public Responder(WindowExt window, final String origin, final ResponseListener listener) {
   final boolean acceptAllOrigins = "*".equals(origin);
   remover =
       Event.addEventListener(
           "message",
           window,
           new EventListener() {
             public void handleEvent(Event event) {
               final Message e = event.cast();
               if (acceptAllOrigins || origin.equals(e.getOrigin())) {
                 listener.onMessageReceived(Responder.this, e);
               }
             }
           });
 }
 /**
  * Creates a new client channel.
  *
  * @param document the document in which to insert the iframe
  * @param url the url to the remote peer
  * @param listener a callback to be notified on channel events
  */
 public Client(Document document, String url, final ClientListener listener) {
   origin = getDomain(url);
   frame = document.getBody().appendChild(createFrame(document, url));
   receiver = new Responder(getCurrentWindow(), origin, listener);
   remover =
       Event.addEventListener(
           "load",
           frame,
           new EventListener() {
             public void handleEvent(Event event) {
               // This should never call synchronously.
               assert remover != null;
               assert !setConnected(true);
               listener.onConnected(Client.this);
               remover.remove();
             }
           });
 }