142 lines
2.8 KiB
Go
142 lines
2.8 KiB
Go
package main
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import (
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"crypto/rand"
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"encoding/binary"
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"log"
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"math"
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"net"
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"sync"
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"time"
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)
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const (
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addrMapHouseKeepInterval = time.Second / 2
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)
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var (
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addr4, addr6 sync.Map
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)
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type AddrMap struct {
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SrcAddr net.IP
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DstAddr net.IP
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Ttl uint32
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Created time.Time
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}
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func (a *AddrMap) GetTtl() int32 {
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x := math.Trunc(time.Since(a.Created).Round(addrMapHouseKeepInterval).Seconds())
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return int32(a.Ttl) - int32(x)
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}
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func setupAddrMapHousekeeping() {
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go func() {
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for {
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time.Sleep(addrMapHouseKeepInterval)
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addr4.Range(func(key, value any) bool {
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a, ok := value.(AddrMap)
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if ok {
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if a.GetTtl() > 1 {
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return true
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}
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}
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// delete if value is bogus or if ttl is less than second
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addr4.Delete(key)
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return true
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})
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}
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}()
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go func() {
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for {
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time.Sleep(addrMapHouseKeepInterval)
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addr6.Range(func(key, value any) bool {
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a, ok := value.(AddrMap)
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if ok {
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if a.GetTtl() > 1 {
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return true
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}
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}
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// delete if value is bogus or if ttl is less than second
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addr6.Delete(key)
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return true
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})
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}
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}()
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}
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func addrMapGet(srcIp net.IP, dstCidr *net.IPNet, ttl uint32) net.IP {
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addrlen := len(srcIp)
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switch addrlen {
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case net.IPv4len, net.IPv6len:
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default:
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log.Fatalf("addrMapGet(): src size mismatch: %v", addrlen)
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}
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if addrlen != len(dstCidr.IP) {
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log.Fatalf("addrMapGet(): src/dst size mismatch: %v vs %v", addrlen, len(dstCidr.IP))
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}
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if addrlen != len(dstCidr.Mask) {
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log.Fatalf("addrMapGet(): src/dst size mismatch: %v vs %v", addrlen, len(dstCidr.IP))
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}
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var hkey any
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switch addrlen {
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case net.IPv4len:
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hkey = binary.NativeEndian.Uint32(srcIp)
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case net.IPv6len:
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hkey = srcIp.To16().String()
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}
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var curr AddrMap
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curr.SrcAddr = make([]byte, addrlen)
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curr.DstAddr = make([]byte, addrlen)
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copy(curr.DstAddr, srcIp)
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curr.Ttl = ttl
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_, err := rand.Read(curr.SrcAddr)
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if err != nil {
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log.Fatalf("rand.Read(): error %v", err)
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}
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// adjust random bytes to dstCidr
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for i := range addrlen / 4 {
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a := binary.NativeEndian.Uint32(dstCidr.IP[i*4:])
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b := binary.NativeEndian.Uint32(curr.SrcAddr[i*4:])
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m := binary.NativeEndian.Uint32(dstCidr.Mask[i*4:])
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a += (b & ^m)
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binary.NativeEndian.PutUint32(curr.SrcAddr[i*4:], a)
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}
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curr.Created = time.Now()
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var xprev any
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var loaded bool
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switch addrlen {
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case net.IPv4len:
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xprev, loaded = addr4.LoadOrStore(hkey, curr)
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case net.IPv6len:
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xprev, loaded = addr6.LoadOrStore(hkey, curr)
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}
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if !loaded {
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// early return
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return curr.SrcAddr
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}
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prev, ok := xprev.(AddrMap)
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if !ok {
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log.Fatalf("addrMapGet(): wrong value type from sync.Map")
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}
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copy(curr.SrcAddr, prev.SrcAddr)
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if prev.GetTtl() < int32(curr.Ttl) {
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switch addrlen {
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case net.IPv4len:
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addr4.Store(hkey, curr)
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case net.IPv6len:
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addr6.Store(hkey, curr)
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}
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}
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return curr.SrcAddr
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}
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