powerdns-remote-http-example/dns.go

package main

import (
	"errors"
	"fmt"
	"log"
	"net"
	"strings"
	"sync"
	"time"

	"github.com/miekg/dns"
)

var (
	dnsStringToType sync.Map
)

func dnsQtypeStringToValue(qtype string) uint16 {
	x, found_qtype := dnsStringToType.Load(qtype)
	if found_qtype {
		return x.(uint16)
	}

	for k, v := range dns.TypeToString {
		if v == qtype {
			dnsStringToType.Store(qtype, k)
			return k
		}
	}

	log.Printf("qtype %#v is not known or found", qtype)
	return dns.TypeNone
}

func dnsCustomResolve(qname string, qtype uint16) (*dns.Msg, error) {
	qtype_s, qtype_known := dns.TypeToString[qtype]
	if !qtype_known {
		log.Printf("qtype is not known (%v) for %v", qtype, qname)
		return nil, fmt.Errorf("qtype is not known: %v", qtype)
	}

	c := new(dns.Client)
	c.Net = cfgResolverProto
	c.Dialer = &net.Dialer{
		Timeout: cfgResolverTimeout,
	}

	req := new(dns.Msg)
	req.Id = dns.Id()
	req.RecursionDesired = true
	req.Question = make([]dns.Question, 1)
	req.Question[0] = dns.Question{Name: qname, Qtype: qtype, Qclass: dns.ClassINET}

	var resp *dns.Msg
	var rtt time.Duration
	var err error
	for i := 0; i < 2; i++ {
		resp, rtt, err = c.Exchange(req, cfgResolverEndpoint)
		if err == nil {
			break
		}
	}
	if err != nil {
		log.Printf("resolving %v/%v (rtt %v) with error: %v", qname, qtype_s, rtt, err)
		return nil, err
	}
	log.Printf("resolved %v/%v (rtt %v)", qname, qtype_s, rtt)

	return resp, nil
}

func dnsClipTtl(ttl uint32) uint32 {
	if ttl < cfgTtlMin {
		return cfgTtlMin
	}
	if ttl > cfgTtlMax {
		return cfgTtlMax
	}
	return ttl
}

type PowerDnsAnswer struct {
	Qname   string `json:"qname"`
	Qtype   string `json:"qtype"`
	Ttl     uint32 `json:"ttl"`
	Content string `json:"content"`
}

func dnsToPowerDnsAnswer(response *dns.Msg) ([]PowerDnsAnswer, error) {
	if response == nil {
		return nil, errors.New("response is nil")
	}

	result := make([]PowerDnsAnswer, 0, len(response.Answer))
	for i := range response.Answer {
		cont, ok := strings.CutPrefix(response.Answer[i].String(), response.Answer[i].Header().String())
		if !ok {
			continue
		}

		qtype, ok := dns.TypeToString[response.Answer[i].Header().Rrtype]
		if !ok {
			continue
		}

		rec := PowerDnsAnswer{
			Qname:   response.Answer[i].Header().Name,
			Qtype:   qtype,
			Ttl:     dnsClipTtl(response.Answer[i].Header().Ttl),
			Content: cont,
		}
		result = append(result, rec)
	}

	return result, nil
}