powerdns-remote-http-example/dns.go

package main

import (
	"fmt"
	"log"
	"math/rand"
	"net"
	"strings"
	"sync"

	"github.com/miekg/dns"
)

var (
	dnsStringToType sync.Map
	dnsExtraQtype   = make(map[uint16]bool)

	dnsTtlRange uint32
)

func setupDns() {
	for _, v := range []uint16{
		dns.TypePTR, dns.TypeMX, dns.TypeTXT, dns.TypeSRV, dns.TypeLOC, dns.TypeHINFO, dns.TypeSPF,
		dns.TypeSIG, dns.TypeKEY, dns.TypeKX, dns.TypeDS, dns.TypeRRSIG, dns.TypeNSEC, dns.TypeDNSKEY, dns.TypeNSEC3, dns.TypeNSEC3PARAM, dns.TypeTLSA, dns.TypeCDS, dns.TypeCDNSKEY, dns.TypeZONEMD, dns.TypeTKEY, dns.TypeTSIG, dns.TypeCAA,
		dns.TypeSVCB, dns.TypeHTTPS, dns.TypeURI,
	} {
		dnsExtraQtype[v] = true
	}

	// warmup
	for _, v := range []string{"SOA", "NS", "A", "AAAA", "ANY", "PTR", "CNAME"} {
		dnsQtypeStringToValue(v)
	}
}

func dnsIsAllowedExtraQtype(qtype uint16) bool {
	_, found := dnsExtraQtype[qtype]
	return found
}

func dnsQtypeStringToValue(qtype string) uint16 {
	x, found := dnsStringToType.Load(qtype)
	if found {
		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, known := dns.TypeToString[qtype]
	if !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}

	resp, rtt, err := c.Exchange(req, cfgResolverEndpoint)
	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
}

func randUint32(v uint32) uint32 {
	if v < 2 {
		return rand.Uint32()
	}
	return rand.Uint32() % v
}

func dnsFuzzClipTtl() uint32 {
	return dnsClipTtl(cfgTtlMin + 1 + randUint32(dnsTtlRange*2) - dnsTtlRange)
}

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

func dnsRrToPowerDnsAnswer(rr dns.RR) (PowerDnsAnswer, error) {
	qname := rr.Header().Name

	rrtype := rr.Header().Rrtype
	qtype_s, ok := dns.TypeToString[rrtype]
	if !ok {
		return PowerDnsAnswer{}, fmt.Errorf("record %v: unknown rrtype: %v", qname, rrtype)
	}

	cont, ok := strings.CutPrefix(rr.String(), rr.Header().String())
	if !ok {
		return PowerDnsAnswer{}, fmt.Errorf("record %v/%v: unable to produce content", qname, qtype_s)
	}

	return PowerDnsAnswer{
		Qname:   qname,
		Qtype:   qtype_s,
		Ttl:     dnsClipTtl(rr.Header().Ttl),
		Content: strings.TrimSpace(cont),
	}, nil
}

func dnsToPowerDnsAnswer(resp *dns.Msg) ([]PowerDnsAnswer, error) {
	result := make([]PowerDnsAnswer, 0, len(resp.Answer)+len(resp.Extra))
	for i := range resp.Answer {
		r, err := dnsRrToPowerDnsAnswer(resp.Answer[i])
		if err != nil {
			log.Printf("%v", err)
			continue
		}
		result = append(result, r)
	}
	for i := range resp.Extra {
		r, err := dnsRrToPowerDnsAnswer(resp.Extra[i])
		if err != nil {
			log.Printf("%v", err)
			continue
		}
		result = append(result, r)
	}

	return result, nil
}