code: func (sr *Receiver) Sizes() []int {
  	sr.Lock()
  	defer sr.Unlock()
  	sizes := make([]int, 0, len(sr.Have))
  	for _, size := range sr.Have {
  		sizes = append(sizes, int(size))
  	}
  	sort.Ints(sizes)
  	return sizes
  }
docs: // Sizes returns the sorted blob sizes.