In the glorious future, all relays cache dir info.

Now if you're a published relay and you set RefuseUnknownExits, even
if your dirport is off, you'll fetch dir info from the authorities,
fetch it early, and cache it.

In the future, RefuseUnknownExits (or something like it) will be on
by default.

src/or/dirserv.c

@@ -1122,12 +1122,12 @@ directory_fetches_from_authorities(or_options_t *options)
     return 0;
   if (server_mode(options) && router_pick_published_address(options, &addr)<0)
     return 1; /* we don't know our IP address; ask an authority. */
-  if (options->DirPort == 0)
+  if (options->DirPort == 0 && !options->RefuseUnknownExits)
     return 0;
   if (!server_mode(options) || !advertised_server_mode())
     return 0;
   me = router_get_my_routerinfo();
-  if (!me || !me->dir_port)
+  if (!me || (!me->dir_port && !options->RefuseUnknownExits))
     return 0; /* if dirport not advertised, return 0 too */
   return 1;
 }
@@ -1167,7 +1167,11 @@ directory_caches_v2_dir_info(or_options_t *options)
 int
 directory_caches_dir_info(or_options_t *options)
 {
-  return options->BridgeRelay != 0 || options->DirPort != 0;
+  if (options->BridgeRelay || options->DirPort)
+    return 1;
+  if (!server_mode(options) || !advertised_server_mode())
+    return 0;
+  return options->RefuseUnknownExits;
 }
 
 /** Return 1 if we want to allow remote people to ask us directory