mod_carboncopy: Don't copy MUC PMs

Carbon copies of private MUC message are generally not desired,
especially not when multiple clients joined the room with the same nick.
In this case, the MUC service usually sends PMs to all joined resources
anyway, so carbon-copying those PMs would create duplicates.

src/mod_carboncopy.erl

@@ -131,8 +131,9 @@ user_receive_packet(Packet, _C2SState, JID, _From, To) ->
 %    - we also replicate "read" notifications
 check_and_forward(JID, To, Packet, Direction)->
     case is_chat_message(Packet) andalso
-	     fxml:get_subtag(Packet, <<"private">>) == false andalso
-		 fxml:get_subtag(Packet, <<"no-copy">>) == false of
+	     not is_muc_pm(To, Packet) andalso
+		 fxml:get_subtag(Packet, <<"private">>) == false andalso
+		     fxml:get_subtag(Packet, <<"no-copy">>) == false of
 	true ->
 	    case is_carbon_copy(Packet) of
 		false ->
@@ -270,6 +271,11 @@ is_chat_message(#xmlel{name = <<"message">>} = Packet) ->
     end;
 is_chat_message(_Packet) -> false.
 
+is_muc_pm(#jid{lresource = <<>>}, _Packet) ->
+    false;
+is_muc_pm(_To, Packet) ->
+    fxml:get_subtag_with_xmlns(Packet, <<"x">>, ?NS_MUC_USER) =/= false.
+
 has_non_empty_body(Packet) ->
     fxml:get_subtag_cdata(Packet, <<"body">>) =/= <<"">>.