Simple Golang DNS Server (simplified version)

main.go

package main

import (
	"fmt"
	"log"
	"strconv"

	"github.com/miekg/dns"
)

func main() {
	// attach request handler func
	dns.HandleFunc(".", func(w dns.ResponseWriter, r *dns.Msg) {
		m := new(dns.Msg)
		m.SetReply(r)
		m.Compress = false

		if r.Opcode == dns.OpcodeQuery {
			for _, q := range m.Question {
				if q.Qtype == dns.TypeA {
					log.Printf("Query for %s\n", q.Name)
					rr, err := dns.NewRR(fmt.Sprintf("%s A %s", q.Name, "1.2.3.4"))
					if err == nil {
						m.Answer = append(m.Answer, rr)
					}
				}
			}
		}

		w.WriteMsg(m)
	})

	port := 53
	server := &dns.Server{Addr: ":" + strconv.Itoa(port), Net: "udp"}
	log.Printf("Starting at %d\n", port)
	err := server.ListenAndServe()
	defer server.Shutdown()
	if err != nil {
		log.Fatalf("Failed to start server: %s\n ", err.Error())
	}
}

test.sh

dig @localhost -p 53 google.com +short