldn't already be set */
+    tor_assert(!(conn->chan));
+    chan_listener = channel_tls_get_listener();
+    if (!chan_listener) {
+      chan_listener = channel_tls_start_listener();
+      command_setup_listener(chan_listener);
+    }
+    chan = channel_tls_handle_incoming(conn);
+    channel_listener_queue_incoming(chan_listener, chan);
+  }
+
+  connection_or_change_state(conn, OR_CONN_STATE_TLS_HANDSHAKING);
   tor_assert(!conn->tls);
   conn->tls = tor_tls_new(conn->_base.s, receiving);
   if (!conn->tls) {
@@ -1201,7 +1266,7 @@ connection_or_tls_renegotiated_cb(tor_tls_t *tls, void *_conn)
   if (connection_tls_finish_handshake(conn) < 0) {
     /* XXXX_TLS double-check that it's ok to do this from inside read. */
     /* XXXX_TLS double-check that this verifies certificates. */
-    connection_mark_for_close(TO_CONN(conn));
+    connection_or_close_for_error(conn, 0);
   }
 }
 
@@ -1242,7 +1307,8 @@ connection_tls_continue_handshake(or_connection_t *conn)
             } else {
               log_debug(LD_OR, "Done with initial SSL handshake (client-side)."
                         " Requesting renegotiation.");
-              conn->_base.state = OR_CONN_STATE_TLS_CLIENT_RENEGOTIATING;
+              connection_or_change_state(conn,
+                  OR_CONN_STATE_TLS_CLIENT_RENEGOTIATING);
               goto again;
             }
           }
@@ -1254,7 +1320,8 @@ connection_tls_continue_handshake(or_connection_t *conn)
           tor_tls_set_renegotiate_callback(conn->tls,
                                            connection_or_tls_renegotiated_cb,
                                            conn);
-          conn->_base.state = OR_CONN_STATE_TLS_SERVER_RENEGOTIATING;
+          connection_or_change_state(conn,
+              OR_CONN_STATE_TLS_SERVER_RENEGOTIATING);
           connection_stop_writing(TO_CONN(conn));
           connection_start_reading(TO_CONN(conn));
           return 0;
@@ -1287,7 +1354,7 @@ connection_or_handle_event_cb(struct bufferevent *bufev, short event,
     if (conn->_base.state == OR_CONN_STATE_TLS_HANDSHAKING) {
       if (tor_tls_finish_handshake(conn->tls) < 0) {
         log_warn(LD_OR, "Problem finishing handshake");
-        connection_mark_for_close(TO_CONN(conn));
+        connection_or_close_for_error(conn, 0);
         return;
       }
     }
@@ -1298,14 +1365,15 @@ connection_or_handle_event_cb(struct bufferevent *bufev, short event,
           if (tor_tls_received_v3_certificate(conn->tls)) {
             log_info(LD_OR, "Client got a v3 cert!");
             if (connection_or_launch_v3_or_handshake(conn) < 0)
-              connection_mark_for_close(TO_CONN(conn));
+              connection_or_close_for_error(conn, 0);
             return;
           } else {
-            conn->_base.state = OR_CONN_STATE_TLS_CLIENT_RENEGOTIATING;
+            connection_or_change_state(conn,
+                OR_CONN_STATE_TLS_CLIENT_RENEGOTIATING);
             tor_tls_unblock_renegotiation(conn->tls);
             if (bufferevent_ssl_renegotiate(conn->_base.bufev)<0) {
               log_warn(LD_OR, "Start_renegotiating went badly.");
-              connection_mark_for_close(TO_CONN(conn));
+              connection_or_close_for_error(conn, 0);
             }
             tor_tls_unblock_renegotiation(conn->tls);
             return; /* ???? */
@@ -1320,7 +1388,8 @@ connection_or_handle_event_cb(struct bufferevent *bufev, short event,
           tor_tls_set_renegotiate_callback(conn->tls,
                                            connection_or_tls_renegotiated_cb,
                                            conn);
-          conn->_base.state = OR_CONN_STATE_TLS_SERVER_RENEGOTIATING;
+          connection_or_change_state(conn,
+              OR_CONN_STATE_TLS_SERVER_RENEGOTIATING);
         } else if (handshakes == 2) {
           /* v2 handshake, as a server.  Two handshakes happened already,
            * so we treat renegotiation as done.
@@ -1329,18 +1398,18 @@ connection_or_handle_event_cb(struct bufferevent *bufev, short event,
         } else if (handshakes > 2) {
           log_warn(LD_OR, "More than two handshakes done on connection. "
                    "Closing.");
-          connection_mark_for_close(TO_CONN(conn));
+          connection_or_close_for_error(conn, 0);
         } else {
           log_warn(LD_BUG, "We were unexpectedly told that a connection "
                    "got %d handshakes. Closing.", handshakes);
-          connection_mark_for_close(TO_CONN(conn));
+          connection_or_close_for_error(conn, 0);
         }
         return;
       }
     }
     connection_watch_events(TO_CONN(conn), READ_EVENT|WRITE_EVENT);
     if (connection_tls_finish_handshake(conn) < 0)
-      connection_mark_for_close(TO_CONN(conn)); /* ???? */
+      connection_or_close_for_error(conn, 0); /* ???? */
     return;
   }
 
@@ -1370,29 +1439,6 @@ connection_or_nonopen_was_started_here(or_connection_t *conn)
   return !tor_tls_is_server(conn->tls);
 }
 
-/** Set the circid_type field of <b>conn</b> (which determines which part of
- * the circuit ID space we're willing to use) based on comparing our ID to
- * <b>identity_rcvd</b> */
-void
-connection_or_set_circid_type(or_connection_t *conn,
-                              crypto_pk_t *identity_rcvd)
-{
-  const int started_here = connection_or_nonopen_was_started_here(conn);
-  crypto_pk_t *our_identity =
-    started_here ? get_tlsclient_identity_key() :
-                   get_server_identity_key();
-
-  if (identity_rcvd) {
-    if (crypto_pk_cmp_keys(our_identity, identity_rcvd)<0) {
-      conn->circ_id_type = CIRC_ID_TYPE_LOWER;
-    } else {
-      conn->circ_id_type = CIRC_ID_TYPE_HIGHER;
-    }
-  } else {
-    conn->circ_id_type = CIRC_ID_TYPE_NEITHER;
-  }
-}
-
 /** <b>Conn</b> just completed its handshake. Return 0 if all is well, and
  * return -1 if he is lying, broken, or otherwise something is wrong.
  *
@@ -1470,7 +1516,8 @@ connection_or_check_valid_tls_handshake(or_connection_t *conn,
     memset(digest_rcvd_out, 0, DIGEST_LEN);
   }
 
-  connection_or_set_circid_type(conn, identity_rcvd);
+  tor_assert(conn->chan);
+  channel_set_circid_type(TLS_CHAN_TO_BASE(conn->chan), identity_rcvd);
   crypto_pk_free(identity_rcvd);
 
   if (started_here)
@@ -1547,6 +1594,19 @@ connection_or_client_learned_peer_id(or_connection_t *conn,
   return 0;
 }
 
+/** Return when a client used this, for connection.c, since client_used
+ * is now one of the timestamps of channel_t */
+
+time_t
+connection_or_client_used(or_connection_t *conn)
+{
+  tor_assert(conn);
+
+  if (conn->chan) {
+    return channel_when_last_client(TLS_CHAN_TO_BASE(conn->chan));
+  } else return 0;
+}
+
 /** The v1/v2 TLS handshake is finished.
  *
  * Make sure we are happy with the person we just handshaked with.
@@ -1588,7 +1648,7 @@ connection_tls_finish_handshake(or_connection_t *conn)
     tor_tls_block_renegotiation(conn->tls);
     return connection_or_set_state_open(conn);
   } else {
-    conn->_base.state = OR_CONN_STATE_OR_HANDSHAKING_V2;
+    connection_or_change_state(conn, OR_CONN_STATE_OR_HANDSHAKING_V2);
     if (connection_init_or_handshake_state(conn, started_here) < 0)
       return -1;
     if (!started_here) {
@@ -1613,7 +1673,7 @@ connection_or_launch_v3_or_handshake(or_connection_t *conn)
 
   circuit_build_times_network_is_live(&circ_times);
 
-  conn->_base.state = OR_CONN_STATE_OR_HANDSHAKING_V3;
+  connection_or_change_state(conn, OR_CONN_STATE_OR_HANDSHAKING_V3);
   if (connection_init_or_handshake_state(conn, 1) < 0)
     return -1;
 
@@ -1732,35 +1792,9 @@ or_handshake_state_record_var_cell(or_handshake_state_t *state,
 int
 connection_or_set_state_open(or_connection_t *conn)
 {
-  int started_here = connection_or_nonopen_was_started_here(conn);
-  time_t now = time(NULL);
-  conn->_base.state = OR_CONN_STATE_OPEN;
+  connection_or_change_state(conn, OR_CONN_STATE_OPEN);
   control_event_or_conn_status(conn, OR_CONN_EVENT_CONNECTED, 0);
 
-  if (started_here) {
-    circuit_build_times_network_is_live(&circ_times);
-    rep_hist_note_connect_succeeded(conn->identity_digest, now);
-    if (entry_guard_register_connect_status(conn->identity_digest,
-                                            1, 0, now) < 0) {
-      /* Close any circuits pending on this conn. We leave it in state
-       * 'open' though, because it didn't actually *fail* -- we just
-       * chose not to use it. (Otherwise
-       * connection_about_to_close_connection() will call a big pile of
-       * functions to indicate we shouldn't try it again.) */
-      log_debug(LD_OR, "New entry guard was reachable, but closing this "
-                "connection so we can retry the earlier entry guards.");
-      circuit_n_conn_done(conn, 0);
-      return -1;
-    }
-    router_set_status(conn->identity_digest, 1);
-  } else {
-    /* only report it to the geoip module if it's not a known router */
-    if (!router_get_by_id_digest(conn->identity_digest)) {
-      geoip_note_client_seen(GEOIP_CLIENT_CONNECT, &TO_CONN(conn)->addr,
-                             now);
-    }
-  }
-
   or_handshake_state_free(conn->handshake_state);
   conn->handshake_state = NULL;
   IF_HAS_BUFFEREVENT(TO_CONN(conn), {
@@ -1769,8 +1803,6 @@ connection_or_set_state_open(or_connection_t *conn)
     connection_start_reading(TO_CONN(conn));
   }
 
-  circuit_n_conn_done(conn, 1); /* send the pending creates, if any. */
-
   return 0;
 }
 
@@ -1790,6 +1822,10 @@ connection_or_write_cell_to_buf(const cell_t *cell, or_connection_t *conn)
 
   connection_write_to_buf(networkcell.body, CELL_NETWORK_SIZE, TO_CONN(conn));
 
+  /* Touch the channel's active timestamp if there is one */
+  if (conn->chan)
+    channel_timestamp_active(TLS_CHAN_TO_BASE(conn->chan));
+
   if (conn->_base.state == OR_CONN_STATE_OR_HANDSHAKING_V3)
     or_handshake_state_record_cell(conn->handshake_state, cell, 0);
 
@@ -1816,6 +1852,10 @@ connection_or_write_var_cell_to_buf(const var_cell_t *cell,
     or_handshake_state_record_var_cell(conn->handshake_state, cell, 0);
   if (cell->command != CELL_PADDING)
     conn->timestamp_last_added_nonpadding = approx_time();
+
+  /* Touch the channel's active timestamp if there is one */
+  if (conn->chan)
+    channel_timestamp_active(TLS_CHAN_TO_BASE(conn->chan));
 }
 
 /** See whether there's a variable-length cell waiting on <b>or_conn</b>'s
@@ -1852,8 +1892,13 @@ connection_or_process_cells_from_inbuf(or_connection_t *conn)
     if (connection_fetch_var_cell_from_buf(conn, &var_cell)) {
       if (!var_cell)
         return 0; /* not yet. */
+
+      /* Touch the channel's active timestamp if there is one */
+      if (conn->chan)
+        channel_timestamp_active(TLS_CHAN_TO_BASE(conn->chan));
+
       circuit_build_times_network_is_live(&circ_times);
-      command_process_var_cell(var_cell, conn);
+      channel_tls_handle_var_cell(var_cell, conn);
       var_cell_free(var_cell);
     } else {
       char buf[CELL_NETWORK_SIZE];
@@ -1862,6 +1907,10 @@ connection_or_process_cells_from_inbuf(or_connection_t *conn)
           < CELL_NETWORK_SIZE) /* whole response available? */
         return 0; /* not yet */
 
+      /* Touch the channel's active timestamp if there is one */
+      if (conn->chan)
+        channel_timestamp_active(TLS_CHAN_TO_BASE(conn->chan));
+
       circuit_build_times_network_is_live(&circ_times);
       connection_fetch_from_buf(buf, CELL_NETWORK_SIZE, TO_CONN(conn));
 
@@ -1869,34 +1918,11 @@ connection_or_process_cells_from_inbuf(or_connection_t *conn)
        * network-order string) */
       cell_unpack(&cell, buf);
 
-      command_process_cell(&cell, conn);
+      channel_tls_handle_cell(&cell, conn);
     }
   }
 }
 
-/** Write a destroy cell with circ ID <b>circ_id</b> and reason <b>reason</b>
- * onto OR connection <b>conn</b>.  Don't perform range-checking on reason:
- * we may want to propagate reasons from other cells.
- *
- * Return 0.
- */
-int
-connection_or_send_destroy(circid_t circ_id, or_connection_t *conn, int reason)
-{
-  cell_t cell;
-
-  tor_assert(conn);
-
-  memset(&cell, 0, sizeof(cell_t));
-  cell.circ_id = circ_id;
-  cell.command = CELL_DESTROY;
-  cell.payload[0] = (uint8_t) reason;
-  log_debug(LD_OR,"Sending destroy (circID %d).", circ_id);
-
-  connection_or_write_cell_to_buf(&cell, conn);
-  return 0;
-}
-
 /** Array of recognized link protocol versions. */
 static const uint16_t or_protocol_versions[] = { 1, 2, 3 };
 /** Number of versions in <b>or_protocol_versions</b>. */
diff --git a/src/or/connection_or.h b/src/or/connection_or.h
index 3e98f5cce..22126b05f 100644
--- a/src/or/connection_or.h
+++ b/src/or/connection_or.h
@@ -33,8 +33,14 @@ void connection_or_update_token_buckets(smartlist_t *conns,
 
 void connection_or_connect_failed(or_connection_t *conn,
                                   int reason, const char *msg);
+void connection_or_notify_error(or_connection_t *conn,
+                                int reason, const char *msg);
 or_connection_t *connection_or_connect(const tor_addr_t *addr, uint16_t port,
-                                       const char *id_digest);
+                                       const char *id_digest,
+                                       channel_tls_t *chan);
+
+void connection_or_close_normally(or_connection_t *orconn, int flush);
+void connection_or_close_for_error(or_connection_t *orconn, int flush);
 
 void connection_or_report_broken_states(int severity, int domain);
 
@@ -50,8 +56,8 @@ void connection_or_init_conn_from_address(or_connection_t *conn,
                                           int started_here);
 int connection_or_client_learned_peer_id(or_connection_t *conn,
                                          const uint8_t *peer_id);
-void connection_or_set_circid_type(or_connection_t *conn,
-                                   crypto_pk_t *identity_rcvd);
+time_t connection_or_client_used(or_connection_t *conn);
+int connection_or_get_num_circuits(or_connection_t *conn);
 void or_handshake_state_free(or_handshake_state_t *state);
 void or_handshake_state_record_cell(or_handshake_state_t *state,
                                     const cell_t *cell,
@@ -65,8 +71,6 @@ void connection_or_write_cell_to_buf(const cell_t *cell,
                                      or_connection_t *conn);
 void connection_or_write_var_cell_to_buf(const var_cell_t *cell,
                                          or_connection_t *conn);
-int connection_or_send_destroy(circid_t circ_id, or_connection_t *conn,
-                               int reason);
 int connection_or_send_versions(or_connection_t *conn, int v3_plus);
 int connection_or_send_netinfo(or_connection_t *conn);
 int connection_or_send_certs_cell(or_connection_t *conn);
diff --git a/src/or/control.c b/src/or/control.c
index 74c6acc00..75a8f5939 100644
--- a/src/or/control.c
+++ b/src/or/control.c
@@ -12,6 +12,8 @@
 
 #include "or.h"
 #include "buffers.h"
+#include "channel.h"
+#include "channeltls.h"
 #include "circuitbuild.h"
 #include "circuitlist.h"
 #include "circuituse.h"
@@ -3822,8 +3824,12 @@ control_event_or_conn_status(or_connection_t *conn, or_conn_status_event_t tp,
       log_warn(LD_BUG, "Unrecognized status code %d", (int)tp);
       return 0;
     }
-  ncircs = circuit_count_pending_on_or_conn(conn);
-  ncircs += conn->n_circuits;
+  if (conn->chan) {
+    ncircs = circuit_count_pending_on_channel(TLS_CHAN_TO_BASE(conn->chan));
+  } else {
+    ncircs = 0;
+  }
+  ncircs += connection_or_get_num_circuits(conn);
   if (ncircs && (tp == OR_CONN_EVENT_FAILED || tp == OR_CONN_EVENT_CLOSED)) {
     tor_snprintf(ncircs_buf, sizeof(ncircs_buf), "%sNCIRCS=%d",
                  reason ? " " : "", ncircs);
diff --git a/src/or/cpuworker.c b/src/or/cpuworker.c
index 0255227e7..119892d71 100644
--- a/src/or/cpuworker.c
+++ b/src/or/cpuworker.c
@@ -14,6 +14,8 @@
 
 #include "or.h"
 #include "buffers.h"
+#include "channel.h"
+#include "channeltls.h"
 #include "circuitbuild.h"
 #include "circuitlist.h"
 #include "config.h"
@@ -68,19 +70,20 @@ connection_cpu_finished_flushing(connection_t *conn)
 /** Pack global_id and circ_id; set *tag to the result. (See note on
  * cpuworker_main for wire format.) */
 static void
-tag_pack(char *tag, uint64_t conn_id, circid_t circ_id)
+tag_pack(char *tag, uint64_t chan_id, circid_t circ_id)
 {
   /*XXXX RETHINK THIS WHOLE MESS !!!! !NM NM NM NM*/
-  set_uint64(tag, conn_id);
+  /*XXXX DOUBLEPLUSTHIS!!!! AS AS AS AS*/
+  set_uint64(tag, chan_id);
   set_uint16(tag+8, circ_id);
 }
 
 /** Unpack <b>tag</b> into addr, port, and circ_id.
  */
 static void
-tag_unpack(const char *tag, uint64_t *conn_id, circid_t *circ_id)
+tag_unpack(const char *tag, uint64_t *chan_id, circid_t *circ_id)
 {
-  *conn_id = get_uint64(tag);
+  *chan_id = get_uint64(tag);
   *circ_id = get_uint16(tag+8);
 }
 
@@ -131,10 +134,9 @@ connection_cpu_process_inbuf(connection_t *conn)
 {
   char success;
   char buf[LEN_ONION_RESPONSE];
-  uint64_t conn_id;
+  uint64_t chan_id;
   circid_t circ_id;
-  connection_t *tmp_conn;
-  or_connection_t *p_conn = NULL;
+  channel_t *p_chan = NULL;
   circuit_t *circ;
 
   tor_assert(conn);
@@ -152,15 +154,16 @@ connection_cpu_process_inbuf(connection_t *conn)
     connection_fetch_from_buf(buf,LEN_ONION_RESPONSE-1,conn);
 
     /* parse out the circ it was talking about */
-    tag_unpack(buf, &conn_id, &circ_id);
+    tag_unpack(buf, &chan_id, &circ_id);
     circ = NULL;
-    tmp_conn = connection_get_by_global_id(conn_id);
-    if (tmp_conn && !tmp_conn->marked_for_close &&
-        tmp_conn->type == CONN_TYPE_OR)
-      p_conn = TO_OR_CONN(tmp_conn);
+    log_debug(LD_OR,
+              "Unpacking cpuworker reply, chan_id is " U64_FORMAT
+              ", circ_id is %d",
+              U64_PRINTF_ARG(chan_id), circ_id);
+    p_chan = channel_find_by_global_id(chan_id);
 
-    if (p_conn)
-      circ = circuit_get_by_circid_orconn(circ_id, p_conn);
+    if (p_chan)
+      circ = circuit_get_by_circid_channel(circ_id, p_chan);
 
     if (success == 0) {
       log_debug(LD_OR,
@@ -475,12 +478,12 @@ assign_onionskin_to_cpuworker(connection_t *cpuworker,
 
     tor_assert(cpuworker);
 
-    if (!circ->p_conn) {
-      log_info(LD_OR,"circ->p_conn gone. Failing circ.");
+    if (!circ->p_chan) {
+      log_info(LD_OR,"circ->p_chan gone. Failing circ.");
       tor_free(onionskin);
       return -1;
     }
-    tag_pack(tag, circ->p_conn->_base.global_identifier,
+    tag_pack(tag, circ->p_chan->global_identifier,
              circ->p_circ_id);
 
     cpuworker->state = CPUWORKER_STATE_BUSY_ONION;
diff --git a/src/or/directory.c b/src/or/directory.c
index 7df91fb57..8003444c6 100644
--- a/src/or/directory.c
+++ b/src/or/directory.c
@@ -2855,8 +2855,8 @@ directory_handle_command_get(dir_connection_t *conn, const char *headers,
         geoip_note_ns_response(act, GEOIP_SUCCESS);
         /* Note that a request for a network status has started, so that we
          * can measure the download time later on. */
-        if (TO_CONN(conn)->dirreq_id)
-          geoip_start_dirreq(TO_CONN(conn)->dirreq_id, dlen, act,
+        if (conn->dirreq_id)
+          geoip_start_dirreq(conn->dirreq_id, dlen, act,
                              DIRREQ_TUNNELED);
         else
           geoip_start_dirreq(TO_CONN(conn)->global_identifier, dlen, act,
@@ -3529,8 +3529,8 @@ connection_dir_finished_flushing(dir_connection_t *conn)
   /* Note that we have finished writing the directory response. For direct
    * connections this means we're done, for tunneled connections its only
    * an intermediate step. */
-  if (TO_CONN(conn)->dirreq_id)
-    geoip_change_dirreq_state(TO_CONN(conn)->dirreq_id, DIRREQ_TUNNELED,
+  if (conn->dirreq_id)
+    geoip_change_dirreq_state(conn->dirreq_id, DIRREQ_TUNNELED,
                               DIRREQ_FLUSHING_DIR_CONN_FINISHED);
   else
     geoip_change_dirreq_state(TO_CONN(conn)->global_identifier,
diff --git a/src/or/dirserv.c b/src/or/dirserv.c
index 0d98324bf..1480cb60d 100644
--- a/src/or/dirserv.c
+++ b/src/or/dirserv.c
@@ -8,6 +8,8 @@
 #include "buffers.h"
 #include "config.h"
 #include "confparse.h"
+#include "channel.h"
+#include "channeltls.h"
 #include "connection.h"
 #include "connection_or.h"
 #include "control.h"
@@ -3410,8 +3412,8 @@ dirserv_single_reachability_test(time_t now, routerinfo_t *router)
   log_debug(LD_OR,"Testing reachability of %s at %s:%u.",
             router->nickname, router->address, router->or_port);
   tor_addr_from_ipv4h(&router_addr, router->addr);
-  connection_or_connect(&router_addr, router->or_port,
-                        router->cache_info.identity_digest);
+  channel_tls_connect(&router_addr, router->or_port,
+                      router->cache_info.identity_digest);
 
   /* Possible IPv6. */
   if (get_options()->AuthDirHasIPv6Connectivity == 1 &&
@@ -3421,8 +3423,8 @@ dirserv_single_reachability_test(time_t now, routerinfo_t *router)
               router->nickname,
               tor_addr_to_str(addrstr, &router->ipv6_addr, sizeof(addrstr), 1),
               router->ipv6_orport);
-    connection_or_connect(&router->ipv6_addr, router->ipv6_orport,
-                          router->cache_info.identity_digest);
+    channel_tls_connect(&router->ipv6_addr, router->ipv6_orport,
+                        router->cache_info.identity_digest);
   }
 }
 
diff --git a/src/or/geoip.c b/src/or/geoip.c
index 6b7cc82b8..a995f8b80 100644
--- a/src/or/geoip.c
+++ b/src/or/geoip.c
@@ -578,7 +578,7 @@ _c_hist_compare(const void **_a, const void **_b)
  * failed, the others as still running. */
 #define DIRREQ_TIMEOUT (10*60)
 
-/** Entry in a map from either conn->global_identifier for direct requests
+/** Entry in a map from either chan->global_identifier for direct requests
  * or a unique circuit identifier for tunneled requests to request time,
  * response size, and completion time of a network status request. Used to
  * measure download times of requests to derive average client
@@ -586,7 +586,7 @@ _c_hist_compare(const void **_a, const void **_b)
 typedef struct dirreq_map_entry_t {
   HT_ENTRY(dirreq_map_entry_t) node;
   /** Unique identifier for this network status request; this is either the
-   * conn->global_identifier of the dir conn (direct request) or a new
+   * chan->global_identifier of the dir channel (direct request) or a new
    * locally unique identifier of a circuit (tunneled request). This ID is
    * only unique among other direct or tunneled requests, respectively. */
   uint64_t dirreq_id;
@@ -705,7 +705,7 @@ geoip_change_dirreq_state(uint64_t dirreq_id, dirreq_type_t type,
   if ((type == DIRREQ_DIRECT &&
          new_state == DIRREQ_FLUSHING_DIR_CONN_FINISHED) ||
       (type == DIRREQ_TUNNELED &&
-         new_state == DIRREQ_OR_CONN_BUFFER_FLUSHED)) {
+         new_state == DIRREQ_CHANNEL_BUFFER_FLUSHED)) {
     tor_gettimeofday(&ent->completion_time);
     ent->completed = 1;
   }
diff --git a/src/or/include.am b/src/or/include.am
index e9811ec96..90dea44ba 100644
--- a/src/or/include.am
+++ b/src/or/include.am
@@ -17,8 +17,12 @@ endif
 
 src_or_libtor_a_SOURCES = \
 	src/or/buffers.c				\
+	src/or/channel.c				\
+	src/or/channeltls.c				\
 	src/or/circuitbuild.c				\
 	src/or/circuitlist.c				\
+	src/or/circuitmux.c				\
+	src/or/circuitmux_ewma.c			\
 	src/or/circuituse.c				\
 	src/or/command.c				\
 	src/or/config.c					\
@@ -86,8 +90,12 @@ src_or_tor_LDADD = src/or/libtor.a src/common/libor.a src/common/libor-crypto.a
 
 ORHEADERS = \
 	src/or/buffers.h				\
+	src/or/channel.h				\
+	src/or/channeltls.h				\
 	src/or/circuitbuild.h				\
 	src/or/circuitlist.h				\
+	src/or/circuitmux.h				\
+	src/or/circuitmux_ewma.h			\
 	src/or/circuituse.h				\
 	src/or/command.h				\
 	src/or/config.h					\
diff --git a/src/or/main.c b/src/or/main.c
index 74bb69672..e0c89a919 100644
--- a/src/or/main.c
+++ b/src/or/main.c
@@ -13,6 +13,8 @@
 #define MAIN_PRIVATE
 #include "or.h"
 #include "buffers.h"
+#include "channel.h"
+#include "channeltls.h"
 #include "circuitbuild.h"
 #include "circuitlist.h"
 #include "circuituse.h"
@@ -398,6 +400,18 @@ connection_unlink(connection_t *conn)
   if (conn->type == CONN_TYPE_OR) {
     if (!tor_digest_is_zero(TO_OR_CONN(conn)->identity_digest))
       connection_or_remove_from_identity_map(TO_OR_CONN(conn));
+    /* connection_unlink() can only get called if the connection
+     * was already on the closeable list, and it got there by
+     * connection_mark_for_close(), which was called from
+     * connection_or_close_normally() or
+     * connection_or_close_for_error(), so the channel should
+     * already be in CHANNEL_STATE_CLOSING, and then the
+     * connection_about_to_close_connection() goes to
+     * connection_or_about_to_close(), which calls channel_closed()
+     * to notify the channel_t layer, and closed the channel, so
+     * nothing more to do here to deal with the channel associated
+     * with an orconn.
+     */
   }
   connection_free(conn);
 }
@@ -1046,7 +1060,8 @@ run_connection_housekeeping(int i, time_t now)
   tor_assert(conn->outbuf);
 #endif
 
-  if (or_conn->is_bad_for_new_circs && !or_conn->n_circuits) {
+  if (channel_is_bad_for_new_circs(TLS_CHAN_TO_BASE(or_conn->chan)) &&
+      !connection_or_get_num_circuits(or_conn)) {
     /* It's bad for new circuits, and has no unmarked circuits on it:
      * mark it now. */
     log_info(LD_OR,
@@ -1056,28 +1071,29 @@ run_connection_housekeeping(int i, time_t now)
       connection_or_connect_failed(TO_OR_CONN(conn),
                                    END_OR_CONN_REASON_TIMEOUT,
                                    "Tor gave up on the connection");
-    connection_mark_and_flush(conn);
+    connection_or_close_normally(TO_OR_CONN(conn), 1);
   } else if (!connection_state_is_open(conn)) {
     if (past_keepalive) {
       /* We never managed to actually get this connection open and happy. */
       log_info(LD_OR,"Expiring non-open OR connection to fd %d (%s:%d).",
                (int)conn->s,conn->address, conn->port);
-      connection_mark_for_close(conn);
+      connection_or_close_normally(TO_OR_CONN(conn), 0);
     }
-  } else if (we_are_hibernating() && !or_conn->n_circuits &&
+  } else if (we_are_hibernating() &&
+             !connection_or_get_num_circuits(or_conn) &&
              !connection_get_outbuf_len(conn)) {
     /* We're hibernating, there's no circuits, and nothing to flush.*/
     log_info(LD_OR,"Expiring non-used OR connection to fd %d (%s:%d) "
              "[Hibernating or exiting].",
              (int)conn->s,conn->address, conn->port);
-    connection_mark_and_flush(conn);
-  } else if (!or_conn->n_circuits &&
+    connection_or_close_normally(TO_OR_CONN(conn), 1);
+  } else if (!connection_or_get_num_circuits(or_conn) &&
              now >= or_conn->timestamp_last_added_nonpadding +
                                          IDLE_OR_CONN_TIMEOUT) {
     log_info(LD_OR,"Expiring non-used OR connection to fd %d (%s:%d) "
              "[idle %d].", (int)conn->s,conn->address, conn->port,
              (int)(now - or_conn->timestamp_last_added_nonpadding));
-    connection_mark_for_close(conn);
+    connection_or_close_normally(TO_OR_CONN(conn), 0);
   } else if (
       now >= or_conn->timestamp_lastempty + options->KeepalivePeriod*10 &&
       now >= conn->timestamp_lastwritten + options->KeepalivePeriod*10) {
@@ -1087,7 +1103,7 @@ run_connection_housekeeping(int i, time_t now)
            (int)conn->s, conn->address, conn->port,
            (int)connection_get_outbuf_len(conn),
            (int)(now-conn->timestamp_lastwritten));
-    connection_mark_for_close(conn);
+    connection_or_close_normally(TO_OR_CONN(conn), 0);
   } else if (past_keepalive && !connection_get_outbuf_len(conn)) {
     /* send a padding cell */
     log_fn(LOG_DEBUG,LD_OR,"Sending keepalive to (%s:%d)",
@@ -1521,6 +1537,10 @@ run_scheduled_events(time_t now)
    * flush it. */
   or_state_save(now);
 
+  /** 8c. Do channel cleanup just like for connections */
+  channel_run_cleanup();
+  channel_listener_run_cleanup();
+
   /** 9. and if we're a server, check whether our DNS is telling stories to
    * us. */
   if (!net_is_disabled() &&
@@ -2151,6 +2171,10 @@ dumpstats(int severity)
     circuit_dump_by_conn(conn, severity); /* dump info about all the circuits
                                            * using this conn */
   } SMARTLIST_FOREACH_END(conn);
+
+  channel_dumpstats(severity);
+  channel_listener_dumpstats(severity);
+
   log(severity, LD_NET,
       "Cells processed: "U64_FORMAT" padding\n"
       "                 "U64_FORMAT" create\n"
@@ -2456,6 +2480,8 @@ tor_free_all(int postfork)
   circuit_free_all();
   entry_guards_free_all();
   pt_free_all();
+  channel_tls_free_all();
+  channel_free_all();
   connection_free_all();
   buf_shrink_freelists(1);
   memarea_clear_freelist();
diff --git a/src/or/networkstatus.c b/src/or/networkstatus.c
index 0cc6a2108..91720b583 100644
--- a/src/or/networkstatus.c
+++ b/src/or/networkstatus.c
@@ -11,7 +11,10 @@
  */
 
 #include "or.h"
+#include "channel.h"
 #include "circuitbuild.h"
+#include "circuitmux.h"
+#include "circuitmux_ewma.h"
 #include "config.h"
 #include "connection.h"
 #include "connection_or.h"
@@ -1634,6 +1637,7 @@ networkstatus_set_current_consensus(const char *consensus,
   consensus_waiting_for_certs_t *waiting = NULL;
   time_t current_valid_after = 0;
   int free_consensus = 1; /* Free 'c' at the end of the function */
+  int old_ewma_enabled;
 
   if (flav < 0) {
     /* XXXX we don't handle unrecognized flavors yet. */
@@ -1827,7 +1831,18 @@ networkstatus_set_current_consensus(const char *consensus,
 
     dirvote_recalculate_timing(options, now);
     routerstatus_list_update_named_server_map();
-    cell_ewma_set_scale_factor(options, current_consensus);
+
+    /* Update ewma and adjust policy if needed; first cache the old value */
+    old_ewma_enabled = cell_ewma_enabled();
+    /* Change the cell EWMA settings */
+    cell_ewma_set_scale_factor(options, networkstatus_get_latest_consensus());
+    /* If we just enabled ewma, set the cmux policy on all active channels */
+    if (cell_ewma_enabled() && !old_ewma_enabled) {
+      channel_set_cmux_policy_everywhere(&ewma_policy);
+    } else if (!cell_ewma_enabled() && old_ewma_enabled) {
+      /* Turn it off everywhere */
+      channel_set_cmux_policy_everywhere(NULL);
+    }
 
     /* XXXX024 this call might be unnecessary here: can changing the
      * current consensus really alter our view of any OR's rate limits? */
diff --git a/src/or/onion.c b/src/or/onion.c
index ff1556c3e..17d8e777a 100644
--- a/src/or/onion.c
+++ b/src/or/onion.c
@@ -106,7 +106,7 @@ onion_next_task(char **onionskin_out)
     return NULL; /* no onions pending, we're done */
 
   tor_assert(ol_list->circ);
-  tor_assert(ol_list->circ->p_conn); /* make sure it's still valid */
+  tor_assert(ol_list->circ->p_chan); /* make sure it's still valid */
   tor_assert(ol_length > 0);
   circ = ol_list->circ;
   *onionskin_out = ol_list->onionskin;
diff --git a/src/or/or.h b/src/or/or.h
index f4e1c5eae..96e029961 100644
--- a/src/or/or.h
+++ b/src/or/or.h
@@ -445,9 +445,9 @@ typedef enum {
 #define CIRCUIT_STATE_BUILDING 0
 /** Circuit state: Waiting to process the onionskin. */
 #define CIRCUIT_STATE_ONIONSKIN_PENDING 1
-/** Circuit state: I'd like to deliver a create, but my n_conn is still
+/** Circuit state: I'd like to deliver a create, but my n_chan is still
  * connecting. */
-#define CIRCUIT_STATE_OR_WAIT 2
+#define CIRCUIT_STATE_CHAN_WAIT 2
 /** Circuit state: onionskin(s) processed, ready to send/receive cells. */
 #define CIRCUIT_STATE_OPEN 3
 
@@ -674,7 +674,7 @@ typedef enum {
 #define END_CIRC_REASON_RESOURCELIMIT   5
 #define END_CIRC_REASON_CONNECTFAILED   6
 #define END_CIRC_REASON_OR_IDENTITY     7
-#define END_CIRC_REASON_OR_CONN_CLOSED  8
+#define END_CIRC_REASON_CHANNEL_CLOSED  8
 #define END_CIRC_REASON_FINISHED        9
 #define END_CIRC_REASON_TIMEOUT         10
 #define END_CIRC_REASON_DESTROYED       11
@@ -879,6 +879,147 @@ typedef uint16_t circid_t;
 /** Identifies a stream on a circuit */
 typedef uint16_t streamid_t;
 
+/* channel_t typedef; struct channel_s is in channel.h */
+
+typedef struct channel_s channel_t;
+
+/* channel_listener_t typedef; struct channel_listener_s is in channel.h */
+
+typedef struct channel_listener_s channel_listener_t;
+
+/* channel states for channel_t */
+
+typedef enum {
+  /*
+   * Closed state - channel is inactive
+   *
+   * Permitted transitions from:
+   *   - CHANNEL_STATE_CLOSING
+   * Permitted transitions to:
+   *   - CHANNEL_STATE_OPENING
+   */
+  CHANNEL_STATE_CLOSED = 0,
+  /*
+   * Opening state - channel is trying to connect
+   *
+   * Permitted transitions from:
+   *   - CHANNEL_STATE_CLOSED
+   * Permitted transitions to:
+   *   - CHANNEL_STATE_CLOSING
+   *   - CHANNEL_STATE_ERROR
+   *   - CHANNEL_STATE_OPEN
+   */
+  CHANNEL_STATE_OPENING,
+  /*
+   * Open state - channel is active and ready for use
+   *
+   * Permitted transitions from:
+   *   - CHANNEL_STATE_MAINT
+   *   - CHANNEL_STATE_OPENING
+   * Permitted transitions to:
+   *   - CHANNEL_STATE_CLOSING
+   *   - CHANNEL_STATE_ERROR
+   *   - CHANNEL_STATE_MAINT
+   */
+  CHANNEL_STATE_OPEN,
+  /*
+   * Maintenance state - channel is temporarily offline for subclass specific
+   *   maintenance activities such as TLS renegotiation.
+   *
+   * Permitted transitions from:
+   *   - CHANNEL_STATE_OPEN
+   * Permitted transitions to:
+   *   - CHANNEL_STATE_CLOSING
+   *   - CHANNEL_STATE_ERROR
+   *   - CHANNEL_STATE_OPEN
+   */
+  CHANNEL_STATE_MAINT,
+  /*
+   * Closing state - channel is shutting down
+   *
+   * Permitted transitions from:
+   *   - CHANNEL_STATE_MAINT
+   *   - CHANNEL_STATE_OPEN
+   * Permitted transitions to:
+   *   - CHANNEL_STATE_CLOSED,
+   *   - CHANNEL_STATE_ERROR
+   */
+  CHANNEL_STATE_CLOSING,
+  /*
+   * Error state - channel has experienced a permanent error
+   *
+   * Permitted transitions from:
+   *   - CHANNEL_STATE_CLOSING
+   *   - CHANNEL_STATE_MAINT
+   *   - CHANNEL_STATE_OPENING
+   *   - CHANNEL_STATE_OPEN
+   * Permitted transitions to:
+   *   - None
+   */
+  CHANNEL_STATE_ERROR,
+  /*
+   * Placeholder for maximum state value
+   */
+  CHANNEL_STATE_LAST
+} channel_state_t;
+
+/* channel listener states for channel_listener_t */
+
+typedef enum {
+  /*
+   * Closed state - channel listener is inactive
+   *
+   * Permitted transitions from:
+   *   - CHANNEL_LISTENER_STATE_CLOSING
+   * Permitted transitions to:
+   *   - CHANNEL_LISTENER_STATE_LISTENING
+   */
+  CHANNEL_LISTENER_STATE_CLOSED = 0,
+  /*
+   * Listening state - channel listener is listening for incoming
+   * connections
+   *
+   * Permitted transitions from:
+   *   - CHANNEL_LISTENER_STATE_CLOSED
+   * Permitted transitions to:
+   *   - CHANNEL_LISTENER_STATE_CLOSING
+   *   - CHANNEL_LISTENER_STATE_ERROR
+   */
+  CHANNEL_LISTENER_STATE_LISTENING,
+  /*
+   * Closing state - channel listener is shutting down
+   *
+   * Permitted transitions from:
+   *   - CHANNEL_LISTENER_STATE_LISTENING
+   * Permitted transitions to:
+   *   - CHANNEL_LISTENER_STATE_CLOSED,
+   *   - CHANNEL_LISTENER_STATE_ERROR
+   */
+  CHANNEL_LISTENER_STATE_CLOSING,
+  /*
+   * Error state - channel listener has experienced a permanent error
+   *
+   * Permitted transitions from:
+   *   - CHANNEL_STATE_CLOSING
+   *   - CHANNEL_STATE_LISTENING
+   * Permitted transitions to:
+   *   - None
+   */
+  CHANNEL_LISTENER_STATE_ERROR,
+  /*
+   * Placeholder for maximum state value
+   */
+  CHANNEL_LISTENER_STATE_LAST
+} channel_listener_state_t;
+
+/* TLS channel stuff */
+
+typedef struct channel_tls_s channel_tls_t;
+
+/* circuitmux_t typedef; struct circuitmux_s is in circuitmux.h */
+
+typedef struct circuitmux_s circuitmux_t;
+
 /** Parsed onion routing cell.  All communication between nodes
  * is via cells. */
 typedef struct cell_t {
@@ -1061,9 +1202,6 @@ typedef struct connection_t {
 
   /** Unique identifier for this connection on this Tor instance. */
   uint64_t global_identifier;
-
-  /** Unique ID for measuring tunneled network status requests. */
-  uint64_t dirreq_id;
 } connection_t;
 
 /** Subtype of connection_t; used for a listener socket. */
@@ -1202,29 +1340,22 @@ typedef struct or_connection_t {
   int tls_error; /**< Last tor_tls error code. */
   /** When we last used this conn for any client traffic. If not
    * recent, we can rate limit it further. */
-  time_t client_used;
+
+  /* Channel using this connection */
+  channel_tls_t *chan;
 
   tor_addr_t real_addr; /**< The actual address that this connection came from
                        * or went to.  The <b>addr</b> field is prone to
                        * getting overridden by the address from the router
                        * descriptor matching <b>identity_digest</b>. */
 
-  circ_id_type_t circ_id_type:2; /**< When we send CREATE cells along this
-                                  * connection, which half of the space should
-                                  * we use? */
   /** Should this connection be used for extending circuits to the server
    * matching the <b>identity_digest</b> field?  Set to true if we're pretty
    * sure we aren't getting MITMed, either because we're connected to an
    * address listed in a server descriptor, or because an authenticated
    * NETINFO cell listed the address we're connected to as recognized. */
   unsigned int is_canonical:1;
-  /** True iff this connection shouldn't get any new circs attached to it,
-   * because the connection is too old, or because there's a better one.
-   * More generally, this flag is used to note an unhealthy connection;
-   * for example, if a bad connection fails we shouldn't assume that the
-   * router itself has a problem.
-   */
-  unsigned int is_bad_for_new_circs:1;
+
   /** True iff we have decided that the other end of this connection
    * is a client.  Connections with this flag set should never be used
    * to satisfy an EXTEND request.  */
@@ -1234,9 +1365,6 @@ typedef struct or_connection_t {
   unsigned int proxy_type:2; /**< One of PROXY_NONE...PROXY_SOCKS5 */
   uint8_t link_proto; /**< What protocol version are we using? 0 for
                        * "none negotiated yet." */
-  circid_t next_circ_id; /**< Which circ_id do we try to use next on
-                          * this connection?  This is always in the
-                          * range 0..1<<15-1. */
 
   or_handshake_state_t *handshake_state; /**< If we are setting this connection
                                           * up, state information to do so. */
@@ -1258,24 +1386,7 @@ typedef struct or_connection_t {
   /* XXXX we could share this among all connections. */
   struct ev_token_bucket_cfg *bucket_cfg;
 #endif
-  int n_circuits; /**< How many circuits use this connection as p_conn or
-                   * n_conn ? */
-
-  /** Double-linked ring of circuits with queued cells waiting for room to
-   * free up on this connection's outbuf.  Every time we pull cells from a
-   * circuit, we advance this pointer to the next circuit in the ring. */
-  struct circuit_t *active_circuits;
-  /** Priority queue of cell_ewma_t for circuits with queued cells waiting for
-   * room to free up on this connection's outbuf.  Kept in heap order
-   * according to EWMA.
-   *
-   * This is redundant with active_circuits; if we ever decide only to use the
-   * cell_ewma algorithm for choosing circuits, we can remove active_circuits.
-   */
-  smartlist_t *active_circuit_pqueue;
-  /** The tick on which the cell_ewma_ts in active_circuit_pqueue last had
-   * their ewma values rescaled. */
-  unsigned active_circuit_pqueue_last_recalibrated;
+
   struct or_connection_t *next_with_same_id; /**< Next connection with same
                                               * identity digest as this one. */
 } or_connection_t;
@@ -1327,6 +1438,10 @@ typedef struct edge_connection_t {
    * cells. */
   unsigned int edge_blocked_on_circ:1;
 
+  /** Unique ID for directory requests; this used to be in connection_t, but
+   * that's going away and being used on channels instead.  We still tag
+   * edge connections with dirreq_id from circuits, so it's copied here. */
+  uint64_t dirreq_id;
 } edge_connection_t;
 
 /** Subtype of edge_connection_t for an "entry connection" -- that is, a SOCKS
@@ -1449,6 +1564,10 @@ typedef struct dir_connection_t {
   char identity_digest[DIGEST_LEN]; /**< Hash of the public RSA key for
                                      * the directory server's signing key. */
 
+  /** Unique ID for directory requests; this used to be in connection_t, but
+   * that's going away and being used on channels instead.  The dirserver still
+   * needs this for the incoming side, so it's moved here. */
+  uint64_t dirreq_id;
 } dir_connection_t;
 
 /** Subtype of connection_t for an connection to a controller. */
@@ -2462,29 +2581,6 @@ typedef struct {
   time_t expiry_time;
 } cpath_build_state_t;
 
-/**
- * The cell_ewma_t structure keeps track of how many cells a circuit has
- * transferred recently.  It keeps an EWMA (exponentially weighted moving
- * average) of the number of cells flushed from the circuit queue onto a
- * connection in connection_or_flush_from_first_active_circuit().
- */
-typedef struct {
-  /** The last 'tick' at which we recalibrated cell_count.
-   *
-   * A cell sent at exactly the start of this tick has weight 1.0. Cells sent
-   * since the start of this tick have weight greater than 1.0; ones sent
-   * earlier have less weight. */
-  unsigned last_adjusted_tick;
-  /** The EWMA of the cell count. */
-  double cell_count;
-  /** True iff this is the cell count for a circuit's previous
-   * connection. */
-  unsigned int is_for_p_conn : 1;
-  /** The position of the circuit within the OR connection's priority
-   * queue. */
-  int heap_index;
-} cell_ewma_t;
-
 #define ORIGIN_CIRCUIT_MAGIC 0x35315243u
 #define OR_CIRCUIT_MAGIC 0x98ABC04Fu
 
@@ -2515,23 +2611,39 @@ typedef struct circuit_t {
   uint32_t magic; /**< For memory and type debugging: must equal
                    * ORIGIN_CIRCUIT_MAGIC or OR_CIRCUIT_MAGIC. */
 
-  /** Queue of cells waiting to be transmitted on n_conn. */
-  cell_queue_t n_conn_cells;
-  /** The OR connection that is next in this circuit. */
-  or_connection_t *n_conn;
-  /** The circuit_id used in the next (forward) hop of this circuit. */
+  /** The channel that is next in this circuit. */
+  channel_t *n_chan;
+
+  /**
+   * The circuit_id used in the next (forward) hop of this circuit;
+   * this is unique to n_chan, but this ordered pair is globally
+   * unique:
+   *
+   * (n_chan->global_identifier, n_circ_id)
+   */
   circid_t n_circ_id;
 
-  /** The hop to which we want to extend this circuit.  Should be NULL if
-   * the circuit has attached to a connection. */
+  /**
+   * Circuit mux associated with n_chan to which this circuit is attached;
+   * NULL if we have no n_chan.
+   */
+  circuitmux_t *n_mux;
+
+  /** Queue of cells waiting to be transmitted on n_chan */
+  cell_queue_t n_chan_cells;
+
+  /**
+   * The hop to which we want to extend this circuit.  Should be NULL if
+   * the circuit has attached to a channel.
+   */
   extend_info_t *n_hop;
 
-  /** True iff we are waiting for n_conn_cells to become less full before
+  /** True iff we are waiting for n_chan_cells to become less full before
    * allowing p_streams to add any more cells. (Origin circuit only.) */
-  unsigned int streams_blocked_on_n_conn : 1;
-  /** True iff we are waiting for p_conn_cells to become less full before
+  unsigned int streams_blocked_on_n_chan : 1;
+  /** True iff we are waiting for p_chan_cells to become less full before
    * allowing n_streams to add any more cells. (OR circuit only.) */
-  unsigned int streams_blocked_on_p_conn : 1;
+  unsigned int streams_blocked_on_p_chan : 1;
 
   uint8_t state; /**< Current status of this circuit. */
   uint8_t purpose; /**< Why are we creating this circuit? */
@@ -2546,10 +2658,10 @@ typedef struct circuit_t {
    * more. */
   int deliver_window;
 
-  /** For storage while n_conn is pending
-    * (state CIRCUIT_STATE_OR_WAIT). When defined, it is always
+  /** For storage while n_chan is pending
+    * (state CIRCUIT_STATE_CHAN_WAIT). When defined, it is always
     * length ONIONSKIN_CHALLENGE_LEN. */
-  char *n_conn_onionskin;
+  char *n_chan_onionskin;
 
   /** When was this circuit created?  We keep this timestamp with a higher
    * resolution than most so that the circuit-build-time tracking code can
@@ -2575,23 +2687,19 @@ typedef struct circuit_t {
   const char *marked_for_close_file; /**< For debugging: in which file was this
                                       * circuit marked for close? */
 
+  /** Unique ID for measuring tunneled network status requests. */
+  uint64_t dirreq_id;
+
+  struct circuit_t *next; /**< Next circuit in linked list of all circuits. */
+
   /** Next circuit in the doubly-linked ring of circuits waiting to add
    * cells to n_conn.  NULL if we have no cells pending, or if we're not
    * linked to an OR connection. */
-  struct circuit_t *next_active_on_n_conn;
+  struct circuit_t *next_active_on_n_chan;
   /** Previous circuit in the doubly-linked ring of circuits waiting to add
    * cells to n_conn.  NULL if we have no cells pending, or if we're not
    * linked to an OR connection. */
-  struct circuit_t *prev_active_on_n_conn;
-  struct circuit_t *next; /**< Next circuit in linked list of all circuits. */
-
-  /** Unique ID for measuring tunneled network status requests. */
-  uint64_t dirreq_id;
-
-  /** The EWMA count for the number of cells flushed from the
-   * n_conn_cells queue.  Used to determine which circuit to flush from next.
-   */
-  cell_ewma_t n_cell_ewma;
+  struct circuit_t *prev_active_on_n_chan;
 } circuit_t;
 
 /** Largest number of relay_early cells that we can send on a given
@@ -2754,20 +2862,25 @@ typedef struct or_circuit_t {
   circuit_t _base;
 
   /** Next circuit in the doubly-linked ring of circuits waiting to add
-   * cells to p_conn.  NULL if we have no cells pending, or if we're not
+   * cells to p_chan.  NULL if we have no cells pending, or if we're not
    * linked to an OR connection. */
-  struct circuit_t *next_active_on_p_conn;
+  struct circuit_t *next_active_on_p_chan;
   /** Previous circuit in the doubly-linked ring of circuits waiting to add
-   * cells to p_conn.  NULL if we have no cells pending, or if we're not
+   * cells to p_chan.  NULL if we have no cells pending, or if we're not
    * linked to an OR connection. */
-  struct circuit_t *prev_active_on_p_conn;
+  struct circuit_t *prev_active_on_p_chan;
 
   /** The circuit_id used in the previous (backward) hop of this circuit. */
   circid_t p_circ_id;
   /** Queue of cells waiting to be transmitted on p_conn. */
-  cell_queue_t p_conn_cells;
-  /** The OR connection that is previous in this circuit. */
-  or_connection_t *p_conn;
+  cell_queue_t p_chan_cells;
+  /** The channel that is previous in this circuit. */
+  channel_t *p_chan;
+  /**
+   * Circuit mux associated with p_chan to which this circuit is attached;
+   * NULL if we have no p_chan.
+   */
+  circuitmux_t *p_mux;
   /** Linked list of Exit streams associated with this circuit. */
   edge_connection_t *n_streams;
   /** Linked list of Exit streams associated with this circuit that are
@@ -2824,10 +2937,6 @@ typedef struct or_circuit_t {
    * exit-ward queues of this circuit; reset every time when writing
    * buffer stats to disk. */
   uint64_t total_cell_waiting_time;
-
-  /** The EWMA count for the number of cells flushed from the
-   * p_conn_cells queue. */
-  cell_ewma_t p_cell_ewma;
 } or_circuit_t;
 
 /** Convert a circuit subtype to a circuit_t. */
@@ -4135,10 +4244,10 @@ typedef enum {
   /** Flushed last cell from queue of the circuit that initiated a
     * tunneled request to the outbuf of the OR connection. */
   DIRREQ_CIRC_QUEUE_FLUSHED = 3,
-  /** Flushed last byte from buffer of the OR connection belonging to the
+  /** Flushed last byte from buffer of the channel belonging to the
     * circuit that initiated a tunneled request; completes a tunneled
     * request. */
-  DIRREQ_OR_CONN_BUFFER_FLUSHED = 4
+  DIRREQ_CHANNEL_BUFFER_FLUSHED = 4
 } dirreq_state_t;
 
 #define WRITE_STATS_INTERVAL (24*60*60)
diff --git a/src/or/reasons.c b/src/or/reasons.c
index c51d8ee6f..a04cd869a 100644
--- a/src/or/reasons.c
+++ b/src/or/reasons.c
@@ -323,8 +323,8 @@ circuit_end_reason_to_control_string(int reason)
       return "CONNECTFAILED";
     case END_CIRC_REASON_OR_IDENTITY:
       return "OR_IDENTITY";
-    case END_CIRC_REASON_OR_CONN_CLOSED:
-      return "OR_CONN_CLOSED";
+    case END_CIRC_REASON_CHANNEL_CLOSED:
+      return "CHANNEL_CLOSED";
     case END_CIRC_REASON_FINISHED:
       return "FINISHED";
     case END_CIRC_REASON_TIMEOUT:
diff --git a/src/or/relay.c b/src/or/relay.c
index 4a50b710d..7c81273a0 100644
--- a/src/or/relay.c
+++ b/src/or/relay.c
@@ -10,10 +10,10 @@
  *    receiving from circuits, plus queuing on circuits.
  **/
 
-#include <math.h>
 #define RELAY_PRIVATE
 #include "or.h"
 #include "buffers.h"
+#include "channel.h"
 #include "circuitbuild.h"
 #include "circuitlist.h"
 #include "config.h"
@@ -166,7 +166,7 @@ int
 circuit_receive_relay_cell(cell_t *cell, circuit_t *circ,
                            cell_direction_t cell_direction)
 {
-  or_connection_t *or_conn=NULL;
+  channel_t *chan = NULL;
   crypt_path_t *layer_hint=NULL;
   char recognized=0;
   int reason;
@@ -213,17 +213,17 @@ circuit_receive_relay_cell(cell_t *cell, circuit_t *circ,
   /* not recognized. pass it on. */
   if (cell_direction == CELL_DIRECTION_OUT) {
     cell->circ_id = circ->n_circ_id; /* switch it */
-    or_conn = circ->n_conn;
+    chan = circ->n_chan;
   } else if (! CIRCUIT_IS_ORIGIN(circ)) {
     cell->circ_id = TO_OR_CIRCUIT(circ)->p_circ_id; /* switch it */
-    or_conn = TO_OR_CIRCUIT(circ)->p_conn;
+    chan = TO_OR_CIRCUIT(circ)->p_chan;
   } else {
     log_fn(LOG_PROTOCOL_WARN, LD_OR,
            "Dropping unrecognized inbound cell on origin circuit.");
     return 0;
   }
 
-  if (!or_conn) {
+  if (!chan) {
     // XXXX Can this splice stuff be done more cleanly?
     if (! CIRCUIT_IS_ORIGIN(circ) &&
         TO_OR_CIRCUIT(circ)->rend_splice &&
@@ -254,7 +254,7 @@ circuit_receive_relay_cell(cell_t *cell, circuit_t *circ,
                                   * we might kill the circ before we relay
                                   * the cells. */
 
-  append_cell_to_circuit_queue(circ, or_conn, cell, cell_direction, 0);
+  append_cell_to_circuit_queue(circ, chan, cell, cell_direction, 0);
   return 0;
 }
 
@@ -353,13 +353,13 @@ circuit_package_relay_cell(cell_t *cell, circuit_t *circ,
                            cell_direction_t cell_direction,
                            crypt_path_t *layer_hint, streamid_t on_stream)
 {
-  or_connection_t *conn; /* where to send the cell */
+  channel_t *chan; /* where to send the cell */
 
   if (cell_direction == CELL_DIRECTION_OUT) {
     crypt_path_t *thishop; /* counter for repeated crypts */
-    conn = circ->n_conn;
-    if (!CIRCUIT_IS_ORIGIN(circ) || !conn) {
-      log_warn(LD_BUG,"outgoing relay cell has n_conn==NULL. Dropping.");
+    chan = circ->n_chan;
+    if (!CIRCUIT_IS_ORIGIN(circ) || !chan) {
+      log_warn(LD_BUG,"outgoing relay cell has n_chan==NULL. Dropping.");
       return 0; /* just drop it */
     }
 
@@ -388,14 +388,14 @@ circuit_package_relay_cell(cell_t *cell, circuit_t *circ,
       return 0; /* just drop it */
     }
     or_circ = TO_OR_CIRCUIT(circ);
-    conn = or_circ->p_conn;
+    chan = or_circ->p_chan;
     relay_set_digest(or_circ->p_digest, cell);
     if (relay_crypt_one_payload(or_circ->p_crypto, cell->payload, 1) < 0)
       return -1;
   }
   ++stats_n_relay_cells_relayed;
 
-  append_cell_to_circuit_queue(circ, conn, cell, cell_direction, on_stream);
+  append_cell_to_circuit_queue(circ, chan, cell, cell_direction, on_stream);
   return 0;
 }
 
@@ -561,9 +561,9 @@ relay_send_command_from_edge(streamid_t stream_id, circuit_t *circ,
     geoip_change_dirreq_state(circ->dirreq_id, DIRREQ_TUNNELED,
                               DIRREQ_END_CELL_SENT);
 
-  if (cell_direction == CELL_DIRECTION_OUT && circ->n_conn) {
+  if (cell_direction == CELL_DIRECTION_OUT && circ->n_chan) {
     /* if we're using relaybandwidthrate, this conn wants priority */
-    circ->n_conn->client_used = approx_time();
+    channel_timestamp_client(circ->n_chan);
   }
 
   if (cell_direction == CELL_DIRECTION_OUT) {
@@ -1095,7 +1095,7 @@ connection_edge_process_relay_cell(cell_t *cell, circuit_t *circ,
          * and linked. */
         static uint64_t next_id = 0;
         circ->dirreq_id = ++next_id;
-        TO_CONN(TO_OR_CIRCUIT(circ)->p_conn)->dirreq_id = circ->dirreq_id;
+        TO_OR_CIRCUIT(circ)->p_chan->dirreq_id = circ->dirreq_id;
       }
 
       return connection_exit_begin_conn(cell, circ);
@@ -1230,12 +1230,12 @@ connection_edge_process_relay_cell(cell_t *cell, circuit_t *circ,
                "'truncate' unsupported at origin. Dropping.");
         return 0;
       }
-      if (circ->n_conn) {
+      if (circ->n_chan) {
         uint8_t trunc_reason = get_uint8(cell->payload + RELAY_HEADER_SIZE);
-        circuit_clear_cell_queue(circ, circ->n_conn);
-        connection_or_send_destroy(circ->n_circ_id, circ->n_conn,
-                                   trunc_reason);
-        circuit_set_n_circid_orconn(circ, 0, NULL);
+        circuit_clear_cell_queue(circ, circ->n_chan);
+        channel_send_destroy(circ->n_circ_id, circ->n_chan,
+                             trunc_reason);
+        circuit_set_n_circid_chan(circ, 0, NULL);
       }
       log_debug(LD_EXIT, "Processed 'truncate', replying.");
       {
@@ -1594,10 +1594,10 @@ circuit_resume_edge_reading_helper(edge_connection_t *first_conn,
    * needed to fill the cell queue. */
   int max_to_package = circ->package_window;
   if (CIRCUIT_IS_ORIGIN(circ)) {
-    cells_on_queue = circ->n_conn_cells.n;
+    cells_on_queue = circ->n_chan_cells.n;
   } else {
     or_circuit_t *or_circ = TO_OR_CIRCUIT(circ);
-    cells_on_queue = or_circ->p_conn_cells.n;
+    cells_on_queue = or_circ->p_chan_cells.n;
   }
   if (CELL_QUEUE_HIGHWATER_SIZE - cells_on_queue < max_to_package)
     max_to_package = CELL_QUEUE_HIGHWATER_SIZE - cells_on_queue;
@@ -1778,10 +1778,10 @@ circuit_consider_sending_sendme(circuit_t *circ, crypt_path_t *layer_hint)
 }
 
 #ifdef ACTIVE_CIRCUITS_PARANOIA
-#define assert_active_circuits_ok_paranoid(conn) \
-     assert_active_circuits_ok(conn)
+#define assert_cmux_ok_paranoid(chan) \
+     assert_circuit_mux_okay(chan)
 #else
-#define assert_active_circuits_ok_paranoid(conn)
+#define assert_cmux_ok_paranoid(chan)
 #endif
 
 /** The total number of cells we have allocated from the memory pool. */
@@ -1842,6 +1842,13 @@ packed_cell_new(void)
   return mp_pool_get(cell_pool);
 }
 
+/** Return a packed cell used outside by channel_t lower layer */
+void
+packed_cell_free(packed_cell_t *cell)
+{
+  packed_cell_free_unchecked(cell);
+}
+
 /** Log current statistics for cell pool allocation at log level
  * <b>severity</b>. */
 void
@@ -1851,9 +1858,9 @@ dump_cell_pool_usage(int severity)
   int n_circs = 0;
   int n_cells = 0;
   for (c = _circuit_get_global_list(); c; c = c->next) {
-    n_cells += c->n_conn_cells.n;
+    n_cells += c->n_chan_cells.n;
     if (!CIRCUIT_IS_ORIGIN(c))
-      n_cells += TO_OR_CIRCUIT(c)->p_conn_cells.n;
+      n_cells += TO_OR_CIRCUIT(c)->p_chan_cells.n;
     ++n_circs;
   }
   log(severity, LD_MM, "%d cells allocated on %d circuits. %d cells leaked.",
@@ -1964,363 +1971,63 @@ cell_queue_pop(cell_queue_t *queue)
   return cell;
 }
 
-/** Return a pointer to the "next_active_on_{n,p}_conn" pointer of <b>circ</b>,
- * depending on whether <b>conn</b> matches n_conn or p_conn. */
-static INLINE circuit_t **
-next_circ_on_conn_p(circuit_t *circ, or_connection_t *conn)
-{
-  tor_assert(circ);
-  tor_assert(conn);
-  if (conn == circ->n_conn) {
-    return &circ->next_active_on_n_conn;
-  } else {
-    or_circuit_t *orcirc = TO_OR_CIRCUIT(circ);
-    tor_assert(conn == orcirc->p_conn);
-    return &orcirc->next_active_on_p_conn;
-  }
-}
-
-/** Return a pointer to the "prev_active_on_{n,p}_conn" pointer of <b>circ</b>,
- * depending on whether <b>conn</b> matches n_conn or p_conn. */
-static INLINE circuit_t **
-prev_circ_on_conn_p(circuit_t *circ, or_connection_t *conn)
-{
-  tor_assert(circ);
-  tor_assert(conn);
-  if (conn == circ->n_conn) {
-    return &circ->prev_active_on_n_conn;
-  } else {
-    or_circuit_t *orcirc = TO_OR_CIRCUIT(circ);
-    tor_assert(conn == orcirc->p_conn);
-    return &orcirc->prev_active_on_p_conn;
-  }
-}
-
-/** Helper for sorting cell_ewma_t values in their priority queue. */
-static int
-compare_cell_ewma_counts(const void *p1, const void *p2)
-{
-  const cell_ewma_t *e1=p1, *e2=p2;
-  if (e1->cell_count < e2->cell_count)
-    return -1;
-  else if (e1->cell_count > e2->cell_count)
-    return 1;
-  else
-    return 0;
-}
-
-/** Given a cell_ewma_t, return a pointer to the circuit containing it. */
-static circuit_t *
-cell_ewma_to_circuit(cell_ewma_t *ewma)
-{
-  if (ewma->is_for_p_conn) {
-    /* This is an or_circuit_t's p_cell_ewma. */
-    or_circuit_t *orcirc = SUBTYPE_P(ewma, or_circuit_t, p_cell_ewma);
-    return TO_CIRCUIT(orcirc);
-  } else {
-    /* This is some circuit's n_cell_ewma. */
-    return SUBTYPE_P(ewma, circuit_t, n_cell_ewma);
-  }
-}
-
-/* ==== Functions for scaling cell_ewma_t ====
-
-   When choosing which cells to relay first, we favor circuits that have been
-   quiet recently.  This gives better latency on connections that aren't
-   pushing lots of data, and makes the network feel more interactive.
-
-   Conceptually, we take an exponentially weighted mean average of the number
-   of cells a circuit has sent, and allow active circuits (those with cells to
-   relay) to send cells in reverse order of their exponentially-weighted mean
-   average (EWMA) cell count.  [That is, a cell sent N seconds ago 'counts'
-   F^N times as much as a cell sent now, for 0<F<1.0, and we favor the
-   circuit that has sent the fewest cells]
-
-   If 'double' had infinite precision, we could do this simply by counting a
-   cell sent at startup as having weight 1.0, and a cell sent N seconds later
-   as having weight F^-N.  This way, we would never need to re-scale
-   any already-sent cells.
-
-   To prevent double from overflowing, we could count a cell sent now as
-   having weight 1.0 and a cell sent N seconds ago as having weight F^N.
-   This, however, would mean we'd need to re-scale *ALL* old circuits every
-   time we wanted to send a cell.
-
-   So as a compromise, we divide time into 'ticks' (currently, 10-second
-   increments) and say that a cell sent at the start of a current tick is
-   worth 1.0, a cell sent N seconds before the start of the current tick is
-   worth F^N, and a cell sent N seconds after the start of the current tick is
-   worth F^-N.  This way we don't overflow, and we don't need to constantly
-   rescale.
- */
-
-/** How long does a tick last (seconds)? */
-#define EWMA_TICK_LEN 10
-
-/** The default per-tick scale factor, if it hasn't been overridden by a
- * consensus or a configuration setting.  zero means "disabled". */
-#define EWMA_DEFAULT_HALFLIFE 0.0
-
-/** Given a timeval <b>now</b>, compute the cell_ewma tick in which it occurs
- * and the fraction of the tick that has elapsed between the start of the tick
- * and <b>now</b>.  Return the former and store the latter in
- * *<b>remainder_out</b>.
- *
- * These tick values are not meant to be shared between Tor instances, or used
- * for other purposes. */
-static unsigned
-cell_ewma_tick_from_timeval(const struct timeval *now,
-                            double *remainder_out)
-{
-  unsigned res = (unsigned) (now->tv_sec / EWMA_TICK_LEN);
-  /* rem */
-  double rem = (now->tv_sec % EWMA_TICK_LEN) +
-    ((double)(now->tv_usec)) / 1.0e6;
-  *remainder_out = rem / EWMA_TICK_LEN;
-  return res;
-}
-
-/** Compute and return the current cell_ewma tick. */
-unsigned
-cell_ewma_get_tick(void)
-{
-  return ((unsigned)approx_time() / EWMA_TICK_LEN);
-}
-
-/** The per-tick scale factor to be used when computing cell-count EWMA
- * values.  (A cell sent N ticks before the start of the current tick
- * has value ewma_scale_factor ** N.)
+/**
+ * Update the number of cells available on the circuit's n_chan or p_chan's
+ * circuit mux.
  */
-static double ewma_scale_factor = 0.1;
-/* DOCDOC ewma_enabled */
-static int ewma_enabled = 0;
-
-/*DOCDOC*/
-#define EPSILON 0.00001
-/*DOCDOC*/
-#define LOG_ONEHALF -0.69314718055994529
-
-/** Adjust the global cell scale factor based on <b>options</b> */
 void
-cell_ewma_set_scale_factor(const or_options_t *options,
-                           const networkstatus_t *consensus)
+update_circuit_on_cmux(circuit_t *circ, cell_direction_t direction)
 {
-  int32_t halflife_ms;
-  double halflife;
-  const char *source;
-  if (options && options->CircuitPriorityHalflife >= -EPSILON) {
-    halflife = options->CircuitPriorityHalflife;
-    source = "CircuitPriorityHalflife in configuration";
-  } else if (consensus && (halflife_ms = networkstatus_get_param(
-                 consensus, "CircuitPriorityHalflifeMsec",
-                 -1, -1, INT32_MAX)) >= 0) {
-    halflife = ((double)halflife_ms)/1000.0;
-    source = "CircuitPriorityHalflifeMsec in consensus";
-  } else {
-    halflife = EWMA_DEFAULT_HALFLIFE;
-    source = "Default value";
-  }
+  channel_t *chan = NULL;
+  or_circuit_t *or_circ = NULL;
+  circuitmux_t *cmux = NULL;
 
-  if (halflife <= EPSILON) {
-    /* The cell EWMA algorithm is disabled. */
-    ewma_scale_factor = 0.1;
-    ewma_enabled = 0;
-    log_info(LD_OR,
-             "Disabled cell_ewma algorithm because of value in %s",
-             source);
-  } else {
-    /* convert halflife into halflife-per-tick. */
-    halflife /= EWMA_TICK_LEN;
-    /* compute per-tick scale factor. */
-    ewma_scale_factor = exp( LOG_ONEHALF / halflife );
-    ewma_enabled = 1;
-    log_info(LD_OR,
-             "Enabled cell_ewma algorithm because of value in %s; "
-             "scale factor is %f per %d seconds",
-             source, ewma_scale_factor, EWMA_TICK_LEN);
-  }
-}
-
-/** Return the multiplier necessary to convert the value of a cell sent in
- * 'from_tick' to one sent in 'to_tick'. */
-static INLINE double
-get_scale_factor(unsigned from_tick, unsigned to_tick)
-{
-  /* This math can wrap around, but that's okay: unsigned overflow is
-     well-defined */
-  int diff = (int)(to_tick - from_tick);
-  return pow(ewma_scale_factor, diff);
-}
-
-/** Adjust the cell count of <b>ewma</b> so that it is scaled with respect to
- * <b>cur_tick</b> */
-static void
-scale_single_cell_ewma(cell_ewma_t *ewma, unsigned cur_tick)
-{
-  double factor = get_scale_factor(ewma->last_adjusted_tick, cur_tick);
-  ewma->cell_count *= factor;
-  ewma->last_adjusted_tick = cur_tick;
-}
-
-/** Adjust the cell count of every active circuit on <b>conn</b> so
- * that they are scaled with respect to <b>cur_tick</b> */
-static void
-scale_active_circuits(or_connection_t *conn, unsigned cur_tick)
-{
-
-  double factor = get_scale_factor(
-              conn->active_circuit_pqueue_last_recalibrated,
-              cur_tick);
-  /** Ordinarily it isn't okay to change the value of an element in a heap,
-   * but it's okay here, since we are preserving the order. */
-  SMARTLIST_FOREACH(conn->active_circuit_pqueue, cell_ewma_t *, e, {
-      tor_assert(e->last_adjusted_tick ==
-                 conn->active_circuit_pqueue_last_recalibrated);
-      e->cell_count *= factor;
-      e->last_adjusted_tick = cur_tick;
-  });
-  conn->active_circuit_pqueue_last_recalibrated = cur_tick;
-}
-
-/** Rescale <b>ewma</b> to the same scale as <b>conn</b>, and add it to
- * <b>conn</b>'s priority queue of active circuits */
-static void
-add_cell_ewma_to_conn(or_connection_t *conn, cell_ewma_t *ewma)
-{
-  tor_assert(ewma->heap_index == -1);
-  scale_single_cell_ewma(ewma,
-                         conn->active_circuit_pqueue_last_recalibrated);
-
-  smartlist_pqueue_add(conn->active_circuit_pqueue,
-                       compare_cell_ewma_counts,
-                       STRUCT_OFFSET(cell_ewma_t, heap_index),
-                       ewma);
-}
-
-/** Remove <b>ewma</b> from <b>conn</b>'s priority queue of active circuits */
-static void
-remove_cell_ewma_from_conn(or_connection_t *conn, cell_ewma_t *ewma)
-{
-  tor_assert(ewma->heap_index != -1);
-  smartlist_pqueue_remove(conn->active_circuit_pqueue,
-                          compare_cell_ewma_counts,
-                          STRUCT_OFFSET(cell_ewma_t, heap_index),
-                          ewma);
-}
-
-/** Remove and return the first cell_ewma_t from conn's priority queue of
- * active circuits.  Requires that the priority queue is nonempty. */
-static cell_ewma_t *
-pop_first_cell_ewma_from_conn(or_connection_t *conn)
-{
-  return smartlist_pqueue_pop(conn->active_circuit_pqueue,
-                              compare_cell_ewma_counts,
-                              STRUCT_OFFSET(cell_ewma_t, heap_index));
-}
-
-/** Add <b>circ</b> to the list of circuits with pending cells on
- * <b>conn</b>.  No effect if <b>circ</b> is already linked. */
-void
-make_circuit_active_on_conn(circuit_t *circ, or_connection_t *conn)
-{
-  circuit_t **nextp = next_circ_on_conn_p(circ, conn);
-  circuit_t **prevp = prev_circ_on_conn_p(circ, conn);
-
-  if (*nextp && *prevp) {
-    /* Already active. */
-    return;
-  }
-
-  assert_active_circuits_ok_paranoid(conn);
-
-  if (! conn->active_circuits) {
-    conn->active_circuits = circ;
-    *prevp = *nextp = circ;
-  } else {
-    circuit_t *head = conn->active_circuits;
-    circuit_t *old_tail = *prev_circ_on_conn_p(head, conn);
-    *next_circ_on_conn_p(old_tail, conn) = circ;
-    *nextp = head;
-    *prev_circ_on_conn_p(head, conn) = circ;
-    *prevp = old_tail;
-  }
+  tor_assert(circ);
 
-  if (circ->n_conn == conn) {
-    add_cell_ewma_to_conn(conn, &circ->n_cell_ewma);
+  /* Okay, get the channel */
+  if (direction == CELL_DIRECTION_OUT) {
+    chan = circ->n_chan;
   } else {
-    or_circuit_t *orcirc = TO_OR_CIRCUIT(circ);
-    tor_assert(conn == orcirc->p_conn);
-    add_cell_ewma_to_conn(conn, &orcirc->p_cell_ewma);
+    or_circ = TO_OR_CIRCUIT(circ);
+    chan = or_circ->p_chan;
   }
 
-  assert_active_circuits_ok_paranoid(conn);
-}
-
-/** Remove <b>circ</b> from the list of circuits with pending cells on
- * <b>conn</b>.  No effect if <b>circ</b> is already unlinked. */
-void
-make_circuit_inactive_on_conn(circuit_t *circ, or_connection_t *conn)
-{
-  circuit_t **nextp = next_circ_on_conn_p(circ, conn);
-  circuit_t **prevp = prev_circ_on_conn_p(circ, conn);
-  circuit_t *next = *nextp, *prev = *prevp;
-
-  if (!next && !prev) {
-    /* Already inactive. */
-    return;
-  }
+  tor_assert(chan);
+  tor_assert(chan->cmux);
 
-  assert_active_circuits_ok_paranoid(conn);
+  /* Now get the cmux */
+  cmux = chan->cmux;
 
-  tor_assert(next && prev);
-  tor_assert(*prev_circ_on_conn_p(next, conn) == circ);
-  tor_assert(*next_circ_on_conn_p(prev, conn) == circ);
+  /* Cmux sanity check */
+  tor_assert(circuitmux_is_circuit_attached(cmux, circ));
+  tor_assert(circuitmux_attached_circuit_direction(cmux, circ) == direction);
 
-  if (next == circ) {
-    conn->active_circuits = NULL;
-  } else {
-    *prev_circ_on_conn_p(next, conn) = prev;
-    *next_circ_on_conn_p(prev, conn) = next;
-    if (conn->active_circuits == circ)
-      conn->active_circuits = next;
-  }
-  *prevp = *nextp = NULL;
+  assert_cmux_ok_paranoid(chan);
 
-  if (circ->n_conn == conn) {
-    remove_cell_ewma_from_conn(conn, &circ->n_cell_ewma);
+  /* Update the number of cells we have for the circuit mux */
+  if (direction == CELL_DIRECTION_OUT) {
+    circuitmux_set_num_cells(cmux, circ, circ->n_chan_cells.n);
   } else {
-    or_circuit_t *orcirc = TO_OR_CIRCUIT(circ);
-    tor_assert(conn == orcirc->p_conn);
-    remove_cell_ewma_from_conn(conn, &orcirc->p_cell_ewma);
+    circuitmux_set_num_cells(cmux, circ, or_circ->p_chan_cells.n);
   }
 
-  assert_active_circuits_ok_paranoid(conn);
+  assert_cmux_ok_paranoid(chan);
 }
 
-/** Remove all circuits from the list of circuits with pending cells on
- * <b>conn</b>. */
+/** Remove all circuits from the cmux on <b>chan</b>. */
 void
-connection_or_unlink_all_active_circs(or_connection_t *orconn)
+channel_unlink_all_circuits(channel_t *chan)
 {
-  circuit_t *head = orconn->active_circuits;
-  circuit_t *cur = head;
-  if (! head)
-    return;
-  do {
-    circuit_t *next = *next_circ_on_conn_p(cur, orconn);
-    *prev_circ_on_conn_p(cur, orconn) = NULL;
-    *next_circ_on_conn_p(cur, orconn) = NULL;
-    cur = next;
-  } while (cur != head);
-  orconn->active_circuits = NULL;
-
-  SMARTLIST_FOREACH(orconn->active_circuit_pqueue, cell_ewma_t *, e,
-                    e->heap_index = -1);
-  smartlist_clear(orconn->active_circuit_pqueue);
+  tor_assert(chan);
+  tor_assert(chan->cmux);
+
+  circuitmux_detach_all_circuits(chan->cmux);
+  chan->num_n_circuits = 0;
+  chan->num_p_circuits = 0;
 }
 
 /** Block (if <b>block</b> is true) or unblock (if <b>block</b> is false)
- * every edge connection that is using <b>circ</b> to write to <b>orconn</b>,
+ * every edge connection that is using <b>circ</b> to write to <b>chan</b>,
  * and start or stop reading as appropriate.
  *
  * If <b>stream_id</b> is nonzero, block only the edge connection whose
@@ -2329,17 +2036,17 @@ connection_or_unlink_all_active_circs(or_connection_t *orconn)
  * Returns the number of streams whose status we changed.
  */
 static int
-set_streams_blocked_on_circ(circuit_t *circ, or_connection_t *orconn,
+set_streams_blocked_on_circ(circuit_t *circ, channel_t *chan,
                             int block, streamid_t stream_id)
 {
   edge_connection_t *edge = NULL;
   int n = 0;
-  if (circ->n_conn == orconn) {
-    circ->streams_blocked_on_n_conn = block;
+  if (circ->n_chan == chan) {
+    circ->streams_blocked_on_n_chan = block;
     if (CIRCUIT_IS_ORIGIN(circ))
       edge = TO_ORIGIN_CIRCUIT(circ)->p_streams;
   } else {
-    circ->streams_blocked_on_p_conn = block;
+    circ->streams_blocked_on_p_chan = block;
     tor_assert(!CIRCUIT_IS_ORIGIN(circ));
     edge = TO_OR_CIRCUIT(circ)->n_streams;
   }
@@ -2374,58 +2081,51 @@ set_streams_blocked_on_circ(circuit_t *circ, or_connection_t *orconn,
 }
 
 /** Pull as many cells as possible (but no more than <b>max</b>) from the
- * queue of the first active circuit on <b>conn</b>, and write them to
- * <b>conn</b>-&gt;outbuf.  Return the number of cells written.  Advance
+ * queue of the first active circuit on <b>chan</b>, and write them to
+ * <b>chan</b>-&gt;outbuf.  Return the number of cells written.  Advance
  * the active circuit pointer to the next active circuit in the ring. */
 int
-connection_or_flush_from_first_active_circuit(or_connection_t *conn, int max,
-                                              time_t now)
+channel_flush_from_first_active_circuit(channel_t *chan, int max)
 {
-  int n_flushed;
+  circuitmux_t *cmux = NULL;
+  int n_flushed = 0;
   cell_queue_t *queue;
   circuit_t *circ;
+  or_circuit_t *or_circ;
   int streams_blocked;
-
-  /* The current (hi-res) time */
-  struct timeval now_hires;
-
-  /* The EWMA cell counter for the circuit we're flushing. */
-  cell_ewma_t *cell_ewma = NULL;
-  double ewma_increment = -1;
-
-  circ = conn->active_circuits;
-  if (!circ) return 0;
-  assert_active_circuits_ok_paranoid(conn);
-
-  /* See if we're doing the ewma circuit selection algorithm. */
-  if (ewma_enabled) {
-    unsigned tick;
-    double fractional_tick;
-    tor_gettimeofday_cached(&now_hires);
-    tick = cell_ewma_tick_from_timeval(&now_hires, &fractional_tick);
-
-    if (tick != conn->active_circuit_pqueue_last_recalibrated) {
-      scale_active_circuits(conn, tick);
+  packed_cell_t *cell;
+
+  /* Get the cmux */
+  tor_assert(chan);
+  tor_assert(chan->cmux);
+  cmux = chan->cmux;
+
+  /* Main loop: pick a circuit, send a cell, update the cmux */
+  while (n_flushed < max) {
+    circ = circuitmux_get_first_active_circuit(cmux);
+    /* If it returns NULL, no cells left to send */
+    if (!circ) break;
+    assert_cmux_ok_paranoid(chan);
+
+    if (circ->n_chan == chan) {
+      queue = &circ->n_chan_cells;
+      streams_blocked = circ->streams_blocked_on_n_chan;
+    } else {
+      or_circ = TO_OR_CIRCUIT(circ);
+      tor_assert(or_circ->p_chan == chan);
+      queue = &TO_OR_CIRCUIT(circ)->p_chan_cells;
+      streams_blocked = circ->streams_blocked_on_p_chan;
     }
 
-    ewma_increment = pow(ewma_scale_factor, -fractional_tick);
+    /* Circuitmux told us this was active, so it should have cells */
+    tor_assert(queue->n > 0);
 
-    cell_ewma = smartlist_get(conn->active_circuit_pqueue, 0);
-    circ = cell_ewma_to_circuit(cell_ewma);
-  }
-
-  if (circ->n_conn == conn) {
-    queue = &circ->n_conn_cells;
-    streams_blocked = circ->streams_blocked_on_n_conn;
-  } else {
-    queue = &TO_OR_CIRCUIT(circ)->p_conn_cells;
-    streams_blocked = circ->streams_blocked_on_p_conn;
-  }
-  tor_assert(*next_circ_on_conn_p(circ,conn));
-
-  for (n_flushed = 0; n_flushed < max && queue->head; ) {
-    packed_cell_t *cell = cell_queue_pop(queue);
-    tor_assert(*next_circ_on_conn_p(circ,conn));
+    /*
+     * Get just one cell here; once we've sent it, that can change the circuit
+     * selection, so we have to loop around for another even if this circuit
+     * has more than one.
+     */
+    cell = cell_queue_pop(queue);
 
     /* Calculate the exact time that this cell has spent in the queue. */
     if (get_options()->CellStatistics && !CIRCUIT_IS_ORIGIN(circ)) {
@@ -2441,8 +2141,8 @@ connection_or_flush_from_first_active_circuit(or_connection_t *conn, int max,
                              "Looks like the CellStatistics option was "
                              "recently enabled.");
       } else {
-        or_circuit_t *orcirc = TO_OR_CIRCUIT(circ);
         insertion_time_elem_t *elem = it_queue->first;
+        or_circ = TO_OR_CIRCUIT(circ);
         cell_waiting_time =
             (uint32_t)((flushed * 10L + SECONDS_IN_A_DAY * 1000L -
                         elem->insertion_time * 10L) %
@@ -2455,66 +2155,58 @@ connection_or_flush_from_first_active_circuit(or_connection_t *conn, int max,
             it_queue->last = NULL;
           mp_pool_release(elem);
         }
-        orcirc->total_cell_waiting_time += cell_waiting_time;
-        orcirc->processed_cells++;
+        or_circ->total_cell_waiting_time += cell_waiting_time;
+        or_circ->processed_cells++;
       }
     }
 
     /* If we just flushed our queue and this circuit is used for a
      * tunneled directory request, possibly advance its state. */
-    if (queue->n == 0 && TO_CONN(conn)->dirreq_id)
-      geoip_change_dirreq_state(TO_CONN(conn)->dirreq_id,
+    if (queue->n == 0 && chan->dirreq_id)
+      geoip_change_dirreq_state(chan->dirreq_id,
                                 DIRREQ_TUNNELED,
                                 DIRREQ_CIRC_QUEUE_FLUSHED);
 
-    connection_write_to_buf(cell->body, CELL_NETWORK_SIZE, TO_CONN(conn));
+    /* Now send the cell */
+    channel_write_packed_cell(chan, cell);
+    cell = NULL;
 
-    packed_cell_free_unchecked(cell);
+    /*
+     * Don't packed_cell_free_unchecked(cell) here because the channel will
+     * do so when it gets out of the channel queue (probably already did, in
+     * which case that was an immediate double-free bug).
+     */
+
+    /* Update the counter */
     ++n_flushed;
-    if (cell_ewma) {
-      cell_ewma_t *tmp;
-      cell_ewma->cell_count += ewma_increment;
-      /* We pop and re-add the cell_ewma_t here, not above, since we need to
-       * re-add it immediately to keep the priority queue consistent with
-       * the linked-list implementation */
-      tmp = pop_first_cell_ewma_from_conn(conn);
-      tor_assert(tmp == cell_ewma);
-      add_cell_ewma_to_conn(conn, cell_ewma);
-    }
-    if (!ewma_enabled && circ != conn->active_circuits) {
-      /* If this happens, the current circuit just got made inactive by
-       * a call in connection_write_to_buf().  That's nothing to worry about:
-       * circuit_make_inactive_on_conn() already advanced conn->active_circuits
-       * for us.
-       */
-      assert_active_circuits_ok_paranoid(conn);
-      goto done;
-    }
-  }
-  tor_assert(*next_circ_on_conn_p(circ,conn));
-  assert_active_circuits_ok_paranoid(conn);
-  conn->active_circuits = *next_circ_on_conn_p(circ, conn);
 
-  /* Is the cell queue low enough to unblock all the streams that are waiting
-   * to write to this circuit? */
-  if (streams_blocked && queue->n <= CELL_QUEUE_LOWWATER_SIZE)
-    set_streams_blocked_on_circ(circ, conn, 0, 0); /* unblock streams */
+    /*
+     * Now update the cmux; tell it we've just sent a cell, and how many
+     * we have left.
+     */
+    circuitmux_notify_xmit_cells(cmux, circ, 1);
+    circuitmux_set_num_cells(cmux, circ, queue->n);
+    if (queue->n == 0)
+      log_debug(LD_GENERAL, "Made a circuit inactive.");
+
+    /* Is the cell queue low enough to unblock all the streams that are waiting
+     * to write to this circuit? */
+    if (streams_blocked && queue->n <= CELL_QUEUE_LOWWATER_SIZE)
+      set_streams_blocked_on_circ(circ, chan, 0, 0); /* unblock streams */
 
-  /* Did we just run out of cells on this circuit's queue? */
-  if (queue->n == 0) {
-    log_debug(LD_GENERAL, "Made a circuit inactive.");
-    make_circuit_inactive_on_conn(circ, conn);
+    /* If n_flushed < max still, loop around and pick another circuit */
   }
- done:
-  if (n_flushed)
-    conn->timestamp_last_added_nonpadding = now;
+
+  /* Okay, we're done sending now */
+  assert_cmux_ok_paranoid(chan);
+
   return n_flushed;
 }
 
-/** Add <b>cell</b> to the queue of <b>circ</b> writing to <b>orconn</b>
+/** Add <b>cell</b> to the queue of <b>circ</b> writing to <b>chan</b>
  * transmitting in <b>direction</b>. */
 void
-append_cell_to_circuit_queue(circuit_t *circ, or_connection_t *orconn,
+append_cell_to_circuit_queue(circuit_t *circ, channel_t *chan,
                              cell_t *cell, cell_direction_t direction,
                              streamid_t fromstream)
 {
@@ -2524,12 +2216,12 @@ append_cell_to_circuit_queue(circuit_t *circ, or_connection_t *orconn,
     return;
 
   if (direction == CELL_DIRECTION_OUT) {
-    queue = &circ->n_conn_cells;
-    streams_blocked = circ->streams_blocked_on_n_conn;
+    queue = &circ->n_chan_cells;
+    streams_blocked = circ->streams_blocked_on_n_chan;
   } else {
     or_circuit_t *orcirc = TO_OR_CIRCUIT(circ);
-    queue = &orcirc->p_conn_cells;
-    streams_blocked = circ->streams_blocked_on_p_conn;
+    queue = &orcirc->p_chan_cells;
+    streams_blocked = circ->streams_blocked_on_p_chan;
   }
 
   cell_queue_append_packed_copy(queue, cell);
@@ -2537,27 +2229,27 @@ append_cell_to_circuit_queue(circuit_t *circ, or_connection_t *orconn,
   /* If we have too many cells on the circuit, we should stop reading from
    * the edge streams for a while. */
   if (!streams_blocked && queue->n >= CELL_QUEUE_HIGHWATER_SIZE)
-    set_streams_blocked_on_circ(circ, orconn, 1, 0); /* block streams */
+    set_streams_blocked_on_circ(circ, chan, 1, 0); /* block streams */
 
   if (streams_blocked && fromstream) {
     /* This edge connection is apparently not blocked; block it. */
-    set_streams_blocked_on_circ(circ, orconn, 1, fromstream);
+    set_streams_blocked_on_circ(circ, chan, 1, fromstream);
   }
 
+  update_circuit_on_cmux(circ, direction);
   if (queue->n == 1) {
-    /* This was the first cell added to the queue.  We need to make this
+    /* This was the first cell added to the queue.  We just made this
      * circuit active. */
     log_debug(LD_GENERAL, "Made a circuit active.");
-    make_circuit_active_on_conn(circ, orconn);
   }
 
-  if (! connection_get_outbuf_len(TO_CONN(orconn))) {
+  if (!channel_has_queued_writes(chan)) {
     /* There is no data at all waiting to be sent on the outbuf.  Add a
      * cell, so that we can notice when it gets flushed, flushed_some can
      * get called, and we can start putting more data onto the buffer then.
      */
     log_debug(LD_GENERAL, "Primed a buffer.");
-    connection_or_flush_from_first_active_circuit(orconn, 1, approx_time());
+    channel_flush_from_first_active_circuit(chan, 1);
   }
 }
 
@@ -2621,58 +2313,39 @@ decode_address_from_payload(tor_addr_t *addr_out, const uint8_t *payload,
   return payload + 2 + payload[1];
 }
 
-/** Remove all the cells queued on <b>circ</b> for <b>orconn</b>. */
+/** Remove all the cells queued on <b>circ</b> for <b>chan</b>. */
 void
-circuit_clear_cell_queue(circuit_t *circ, or_connection_t *orconn)
+circuit_clear_cell_queue(circuit_t *circ, channel_t *chan)
 {
   cell_queue_t *queue;
-  if (circ->n_conn == orconn) {
-    queue = &circ->n_conn_cells;
+  cell_direction_t direction;
+
+  if (circ->n_chan == chan) {
+    queue = &circ->n_chan_cells;
+    direction = CELL_DIRECTION_OUT;
   } else {
     or_circuit_t *orcirc = TO_OR_CIRCUIT(circ);
-    tor_assert(orcirc->p_conn == orconn);
-    queue = &orcirc->p_conn_cells;
+    tor_assert(orcirc->p_chan == chan);
+    queue = &orcirc->p_chan_cells;
+    direction = CELL_DIRECTION_IN;
   }
 
-  if (queue->n)
-    make_circuit_inactive_on_conn(circ,orconn);
-
+  /* Clear the queue */
   cell_queue_clear(queue);
+
+  /* Update the cell counter in the cmux */
+  update_circuit_on_cmux(circ, direction);
 }
 
-/** Fail with an assert if the active circuits ring on <b>orconn</b> is
- * corrupt.  */
+/** Fail with an assert if the circuit mux on chan is corrupt
+ */
 void
-assert_active_circuits_ok(or_connection_t *orconn)
+assert_circuit_mux_okay(channel_t *chan)
 {
-  circuit_t *head = orconn->active_circuits;
-  circuit_t *cur = head;
-  int n = 0;
-  if (! head)
-    return;
-  do {
-    circuit_t *next = *next_circ_on_conn_p(cur, orconn);
-    circuit_t *prev = *prev_circ_on_conn_p(cur, orconn);
-    cell_ewma_t *ewma;
-    tor_assert(next);
-    tor_assert(prev);
-    tor_assert(*next_circ_on_conn_p(prev, orconn) == cur);
-    tor_assert(*prev_circ_on_conn_p(next, orconn) == cur);
-    if (orconn == cur->n_conn) {
-      ewma = &cur->n_cell_ewma;
-      tor_assert(!ewma->is_for_p_conn);
-    } else {
-      ewma = &TO_OR_CIRCUIT(cur)->p_cell_ewma;
-      tor_assert(ewma->is_for_p_conn);
-    }
-    tor_assert(ewma->heap_index != -1);
-    tor_assert(ewma == smartlist_get(orconn->active_circuit_pqueue,
-                                     ewma->heap_index));
-    n++;
-    cur = next;
-  } while (cur != head);
-
-  tor_assert(n == smartlist_len(orconn->active_circuit_pqueue));
+  tor_assert(chan);
+  tor_assert(chan->cmux);
+
+  circuitmux_assert_okay(chan->cmux);
 }
 
 /** Return 1 if we shouldn't restart reading on this circuit, even if
@@ -2682,9 +2355,9 @@ static int
 circuit_queue_streams_are_blocked(circuit_t *circ)
 {
   if (CIRCUIT_IS_ORIGIN(circ)) {
-    return circ->streams_blocked_on_n_conn;
+    return circ->streams_blocked_on_n_chan;
   } else {
-    return circ->streams_blocked_on_p_conn;
+    return circ->streams_blocked_on_p_chan;
   }
 }
 
diff --git a/src/or/relay.h b/src/or/relay.h
index 41675e210..5759c5180 100644
--- a/src/or/relay.h
+++ b/src/or/relay.h
@@ -41,28 +41,26 @@ void free_cell_pool(void);
 void clean_cell_pool(void);
 void dump_cell_pool_usage(int severity);
 
+/* For channeltls.c */
+void packed_cell_free(packed_cell_t *cell);
+
 void cell_queue_clear(cell_queue_t *queue);
 void cell_queue_append(cell_queue_t *queue, packed_cell_t *cell);
 void cell_queue_append_packed_copy(cell_queue_t *queue, const cell_t *cell);
 
-void append_cell_to_circuit_queue(circuit_t *circ, or_connection_t *orconn,
+void append_cell_to_circuit_queue(circuit_t *circ, channel_t *chan,
                                   cell_t *cell, cell_direction_t direction,
                                   streamid_t fromstream);
-void connection_or_unlink_all_active_circs(or_connection_t *conn);
-int connection_or_flush_from_first_active_circuit(or_connection_t *conn,
-                                                  int max, time_t now);
-void assert_active_circuits_ok(or_connection_t *orconn);
-void make_circuit_inactive_on_conn(circuit_t *circ, or_connection_t *conn);
-void make_circuit_active_on_conn(circuit_t *circ, or_connection_t *conn);
+void channel_unlink_all_circuits(channel_t *chan);
+int channel_flush_from_first_active_circuit(channel_t *chan, int max);
+void assert_circuit_mux_okay(channel_t *chan);
+void update_circuit_on_cmux(circuit_t *circ, cell_direction_t direction);
 
 int append_address_to_payload(uint8_t *payload_out, const tor_addr_t *addr);
 const uint8_t *decode_address_from_payload(tor_addr_t *addr_out,
                                         const uint8_t *payload,
                                         int payload_len);
-unsigned cell_ewma_get_tick(void);
-void cell_ewma_set_scale_factor(const or_options_t *options,
-                                const networkstatus_t *consensus);
-void circuit_clear_cell_queue(circuit_t *circ, or_connection_t *orconn);
+void circuit_clear_cell_queue(circuit_t *circ, channel_t *chan);
 
 #ifdef RELAY_PRIVATE
 int relay_crypt(circuit_t *circ, cell_t *cell, cell_direction_t cell_direction,
diff --git a/src/or/rendmid.c b/src/or/rendmid.c
index bacd0ef93..00bbd28fa 100644
--- a/src/or/rendmid.c
+++ b/src/or/rendmid.c
@@ -35,7 +35,7 @@ rend_mid_establish_intro(or_circuit_t *circ, const uint8_t *request,
            "Received an ESTABLISH_INTRO request on circuit %d",
            circ->p_circ_id);
 
-  if (circ->_base.purpose != CIRCUIT_PURPOSE_OR || circ->_base.n_conn) {
+  if (circ->_base.purpose != CIRCUIT_PURPOSE_OR || circ->_base.n_chan) {
     log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
          "Rejecting ESTABLISH_INTRO on non-OR or non-edge circuit.");
     reason = END_CIRC_REASON_TORPROTOCOL;
@@ -142,7 +142,7 @@ rend_mid_introduce(or_circuit_t *circ, const uint8_t *request,
   log_info(LD_REND, "Received an INTRODUCE1 request on circuit %d",
            circ->p_circ_id);
 
-  if (circ->_base.purpose != CIRCUIT_PURPOSE_OR || circ->_base.n_conn) {
+  if (circ->_base.purpose != CIRCUIT_PURPOSE_OR || circ->_base.n_chan) {
     log_warn(LD_PROTOCOL,
              "Rejecting INTRODUCE1 on non-OR or non-edge circuit %d.",
              circ->p_circ_id);
@@ -224,7 +224,7 @@ rend_mid_establish_rendezvous(or_circuit_t *circ, const uint8_t *request,
   log_info(LD_REND, "Received an ESTABLISH_RENDEZVOUS request on circuit %d",
            circ->p_circ_id);
 
-  if (circ->_base.purpose != CIRCUIT_PURPOSE_OR || circ->_base.n_conn) {
+  if (circ->_base.purpose != CIRCUIT_PURPOSE_OR || circ->_base.n_chan) {
     log_warn(LD_PROTOCOL,
              "Tried to establish rendezvous on non-OR or non-edge circuit.");
     goto err;
@@ -277,7 +277,7 @@ rend_mid_rendezvous(or_circuit_t *circ, const uint8_t *request,
   char hexid[9];
   int reason = END_CIRC_REASON_INTERNAL;
 
-  if (circ->_base.purpose != CIRCUIT_PURPOSE_OR || circ->_base.n_conn) {
+  if (circ->_base.purpose != CIRCUIT_PURPOSE_OR || circ->_base.n_chan) {
     log_info(LD_REND,
              "Tried to complete rendezvous on non-OR or non-edge circuit %d.",
              circ->p_circ_id);
diff --git a/src/or/router.h b/src/or/router.h
index c43c30849..39640855e 100644
--- a/src/or/router.h
+++ b/src/or/router.h
@@ -86,13 +86,18 @@ int router_pick_published_address(const or_options_t *options, uint32_t *addr);
 int router_rebuild_descriptor(int force);
 int router_dump_router_to_string(char *s, size_t maxlen, routerinfo_t *router,
                                  crypto_pk_t *ident_key);
-int extrainfo_dump_to_string(char **s, extrainfo_t *extrainfo,
-                             crypto_pk_t *ident_key);
 void router_get_prim_orport(const routerinfo_t *router,
-                            tor_addr_port_t *ap_out);
+                            tor_addr_port_t *addr_port_out);
+void router_get_pref_orport(const routerinfo_t *router,
+                            tor_addr_port_t *addr_port_out);
+void router_get_pref_ipv6_orport(const routerinfo_t *router,
+                                 tor_addr_port_t *addr_port_out);
+int router_ipv6_preferred(const routerinfo_t *router);
 int router_has_addr(const routerinfo_t *router, const tor_addr_t *addr);
 int router_has_orport(const routerinfo_t *router,
                       const tor_addr_port_t *orport);
+int extrainfo_dump_to_string(char **s, extrainfo_t *extrainfo,
+                             crypto_pk_t *ident_key);
 int is_legal_nickname(const char *s);
 int is_legal_nickname_or_hexdigest(const char *s);
 int is_legal_hexdigest(const char *s);