code: func IsUserAllowed(user string, allowed *RangeList) bool {
  	if allowed == nil || allowed.Empty() {
  		return true
  	}
  	uid, err := strconv.Atoi(user)
  	if err != nil {
  		return false
  	}
  	return allowed.Contains(uid)
  }
docs: // IsUserAllowed checks that the given user is numeric and is
  // contained by the given RangeList.  Returns true if
  // allowed is nil or empty.