code: func backoff(min, max float64, iter int) time.Duration {
  	backoff := math.Pow(2, float64(iter)/5) * min
  	if backoff > max {
  		backoff = max
  	}
  	return time.Duration(backoff) * time.Millisecond
  }
docs: // backoff will perform exponential backoff based on the iteration and
  // limited by the provided min and max (in milliseconds) durations.