code: func labelsToString(labels map[string][]string) string {
  	ls := []string{}
  	for k, v := range labels {
  		ls = append(ls, fmt.Sprintf("%s:%v", k, v))
  	}
  	sort.Strings(ls)
  	return strings.Join(ls, " ")
  }
docs: // labelsToString returns a string representation of a
  // map representing labels.