code: func (i *Image) LayerURLs(id string) []string {
  	var urls []string
  	for _, ep := range i.endpoints {
  		urls = append(urls, fmt.Sprintf("%s://%s/v1/images/%s/layer", i.scheme, ep, id))
  	}
  	return urls
  }
docs: // LayerURLs returns several URLs for a specific layer.