test.go

package main

import (
	"github.com/miekg/dns"
	"log"
	"net"
	"time"
)

const (
	recursor = "8.8.8.8:53" // Google DNS
)

func main() {
	mux := dns.NewServeMux()
	udp := &dns.Server{
		Addr:    "127.0.0.1:8600",
		Net:     "udp",
		Handler: mux,
		UDPSize: 65535,
	}
	tcp := &dns.Server{
		Addr:    "127.0.0.1:8600",
		Net:     "tcp",
		Handler: mux,
	}

	mux.HandleFunc(".", handleRecurse)

	go udp.ListenAndServe()
	go tcp.ListenAndServe()
	select {}
}

func handleRecurse(resp dns.ResponseWriter, req *dns.Msg) {
	q := req.Question[0]
	network := "udp"
	defer func(s time.Time) {
		log.Printf("[DEBUG] dns: request for %v (%s) (%v)", q, network, time.Now().Sub(s))
	}(time.Now())

	// Switch to TCP if the client is
	if _, ok := resp.RemoteAddr().(*net.TCPAddr); ok {
		network = "tcp"
	}

	// Recursively resolve
	c := &dns.Client{Net: network}
	r, rtt, err := c.Exchange(req, recursor)

	// On failure, return a SERVFAIL message
	if err != nil {
		log.Printf("[ERR] dns: recurse failed: %v", err)
		m := &dns.Msg{}
		m.SetReply(req)
		m.SetRcode(req, dns.RcodeServerFailure)
		resp.WriteMsg(m)
		return
	}
	log.Printf("[DEBUG] dns: recurse RTT for %v (%v)", q, rtt)

	// TOGGLE COMPRESS TO BREAK RESPONSE
	r.Compress = true

	// Forward the response
	if err := resp.WriteMsg(r); err != nil {
		log.Printf("[WARN] dns: failed to respond: %v", err)
	}
}