juneym/try

Simple idiomatic retry package for Go

try

Idiomatic Go retry package. Thanks to @rowland for code review.

go get gopkg.in/matryer/try.v1

Usage

Just call try.Do with the function you want to retry in the event of an error:

• Call try.Do that returns a bool indicating whether to retry or not, and an error
• The attempt argument will start at 1 and count up
• try.Do blocks until you return false, or a nil error
• try.Do returns the last error or nil if it was successful

var value string
err := try.Do(func(attempt int) (bool, error) {
  var err error
  value, err = SomeFunction()
  return attempt < 5, err // try 5 times
})
if err != nil {
  log.Fatalln("error:", err)
}

In the above example the function will be called repeatedly until error is nil, while attempt < 5 (i.e. try 5 times)

Retrying panics

Try supports retrying in the event of a panic.

• Use named return parameters
• Set retry first
• Defer the recovery code, and set err manually in the case of a panic
• Use empty return statement at the end

var value string
err := try.Do(func(attempt int) (retry bool, err error) {
  retry = attempt < 5 // try 5 times
  defer func() {
    if r := recover(); r != nil {
      err = errors.New(fmt.Sprintf("panic: %v", r))
    }
  }()
  value, err = SomeFunction()
  return
})
if err != nil {
  log.Fatalln("error:", err)
}

Delay between retries

To introduce a delay between retries, just make a time.Sleep call before you return from the function if you are returning an error.

var value string
err := try.Do(func(attempt int) (bool, error) {
  var err error
  value, err = SomeFunction()
  if err != nil {
    time.Sleep(1 * time.Minute) // wait a minute
  }
  return attempt < 5, err
})
if err != nil {
  log.Fatalln("error:", err)
}

Maximum retry limit

To avoid infinite loops, Try will ensure it only makes try.MaxRetries attempts. By default, this value is 10, but you can change it:

try.MaxRetries = 20

To see if a Do operation failed due to reaching the limit, you can check the error with try.IsMaxRetries(err).