powerdns-remote-http-example/dns-remap.go

package main

import (
	"net"
	"sync"
	"time"

	nft "github.com/google/nftables"
	"github.com/miekg/dns"
)

type DnsAnswer struct {
	Qname   string
	Qtype   uint16
	Ttl     uint32
	AddrLen uint32
	Addr    net.IP
}

func dnsRemap(qname string, qtype uint16, orig *dns.Msg) ([]PowerDnsAnswer, error) {
	result := make([]PowerDnsAnswer, 0)
	interim := make([]DnsAnswer, 0, len(orig.Answer))

	needle := qname
	name_seen := map[string]bool{
		needle: true,
	}
	cname_dive := true
	for {
		if !cname_dive {
			break
		}
		cname_dive = false

		for _, rr := range orig.Answer {
			if rr.Header().Name != needle {
				continue
			}
			if rr.Header().Rrtype != dns.TypeCNAME {
				continue
			}

			cname_dive = true
			cname := rr.(*dns.CNAME)
			_, seen := name_seen[cname.Target]
			if seen {
				// CNAME loop?
				return []PowerDnsAnswer{}, nil
			}

			needle = cname.Target
			name_seen[needle] = true
			break
		}
		if cname_dive {
			continue
		}

		for _, rr := range orig.Answer {
			if rr.Header().Name != needle {
				continue
			}

			t := rr.Header().Rrtype
			switch t {
			case dns.TypeA, dns.TypeAAAA:
				// continue below
			default:
				continue
			}

			r := DnsAnswer{
				Qname: qname,
				Qtype: t,
				Ttl:   dnsClipTtl(rr.Header().Ttl),
			}
			switch r.Qtype {
			case dns.TypeA:
				r.Addr = rr.(*dns.A).A
				r.AddrLen = net.IPv4len
			case dns.TypeAAAA:
				r.Addr = rr.(*dns.AAAA).AAAA
				r.AddrLen = net.IPv6len
			}
			interim = append(interim, r)
		}
	}

	// fix missing A/AAAA records
	if (len(interim) == 0) && ((needle != qname) || (qtype == dns.TypeANY)) {
		var wg sync.WaitGroup
		var a, aaaa []PowerDnsAnswer

		if qtype != dns.TypeAAAA {
			wg.Add(1)
			go func() {
				defer wg.Done()
				x, _ := dnsApi_lookup_int(needle, dns.TypeA)
				if x != nil {
					a = x.([]PowerDnsAnswer)
				}
			}()
		}
		if qtype != dns.TypeA {
			wg.Add(1)
			go func() {
				defer wg.Done()
				x, _ := dnsApi_lookup_int(needle, dns.TypeAAAA)
				if x != nil {
					aaaa = x.([]PowerDnsAnswer)
				}
			}()
		}

		wg.Wait()

		if a != nil {
			result = append(result, a...)
		}
		if aaaa != nil {
			result = append(result, aaaa...)
		}

		// HACK: replace qname
		for i := range result {
			result[i].Qname = qname
		}

		return result, nil
	}

	unix_start := time.Unix(0, 0)
	nft_ipv4 := make([]nft.SetElement, 0, len(interim))
	nft_ipv6 := make([]nft.SetElement, 0, len(interim))
	// fill map elements
	for _, r := range interim {
		switch r.AddrLen {
		case net.IPv4len, net.IPv6len:
		default:
			continue
		}

		// HACK: clip ttl
		r.Ttl = dnsClipTtl(r.Ttl)

		var srcAddr net.IP = make([]byte, r.AddrLen)
		copy(srcAddr, r.Addr)
		var dstAddr net.IP
		switch r.AddrLen {
		case net.IPv4len:
			dstAddr = addrMapGet(r.Addr, nftCidrV4, r.Ttl)
		case net.IPv6len:
			dstAddr = addrMapGet(r.Addr, nftCidrV6, r.Ttl)
		}

		// HACK: replace addr
		copy(r.Addr, dstAddr)

		elem := nft.SetElement{
			Key: []byte(dstAddr),
			Val: []byte(srcAddr),
			// Timeout: time.Duration(r.Ttl),
			Timeout: time.Unix(int64(r.Ttl), 0).Sub(unix_start),
		}

		switch r.AddrLen {
		case net.IPv4len:
			nft_ipv4 = append(nft_ipv4, elem)
		case net.IPv6len:
			nft_ipv6 = append(nft_ipv6, elem)
		}
	}

	// perform nftables assignment
	if len(nft_ipv4) > 0 {
		nftDoWithMap(cfgNftTable, cfgNftTableFamily, cfgNftMapV4, func(c *nft.Conn, t *nft.Table, m *nft.Set) error {
			_ = c.SetDeleteElements(m, nft_ipv4)
			return nil
		})
		nftDoWithMap(cfgNftTable, cfgNftTableFamily, cfgNftMapV4, func(c *nft.Conn, t *nft.Table, m *nft.Set) error {
			return c.SetAddElements(m, nft_ipv4)
		})
	}
	if len(nft_ipv6) > 0 {
		nftDoWithMap(cfgNftTable, cfgNftTableFamily, cfgNftMapV6, func(c *nft.Conn, t *nft.Table, m *nft.Set) error {
			_ = c.SetDeleteElements(m, nft_ipv6)
			return nil
		})
		nftDoWithMap(cfgNftTable, cfgNftTableFamily, cfgNftMapV6, func(c *nft.Conn, t *nft.Table, m *nft.Set) error {
			return c.SetAddElements(m, nft_ipv6)
		})
	}

	for _, i := range interim {
		t, ok := dns.TypeToString[i.Qtype]
		if !ok {
			continue
		}

		r := PowerDnsAnswer{
			Qname:   i.Qname,
			Qtype:   t,
			Ttl:     i.Ttl,
			Content: i.Addr.String(),
		}
		result = append(result, r)
	}

	return result, nil
}