diff --git a/changes/feature5956 b/changes/feature5956
new file mode 100644
index 0000000000000000000000000000000000000000..dbc6a1ef80f269dd4874058c0b39b554971e48eb
--- /dev/null
+++ b/changes/feature5956
@@ -0,0 +1,6 @@
+ o Major features:
+ - When deciding whether we have enough descriptors to build circuits,
+ instead of looking at raw circuit counts, look at which fraction of
+ (bandwidth-weighted) paths we're able to build. This approach keeps
+ clients from building circuits if their paths are likely to stand out
+ statistically. Fixes issue 5956.
diff --git a/src/or/nodelist.c b/src/or/nodelist.c
index add9c033b01ee3841ef552f533bb83ff886c4028..77e4ae0fed9c219801741ef29761c6e01dd8fb63 100644
--- a/src/or/nodelist.c
+++ b/src/or/nodelist.c
@@ -1213,7 +1213,7 @@ static int have_min_dir_info = 0;
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[128] = "";
+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
@@ -1299,6 +1299,66 @@ count_usable_descriptors(int *num_present, int *num_usable,
md ? "microdesc" : "desc", exit_only ? " exits" : "s");
}
+/** Return an extimate of which fraction of usable paths through the Tor
+ * network we have available for use. */
+static double
+compute_frac_paths_available(const networkstatus_t *consensus,
+ const or_options_t *options, time_t now,
+ int *num_present_out, int *num_usable_out,
+ char **status_out)
+{
+ smartlist_t *guards = smartlist_new();
+ smartlist_t *mid = smartlist_new();
+ smartlist_t *exits = smartlist_new();
+ smartlist_t *myexits= smartlist_new();
+ double f_guard, f_mid, f_exit, f_myexit;
+ int np, nu; /* Ignored */
+
+ count_usable_descriptors(num_present_out, num_usable_out,
+ mid, consensus, options, now, NULL, 0);
+ if (options->EntryNodes) {
+ count_usable_descriptors(&np, &nu, guards, consensus, options, now,
+ options->EntryNodes, 0);
+ } else {
+ SMARTLIST_FOREACH(mid, const node_t *, node, {
+ if (node->is_possible_guard)
+ smartlist_add(guards, (node_t*)node);
+ });
+ }
+
+ count_usable_descriptors(&np, &nu, exits, consensus, options, now,
+ NULL, 1);
+ count_usable_descriptors(&np, &nu, myexits, consensus, options, now,
+ options->ExitNodes, 1);
+
+ f_guard = frac_nodes_with_descriptors(guards, WEIGHT_FOR_GUARD);
+ f_mid = frac_nodes_with_descriptors(mid, WEIGHT_FOR_MID);
+ f_exit = frac_nodes_with_descriptors(exits, WEIGHT_FOR_EXIT);
+ f_myexit= frac_nodes_with_descriptors(myexits,WEIGHT_FOR_EXIT);
+
+ smartlist_free(guards);
+ smartlist_free(mid);
+ smartlist_free(exits);
+ smartlist_free(myexits);
+
+ /* This is a tricky point here: we don't want to make it easy for a
+ * directory to trickle exits to us until it learns which exits we have
+ * configured, so require that we have a threshold both of total exits
+ * and usable exits. */
+ if (f_myexit < f_exit)
+ f_exit = f_myexit;
+
+ tor_asprintf(status_out,
+ "%02d%% of guards bw, "
+ "%02d%% of midpoint bw, and "
+ "%02d%% of exit bw",
+ (int)(f_guard*100),
+ (int)(f_mid*100),
+ (int)(f_exit*100));
+
+ return f_guard * f_mid * f_exit;
+}
+
/** We just fetched a new set of descriptors. Compute how far through
* the "loading descriptors" bootstrapping phase we are, so we can inform
* the controller of our progress. */
@@ -1333,8 +1393,6 @@ count_loading_descriptors_progress(void)
static void
update_router_have_minimum_dir_info(void)
{
- int num_present = 0, num_usable=0;
- int num_exit_present = 0, num_exit_usable = 0;
time_t now = time(NULL);
int res;
const or_options_t *options = get_options();
@@ -1363,57 +1421,32 @@ update_router_have_minimum_dir_info(void)
using_md = consensus->flavor == FLAV_MICRODESC;
- count_usable_descriptors(&num_present, &num_usable, NULL,
- consensus, options, now,
- NULL, 0);
- count_usable_descriptors(&num_exit_present, &num_exit_usable, NULL,
- consensus, options, now, options->ExitNodes, 1);
-
-/* What fraction of desired server descriptors do we need before we will
- * build circuits? */
-#define FRAC_USABLE_NEEDED .75
-/* What fraction of desired _exit_ server descriptors do we need before we
- * will build circuits? */
-#define FRAC_EXIT_USABLE_NEEDED .5
-
- if (num_present < num_usable * FRAC_USABLE_NEEDED) {
- tor_snprintf(dir_info_status, sizeof(dir_info_status),
- "We have only %d/%d usable %sdescriptors.",
- num_present, num_usable, using_md ? "micro" : "");
- res = 0;
- control_event_bootstrap(BOOTSTRAP_STATUS_REQUESTING_DESCRIPTORS, 0);
- goto done;
- } else if (num_present < 2) {
- tor_snprintf(dir_info_status, sizeof(dir_info_status),
- "Only %d %sdescriptor%s here and believed reachable!",
- num_present, using_md ? "micro" : "", num_present ? "" : "s");
- res = 0;
- goto done;
- } else if (num_exit_present < num_exit_usable * FRAC_EXIT_USABLE_NEEDED) {
- tor_snprintf(dir_info_status, sizeof(dir_info_status),
- "We have only %d/%d usable exit node descriptors.",
- num_exit_present, num_exit_usable);
- res = 0;
- control_event_bootstrap(BOOTSTRAP_STATUS_REQUESTING_DESCRIPTORS, 0);
- goto done;
- }
+ {
+ char *status = NULL;
+ int num_present=0, num_usable=0;
+ double paths = compute_frac_paths_available(consensus, options, now,
+ &num_present, &num_usable,
+ &status);
- /* Check for entry nodes. */
- if (options->EntryNodes) {
- count_usable_descriptors(&num_present, &num_usable, NULL,
- consensus, options,
- now, options->EntryNodes, 0);
+/* What fraction of desired paths do we need before we will build circuits? */
+#define FRAC_USABLE_NEEDED .6
- if (!num_usable || !num_present) {
+ if (paths < FRAC_USABLE_NEEDED) {
tor_snprintf(dir_info_status, sizeof(dir_info_status),
- "We have only %d/%d usable entry node %sdescriptors.",
- num_present, num_usable, using_md?"micro":"");
+ "We need more %sdescriptors: we have %d/%d, and "
+ "can only build %02d%% 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); */
+ tor_free(status);
res = 0;
+ control_event_bootstrap(BOOTSTRAP_STATUS_REQUESTING_DESCRIPTORS, 0);
goto done;
}
- }
- res = 1;
+ tor_free(status);
+ res = 1;
+ }
done:
if (res && !have_min_dir_info) {