You can specify any condition for upgrading to a WebSocket connection. You can even upgrade any connection request to a WebSocket connection without specifying a condition like this:
WebSocketTransformer.upgrade(request).then((WebSocket websocket) {
websocket.listen((String text) {
// process sent data
});
websocket.add(JSON.encode("Hello"));
});
If the request is not a valid web socket upgrade request a HTTP response with status code 500 will be returned. Otherwise the returned future will complete with the [WebSocket] when the upgrade process is complete.