Don't expand guard sample set unless consensus is "reasonably live"

  o Major bugfixes (entry guards):

    - When starting with an old consensus, do not add new entry guards

      unless the consensus is "reasonably live" (under 1 day old). Fixes

      one root cause of bug 22400; bugfix on 0.3.0.1-alpha.

{

  tor_assert(gs);

  const or_options_t *options = get_options();

  if (gs->type != GS_TYPE_BRIDGE) {

    networkstatus_t *consensus = networkstatus_get_latest_consensus();

    time_t now = approx_time();

    if (consensus == NULL) {

      log_info(LD_GUARD, "Not expanding the sample guard set; we have "

               "no consensus.");

      return NULL;

    } else if (!networkstatus_consensus_reasonably_live(consensus, now)) {

      log_info(LD_GUARD, "Not expanding the sample guard set; we have "

               "a consensus, but it is far too old.");

      return NULL;

    }

  }

  int n_sampled = smartlist_len(gs->sampled_entry_guards);

  entry_guard_t *added_guard = NULL;

  int n_usable_filtered_guards = num_reachable_filtered_guards(gs, NULL);