code: func (s *cryptoStreamImpl) GetCryptoData() []byte {
  	if len(s.msgBuf) < 4 {
  		return nil
  	}
  	msgLen := 4 + int(s.msgBuf[1])<<16 + int(s.msgBuf[2])<<8 + int(s.msgBuf[3])
  	if len(s.msgBuf) < msgLen {
  		return nil
  	}
  	msg := make([]byte, msgLen)
  	copy(msg, s.msgBuf[:msgLen])
  	s.msgBuf = s.msgBuf[msgLen:]
  	return msg
  }
docs: // GetCryptoData retrieves data that was received in CRYPTO frames