Check for "the right descriptor", not just "any descriptor".

This patch adds a new node_has_preferred_descriptor() function, and
replaces most users of node_has_descriptor() with it.  That's an
important change, since as of d1874b433953f64 (our fix for #25213),
we are willing to say that a node has _some_ descriptor, but not the
_right_ descriptor for a particular use case.

Part of a fix for 25691 and 25692.

1 files changed, 12 insertions, 16 deletions

diff --git a/src/or/circuitbuild.c b/src/or/circuitbuild.c
index 5f1f8122fd..019b9c51fd 100644
--- a/src/or/circuitbuild.c
+++ b/src/or/circuitbuild.c
@@ -417,7 +417,7 @@ onion_populate_cpath(origin_circuit_t *circ)
                                     circ->cpath->extend_info->identity_digest);
     /* If we don't know the node and its descriptor, we must be bootstrapping.
      */
-    if (!node || !node_has_descriptor(node)) {
+    if (!node || !node_has_preferred_descriptor(node, 1)) {
       return 0;
     }
   }
@@ -1869,7 +1869,7 @@ choose_good_exit_server_general(int need_uptime, int need_capacity)
        */
       continue;
     }
-    if (!node_has_descriptor(node)) {
+    if (!node_has_preferred_descriptor(node, 0)) {
       n_supported[i] = -1;
       continue;
     }
@@ -2443,6 +2443,10 @@ circuit_extend_to_new_exit(origin_circuit_t *circ, extend_info_t *exit_ei)
 
 /** Return the number of routers in <b>routers</b> that are currently up
  * and available for building circuits through.
+ *
+ * (Note that this function may overcount or undercount, if we have
+ * descriptors that are not the type we would prefer to use for some
+ * particular router. See bug #25885.)
  */
 MOCK_IMPL(STATIC int,
 count_acceptable_nodes, (smartlist_t *nodes))
@@ -2847,9 +2851,10 @@ extend_info_new(const char *nickname,
  * of the node (i.e. its IPv4 address) unless
  * <b>for_direct_connect</b> is true, in which case the preferred
  * address is used instead. May return NULL if there is not enough
- * info about <b>node</b> to extend to it--for example, if there is no
- * routerinfo_t or microdesc_t, or if for_direct_connect is true and none of
- * the node's addresses are allowed by tor's firewall and IP version config.
+ * info about <b>node</b> to extend to it--for example, if the preferred
+ * routerinfo_t or microdesc_t is missing, or if for_direct_connect is
+ * true and none of the node's addresses is allowed by tor's firewall
+ * and IP version config.
  **/
 extend_info_t *
 extend_info_from_node(const node_t *node, int for_direct_connect)
@@ -2857,17 +2862,8 @@ extend_info_from_node(const node_t *node, int for_direct_connect)
   tor_addr_port_t ap;
   int valid_addr = 0;
 
-  const int is_bridge = node_is_a_configured_bridge(node);
-  const int we_use_mds = we_use_microdescriptors_for_circuits(get_options());
-
-  if ((is_bridge && for_direct_connect) || !we_use_mds) {
-    /* We need an ri in this case. */
-    if (!node->ri)
-      return NULL;
-  } else {
-    /* Otherwise we need an md. */
-    if (node->rs == NULL || node->md == NULL)
-      return NULL;
+  if (!node_has_preferred_descriptor(node, for_direct_connect)) {
+    return NULL;
   }
 
   /* Choose a preferred address first, but fall back to an allowed address.