Allow tor to build circuits using a consensus with no exits

If the consensus has no exits (typical of a bootstrapping
test network), allow tor to build circuits once enough
descriptors have been downloaded.

When there are no exits, we always have "enough"
exit descriptors. (We treat the proportion of available
exit descriptors as 100%.)

This assists in bootstrapping a testing Tor network.

Fixes bug 13718.
Makes bug 13161's TestingDirAuthVoteExit non-essential.
(But still useful for speeding up a bootstrap.)

changes/bug13814-reachability-without-exits

@@ -0,0 +1,15 @@
+  o Minor bugfixes:
+    - Allow tor to build circuits using a consensus with
+      no exits. If the consensus has no exits (typical of
+      a bootstrapping test network), allow tor to build
+      circuits once enough descriptors have been
+      downloaded.
+      When there are no exits, we always have "enough"
+      exit descriptors. (We treat the proportion of
+      available exit descriptors as 100%.)
+      This assists in bootstrapping a testing Tor
+      network.
+      Fixes bug 13718.
+      Makes bug 13161's TestingDirAuthVoteExit
+      non-essential.
+      (But still useful for speeding up a bootstrap.)

src/or/nodelist.c

@@ -1273,7 +1273,8 @@ router_set_status(const char *digest, int up)
 }
 
 /** True iff, the last time we checked whether we had enough directory info
- * to build circuits, the answer was "yes". */
+ * to build circuits, the answer was "yes". If there are no exits in the
+ * consensus, we act as if we have 100% of the exit directory info. */
 static int have_min_dir_info = 0;
 
 /** Does the consensus contain nodes that can exit? */
@@ -1285,12 +1286,15 @@ static consensus_path_type_t have_consensus_path = CONSENSUS_PATH_UNKNOWN;
 static int need_to_update_have_min_dir_info = 1;
 /** String describing what we're missing before we have enough directory
  * info. */
-static char dir_info_status[256] = "";
-
-/** Return true iff we have enough networkstatus and router information to
- * start building circuits.  Right now, this means "more than half the
- * networkstatus documents, and at least 1/4 of expected routers." */
-//XXX should consider whether we have enough exiting nodes here.
+static char dir_info_status[512] = "";
+
+/** Return true iff we have enough consensus information to
+ * start building circuits.  Right now, this means "a consensus that's
+ * less than a day old, and at least 60% of router descriptors (configurable),
+ * weighted by bandwidth. Treat the exit fraction as 100% if there are
+ * no exits in the consensus."
+ * To obtain the final weighted bandwidth, we multiply the
+ * weighted bandwidth fraction for each position (guard, middle, exit). */
 int
 router_have_minimum_dir_info(void)
 {
@@ -1405,7 +1409,16 @@ count_usable_descriptors(int *num_present, int *num_usable,
 }
 
 /** Return an estimate of which fraction of usable paths through the Tor
- * network we have available for use. */
+ * network we have available for use.
+ * Count how many routers seem like ones we'd use, and how many of
+ * <em>those</em> we have descriptors for.  Store the former in
+ * *<b>num_usable_out</b> and the latter in *<b>num_present_out</b>.
+ * If **<b>status_out</b> is present, allocate a new string and print the
+ * available percentages of guard, middle, and exit nodes to it, noting
+ * whether there are exits in the consensus.
+ * If there are no guards in the consensus,
+ * we treat the exit fraction as 100%.
+ */
 static double
 compute_frac_paths_available(const networkstatus_t *consensus,
                              const or_options_t *options, time_t now,
@@ -1549,16 +1562,28 @@ compute_frac_paths_available(const networkstatus_t *consensus,
   if (f_myexit < f_exit)
     f_exit = f_myexit;
 
+  /* if the consensus has no exits, treat the exit fraction as 100% */
+  if (router_have_consensus_path() != CONSENSUS_PATH_EXIT) {
+    f_exit = 1.0;
+  }
+
+  f_path = f_guard * f_mid * f_exit;
+
   if (status_out)
     tor_asprintf(status_out,
                  "%d%% of guards bw, "
                  "%d%% of midpoint bw, and "
-                 "%d%% of exit bw",
+                 "%d%% of exit bw%s = "
+                 "%d%% of path bw",
                  (int)(f_guard*100),
                  (int)(f_mid*100),
-                 (int)(f_exit*100));
+                 (int)(f_exit*100),
+                 (router_have_consensus_path() == CONSENSUS_PATH_EXIT ?
+                  "" :
+                  " (no exits in consensus)"),
+                 (int)(f_path*100));
 
-  return f_guard * f_mid * f_exit;
+  return f_path;
 }
 
 /** We just fetched a new set of descriptors. Compute how far through
@@ -1631,6 +1656,9 @@ update_router_have_minimum_dir_info(void)
 
   using_md = consensus->flavor == FLAV_MICRODESC;
 
+#define NOTICE_DIR_INFO_STATUS_INTERVAL (60)
+
+  /* Check fraction of available paths */
   {
     char *status = NULL;
     int num_present=0, num_usable=0;
@@ -1639,16 +1667,37 @@ update_router_have_minimum_dir_info(void)
                                                 &status);
 
     if (paths < get_frac_paths_needed_for_circs(options,consensus)) {
-      tor_snprintf(dir_info_status, sizeof(dir_info_status),
-                   "We need more %sdescriptors: we have %d/%d, and "
-                   "can only build %d%% of likely paths. (We have %s.)",
-                   using_md?"micro":"", num_present, num_usable,
-                   (int)(paths*100), status);
-      /* log_notice(LD_NET, "%s", dir_info_status); */
+      /* these messages can be excessive in testing networks */
+      static ratelim_t last_warned =
+        RATELIM_INIT(NOTICE_DIR_INFO_STATUS_INTERVAL);
+      char *suppression_msg = NULL;
+      if ((suppression_msg = rate_limit_log(&last_warned, time(NULL)))) {
+        tor_snprintf(dir_info_status, sizeof(dir_info_status),
+                     "We need more %sdescriptors: we have %d/%d, and "
+                     "can only build %d%% of likely paths. (We have %s.)",
+                     using_md?"micro":"", num_present, num_usable,
+                     (int)(paths*100), status);
+        log_warn(LD_NET, "%s%s", dir_info_status, suppression_msg);
+        tor_free(suppression_msg);
+      }
       tor_free(status);
       res = 0;
       control_event_bootstrap(BOOTSTRAP_STATUS_REQUESTING_DESCRIPTORS, 0);
       goto done;
+    } else {
+      /* these messages can be excessive in testing networks */
+      static ratelim_t last_warned =
+      RATELIM_INIT(NOTICE_DIR_INFO_STATUS_INTERVAL);
+      char *suppression_msg = NULL;
+      if ((suppression_msg = rate_limit_log(&last_warned, time(NULL)))) {
+        tor_snprintf(dir_info_status, sizeof(dir_info_status),
+                     "We have enough %sdescriptors: we have %d/%d, and "
+                     "can build %d%% of likely paths. (We have %s.)",
+                     using_md?"micro":"", num_present, num_usable,
+                     (int)(paths*100), status);
+        log_info(LD_NET, "%s%s", dir_info_status, suppression_msg);
+        tor_free(suppression_msg);
+      }
     }
 
     tor_free(status);
@@ -1656,12 +1705,16 @@ update_router_have_minimum_dir_info(void)
   }
 
  done:
+
+  /* If paths have just become available in this update. */
   if (res && !have_min_dir_info) {
     log_notice(LD_DIR,
         "We now have enough directory information to build circuits.");
     control_event_client_status(LOG_NOTICE, "ENOUGH_DIR_INFO");
     control_event_bootstrap(BOOTSTRAP_STATUS_CONN_OR, 0);
   }
+
+  /* If paths have just become unavailable in this update. */
   if (!res && have_min_dir_info) {
     int quiet = directory_too_idle_to_fetch_descriptors(options, now);
     tor_log(quiet ? LOG_INFO : LOG_NOTICE, LD_DIR,

src/or/nodelist.h

@@ -79,6 +79,14 @@ int node_is_unreliable(const node_t *router, int need_uptime,
 int router_exit_policy_all_nodes_reject(const tor_addr_t *addr, uint16_t port,
                                         int need_uptime);
 void router_set_status(const char *digest, int up);
+
+/** router_have_minimum_dir_info tests to see if we have enough
+ * descriptor information to create circuits.
+ * If there are exits in the consensus, we wait until we have enough
+ * info to create exit paths before creating any circuits. If there are
+ * no exits in the consensus, we wait for enough info to create internal
+ * paths, and should avoid creating exit paths, as they will simply fail.
+ * We make sure we create all available circuit types at the same time. */
 int router_have_minimum_dir_info(void);
 
 /** Set to CONSENSUS_PATH_EXIT if there is at least one exit node