code: func Pack(w io.Writer, buf []byte) error {
  	if len(buf) > messageMax {
  		return errors.New("message is too large")
  	}
  
  	var bl [2]byte
  	binary.LittleEndian.PutUint16(bl[:], uint16(len(buf)))
  	_, err := w.Write(bl[:])
  	if err != nil {
  		return err
  	}
  
  	_, err = w.Write(buf)
  	return err
  }
docs: // Pack writes a message to an io.Writer.