code: func issueRedirect(urlPath string) (string, bool) {
  	m := issueNum.FindStringSubmatch(urlPath)
  	if m == nil {
  		return "", false
  	}
  	issueNumber := strings.TrimPrefix(m[1], "/")
  	suffix := ""
  	if issueNumber != "" {
  		suffix = "/" + issueNumber
  	}
  	return "https://github.com/perkeep/perkeep/issues" + suffix, true
  }
docs: // issueRedirect returns whether the request should be redirected to the
  // issues tracker, and the url for that redirection if yes, the empty
  // string otherwise.