try

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

It is based on Mat Reyer's try package, modified to return multierror.

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).