Don't send error stanza as reply to error stanza (EJAB-930)

src/ejabberd_router.erl

@@ -31,6 +31,7 @@
 
 %% API
 -export([route/3,
+	 route_error/4,
 	 register_route/1,
 	 register_route/2,
 	 register_routes/1,
@@ -72,6 +73,17 @@ route(From, To, Packet) ->
 	    ok
     end.
 
+%% Route the error packet only if the originating packet is not an error itself.
+%% RFC3920 9.3.1
+route_error(From, To, ErrPacket, OrigPacket) ->
+    {xmlelement, _Name, Attrs, _Els} = OrigPacket,
+    case "error" == xml:get_attr_s("type", Attrs) of
+	false ->
+	    route(From, To, ErrPacket);
+	true ->
+	    ok
+    end.
+
 register_route(Domain) ->
     register_route(Domain, undefined).
 

src/ejabberd_service.erl

@@ -351,7 +351,7 @@ handle_info({route, From, To, Packet}, StateName, StateData) ->
 	    send_text(StateData, Text);
 	deny ->
 	    Err = jlib:make_error_reply(Packet, ?ERR_NOT_ALLOWED),
-	    ejabberd_router:route(To, From, Err)
+	    ejabberd_router:route_error(To, From, Err, Packet)
     end,
     {next_state, StateName, StateData}.
 

src/mod_muc/mod_muc.erl

@@ -336,7 +336,7 @@ do_route(Host, ServerHost, Access, HistorySize, RoomShaper,
 	    ErrText = "Access denied by service policy",
 	    Err = jlib:make_error_reply(Packet,
 					?ERRT_FORBIDDEN(Lang, ErrText)),
-	    ejabberd_router:route(To, From, Err)
+	    ejabberd_router:route_error(To, From, Err, Packet)
     end.