Fix failing bridges+ipv6-min integration test.

The bridges+ipv6-min integration test has a client with bridges:
    Bridge 127.0.0.1:5003
    Bridge [::1]:5003
which got stuck in guard_selection_have_enough_dir_info_to_build_circuits()
because it couldn't find the descriptor of both bridges.

Specifically, the guard_has_descriptor() function could not find the
node_t of the [::1] bridge, because the [::1] bridge had no identity
digest assigned to it.

After further examination, it seems that during fetching the descriptor
for our bridges, we used the CERTS cell to fill the identity digest of
127.0.0.1:5003 properly. However, when we received a CERTS cell from
[::1]:5003 we actually ignored its identity digest because the
learned_router_identity() function was using
get_configured_bridge_by_addr_port_digest() which was returning the
127.0.0.1 bridge instead of the [::1] bridge (because it prioritizes
digest matching over addrport matching).

The fix replaces get_configured_bridge_by_addr_port_digest() with the
recent get_configured_bridge_by_exact_addr_port_digest() function. It
also relaxes the constraints of the
get_configured_bridge_by_exact_addr_port_digest() function by making it
return bridges whose identity digest is not yet known.

By using the _exact_() function, learned_router_identity() actually
fills in the identity digest of the [::1] bridge, which then allows
guard_has_descriptor() to find the right node_t and verify that the
descriptor is there.

FWIW, in the bridges+ipv6-min test both 127.0.0.1 and [::1] bridges
correspond to the same node_t, which I guess makes sense given that it's
actually the same underlying bridge.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/or/bridges.c b/src/or/bridges.c
index f766931b46..88154c6c8a 100644
--- a/src/or/bridges.c
+++ b/src/or/bridges.c
@@ -218,7 +218,7 @@ get_configured_bridge_by_exact_addr_port_digest(const tor_addr_t *addr,
 
       if (digest && tor_memeq(bridge->identity, digest, DIGEST_LEN))
         return bridge;
-      else if (!digest)
+      else if (!digest || tor_digest_is_zero(bridge->identity))
         return bridge;
     }
 
@@ -297,7 +297,7 @@ learned_router_identity(const tor_addr_t *addr, uint16_t port,
   (void)ed_id;
   int learned = 0;
   bridge_info_t *bridge =
-    get_configured_bridge_by_addr_port_digest(addr, port, digest);
+    get_configured_bridge_by_exact_addr_port_digest(addr, port, digest);
   if (bridge && tor_digest_is_zero(bridge->identity)) {
     memcpy(bridge->identity, digest, DIGEST_LEN);
     learned = 1;