code: func (h *receivedPacketHistory) GetAckRanges() []wire.AckRange {
  	if h.ranges.Len() == 0 {
  		return nil
  	}
  
  	ackRanges := make([]wire.AckRange, h.ranges.Len())
  	i := 0
  	for el := h.ranges.Back(); el != nil; el = el.Prev() {
  		ackRanges[i] = wire.AckRange{Smallest: el.Value.Start, Largest: el.Value.End}
  		i++
  	}
  	return ackRanges
  }
docs: // GetAckRanges gets a slice of all AckRanges that can be used in an AckFrame