relay: Emit log warning if Address is internal and can't be used

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

changes/ticket40290

+  o Minor bugfix (logging, relay):
+    - Emit a warning if an Address is found to be internal and tor can't use it.
+      Fixes bug 40290; bugfix on 0.4.5.1-alpha.

src/app/config/resolve_addr.c

@@ -343,6 +343,18 @@ get_address_from_config(const or_options_t *options, int warn_severity,
      * used, custom authorities must be defined else it is a fatal error.
      * Furthermore, if the Address was resolved to an internal interface, we
      * stop immediately. */
+    if (ret == ERR_ADDRESS_IS_INTERNAL) {
+      static bool logged_once = false;
+      if (!logged_once) {
+        log_warn(LD_CONFIG, "Address set with an internal address. Tor will "
+                            "not work unless custom directory authorities "
+                            "are defined (AlternateDirAuthority). It is also "
+                            "possible to use an internal address if "
+                            "PublishServerDescriptor is set to 0 and "
+                            "AssumeReachable(IPv6) to 1.");
+        logged_once = true;
+      }
+    }
     tor_free(*hostname_out);
     return FN_RET_BAIL;
   }