code: func validateUserAgent(userAgent string) error {
  	if len(userAgent) > MaxUserAgentLen {
  		str := fmt.Sprintf("user agent too long [len %v, max %v]",
  			len(userAgent), MaxUserAgentLen)
  		return messageError("MsgVersion", str)
  	}
  	return nil
  }
docs: // validateUserAgent checks userAgent length against MaxUserAgentLen