Golang常用的工具函数，无依赖，常更

util.go

// Execute f() n times on fail
func RetryHandler(n int, f func() (bool, error)) error {
  ok, er := f()
  if ok && er == nil {
    return nil
  }
  if n-1 > 0 {
    return RetryHandler(n-1, f)
  }
  return er
}

// Execute f() n times on fail, each time on fail will keep specific interval in order of `secondIntervals`
// If n < 0, it will forever execute f(), interval will used in order of `secondIntervals` and keep using the last interval element at last.
// Work in serial.
func RetryHandlerWithInterval(n int, f func() (bool, error), secondIntervals ... int) error {
  var offset = 0
  var ok bool
  var e error
  return retryHandlerWithIntervalOffset(&ok, &e, n, f, &offset, secondIntervals...)
}

// sub function of RetryHandlerWithInterval
func retryHandlerWithIntervalOffset(ok *bool, e *error, n int, f func() (bool, error), offset *int, secondIntervals ... int) error {
  if n == 0 {
    return nil
  }
  *ok, *e = f()
  if *ok && *e == nil {
    return nil
  }

  if n-1 > 0 && !(n < 0) {
    if *offset < len(secondIntervals) {
      time.Sleep(time.Duration(secondIntervals[*offset]) * time.Second)
      if *offset < len(secondIntervals)-1 {
        *offset ++
      }
    }
    return retryHandlerWithIntervalOffset(ok, e, n-1, f, offset, secondIntervals...)
  } else {
    if n != 1 {
      if *offset < len(secondIntervals) {
        time.Sleep(time.Duration(secondIntervals[*offset]) * time.Second)
        if *offset < len(secondIntervals)-1 {
          *offset ++
        }
      }
      return retryHandlerWithIntervalOffset(ok, e, n, f, offset, secondIntervals...)
    }
  }
  return *e
}

// Generate random string 32 bit
func RandomString() string {
  str := "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
  var r *rand.Rand
  var once = sync.Once{}
  once.Do(func() {
    r = rand.New(rand.NewSource(time.Now().UnixNano()))
  })
  var result string
  for i := 0; i < 32; i++ {
    result += string(str[r.Intn(len(str))])
  }
  return result
}
// MD5 encrypt returning upper case 
func MD5(rawMsg string) string {
  data := []byte(rawMsg)
  has := md5.Sum(data)
  md5str1 := fmt.Sprintf("%x", has)
  return strings.ToUpper(md5str1)
}

// Returns well format output in json
func Debug(src interface{}) string {
  buf, e := json.MarshalIndent(src, "  ", "  ")
  if e != nil {
    fmt.Println(errorx.Wrap(e).Error())
  }
  return string(buf)
}