lower time limit for upstream resolver

addr-map.go

@@ -1,43 +1,148 @@
 package main
 
 import (
+	"crypto/rand"
 	"encoding/binary"
 	"log"
+	"math"
 	"net"
+	"sync"
+	"time"
 
 	"github.com/cespare/xxhash/v2"
 )
 
-// TODO: write more convenient version
-func addrMap(srcIp net.IP, dstCidr *net.IPNet) net.IP {
+const (
+	addrMapHouseKeepInterval = time.Second / 2
+)
+
+var (
+	addr4, addr6 sync.Map
+)
+
+type AddrMap struct {
+	SrcAddr net.IP
+	DstAddr net.IP
+	Ttl     uint32
+	Created time.Time
+}
+
+func (a *AddrMap) GetTtl() int32 {
+	x := math.Trunc(time.Since(a.Created).Round(addrMapHouseKeepInterval).Seconds())
+	return int32(a.Ttl) - int32(x)
+}
+
+func setupAddrMapHousekeeping() {
+	go func() {
+		for {
+			time.Sleep(addrMapHouseKeepInterval)
+			addr4.Range(func(key, value any) bool {
+				a, ok := value.(AddrMap)
+				if ok {
+					if a.GetTtl() > 1 {
+						return true
+					}
+				}
+				// delete if value is bogus or if ttl is less than second
+				addr4.Delete(key)
+				return true
+			})
+		}
+	}()
+	go func() {
+		for {
+			time.Sleep(addrMapHouseKeepInterval)
+			addr6.Range(func(key, value any) bool {
+				a, ok := value.(AddrMap)
+				if ok {
+					if a.GetTtl() > 1 {
+						return true
+					}
+				}
+				// delete if value is bogus or if ttl is less than second
+				addr6.Delete(key)
+				return true
+			})
+		}
+	}()
+}
+
+func addrMapGet(srcIp net.IP, dstCidr *net.IPNet, ttl uint32) net.IP {
 	addrlen := len(srcIp)
+	switch addrlen {
+	case net.IPv4len, net.IPv6len:
+	default:
+		log.Fatalf("addrMapGet(): src size mismatch: %v", addrlen)
+	}
 	if addrlen != len(dstCidr.IP) {
-		log.Fatalf("addrMap(): src/dst size mismatch: %v vs %v", len(srcIp), len(dstCidr.IP))
+		log.Fatalf("addrMapGet(): src/dst size mismatch: %v vs %v", addrlen, len(dstCidr.IP))
+	}
+	if addrlen != len(dstCidr.Mask) {
+		log.Fatalf("addrMapGet(): src/dst size mismatch: %v vs %v", addrlen, len(dstCidr.IP))
 	}
 
-	var addr net.IP = make([]byte, addrlen)
+	var curr AddrMap
+	curr.SrcAddr = make([]byte, addrlen)
+	curr.DstAddr = make([]byte, addrlen)
+	copy(curr.DstAddr, srcIp)
+	curr.Ttl = ttl
 
-	hsum := xxhash.Sum64(srcIp)
-	bsum := binary.NativeEndian.AppendUint64([]byte{}, hsum)
-	blen := len(bsum)
-	if addrlen > blen {
-		// extend bsum
-		tmp := append(make([]byte, addrlen-blen), bsum...)
-		bsum = tmp
-	}
-	if addrlen < blen {
-		// trim bsum
-		bsum = bsum[:addrlen]
+	for {
+		_, err := rand.Read(curr.SrcAddr)
+		if err != nil {
+			log.Fatalf("rand.Read(): error %v", err)
 		}
 
-	// apply inverted mask to bsum and sum with addr
+		// adjust random bytes to dstCidr
 		for i := range addrlen / 4 {
 			a := binary.NativeEndian.Uint32(dstCidr.IP[i*4:])
-		b := binary.NativeEndian.Uint32(bsum[i*4:])
+			b := binary.NativeEndian.Uint32(curr.SrcAddr[i*4:])
 			m := binary.NativeEndian.Uint32(dstCidr.Mask[i*4:])
 			a += (b & ^m)
-		binary.NativeEndian.PutUint32(addr[i*4:], a)
+			binary.NativeEndian.PutUint32(curr.SrcAddr[i*4:], a)
+		}
+		hsum := xxhash.Sum64(curr.SrcAddr)
+
+		curr.Created = time.Now()
+
+		var xprev any
+		var loaded bool
+		switch addrlen {
+		case net.IPv4len:
+			xprev, loaded = addr4.LoadOrStore(hsum, curr)
+		case net.IPv6len:
+			xprev, loaded = addr6.LoadOrStore(hsum, curr)
+		}
+		if !loaded {
+			// early return
+			return curr.SrcAddr
 		}
 
-	return addr
+		prev, ok := xprev.(AddrMap)
+		if !ok {
+			log.Fatalf("addrMapGet(): wrong value type from sync.Map")
+		}
+
+		if !net.IP.Equal(curr.SrcAddr, prev.SrcAddr) {
+			// generate next random address
+			continue
+		}
+		if !net.IP.Equal(curr.DstAddr, prev.DstAddr) {
+			// generate next random address
+			continue
+		}
+
+		if prev.GetTtl() < int32(curr.Ttl) {
+			switch addrlen {
+			case net.IPv4len:
+				addr4.Store(hsum, curr)
+			case net.IPv6len:
+				addr6.Store(hsum, curr)
+			}
+		}
+
+		break
+	}
+
+	return curr.SrcAddr
 }

cfg.go

@@ -14,14 +14,14 @@ const (
 
 	cfgResolverEndpoint = "127.1.0.1:53"
 	cfgResolverProto    = "tcp"
-	cfgResolverTimeout  = 2500 * time.Millisecond
+	cfgResolverTimeout  = 2000 * time.Millisecond
 
 	cfgNftTable       = "uni"
 	cfgNftTableFamily = nft.TableFamilyINet
 	cfgNftMapV4       = "tele4"
 	cfgNftMapV6       = "tele6"
-	cfgNftCidrV4      = "251.0.0.0/8"
-	cfgNftCidrV6      = "2001:db8:11::/48"
+	cfgNftCidrV4      = "198.18.0.0/15"
+	cfgNftCidrV6      = "2001:db8:11::/80"
 
 	cfgSoaNs   = "gw.vpn."
 	cfgSoaMbox = "dns.gw.vpn."

dns-remap.go

@@ -140,18 +140,19 @@ func dnsRemap(qname string, qtype uint16, orig *dns.Msg) ([]PowerDnsAnswer, erro
 			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 = addrMap(r.Addr, nftCidrV4)
+			dstAddr = addrMapGet(r.Addr, nftCidrV4, r.Ttl)
 		case net.IPv6len:
-			dstAddr = addrMap(r.Addr, nftCidrV6)
+			dstAddr = addrMapGet(r.Addr, nftCidrV6, r.Ttl)
 		}
 
-		// HACK: clip ttl
-		r.Ttl = dnsClipTtl(r.Ttl)
 		// HACK: replace addr
 		copy(r.Addr, dstAddr)
 

example-conf/nftables.conf

@@ -1,7 +1,7 @@
 #!/usr/sbin/nft -f
 
-define n_tele4 = 251.0.0.0/8
-define n_tele6 = 2001:db8:11::/48
+define n_tele4 = 198.18.0.0/15
+define n_tele6 = 2001:db8:11::/80
 
 table inet uni {
 

go.mod

@@ -40,13 +40,13 @@ require (
 	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
 	github.com/ugorji/go/codec v1.2.12 // indirect
 	golang.org/x/arch v0.8.0 // indirect
-	golang.org/x/crypto v0.23.0 // indirect
-	golang.org/x/mod v0.17.0 // indirect
-	golang.org/x/net v0.25.0 // indirect
+	golang.org/x/crypto v0.24.0 // indirect
+	golang.org/x/mod v0.18.0 // indirect
+	golang.org/x/net v0.26.0 // indirect
 	golang.org/x/sync v0.7.0 // indirect
-	golang.org/x/sys v0.20.0 // indirect
-	golang.org/x/text v0.15.0 // indirect
-	golang.org/x/tools v0.21.0 // indirect
+	golang.org/x/sys v0.21.0 // indirect
+	golang.org/x/text v0.16.0 // indirect
+	golang.org/x/tools v0.22.0 // indirect
 	google.golang.org/protobuf v1.34.1 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -97,22 +97,22 @@ github.com/vishvananda/netns v0.0.0-20180720170159-13995c7128cc/go.mod h1:ZjcWmF
 golang.org/x/arch v0.0.0-20210923205945-b76863e36670/go.mod h1:5om86z9Hs0C8fWVUuoMHwpExlXzs5Tkyp9hOrfG7pp8=
 golang.org/x/arch v0.8.0 h1:3wRIsP3pM4yUptoR96otTUOXI367OS0+c9eeRi9doIc=
 golang.org/x/arch v0.8.0/go.mod h1:FEVrYAQjsQXMVJ1nsMoVVXPZg6p2JE2mx8psSWTDQys=
-golang.org/x/crypto v0.23.0 h1:dIJU/v2J8Mdglj/8rJ6UUOM3Zc9zLZxVZwwxMooUSAI=
-golang.org/x/crypto v0.23.0/go.mod h1:CKFgDieR+mRhux2Lsu27y0fO304Db0wZe70UKqHu0v8=
-golang.org/x/mod v0.17.0 h1:zY54UmvipHiNd+pm+m0x9KhZ9hl1/7QNMyxXbc6ICqA=
-golang.org/x/mod v0.17.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
-golang.org/x/net v0.25.0 h1:d/OCCoBEUq33pjydKrGQhw7IlUPI2Oylr+8qLx49kac=
-golang.org/x/net v0.25.0/go.mod h1:JkAGAh7GEvH74S6FOH42FLoXpXbE/aqXSrIQjXgsiwM=
+golang.org/x/crypto v0.24.0 h1:mnl8DM0o513X8fdIkmyFE/5hTYxbwYOjDS/+rK6qpRI=
+golang.org/x/crypto v0.24.0/go.mod h1:Z1PMYSOR5nyMcyAVAIQSKCDwalqy85Aqn1x3Ws4L5DM=
+golang.org/x/mod v0.18.0 h1:5+9lSbEzPSdWkH32vYPBwEpX8KwDbM52Ud9xBUvNlb0=
+golang.org/x/mod v0.18.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
+golang.org/x/net v0.26.0 h1:soB7SVo0PWrY4vPW/+ay0jKDNScG2X9wFeYlXIvJsOQ=
+golang.org/x/net v0.26.0/go.mod h1:5YKkiSynbBIh3p6iOc/vibscux0x38BZDkn8sCUPxHE=
 golang.org/x/sync v0.7.0 h1:YsImfSBoP9QPYL0xyKJPq0gcaJdG3rInoqxTWbfQu9M=
 golang.org/x/sync v0.7.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
 golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.20.0 h1:Od9JTbYCk261bKm4M/mw7AklTlFYIa0bIp9BgSm1S8Y=
-golang.org/x/sys v0.20.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
-golang.org/x/text v0.15.0 h1:h1V/4gjBv8v9cjcR6+AR5+/cIYK5N/WAgiv4xlsEtAk=
-golang.org/x/text v0.15.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
-golang.org/x/tools v0.21.0 h1:qc0xYgIbsSDt9EyWz05J5wfa7LOVW0YTLOXrqdLAWIw=
-golang.org/x/tools v0.21.0/go.mod h1:aiJjzUbINMkxbQROHiO6hDPo2LHcIPhhQsa9DLh0yGk=
+golang.org/x/sys v0.21.0 h1:rF+pYz3DAGSQAxAu1CbC7catZg4ebC4UIeIhKxBZvws=
+golang.org/x/sys v0.21.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/text v0.16.0 h1:a94ExnEXNtEwYLGJSIUxnWoxoRz/ZcCsV63ROupILh4=
+golang.org/x/text v0.16.0/go.mod h1:GhwF1Be+LQoKShO3cGOHzqOgRrGaYc9AvblQOmPVHnI=
+golang.org/x/tools v0.22.0 h1:gqSGLZqv+AI9lIQzniJ0nZDRG5GBPsSi+DRNHWNz6yA=
+golang.org/x/tools v0.22.0/go.mod h1:aCwcsjqvq7Yqt6TNyX7QMU2enbQ/Gt0bo6krSeEri+c=
 google.golang.org/protobuf v1.34.1 h1:9ddQBjfCyZPOHPUiPxpYESBLc+T8P3E+Vo4IbKZgFWg=
 google.golang.org/protobuf v1.34.1/go.mod h1:c6P6GXX6sHbq/GpV6MGZEdwhWPcYBgnhAHhKbcUYpos=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=

main.go

@@ -25,6 +25,7 @@ func main() {
 
 	setupNftables()
 	r := setupGin()
+	setupAddrMapHousekeeping()
 	log.Printf("%s: ready\n", userAgent)
 
 	if err := r.Run(cfgListen); err != nil {