file_server.go

package main

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

var addr = flag.String("l", ":8000", "Listening address")
var dir = flag.String("d", ".", "serving directory")
var v4 = flag.Bool("4", false, "serving ipv4 only")
var v6 = flag.Bool("6", false, "serving ipv6 only")

func main() {
	flag.Parse()
	fs := http.FileServer(http.Dir(*dir))

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		log.Printf("%s %s %s %s", r.RemoteAddr, r.Method, r.URL.Path, r.UserAgent())
		fs.ServeHTTP(w, r)
	})

	var ln net.Listener
	var err error

	switch {
	case *v4 && !*v6:
		log.Printf("Listening on %v (ipv4)", *addr)
		ln, err = net.Listen("tcp4", *addr)
	case *v6 && !*v4:
		log.Printf("Listening on %v (ipv6)", *addr)
		ln, err = net.Listen("tcp6", *addr)
	default:
		log.Printf("Listening on %v", *addr)
		ln, err = net.Listen("tcp", *addr)
	}
	if err != nil {
		log.Fatal(err)
	}

	err = http.Serve(ln, nil)
	if err != nil {
		log.Fatal(err)
	}
}