code: func ReadNextTokenBytes(rw io.ReadWriter) ([]byte, error) {
  	data, err := lpReadBuf(rw)
  	switch err {
  	case nil:
  		return data, nil
  	case ErrTooLarge:
  		err := delimWriteBuffered(rw, []byte("messages over 64k are not allowed"))
  		if err != nil {
  			return nil, err
  		}
  		return nil, ErrTooLarge
  	default:
  		return nil, err
  	}
  }
docs: // ReadNextTokenBytes extracts a token from a ReadWriter. It is used
  // during protocol negotiation and returns a byte slice.