Socket.io v1.x Library for W5100 & ENC28J60 + ESP8266

I got the library working with communication between server and web-client and between server and ESP8266.

I have one problem: data are received on the ESP8266 (log-msg) but not delivered to the application.

  if (client.monitor()) {
    lastreply = millis();
    Serial.println(RID);
    Serial.println(Rname);
    Serial.println(Rcontent);
    }
  }

I get no print of RID, Rname and Rcontent in my client.monitor

I also tried to implement a callback routing like this:

void ondata(SocketIOClient client, char *data) {
  Serial.print(data);
}

registering the callback in setup() like this:

client.setDataArrivedDelegate(ondata);

But this also not works.

I cannot understand from the SocketIOClient.cpp how the callback is called???

Any help is highly appreciated.