code: func RandomStr(length int) string {
  	str := "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
  	bytes := []byte(str)
  	result := []byte{}
  	r := rand.New(rand.NewSource(time.Now().UnixNano()))
  	for i := 0; i < length; i++ {
  		result = append(result, bytes[r.Intn(len(bytes))])
  	}
  	return string(result)
  }
docs: //RandomStr 随机生成字符串