code: public ByteBuffer nextBinary() throws IOException {
          WebSocketMessageType msgType = null;
          
          while ((msgType = _messageReader.next()) != WebSocketMessageType.EOS) {
              if (msgType == WebSocketMessageType.BINARY) {
                  return _messageReader.getBinary();
              }
          }
  
          return null;
      }
docs: Returns the next binary message received on this connection. This method
  will block till a binar message is received. Any text messages that may
  arrive will be ignored. A null is returned when the connection is closed.
  <p>
  An IOException is thrown if the connection has not been established
  before invoking this method.
  
  @return ByteBuffer     the payload of the binary message
  @throws IOException    if the connection has not been established