code: func (cc ConnackCode) String() string {
  	switch cc {
  	case ConnectionAccepted:
  		return "connection accepted"
  	case InvalidProtocolVersion:
  		return "connection refused: unacceptable protocol version"
  	case IdentifierRejected:
  		return "connection refused: identifier rejected"
  	case ServerUnavailable:
  		return "connection refused: server unavailable"
  	case BadUsernameOrPassword:
  		return "connection refused: bad user name or password"
  	case NotAuthorized:
  		return "connection refused: not authorized"
  	}
  
  	return "invalid connack code"
  }
docs: // String returns the corresponding error string for the ConnackCode.