Download microdescriptors if you're a cache

This commit adds some functions to see what microdescriptors we're missing,
and adds fetch-microdesc/store-microdesc logic to the directory code.

9 files changed, 359 insertions, 63 deletions

diff --git a/src/or/directory.c b/src/or/directory.c
index 4411278d8..52a0f9f3e 100644
--- a/src/or/directory.c
+++ b/src/or/directory.c
@@ -15,6 +15,7 @@
 #include "dirvote.h"
 #include "geoip.h"
 #include "main.h"
+#include "microdesc.h"
 #include "networkstatus.h"
 #include "policies.h"
 #include "rendclient.h"
@@ -78,6 +79,8 @@ static void dir_routerdesc_download_failed(smartlist_t *failed,
                                            int router_purpose,
                                            int was_extrainfo,
                                            int was_descriptor_digests);
+static void dir_microdesc_download_failed(smartlist_t *failed,
+                                          int status_code);
 static void note_client_request(int purpose, int compressed, size_t bytes);
 static int client_likes_consensus(networkstatus_t *v, const char *want_url);
 
@@ -137,7 +140,8 @@ purpose_needs_anonymity(uint8_t dir_purpose, uint8_t router_purpose)
       dir_purpose == DIR_PURPOSE_FETCH_CONSENSUS ||
       dir_purpose == DIR_PURPOSE_FETCH_CERTIFICATE ||
       dir_purpose == DIR_PURPOSE_FETCH_SERVERDESC ||
-      dir_purpose == DIR_PURPOSE_FETCH_EXTRAINFO)
+      dir_purpose == DIR_PURPOSE_FETCH_EXTRAINFO ||
+      dir_purpose == DIR_PURPOSE_FETCH_MICRODESC)
     return 0;
   return 1;
 }
@@ -201,6 +205,8 @@ dir_conn_purpose_to_string(int purpose)
       return "hidden-service v2 descriptor fetch";
     case DIR_PURPOSE_UPLOAD_RENDDESC_V2:
       return "hidden-service v2 descriptor upload";
+    case DIR_PURPOSE_FETCH_MICRODESC:
+      return "microdescriptor fetch";
     }
 
   log_warn(LD_BUG, "Called with unknown purpose %d", purpose);
@@ -355,6 +361,9 @@ directory_get_from_dirserver(uint8_t dir_purpose, uint8_t router_purpose,
     case DIR_PURPOSE_FETCH_CERTIFICATE:
       type = V3_AUTHORITY;
       break;
+    case DIR_PURPOSE_FETCH_MICRODESC:
+      type = V3_AUTHORITY;
+      break;
     default:
       log_warn(LD_BUG, "Unexpected purpose %d", (int)dir_purpose);
       return;
@@ -410,7 +419,8 @@ directory_get_from_dirserver(uint8_t dir_purpose, uint8_t router_purpose,
       if (prefer_authority || type == BRIDGE_AUTHORITY) {
         /* only ask authdirservers, and don't ask myself */
         rs = router_pick_trusteddirserver(type, pds_flags);
-        if (rs == NULL && (pds_flags & PDS_NO_EXISTING_SERVERDESC_FETCH)) {
+        if (rs == NULL && (pds_flags & (PDS_NO_EXISTING_SERVERDESC_FETCH|
+                                        PDS_NO_EXISTING_MICRODESC_FETCH))) {
           /* We don't want to fetch from any authorities that we're currently
            * fetching server descriptors from, and we got no match.  Did we
            * get no match because all the authorities have connections
@@ -418,7 +428,8 @@ directory_get_from_dirserver(uint8_t dir_purpose, uint8_t router_purpose,
            * return,) or because all the authorities are down or on fire or
            * unreachable or something (in which case we should go on with
            * our fallback code)? */
-          pds_flags &= ~PDS_NO_EXISTING_SERVERDESC_FETCH;
+          pds_flags &= ~(PDS_NO_EXISTING_SERVERDESC_FETCH|
+                         PDS_NO_EXISTING_MICRODESC_FETCH);
           rs = router_pick_trusteddirserver(type, pds_flags);
           if (rs) {
             log_debug(LD_DIR, "Deferring serverdesc fetch: all authorities "
@@ -607,7 +618,8 @@ connection_dir_request_failed(dir_connection_t *conn)
     connection_dir_download_networkstatus_failed(conn, -1);
   } else if (conn->_base.purpose == DIR_PURPOSE_FETCH_SERVERDESC ||
              conn->_base.purpose == DIR_PURPOSE_FETCH_EXTRAINFO) {
-    log_info(LD_DIR, "Giving up on directory server at '%s'; retrying",
+    log_info(LD_DIR, "Giving up on serverdesc/extrainfo fetch from "
+             "directory server at '%s'; retrying",
              conn->_base.address);
     if (conn->router_purpose == ROUTER_PURPOSE_BRIDGE)
       connection_dir_bridge_routerdesc_failed(conn);
@@ -617,7 +629,8 @@ connection_dir_request_failed(dir_connection_t *conn)
       conn->requested_resource ? conn->requested_resource : "ns";
     networkstatus_consensus_download_failed(0, flavname);
   } else if (conn->_base.purpose == DIR_PURPOSE_FETCH_CERTIFICATE) {
-    log_info(LD_DIR, "Giving up on directory server at '%s'; retrying",
+    log_info(LD_DIR, "Giving up on certificate fetch from directory server "
+             "at '%s'; retrying",
              conn->_base.address);
     connection_dir_download_cert_failed(conn, 0);
   } else if (conn->_base.purpose == DIR_PURPOSE_FETCH_DETACHED_SIGNATURES) {
@@ -626,6 +639,10 @@ connection_dir_request_failed(dir_connection_t *conn)
   } else if (conn->_base.purpose == DIR_PURPOSE_FETCH_STATUS_VOTE) {
     log_info(LD_DIR, "Giving up downloading votes from '%s'",
              conn->_base.address);
+  } else if (conn->_base.purpose == DIR_PURPOSE_FETCH_MICRODESC) {
+    log_info(LD_DIR, "Giving up on downloading microdescriptors from "
+             " directory server at '%s'; will retry", conn->_base.address);
+    connection_dir_download_routerdesc_failed(conn);
   }
 }
 
@@ -696,7 +713,8 @@ connection_dir_download_routerdesc_failed(dir_connection_t *conn)
   /* No need to relaunch descriptor downloads here: we already do it
    * every 10 or 60 seconds (FOO_DESCRIPTOR_RETRY_INTERVAL) in main.c. */
   tor_assert(conn->_base.purpose == DIR_PURPOSE_FETCH_SERVERDESC ||
-             conn->_base.purpose == DIR_PURPOSE_FETCH_EXTRAINFO);
+             conn->_base.purpose == DIR_PURPOSE_FETCH_EXTRAINFO ||
+             conn->_base.purpose == DIR_PURPOSE_FETCH_MICRODESC);
 
   (void) conn;
 }
@@ -1136,6 +1154,11 @@ directory_send_command(dir_connection_t *conn,
       url = tor_malloc(len);
       tor_snprintf(url, len, "/tor/extra/%s", resource);
       break;
+    case DIR_PURPOSE_FETCH_MICRODESC:
+      tor_assert(resource);
+      httpcommand = "GET";
+      tor_asprintf(&url, "/tor/micro/%s.z", resource);
+      break;
     case DIR_PURPOSE_UPLOAD_DIR:
       tor_assert(!resource);
       tor_assert(payload);
@@ -1411,6 +1434,9 @@ body_is_plausible(const char *body, size_t len, int purpose)
     return 1; /* empty bodies don't need decompression */
   if (len < 32)
     return 0;
+  if (purpose == DIR_PURPOSE_FETCH_MICRODESC) {
+    return (!strcmpstart(body,"onion-key"));
+  }
   if (purpose != DIR_PURPOSE_FETCH_RENDDESC) {
     if (!strcmpstart(body,"router") ||
         !strcmpstart(body,"signed-directory") ||
@@ -1487,7 +1513,8 @@ connection_dir_client_reached_eof(dir_connection_t *conn)
   int plausible;
   int skewed=0;
   int allow_partial = (conn->_base.purpose == DIR_PURPOSE_FETCH_SERVERDESC ||
-                       conn->_base.purpose == DIR_PURPOSE_FETCH_EXTRAINFO);
+                       conn->_base.purpose == DIR_PURPOSE_FETCH_EXTRAINFO ||
+                       conn->_base.purpose == DIR_PURPOSE_FETCH_MICRODESC);
   int was_compressed=0;
   time_t now = time(NULL);
 
@@ -1886,6 +1913,41 @@ connection_dir_client_reached_eof(dir_connection_t *conn)
     if (directory_conn_is_self_reachability_test(conn))
       router_dirport_found_reachable();
   }
+  if (conn->_base.purpose == DIR_PURPOSE_FETCH_MICRODESC) {
+    smartlist_t *which = NULL;
+    log_info(LD_DIR,"Received answer to microdescriptor request (status %d, "
+             "size %d) from server '%s:%d'",
+             status_code, (int)body_len, conn->_base.address, conn->_base.port);
+    tor_assert(conn->requested_resource &&
+               !strcmpstart(conn->requested_resource, "d/"));
+    which = smartlist_create();
+    dir_split_resource_into_fingerprints(conn->requested_resource+2,
+                                         which, NULL,
+                                         DSR_DIGEST256|DSR_BASE64);
+    if (status_code != 200) {
+      log_info(LD_DIR, "Received status code %d (%s) from server "
+               "'%s:%d' while fetching \"/tor/micro/%s\".  I'll try again "
+               "soon.",
+               status_code, escaped(reason), conn->_base.address,
+               (int)conn->_base.port, conn->requested_resource);
+      dir_microdesc_download_failed(which, status_code);
+      SMARTLIST_FOREACH(which, char *, cp, tor_free(cp));
+      smartlist_free(which);
+      tor_free(body); tor_free(headers); tor_free(reason);
+      return 0;
+    } else {
+      smartlist_t *mds;
+      mds = microdescs_add_to_cache(get_microdesc_cache(),
+                                    body, body+body_len, SAVED_NOWHERE, 0,
+                                    now, which);
+      if (smartlist_len(which)) {
+        /* Mark remaining ones as failed. */
+        dir_microdesc_download_failed(which, status_code);
+      }
+      SMARTLIST_FOREACH(which, char *, cp, tor_free(cp));
+      smartlist_free(which);
+    }
+  }
 
   if (conn->_base.purpose == DIR_PURPOSE_UPLOAD_DIR) {
     switch (status_code) {
@@ -3612,6 +3674,36 @@ dir_routerdesc_download_failed(smartlist_t *failed, int status_code,
    * every 10 or 60 seconds (FOO_DESCRIPTOR_RETRY_INTERVAL) in main.c. */
 }
 
+/* DOCDOC NM */
+static void
+dir_microdesc_download_failed(smartlist_t *failed,
+                              int status_code)
+{
+  networkstatus_t *consensus
+    = networkstatus_get_latest_consensus_by_flavor(FLAV_MICRODESC);
+  routerstatus_t *rs;
+  download_status_t *dls;
+  time_t now = time(NULL);
+  int server = directory_fetches_from_authorities(get_options());
+
+  if (! consensus)
+    return;
+  SMARTLIST_FOREACH_BEGIN(failed, const char *, d) {
+    rs = router_get_consensus_status_by_descriptor_digest(consensus, d);
+    if (!rs)
+      continue;
+    dls = &rs->dl_status;
+    if (dls->n_download_failures >= MAX_MICRODESC_DOWNLOAD_FAILURES)
+      continue;
+    {
+      char buf[BASE64_DIGEST256_LEN+1];
+      digest256_to_base64(buf, d);
+      download_status_increment_failure(dls, status_code, buf,
+                                        server, now);
+    }
+  } SMARTLIST_FOREACH_END(d);
+}
+
 /** Helper.  Compare two fp_pair_t objects, and return -1, 0, or 1 as
  * appropriate. */
 static int
diff --git a/src/or/main.c b/src/or/main.c
index adc2d3dae..8ea1728fb 100644
--- a/src/or/main.c
+++ b/src/or/main.c
@@ -851,10 +851,13 @@ directory_info_has_arrived(time_t now, int from_cache)
         "I learned some more directory information, but not enough to "
         "build a circuit: %s", get_dir_info_status_string());
     update_router_descriptor_downloads(now);
+    update_microdesc_downloads(now);
     return;
   } else {
-    if (directory_fetches_from_authorities(options))
+    if (directory_fetches_from_authorities(options)) {
       update_router_descriptor_downloads(now);
+      update_microdesc_downloads(now);
+    }
 
     /* if we have enough dir info, then update our guard status with
      * whatever we just learned. */
@@ -1062,6 +1065,7 @@ run_scheduled_events(time_t now)
   if (time_to_try_getting_descriptors < now) {
     update_router_descriptor_downloads(now);
     update_extrainfo_downloads(now);
+    update_microdesc_downloads(now);
     if (options->UseBridges)
       fetch_bridge_descriptors(now);
     if (router_have_minimum_dir_info())
diff --git a/src/or/microdesc.c b/src/or/microdesc.c
index e8f3e7c59..e42d55a1d 100644
--- a/src/or/microdesc.c
+++ b/src/or/microdesc.c
@@ -3,8 +3,12 @@
 
 #include "or.h"
 #include "config.h"
+#include "directory.h"
 #include "microdesc.h"
 #include "routerparse.h"
+#include "networkstatus.h"
+#include "routerlist.h"
+#include "dirserv.h"
 
 /** A data structure to hold a bunch of cached microdescriptors.  There are
  * two active files in the cache: a "cache file" that we mmap, and a "journal
@@ -119,15 +123,19 @@ get_microdesc_cache(void)
  * ending at <b>eos</b>, and store them in <b>cache</b>.  If <b>no-save</b>,
  * mark them as non-writable to disk.  If <b>where</b> is SAVED_IN_CACHE,
  * leave their bodies as pointers to the mmap'd cache.  If where is
- * <b>SAVED_NOWHERE</b>, do not allow annotations.  Return a list of the added
- * microdescriptors.  */
+ * <b>SAVED_NOWHERE</b>, do not allow annotations.  If listed_at is positive,
+ * set the last_listed field of every microdesc to listed_at.  If
+ * requested_digests is non-null, then it contains a list of digests we mean
+ * to allow, so we should reject any non-requested microdesc with a different
+ * digest, and alter the list to contain only the digests of those microdescs we
+ * didn't find.
+ * Return a list of the added microdescriptors.  */
 smartlist_t *
 microdescs_add_to_cache(microdesc_cache_t *cache,
                         const char *s, const char *eos, saved_location_t where,
-                        int no_save)
+                        int no_save, time_t listed_at,
+                        smartlist_t *requested_digests256)
 {
-  /*XXXX need an argument that sets last_listed as appropriate. */
-
   smartlist_t *descriptors, *added;
   const int allow_annotations = (where != SAVED_NOWHERE);
   const int copy_body = (where != SAVED_IN_CACHE);
@@ -135,6 +143,33 @@ microdescs_add_to_cache(microdesc_cache_t *cache,
   descriptors = microdescs_parse_from_string(s, eos,
                                              allow_annotations,
                                              copy_body);
+  if (listed_at > 0) {
+    SMARTLIST_FOREACH(descriptors, microdesc_t *, md,
+                      md->last_listed = listed_at);
+  }
+  if (requested_digests256) {
+    digestmap_t *requested; /* XXXX actuqlly we should just use a
+                               digest256map */
+    requested = digestmap_new();
+    SMARTLIST_FOREACH(requested_digests256, const char *, cp,
+      digestmap_set(requested, cp, (void*)1));
+    SMARTLIST_FOREACH_BEGIN(descriptors, microdesc_t *, md) {
+      if (digestmap_get(requested, md->digest)) {
+        digestmap_set(requested, md->digest, (void*)2);
+      } else {
+        log_fn(LOG_PROTOCOL_WARN, LD_DIR, "Received non-requested microcdesc");
+        microdesc_free(md);
+        SMARTLIST_DEL_CURRENT(descriptors, md);
+      }
+    } SMARTLIST_FOREACH_END(md);
+    SMARTLIST_FOREACH_BEGIN(requested_digests256, char *, cp) {
+      if (digestmap_get(requested, cp) == (void*)2) {
+        tor_free(cp);
+        SMARTLIST_DEL_CURRENT(requested_digests256, cp);
+      }
+    } SMARTLIST_FOREACH_END(cp);
+    digestmap_free(requested, NULL);
+  }
 
   added = microdescs_add_list_to_cache(cache, descriptors, where, no_save);
   smartlist_free(descriptors);
@@ -251,7 +286,7 @@ microdesc_cache_reload(microdesc_cache_t *cache)
   mm = cache->cache_content = tor_mmap_file(cache->cache_fname);
   if (mm) {
     added = microdescs_add_to_cache(cache, mm->data, mm->data+mm->size,
-                                    SAVED_IN_CACHE, 0);
+                                    SAVED_IN_CACHE, 0, -1, NULL);
     if (added) {
       total += smartlist_len(added);
       smartlist_free(added);
@@ -263,7 +298,7 @@ microdesc_cache_reload(microdesc_cache_t *cache)
   if (journal_content) {
     added = microdescs_add_to_cache(cache, journal_content,
                                     journal_content+st.st_size,
-                                    SAVED_IN_JOURNAL, 0);
+                                    SAVED_IN_JOURNAL, 0, -1, NULL);
     if (added) {
       total += smartlist_len(added);
       smartlist_free(added);
@@ -412,3 +447,69 @@ microdesc_average_size(microdesc_cache_t *cache)
   return (size_t)(cache->total_len_seen / cache->n_seen);
 }
 
+/** Return a smartlist of all the sha256 digest of the microdescriptors that
+ * are listed in <b>ns</b> but not present in <b>cache</b>. Returns pointers
+ * to internals of <b>ns</b>; you should not free the members of the resulting
+ * smartlist.  Omit all microdescriptors whose digest appear in <b>skip</b>. */
+smartlist_t *
+microdesc_list_missing_digest256(networkstatus_t *ns, microdesc_cache_t *cache,
+                                 int downloadable_only, digestmap_t *skip)
+{
+  smartlist_t *result = smartlist_create();
+  time_t now = time(NULL);
+  tor_assert(ns->flavor == FLAV_MICRODESC);
+  SMARTLIST_FOREACH_BEGIN(ns->routerstatus_list, routerstatus_t *, rs) {
+    if (microdesc_cache_lookup_by_digest256(cache, rs->descriptor_digest))
+      continue;
+    if (downloadable_only &&
+        !download_status_is_ready(&rs->dl_status, now,
+                                  MAX_MICRODESC_DOWNLOAD_FAILURES))
+      continue;
+    if (skip && digestmap_get(skip, rs->descriptor_digest))
+      continue;
+    /* XXXX Also skip if we're a noncache and wouldn't use this router.
+     * XXXX NM Microdesc
+     */
+    smartlist_add(result, rs->descriptor_digest);
+  } SMARTLIST_FOREACH_END(rs);
+  return result;
+}
+
+/** DOCDOC */
+void
+update_microdesc_downloads(time_t now)
+{
+  or_options_t *options = get_options();
+  networkstatus_t *consensus;
+  smartlist_t *missing;
+  digestmap_t *pending;
+
+  if (should_delay_dir_fetches(options))
+    return;
+  if (directory_too_idle_to_fetch_descriptors(options, now))
+    return;
+
+  consensus = networkstatus_get_reasonably_live_consensus(now, FLAV_MICRODESC);
+  if (!consensus)
+    return;
+
+  if (!directory_caches_dir_info(options)) {
+    /* Right now, only caches fetch microdescriptors.
+     * XXXX NM Microdescs */
+    return;
+  }
+
+  pending = digestmap_new();
+  list_pending_microdesc_downloads(pending);
+
+  missing = microdesc_list_missing_digest256(consensus,
+                                             get_microdesc_cache(),
+                                             1,
+                                             pending);
+  digestmap_free(pending, NULL);
+
+  launch_descriptor_downloads(DIR_PURPOSE_FETCH_MICRODESC,
+                              missing, NULL, now);
+
+  smartlist_free(missing);
+}
diff --git a/src/or/microdesc.h b/src/or/microdesc.h
index 2d1a60ad0..7cba3a385 100644
--- a/src/or/microdesc.h
+++ b/src/or/microdesc.h
@@ -16,7 +16,8 @@ microdesc_cache_t *get_microdesc_cache(void);
 
 smartlist_t *microdescs_add_to_cache(microdesc_cache_t *cache,
                         const char *s, const char *eos, saved_location_t where,
-                        int no_save);
+                        int no_save, time_t listed_at,
+                        smartlist_t *requested_digests256);
 smartlist_t *microdescs_add_list_to_cache(microdesc_cache_t *cache,
                         smartlist_t *descriptors, saved_location_t where,
                         int no_save);
@@ -30,8 +31,16 @@ microdesc_t *microdesc_cache_lookup_by_digest256(microdesc_cache_t *cache,
 
 size_t microdesc_average_size(microdesc_cache_t *cache);
 
+smartlist_t *microdesc_list_missing_digest256(networkstatus_t *ns,
+                                              microdesc_cache_t *cache,
+                                              int downloadable_only,
+                                              digestmap_t *skip);
+
 void microdesc_free(microdesc_t *md);
 void microdesc_free_all(void);
 
+void update_microdesc_downloads(time_t now);
+
+
 #endif
 
diff --git a/src/or/networkstatus.c b/src/or/networkstatus.c
index 4ccd1aed4..704e66525 100644
--- a/src/or/networkstatus.c
+++ b/src/or/networkstatus.c
@@ -978,21 +978,25 @@ networkstatus_get_v2_list(void)
 }
 
 /** Return the consensus view of the status of the router whose current
- * <i>descriptor</i> digest is <b>digest</b>, or NULL if no such router is
- * known. */
+ * <i>descriptor</i> digest in <b>consensus</b> is <b>digest</b>, or NULL if
+ * no such router is known. */
 routerstatus_t *
-router_get_consensus_status_by_descriptor_digest(const char *digest)
+router_get_consensus_status_by_descriptor_digest(networkstatus_t *consensus,
+                                                 const char *digest)
 {
-  if (!current_consensus) return NULL;
-  if (!current_consensus->desc_digest_map) {
-    digestmap_t * m = current_consensus->desc_digest_map = digestmap_new();
-    SMARTLIST_FOREACH(current_consensus->routerstatus_list,
+  if (!consensus)
+    consensus = current_consensus;
+  if (!consensus)
+    return NULL;
+  if (!consensus->desc_digest_map) {
+    digestmap_t *m = consensus->desc_digest_map = digestmap_new();
+    SMARTLIST_FOREACH(consensus->routerstatus_list,
                       routerstatus_t *, rs,
      {
        digestmap_set(m, rs->descriptor_digest, rs);
      });
   }
-  return digestmap_get(current_consensus->desc_digest_map, digest);
+  return digestmap_get(consensus->desc_digest_map, digest);
 }
 
 /** Given the digest of a router descriptor, return its current download
@@ -1001,7 +1005,10 @@ download_status_t *
 router_get_dl_status_by_descriptor_digest(const char *d)
 {
   routerstatus_t *rs;
-  if ((rs = router_get_consensus_status_by_descriptor_digest(d)))
+  if (!current_ns_consensus)
+    return NULL;
+  if ((rs = router_get_consensus_status_by_descriptor_digest(
+                                                 current_ns_consensus, d)))
     return &rs->dl_status;
   if (v2_download_status_map)
     return digestmap_get(v2_download_status_map, d);
@@ -2118,7 +2125,7 @@ signed_descs_update_status_from_consensus_networkstatus(smartlist_t *descs)
     char dummy[DIGEST_LEN];
     /* instantiates the digest map. */
     memset(dummy, 0, sizeof(dummy));
-    router_get_consensus_status_by_descriptor_digest(dummy);
+    router_get_consensus_status_by_descriptor_digest(ns, dummy);
   }
   SMARTLIST_FOREACH(descs, signed_descriptor_t *, d,
   {
diff --git a/src/or/networkstatus.h b/src/or/networkstatus.h
index 566171c79..adaddc498 100644
--- a/src/or/networkstatus.h
+++ b/src/or/networkstatus.h
@@ -48,7 +48,8 @@ const smartlist_t *networkstatus_get_v2_list(void);
 download_status_t *router_get_dl_status_by_descriptor_digest(const char *d);
 routerstatus_t *router_get_consensus_status_by_id(const char *digest);
 routerstatus_t *router_get_consensus_status_by_descriptor_digest(
-                                                        const char *digest);
+                                   networkstatus_t *consensus,
+                                   const char *digest);
 routerstatus_t *router_get_consensus_status_by_nickname(const char *nickname,
                                                        int warn_if_unnamed);
 const char *networkstatus_get_router_digest_by_nickname(const char *nickname);
diff --git a/src/or/or.h b/src/or/or.h
index cd542797c..4741cc341 100644
--- a/src/or/or.h
+++ b/src/or/or.h
@@ -391,7 +391,9 @@ typedef enum {
 /** A connection to a hidden service directory server: download a v2 rendezvous
  * descriptor. */
 #define DIR_PURPOSE_FETCH_RENDDESC_V2 18
-#define _DIR_PURPOSE_MAX 18
+/** A connection to a directory server: download a microdescriptor. */
+#define DIR_PURPOSE_FETCH_MICRODESC 19
+#define _DIR_PURPOSE_MAX 19
 
 /** True iff <b>p</b> is a purpose corresponding to uploading data to a
  * directory server. */
@@ -1191,8 +1193,13 @@ typedef struct edge_connection_t {
 typedef struct dir_connection_t {
   connection_t _base;
 
-  char *requested_resource; /**< Which 'resource' did we ask the directory
-                             * for? */
+ /** Which 'resource' did we ask the directory for? This is typically the part
+  * of the URL string that defines, relative to the directory conn purpose,
+  * what thing we want.  For example, in router descriptor downloads by
+  * descriptor digest, it contains "d/", then one ore more +-separated
+  * fingerprints.
+  **/
+  char *requested_resource;
   unsigned int dirconn_direct:1; /**< Is this dirconn direct, or via Tor? */
 
   /* Used only for server sides of some dir connections, to implement
@@ -1690,6 +1697,10 @@ typedef struct microdesc_t {
  * up? */
 #define MAX_ROUTERDESC_DOWNLOAD_FAILURES 8
 
+/** How many times will we try to download a microdescriptor before giving
+ * up? */
+#define MAX_MICRODESC_DOWNLOAD_FAILURES 8
+
 /** Contents of a v2 (non-consensus, non-vote) network status object. */
 typedef struct networkstatus_v2_t {
   /** When did we receive the network-status document? */
@@ -3517,6 +3528,8 @@ typedef struct trusted_dir_server_t {
  *  fetches to _any_ single directory server.]
  */
 #define PDS_NO_EXISTING_SERVERDESC_FETCH (1<<3)
+#define PDS_NO_EXISTING_MICRODESC_FETCH (1<<4)
+
 #define _PDS_PREFER_TUNNELED_DIR_CONNS (1<<16)
 
 /** Possible ways to weight routers when choosing one randomly.  See
diff --git a/src/or/routerlist.c b/src/or/routerlist.c
index 27b870da3..e55973f4c 100644
--- a/src/or/routerlist.c
+++ b/src/or/routerlist.c
@@ -22,6 +22,7 @@
 #include "geoip.h"
 #include "hibernate.h"
 #include "main.h"
+#include "microdesc.h"
 #include "networkstatus.h"
 #include "policies.h"
 #include "reasons.h"
@@ -44,9 +45,6 @@ static routerstatus_t *router_pick_trusteddirserver_impl(
 static void mark_all_trusteddirservers_up(void);
 static int router_nickname_matches(routerinfo_t *router, const char *nickname);
 static void trusted_dir_server_free(trusted_dir_server_t *ds);
-static void launch_router_descriptor_downloads(smartlist_t *downloadable,
-                                               routerstatus_t *source,
-                                               time_t now);
 static int signed_desc_digest_is_recognized(signed_descriptor_t *desc);
 static void update_router_have_minimum_dir_info(void);
 static const char *signed_descriptor_get_body_impl(signed_descriptor_t *desc,
@@ -1047,7 +1045,8 @@ router_pick_trusteddirserver(authority_type_t type, int flags)
     /* If the reason that we got no server is that servers are "busy",
      * we must be excluding good servers because we already have serverdesc
      * fetches with them.  Do not mark down servers up because of this. */
-    tor_assert((flags & PDS_NO_EXISTING_SERVERDESC_FETCH));
+    tor_assert((flags & (PDS_NO_EXISTING_SERVERDESC_FETCH|
+                         PDS_NO_EXISTING_MICRODESC_FETCH)));
     return NULL;
   }
 
@@ -1174,6 +1173,7 @@ router_pick_trusteddirserver_impl(authority_type_t type, int flags,
   const int fascistfirewall = ! (flags & PDS_IGNORE_FASCISTFIREWALL);
   const int prefer_tunnel = (flags & _PDS_PREFER_TUNNELED_DIR_CONNS);
   const int no_serverdesc_fetching =(flags & PDS_NO_EXISTING_SERVERDESC_FETCH);
+  const int no_microdesc_fetching =(flags & PDS_NO_EXISTING_MICRODESC_FETCH);
   int n_busy = 0;
 
   if (!trusted_dir_servers)
@@ -1212,6 +1212,13 @@ router_pick_trusteddirserver_impl(authority_type_t type, int flags,
           continue;
         }
       }
+      if (no_microdesc_fetching) {
+        if (connection_get_by_type_addr_port_purpose(
+             CONN_TYPE_DIR, &addr, d->dir_port, DIR_PURPOSE_FETCH_MICRODESC)) {
+          ++n_busy;
+          continue;
+        }
+      }
 
       if (prefer_tunnel &&
           d->or_port &&
@@ -3874,6 +3881,7 @@ routerlist_retry_directory_downloads(time_t now)
   router_reset_descriptor_download_failures();
   update_networkstatus_downloads(now);
   update_router_descriptor_downloads(now);
+  update_microdesc_downloads(now);
 }
 
 /** Return 1 if all running sufficiently-stable routers will reject
@@ -4035,7 +4043,9 @@ any_trusted_dir_is_v1_authority(void)
 /** For every current directory connection whose purpose is <b>purpose</b>,
  * and where the resource being downloaded begins with <b>prefix</b>, split
  * rest of the resource into base16 fingerprints, decode them, and set the
- * corresponding elements of <b>result</b> to a nonzero value. */
+ * corresponding elements of <b>result</b> to a nonzero value.
+ * DOCDOC purpose==microdesc
+ */
 static void
 list_pending_downloads(digestmap_t *result,
                        int purpose, const char *prefix)
@@ -4043,20 +4053,23 @@ list_pending_downloads(digestmap_t *result,
   const size_t p_len = strlen(prefix);
   smartlist_t *tmp = smartlist_create();
   smartlist_t *conns = get_connection_array();
+  int flags = DSR_HEX;
+  if (purpose == DIR_PURPOSE_FETCH_MICRODESC)
+    flags = DSR_DIGEST256|DSR_BASE64;
 
   tor_assert(result);
 
-  SMARTLIST_FOREACH(conns, connection_t *, conn,
-  {
+  SMARTLIST_FOREACH_BEGIN(conns, connection_t *, conn) {
     if (conn->type == CONN_TYPE_DIR &&
         conn->purpose == purpose &&
         !conn->marked_for_close) {
       const char *resource = TO_DIR_CONN(conn)->requested_resource;
       if (!strcmpstart(resource, prefix))
         dir_split_resource_into_fingerprints(resource + p_len,
-                                             tmp, NULL, DSR_HEX);
+                                             tmp, NULL, flags);
     }
-  });
+  } SMARTLIST_FOREACH_END(conn);
+
   SMARTLIST_FOREACH(tmp, char *, d,
                     {
                       digestmap_set(result, d, (void*)1);
@@ -4076,10 +4089,18 @@ list_pending_descriptor_downloads(digestmap_t *result, int extrainfo)
   list_pending_downloads(result, purpose, "d/");
 }
 
-/** Launch downloads for all the descriptors whose digests are listed
- * as digests[i] for lo <= i < hi.  (Lo and hi may be out of range.)
- * If <b>source</b> is given, download from <b>source</b>; otherwise,
- * download from an appropriate random directory server.
+/** DOCDOC */
+/*XXXX NM should use digest256, if one comes into being. */
+void
+list_pending_microdesc_downloads(digestmap_t *result)
+{
+  list_pending_downloads(result, DIR_PURPOSE_FETCH_MICRODESC, "d/");
+}
+
+/** Launch downloads for all the descriptors whose digests or digests256
+ * are listed as digests[i] for lo <= i < hi.  (Lo and hi may be out of
+ * range.)  If <b>source</b> is given, download from <b>source</b>;
+ * otherwise, download from an appropriate random directory server.
  */
 static void
 initiate_descriptor_downloads(routerstatus_t *source,
@@ -4090,6 +4111,20 @@ initiate_descriptor_downloads(routerstatus_t *source,
   int i, n = hi-lo;
   char *resource, *cp;
   size_t r_len;
+
+  int digest_len = DIGEST_LEN, enc_digest_len = HEX_DIGEST_LEN;
+  char sep = '+';
+  int b64_256 = 0;
+
+  if (purpose == DIR_PURPOSE_FETCH_MICRODESC) {
+    /* Microdescriptors are downloaded by "-"-separated base64-encoded
+     * 256-bit digests. */
+    digest_len = DIGEST256_LEN;
+    enc_digest_len = BASE64_DIGEST256_LEN;
+    sep = '-';
+    b64_256 = 1;
+  }
+
   if (n <= 0)
     return;
   if (lo < 0)
@@ -4097,15 +4132,19 @@ initiate_descriptor_downloads(routerstatus_t *source,
   if (hi > smartlist_len(digests))
     hi = smartlist_len(digests);
 
-  r_len = 8 + (HEX_DIGEST_LEN+1)*n;
+  r_len = 8 + (enc_digest_len+1)*n;
   cp = resource = tor_malloc(r_len);
   memcpy(cp, "d/", 2);
   cp += 2;
   for (i = lo; i < hi; ++i) {
-    base16_encode(cp, r_len-(cp-resource),
-                  smartlist_get(digests,i), DIGEST_LEN);
-    cp += HEX_DIGEST_LEN;
-    *cp++ = '+';
+    if (b64_256) {
+      digest256_to_base64(cp, smartlist_get(digests, i));
+    } else {
+      base16_encode(cp, r_len-(cp-resource),
+                    smartlist_get(digests,i), digest_len);
+    }
+    cp += enc_digest_len;
+    *cp++ = sep;
   }
   memcpy(cp-1, ".z", 3);
 
@@ -4152,6 +4191,7 @@ client_would_use_router(routerstatus_t *rs, time_t now, or_options_t *options)
  *   So use 96 because it's a nice number.
  */
 #define MAX_DL_PER_REQUEST 96
+#define MAX_MICRODESC_DL_PER_REQUEST 92
 /** Don't split our requests so finely that we are requesting fewer than
  * this number per server. */
 #define MIN_DL_PER_REQUEST 4
@@ -4166,21 +4206,33 @@ client_would_use_router(routerstatus_t *rs, time_t now, or_options_t *options)
  * them until they have more, or until this amount of time has passed. */
 #define MAX_CLIENT_INTERVAL_WITHOUT_REQUEST (10*60)
 
-/** Given a list of router descriptor digests in <b>downloadable</b>, decide
- * whether to delay fetching until we have more.  If we don't want to delay,
- * launch one or more requests to the appropriate directory authorities. */
-static void
-launch_router_descriptor_downloads(smartlist_t *downloadable,
-                                   routerstatus_t *source, time_t now)
+/** Given a <b>purpose</b> (FETCH_MICRODESC or FETCH_SERVERDESC) and a list of
+ * router descriptor digests or microdescriptor digest256s in
+ * <b>downloadable</b>, decide whether to delay fetching until we have more.
+ * If we don't want to delay, launch one or more requests to the appropriate
+ * directory authorities.
+ */
+void
+launch_descriptor_downloads(int purpose,
+                            smartlist_t *downloadable,
+                            routerstatus_t *source, time_t now)
 {
   int should_delay = 0, n_downloadable;
   or_options_t *options = get_options();
+  const char *descname;
+
+  tor_assert(purpose == DIR_PURPOSE_FETCH_SERVERDESC ||
+             purpose == DIR_PURPOSE_FETCH_MICRODESC);
+
+  descname = (purpose == DIR_PURPOSE_FETCH_SERVERDESC) ?
+    "routerdesc" : "microdesc";
 
   n_downloadable = smartlist_len(downloadable);
   if (!directory_fetches_dir_info_early(options)) {
     if (n_downloadable >= MAX_DL_TO_DELAY) {
       log_debug(LD_DIR,
-             "There are enough downloadable routerdescs to launch requests.");
+                "There are enough downloadable %ss to launch requests.",
+                descname);
       should_delay = 0;
     } else {
       should_delay = (last_routerdesc_download_attempted +
@@ -4188,13 +4240,15 @@ launch_router_descriptor_downloads(smartlist_t *downloadable,
       if (!should_delay && n_downloadable) {
         if (last_routerdesc_download_attempted) {
           log_info(LD_DIR,
-                   "There are not many downloadable routerdescs, but we've "
+                   "There are not many downloadable %ss, but we've "
                    "been waiting long enough (%d seconds). Downloading.",
+                   descname,
                    (int)(now-last_routerdesc_download_attempted));
         } else {
           log_info(LD_DIR,
-                 "There are not many downloadable routerdescs, but we haven't "
-                 "tried downloading descriptors recently. Downloading.");
+                   "There are not many downloadable %ss, but we haven't "
+                   "tried downloading descriptors recently. Downloading.",
+                   descname);
         }
       }
     }
@@ -4221,12 +4275,20 @@ launch_router_descriptor_downloads(smartlist_t *downloadable,
        * update_router_descriptor_downloads() later on, once the connections
        * have succeeded or failed.
        */
-      pds_flags |= PDS_NO_EXISTING_SERVERDESC_FETCH;
+      pds_flags |= (purpose == DIR_PURPOSE_FETCH_MICRODESC) ?
+        PDS_NO_EXISTING_MICRODESC_FETCH :
+        PDS_NO_EXISTING_SERVERDESC_FETCH;
+
     }
 
     n_per_request = CEIL_DIV(n_downloadable, MIN_REQUESTS);
-    if (n_per_request > MAX_DL_PER_REQUEST)
-      n_per_request = MAX_DL_PER_REQUEST;
+    if (purpose == DIR_PURPOSE_FETCH_MICRODESC) {
+      if (n_per_request > MAX_MICRODESC_DL_PER_REQUEST)
+        n_per_request = MAX_MICRODESC_DL_PER_REQUEST;
+    } else {
+      if (n_per_request > MAX_DL_PER_REQUEST)
+        n_per_request = MAX_DL_PER_REQUEST;
+    }
     if (n_per_request < MIN_DL_PER_REQUEST)
       n_per_request = MIN_DL_PER_REQUEST;
 
@@ -4241,7 +4303,7 @@ launch_router_descriptor_downloads(smartlist_t *downloadable,
              req_plural, n_downloadable, rtr_plural, n_per_request);
     smartlist_sort_digests(downloadable);
     for (i=0; i < n_downloadable; i += n_per_request) {
-      initiate_descriptor_downloads(source, DIR_PURPOSE_FETCH_SERVERDESC,
+      initiate_descriptor_downloads(source, purpose,
                                     downloadable, i, i+n_per_request,
                                     pds_flags);
     }
@@ -4514,7 +4576,8 @@ update_consensus_router_descriptor_downloads(time_t now, int is_vote,
            smartlist_len(downloadable), n_delayed, n_have, n_in_oldrouters,
            n_would_reject, n_wouldnt_use, n_inprogress);
 
-  launch_router_descriptor_downloads(downloadable, source, now);
+  launch_descriptor_downloads(DIR_PURPOSE_FETCH_SERVERDESC,
+                              downloadable, source, now);
 
   digestmap_free(map, NULL);
  done:
diff --git a/src/or/routerlist.h b/src/or/routerlist.h
index 574bce7ff..804be2aba 100644
--- a/src/or/routerlist.h
+++ b/src/or/routerlist.h
@@ -192,5 +192,11 @@ int hid_serv_get_responsible_directories(smartlist_t *responsible_dirs,
 int hid_serv_acting_as_directory(void);
 int hid_serv_responsible_for_desc_id(const char *id);
 
+void list_pending_microdesc_downloads(digestmap_t *result);
+void launch_descriptor_downloads(int purpose,
+                                 smartlist_t *downloadable,
+                                 routerstatus_t *source,
+                                 time_t now);
+
 #endif