code: func (cb *constantBackoff) Next(retry int) time.Duration {
  	if retry <= 0 {
  		return 0 * time.Millisecond
  	}
  	return (time.Duration(cb.backoffInterval) * time.Millisecond) + (time.Duration(rand.Int63n(cb.maximumJitterInterval)) * time.Millisecond)
  }
docs: // Next returns next time for retrying operation with constant strategy