!include once #1015699 // websocket

static WebSocketClient webSocketOnMessage(S url, final VF1<S> onMessage) {
  ret webSocketOnMessage(url, onMessage, null);
}

static WebSocketClient webSocketOnMessage(S url, final VF1<S> onMessage, fS initialMessage, fO... args) ctex {
  WebSocketClient client = new WebSocketClient(new URI(url)) {
    public void onMessage(S s) {
      if (!licensed()) ret with close(); // program exit
      // s = dropTrailingNullChars(s); // older server bug
      pcallF(onMessage, s);
    }

    public void onOpen(ServerHandshake handshake) {
      if (nempty(initialMessage))
        send(format(initialMessage, args));
    }
    
    public void onClose(int code, S reason, bool remote) {}
    public void onError(Exception e) { printStackTrace(e); }
  };
  
  client.connect();
  ret client;
}

Began life as a copy of #1015081