code: public static void sendPong(final ByteBuffer[] data, final WebSocketChannel wsChannel, final WebSocketCallback<Void> callback, long timeoutmillis) {
          sendInternal(mergeBuffers(data), WebSocketFrameType.PONG, wsChannel, callback, null, timeoutmillis);
      }
docs: Sends a complete pong message, invoking the callback when complete
  
  @param data The data to send
  @param wsChannel The web socket channel
  @param callback The callback to invoke on completion
  @param timeoutmillis the timeout in milliseconds