package main

import (
	"log"
	"net"
	"net/http"
	"strings"
)

func main() {
	http.HandleFunc("/", handler)
	err := http.ListenAndServe(":8080", nil)
	if err != nil {
		log.Fatal(err)
	}
}

func handler(w http.ResponseWriter, req *http.Request) {
	ip := ""
	ips := proxy(req)
	if len(ips) > 0 && len(ips[0]) > 0 {
		rip, _, err := net.SplitHostPort(ips[0])
		ip = rip
		if err != nil {
			ip = ips[0]
		}
	} else {
		if rip, _, err := net.SplitHostPort(req.RemoteAddr); err == nil {
			ip = rip
		} else {
			ip = req.RemoteAddr
		}
	}
	w.WriteHeader(200)
	w.Write([]byte(ip))
}

func proxy(req *http.Request) []string {
	if ips := req.Header.Get("X-Forwarded-For"); len(ips) > 0 {
		return strings.Split(ips, ",")
	}
	return []string{}
}