Add multiple fallback IP lookup services

src/mtp_config.erl

@@ -163,14 +163,25 @@ update_range(Range, Tab) ->
     true = ets:insert(Tab, {id_range, Range}).
 
 update_ip() ->
-    case application:get_env(?APP, ip_lookup_service) of
+    case application:get_env(?APP, ip_lookup_services) of
         undefined -> false;
-        {ok, URL} ->
-            {ok, {{_, 200, _}, _, Body}} = httpc:request(URL),
+        {ok, URLs} ->
+            update_ip(URLs)
+    end.
+
+update_ip([Url | Fallbacks]) ->
+    try
+        {ok, {{_, 200, _}, _, Body}} = httpc:request(Url),
         IpStr= string:trim(Body),
         {ok, _} = inet:parse_ipv4strict_address(IpStr), %assert
         application:set_env(?APP, external_ip, IpStr)
-    end.
+    catch Class:Reason ->
+            lager:error("Failed to update IP with ~s service: ~s",
+                        [Url, lager:pr_stacktrace(erlang:get_stacktrace(), {Class, Reason})]),
+            update_ip(Fallbacks)
+    end;
+update_ip([]) ->
+    error(ip_lookup_failed).
 
 
 -ifdef(TEST).

src/mtproto_proxy.app.src

 {application, mtproto_proxy,
  [{description, "An OTP application"},
-  {vsn, "0.1.0"},
+  {vsn, "0.2.0"},
   {registered, []},
   {mod, { mtproto_proxy_app, []}},
   {applications,
@@ -21,12 +21,17 @@
 
         %% Telegram server uses your external IP address as part of encryption
         %% key, so, you should know it.
-        %% You can configure IP lookup service by `ip_lookup_service' (should
+        %% You can configure IP lookup services by `ip_lookup_services' (should
         %% return my IP address as one line from this URL) or set IP address
         %% statically by `external_ip' (not both).
-        %% If both are unset, we will try to guess IP address
+        %% If both are unset, proxy will try to guess IP address
         %% from getsockname().
-        {ip_lookup_service, "https://digitalresistance.dog/myIp"},
+        %% `ip_lookup_services' will be tried one-by-one: if 1st is not responding,
+        %% 2nd one will be tried and so on
+        {ip_lookup_services,
+         ["http://ip.seriyps.ru/",
+          "https://digitalresistance.dog/myIp",
+          "http://ipv4.myexternalip.com/raw"]},
         %% {external_ip, "YOUR.SERVER.EXTERNAL.IP"},
 
         %% Interface to listen for incoming connections