code: func (eb *exponentialBackoff) Next(retry int) time.Duration {
  	if retry <= 0 {
  		return 0 * time.Millisecond
  	}
  	return time.Duration(math.Min(eb.initialTimeout+math.Pow(eb.exponentFactor, float64(retry)), eb.maxTimeout)+float64(rand.Int63n(eb.maximumJitterInterval))) * time.Millisecond
  }
docs: // Next returns next time for retrying operation with exponential strategy