go-dnsproxy.go

package main

import (
	"flag"
	"fmt"
	"github.com/miekg/dns"
	"os"
)

var (
	remote = flag.String("remote", "8.8.4.4:53", "remote dns address")
	local  = flag.String("local", ":53", "local listen address")
	quiet  = flag.Bool("quiet", false, "suppress output")
)

func main() {
	flag.Parse()

	dns.HandleFunc(".", proxyServe)

	failure := make(chan error, 1)

	go func(failure chan error) {
		failure <- dns.ListenAndServe(*local, "tcp", nil)
	}(failure)

	go func(failure chan error) {
		failure <- dns.ListenAndServe(*local, "udp", nil)
	}(failure)

	fmt.Println(<-failure)
	os.Exit(1)
}

func proxyServe(w dns.ResponseWriter, req *dns.Msg) {
	if req.MsgHdr.Response == true { // supposed responses sent to us are bogus
		return
	}

	c := new(dns.Client)
	c.Net = "tcp"
	m, _, err := c.Exchange(req, *remote)

	if !*quiet {
		fmt.Println(req)
		fmt.Println(m)
	}

	if err != nil {
		fmt.Println(err)
	} else {
		w.WriteMsg(m)
	}
}