main.go

package main

import (
	"context"
	"log"
	"net"
	"strconv"

	"github.com/miekg/dns"
	"github.com/redis/go-redis/v9"
)

var client = redis.NewClient(&redis.Options{
	Addr:     "localhost:6379",
	Password: "", // no password set
	DB:       0,  // use default DB
})

var domainsToAddresses map[string]string = map[string]string{
	"google.com.":     "1.2.3.4",
	"cloudflare.com.": "1.1.1.1",
}

type handler struct{}

func (this *handler) ServeDNS(w dns.ResponseWriter, r *dns.Msg) {
	ctx := context.Background()
	msg := dns.Msg{}
	msg.SetReply(r)
	switch r.Question[0].Qtype {
	case dns.TypeA:
		msg.Authoritative = true
		domain := msg.Question[0].Name
		// address, errs := client.Get(ctx, domain).Result()
		address, errs := client.Do(ctx, "get", domain).Result()
		if errs == nil {
			log.Println(address)
			msg.Answer = append(msg.Answer, &dns.A{
				Hdr: dns.RR_Header{Name: domain, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 60},
				A:   net.ParseIP(address.(string)),
			})
		}
		if errs != nil {
			msg.Answer = append(msg.Answer, &dns.A{
				Hdr: dns.RR_Header{Name: domain, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 60},
				A:   net.ParseIP("8.8.8.8"),
			})
		}
	}
	w.WriteMsg(&msg)
}

func main() {
	srv := &dns.Server{Addr: ":" + strconv.Itoa(53), Net: "udp"}
	srv.Handler = &handler{}
	if err := srv.ListenAndServe(); err != nil {
		log.Fatalf("Failed to set udp listener %s\n", err.Error())
	}
	log.Println()
}