Golang webserver which echo's the request back to you and prints your IP address

whoami.go

package main

import (
	"errors"
	"log"
	"net"
	"net/http"
	"strings"
	"net/http/httputil"
	"flag"
	"strconv"
)

func getIP(r *http.Request) (string, error) {
	ips := r.Header.Get("X-Forwarded-For")

	log.Println("[.] X-Fowarded-For:",ips)

	splitIps := strings.Split(ips, ",")

	if len(splitIps) > 0 {
		// this mght be wrong
		netIP := net.ParseIP(splitIps[len(splitIps)-1])
		if netIP != nil {
			return netIP.String(), nil
		}
	}

	ip, _, err := net.SplitHostPort(r.RemoteAddr)
	if err != nil {
		return "", err
	}

	netIP := net.ParseIP(ip)
	if netIP != nil {
		ip := netIP.String()
		if ip == "::1" {
			return "127.0.0.1", nil
		}
		return ip, nil
	}

	return "", errors.New("IP not found")
}

func handler(w http.ResponseWriter, r *http.Request) {
	log.Println("[!] New request received")
	ip, err := getIP(r)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		log.Println(err)
		return
	}

	w.WriteHeader(http.StatusOK)

	lastHopIp, _, err := net.SplitHostPort(r.RemoteAddr)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		log.Println(err)
		return
	}

	log.Println("[.] Original IP:", ip)
	if ip == lastHopIp {
		w.Write([]byte("Your ip is " + ip + "\n\n"))
	} else {
		log.Println("[.] Proxy IP:", lastHopIp)
		w.Write([]byte("Your ip is " + ip + " and your request has been proxied via " + lastHopIp + "\n\n"))
	}

	requestDump, err := httputil.DumpRequest(r, true)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		log.Println(err)
		return
	}
	w.Write(requestDump)
}

func isValidPort(p int) bool {
	return (p > 0 && p < 65535)
}

func main() {
	port := flag.Int("p", 80, "port to listen on")
	flag.Parse()

	portStr := strconv.Itoa(*port)

	if !isValidPort(*port) {
		log.Println("[?] Port", portStr, "is invalid")
		return
	}

	log.Println("[-] Server starting on port", portStr)
	http.HandleFunc("/", handler)
	log.Fatal(http.ListenAndServe(":"+portStr, nil))
}