Teach resolve_my_address() to return a cached answer

I didn't make any of the callers use this feature yet.

src/or/config.c

@@ -1908,12 +1908,16 @@ static uint32_t last_resolved_addr = 0;
  *     holding that hostname. (If we didn't get our address by resolving a
  *     hostname, set *<b>hostname_out</b> to NULL.)
  *
+ * If <b>use_cached_addr</b> is true, and we have a plausible answer,
+ * provide that answer and return.
+ *
  * XXXX ipv6
  */
 int
 resolve_my_address(int warn_severity, const or_options_t *options,
                    uint32_t *addr_out,
-                   const char **method_out, char **hostname_out)
+                   const char **method_out, char **hostname_out,
+                   int use_cached_addr)
 {
   struct in_addr in;
   uint32_t addr; /* host order */
@@ -1930,6 +1934,18 @@ resolve_my_address(int warn_severity, const or_options_t *options,
 
   tor_assert(addr_out);
 
+  /*
+   * Step zero: if used_cached_addr is true, and we have a cached answer,
+   * just return it and be done.
+   */
+
+  if (use_cached_addr && last_resolved_addr) {
+    *addr_out = last_resolved_addr;
+    if (method_out)
+      *method_out = "CACHED";
+    return 0;
+  }
+
   /*
    * Step one: Fill in 'hostname' to be our best guess.
    */
@@ -2343,7 +2359,7 @@ options_validate(or_options_t *old_options, or_options_t *options,
   if (authdir_mode(options)) {
     /* confirm that our address isn't broken, so we can complain now */
     uint32_t tmp;
-    if (resolve_my_address(LOG_WARN, options, &tmp, NULL, NULL) < 0)
+    if (resolve_my_address(LOG_WARN, options, &tmp, NULL, NULL, 0) < 0)
       REJECT("Failed to resolve/guess local address. See logs for details.");
   }
 

src/or/config.h

@@ -28,7 +28,8 @@ setopt_err_t options_trial_assign(config_line_t *list, int use_defaults,
 
 int resolve_my_address(int warn_severity, const or_options_t *options,
                        uint32_t *addr_out,
-                       const char **method_out, char **hostname_out);
+                       const char **method_out, char **hostname_out,
+                       int use_cached_addr);
 int is_local_addr(const tor_addr_t *addr);
 void options_init(or_options_t *options);
 char *options_dump(const or_options_t *options, int minimal);

src/or/dirserv.c

@@ -2750,7 +2750,7 @@ dirserv_generate_networkstatus_vote_obj(crypto_pk_t *private_key,
   tor_assert(private_key);
   tor_assert(cert);
 
-  if (resolve_my_address(LOG_WARN, options, &addr, NULL, &hostname)<0) {
+  if (resolve_my_address(LOG_WARN, options, &addr, NULL, &hostname, 0)<0) {
     log_warn(LD_NET, "Couldn't resolve my hostname");
     return NULL;
   }
@@ -2960,7 +2960,7 @@ generate_v2_networkstatus_opinion(void)
 
   private_key = get_server_identity_key();
 
-  if (resolve_my_address(LOG_WARN, options, &addr, NULL, &hostname)<0) {
+  if (resolve_my_address(LOG_WARN, options, &addr, NULL, &hostname, 0)<0) {
     log_warn(LD_NET, "Couldn't resolve my hostname");
     goto done;
   }

src/or/router.c

@@ -1712,7 +1712,7 @@ static int router_guess_address_from_dir_headers(uint32_t *guess);
 int
 router_pick_published_address(const or_options_t *options, uint32_t *addr)
 {
-  if (resolve_my_address(LOG_INFO, options, addr, NULL, NULL) < 0) {
+  if (resolve_my_address(LOG_INFO, options, addr, NULL, NULL, 0) < 0) {
     log_info(LD_CONFIG, "Could not determine our address locally. "
              "Checking if directory headers provide any hints.");
     if (router_guess_address_from_dir_headers(addr) < 0) {
@@ -2103,7 +2103,7 @@ check_descriptor_ipaddress_changed(time_t now)
 
   /* XXXX ipv6 */
   prev = desc_routerinfo->addr;
-  if (resolve_my_address(LOG_INFO, options, &cur, &method, &hostname) < 0) {
+  if (resolve_my_address(LOG_INFO, options, &cur, &method, &hostname, 0) < 0) {
     log_info(LD_CONFIG,"options->Address didn't resolve into an IP.");
     return;
   }
@@ -2159,7 +2159,7 @@ router_new_address_suggestion(const char *suggestion,
   }
 
   /* XXXX ipv6 */
-  if (resolve_my_address(LOG_INFO, options, &cur, NULL, NULL) >= 0) {
+  if (resolve_my_address(LOG_INFO, options, &cur, NULL, NULL, 0) >= 0) {
     /* We're all set -- we already know our address. Great. */
     tor_addr_from_ipv4h(&last_guessed_ip, cur); /* store it in case we
                                                    need it later */

src/or/routerlist.c

@@ -3951,7 +3951,8 @@ trusted_dir_server_new(const char *nickname, const char *address,
   dir_server_t *result;
 
   if (!address) { /* The address is us; we should guess. */
-    if (resolve_my_address(LOG_WARN, get_options(), &a, NULL, &hostname) < 0) {
+    if (resolve_my_address(LOG_WARN, get_options(),
+                           &a, NULL, &hostname, 0) < 0) {
       log_warn(LD_CONFIG,
                "Couldn't find a suitable address when adding ourself as a "
                "trusted directory server.");