tor/src/or/networkstatus.c

/* Copyright (c) 2001 Matej Pfajfar.
 * Copyright (c) 2001-2004, Roger Dingledine.
 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
 * Copyright (c) 2007-2013, The Tor Project, Inc. */
/* See LICENSE for licensing information */

/**
 * \file networkstatus.c
 * \brief Functions and structures for handling network status documents as a
 * client or cache.
 */

#include "or.h"
#include "channel.h"
#include "circuitmux.h"
#include "circuitmux_ewma.h"
#include "circuitstats.h"
#include "config.h"
#include "connection.h"
#include "connection_or.h"
#include "control.h"
#include "directory.h"
#include "dirserv.h"
#include "dirvote.h"
#include "entrynodes.h"
#include "main.h"
#include "microdesc.h"
#include "networkstatus.h"
#include "nodelist.h"
#include "relay.h"
#include "router.h"
#include "routerlist.h"
#include "routerparse.h"
#include "transports.h"

/** Map from lowercase nickname to identity digest of named server, if any. */
static strmap_t *named_server_map = NULL;
/** Map from lowercase nickname to (void*)1 for all names that are listed
 * as unnamed for some server in the consensus. */
static strmap_t *unnamed_server_map = NULL;

/** Most recently received and validated v3 consensus network status,
 * of whichever type we are using for our own circuits.  This will be the same
 * as one of current_ns_consensus or current_md_consensus.
 */
#define current_consensus                                       \
  (we_use_microdescriptors_for_circuits(get_options()) ?        \
   current_md_consensus : current_ns_consensus)

/** Most recently received and validated v3 "ns"-flavored consensus network
 * status. */
static networkstatus_t *current_ns_consensus = NULL;

/** Most recently received and validated v3 "microdec"-flavored consensus
 * network status. */
static networkstatus_t *current_md_consensus = NULL;

/** A v3 consensus networkstatus that we've received, but which we don't
 * have enough certificates to be happy about. */
typedef struct consensus_waiting_for_certs_t {
  /** The consensus itself. */
  networkstatus_t *consensus;
  /** The encoded version of the consensus, nul-terminated. */
  char *body;
  /** When did we set the current value of consensus_waiting_for_certs?  If
   * this is too recent, we shouldn't try to fetch a new consensus for a
   * little while, to give ourselves time to get certificates for this one. */
  time_t set_at;
  /** Set to 1 if we've been holding on to it for so long we should maybe
   * treat it as being bad. */
  int dl_failed;
} consensus_waiting_for_certs_t;

/** An array, for each flavor of consensus we might want, of consensuses that
 * we have downloaded, but which we cannot verify due to having insufficient
 * authority certificates. */
static consensus_waiting_for_certs_t
       consensus_waiting_for_certs[N_CONSENSUS_FLAVORS];

/** A time before which we shouldn't try to replace the current consensus:
 * this will be at some point after the next consensus becomes valid, but
 * before the current consensus becomes invalid. */
static time_t time_to_download_next_consensus[N_CONSENSUS_FLAVORS];
/** Download status for the current consensus networkstatus. */
static download_status_t consensus_dl_status[N_CONSENSUS_FLAVORS];

/** True iff we have logged a warning about this OR's version being older than
 * listed by the authorities. */
static int have_warned_about_old_version = 0;
/** True iff we have logged a warning about this OR's version being newer than
 * listed by the authorities. */
static int have_warned_about_new_version = 0;

static void routerstatus_list_update_named_server_map(void);

/** Forget that we've warned about anything networkstatus-related, so we will
 * give fresh warnings if the same behavior happens again. */
void
networkstatus_reset_warnings(void)
{
  if (current_consensus) {
    SMARTLIST_FOREACH(nodelist_get_list(), node_t *, node,
                      node->name_lookup_warned = 0);
  }

  have_warned_about_old_version = 0;
  have_warned_about_new_version = 0;
}

/** Reset the descriptor download failure count on all networkstatus docs, so
 * that we can retry any long-failed documents immediately.
 */
void
networkstatus_reset_download_failures(void)
{
  int i;

  for (i=0; i < N_CONSENSUS_FLAVORS; ++i)
    download_status_reset(&consensus_dl_status[i]);
}

/** Read every cached v3 consensus networkstatus from the disk. */
int
router_reload_consensus_networkstatus(void)
{
  char *filename;
  char *s;
  const unsigned int flags = NSSET_FROM_CACHE | NSSET_DONT_DOWNLOAD_CERTS;
  int flav;

  /* FFFF Suppress warnings if cached consensus is bad? */
  for (flav = 0; flav < N_CONSENSUS_FLAVORS; ++flav) {
    char buf[128];
    const char *flavor = networkstatus_get_flavor_name(flav);
    if (flav == FLAV_NS) {
      filename = get_datadir_fname("cached-consensus");
    } else {
      tor_snprintf(buf, sizeof(buf), "cached-%s-consensus", flavor);
      filename = get_datadir_fname(buf);
    }
    s = read_file_to_str(filename, RFTS_IGNORE_MISSING, NULL);
    if (s) {
      if (networkstatus_set_current_consensus(s, flavor, flags) < -1) {
        log_warn(LD_FS, "Couldn't load consensus %s networkstatus from \"%s\"",
                 flavor, filename);
      }
      tor_free(s);
    }
    tor_free(filename);

    if (flav == FLAV_NS) {
      filename = get_datadir_fname("unverified-consensus");
    } else {
      tor_snprintf(buf, sizeof(buf), "unverified-%s-consensus", flavor);
      filename = get_datadir_fname(buf);
    }

    s = read_file_to_str(filename, RFTS_IGNORE_MISSING, NULL);
    if (s) {
      if (networkstatus_set_current_consensus(s, flavor,
                                     flags|NSSET_WAS_WAITING_FOR_CERTS)) {
      log_info(LD_FS, "Couldn't load consensus %s networkstatus from \"%s\"",
               flavor, filename);
    }
      tor_free(s);
    }
    tor_free(filename);
  }

  if (!current_consensus) {
    if (!named_server_map)
      named_server_map = strmap_new();
    if (!unnamed_server_map)
      unnamed_server_map = strmap_new();
  }

  update_certificate_downloads(time(NULL));

  routers_update_all_from_networkstatus(time(NULL), 3);
  update_microdescs_from_networkstatus(time(NULL));

  return 0;
}

/** Free all storage held by the vote_routerstatus object <b>rs</b>. */
static void
vote_routerstatus_free(vote_routerstatus_t *rs)
{
  vote_microdesc_hash_t *h, *next;
  if (!rs)
    return;
  tor_free(rs->version);
  tor_free(rs->status.exitsummary);
  for (h = rs->microdesc; h; h = next) {
    tor_free(h->microdesc_hash_line);
    next = h->next;
    tor_free(h);
  }
  tor_free(rs);
}

/** Free all storage held by the routerstatus object <b>rs</b>. */
void
routerstatus_free(routerstatus_t *rs)
{
  if (!rs)
    return;
  tor_free(rs->exitsummary);
  tor_free(rs);
}

/** Free all storage held in <b>sig</b> */
void
document_signature_free(document_signature_t *sig)
{
  tor_free(sig->signature);
  tor_free(sig);
}

/** Return a newly allocated copy of <b>sig</b> */
document_signature_t *
document_signature_dup(const document_signature_t *sig)
{
  document_signature_t *r = tor_memdup(sig, sizeof(document_signature_t));
  if (r->signature)
    r->signature = tor_memdup(sig->signature, sig->signature_len);
  return r;
}

/** Free all storage held in <b>ns</b>. */
void
networkstatus_vote_free(networkstatus_t *ns)
{
  if (!ns)
    return;

  tor_free(ns->client_versions);
  tor_free(ns->server_versions);
  if (ns->known_flags) {
    SMARTLIST_FOREACH(ns->known_flags, char *, c, tor_free(c));
    smartlist_free(ns->known_flags);
  }
  if (ns->weight_params) {
    SMARTLIST_FOREACH(ns->weight_params, char *, c, tor_free(c));
    smartlist_free(ns->weight_params);
  }
  if (ns->net_params) {
    SMARTLIST_FOREACH(ns->net_params, char *, c, tor_free(c));
    smartlist_free(ns->net_params);
  }
  if (ns->supported_methods) {
    SMARTLIST_FOREACH(ns->supported_methods, char *, c, tor_free(c));
    smartlist_free(ns->supported_methods);
  }
  if (ns->voters) {
    SMARTLIST_FOREACH_BEGIN(ns->voters, networkstatus_voter_info_t *, voter) {
      tor_free(voter->nickname);
      tor_free(voter->address);
      tor_free(voter->contact);
      if (voter->sigs) {
        SMARTLIST_FOREACH(voter->sigs, document_signature_t *, sig,
                          document_signature_free(sig));
        smartlist_free(voter->sigs);
      }
      tor_free(voter);
    } SMARTLIST_FOREACH_END(voter);
    smartlist_free(ns->voters);
  }
  authority_cert_free(ns->cert);

  if (ns->routerstatus_list) {
    if (ns->type == NS_TYPE_VOTE || ns->type == NS_TYPE_OPINION) {
      SMARTLIST_FOREACH(ns->routerstatus_list, vote_routerstatus_t *, rs,
                        vote_routerstatus_free(rs));
    } else {
      SMARTLIST_FOREACH(ns->routerstatus_list, routerstatus_t *, rs,
                        routerstatus_free(rs));
    }

    smartlist_free(ns->routerstatus_list);
  }

  digestmap_free(ns->desc_digest_map, NULL);

  memwipe(ns, 11, sizeof(*ns));
  tor_free(ns);
}

/** Return the voter info from <b>vote</b> for the voter whose identity digest
 * is <b>identity</b>, or NULL if no such voter is associated with
 * <b>vote</b>. */
networkstatus_voter_info_t *
networkstatus_get_voter_by_id(networkstatus_t *vote,
                              const char *identity)
{
  if (!vote || !vote->voters)
    return NULL;
  SMARTLIST_FOREACH(vote->voters, networkstatus_voter_info_t *, voter,
    if (fast_memeq(voter->identity_digest, identity, DIGEST_LEN))
      return voter);
  return NULL;
}

/** Check whether the signature <b>sig</b> is correctly signed with the
 * signing key in <b>cert</b>.  Return -1 if <b>cert</b> doesn't match the
 * signing key; otherwise set the good_signature or bad_signature flag on
 * <b>voter</b>, and return 0. */
int
networkstatus_check_document_signature(const networkstatus_t *consensus,
                                       document_signature_t *sig,
                                       const authority_cert_t *cert)
{
  char key_digest[DIGEST_LEN];
  const int dlen = sig->alg == DIGEST_SHA1 ? DIGEST_LEN : DIGEST256_LEN;
  char *signed_digest;
  size_t signed_digest_len;

  if (crypto_pk_get_digest(cert->signing_key, key_digest)<0)
    return -1;
  if (tor_memneq(sig->signing_key_digest, key_digest, DIGEST_LEN) ||
      tor_memneq(sig->identity_digest, cert->cache_info.identity_digest,
                 DIGEST_LEN))
    return -1;

  if (authority_cert_is_blacklisted(cert)) {
    /* We implement blacklisting for authority signing keys by treating
     * all their signatures as always bad. That way we don't get into
     * crazy loops of dropping and re-fetching signatures. */
    log_warn(LD_DIR, "Ignoring a consensus signature made with deprecated"
             " signing key %s",
             hex_str(cert->signing_key_digest, DIGEST_LEN));
    sig->bad_signature = 1;
    return 0;
  }

  signed_digest_len = crypto_pk_keysize(cert->signing_key);
  signed_digest = tor_malloc(signed_digest_len);
  if (crypto_pk_public_checksig(cert->signing_key,
                                signed_digest,
                                signed_digest_len,
                                sig->signature,
                                sig->signature_len) < dlen ||
      tor_memneq(signed_digest, consensus->digests.d[sig->alg], dlen)) {
    log_warn(LD_DIR, "Got a bad signature on a networkstatus vote");
    sig->bad_signature = 1;
  } else {
    sig->good_signature = 1;
  }
  tor_free(signed_digest);
  return 0;
}

/** Given a v3 networkstatus consensus in <b>consensus</b>, check every
 * as-yet-unchecked signature on <b>consensus</b>.  Return 1 if there is a
 * signature from every recognized authority on it, 0 if there are
 * enough good signatures from recognized authorities on it, -1 if we might
 * get enough good signatures by fetching missing certificates, and -2
 * otherwise.  Log messages at INFO or WARN: if <b>warn</b> is over 1, warn
 * about every problem; if warn is at least 1, warn only if we can't get
 * enough signatures; if warn is negative, log nothing at all. */
int
networkstatus_check_consensus_signature(networkstatus_t *consensus,
                                        int warn)
{
  int n_good = 0;
  int n_missing_key = 0, n_dl_failed_key = 0;
  int n_bad = 0;
  int n_unknown = 0;
  int n_no_signature = 0;
  int n_v3_authorities = get_n_authorities(V3_DIRINFO);
  int n_required = n_v3_authorities/2 + 1;
  smartlist_t *list_good = smartlist_new();
  smartlist_t *list_no_signature = smartlist_new();
  smartlist_t *need_certs_from = smartlist_new();
  smartlist_t *unrecognized = smartlist_new();
  smartlist_t *missing_authorities = smartlist_new();
  int severity;
  time_t now = time(NULL);

  tor_assert(consensus->type == NS_TYPE_CONSENSUS);

  SMARTLIST_FOREACH_BEGIN(consensus->voters, networkstatus_voter_info_t *,
                          voter) {
    int good_here = 0;
    int bad_here = 0;
    int unknown_here = 0;
    int missing_key_here = 0, dl_failed_key_here = 0;
    SMARTLIST_FOREACH_BEGIN(voter->sigs, document_signature_t *, sig) {
      if (!sig->good_signature && !sig->bad_signature &&
          sig->signature) {
        /* we can try to check the signature. */
        int is_v3_auth = trusteddirserver_get_by_v3_auth_digest(
                                              sig->identity_digest) != NULL;
        authority_cert_t *cert =
          authority_cert_get_by_digests(sig->identity_digest,
                                        sig->signing_key_digest);
        tor_assert(tor_memeq(sig->identity_digest, voter->identity_digest,
                           DIGEST_LEN));

        if (!is_v3_auth) {
          smartlist_add(unrecognized, voter);
          ++unknown_here;
          continue;
        } else if (!cert || cert->expires < now) {
          smartlist_add(need_certs_from, voter);
          ++missing_key_here;
          if (authority_cert_dl_looks_uncertain(sig->identity_digest))
            ++dl_failed_key_here;
          continue;
        }
        if (networkstatus_check_document_signature(consensus, sig, cert) < 0) {
          smartlist_add(need_certs_from, voter);
          ++missing_key_here;
          if (authority_cert_dl_looks_uncertain(sig->identity_digest))
            ++dl_failed_key_here;
          continue;
        }
      }
      if (sig->good_signature)
        ++good_here;
      else if (sig->bad_signature)
        ++bad_here;
    } SMARTLIST_FOREACH_END(sig);

    if (good_here) {
      ++n_good;
      smartlist_add(list_good, voter->nickname);
    } else if (bad_here) {
      ++n_bad;
    } else if (missing_key_here) {
      ++n_missing_key;
      if (dl_failed_key_here)
        ++n_dl_failed_key;
    } else if (unknown_here) {
      ++n_unknown;
    } else {
      ++n_no_signature;
      smartlist_add(list_no_signature, voter->nickname);
    }
  } SMARTLIST_FOREACH_END(voter);

  /* Now see whether we're missing any voters entirely. */
  SMARTLIST_FOREACH(router_get_trusted_dir_servers(),
                    dir_server_t *, ds,
    {
      if ((ds->type & V3_DIRINFO) &&
          !networkstatus_get_voter_by_id(consensus, ds->v3_identity_digest))
        smartlist_add(missing_authorities, ds);
    });

  if (warn > 1 || (warn >= 0 &&
                   (n_good + n_missing_key - n_dl_failed_key < n_required))) {
    severity = LOG_WARN;
  } else {
    severity = LOG_INFO;
  }

  if (warn >= 0) {
    SMARTLIST_FOREACH(unrecognized, networkstatus_voter_info_t *, voter,
      {
        tor_log(severity, LD_DIR, "Consensus includes unrecognized authority "
                 "'%s' at %s:%d (contact %s; identity %s)",
                 voter->nickname, voter->address, (int)voter->dir_port,
                 voter->contact?voter->contact:"n/a",
                 hex_str(voter->identity_digest, DIGEST_LEN));
      });
    SMARTLIST_FOREACH(need_certs_from, networkstatus_voter_info_t *, voter,
      {
        tor_log(severity, LD_DIR, "Looks like we need to download a new "
                 "certificate from authority '%s' at %s:%d (contact %s; "
                 "identity %s)",
                 voter->nickname, voter->address, (int)voter->dir_port,
                 voter->contact?voter->contact:"n/a",
                 hex_str(voter->identity_digest, DIGEST_LEN));
      });
    SMARTLIST_FOREACH(missing_authorities, dir_server_t *, ds,
      {
        tor_log(severity, LD_DIR, "Consensus does not include configured "
                 "authority '%s' at %s:%d (identity %s)",
                 ds->nickname, ds->address, (int)ds->dir_port,
                 hex_str(ds->v3_identity_digest, DIGEST_LEN));
      });
    {
      char *joined;
      smartlist_t *sl = smartlist_new();
      char *tmp = smartlist_join_strings(list_good, " ", 0, NULL);
      smartlist_add_asprintf(sl,
                   "A consensus needs %d good signatures from recognized "
                   "authorities for us to accept it. This one has %d (%s).",
                   n_required, n_good, tmp);
      tor_free(tmp);
      if (n_no_signature) {
        tmp = smartlist_join_strings(list_no_signature, " ", 0, NULL);
        smartlist_add_asprintf(sl,
                     "%d (%s) of the authorities we know didn't sign it.",
                     n_no_signature, tmp);
        tor_free(tmp);
      }
      if (n_unknown) {
        smartlist_add_asprintf(sl,
                      "It has %d signatures from authorities we don't "
                      "recognize.", n_unknown);
      }
      if (n_bad) {
        smartlist_add_asprintf(sl, "%d of the signatures on it didn't verify "
                      "correctly.", n_bad);
      }
      if (n_missing_key) {
        smartlist_add_asprintf(sl,
                      "We were unable to check %d of the signatures, "
                      "because we were missing the keys.", n_missing_key);
      }
      joined = smartlist_join_strings(sl, " ", 0, NULL);
      tor_log(severity, LD_DIR, "%s", joined);
      tor_free(joined);
      SMARTLIST_FOREACH(sl, char *, c, tor_free(c));
      smartlist_free(sl);
    }
  }

  smartlist_free(list_good);
  smartlist_free(list_no_signature);
  smartlist_free(unrecognized);
  smartlist_free(need_certs_from);
  smartlist_free(missing_authorities);

  if (n_good == n_v3_authorities)
    return 1;
  else if (n_good >= n_required)
    return 0;
  else if (n_good + n_missing_key >= n_required)
    return -1;
  else
    return -2;
}

/** How far in the future do we allow a network-status to get before removing
 * it? (seconds) */
#define NETWORKSTATUS_ALLOW_SKEW (24*60*60)

/** Helper for bsearching a list of routerstatus_t pointers: compare a
 * digest in the key to the identity digest of a routerstatus_t. */
int
compare_digest_to_routerstatus_entry(const void *_key, const void **_member)
{
  const char *key = _key;
  const routerstatus_t *rs = *_member;
  return tor_memcmp(key, rs->identity_digest, DIGEST_LEN);
}

/** Helper for bsearching a list of routerstatus_t pointers: compare a
 * digest in the key to the identity digest of a routerstatus_t. */
int
compare_digest_to_vote_routerstatus_entry(const void *_key,
                                          const void **_member)
{
  const char *key = _key;
  const vote_routerstatus_t *vrs = *_member;
  return tor_memcmp(key, vrs->status.identity_digest, DIGEST_LEN);
}

/** As networkstatus_find_entry, but do not return a const pointer */
routerstatus_t *
networkstatus_vote_find_mutable_entry(networkstatus_t *ns, const char *digest)
{
  return smartlist_bsearch(ns->routerstatus_list, digest,
                           compare_digest_to_routerstatus_entry);
}

/** Return the entry in <b>ns</b> for the identity digest <b>digest</b>, or
 * NULL if none was found. */
const routerstatus_t *
networkstatus_vote_find_entry(networkstatus_t *ns, const char *digest)
{
  return networkstatus_vote_find_mutable_entry(ns, digest);
}

/*XXXX MOVE make this static once functions are moved into this file. */
/** Search the routerstatuses in <b>ns</b> for one whose identity digest is
 * <b>digest</b>.  Return value and set *<b>found_out</b> as for
 * smartlist_bsearch_idx(). */
int
networkstatus_vote_find_entry_idx(networkstatus_t *ns,
                                  const char *digest, int *found_out)
{
  return smartlist_bsearch_idx(ns->routerstatus_list, digest,
                               compare_digest_to_routerstatus_entry,
                               found_out);
}

/** As router_get_consensus_status_by_descriptor_digest, but does not return
 * a const pointer. */
routerstatus_t *
router_get_mutable_consensus_status_by_descriptor_digest(
                                                 networkstatus_t *consensus,
                                                 const char *digest)
{
  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(consensus->desc_digest_map, digest);
}

/** Return the consensus view of the status of the router whose current
 * <i>descriptor</i> digest in <b>consensus</b> is <b>digest</b>, or NULL if
 * no such router is known. */
const routerstatus_t *
router_get_consensus_status_by_descriptor_digest(networkstatus_t *consensus,
                                                 const char *digest)
{
  return router_get_mutable_consensus_status_by_descriptor_digest(
                                                          consensus, digest);
}

/** Given the digest of a router descriptor, return its current download
 * status, or NULL if the digest is unrecognized. */
download_status_t *
router_get_dl_status_by_descriptor_digest(const char *d)
{
  routerstatus_t *rs;
  if (!current_ns_consensus)
    return NULL;
  if ((rs = router_get_mutable_consensus_status_by_descriptor_digest(
                                              current_ns_consensus, d)))
    return &rs->dl_status;

  return NULL;
}

/** As router_get_consensus_status_by_id, but do not return a const pointer */
routerstatus_t *
router_get_mutable_consensus_status_by_id(const char *digest)
{
  if (!current_consensus)
    return NULL;
  return smartlist_bsearch(current_consensus->routerstatus_list, digest,
                           compare_digest_to_routerstatus_entry);
}

/** Return the consensus view of the status of the router whose identity
 * digest is <b>digest</b>, or NULL if we don't know about any such router. */
const routerstatus_t *
router_get_consensus_status_by_id(const char *digest)
{
  return router_get_mutable_consensus_status_by_id(digest);
}

/** Given a nickname (possibly verbose, possibly a hexadecimal digest), return
 * the corresponding routerstatus_t, or NULL if none exists.  Warn the
 * user if <b>warn_if_unnamed</b> is set, and they have specified a router by
 * nickname, but the Named flag isn't set for that router. */
const routerstatus_t *
router_get_consensus_status_by_nickname(const char *nickname,
                                        int warn_if_unnamed)
{
  const node_t *node = node_get_by_nickname(nickname, warn_if_unnamed);
  if (node)
    return node->rs;
  else
    return NULL;
}

/** Return the identity digest that's mapped to officially by
 * <b>nickname</b>. */
const char *
networkstatus_get_router_digest_by_nickname(const char *nickname)
{
  if (!named_server_map)
    return NULL;
  return strmap_get_lc(named_server_map, nickname);
}

/** Return true iff <b>nickname</b> is disallowed from being the nickname
 * of any server. */
int
networkstatus_nickname_is_unnamed(const char *nickname)
{
  if (!unnamed_server_map)
    return 0;
  return strmap_get_lc(unnamed_server_map, nickname) != NULL;
}

/** How frequently do directory authorities re-download fresh networkstatus
 * documents? */
#define AUTHORITY_NS_CACHE_INTERVAL (10*60)

/** How frequently do non-authority directory caches re-download fresh
 * networkstatus documents? */
#define NONAUTHORITY_NS_CACHE_INTERVAL (60*60)

/** Return true iff, given the options listed in <b>options</b>, <b>flavor</b>
 *  is the flavor of a consensus networkstatus that we would like to fetch. */
static int
we_want_to_fetch_flavor(const or_options_t *options, int flavor)
{
  if (flavor < 0 || flavor > N_CONSENSUS_FLAVORS) {
    /* This flavor is crazy; we don't want it */
    /*XXXX handle unrecognized flavors later */
    return 0;
  }
  if (authdir_mode_v3(options) || directory_caches_dir_info(options)) {
    /* We want to serve all flavors to others, regardless if we would use
     * it ourselves. */
    return 1;
  }
  if (options->FetchUselessDescriptors) {
    /* In order to get all descriptors, we need to fetch all consensuses. */
    return 1;
  }
  /* Otherwise, we want the flavor only if we want to use it to build
   * circuits. */
  return flavor == usable_consensus_flavor();
}

/** How long will we hang onto a possibly live consensus for which we're
 * fetching certs before we check whether there is a better one? */
#define DELAY_WHILE_FETCHING_CERTS (20*60)

/** If we want to download a fresh consensus, launch a new download as
 * appropriate. */
static void
update_consensus_networkstatus_downloads(time_t now)
{
  int i;
  const or_options_t *options = get_options();

  for (i=0; i < N_CONSENSUS_FLAVORS; ++i) {
    /* XXXX need some way to download unknown flavors if we are caching. */
    const char *resource;
    consensus_waiting_for_certs_t *waiting;
    networkstatus_t *c;

    if (! we_want_to_fetch_flavor(options, i))
      continue;

    c = networkstatus_get_latest_consensus_by_flavor(i);
    if (! (c && c->valid_after <= now && now <= c->valid_until)) {
      /* No live consensus? Get one now!*/
      time_to_download_next_consensus[i] = now;
    }

    if (time_to_download_next_consensus[i] > now)
      continue; /* Wait until the current consensus is older. */

    resource = networkstatus_get_flavor_name(i);

    if (!download_status_is_ready(&consensus_dl_status[i], now,
                             options->TestingConsensusMaxDownloadTries))
      continue; /* We failed downloading a consensus too recently. */
    if (connection_dir_get_by_purpose_and_resource(
                                DIR_PURPOSE_FETCH_CONSENSUS, resource))
      continue; /* There's an in-progress download.*/

    waiting = &consensus_waiting_for_certs[i];
    if (waiting->consensus) {
      /* XXXX make sure this doesn't delay sane downloads. */
      if (waiting->set_at + DELAY_WHILE_FETCHING_CERTS > now) {
        continue; /* We're still getting certs for this one. */
      } else {
        if (!waiting->dl_failed) {
          download_status_failed(&consensus_dl_status[i], 0);
          waiting->dl_failed=1;
        }
      }
    }

    log_info(LD_DIR, "Launching %s networkstatus consensus download.",
             networkstatus_get_flavor_name(i));

    directory_get_from_dirserver(DIR_PURPOSE_FETCH_CONSENSUS,
                                 ROUTER_PURPOSE_GENERAL, resource,
                                 PDS_RETRY_IF_NO_SERVERS);
  }
}

/** Called when an attempt to download a consensus fails: note that the
 * failure occurred, and possibly retry. */
void
networkstatus_consensus_download_failed(int status_code, const char *flavname)
{
  int flav = networkstatus_parse_flavor_name(flavname);
  if (flav >= 0) {
    tor_assert(flav < N_CONSENSUS_FLAVORS);
    /* XXXX handle unrecognized flavors */
    download_status_failed(&consensus_dl_status[flav], status_code);
    /* Retry immediately, if appropriate. */
    update_consensus_networkstatus_downloads(time(NULL));
  }
}

/** How long do we (as a cache) wait after a consensus becomes non-fresh
 * before trying to fetch another? */
#define CONSENSUS_MIN_SECONDS_BEFORE_CACHING 120

/** Update the time at which we'll consider replacing the current
 * consensus of flavor <b>flav</b> */
static void
update_consensus_networkstatus_fetch_time_impl(time_t now, int flav)
{
  const or_options_t *options = get_options();
  networkstatus_t *c = networkstatus_get_latest_consensus_by_flavor(flav);
  const char *flavor = networkstatus_get_flavor_name(flav);
  if (! we_want_to_fetch_flavor(get_options(), flav))
    return;

  if (c && c->valid_after <= now && now <= c->valid_until) {
    long dl_interval;
    long interval = c->fresh_until - c->valid_after;
    long min_sec_before_caching = CONSENSUS_MIN_SECONDS_BEFORE_CACHING;
    time_t start;

    if (min_sec_before_caching > interval/16) {
      /* Usually we allow 2-minutes slop factor in case clocks get
         desynchronized a little.  If we're on a private network with
         a crazy-fast voting interval, though, 2 minutes may be too
         much. */
      min_sec_before_caching = interval/16;
    }

    if (directory_fetches_dir_info_early(options)) {
      /* We want to cache the next one at some point after this one
       * is no longer fresh... */
      start = c->fresh_until + min_sec_before_caching;
      /* Some clients may need the consensus sooner than others. */
      if (options->FetchDirInfoExtraEarly || authdir_mode_v3(options)) {
        dl_interval = 60;
        if (min_sec_before_caching + dl_interval > interval)
          dl_interval = interval/2;
      } else {
        /* But only in the first half-interval after that. */
        dl_interval = interval/2;
      }
    } else {
      /* We're an ordinary client or a bridge. Give all the caches enough
       * time to download the consensus. */
      start = c->fresh_until + (interval*3)/4;
      /* But download the next one well before this one is expired. */
      dl_interval = ((c->valid_until - start) * 7 )/ 8;

      /* If we're a bridge user, make use of the numbers we just computed
       * to choose the rest of the interval *after* them. */
      if (directory_fetches_dir_info_later(options)) {
        /* Give all the *clients* enough time to download the consensus. */
        start = start + dl_interval + min_sec_before_caching;
        /* But try to get it before ours actually expires. */
        dl_interval = (c->valid_until - start) - min_sec_before_caching;
      }
    }
    if (dl_interval < 1)
      dl_interval = 1;
    /* We must not try to replace c while it's still fresh: */
    tor_assert(c->fresh_until < start);
    /* We must download the next one before c is invalid: */
    tor_assert(start+dl_interval < c->valid_until);
    time_to_download_next_consensus[flav] =
      start + crypto_rand_int((int)dl_interval);
    {
      char tbuf1[ISO_TIME_LEN+1];
      char tbuf2[ISO_TIME_LEN+1];
      char tbuf3[ISO_TIME_LEN+1];
      format_local_iso_time(tbuf1, c->fresh_until);
      format_local_iso_time(tbuf2, c->valid_until);
      format_local_iso_time(tbuf3, time_to_download_next_consensus[flav]);
      log_info(LD_DIR, "Live %s consensus %s the most recent until %s and "
               "will expire at %s; fetching the next one at %s.",
               flavor, (c->fresh_until > now) ? "will be" : "was",
               tbuf1, tbuf2, tbuf3);
    }
  } else {
    time_to_download_next_consensus[flav] = now;
    log_info(LD_DIR, "No live %s consensus; we should fetch one immediately.",
             flavor);
  }
}

/** Update the time at which we'll consider replacing the current
 * consensus of flavor 'flavor' */
void
update_consensus_networkstatus_fetch_time(time_t now)
{
  int i;
  for (i = 0; i < N_CONSENSUS_FLAVORS; ++i) {
    if (we_want_to_fetch_flavor(get_options(), i))
      update_consensus_networkstatus_fetch_time_impl(now, i);
  }
}

/** Return 1 if there's a reason we shouldn't try any directory
 * fetches yet (e.g. we demand bridges and none are yet known).
 * Else return 0.

 * If we return 1 and <b>msg_out</b> is provided, set <b>msg_out</b>
 * to an explanation of why directory fetches are delayed. (If we
 * return 0, we set msg_out to NULL.)
 */
int
should_delay_dir_fetches(const or_options_t *options, const char **msg_out)
{
  if (msg_out) {
    *msg_out = NULL;
  }

  if (options->UseBridges) {
    if (!any_bridge_descriptors_known()) {
      if (msg_out) {
        *msg_out = "No running bridges";
      }
      log_info(LD_DIR, "Delaying dir fetches (no running bridges known)");
      return 1;
    }

    if (pt_proxies_configuration_pending()) {
      if (msg_out) {
        *msg_out = "Pluggable transport proxies still configuring";
      }
      log_info(LD_DIR, "Delaying dir fetches (pt proxies still configuring)");
      return 1;
    }
  }

  return 0;
}

/** Launch requests for networkstatus documents and authority certificates as
 * appropriate. */
void
update_networkstatus_downloads(time_t now)
{
  const or_options_t *options = get_options();
  if (should_delay_dir_fetches(options, NULL))
    return;
  update_consensus_networkstatus_downloads(now);
  update_certificate_downloads(now);
}

/** Launch requests as appropriate for missing directory authority
 * certificates. */
void
update_certificate_downloads(time_t now)
{
  int i;
  for (i = 0; i < N_CONSENSUS_FLAVORS; ++i) {
    if (consensus_waiting_for_certs[i].consensus)
      authority_certs_fetch_missing(consensus_waiting_for_certs[i].consensus,
                                    now);
  }

  if (current_ns_consensus)
    authority_certs_fetch_missing(current_ns_consensus, now);
  if (current_md_consensus)
    authority_certs_fetch_missing(current_md_consensus, now);
}

/** Return 1 if we have a consensus but we don't have enough certificates
 * to start using it yet. */
int
consensus_is_waiting_for_certs(void)
{
  return consensus_waiting_for_certs[usable_consensus_flavor()].consensus
    ? 1 : 0;
}

/** Return the most recent consensus that we have downloaded, or NULL if we
 * don't have one. */
networkstatus_t *
networkstatus_get_latest_consensus(void)
{
  return current_consensus;
}

/** Return the latest consensus we have whose flavor matches <b>f</b>, or NULL
 * if we don't have one. */
networkstatus_t *
networkstatus_get_latest_consensus_by_flavor(consensus_flavor_t f)
{
  if (f == FLAV_NS)
    return current_ns_consensus;
  else if (f == FLAV_MICRODESC)
    return current_md_consensus;
  else {
    tor_assert(0);
    return NULL;
  }
}

/** Return the most recent consensus that we have downloaded, or NULL if it is
 * no longer live. */
networkstatus_t *
networkstatus_get_live_consensus(time_t now)
{
  if (current_consensus &&
      current_consensus->valid_after <= now &&
      now <= current_consensus->valid_until)
    return current_consensus;
  else
    return NULL;
}

/* XXXX remove this in favor of get_live_consensus. But actually,
 * leave something like it for bridge users, who need to not totally
 * lose if they spend a while fetching a new consensus. */
/** As networkstatus_get_live_consensus(), but is way more tolerant of expired
 * consensuses. */
networkstatus_t *
networkstatus_get_reasonably_live_consensus(time_t now, int flavor)
{
#define REASONABLY_LIVE_TIME (24*60*60)
  networkstatus_t *consensus =
    networkstatus_get_latest_consensus_by_flavor(flavor);
  if (consensus &&
      consensus->valid_after <= now &&
      now <= consensus->valid_until+REASONABLY_LIVE_TIME)
    return consensus;
  else
    return NULL;
}

/** Given two router status entries for the same router identity, return 1 if
 * if the contents have changed between them. Otherwise, return 0. */
static int
routerstatus_has_changed(const routerstatus_t *a, const routerstatus_t *b)
{
  tor_assert(tor_memeq(a->identity_digest, b->identity_digest, DIGEST_LEN));

  return strcmp(a->nickname, b->nickname) ||
         fast_memneq(a->descriptor_digest, b->descriptor_digest, DIGEST_LEN) ||
         a->addr != b->addr ||
         a->or_port != b->or_port ||
         a->dir_port != b->dir_port ||
         a->is_authority != b->is_authority ||
         a->is_exit != b->is_exit ||
         a->is_stable != b->is_stable ||
         a->is_fast != b->is_fast ||
         a->is_flagged_running != b->is_flagged_running ||
         a->is_named != b->is_named ||
         a->is_unnamed != b->is_unnamed ||
         a->is_valid != b->is_valid ||
         a->is_possible_guard != b->is_possible_guard ||
         a->is_bad_exit != b->is_bad_exit ||
         a->is_bad_directory != b->is_bad_directory ||
         a->is_hs_dir != b->is_hs_dir ||
         a->version_known != b->version_known;
}

/** Notify controllers of any router status entries that changed between
 * <b>old_c</b> and <b>new_c</b>. */
static void
notify_control_networkstatus_changed(const networkstatus_t *old_c,
                                     const networkstatus_t *new_c)
{
  smartlist_t *changed;
  if (old_c == new_c)
    return;

  /* tell the controller exactly which relays are still listed, as well
   * as what they're listed as */
  control_event_newconsensus(new_c);

  if (!control_event_is_interesting(EVENT_NS))
    return;

  if (!old_c) {
    control_event_networkstatus_changed(new_c->routerstatus_list);
    return;
  }
  changed = smartlist_new();

  SMARTLIST_FOREACH_JOIN(
                     old_c->routerstatus_list, const routerstatus_t *, rs_old,
                     new_c->routerstatus_list, const routerstatus_t *, rs_new,
                     tor_memcmp(rs_old->identity_digest,
                            rs_new->identity_digest, DIGEST_LEN),
                     smartlist_add(changed, (void*) rs_new)) {
    if (routerstatus_has_changed(rs_old, rs_new))
      smartlist_add(changed, (void*)rs_new);
  } SMARTLIST_FOREACH_JOIN_END(rs_old, rs_new);

  control_event_networkstatus_changed(changed);
  smartlist_free(changed);
}

/** Copy all the ancillary information (like router download status and so on)
 * from <b>old_c</b> to <b>new_c</b>. */
static void
networkstatus_copy_old_consensus_info(networkstatus_t *new_c,
                                      const networkstatus_t *old_c)
{
  if (old_c == new_c)
    return;
  if (!old_c || !smartlist_len(old_c->routerstatus_list))
    return;

  SMARTLIST_FOREACH_JOIN(old_c->routerstatus_list, routerstatus_t *, rs_old,
                         new_c->routerstatus_list, routerstatus_t *, rs_new,
                         tor_memcmp(rs_old->identity_digest,
                                rs_new->identity_digest, DIGEST_LEN),
                         STMT_NIL) {
    /* Okay, so we're looking at the same identity. */
    rs_new->last_dir_503_at = rs_old->last_dir_503_at;

    if (tor_memeq(rs_old->descriptor_digest, rs_new->descriptor_digest,
                DIGEST_LEN)) {
      /* And the same descriptor too! */
      memcpy(&rs_new->dl_status, &rs_old->dl_status,sizeof(download_status_t));
    }
  } SMARTLIST_FOREACH_JOIN_END(rs_old, rs_new);
}

/** Try to replace the current cached v3 networkstatus with the one in
 * <b>consensus</b>.  If we don't have enough certificates to validate it,
 * store it in consensus_waiting_for_certs and launch a certificate fetch.
 *
 * If flags & NSSET_FROM_CACHE, this networkstatus has come from the disk
 * cache.  If flags & NSSET_WAS_WAITING_FOR_CERTS, this networkstatus was
 * already received, but we were waiting for certificates on it.  If flags &
 * NSSET_DONT_DOWNLOAD_CERTS, do not launch certificate downloads as needed.
 * If flags & NSSET_ACCEPT_OBSOLETE, then we should be willing to take this
 * consensus, even if it comes from many days in the past.
 *
 * Return 0 on success, <0 on failure.  On failure, caller should increment
 * the failure count as appropriate.
 *
 * We return -1 for mild failures that don't need to be reported to the
 * user, and -2 for more serious problems.
 */
int
networkstatus_set_current_consensus(const char *consensus,
                                    const char *flavor,
                                    unsigned flags)
{
  networkstatus_t *c=NULL;
  int r, result = -1;
  time_t now = time(NULL);
  const or_options_t *options = get_options();
  char *unverified_fname = NULL, *consensus_fname = NULL;
  int flav = networkstatus_parse_flavor_name(flavor);
  const unsigned from_cache = flags & NSSET_FROM_CACHE;
  const unsigned was_waiting_for_certs = flags & NSSET_WAS_WAITING_FOR_CERTS;
  const unsigned dl_certs = !(flags & NSSET_DONT_DOWNLOAD_CERTS);
  const unsigned accept_obsolete = flags & NSSET_ACCEPT_OBSOLETE;
  const unsigned require_flavor = flags & NSSET_REQUIRE_FLAVOR;
  const digests_t *current_digests = NULL;
  consensus_waiting_for_certs_t *waiting = NULL;
  time_t current_valid_after = 0;
  int free_consensus = 1; /* Free 'c' at the end of the function */
  int old_ewma_enabled;

  if (flav < 0) {
    /* XXXX we don't handle unrecognized flavors yet. */
    log_warn(LD_BUG, "Unrecognized consensus flavor %s", flavor);
    return -2;
  }

  /* Make sure it's parseable. */
  c = networkstatus_parse_vote_from_string(consensus, NULL, NS_TYPE_CONSENSUS);
  if (!c) {
    log_warn(LD_DIR, "Unable to parse networkstatus consensus");
    result = -2;
    goto done;
  }

  if ((int)c->flavor != flav) {
    /* This wasn't the flavor we thought we were getting. */
    if (require_flavor) {
      log_warn(LD_DIR, "Got consensus with unexpected flavor %s (wanted %s)",
               networkstatus_get_flavor_name(c->flavor), flavor);
      goto done;
    }
    flav = c->flavor;
    flavor = networkstatus_get_flavor_name(flav);
  }

  if (flav != usable_consensus_flavor() &&
      !directory_caches_dir_info(options)) {
    /* This consensus is totally boring to us: we won't use it, and we won't
     * serve it.  Drop it. */
    goto done;
  }

  if (from_cache && !accept_obsolete &&
      c->valid_until < now-OLD_ROUTER_DESC_MAX_AGE) {
    log_info(LD_DIR, "Loaded an expired consensus. Discarding.");
    goto done;
  }

  if (!strcmp(flavor, "ns")) {
    consensus_fname = get_datadir_fname("cached-consensus");
    unverified_fname = get_datadir_fname("unverified-consensus");
    if (current_ns_consensus) {
      current_digests = &current_ns_consensus->digests;
      current_valid_after = current_ns_consensus->valid_after;
    }
  } else if (!strcmp(flavor, "microdesc")) {
    consensus_fname = get_datadir_fname("cached-microdesc-consensus");
    unverified_fname = get_datadir_fname("unverified-microdesc-consensus");
    if (current_md_consensus) {
      current_digests = &current_md_consensus->digests;
      current_valid_after = current_md_consensus->valid_after;
    }
  } else {
    cached_dir_t *cur;
    char buf[128];
    tor_snprintf(buf, sizeof(buf), "cached-%s-consensus", flavor);
    consensus_fname = get_datadir_fname(buf);
    tor_snprintf(buf, sizeof(buf), "unverified-%s-consensus", flavor);
    unverified_fname = get_datadir_fname(buf);
    cur = dirserv_get_consensus(flavor);
    if (cur) {
      current_digests = &cur->digests;
      current_valid_after = cur->published;
    }
  }

  if (current_digests &&
      tor_memeq(&c->digests, current_digests, sizeof(c->digests))) {
    /* We already have this one. That's a failure. */
    log_info(LD_DIR, "Got a %s consensus we already have", flavor);
    goto done;
  }

  if (current_valid_after && c->valid_after <= current_valid_after) {
    /* We have a newer one.  There's no point in accepting this one,
     * even if it's great. */
    log_info(LD_DIR, "Got a %s consensus at least as old as the one we have",
             flavor);
    goto done;
  }

  /* Make sure it's signed enough. */
  if ((r=networkstatus_check_consensus_signature(c, 1))<0) {
    if (r == -1) {
      /* Okay, so it _might_ be signed enough if we get more certificates. */
      if (!was_waiting_for_certs) {
        log_info(LD_DIR,
                 "Not enough certificates to check networkstatus consensus");
      }
      if (!current_valid_after ||
          c->valid_after > current_valid_after) {
        waiting = &consensus_waiting_for_certs[flav];
        networkstatus_vote_free(waiting->consensus);
        tor_free(waiting->body);
        waiting->consensus = c;
        free_consensus = 0;
        waiting->body = tor_strdup(consensus);
        waiting->set_at = now;
        waiting->dl_failed = 0;
        if (!from_cache) {
          write_str_to_file(unverified_fname, consensus, 0);
        }
        if (dl_certs)
          authority_certs_fetch_missing(c, now);
        /* This case is not a success or a failure until we get the certs
         * or fail to get the certs. */
        result = 0;
      } else {
        /* Even if we had enough signatures, we'd never use this as the
         * latest consensus. */
        if (was_waiting_for_certs && from_cache)
          if (unlink(unverified_fname) != 0) {
            log_warn(LD_FS,
                     "Failed to unlink %s: %s",
                     unverified_fname, strerror(errno));
          }
      }
      goto done;
    } else {
      /* This can never be signed enough:  Kill it. */
      if (!was_waiting_for_certs) {
        log_warn(LD_DIR, "Not enough good signatures on networkstatus "
                 "consensus");
        result = -2;
      }
      if (was_waiting_for_certs && (r < -1) && from_cache) {
        if (unlink(unverified_fname) != 0) {
            log_warn(LD_FS,
                     "Failed to unlink %s: %s",
                     unverified_fname, strerror(errno));
        }
      }
      goto done;
    }
  }

  if (!from_cache && flav == usable_consensus_flavor())
    control_event_client_status(LOG_NOTICE, "CONSENSUS_ARRIVED");

  /* Are we missing any certificates at all? */
  if (r != 1 && dl_certs)
    authority_certs_fetch_missing(c, now);

  if (flav == usable_consensus_flavor()) {
    notify_control_networkstatus_changed(current_consensus, c);
  }
  if (flav == FLAV_NS) {
    if (current_ns_consensus) {
      networkstatus_copy_old_consensus_info(c, current_ns_consensus);
      networkstatus_vote_free(current_ns_consensus);
      /* Defensive programming : we should set current_consensus very soon,
       * but we're about to call some stuff in the meantime, and leaving this
       * dangling pointer around has proven to be trouble. */
      current_ns_consensus = NULL;
    }
    current_ns_consensus = c;
    free_consensus = 0; /* avoid free */
  } else if (flav == FLAV_MICRODESC) {
    if (current_md_consensus) {
      networkstatus_copy_old_consensus_info(c, current_md_consensus);
      networkstatus_vote_free(current_md_consensus);
      /* more defensive programming */
      current_md_consensus = NULL;
    }
    current_md_consensus = c;
    free_consensus = 0; /* avoid free */
  }

  waiting = &consensus_waiting_for_certs[flav];
  if (waiting->consensus &&
      waiting->consensus->valid_after <= c->valid_after) {
    networkstatus_vote_free(waiting->consensus);
    waiting->consensus = NULL;
    if (consensus != waiting->body)
      tor_free(waiting->body);
    else
      waiting->body = NULL;
    waiting->set_at = 0;
    waiting->dl_failed = 0;
    if (unlink(unverified_fname) != 0) {
      log_warn(LD_FS,
               "Failed to unlink %s: %s",
               unverified_fname, strerror(errno));
    }
  }

  /* Reset the failure count only if this consensus is actually valid. */
  if (c->valid_after <= now && now <= c->valid_until) {
    download_status_reset(&consensus_dl_status[flav]);
  } else {
    if (!from_cache)
      download_status_failed(&consensus_dl_status[flav], 0);
  }

  if (flav == usable_consensus_flavor()) {
    /* XXXXNM Microdescs: needs a non-ns variant. ???? NM*/
    update_consensus_networkstatus_fetch_time(now);

    nodelist_set_consensus(current_consensus);

    dirvote_recalculate_timing(options, now);
    routerstatus_list_update_named_server_map();

    /* Update ewma and adjust policy if needed; first cache the old value */
    old_ewma_enabled = cell_ewma_enabled();
    /* Change the cell EWMA settings */
    cell_ewma_set_scale_factor(options, networkstatus_get_latest_consensus());
    /* If we just enabled ewma, set the cmux policy on all active channels */
    if (cell_ewma_enabled() && !old_ewma_enabled) {
      channel_set_cmux_policy_everywhere(&ewma_policy);
    } else if (!cell_ewma_enabled() && old_ewma_enabled) {
      /* Turn it off everywhere */
      channel_set_cmux_policy_everywhere(NULL);
    }

    /* XXXX024 this call might be unnecessary here: can changing the
     * current consensus really alter our view of any OR's rate limits? */
    connection_or_update_token_buckets(get_connection_array(), options);

    circuit_build_times_new_consensus_params(get_circuit_build_times_mutable(),
        current_consensus);
  }

  if (directory_caches_dir_info(options)) {
    dirserv_set_cached_consensus_networkstatus(consensus,
                                               flavor,
                                               &c->digests,
                                               c->valid_after);
  }

  if (!from_cache) {
    write_str_to_file(consensus_fname, consensus, 0);
  }

/** If a consensus appears more than this many seconds before its declared
 * valid-after time, declare that our clock is skewed. */
#define EARLY_CONSENSUS_NOTICE_SKEW 60

  if (now < c->valid_after - EARLY_CONSENSUS_NOTICE_SKEW) {
    char tbuf[ISO_TIME_LEN+1];
    char dbuf[64];
    long delta = now - c->valid_after;
    format_iso_time(tbuf, c->valid_after);
    format_time_interval(dbuf, sizeof(dbuf), delta);
    log_warn(LD_GENERAL, "Our clock is %s behind the time published in the "
             "consensus network status document (%s UTC).  Tor needs an "
             "accurate clock to work correctly. Please check your time and "
             "date settings!", dbuf, tbuf);
    control_event_general_status(LOG_WARN,
                    "CLOCK_SKEW MIN_SKEW=%ld SOURCE=CONSENSUS", delta);
  }

  router_dir_info_changed();

  result = 0;
 done:
  if (free_consensus)
    networkstatus_vote_free(c);
  tor_free(consensus_fname);
  tor_free(unverified_fname);
  return result;
}

/** Called when we have gotten more certificates: see whether we can
 * now verify a pending consensus. */
void
networkstatus_note_certs_arrived(void)
{
  int i;
  for (i=0; i<N_CONSENSUS_FLAVORS; ++i) {
    consensus_waiting_for_certs_t *waiting = &consensus_waiting_for_certs[i];
    if (!waiting->consensus)
      continue;
    if (networkstatus_check_consensus_signature(waiting->consensus, 0)>=0) {
      char *waiting_body = waiting->body;
      if (!networkstatus_set_current_consensus(
                                 waiting_body,
                                 networkstatus_get_flavor_name(i),
                                 NSSET_WAS_WAITING_FOR_CERTS)) {
        tor_free(waiting_body);
      }
    }
  }
}

/** If the network-status list has changed since the last time we called this
 * function, update the status of every routerinfo from the network-status
 * list. If <b>dir_version</b> is 2, it's a v2 networkstatus that changed.
 * If <b>dir_version</b> is 3, it's a v3 consensus that changed.
 */
void
routers_update_all_from_networkstatus(time_t now, int dir_version)
{
  routerlist_t *rl = router_get_routerlist();
  networkstatus_t *consensus = networkstatus_get_reasonably_live_consensus(now,
                                                                     FLAV_NS);

  if (!consensus || dir_version < 3) /* nothing more we should do */
    return;

  /* calls router_dir_info_changed() when it's done -- more routers
   * might be up or down now, which might affect whether there's enough
   * directory info. */
  routers_update_status_from_consensus_networkstatus(rl->routers, 0);

  SMARTLIST_FOREACH(rl->routers, routerinfo_t *, ri,
                    ri->cache_info.routerlist_index = ri_sl_idx);
  if (rl->old_routers)
    signed_descs_update_status_from_consensus_networkstatus(rl->old_routers);

  if (!have_warned_about_old_version) {
    int is_server = server_mode(get_options());
    version_status_t status;
    const char *recommended = is_server ?
      consensus->server_versions : consensus->client_versions;
    status = tor_version_is_obsolete(VERSION, recommended);

    if (status == VS_RECOMMENDED) {
      log_info(LD_GENERAL, "The directory authorities say my version is ok.");
    } else if (status == VS_EMPTY) {
      log_info(LD_GENERAL,
               "The directory authorities don't recommend any versions.");
    } else if (status == VS_NEW || status == VS_NEW_IN_SERIES) {
      if (!have_warned_about_new_version) {
        log_notice(LD_GENERAL, "This version of Tor (%s) is newer than any "
                   "recommended version%s, according to the directory "
                   "authorities. Recommended versions are: %s",
                   VERSION,
                   status == VS_NEW_IN_SERIES ? " in its series" : "",
                   recommended);
        have_warned_about_new_version = 1;
        control_event_general_status(LOG_WARN, "DANGEROUS_VERSION "
                                     "CURRENT=%s REASON=%s RECOMMENDED=\"%s\"",
                                     VERSION, "NEW", recommended);
      }
    } else {
      log_warn(LD_GENERAL, "Please upgrade! "
               "This version of Tor (%s) is %s, according to the directory "
               "authorities. Recommended versions are: %s",
               VERSION,
               status == VS_OLD ? "obsolete" : "not recommended",
               recommended);
      have_warned_about_old_version = 1;
      control_event_general_status(LOG_WARN, "DANGEROUS_VERSION "
           "CURRENT=%s REASON=%s RECOMMENDED=\"%s\"",
           VERSION, status == VS_OLD ? "OBSOLETE" : "UNRECOMMENDED",
           recommended);
    }
  }
}

/** Update our view of the list of named servers from the most recently
 * retrieved networkstatus consensus. */
static void
routerstatus_list_update_named_server_map(void)
{
  if (!current_consensus)
    return;

  strmap_free(named_server_map, tor_free_);
  named_server_map = strmap_new();
  strmap_free(unnamed_server_map, NULL);
  unnamed_server_map = strmap_new();
  SMARTLIST_FOREACH_BEGIN(current_consensus->routerstatus_list,
                          const routerstatus_t *, rs) {
      if (rs->is_named) {
        strmap_set_lc(named_server_map, rs->nickname,
                      tor_memdup(rs->identity_digest, DIGEST_LEN));
      }
      if (rs->is_unnamed) {
        strmap_set_lc(unnamed_server_map, rs->nickname, (void*)1);
      }
  } SMARTLIST_FOREACH_END(rs);
}

/** Given a list <b>routers</b> of routerinfo_t *, update each status field
 * according to our current consensus networkstatus.  May re-order
 * <b>routers</b>. */
void
routers_update_status_from_consensus_networkstatus(smartlist_t *routers,
                                                   int reset_failures)
{
  const or_options_t *options = get_options();
  int authdir = authdir_mode_v3(options);
  networkstatus_t *ns = current_consensus;
  if (!ns || !smartlist_len(ns->routerstatus_list))
    return;

  routers_sort_by_identity(routers);

  SMARTLIST_FOREACH_JOIN(ns->routerstatus_list, routerstatus_t *, rs,
                         routers, routerinfo_t *, router,
                         tor_memcmp(rs->identity_digest,
                               router->cache_info.identity_digest, DIGEST_LEN),
  {
  }) {
    /* Is it the same descriptor, or only the same identity? */
    if (tor_memeq(router->cache_info.signed_descriptor_digest,
                rs->descriptor_digest, DIGEST_LEN)) {
      if (ns->valid_until > router->cache_info.last_listed_as_valid_until)
        router->cache_info.last_listed_as_valid_until = ns->valid_until;
    }

    if (authdir) {
      /* If we _are_ an authority, we should check whether this router
       * is one that will cause us to need a reachability test. */
      routerinfo_t *old_router =
        router_get_mutable_by_digest(router->cache_info.identity_digest);
      if (old_router != router) {
        router->needs_retest_if_added =
          dirserv_should_launch_reachability_test(router, old_router);
      }
    }
    if (reset_failures) {
      download_status_reset(&rs->dl_status);
    }
  } SMARTLIST_FOREACH_JOIN_END(rs, router);

  router_dir_info_changed();
}

/** Given a list of signed_descriptor_t, update their fields (mainly, when
 * they were last listed) from the most recent consensus. */
void
signed_descs_update_status_from_consensus_networkstatus(smartlist_t *descs)
{
  networkstatus_t *ns = current_ns_consensus;
  if (!ns)
    return;

  if (!ns->desc_digest_map) {
    char dummy[DIGEST_LEN];
    /* instantiates the digest map. */
    memset(dummy, 0, sizeof(dummy));
    router_get_consensus_status_by_descriptor_digest(ns, dummy);
  }
  SMARTLIST_FOREACH(descs, signed_descriptor_t *, d,
  {
    const routerstatus_t *rs = digestmap_get(ns->desc_digest_map,
                                       d->signed_descriptor_digest);
    if (rs) {
      if (ns->valid_until > d->last_listed_as_valid_until)
        d->last_listed_as_valid_until = ns->valid_until;
    }
  });
}

/** Generate networkstatus lines for a single routerstatus_t object, and
 * return the result in a newly allocated string.  Used only by controller
 * interface (for now.) */
char *
networkstatus_getinfo_helper_single(const routerstatus_t *rs)
{
  return routerstatus_format_entry(rs, NULL, NS_CONTROL_PORT, NULL);
}

/** Alloc and return a string describing routerstatuses for the most
 * recent info of each router we know about that is of purpose
 * <b>purpose_string</b>. Return NULL if unrecognized purpose.
 *
 * Right now this function is oriented toward listing bridges (you
 * shouldn't use this for general-purpose routers, since those
 * should be listed from the consensus, not from the routers list). */
char *
networkstatus_getinfo_by_purpose(const char *purpose_string, time_t now)
{
  time_t cutoff = now - ROUTER_MAX_AGE_TO_PUBLISH;
  char *answer;
  routerlist_t *rl = router_get_routerlist();
  smartlist_t *statuses;
  uint8_t purpose = router_purpose_from_string(purpose_string);
  routerstatus_t rs;
  int bridge_auth = authdir_mode_bridge(get_options());

  if (purpose == ROUTER_PURPOSE_UNKNOWN) {
    log_info(LD_DIR, "Unrecognized purpose '%s' when listing router statuses.",
             purpose_string);
    return NULL;
  }

  statuses = smartlist_new();
  SMARTLIST_FOREACH_BEGIN(rl->routers, routerinfo_t *, ri) {
    node_t *node = node_get_mutable_by_id(ri->cache_info.identity_digest);
    if (!node)
      continue;
    if (ri->cache_info.published_on < cutoff)
      continue;
    if (ri->purpose != purpose)
      continue;
    if (bridge_auth && ri->purpose == ROUTER_PURPOSE_BRIDGE)
      dirserv_set_router_is_running(ri, now);
    /* then generate and write out status lines for each of them */
    set_routerstatus_from_routerinfo(&rs, node, ri, now, 0, 0, 0, 0);
    smartlist_add(statuses, networkstatus_getinfo_helper_single(&rs));
  } SMARTLIST_FOREACH_END(ri);

  answer = smartlist_join_strings(statuses, "", 0, NULL);
  SMARTLIST_FOREACH(statuses, char *, cp, tor_free(cp));
  smartlist_free(statuses);
  return answer;
}

/** Write out router status entries for all our bridge descriptors. */
void
networkstatus_dump_bridge_status_to_file(time_t now)
{
  char *status = networkstatus_getinfo_by_purpose("bridge", now);
  const or_options_t *options = get_options();
  char *fname = NULL;
  char *thresholds = NULL, *thresholds_and_status = NULL;
  routerlist_t *rl = router_get_routerlist();
  dirserv_compute_bridge_flag_thresholds(rl);
  thresholds = dirserv_get_flag_thresholds_line();
  tor_asprintf(&thresholds_and_status, "flag-thresholds %s\n%s",
               thresholds, status);
  tor_asprintf(&fname, "%s"PATH_SEPARATOR"networkstatus-bridges",
               options->DataDirectory);
  write_str_to_file(fname,thresholds_and_status,0);
  tor_free(thresholds);
  tor_free(thresholds_and_status);
  tor_free(fname);
  tor_free(status);
}

/* DOCDOC get_net_param_from_list */
static int32_t
get_net_param_from_list(smartlist_t *net_params, const char *param_name,
                        int32_t default_val, int32_t min_val, int32_t max_val)
{
  int32_t res = default_val;
  size_t name_len = strlen(param_name);

  tor_assert(max_val > min_val);
  tor_assert(min_val <= default_val);
  tor_assert(max_val >= default_val);

  SMARTLIST_FOREACH_BEGIN(net_params, const char *, p) {
    if (!strcmpstart(p, param_name) && p[name_len] == '=') {
      int ok=0;
      long v = tor_parse_long(p+name_len+1, 10, INT32_MIN,
                              INT32_MAX, &ok, NULL);
      if (ok) {
        res = (int32_t) v;
        break;
      }
    }
  } SMARTLIST_FOREACH_END(p);

  if (res < min_val) {
    log_warn(LD_DIR, "Consensus parameter %s is too small. Got %d, raising to "
             "%d.", param_name, res, min_val);
    res = min_val;
  } else if (res > max_val) {
    log_warn(LD_DIR, "Consensus parameter %s is too large. Got %d, capping to "
             "%d.", param_name, res, max_val);
    res = max_val;
  }

  return res;
}

/** Return the value of a integer parameter from the networkstatus <b>ns</b>
 * whose name is <b>param_name</b>.  If <b>ns</b> is NULL, try loading the
 * latest consensus ourselves. Return <b>default_val</b> if no latest
 * consensus, or if it has no parameter called <b>param_name</b>.
 * Make sure the value parsed from the consensus is at least
 * <b>min_val</b> and at most <b>max_val</b> and raise/cap the parsed value
 * if necessary. */
int32_t
networkstatus_get_param(const networkstatus_t *ns, const char *param_name,
                        int32_t default_val, int32_t min_val, int32_t max_val)
{
  if (!ns) /* if they pass in null, go find it ourselves */
    ns = networkstatus_get_latest_consensus();

  if (!ns || !ns->net_params)
    return default_val;

  return get_net_param_from_list(ns->net_params, param_name,
                                 default_val, min_val, max_val);
}

/**
 * Retrieve the consensus parameter that governs the
 * fixed-point precision of our network balancing 'bandwidth-weights'
 * (which are themselves integer consensus values). We divide them
 * by this value and ensure they never exceed this value.
 */
int
networkstatus_get_weight_scale_param(networkstatus_t *ns)
{
  return networkstatus_get_param(ns, "bwweightscale",
                                 BW_WEIGHT_SCALE,
                                 BW_MIN_WEIGHT_SCALE,
                                 BW_MAX_WEIGHT_SCALE);
}

/** Return the value of a integer bw weight parameter from the networkstatus
 * <b>ns</b> whose name is <b>weight_name</b>.  If <b>ns</b> is NULL, try
 * loading the latest consensus ourselves. Return <b>default_val</b> if no
 * latest consensus, or if it has no parameter called <b>weight_name</b>. */
int32_t
networkstatus_get_bw_weight(networkstatus_t *ns, const char *weight_name,
                            int32_t default_val)
{
  int32_t param;
  int max;
  if (!ns) /* if they pass in null, go find it ourselves */
    ns = networkstatus_get_latest_consensus();

  if (!ns || !ns->weight_params)
    return default_val;

  max = networkstatus_get_weight_scale_param(ns);
  param = get_net_param_from_list(ns->weight_params, weight_name,
                                  default_val, -1,
                                  BW_MAX_WEIGHT_SCALE);
  if (param > max) {
    log_warn(LD_DIR, "Value of consensus weight %s was too large, capping "
             "to %d", weight_name, max);
    param = max;
  }
  return param;
}

/** Return the name of the consensus flavor <b>flav</b> as used to identify
 * the flavor in directory documents. */
const char *
networkstatus_get_flavor_name(consensus_flavor_t flav)
{
  switch (flav) {
    case FLAV_NS:
      return "ns";
    case FLAV_MICRODESC:
      return "microdesc";
    default:
      tor_fragile_assert();
      return "??";
  }
}

/** Return the consensus_flavor_t value for the flavor called <b>flavname</b>,
 * or -1 if the flavor is not recognized. */
int
networkstatus_parse_flavor_name(const char *flavname)
{
  if (!strcmp(flavname, "ns"))
    return FLAV_NS;
  else if (!strcmp(flavname, "microdesc"))
    return FLAV_MICRODESC;
  else
    return -1;
}

/** Return 0 if this routerstatus is obsolete, too new, isn't
 * running, or otherwise not a descriptor that we would make any
 * use of even if we had it. Else return 1. */
int
client_would_use_router(const routerstatus_t *rs, time_t now,
                        const or_options_t *options)
{
  if (!rs->is_flagged_running && !options->FetchUselessDescriptors) {
    /* If we had this router descriptor, we wouldn't even bother using it.
     * But, if we want to have a complete list, fetch it anyway. */
    return 0;
  }
  if (rs->published_on + options->TestingEstimatedDescriptorPropagationTime
      > now) {
    /* Most caches probably don't have this descriptor yet. */
    return 0;
  }
  if (rs->published_on + OLD_ROUTER_DESC_MAX_AGE < now) {
    /* We'd drop it immediately for being too old. */
    return 0;
  }
  return 1;
}

/** If <b>question</b> is a string beginning with "ns/" in a format the
 * control interface expects for a GETINFO question, set *<b>answer</b> to a
 * newly-allocated string containing networkstatus lines for the appropriate
 * ORs.  Return 0 on success, -1 on unrecognized question format. */
int
getinfo_helper_networkstatus(control_connection_t *conn,
                             const char *question, char **answer,
                             const char **errmsg)
{
  const routerstatus_t *status;
  (void) conn;

  if (!current_consensus) {
    *answer = tor_strdup("");
    return 0;
  }

  if (!strcmp(question, "ns/all")) {
    smartlist_t *statuses = smartlist_new();
    SMARTLIST_FOREACH(current_consensus->routerstatus_list,
                      const routerstatus_t *, rs,
      {
        smartlist_add(statuses, networkstatus_getinfo_helper_single(rs));
      });
    *answer = smartlist_join_strings(statuses, "", 0, NULL);
    SMARTLIST_FOREACH(statuses, char *, cp, tor_free(cp));
    smartlist_free(statuses);
    return 0;
  } else if (!strcmpstart(question, "ns/id/")) {
    char d[DIGEST_LEN];
    const char *q = question + 6;
    if (*q == '$')
      ++q;

    if (base16_decode(d, DIGEST_LEN, q, strlen(q))) {
      *errmsg = "Data not decodeable as hex";
      return -1;
    }
    status = router_get_consensus_status_by_id(d);
  } else if (!strcmpstart(question, "ns/name/")) {
    status = router_get_consensus_status_by_nickname(question+8, 0);
  } else if (!strcmpstart(question, "ns/purpose/")) {
    *answer = networkstatus_getinfo_by_purpose(question+11, time(NULL));
    return *answer ? 0 : -1;
  } else {
    return 0;
  }

  if (status)
    *answer = networkstatus_getinfo_helper_single(status);
  return 0;
}

/** Free all storage held locally in this module. */
void
networkstatus_free_all(void)
{
  int i;
  networkstatus_vote_free(current_ns_consensus);
  networkstatus_vote_free(current_md_consensus);
  current_md_consensus = current_ns_consensus = NULL;

  for (i=0; i < N_CONSENSUS_FLAVORS; ++i) {
    consensus_waiting_for_certs_t *waiting = &consensus_waiting_for_certs[i];
    if (waiting->consensus) {
      networkstatus_vote_free(waiting->consensus);
      waiting->consensus = NULL;
    }
    tor_free(waiting->body);
  }

  strmap_free(named_server_map, tor_free_);
  strmap_free(unnamed_server_map, NULL);
}