relay: Query our cache when deciding for dummy descriptor fetch

Instead of looking at the "Address" option alone, instead check if we have an
address in our cache (that is discovered by tor). If not, then it tells us
that tor does not have an address to work with so we can then ask a directory
authority for a suggestion.

Related #2178
Signed-off-by: David Goulet <dgoulet@torproject.org>

src/feature/nodelist/routerlist.c

@@ -89,6 +89,7 @@
 #include "feature/nodelist/routerset.h"
 #include "feature/nodelist/torcert.h"
 #include "feature/relay/routermode.h"
+#include "feature/relay/relay_find_addr.h"
 #include "feature/stats/rephist.h"
 #include "lib/crypt_ops/crypto_format.h"
 #include "lib/crypt_ops/crypto_rand.h"
@@ -2772,12 +2773,27 @@ launch_dummy_descriptor_download_as_needed(time_t now,
                                            const or_options_t *options)
 {
   static time_t last_dummy_download = 0;
+  bool have_addr;
+  tor_addr_t addr_out;
+
+  /* This dummy fetch only matter for relays. */
+  if (!server_mode(options)) {
+    return;
+  }
+
+  /* Lookup the address cache to learn if we have a good usable address. We
+   * still force relays to have an IPv4 so that alone is enough to learn if we
+   * need a lookup. In case we don't have one, we might want to attempt a
+   * dummy fetch to learn our address as a suggestion from an authority. */
+  have_addr = relay_find_addr_to_publish(options, AF_INET,
+                                         RELAY_FIND_ADDR_CACHE_ONLY,
+                                         &addr_out);
+
   /* XXXX+ we could be smarter here; see notes on bug 652. */
-  /* If we're a server that doesn't have a configured address, we rely on
-   * directory fetches to learn when our address changes.  So if we haven't
-   * tried to get any routerdescs in a long time, try a dummy fetch now. */
-  if (!options->Address &&
-      server_mode(options) &&
+  /* If we're a server that doesn't have an address, we rely on directory
+   * fetches to learn when our address changes.  So if we haven't tried to get
+   * any routerdescs in a long time, try a dummy fetch now. */
+  if (!have_addr &&
       last_descriptor_download_attempted + DUMMY_DOWNLOAD_INTERVAL < now &&
       last_dummy_download + DUMMY_DOWNLOAD_INTERVAL < now) {
     last_dummy_download = now;