private void onOpen() {
        logger.fine("socket open");
        this.readyState = ReadyState.OPEN;
        Socket.priorWebsocketSuccess = WebSocket.NAME.equals(this.transport.name);
        this.emit(EVENT_OPEN);
        this.flush();

        if (this.readyState == ReadyState.OPEN && this.upgrade && this.transport instanceof Polling) {
            logger.fine("starting upgrade probes");
            for (String upgrade: this.upgrades) {
                this.probe(upgrade);
            }
        }
    }