initial commit

addr-map.go

@@ -0,0 +1,143 @@
+package main
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+	"log"
+	"math"
+	"net"
+	"sync"
+	"time"
+)
+
+const (
+	addrMapHouseKeepInterval = time.Second / 4
+)
+
+var (
+	addr4, addr6 sync.Map
+)
+
+type AddrMap struct {
+	SrcAddr net.IP    `json:"src"`
+	DstAddr net.IP    `json:"dst"`
+	Ttl     uint32    `json:"ttl"`
+	Created time.Time `json:"created"`
+}
+
+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, uint32) {
+	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("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 hkey any
+	switch addrlen {
+	case net.IPv4len:
+		hkey = binary.NativeEndian.Uint32(srcIp)
+	case net.IPv6len:
+		hkey = srcIp.To16().String()
+	}
+
+	var curr AddrMap
+	curr.SrcAddr = make([]byte, addrlen)
+	curr.DstAddr = make([]byte, addrlen)
+	copy(curr.DstAddr, srcIp)
+	curr.Ttl = ttl
+
+	_, err := rand.Read(curr.SrcAddr)
+	if err != nil {
+		log.Fatalf("rand.Read(): error %v", err)
+	}
+
+	// adjust random bytes to dstCidr
+	for i := range addrlen / 4 {
+		a := binary.NativeEndian.Uint32(dstCidr.IP[i*4:])
+		b := binary.NativeEndian.Uint32(curr.SrcAddr[i*4:])
+		m := binary.NativeEndian.Uint32(dstCidr.Mask[i*4:])
+		a += (b & ^m)
+		binary.NativeEndian.PutUint32(curr.SrcAddr[i*4:], a)
+	}
+
+	curr.Created = time.Now()
+
+	var xprev any
+	var loaded bool
+	switch addrlen {
+	case net.IPv4len:
+		xprev, loaded = addr4.LoadOrStore(hkey, curr)
+	case net.IPv6len:
+		xprev, loaded = addr6.LoadOrStore(hkey, curr)
+	}
+	if !loaded {
+		// early return
+		return curr.SrcAddr, curr.Ttl
+	}
+
+	prev, ok := xprev.(AddrMap)
+	if !ok {
+		log.Fatalf("addrMapGet(): wrong value type from sync.Map")
+	}
+
+	copy(curr.SrcAddr, prev.SrcAddr)
+	if prev.GetTtl() < int32(curr.Ttl) {
+		switch addrlen {
+		case net.IPv4len:
+			addr4.Store(hkey, curr)
+		case net.IPv6len:
+			addr6.Store(hkey, curr)
+		}
+	} else {
+		curr.Ttl = uint32(prev.GetTtl())
+	}
+
+	return curr.SrcAddr, curr.Ttl
+}