code: func NewRateLimiter(bandwidth float64) *RateLimiter {
  	//  convert bandwidth to bytes per nanosecond
  	b := bandwidth / float64(time.Second)
  	return &RateLimiter{
  		bandwidth:    b,
  		allowance:    0,
  		maxAllowance: bandwidth,
  		lastUpdate:   time.Now(),
  	}
  }
docs: //  Creates a new RateLimiter with bandwidth (in bytes/sec)