reverse proxy i use at my raspberry pi

reverse_proxy.go

package main

import (
	"log"
	"net/http"
	"net/http/httputil"
	"net/url"
)

func makeHandler(hostTarget map[string]string) func(w http.ResponseWriter, r *http.Request) {
	hostProxy := map[string]*httputil.ReverseProxy{}
	for k, v := range hostTarget {
		remoteUrl, err := url.Parse(v)
		if err != nil {
			log.Println("target parse fail:", err)
			return nil
		}

		proxy := httputil.NewSingleHostReverseProxy(remoteUrl)
		hostProxy[k] = proxy
	}
	return func(w http.ResponseWriter, r *http.Request) {
		host := r.Host
		log.Println(host + ": " + ReadUserIP(r))

		if fn, ok := hostProxy[host]; ok {
			fn.ServeHTTP(w, r)
			return
		}
		w.Write([]byte("403: Host forbidden " + host))
	}
}

func ReadUserIP(r *http.Request) string {
	IPAddress := r.Header.Get("X-Real-Ip")
	if IPAddress == "" {
		IPAddress = r.Header.Get("X-Forwarded-For")
	}
	if IPAddress == "" {
		IPAddress = r.RemoteAddr
	}
	return IPAddress
}

func main() {
	var (
		hostTarget = map[string]string{
			"caue.site":         "http://localhost:8080",
			"home.caue.site":    "http://localhost:8081",
			"torrent.caue.site": "http://localhost:8082",
			"code.caue.site":    "http://localhost:8083",
		}
	)
	http.HandleFunc("/", makeHandler(hostTarget))
	log.Fatal(http.ListenAndServe(":80", nil))
}