addr: New function to find address to publish

In order for a relay to find which address to publish in its descriptor,
router_pick_published_address() is used. However, that function only supports
AF_INET and uses the directory server suggested address discovery mechanism.

This new function uses a new interface so that the caller can request an
address family and get the tor_addr_t object. Furthermore, it drops the use of
directory servers address discovery (tor#33244) and instead uses the new
suggested cache that is populated at the moment from data in the NETINFO cell
coming from the directory authorities.

At this commit, function is unused.

Related to #40025

Signed-off-by: David Goulet <dgoulet@torproject.org>

src/feature/relay/relay_find_addr.c

@@ -164,6 +164,58 @@ router_new_address_suggestion(const char *suggestion,
   }
 }
 
+/** Find our address to be published in our descriptor. Three places are
+ * looked at:
+ *
+ *    1. Resolved cache. Populated by find_my_address() during the relay
+ *       periodic event that attempts to learn if our address has changed.
+ *
+ *    2. If cache_only is false, attempt to find the address using the
+ *       relay_find_addr.h interface.
+ *
+ *    3. Finally, if all fails, use the suggested address cache which is
+ *       populated by the NETINFO cell values.
+ *
+ * Return true on success and addr_out contains the address to use for the
+ * given family. On failure to find the address, false is returned and
+ * addr_out is set to an AF_UNSPEC address. */
+bool
+relay_find_addr_to_publish(const or_options_t *options, int family,
+                           bool cache_only, tor_addr_t *addr_out)
+{
+  tor_assert(options);
+  tor_assert(addr_out);
+
+  tor_addr_make_unspec(addr_out);
+
+  /* First, check our resolved address cache. It should contain the address
+   * we've discovered from the periodic relay event. */
+  resolved_addr_get_last(family, addr_out);
+  if (!tor_addr_is_null(addr_out)) {
+    goto found;
+  }
+
+  /* Second, attempt to find our address. The following can do a DNS resolve
+   * thus only do it when the no cache only flag is flipped. */
+  if (!cache_only) {
+    if (find_my_address(options, family, LOG_INFO, addr_out, NULL, NULL)) {
+      goto found;
+    }
+  }
+
+  /* Third, consider address from our suggestion cache. */
+  resolved_addr_get_suggested(family, addr_out);
+  if (!tor_addr_is_null(addr_out)) {
+    goto found;
+  }
+
+  /* No publishable address was found. */
+  return false;
+
+ found:
+  return true;
+}
+
 /** Make a current best guess at our address, either because
  * it's configured in torrc, or because we've learned it from
  * dirserver headers. Place the answer in *<b>addr</b> and return

src/feature/relay/relay_find_addr.h

@@ -19,6 +19,9 @@ void relay_address_new_suggestion(const tor_addr_t *suggested_addr,
                                   const tor_addr_t *peer_addr,
                                   const char *identity_digest);
 
+bool relay_find_addr_to_publish(const or_options_t *options, int family,
+                                bool cache_only, tor_addr_t *addr_out);
+
 #ifdef RELAY_FIND_ADDR_PRIVATE
 
 #endif /* RELAY_FIND_ADDR_PRIVATE */