XEP-0352: Pass chat states of other resources

Don't hold back (carbon copies of) chat states from other resources, as
they might be used to sync the state of conversations across clients.
E.g., if one client becomes active, another one might want to remove a
notification (immediately).

src/mod_client_state.erl

@@ -165,10 +165,21 @@ filter_presence(Acc, _Host, _Stanza) -> Acc.
 
 filter_chat_states({C2SState, _OutStanzas} = Acc, Host,
 		   #xmlel{name = <<"message">>} = Stanza) ->
-    case jlib:is_standalone_chat_state(jlib:unwrap_carbon(Stanza)) of
+    Payload = jlib:unwrap_carbon(Stanza),
+    case jlib:is_standalone_chat_state(Payload) of
       true ->
-	  ?DEBUG("Got standalone chat state notification", []),
-	  queue_add(chatstate, Stanza, Host, C2SState);
+	  From = fxml:get_tag_attr_s(<<"from">>, Payload),
+	  To = fxml:get_tag_attr_s(<<"to">>, Payload),
+	  case {jid:from_string(From), jid:from_string(To)} of
+	    {#jid{luser = U, lserver = S}, #jid{luser = U, lserver = S}} ->
+		%% Don't queue (carbon copies of) chat states from other
+		%% resources, as they might be used to sync the state of
+		%% conversations across clients.
+		Acc;
+	    _ ->
+		?DEBUG("Got standalone chat state notification", []),
+		queue_add(chatstate, Stanza, Host, C2SState)
+	  end;
       false ->
 	  Acc
     end;