use microdescriptors if *any* of our bridges can handle them

Now as we move into a future where most bridges can handle microdescs
we will generally find ourselves using them, rather than holding back
just because one of our bridges doesn't use them.

6 files changed, 60 insertions, 30 deletions

diff --git a/changes/feature4994 b/changes/feature4994
new file mode 100644
index 000000000..4fa0e037b
--- /dev/null
+++ b/changes/feature4994
@@ -0,0 +1,7 @@
+  o Minor features:
+    - Teach bridge-using clients to avoid 0.2.2 bridges when making
+      microdescriptor-related dir requests, and only fall back to normal
+      descriptors if none of their bridges can handle microdescriptors
+      (as opposed to the fix in ticket 4013, which caused them to fall
+      back to normal descriptors if *any* of their bridges preferred
+      them). Resolves ticket 4994.
diff --git a/src/or/circuitbuild.c b/src/or/circuitbuild.c
index 5a5a3afea..8c86aac90 100644
--- a/src/or/circuitbuild.c
+++ b/src/or/circuitbuild.c
@@ -25,6 +25,7 @@
 #include "directory.h"
 #include "entrynodes.h"
 #include "main.h"
+#include "microdesc.h"
 #include "networkstatus.h"
 #include "nodelist.h"
 #include "onion.h"
@@ -3372,7 +3373,7 @@ choose_good_entry_server(uint8_t purpose, cpath_build_state_t *state)
       (purpose != CIRCUIT_PURPOSE_TESTING || options->BridgeRelay)) {
     /* This request is for an entry server to use for a regular circuit,
      * and we use entry guard nodes.  Just return one of the guard nodes.  */
-    return choose_random_entry(state);
+    return choose_random_entry(state, 0);
   }
 
   excluded = smartlist_new();
diff --git a/src/or/directory.c b/src/or/directory.c
index c10141844..c1bbe6bd8 100644
--- a/src/or/directory.c
+++ b/src/or/directory.c
@@ -472,12 +472,14 @@ directory_get_from_dirserver(uint8_t dir_purpose, uint8_t router_purpose,
     if (options->UseBridges && type != BRIDGE_DIRINFO) {
       /* We want to ask a running bridge for which we have a descriptor.
        *
-       * Be careful here: we should only ask questions that we know our
-       * bridges can answer. So far we're solving that by backing off to
-       * the behavior supported by our oldest bridge; see for example
-       * any_bridges_dont_support_microdescriptors().
+       * When we ask choose_random_entry() for a bridge, we specify that
+       * we're going to be using it for a dir fetch: if any of our bridges
+       * can handle microdescriptor questions, we'll get one of the ones
+       * that can.
        */
-      const node_t *node = choose_random_entry(NULL);
+      /* XXX024 Not all bridges handle conditional consensus downloading,
+       * so, for now, never assume the server supports that. -PP */
+      const node_t *node = choose_random_entry(NULL, 1);
       if (node && node->ri) {
         /* every bridge has a routerinfo. */
         tor_addr_t addr;
diff --git a/src/or/entrynodes.c b/src/or/entrynodes.c
index 4ca56cbac..d029d8593 100644
--- a/src/or/entrynodes.c
+++ b/src/or/entrynodes.c
@@ -23,6 +23,7 @@
 #include "directory.h"
 #include "entrynodes.h"
 #include "main.h"
+#include "microdesc.h"
 #include "nodelist.h"
 #include "policies.h"
 #include "router.h"
@@ -63,7 +64,8 @@ static int entry_guards_dirty = 0;
 static void bridge_free(bridge_info_t *bridge);
 static const node_t *choose_random_entry_impl(cpath_build_state_t *state,
                                               int for_directory,
-                                              dirinfo_type_t dirtype);
+                                              dirinfo_type_t dirtype,
+                                              int prefer_microdescs);
 
 /** Return the list of entry guards, creating it if necessary. */
 const smartlist_t *
@@ -829,15 +831,33 @@ entry_list_is_constrained(const or_options_t *options)
   return 0;
 }
 
+/** Return true iff this node can answer directory questions about
+ * microdescriptors. */
+static int
+node_understands_microdescriptors(const node_t *node)
+{
+  tor_assert(node);
+  if (node->rs && node->rs->version_supports_microdesc_cache)
+    return 1;
+  if (node->ri && tor_version_supports_microdescriptors(node->ri->platform))
+    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). */
+ * guard (likely a bridge).
+ *
+ * If the prefer_microdescs flag is set, we are looking for a bridge to
+ * use for directory fetching and pick a bridge that supports microdescriptors
+ * if we know any that do so.
+ */
 const node_t *
-choose_random_entry(cpath_build_state_t *state)
+choose_random_entry(cpath_build_state_t *state, int prefer_microdescs)
 {
-  return choose_random_entry_impl(state, 0, 0);
+  return choose_random_entry_impl(state, 0, 0, prefer_microdescs);
 }
 
 /** Pick a live (up and listed) directory guard from entry_guards for
@@ -845,13 +865,13 @@ choose_random_entry(cpath_build_state_t *state)
 const node_t *
 choose_random_dirguard(dirinfo_type_t type)
 {
-  return choose_random_entry_impl(NULL, 1, type);
+  return choose_random_entry_impl(NULL, 1, type, 0);
 }
 
 /** Helper for choose_random{entry,dirguard}. */
 static const node_t *
 choose_random_entry_impl(cpath_build_state_t *state, int for_directory,
-                         dirinfo_type_t dirinfo_type)
+                         dirinfo_type_t dirinfo_type, int prefer_microdescs)
 {
   const or_options_t *options = get_options();
   smartlist_t *live_entry_guards = smartlist_new();
@@ -903,6 +923,10 @@ choose_random_entry_impl(cpath_build_state_t *state, int for_directory,
         continue; /* don't pick the same node for entry and exit */
       if (consider_exit_family && smartlist_contains(exit_family, node))
         continue; /* avoid relays that are family members of our exit */
+      if (prefer_microdescs &&
+          we_use_microdescriptors_for_circuits(options) &&
+          !node_understands_microdescriptors(node))
+        continue; /* this node won't be able to answer our dir questions */
 #if 0 /* since EntryNodes is always strict now, this clause is moot */
       if (options->EntryNodes &&
           !routerset_contains_node(options->EntryNodes, node)) {
@@ -1982,7 +2006,7 @@ int
 any_bridge_descriptors_known(void)
 {
   tor_assert(get_options()->UseBridges);
-  return choose_random_entry(NULL)!=NULL ? 1 : 0;
+  return choose_random_entry(NULL, 0)!=NULL ? 1 : 0;
 }
 
 /** Return 1 if there are any directory conns fetching bridge descriptors
@@ -2064,29 +2088,24 @@ entries_retry_all(const or_options_t *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. */
+/** Return true if at least one of our bridges runs a Tor version that can
+ * provide microdescriptors to us. If not, we'll fall back to asking for
+ * full descriptors. */
 int
-any_bridges_dont_support_microdescriptors(void)
+any_bridge_supports_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 &&
+    if (node && node->is_running &&
         node_is_bridge(node) && node_is_a_configured_bridge(node) &&
-        !tor_version_supports_microdescriptors(node->ri->platform)) {
+        node_understands_microdescriptors(node)) {
       /* 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
+       * it to know that it will be able to answer our microdescriptor
        * questions. */
-      ever_answered_yes = 1;
-      return 1;
+       return 1;
     }
   } SMARTLIST_FOREACH_END(e);
   return 0;
diff --git a/src/or/entrynodes.h b/src/or/entrynodes.h
index e6c973c95..8ed429c8f 100644
--- a/src/or/entrynodes.h
+++ b/src/or/entrynodes.h
@@ -78,7 +78,8 @@ int entry_guard_register_connect_status(const char *digest, int succeeded,
                                         int mark_relay_status, time_t now);
 void entry_nodes_should_be_added(void);
 int entry_list_is_constrained(const or_options_t *options);
-const node_t *choose_random_entry(cpath_build_state_t *state);
+const node_t *choose_random_entry(cpath_build_state_t *state,
+                                  int prefer_microdescs);
 const node_t *choose_random_dirguard(dirinfo_type_t t);
 int entry_guards_parse_state(or_state_t *state, int set, char **msg);
 void entry_guards_update_state(or_state_t *state);
@@ -104,7 +105,7 @@ int any_pending_bridge_descriptor_fetches(void);
 int entries_known_but_down(const or_options_t *options);
 void entries_retry_all(const or_options_t *options);
 
-int any_bridges_dont_support_microdescriptors(void);
+int any_bridge_supports_microdescriptors(void);
 
 void entry_guards_free_all(void);
 
diff --git a/src/or/microdesc.c b/src/or/microdesc.c
index e99b3ebe7..ac48930fa 100644
--- a/src/or/microdesc.c
+++ b/src/or/microdesc.c
@@ -730,9 +730,9 @@ we_use_microdescriptors_for_circuits(const or_options_t *options)
   int ret = options->UseMicrodescriptors;
   if (ret == -1) {
     /* UseMicrodescriptors is "auto"; we need to decide: */
-    /* If we are configured to use bridges and one of our bridges doesn't
+    /* If we are configured to use bridges and none of our bridges
      * know what a microdescriptor is, the answer is no. */
-    if (options->UseBridges && any_bridges_dont_support_microdescriptors())
+    if (options->UseBridges && !any_bridge_supports_microdescriptors())
       return 0;
     /* Otherwise, we decide that we'll use microdescriptors iff we are
      * not a server, and we're not autofetching everything. */