code: func GetRequesterAddress(r *http.Request) string {
  	if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
  		return ParseForwarded(xff)
  	}
  
  	if ip, _, err := net.SplitHostPort(r.RemoteAddr); err == nil {
  		return ip
  	}
  
  	return ""
  }
docs: // GetRequesterAddress does a best effort lookup for the real IP address of the
  // requester. Many load balancers (such as AWS's ELB) set a X-Forwarded-For
  // header which can be used to determine the IP address of the client when the
  // server is behind a load balancer.
  //
  // It is possible however for the client to spoof this header if the load
  // balancer is not configured to remove it from the request or if the server is
  // accessed directly.
  //
  // For uses such as rate limitting, only use this function if you can trust that
  // the load balancer will strip the header from the client and that the server
  // will not be directly accessible by the public (only though the load
  // balancer).