/* Copyright (c) 2001 Matej Pfajfar.
 * Copyright (c) 2001-2004, Roger Dingledine.
 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
 * Copyright (c) 2007-2012, The Tor Project, Inc. */
/* See LICENSE for licensing information */

/**
 * \file entrynodes.c
 * \brief Code to manage our fixed first nodes for various functions.
 *
 * Entry nodes can be guards (for general use) or bridges (for censorship
 * circumvention).
 **/

#include "or.h"
#include "circuitbuild.h"
#include "circuitstats.h"
#include "config.h"
#include "confparse.h"
#include "connection.h"
#include "connection_or.h"
#include "control.h"
#include "directory.h"
#include "entrynodes.h"
#include "main.h"
#include "nodelist.h"
#include "policies.h"
#include "router.h"
#include "routerlist.h"
#include "routerparse.h"
#include "routerset.h"
#include "transports.h"
#include "statefile.h"

/** Information about a configured bridge. Currently this just matches the
 * ones in the torrc file, but one day we may be able to learn about new
 * bridges on our own, and remember them in the state file. */
typedef struct {
  /** Address of the bridge. */
  tor_addr_t addr;
  /** TLS port for the bridge. */
  uint16_t port;
  /** Boolean: We are re-parsing our bridge list, and we are going to remove
   * this one if we don't find it in the list of configured bridges. */
  unsigned marked_for_removal : 1;
  /** Expected identity digest, or all zero bytes if we don't know what the
   * digest should be. */
  char identity[DIGEST_LEN];

  /** Name of pluggable transport protocol taken from its config line. */
  char *transport_name;

  /** When should we next try to fetch a descriptor for this bridge? */
  download_status_t fetch_status;
} bridge_info_t;

/** A list of our chosen entry guards. */
static smartlist_t *entry_guards = NULL;
/** A value of 1 means that the entry_guards list has changed
 * and those changes need to be flushed to disk. */
static int entry_guards_dirty = 0;

static void bridge_free(bridge_info_t *bridge);

/** Return the list of entry guards, creating it if necessary. */
const smartlist_t *
get_entry_guards(void)
{
  if (! entry_guards)
    entry_guards = smartlist_new();
  return entry_guards;
}

/** Check whether the entry guard <b>e</b> is usable, given the directory
 * authorities' opinion about the router (stored in <b>ri</b>) and the user's
 * configuration (in <b>options</b>). Set <b>e</b>-&gt;bad_since
 * accordingly. Return true iff the entry guard's status changes.
 *
 * If it's not usable, set *<b>reason</b> to a static string explaining why.
 */
static int
entry_guard_set_status(entry_guard_t *e, const node_t *node,
                       time_t now, const or_options_t *options,
                       const char **reason)
{
  char buf[HEX_DIGEST_LEN+1];
  int changed = 0;

  *reason = NULL;

  /* Do we want to mark this guard as bad? */
  if (!node)
    *reason = "unlisted";
  else if (!node->is_running)
    *reason = "down";
  else if (options->UseBridges && (!node->ri ||
                                   node->ri->purpose != ROUTER_PURPOSE_BRIDGE))
    *reason = "not a bridge";
  else if (options->UseBridges && !node_is_a_configured_bridge(node))
    *reason = "not a configured bridge";
  else if (!options->UseBridges && !node->is_possible_guard &&
           !routerset_contains_node(options->EntryNodes,node))
    *reason = "not recommended as a guard";
  else if (routerset_contains_node(options->ExcludeNodes, node))
    *reason = "excluded";
  else if (e->path_bias_disabled)
    *reason = "path-biased";

  if (*reason && ! e->bad_since) {
    /* Router is newly bad. */
    base16_encode(buf, sizeof(buf), e->identity, DIGEST_LEN);
    log_info(LD_CIRC, "Entry guard %s (%s) is %s: marking as unusable.",
             e->nickname, buf, *reason);

    e->bad_since = now;
    control_event_guard(e->nickname, e->identity, "BAD");
    changed = 1;
  } else if (!*reason && e->bad_since) {
    /* There's nothing wrong with the router any more. */
    base16_encode(buf, sizeof(buf), e->identity, DIGEST_LEN);
    log_info(LD_CIRC, "Entry guard %s (%s) is no longer unusable: "
             "marking as ok.", e->nickname, buf);

    e->bad_since = 0;
    control_event_guard(e->nickname, e->identity, "GOOD");
    changed = 1;
  }
  return changed;
}

/** Return true iff enough time has passed since we last tried to connect
 * to the unreachable guard <b>e</b> that we're willing to try again. */
static int
entry_is_time_to_retry(entry_guard_t *e, time_t now)
{
  long diff;
  if (e->last_attempted < e->unreachable_since)
    return 1;
  diff = now - e->unreachable_since;
  if (diff < 6*60*60)
    return now > (e->last_attempted + 60*60);
  else if (diff < 3*24*60*60)
    return now > (e->last_attempted + 4*60*60);
  else if (diff < 7*24*60*60)
    return now > (e->last_attempted + 18*60*60);
  else
    return now > (e->last_attempted + 36*60*60);
}

/** Return the node corresponding to <b>e</b>, if <b>e</b> is
 * working well enough that we are willing to use it as an entry
 * right now. (Else return NULL.) In particular, it must be
 * - Listed as either up or never yet contacted;
 * - Present in the routerlist;
 * - Listed as 'stable' or 'fast' by the current dirserver consensus,
 *   if demanded by <b>need_uptime</b> or <b>need_capacity</b>
 *   (unless it's a configured EntryNode);
 * - Allowed by our current ReachableORAddresses config option; and
 * - Currently thought to be reachable by us (unless <b>assume_reachable</b>
 *   is true).
 *
 * If the answer is no, set *<b>msg</b> to an explanation of why.
 */
static INLINE const node_t *
entry_is_live(entry_guard_t *e, int need_uptime, int need_capacity,
              int assume_reachable, const char **msg)
{
  const node_t *node;
  const or_options_t *options = get_options();
  tor_assert(msg);

  if (e->path_bias_disabled) {
    *msg = "path-biased";
    return NULL;
  }
  if (e->bad_since) {
    *msg = "bad";
    return NULL;
  }
  /* no good if it's unreachable, unless assume_unreachable or can_retry. */
  if (!assume_reachable && !e->can_retry &&
      e->unreachable_since && !entry_is_time_to_retry(e, time(NULL))) {
    *msg = "unreachable";
    return NULL;
  }
  node = node_get_by_id(e->identity);
  if (!node || !node_has_descriptor(node)) {
    *msg = "no descriptor";
    return NULL;
  }
  if (get_options()->UseBridges) {
    if (node_get_purpose(node) != ROUTER_PURPOSE_BRIDGE) {
      *msg = "not a bridge";
      return NULL;
    }
    if (!node_is_a_configured_bridge(node)) {
      *msg = "not a configured bridge";
      return NULL;
    }
  } else { /* !get_options()->UseBridges */
    if (node_get_purpose(node) != ROUTER_PURPOSE_GENERAL) {
      *msg = "not general-purpose";
      return NULL;
    }
  }
  if (routerset_contains_node(options->EntryNodes, node)) {
    /* they asked for it, they get it */
    need_uptime = need_capacity = 0;
  }
  if (node_is_unreliable(node, need_uptime, need_capacity, 0)) {
    *msg = "not fast/stable";
    return NULL;
  }
  if (!fascist_firewall_allows_node(node)) {
    *msg = "unreachable by config";
    return NULL;
  }
  return node;
}

/** Return the number of entry guards that we think are usable. */
int
num_live_entry_guards(void)
{
  int n = 0;
  const char *msg;
  if (! entry_guards)
    return 0;
  SMARTLIST_FOREACH(entry_guards, entry_guard_t *, entry,
    {
      if (entry_is_live(entry, 0, 1, 0, &msg))
        ++n;
    });
  return n;
}

/** If <b>digest</b> matches the identity of any node in the
 * entry_guards list, return that node. Else return NULL. */
entry_guard_t *
entry_guard_get_by_id_digest(const char *digest)
{
  SMARTLIST_FOREACH(entry_guards, entry_guard_t *, entry,
                    if (tor_memeq(digest, entry->identity, DIGEST_LEN))
                      return entry;
                   );
  return NULL;
}

/** Dump a description of our list of entry guards to the log at level
 * <b>severity</b>. */
static void
log_entry_guards(int severity)
{
  smartlist_t *elements = smartlist_new();
  char *s;

  SMARTLIST_FOREACH_BEGIN(entry_guards, entry_guard_t *, e)
    {
      const char *msg = NULL;
      if (entry_is_live(e, 0, 1, 0, &msg))
        smartlist_add_asprintf(elements, "%s [%s] (up %s)",
                     e->nickname,
                     hex_str(e->identity, DIGEST_LEN),
                     e->made_contact ? "made-contact" : "never-contacted");
      else
        smartlist_add_asprintf(elements, "%s [%s] (%s, %s)",
                     e->nickname,
                     hex_str(e->identity, DIGEST_LEN),
                     msg,
                     e->made_contact ? "made-contact" : "never-contacted");
    }
  SMARTLIST_FOREACH_END(e);

  s = smartlist_join_strings(elements, ",", 0, NULL);
  SMARTLIST_FOREACH(elements, char*, cp, tor_free(cp));
  smartlist_free(elements);
  log_fn(severity,LD_CIRC,"%s",s);
  tor_free(s);
}

/** Called when one or more guards that we would previously have used for some
 * purpose are no longer in use because a higher-priority guard has become
 * usable again. */
static void
control_event_guard_deferred(void)
{
  /* XXXX We don't actually have a good way to figure out _how many_ entries
   * are live for some purpose.  We need an entry_is_even_slightly_live()
   * function for this to work right.  NumEntryGuards isn't reliable: if we
   * need guards with weird properties, we can have more than that number
   * live.
   **/
#if 0
  int n = 0;
  const char *msg;
  const or_options_t *options = get_options();
  if (!entry_guards)
    return;
  SMARTLIST_FOREACH(entry_guards, entry_guard_t *, entry,
    {
      if (entry_is_live(entry, 0, 1, 0, &msg)) {
        if (n++ == options->NumEntryGuards) {
          control_event_guard(entry->nickname, entry->identity, "DEFERRED");
          return;
        }
      }
    });
#endif
}

/** Add a new (preferably stable and fast) router to our
 * entry_guards list. Return a pointer to the router if we succeed,
 * or NULL if we can't find any more suitable entries.
 *
 * If <b>chosen</b> is defined, use that one, and if it's not
 * already in our entry_guards list, put it at the *beginning*.
 * Else, put the one we pick at the end of the list. */
static const node_t *
add_an_entry_guard(const node_t *chosen, int reset_status, int prepend)
{
  const node_t *node;
  entry_guard_t *entry;

  if (chosen) {
    node = chosen;
    entry = entry_guard_get_by_id_digest(node->identity);
    if (entry) {
      if (reset_status) {
        entry->bad_since = 0;
        entry->can_retry = 1;
      }
      return NULL;
    }
  } else {
    node = choose_good_entry_server(CIRCUIT_PURPOSE_C_GENERAL, NULL);
    if (!node)
      return NULL;
  }
  entry = tor_malloc_zero(sizeof(entry_guard_t));
  log_info(LD_CIRC, "Chose %s as new entry guard.",
           node_describe(node));
  strlcpy(entry->nickname, node_get_nickname(node), sizeof(entry->nickname));
  memcpy(entry->identity, node->identity, DIGEST_LEN);
  /* Choose expiry time smudged over the past month. The goal here
   * is to a) spread out when Tor clients rotate their guards, so they
   * don't all select them on the same day, and b) avoid leaving a
   * precise timestamp in the state file about when we first picked
   * this guard. For details, see the Jan 2010 or-dev thread. */
  entry->chosen_on_date = time(NULL) - crypto_rand_int(3600*24*30);
  entry->chosen_by_version = tor_strdup(VERSION);
  if (prepend)
    smartlist_insert(entry_guards, 0, entry);
  else
    smartlist_add(entry_guards, entry);
  control_event_guard(entry->nickname, entry->identity, "NEW");
  control_event_guard_deferred();
  log_entry_guards(LOG_INFO);
  return node;
}

/** If the use of entry guards is configured, choose more entry guards
 * until we have enough in the list. */
static void
pick_entry_guards(const or_options_t *options)
{
  int changed = 0;

  tor_assert(entry_guards);

  while (num_live_entry_guards() < options->NumEntryGuards) {
    if (!add_an_entry_guard(NULL, 0, 0))
      break;
    changed = 1;
  }
  if (changed)
    entry_guards_changed();
}

/** How long (in seconds) do we allow an entry guard to be nonfunctional,
 * unlisted, excluded, or otherwise nonusable before we give up on it? */
#define ENTRY_GUARD_REMOVE_AFTER (30*24*60*60)

/** Release all storage held by <b>e</b>. */
static void
entry_guard_free(entry_guard_t *e)
{
  if (!e)
    return;
  tor_free(e->chosen_by_version);
  tor_free(e);
}

/** Remove any entry guard which was selected by an unknown version of Tor,
 * or which was selected by a version of Tor that's known to select
 * entry guards badly, or which was selected more 2 months ago. */
/* XXXX The "obsolete guards" and "chosen long ago guards" things should
 * probably be different functions. */
static int
remove_obsolete_entry_guards(time_t now)
{
  int changed = 0, i;

  for (i = 0; i < smartlist_len(entry_guards); ++i) {
    entry_guard_t *entry = smartlist_get(entry_guards, i);
    const char *ver = entry->chosen_by_version;
    const char *msg = NULL;
    tor_version_t v;
    int version_is_bad = 0, date_is_bad = 0;
    if (!ver) {
      msg = "does not say what version of Tor it was selected by";
      version_is_bad = 1;
    } else if (tor_version_parse(ver, &v)) {
      msg = "does not seem to be from any recognized version of Tor";
      version_is_bad = 1;
    } else {
      char *tor_ver = NULL;
      tor_asprintf(&tor_ver, "Tor %s", ver);
      if ((tor_version_as_new_as(tor_ver, "0.1.0.10-alpha") &&
           !tor_version_as_new_as(tor_ver, "0.1.2.16-dev")) ||
          (tor_version_as_new_as(tor_ver, "0.2.0.0-alpha") &&
           !tor_version_as_new_as(tor_ver, "0.2.0.6-alpha")) ||
          /* above are bug 440; below are bug 1217 */
          (tor_version_as_new_as(tor_ver, "0.2.1.3-alpha") &&
           !tor_version_as_new_as(tor_ver, "0.2.1.23")) ||
          (tor_version_as_new_as(tor_ver, "0.2.2.0-alpha") &&
           !tor_version_as_new_as(tor_ver, "0.2.2.7-alpha"))) {
        msg = "was selected without regard for guard bandwidth";
        version_is_bad = 1;
      }
      tor_free(tor_ver);
    }
    if (!version_is_bad && entry->chosen_on_date + 3600*24*60 < now) {
      /* It's been 2 months since the date listed in our state file. */
      msg = "was selected several months ago";
      date_is_bad = 1;
    }

    if (version_is_bad || date_is_bad) { /* we need to drop it */
      char dbuf[HEX_DIGEST_LEN+1];
      tor_assert(msg);
      base16_encode(dbuf, sizeof(dbuf), entry->identity, DIGEST_LEN);
      log_fn(version_is_bad ? LOG_NOTICE : LOG_INFO, LD_CIRC,
             "Entry guard '%s' (%s) %s. (Version=%s.) Replacing it.",
             entry->nickname, dbuf, msg, ver?escaped(ver):"none");
      control_event_guard(entry->nickname, entry->identity, "DROPPED");
      entry_guard_free(entry);
      smartlist_del_keeporder(entry_guards, i--);
      log_entry_guards(LOG_INFO);
      changed = 1;
    }
  }

  return changed ? 1 : 0;
}

/** Remove all entry guards that have been down or unlisted for so
 * long that we don't think they'll come up again. Return 1 if we
 * removed any, or 0 if we did nothing. */
static int
remove_dead_entry_guards(time_t now)
{
  char dbuf[HEX_DIGEST_LEN+1];
  char tbuf[ISO_TIME_LEN+1];
  int i;
  int changed = 0;

  for (i = 0; i < smartlist_len(entry_guards); ) {
    entry_guard_t *entry = smartlist_get(entry_guards, i);
    if (entry->bad_since &&
        ! entry->path_bias_disabled &&
        entry->bad_since + ENTRY_GUARD_REMOVE_AFTER < now) {

      base16_encode(dbuf, sizeof(dbuf), entry->identity, DIGEST_LEN);
      format_local_iso_time(tbuf, entry->bad_since);
      log_info(LD_CIRC, "Entry guard '%s' (%s) has been down or unlisted "
               "since %s local time; removing.",
               entry->nickname, dbuf, tbuf);
      control_event_guard(entry->nickname, entry->identity, "DROPPED");
      entry_guard_free(entry);
      smartlist_del_keeporder(entry_guards, i);
      log_entry_guards(LOG_INFO);
      changed = 1;
    } else
      ++i;
  }
  return changed ? 1 : 0;
}

/** A new directory or router-status has arrived; update the down/listed
 * status of the entry guards.
 *
 * An entry is 'down' if the directory lists it as nonrunning.
 * An entry is 'unlisted' if the directory doesn't include it.
 *
 * Don't call this on startup; only on a fresh download. Otherwise we'll
 * think that things are unlisted.
 */
void
entry_guards_compute_status(const or_options_t *options, time_t now)
{
  int changed = 0;
  digestmap_t *reasons;

  if (! entry_guards)
    return;

  if (options->EntryNodes) /* reshuffle the entry guard list if needed */
    entry_nodes_should_be_added();

  reasons = digestmap_new();
  SMARTLIST_FOREACH_BEGIN(entry_guards, entry_guard_t *, entry)
    {
      const node_t *r = node_get_by_id(entry->identity);
      const char *reason = NULL;
      if (entry_guard_set_status(entry, r, now, options, &reason))
        changed = 1;

      if (entry->bad_since)
        tor_assert(reason);
      if (reason)
        digestmap_set(reasons, entry->identity, (char*)reason);
    }
  SMARTLIST_FOREACH_END(entry);

  if (remove_dead_entry_guards(now))
    changed = 1;
  if (remove_obsolete_entry_guards(now))
    changed = 1;

  if (changed) {
    SMARTLIST_FOREACH_BEGIN(entry_guards, entry_guard_t *, entry) {
      const char *reason = digestmap_get(reasons, entry->identity);
      const char *live_msg = "";
      const node_t *r = entry_is_live(entry, 0, 1, 0, &live_msg);
      log_info(LD_CIRC, "Summary: Entry %s [%s] is %s, %s%s%s, and %s%s.",
               entry->nickname,
               hex_str(entry->identity, DIGEST_LEN),
               entry->unreachable_since ? "unreachable" : "reachable",
               entry->bad_since ? "unusable" : "usable",
               reason ? ", ": "",
               reason ? reason : "",
               r ? "live" : "not live / ",
               r ? "" : live_msg);
    } SMARTLIST_FOREACH_END(entry);
    log_info(LD_CIRC, "    (%d/%d entry guards are usable/new)",
             num_live_entry_guards(), smartlist_len(entry_guards));
    log_entry_guards(LOG_INFO);
    entry_guards_changed();
  }

  digestmap_free(reasons, NULL);
}

/** Called when a connection to an OR with the identity digest <b>digest</b>
 * is established (<b>succeeded</b>==1) or has failed (<b>succeeded</b>==0).
 * If the OR is an entry, change that entry's up/down status.
 * Return 0 normally, or -1 if we want to tear down the new connection.
 *
 * If <b>mark_relay_status</b>, also call router_set_status() on this
 * relay.
 *
 * XXX024 change succeeded and mark_relay_status into 'int flags'.
 */
int
entry_guard_register_connect_status(const char *digest, int succeeded,
                                    int mark_relay_status, time_t now)
{
  int changed = 0;
  int refuse_conn = 0;
  int first_contact = 0;
  entry_guard_t *entry = NULL;
  int idx = -1;
  char buf[HEX_DIGEST_LEN+1];

  if (! entry_guards)
    return 0;

  SMARTLIST_FOREACH_BEGIN(entry_guards, entry_guard_t *, e) {
    tor_assert(e);
    if (tor_memeq(e->identity, digest, DIGEST_LEN)) {
      entry = e;
      idx = e_sl_idx;
      break;
    }
  } SMARTLIST_FOREACH_END(e);

  if (!entry)
    return 0;

  base16_encode(buf, sizeof(buf), entry->identity, DIGEST_LEN);

  if (succeeded) {
    if (entry->unreachable_since) {
      log_info(LD_CIRC, "Entry guard '%s' (%s) is now reachable again. Good.",
               entry->nickname, buf);
      entry->can_retry = 0;
      entry->unreachable_since = 0;
      entry->last_attempted = now;
      control_event_guard(entry->nickname, entry->identity, "UP");
      changed = 1;
    }
    if (!entry->made_contact) {
      entry->made_contact = 1;
      first_contact = changed = 1;
    }
  } else { /* ! succeeded */
    if (!entry->made_contact) {
      /* We've never connected to this one. */
      log_info(LD_CIRC,
               "Connection to never-contacted entry guard '%s' (%s) failed. "
               "Removing from the list. %d/%d entry guards usable/new.",
               entry->nickname, buf,
               num_live_entry_guards()-1, smartlist_len(entry_guards)-1);
      control_event_guard(entry->nickname, entry->identity, "DROPPED");
      entry_guard_free(entry);
      smartlist_del_keeporder(entry_guards, idx);
      log_entry_guards(LOG_INFO);
      changed = 1;
    } else if (!entry->unreachable_since) {
      log_info(LD_CIRC, "Unable to connect to entry guard '%s' (%s). "
               "Marking as unreachable.", entry->nickname, buf);
      entry->unreachable_since = entry->last_attempted = now;
      control_event_guard(entry->nickname, entry->identity, "DOWN");
      changed = 1;
      entry->can_retry = 0; /* We gave it an early chance; no good. */
    } else {
      char tbuf[ISO_TIME_LEN+1];
      format_iso_time(tbuf, entry->unreachable_since);
      log_debug(LD_CIRC, "Failed to connect to unreachable entry guard "
                "'%s' (%s).  It has been unreachable since %s.",
                entry->nickname, buf, tbuf);
      entry->last_attempted = now;
      entry->can_retry = 0; /* We gave it an early chance; no good. */
    }
  }

  /* if the caller asked us to, also update the is_running flags for this
   * relay */
  if (mark_relay_status)
    router_set_status(digest, succeeded);

  if (first_contact) {
    /* We've just added a new long-term entry guard. Perhaps the network just
     * came back? We should give our earlier entries another try too,
     * and close this connection so we don't use it before we've given
     * the others a shot. */
    SMARTLIST_FOREACH_BEGIN(entry_guards, entry_guard_t *, e) {
        if (e == entry)
          break;
        if (e->made_contact) {
          const char *msg;
          const node_t *r = entry_is_live(e, 0, 1, 1, &msg);
          if (r && e->unreachable_since) {
            refuse_conn = 1;
            e->can_retry = 1;
          }
        }
    } SMARTLIST_FOREACH_END(e);
    if (refuse_conn) {
      log_info(LD_CIRC,
               "Connected to new entry guard '%s' (%s). Marking earlier "
               "entry guards up. %d/%d entry guards usable/new.",
               entry->nickname, buf,
               num_live_entry_guards(), smartlist_len(entry_guards));
      log_entry_guards(LOG_INFO);
      changed = 1;
    }
  }

  if (changed)
    entry_guards_changed();
  return refuse_conn ? -1 : 0;
}

/** When we try to choose an entry guard, should we parse and add
 * config's EntryNodes first? */
static int should_add_entry_nodes = 0;

/** Called when the value of EntryNodes changes in our configuration. */
void
entry_nodes_should_be_added(void)
{
  log_info(LD_CIRC, "EntryNodes config option set. Putting configured "
           "relays at the front of the entry guard list.");
  should_add_entry_nodes = 1;
}

/** Adjust the entry guards list so that it only contains entries from
 * EntryNodes, adding new entries from EntryNodes to the list as needed. */
static void
entry_guards_set_from_config(const or_options_t *options)
{
  smartlist_t *entry_nodes, *worse_entry_nodes, *entry_fps;
  smartlist_t *old_entry_guards_on_list, *old_entry_guards_not_on_list;
  tor_assert(entry_guards);

  should_add_entry_nodes = 0;

  if (!options->EntryNodes) {
    /* It's possible that a controller set EntryNodes, thus making
     * should_add_entry_nodes set, then cleared it again, all before the
     * call to choose_random_entry() that triggered us. If so, just return.
     */
    return;
  }

  {
    char *string = routerset_to_string(options->EntryNodes);
    log_info(LD_CIRC,"Adding configured EntryNodes '%s'.", string);
    tor_free(string);
  }

  entry_nodes = smartlist_new();
  worse_entry_nodes = smartlist_new();
  entry_fps = smartlist_new();
  old_entry_guards_on_list = smartlist_new();
  old_entry_guards_not_on_list = smartlist_new();

  /* Split entry guards into those on the list and those not. */

  routerset_get_all_nodes(entry_nodes, options->EntryNodes,
                          options->ExcludeNodes, 0);
  SMARTLIST_FOREACH(entry_nodes, const node_t *,node,
                    smartlist_add(entry_fps, (void*)node->identity));

  SMARTLIST_FOREACH(entry_guards, entry_guard_t *, e, {
    if (smartlist_digest_isin(entry_fps, e->identity))
      smartlist_add(old_entry_guards_on_list, e);
    else
      smartlist_add(old_entry_guards_not_on_list, e);
  });

  /* Remove all currently configured guard nodes, excluded nodes, unreachable
   * nodes, or non-Guard nodes from entry_nodes. */
  SMARTLIST_FOREACH_BEGIN(entry_nodes, const node_t *, node) {
    if (entry_guard_get_by_id_digest(node->identity)) {
      SMARTLIST_DEL_CURRENT(entry_nodes, node);
      continue;
    } else if (routerset_contains_node(options->ExcludeNodes, node)) {
      SMARTLIST_DEL_CURRENT(entry_nodes, node);
      continue;
    } else if (!fascist_firewall_allows_node(node)) {
      SMARTLIST_DEL_CURRENT(entry_nodes, node);
      continue;
    } else if (! node->is_possible_guard) {
      smartlist_add(worse_entry_nodes, (node_t*)node);
      SMARTLIST_DEL_CURRENT(entry_nodes, node);
    }
  } SMARTLIST_FOREACH_END(node);

  /* Now build the new entry_guards list. */
  smartlist_clear(entry_guards);
  /* First, the previously configured guards that are in EntryNodes. */
  smartlist_add_all(entry_guards, old_entry_guards_on_list);
  /* Next, scramble the rest of EntryNodes, putting the guards first. */
  smartlist_shuffle(entry_nodes);
  smartlist_shuffle(worse_entry_nodes);
  smartlist_add_all(entry_nodes, worse_entry_nodes);

  /* Next, the rest of EntryNodes */
  SMARTLIST_FOREACH_BEGIN(entry_nodes, const node_t *, node) {
    add_an_entry_guard(node, 0, 0);
    if (smartlist_len(entry_guards) > options->NumEntryGuards * 10)
      break;
  } SMARTLIST_FOREACH_END(node);
  log_notice(LD_GENERAL, "%d entries in guards", smartlist_len(entry_guards));
  /* Finally, free the remaining previously configured guards that are not in
   * EntryNodes. */
  SMARTLIST_FOREACH(old_entry_guards_not_on_list, entry_guard_t *, e,
                    entry_guard_free(e));

  smartlist_free(entry_nodes);
  smartlist_free(worse_entry_nodes);
  smartlist_free(entry_fps);
  smartlist_free(old_entry_guards_on_list);
  smartlist_free(old_entry_guards_not_on_list);
  entry_guards_changed();
}

/** Return 0 if we're fine adding arbitrary routers out of the
 * directory to our entry guard list, or return 1 if we have a
 * list already and we must stick to it.
 */
int
entry_list_is_constrained(const or_options_t *options)
{
  if (options->EntryNodes)
    return 1;
  if (options->UseBridges)
    return 1;
  return 0;
}

/** Pick a live (up and listed) entry guard from entry_guards. If
 * <b>state</b> is non-NULL, this is for a specific circuit --
 * make sure not to pick this circuit's exit or any node in the
 * exit's family. If <b>state</b> is NULL, we're looking for a random
 * guard (likely a bridge). */
const node_t *
choose_random_entry(cpath_build_state_t *state)
{
  const or_options_t *options = get_options();
  smartlist_t *live_entry_guards = smartlist_new();
  smartlist_t *exit_family = smartlist_new();
  const node_t *chosen_exit =
    state?build_state_get_exit_node(state) : NULL;
  const node_t *node = NULL;
  int need_uptime = state ? state->need_uptime : 0;
  int need_capacity = state ? state->need_capacity : 0;
  int preferred_min, consider_exit_family = 0;

  if (chosen_exit) {
    nodelist_add_node_and_family(exit_family, chosen_exit);
    consider_exit_family = 1;
  }

  if (!entry_guards)
    entry_guards = smartlist_new();

  if (should_add_entry_nodes)
    entry_guards_set_from_config(options);

  if (!entry_list_is_constrained(options) &&
      smartlist_len(entry_guards) < options->NumEntryGuards)
    pick_entry_guards(options);

 retry:
  smartlist_clear(live_entry_guards);
  SMARTLIST_FOREACH_BEGIN(entry_guards, entry_guard_t *, entry) {
      const char *msg;
      node = entry_is_live(entry, need_uptime, need_capacity, 0, &msg);
      if (!node)
        continue; /* down, no point */
      if (node == chosen_exit)
        continue; /* don't pick the same node for entry and exit */
      if (consider_exit_family && smartlist_isin(exit_family, node))
        continue; /* avoid relays that are family members of our exit */
#if 0 /* since EntryNodes is always strict now, this clause is moot */
      if (options->EntryNodes &&
          !routerset_contains_node(options->EntryNodes, node)) {
        /* We've come to the end of our preferred entry nodes. */
        if (smartlist_len(live_entry_guards))
          goto choose_and_finish; /* only choose from the ones we like */
        if (options->StrictNodes) {
          /* in theory this case should never happen, since
           * entry_guards_set_from_config() drops unwanted relays */
          tor_fragile_assert();
        } else {
          log_info(LD_CIRC,
                   "No relays from EntryNodes available. Using others.");
        }
      }
#endif
      smartlist_add(live_entry_guards, (void*)node);
      if (!entry->made_contact) {
        /* Always start with the first not-yet-contacted entry
         * guard. Otherwise we might add several new ones, pick
         * the second new one, and now we've expanded our entry
         * guard list without needing to. */
        goto choose_and_finish;
      }
      if (smartlist_len(live_entry_guards) >= options->NumEntryGuards)
        goto choose_and_finish; /* we have enough */
  } SMARTLIST_FOREACH_END(entry);

  if (entry_list_is_constrained(options)) {
    /* If we prefer the entry nodes we've got, and we have at least
     * one choice, that's great. Use it. */
    preferred_min = 1;
  } else {
    /* Try to have at least 2 choices available. This way we don't
     * get stuck with a single live-but-crummy entry and just keep
     * using him.
     * (We might get 2 live-but-crummy entry guards, but so be it.) */
    preferred_min = 2;
  }

  if (smartlist_len(live_entry_guards) < preferred_min) {
    if (!entry_list_is_constrained(options)) {
      /* still no? try adding a new entry then */
      /* XXX if guard doesn't imply fast and stable, then we need
       * to tell add_an_entry_guard below what we want, or it might
       * be a long time til we get it. -RD */
      node = add_an_entry_guard(NULL, 0, 0);
      if (node) {
        entry_guards_changed();
        /* XXX we start over here in case the new node we added shares
         * a family with our exit node. There's a chance that we'll just
         * load up on entry guards here, if the network we're using is
         * one big family. Perhaps we should teach add_an_entry_guard()
         * to understand nodes-to-avoid-if-possible? -RD */
        goto retry;
      }
    }
    if (!node && need_uptime) {
      need_uptime = 0; /* try without that requirement */
      goto retry;
    }
    if (!node && need_capacity) {
      /* still no? last attempt, try without requiring capacity */
      need_capacity = 0;
      goto retry;
    }
#if 0
    /* Removing this retry logic: if we only allow one exit, and it is in the
       same family as all our entries, then we are just plain not going to win
       here. */
    if (!node && entry_list_is_constrained(options) && consider_exit_family) {
      /* still no? if we're using bridges or have strictentrynodes
       * set, and our chosen exit is in the same family as all our
       * bridges/entry guards, then be flexible about families. */
      consider_exit_family = 0;
      goto retry;
    }
#endif
    /* live_entry_guards may be empty below. Oh well, we tried. */
  }

 choose_and_finish:
  if (entry_list_is_constrained(options)) {
    /* We need to weight by bandwidth, because our bridges or entryguards
     * were not already selected proportional to their bandwidth. */
    node = node_sl_choose_by_bandwidth(live_entry_guards, WEIGHT_FOR_GUARD);
  } else {
    /* We choose uniformly at random here, because choose_good_entry_server()
     * already weights its choices by bandwidth, so we don't want to
     * *double*-weight our guard selection. */
    node = smartlist_choose(live_entry_guards);
  }
  smartlist_free(live_entry_guards);
  smartlist_free(exit_family);
  return node;
}

/** Parse <b>state</b> and learn about the entry guards it describes.
 * If <b>set</b> is true, and there are no errors, replace the global
 * entry_list with what we find.
 * On success, return 0. On failure, alloc into *<b>msg</b> a string
 * describing the error, and return -1.
 */
int
entry_guards_parse_state(or_state_t *state, int set, char **msg)
{
  entry_guard_t *node = NULL;
  smartlist_t *new_entry_guards = smartlist_new();
  config_line_t *line;
  time_t now = time(NULL);
  const char *state_version = state->TorVersion;
  digestmap_t *added_by = digestmap_new();

  *msg = NULL;
  for (line = state->EntryGuards; line; line = line->next) {
    if (!strcasecmp(line->key, "EntryGuard")) {
      smartlist_t *args = smartlist_new();
      node = tor_malloc_zero(sizeof(entry_guard_t));
      /* all entry guards on disk have been contacted */
      node->made_contact = 1;
      smartlist_add(new_entry_guards, node);
      smartlist_split_string(args, line->value, " ",
                             SPLIT_SKIP_SPACE|SPLIT_IGNORE_BLANK, 0);
      if (smartlist_len(args)<2) {
        *msg = tor_strdup("Unable to parse entry nodes: "
                          "Too few arguments to EntryGuard");
      } else if (!is_legal_nickname(smartlist_get(args,0))) {
        *msg = tor_strdup("Unable to parse entry nodes: "
                          "Bad nickname for EntryGuard");
      } else {
        strlcpy(node->nickname, smartlist_get(args,0), MAX_NICKNAME_LEN+1);
        if (base16_decode(node->identity, DIGEST_LEN, smartlist_get(args,1),
                          strlen(smartlist_get(args,1)))<0) {
          *msg = tor_strdup("Unable to parse entry nodes: "
                            "Bad hex digest for EntryGuard");
        }
      }
      SMARTLIST_FOREACH(args, char*, cp, tor_free(cp));
      smartlist_free(args);
      if (*msg)
        break;
    } else if (!strcasecmp(line->key, "EntryGuardDownSince") ||
               !strcasecmp(line->key, "EntryGuardUnlistedSince")) {
      time_t when;
      time_t last_try = 0;
      if (!node) {
        *msg = tor_strdup("Unable to parse entry nodes: "
               "EntryGuardDownSince/UnlistedSince without EntryGuard");
        break;
      }
      if (parse_iso_time(line->value, &when)<0) {
        *msg = tor_strdup("Unable to parse entry nodes: "
                          "Bad time in EntryGuardDownSince/UnlistedSince");
        break;
      }
      if (when > now) {
        /* It's a bad idea to believe info in the future: you can wind
         * up with timeouts that aren't allowed to happen for years. */
        continue;
      }
      if (strlen(line->value) >= ISO_TIME_LEN+ISO_TIME_LEN+1) {
        /* ignore failure */
        (void) parse_iso_time(line->value+ISO_TIME_LEN+1, &last_try);
      }
      if (!strcasecmp(line->key, "EntryGuardDownSince")) {
        node->unreachable_since = when;
        node->last_attempted = last_try;
      } else {
        node->bad_since = when;
      }
    } else if (!strcasecmp(line->key, "EntryGuardAddedBy")) {
      char d[DIGEST_LEN];
      /* format is digest version date */
      if (strlen(line->value) < HEX_DIGEST_LEN+1+1+1+ISO_TIME_LEN) {
        log_warn(LD_BUG, "EntryGuardAddedBy line is not long enough.");
        continue;
      }
      if (base16_decode(d, sizeof(d), line->value, HEX_DIGEST_LEN)<0 ||
          line->value[HEX_DIGEST_LEN] != ' ') {
        log_warn(LD_BUG, "EntryGuardAddedBy line %s does not begin with "
                 "hex digest", escaped(line->value));
        continue;
      }
      digestmap_set(added_by, d, tor_strdup(line->value+HEX_DIGEST_LEN+1));
    } else if (!strcasecmp(line->key, "EntryGuardPathBias")) {
      const or_options_t *options = get_options();
      unsigned hop_cnt, success_cnt, timeouts, collapsed, successful_closed,
               unusable;

      if (!node) {
        *msg = tor_strdup("Unable to parse entry nodes: "
               "EntryGuardPathBias without EntryGuard");
        break;
      }

      /* First try 3 params, then 2. */
      // XXX: We want to convert this to floating point before merge
      /* In the long run: circuit_success ~= successful_circuit_close + 
       *                                     collapsed_circuits +
       *                                     unusable_circuits */
      if (tor_sscanf(line->value, "%u %u %u %u %u %u",
                  &hop_cnt, &success_cnt, &successful_closed,
                  &collapsed, &unusable, &timeouts) != 6) {
        if (tor_sscanf(line->value, "%u %u", &success_cnt, &hop_cnt) != 2) {
          continue;
        }
        log_info(LD_GENERAL, "Reading old-style EntryGuardPathBias %s",
                 escaped(line->value));

        successful_closed = success_cnt;
        timeouts = 0;
        collapsed = 0;
        unusable = 0;
      }

      node->circ_attempts = hop_cnt;
      node->circ_successes = success_cnt;

      node->successful_circuits_closed = successful_closed;
      node->timeouts = timeouts;
      node->collapsed_circuits = collapsed;
      node->unusable_circuits = unusable;

      log_info(LD_GENERAL, "Read %u/%u path bias for node %s",
               node->circ_successes, node->circ_attempts, node->nickname);
      /* Note: We rely on the < comparison here to allow us to set a 0
       * rate and disable the feature entirely. If refactoring, don't
       * change to <= */
      if ((node->circ_successes/((double)node->circ_attempts)
          < pathbias_get_extreme_rate(options)) &&
          pathbias_get_dropguards(options)) {
        node->path_bias_disabled = 1;
        log_info(LD_GENERAL,
                 "Path bias is too high (%u/%u); disabling node %s",
                 node->circ_successes, node->circ_attempts, node->nickname);
      }

    } else {
      log_warn(LD_BUG, "Unexpected key %s", line->key);
    }
  }

  SMARTLIST_FOREACH_BEGIN(new_entry_guards, entry_guard_t *, e) {
     char *sp;
     char *val = digestmap_get(added_by, e->identity);
     if (val && (sp = strchr(val, ' '))) {
       time_t when;
       *sp++ = '\0';
       if (parse_iso_time(sp, &when)<0) {
         log_warn(LD_BUG, "Can't read time %s in EntryGuardAddedBy", sp);
       } else {
         e->chosen_by_version = tor_strdup(val);
         e->chosen_on_date = when;
       }
     } else {
       if (state_version) {
         e->chosen_by_version = tor_strdup(state_version);
         e->chosen_on_date = time(NULL) - crypto_rand_int(3600*24*30);
       }
     }
     if (e->path_bias_disabled && !e->bad_since)
       e->bad_since = time(NULL);
    }
  SMARTLIST_FOREACH_END(e);

  if (*msg || !set) {
    SMARTLIST_FOREACH(new_entry_guards, entry_guard_t *, e,
                      entry_guard_free(e));
    smartlist_free(new_entry_guards);
  } else { /* !err && set */
    if (entry_guards) {
      SMARTLIST_FOREACH(entry_guards, entry_guard_t *, e,
                        entry_guard_free(e));
      smartlist_free(entry_guards);
    }
    entry_guards = new_entry_guards;
    entry_guards_dirty = 0;
    /* XXX024 hand new_entry_guards to this func, and move it up a
     * few lines, so we don't have to re-dirty it */
    if (remove_obsolete_entry_guards(now))
      entry_guards_dirty = 1;
  }
  digestmap_free(added_by, tor_free_);
  return *msg ? -1 : 0;
}

/** Our list of entry guards has changed, or some element of one
 * of our entry guards has changed. Write the changes to disk within
 * the next few minutes.
 */
void
entry_guards_changed(void)
{
  time_t when;
  entry_guards_dirty = 1;

  /* or_state_save() will call entry_guards_update_state(). */
  when = get_options()->AvoidDiskWrites ? time(NULL) + 3600 : time(NULL)+600;
  or_state_mark_dirty(get_or_state(), when);
}

/** If the entry guard info has not changed, do nothing and return.
 * Otherwise, free the EntryGuards piece of <b>state</b> and create
 * a new one out of the global entry_guards list, and then mark
 * <b>state</b> dirty so it will get saved to disk.
 */
void
entry_guards_update_state(or_state_t *state)
{
  config_line_t **next, *line;
  if (! entry_guards_dirty)
    return;

  config_free_lines(state->EntryGuards);
  next = &state->EntryGuards;
  *next = NULL;
  if (!entry_guards)
    entry_guards = smartlist_new();
  SMARTLIST_FOREACH_BEGIN(entry_guards, entry_guard_t *, e) {
      char dbuf[HEX_DIGEST_LEN+1];
      if (!e->made_contact)
        continue; /* don't write this one to disk */
      *next = line = tor_malloc_zero(sizeof(config_line_t));
      line->key = tor_strdup("EntryGuard");
      base16_encode(dbuf, sizeof(dbuf), e->identity, DIGEST_LEN);
      tor_asprintf(&line->value, "%s %s", e->nickname, dbuf);
      next = &(line->next);
      if (e->unreachable_since) {
        *next = line = tor_malloc_zero(sizeof(config_line_t));
        line->key = tor_strdup("EntryGuardDownSince");
        line->value = tor_malloc(ISO_TIME_LEN+1+ISO_TIME_LEN+1);
        format_iso_time(line->value, e->unreachable_since);
        if (e->last_attempted) {
          line->value[ISO_TIME_LEN] = ' ';
          format_iso_time(line->value+ISO_TIME_LEN+1, e->last_attempted);
        }
        next = &(line->next);
      }
      if (e->bad_since) {
        *next = line = tor_malloc_zero(sizeof(config_line_t));
        line->key = tor_strdup("EntryGuardUnlistedSince");
        line->value = tor_malloc(ISO_TIME_LEN+1);
        format_iso_time(line->value, e->bad_since);
        next = &(line->next);
      }
      if (e->chosen_on_date && e->chosen_by_version &&
          !strchr(e->chosen_by_version, ' ')) {
        char d[HEX_DIGEST_LEN+1];
        char t[ISO_TIME_LEN+1];
        *next = line = tor_malloc_zero(sizeof(config_line_t));
        line->key = tor_strdup("EntryGuardAddedBy");
        base16_encode(d, sizeof(d), e->identity, DIGEST_LEN);
        format_iso_time(t, e->chosen_on_date);
        tor_asprintf(&line->value, "%s %s %s",
                     d, e->chosen_by_version, t);
        next = &(line->next);
      }
      if (e->circ_attempts) {
        *next = line = tor_malloc_zero(sizeof(config_line_t));
        line->key = tor_strdup("EntryGuardPathBias");
        /* In the long run: circuit_success ~= successful_circuit_close + 
         *                                     collapsed_circuits +
         *                                     unusable_circuits */
        tor_asprintf(&line->value, "%u %u %u %u %u %u",
                     e->circ_attempts, e->circ_successes,
                     pathbias_get_closed_count(e), e->collapsed_circuits,
                     e->unusable_circuits, e->timeouts);
        next = &(line->next);
      }

  } SMARTLIST_FOREACH_END(e);
  if (!get_options()->AvoidDiskWrites)
    or_state_mark_dirty(get_or_state(), 0);
  entry_guards_dirty = 0;
}

/** If <b>question</b> is the string "entry-guards", then dump
 * to *<b>answer</b> a newly allocated string describing all of
 * the nodes in the global entry_guards list. See control-spec.txt
 * for details.
 * For backward compatibility, we also handle the string "helper-nodes".
 * */
int
getinfo_helper_entry_guards(control_connection_t *conn,
                            const char *question, char **answer,
                            const char **errmsg)
{
  (void) conn;
  (void) errmsg;

  if (!strcmp(question,"entry-guards") ||
      !strcmp(question,"helper-nodes")) {
    smartlist_t *sl = smartlist_new();
    char tbuf[ISO_TIME_LEN+1];
    char nbuf[MAX_VERBOSE_NICKNAME_LEN+1];
    if (!entry_guards)
      entry_guards = smartlist_new();
    SMARTLIST_FOREACH_BEGIN(entry_guards, entry_guard_t *, e) {
        const char *status = NULL;
        time_t when = 0;
        const node_t *node;

        if (!e->made_contact) {
          status = "never-connected";
        } else if (e->bad_since) {
          when = e->bad_since;
          status = "unusable";
        } else {
          status = "up";
        }

        node = node_get_by_id(e->identity);
        if (node) {
          node_get_verbose_nickname(node, nbuf);
        } else {
          nbuf[0] = '$';
          base16_encode(nbuf+1, sizeof(nbuf)-1, e->identity, DIGEST_LEN);
          /* e->nickname field is not very reliable if we don't know about
           * this router any longer; don't include it. */
        }

        if (when) {
          format_iso_time(tbuf, when);
          smartlist_add_asprintf(sl, "%s %s %s\n", nbuf, status, tbuf);
        } else {
          smartlist_add_asprintf(sl, "%s %s\n", nbuf, status);
        }
    } SMARTLIST_FOREACH_END(e);
    *answer = smartlist_join_strings(sl, "", 0, NULL);
    SMARTLIST_FOREACH(sl, char *, c, tor_free(c));
    smartlist_free(sl);
  }
  return 0;
}

/** A list of configured bridges. Whenever we actually get a descriptor
 * for one, we add it as an entry guard.  Note that the order of bridges
 * in this list does not necessarily correspond to the order of bridges
 * in the torrc. */
static smartlist_t *bridge_list = NULL;

/** Mark every entry of the bridge list to be removed on our next call to
 * sweep_bridge_list unless it has first been un-marked. */
void
mark_bridge_list(void)
{
  if (!bridge_list)
    bridge_list = smartlist_new();
  SMARTLIST_FOREACH(bridge_list, bridge_info_t *, b,
                    b->marked_for_removal = 1);
}

/** Remove every entry of the bridge list that was marked with
 * mark_bridge_list if it has not subsequently been un-marked. */
void
sweep_bridge_list(void)
{
  if (!bridge_list)
    bridge_list = smartlist_new();
  SMARTLIST_FOREACH_BEGIN(bridge_list, bridge_info_t *, b) {
    if (b->marked_for_removal) {
      SMARTLIST_DEL_CURRENT(bridge_list, b);
      bridge_free(b);
    }
  } SMARTLIST_FOREACH_END(b);
}

/** Initialize the bridge list to empty, creating it if needed. */
static void
clear_bridge_list(void)
{
  if (!bridge_list)
    bridge_list = smartlist_new();
  SMARTLIST_FOREACH(bridge_list, bridge_info_t *, b, bridge_free(b));
  smartlist_clear(bridge_list);
}

/** Free the bridge <b>bridge</b>. */
static void
bridge_free(bridge_info_t *bridge)
{
  if (!bridge)
    return;

  tor_free(bridge->transport_name);
  tor_free(bridge);
}

/** If we have a bridge configured whose digest matches <b>digest</b>, or a
 * bridge with no known digest whose address matches any of the
 * tor_addr_port_t's in <b>orports</b>, return that bridge.  Else return
 * NULL. */
static bridge_info_t *
get_configured_bridge_by_orports_digest(const char *digest,
                                        const smartlist_t *orports)
{
  if (!bridge_list)
    return NULL;
  SMARTLIST_FOREACH_BEGIN(bridge_list, bridge_info_t *, bridge)
    {
      if (tor_digest_is_zero(bridge->identity)) {
        SMARTLIST_FOREACH_BEGIN(orports, tor_addr_port_t *, ap)
          {
            if (tor_addr_compare(&bridge->addr, &ap->addr, CMP_EXACT) == 0 &&
                bridge->port == ap->port)
              return bridge;
          }
        SMARTLIST_FOREACH_END(ap);
      }
      if (digest && tor_memeq(bridge->identity, digest, DIGEST_LEN))
        return bridge;
    }
  SMARTLIST_FOREACH_END(bridge);
  return NULL;
}

/** If we have a bridge configured whose digest matches <b>digest</b>, or a
 * bridge with no known digest whose address matches <b>addr</b>:<b>/port</b>,
 * return that bridge.  Else return NULL. */
static bridge_info_t *
get_configured_bridge_by_addr_port_digest(const tor_addr_t *addr,
                                          uint16_t port,
                                          const char *digest)
{
  if (!bridge_list)
    return NULL;
  SMARTLIST_FOREACH_BEGIN(bridge_list, bridge_info_t *, bridge)
    {
      if (tor_digest_is_zero(bridge->identity) &&
          !tor_addr_compare(&bridge->addr, addr, CMP_EXACT) &&
          bridge->port == port)
        return bridge;
      if (digest && tor_memeq(bridge->identity, digest, DIGEST_LEN))
        return bridge;
    }
  SMARTLIST_FOREACH_END(bridge);
  return NULL;
}

/** Wrapper around get_configured_bridge_by_addr_port_digest() to look
 * it up via router descriptor <b>ri</b>. */
static bridge_info_t *
get_configured_bridge_by_routerinfo(const routerinfo_t *ri)
{
  bridge_info_t *bi = NULL;
  smartlist_t *orports = router_get_all_orports(ri);
  bi = get_configured_bridge_by_orports_digest(ri->cache_info.identity_digest,
                                               orports);
  SMARTLIST_FOREACH(orports, tor_addr_port_t *, p, tor_free(p));
  smartlist_free(orports);
  return bi;
}

/** Return 1 if <b>ri</b> is one of our known bridges, else 0. */
int
routerinfo_is_a_configured_bridge(const routerinfo_t *ri)
{
  return get_configured_bridge_by_routerinfo(ri) ? 1 : 0;
}

/** Return 1 if <b>node</b> is one of our configured bridges, else 0. */
int
node_is_a_configured_bridge(const node_t *node)
{
  int retval = 0;
  smartlist_t *orports = node_get_all_orports(node);
  retval = get_configured_bridge_by_orports_digest(node->identity,
                                                   orports) != NULL;
  SMARTLIST_FOREACH(orports, tor_addr_port_t *, p, tor_free(p));
  smartlist_free(orports);
  return retval;
}

/** We made a connection to a router at <b>addr</b>:<b>port</b>
 * without knowing its digest. Its digest turned out to be <b>digest</b>.
 * If it was a bridge, and we still don't know its digest, record it.
 */
void
learned_router_identity(const tor_addr_t *addr, uint16_t port,
                        const char *digest)
{
  bridge_info_t *bridge =
    get_configured_bridge_by_addr_port_digest(addr, port, digest);
  if (bridge && tor_digest_is_zero(bridge->identity)) {
    memcpy(bridge->identity, digest, DIGEST_LEN);
    log_notice(LD_DIR, "Learned fingerprint %s for bridge %s",
               hex_str(digest, DIGEST_LEN), fmt_addrport(addr, port));
  }
}

/** Return true if <b>bridge</b> has the same identity digest as
 *  <b>digest</b>. If <b>digest</b> is NULL, it matches
 *  bridges with unspecified identity digests. */
static int
bridge_has_digest(const bridge_info_t *bridge, const char *digest)
{
  if (digest)
    return tor_memeq(digest, bridge->identity, DIGEST_LEN);
  else
    return tor_digest_is_zero(bridge->identity);
}

/** We are about to add a new bridge at <b>addr</b>:<b>port</b>, with optional
 * <b>digest</b> and <b>transport_name</b>. Mark for removal any previously
 * existing bridge with the same address and port, and warn the user as
 * appropriate.
 */
static void
bridge_resolve_conflicts(const tor_addr_t *addr, uint16_t port,
                         const char *digest, const char *transport_name)
{
  /* Iterate the already-registered bridge list:

     If you find a bridge with the same adress and port, mark it for
     removal. It doesn't make sense to have two active bridges with
     the same IP:PORT. If the bridge in question has a different
     digest or transport than <b>digest</b>/<b>transport_name</b>,
     it's probably a misconfiguration and we should warn the user.
  */
  SMARTLIST_FOREACH_BEGIN(bridge_list, bridge_info_t *, bridge) {
    if (bridge->marked_for_removal)
      continue;

    if (tor_addr_eq(&bridge->addr, addr) && (bridge->port == port)) {

      bridge->marked_for_removal = 1;

      if (!bridge_has_digest(bridge, digest) ||
          strcmp_opt(bridge->transport_name, transport_name)) {
        /* warn the user */
        char *bridge_description_new, *bridge_description_old;
        tor_asprintf(&bridge_description_new, "%s:%s:%s",
                     fmt_addrport(addr, port),
                     digest ? hex_str(digest, DIGEST_LEN) : "",
                     transport_name ? transport_name : "");
        tor_asprintf(&bridge_description_old, "%s:%s:%s",
                     fmt_addrport(&bridge->addr, bridge->port),
                     tor_digest_is_zero(bridge->identity) ?
                     "" : hex_str(bridge->identity,DIGEST_LEN),
                     bridge->transport_name ? bridge->transport_name : "");

        log_warn(LD_GENERAL,"Tried to add bridge '%s', but we found a conflict"
                 " with the already registered bridge '%s'. We will discard"
                 " the old bridge and keep '%s'. If this is not what you"
                 " wanted, please change your configuration file accordingly.",
                 bridge_description_new, bridge_description_old,
                 bridge_description_new);

        tor_free(bridge_description_new);
        tor_free(bridge_description_old);
      }
    }
  } SMARTLIST_FOREACH_END(bridge);
}

/** Remember a new bridge at <b>addr</b>:<b>port</b>. If <b>digest</b>
 * is set, it tells us the identity key too.  If we already had the
 * bridge in our list, unmark it, and don't actually add anything new.
 * If <b>transport_name</b> is non-NULL - the bridge is associated with a
 * pluggable transport - we assign the transport to the bridge. */
void
bridge_add_from_config(const tor_addr_t *addr, uint16_t port,
                       const char *digest, const char *transport_name)
{
  bridge_info_t *b;

  bridge_resolve_conflicts(addr, port, digest, transport_name);

  b = tor_malloc_zero(sizeof(bridge_info_t));
  tor_addr_copy(&b->addr, addr);
  b->port = port;
  if (digest)
    memcpy(b->identity, digest, DIGEST_LEN);
  if (transport_name)
    b->transport_name = tor_strdup(transport_name);
  b->fetch_status.schedule = DL_SCHED_BRIDGE;
  if (!bridge_list)
    bridge_list = smartlist_new();

  smartlist_add(bridge_list, b);
}

/** Return true iff <b>routerset</b> contains the bridge <b>bridge</b>. */
static int
routerset_contains_bridge(const routerset_t *routerset,
                          const bridge_info_t *bridge)
{
  int result;
  extend_info_t *extinfo;
  tor_assert(bridge);
  if (!routerset)
    return 0;

  extinfo = extend_info_new(
         NULL, bridge->identity, NULL, &bridge->addr, bridge->port);
  result = routerset_contains_extendinfo(routerset, extinfo);
  extend_info_free(extinfo);
  return result;
}

/** If <b>digest</b> is one of our known bridges, return it. */
static bridge_info_t *
find_bridge_by_digest(const char *digest)
{
  SMARTLIST_FOREACH(bridge_list, bridge_info_t *, bridge,
    {
      if (tor_memeq(bridge->identity, digest, DIGEST_LEN))
        return bridge;
    });
  return NULL;
}

/* DOCDOC find_transport_name_by_bridge_addrport */
const char *
find_transport_name_by_bridge_addrport(const tor_addr_t *addr, uint16_t port)
{
  if (!bridge_list)
    return NULL;

  SMARTLIST_FOREACH_BEGIN(bridge_list, const bridge_info_t *, bridge) {
    if (tor_addr_eq(&bridge->addr, addr) &&
        (bridge->port == port))
      return bridge->transport_name;
  } SMARTLIST_FOREACH_END(bridge);

  return NULL;
}

/** If <b>addr</b> and <b>port</b> match the address and port of a
 * bridge of ours that uses pluggable transports, place its transport
 * in <b>transport</b>.
 *
 * Return 0 on success (found a transport, or found a bridge with no
 * transport, or found no bridge); return -1 if we should be using a
 * transport, but the transport could not be found.
 */
int
find_transport_by_bridge_addrport(const tor_addr_t *addr, uint16_t port,
                                  const transport_t **transport)
{
  *transport = NULL;
  if (!bridge_list)
    return 0;

  SMARTLIST_FOREACH_BEGIN(bridge_list, const bridge_info_t *, bridge) {
    if (tor_addr_eq(&bridge->addr, addr) &&
        (bridge->port == port)) { /* bridge matched */
      if (bridge->transport_name) { /* it also uses pluggable transports */
        *transport = transport_get_by_name(bridge->transport_name);
        if (*transport == NULL) { /* it uses pluggable transports, but
                                     the transport could not be found! */
          return -1;
        }
        return 0;
      } else { /* bridge matched, but it doesn't use transports. */
        break;
      }
    }
  } SMARTLIST_FOREACH_END(bridge);

  *transport = NULL;
  return 0;
}

/** We need to ask <b>bridge</b> for its server descriptor. */
static void
launch_direct_bridge_descriptor_fetch(bridge_info_t *bridge)
{
  char *address;
  const or_options_t *options = get_options();

  if (connection_get_by_type_addr_port_purpose(
      CONN_TYPE_DIR, &bridge->addr, bridge->port,
      DIR_PURPOSE_FETCH_SERVERDESC))
    return; /* it's already on the way */

  if (routerset_contains_bridge(options->ExcludeNodes, bridge)) {
    download_status_mark_impossible(&bridge->fetch_status);
    log_warn(LD_APP, "Not using bridge at %s: it is in ExcludeNodes.",
             safe_str_client(fmt_and_decorate_addr(&bridge->addr)));
    return;
  }

  address = tor_dup_addr(&bridge->addr);

  directory_initiate_command(address, &bridge->addr,
                             bridge->port, 0/*no dirport*/,
                             bridge->identity,
                             DIR_PURPOSE_FETCH_SERVERDESC,
                             ROUTER_PURPOSE_BRIDGE,
                             DIRIND_ONEHOP, "authority.z", NULL, 0, 0);
  tor_free(address);
}

/** Fetching the bridge descriptor from the bridge authority returned a
 * "not found". Fall back to trying a direct fetch. */
void
retry_bridge_descriptor_fetch_directly(const char *digest)
{
  bridge_info_t *bridge = find_bridge_by_digest(digest);
  if (!bridge)
    return; /* not found? oh well. */

  launch_direct_bridge_descriptor_fetch(bridge);
}

/** For each bridge in our list for which we don't currently have a
 * descriptor, fetch a new copy of its descriptor -- either directly
 * from the bridge or via a bridge authority. */
void
fetch_bridge_descriptors(const or_options_t *options, time_t now)
{
  int num_bridge_auths = get_n_authorities(BRIDGE_DIRINFO);
  int ask_bridge_directly;
  int can_use_bridge_authority;

  if (!bridge_list)
    return;

  /* If we still have unconfigured managed proxies, don't go and
     connect to a bridge. */
  if (pt_proxies_configuration_pending())
    return;

  SMARTLIST_FOREACH_BEGIN(bridge_list, bridge_info_t *, bridge)
    {
      if (!download_status_is_ready(&bridge->fetch_status, now,
                                    IMPOSSIBLE_TO_DOWNLOAD))
        continue; /* don't bother, no need to retry yet */
      if (routerset_contains_bridge(options->ExcludeNodes, bridge)) {
        download_status_mark_impossible(&bridge->fetch_status);
        log_warn(LD_APP, "Not using bridge at %s: it is in ExcludeNodes.",
                 safe_str_client(fmt_and_decorate_addr(&bridge->addr)));
        continue;
      }

      /* schedule another fetch as if this one will fail, in case it does */
      download_status_failed(&bridge->fetch_status, 0);

      can_use_bridge_authority = !tor_digest_is_zero(bridge->identity) &&
                                 num_bridge_auths;
      ask_bridge_directly = !can_use_bridge_authority ||
                            !options->UpdateBridgesFromAuthority;
      log_debug(LD_DIR, "ask_bridge_directly=%d (%d, %d, %d)",
                ask_bridge_directly, tor_digest_is_zero(bridge->identity),
                !options->UpdateBridgesFromAuthority, !num_bridge_auths);

      if (ask_bridge_directly &&
          !fascist_firewall_allows_address_or(&bridge->addr, bridge->port)) {
        log_notice(LD_DIR, "Bridge at '%s' isn't reachable by our "
                   "firewall policy. %s.",
                   fmt_addrport(&bridge->addr, bridge->port),
                   can_use_bridge_authority ?
                     "Asking bridge authority instead" : "Skipping");
        if (can_use_bridge_authority)
          ask_bridge_directly = 0;
        else
          continue;
      }

      if (ask_bridge_directly) {
        /* we need to ask the bridge itself for its descriptor. */
        launch_direct_bridge_descriptor_fetch(bridge);
      } else {
        /* We have a digest and we want to ask an authority. We could
         * combine all the requests into one, but that may give more
         * hints to the bridge authority than we want to give. */
        char resource[10 + HEX_DIGEST_LEN];
        memcpy(resource, "fp/", 3);
        base16_encode(resource+3, HEX_DIGEST_LEN+1,
                      bridge->identity, DIGEST_LEN);
        memcpy(resource+3+HEX_DIGEST_LEN, ".z", 3);
        log_info(LD_DIR, "Fetching bridge info '%s' from bridge authority.",
                 resource);
        directory_get_from_dirserver(DIR_PURPOSE_FETCH_SERVERDESC,
                ROUTER_PURPOSE_BRIDGE, resource, 0);
      }
    }
  SMARTLIST_FOREACH_END(bridge);
}

/** If our <b>bridge</b> is configured to be a different address than
 * the bridge gives in <b>node</b>, rewrite the routerinfo
 * we received to use the address we meant to use. Now we handle
 * multihomed bridges better.
 */
static void
rewrite_node_address_for_bridge(const bridge_info_t *bridge, node_t *node)
{
  /* XXXX move this function. */
  /* XXXX overridden addresses should really live in the node_t, so that the
   *   routerinfo_t and the microdesc_t can be immutable.  But we can only
   *   do that safely if we know that no function that connects to an OR
   *   does so through an address from any source other than node_get_addr().
   */
  tor_addr_t addr;

  if (node->ri) {
    routerinfo_t *ri = node->ri;
    tor_addr_from_ipv4h(&addr, ri->addr);

    if ((!tor_addr_compare(&bridge->addr, &addr, CMP_EXACT) &&
         bridge->port == ri->or_port) ||
        (!tor_addr_compare(&bridge->addr, &ri->ipv6_addr, CMP_EXACT) &&
         bridge->port == ri->ipv6_orport)) {
      /* they match, so no need to do anything */
    } else {
      if (tor_addr_family(&bridge->addr) == AF_INET) {
        ri->addr = tor_addr_to_ipv4h(&bridge->addr);
        tor_free(ri->address);
        ri->address = tor_dup_ip(ri->addr);
        ri->or_port = bridge->port;
        log_info(LD_DIR,
                 "Adjusted bridge routerinfo for '%s' to match configured "
                 "address %s:%d.",
                 ri->nickname, ri->address, ri->or_port);
      } else if (tor_addr_family(&bridge->addr) == AF_INET6) {
        tor_addr_copy(&ri->ipv6_addr, &bridge->addr);
        ri->ipv6_orport = bridge->port;
        log_info(LD_DIR,
                 "Adjusted bridge routerinfo for '%s' to match configured "
                 "address %s.",
                 ri->nickname, fmt_addrport(&ri->ipv6_addr, ri->ipv6_orport));
      } else {
        log_err(LD_BUG, "Address family not supported: %d.",
                tor_addr_family(&bridge->addr));
        return;
      }
    }

    /* Mark which address to use based on which bridge_t we got. */
    node->ipv6_preferred = (tor_addr_family(&bridge->addr) == AF_INET6 &&
                            !tor_addr_is_null(&node->ri->ipv6_addr));

    /* XXXipv6 we lack support for falling back to another address for
       the same relay, warn the user */
    if (!tor_addr_is_null(&ri->ipv6_addr)) {
      tor_addr_port_t ap;
      node_get_pref_orport(node, &ap);
      log_notice(LD_CONFIG,
                 "Bridge '%s' has both an IPv4 and an IPv6 address.  "
                 "Will prefer using its %s address (%s).",
                 ri->nickname,
                 tor_addr_family(&ap.addr) == AF_INET6 ? "IPv6" : "IPv4",
                 fmt_addrport(&ap.addr, ap.port));
    }
  }
  if (node->rs) {
    routerstatus_t *rs = node->rs;
    tor_addr_from_ipv4h(&addr, rs->addr);

    if (!tor_addr_compare(&bridge->addr, &addr, CMP_EXACT) &&
        bridge->port == rs->or_port) {
      /* they match, so no need to do anything */
    } else {
      rs->addr = tor_addr_to_ipv4h(&bridge->addr);
      rs->or_port = bridge->port;
      log_info(LD_DIR,
               "Adjusted bridge routerstatus for '%s' to match "
               "configured address %s.",
               rs->nickname, fmt_addrport(&bridge->addr, rs->or_port));
    }
  }
}

/** We just learned a descriptor for a bridge. See if that
 * digest is in our entry guard list, and add it if not. */
void
learned_bridge_descriptor(routerinfo_t *ri, int from_cache)
{
  tor_assert(ri);
  tor_assert(ri->purpose == ROUTER_PURPOSE_BRIDGE);
  if (get_options()->UseBridges) {
    int first = !any_bridge_descriptors_known();
    bridge_info_t *bridge = get_configured_bridge_by_routerinfo(ri);
    time_t now = time(NULL);
    router_set_status(ri->cache_info.identity_digest, 1);

    if (bridge) { /* if we actually want to use this one */
      node_t *node;
      /* it's here; schedule its re-fetch for a long time from now. */
      if (!from_cache)
        download_status_reset(&bridge->fetch_status);

      node = node_get_mutable_by_id(ri->cache_info.identity_digest);
      tor_assert(node);
      rewrite_node_address_for_bridge(bridge, node);
      add_an_entry_guard(node, 1, 1);

      log_notice(LD_DIR, "new bridge descriptor '%s' (%s): %s", ri->nickname,
                 from_cache ? "cached" : "fresh", router_describe(ri));
      /* set entry->made_contact so if it goes down we don't drop it from
       * our entry node list */
      entry_guard_register_connect_status(ri->cache_info.identity_digest,
                                          1, 0, now);
      if (first)
        routerlist_retry_directory_downloads(now);
    }
  }
}

/** Return 1 if any of our entry guards have descriptors that
 * are marked with purpose 'bridge' and are running. Else return 0.
 *
 * We use this function to decide if we're ready to start building
 * circuits through our bridges, or if we need to wait until the
 * directory "server/authority" requests finish. */
int
any_bridge_descriptors_known(void)
{
  tor_assert(get_options()->UseBridges);
  return choose_random_entry(NULL)!=NULL ? 1 : 0;
}

/** Return 1 if there are any directory conns fetching bridge descriptors
 * that aren't marked for close. We use this to guess if we should tell
 * the controller that we have a problem. */
int
any_pending_bridge_descriptor_fetches(void)
{
  smartlist_t *conns = get_connection_array();
  SMARTLIST_FOREACH_BEGIN(conns, connection_t *, conn) {
    if (conn->type == CONN_TYPE_DIR &&
        conn->purpose == DIR_PURPOSE_FETCH_SERVERDESC &&
        TO_DIR_CONN(conn)->router_purpose == ROUTER_PURPOSE_BRIDGE &&
        !conn->marked_for_close &&
        conn->linked &&
        conn->linked_conn && !conn->linked_conn->marked_for_close) {
      log_debug(LD_DIR, "found one: %s", conn->address);
      return 1;
    }
  } SMARTLIST_FOREACH_END(conn);
  return 0;
}

/** Return 1 if we have at least one descriptor for an entry guard
 * (bridge or member of EntryNodes) and all descriptors we know are
 * down. Else return 0. If <b>act</b> is 1, then mark the down guards
 * up; else just observe and report. */
static int
entries_retry_helper(const or_options_t *options, int act)
{
  const node_t *node;
  int any_known = 0;
  int any_running = 0;
  int need_bridges = options->UseBridges != 0;
  if (!entry_guards)
    entry_guards = smartlist_new();
  SMARTLIST_FOREACH_BEGIN(entry_guards, entry_guard_t *, e) {
      node = node_get_by_id(e->identity);
      if (node && node_has_descriptor(node) &&
          node_is_bridge(node) == need_bridges) {
        any_known = 1;
        if (node->is_running)
          any_running = 1; /* some entry is both known and running */
        else if (act) {
          /* Mark all current connections to this OR as unhealthy, since
           * otherwise there could be one that started 30 seconds
           * ago, and in 30 seconds it will time out, causing us to mark
           * the node down and undermine the retry attempt. We mark even
           * the established conns, since if the network just came back
           * we'll want to attach circuits to fresh conns. */
          connection_or_set_bad_connections(node->identity, 1);

          /* mark this entry node for retry */
          router_set_status(node->identity, 1);
          e->can_retry = 1;
          e->bad_since = 0;
        }
      }
  } SMARTLIST_FOREACH_END(e);
  log_debug(LD_DIR, "%d: any_known %d, any_running %d",
            act, any_known, any_running);
  return any_known && !any_running;
}

/** Do we know any descriptors for our bridges / entrynodes, and are
 * all the ones we have descriptors for down? */
int
entries_known_but_down(const or_options_t *options)
{
  tor_assert(entry_list_is_constrained(options));
  return entries_retry_helper(options, 0);
}

/** Mark all down known bridges / entrynodes up. */
void
entries_retry_all(const or_options_t *options)
{
  tor_assert(entry_list_is_constrained(options));
  entries_retry_helper(options, 1);
}

/** Return true if we've ever had a bridge running a Tor version that can't
 * provide microdescriptors to us. In that case fall back to asking for
 * full descriptors. Eventually all bridges will support microdescriptors
 * and we can take this check out; see bug 4013. */
int
any_bridges_dont_support_microdescriptors(void)
{
  const node_t *node;
  static int ever_answered_yes = 0;
  if (!get_options()->UseBridges || !entry_guards)
    return 0;
  if (ever_answered_yes)
    return 1; /* if we ever answer 'yes', always answer 'yes' */
  SMARTLIST_FOREACH_BEGIN(entry_guards, entry_guard_t *, e) {
    node = node_get_by_id(e->identity);
    if (node && node->ri &&
        node_is_bridge(node) && node_is_a_configured_bridge(node) &&
        !tor_version_supports_microdescriptors(node->ri->platform)) {
      /* This is one of our current bridges, and we know enough about
       * it to know that it won't be able to answer our microdescriptor
       * questions. */
      ever_answered_yes = 1;
      return 1;
    }
  } SMARTLIST_FOREACH_END(e);
  return 0;
}

/** Release all storage held by the list of entry guards and related
 * memory structs. */
void
entry_guards_free_all(void)
{
  if (entry_guards) {
    SMARTLIST_FOREACH(entry_guards, entry_guard_t *, e,
                      entry_guard_free(e));
    smartlist_free(entry_guards);
    entry_guards = NULL;
  }
  clear_bridge_list();
  smartlist_free(bridge_list);
  bridge_list = NULL;
  circuit_build_times_free_timeouts(&circ_times);
}