code: func from(req *http.Request) string {
  	if f := req.Header.Get("X-Forwarded-For"); f != "" {
  		return f
  	}
  	f := req.RemoteAddr
  	ip, _, err := net.SplitHostPort(f)
  	if err != nil {
  		return f
  	}
  	return ip
  }
docs: // from makes a best effort to compute the request client IP.