system stack: self-heal the TCP forwarder accept loop (sing-box-lx SPEC 040)

Upstream acceptLoop treats any Accept error as terminal and silently
returns, leaving the stack alive but every new TCP SYN NAT-rewritten onto
a dead port (instant RST) until a full restart. When the listener fd is
closed out from under the stack (a stray close on a reused fd number from
another runtime in the same process), all new TCP dies forever while
UDP/QUIC/DNS keep working.

- System.Close() now marks a deliberate shutdown first; acceptLoop still
  exits quietly on it.
- Any other Accept error is logged (the errno names the killer path),
  the listener is recreated on the same address, the forwarder port is
  republished atomically, and the loop keeps serving.
- If the rebind fails, the loop logs an error and gives up - no worse
  than upstream.
- acceptRecoveries counter is kept as telemetry.

tcpPort/tcpPort6 become atomic (written by the heal path, read from the
tunLoop dispatch/NAT path); listener replacement is serialized against
Close() with a mutex.

flow.go

@@ -21,6 +21,7 @@ const (
 	ActionReject
 	ActionDrop
 	ActionBypass
+	ActionHijackDNS
 )
 
 type FlowTracker interface {

flow_dispatch.go

@@ -3,6 +3,7 @@ package tun
 import (
 	"maps"
 	"net/netip"
+	"sync"
 	"sync/atomic"
 	"time"
 
@@ -113,12 +114,14 @@ type ForwardDispatcher struct {
 	logger      logger.Logger
 	udpTimeout  time.Duration
 	icmpTimeout time.Duration
+	access      sync.RWMutex
 
-	table     map[flowKey]*flowEntry
+	table        map[flowKey]*flowEntry
-	lastSweep int64
+	lastSweep    int64
-	ports     map[Port]*portNAT
+	resetPending atomic.Bool
-	natList   atomic.Pointer[[]*portNAT]
+	ports        map[Port]*portNAT
-	revNAT    atomic.Pointer[map[netip.Addr]*portNAT]
+	natList      atomic.Pointer[[]*portNAT]
+	revNAT       atomic.Pointer[map[netip.Addr]*portNAT]
 
 	activeNATs     []*portNAT
 	writebackBatch [][]byte
@@ -167,26 +170,41 @@ func (d *ForwardDispatcher) Close() {
 		return
 	}
 	d.returnPath.closed.Store(true)
+	d.access.Lock()
+	flows := make([]*forwardFlow, 0, len(d.table))
 	for _, entry := range d.table {
 		if entry.flow != nil {
-			entry.flow.close(FlowCloseReset)
+			flows = append(flows, entry.flow)
 		}
 	}
+	ports := make([]Port, 0, len(d.ports))
 	for port, nat := range d.ports {
 		if nat != nil {
-			port.DetachReturn(&d.returnPath)
+			ports = append(ports, port)
 		}
 	}
+	d.access.Unlock()
+	for _, flow := range flows {
+		flow.close(FlowCloseReset)
+	}
+	for _, port := range ports {
+		port.DetachReturn(&d.returnPath)
+	}
 }
 
 func (d *ForwardDispatcher) Dispatch(packet []byte) bool {
-	if d == nil {
+	if d == nil || d.returnPath.closed.Load() {
 		return false
 	}
 	parsed, ok := parseForwardPacket(packet)
 	if !ok || parsed.fragment || !parsed.hasFlow {
 		return false
 	}
+	d.access.RLock()
+	if d.returnPath.closed.Load() {
+		d.access.RUnlock()
+		return false
+	}
 	key := parsed.flowKey()
 	now := d.now()
 	entry, loaded := d.table[key]
@@ -195,13 +213,16 @@ func (d *ForwardDispatcher) Dispatch(packet []byte) bool {
 		loaded = false
 	}
 	if loaded {
-		return d.handleHit(key, entry, &parsed, packet, now)
+		handled := d.handleHit(key, entry, &parsed, packet, now)
+		d.access.RUnlock()
+		return handled
 	}
+	d.access.RUnlock()
 	if parsed.protocol == uint8(header.TCPProtocolNumber) &&
 		(parsed.tcpFlags&header.TCPFlagSyn == 0 || parsed.tcpFlags&header.TCPFlagAck != 0) {
 		return false
 	}
-	return d.judgeAndInstall(key, &parsed, packet, now)
+	return d.judgeAndInstall(key, &parsed, packet)
 }
 
 func (d *ForwardDispatcher) handleHit(key flowKey, entry *flowEntry, packet *forwardPacket, raw []byte, now int64) bool {
@@ -255,12 +276,18 @@ func (d *ForwardDispatcher) handleHit(key flowKey, entry *flowEntry, packet *for
 	}
 }
 
-func (d *ForwardDispatcher) judgeAndInstall(key flowKey, packet *forwardPacket, raw []byte, now int64) bool {
+func (d *ForwardDispatcher) judgeAndInstall(key flowKey, packet *forwardPacket, raw []byte) bool {
 	var firstPacket []byte
 	if packet.protocol == uint8(header.UDPProtocolNumber) {
 		firstPacket = header.UDP(packet.transport).Payload()
 	}
 	verdict := d.handler.JudgeFlow(packet.protocol, packet.source, packet.destination, firstPacket)
+	d.access.RLock()
+	defer d.access.RUnlock()
+	if d.returnPath.closed.Load() {
+		return false
+	}
+	now := d.now()
 	switch verdict.Action {
 	case ActionFlow:
 		if verdict.Port != nil {
@@ -291,6 +318,13 @@ func (d *ForwardDispatcher) judgeAndInstall(key flowKey, packet *forwardPacket,
 	case ActionDrop:
 		d.installSimple(key, ActionDrop, packet.protocol, now)
 		return true
+	case ActionHijackDNS:
+		if packet.protocol == uint8(header.UDPProtocolNumber) {
+			d.hijackDNSPacket(packet)
+			return true
+		}
+		d.installSimple(key, ActionAccept, packet.protocol, now)
+		return false
 	default:
 		d.installSimple(key, ActionAccept, packet.protocol, now)
 		return false
@@ -537,10 +571,27 @@ func (d *ForwardDispatcher) stageReject(packet *forwardPacket) {
 	}
 }
 
-func (d *ForwardDispatcher) Flush() {
+func (d *ForwardDispatcher) ResetNetwork() {
 	if d == nil {
 		return
 	}
+	d.resetPending.Store(true)
+}
+
+func (d *ForwardDispatcher) Flush() {
+	if d == nil || d.returnPath.closed.Load() {
+		return
+	}
+	d.access.RLock()
+	defer d.access.RUnlock()
+	if d.returnPath.closed.Load() {
+		return
+	}
+	if d.resetPending.Swap(false) {
+		for key, entry := range d.table {
+			d.removeEntry(key, entry, FlowCloseReset)
+		}
+	}
 	for _, nat := range d.activeNATs {
 		d.flushPort(nat)
 	}

flow_dns.go

@@ -0,0 +1,89 @@
+package tun
+
+import (
+	"net/netip"
+
+	"github.com/sagernet/sing-tun/gtcpip/checksum"
+	"github.com/sagernet/sing-tun/gtcpip/header"
+	"github.com/sagernet/sing/common/buf"
+	E "github.com/sagernet/sing/common/exceptions"
+	M "github.com/sagernet/sing/common/metadata"
+	N "github.com/sagernet/sing/common/network"
+)
+
+func (d *ForwardDispatcher) hijackDNSPacket(packet *forwardPacket) {
+	writer := &dnsResponseWriter{
+		writeback: d.writeback,
+		source:    packet.source,
+	}
+	d.handler.NewDNSPacket(header.UDP(packet.transport).Payload(), M.SocksaddrFromNetIP(packet.source), M.SocksaddrFromNetIP(packet.destination), writer)
+}
+
+var _ N.PacketWriter = (*dnsResponseWriter)(nil)
+
+type dnsResponseWriter struct {
+	writeback ForwardWriteback
+	source    netip.AddrPort
+}
+
+func (w *dnsResponseWriter) WritePacket(buffer *buf.Buffer, destination M.Socksaddr) error {
+	defer buffer.Release()
+	if !destination.IsIP() {
+		return E.New("invalid destination: ", destination)
+	}
+	sourceAddr := w.source.Addr().Unmap()
+	destinationAddr := destination.Addr.Unmap()
+	headroom := w.writeback.ReturnHeadroom()
+	udpLen := header.UDPMinimumSize + buffer.Len()
+	var (
+		packet []byte
+		udpHdr header.UDP
+		ipHdr  header.Network
+	)
+	if sourceAddr.Is4() {
+		if !destinationAddr.Is4() {
+			return E.New("send IPv6 packet to IPv4 connection")
+		}
+		size := header.IPv4MinimumSize + udpLen
+		packet = make([]byte, headroom+size)
+		inet4Hdr := header.IPv4(packet[headroom:])
+		inet4Hdr.Encode(&header.IPv4Fields{
+			TotalLength: uint16(size),
+			TTL:         synthesizedTTL,
+			Protocol:    uint8(header.UDPProtocolNumber),
+			SrcAddr:     destinationAddr,
+			DstAddr:     sourceAddr,
+		})
+		udpHdr = header.UDP(inet4Hdr.Payload())
+		ipHdr = inet4Hdr
+	} else {
+		if destinationAddr.Is4() {
+			destinationAddr = netip.AddrFrom16(destinationAddr.As16())
+		}
+		size := header.IPv6MinimumSize + udpLen
+		packet = make([]byte, headroom+size)
+		inet6Hdr := header.IPv6(packet[headroom:])
+		inet6Hdr.Encode(&header.IPv6Fields{
+			PayloadLength:     uint16(udpLen),
+			TransportProtocol: header.UDPProtocolNumber,
+			HopLimit:          synthesizedTTL,
+			SrcAddr:           destinationAddr,
+			DstAddr:           sourceAddr,
+		})
+		udpHdr = header.UDP(inet6Hdr.Payload())
+		ipHdr = inet6Hdr
+	}
+	udpHdr.Encode(&header.UDPFields{
+		SrcPort: destination.Port,
+		DstPort: w.source.Port(),
+		Length:  uint16(udpLen),
+	})
+	copy(udpHdr.Payload(), buffer.Bytes())
+	udpHdr.SetChecksum(^checksum.Checksum(udpHdr.Payload(), udpHdr.CalculateChecksum(
+		header.PseudoHeaderChecksum(header.UDPProtocolNumber, ipHdr.SourceAddressSlice(), ipHdr.DestinationAddressSlice(), uint16(udpLen)),
+	)))
+	if inet4Hdr, isInet4 := ipHdr.(header.IPv4); isInet4 {
+		inet4Hdr.SetChecksum(^inet4Hdr.CalculateChecksum())
+	}
+	return w.writeback.WriteReturnPackets([][]byte{packet})
+}

go.mod

@@ -1,32 +1,32 @@
 module github.com/sagernet/sing-tun
 
-go 1.24.7
+go 1.25.0
 
 require (
-	github.com/florianl/go-nfqueue/v2 v2.0.2
+	github.com/florianl/go-nfqueue/v2 v2.1.0
 	github.com/go-ole/go-ole v1.3.0
 	github.com/google/btree v1.1.3
-	github.com/mdlayher/netlink v1.9.0
+	github.com/mdlayher/netlink v1.11.2
-	github.com/sagernet/fswatch v0.1.1
+	github.com/sagernet/fswatch v0.1.2
-	github.com/sagernet/gvisor v0.0.0-20250811.0-sing-box-mod.1
+	github.com/sagernet/gvisor v0.0.0-20260727.0-sing-box-mod.1
 	github.com/sagernet/netlink v0.0.0-20240612041022-b9a21c07ac6a
-	github.com/sagernet/nftables v0.3.0-mod.2
+	github.com/sagernet/nftables v0.3.0-mod.4
-	github.com/sagernet/sing v0.8.0
+	github.com/sagernet/sing v0.8.12-0.20260717023913-84ab32b56cb8
 	github.com/stretchr/testify v1.11.1
 	go4.org/netipx v0.0.0-20231129151722-fdeea329fbba
-	golang.org/x/exp v0.0.0-20240613232115-7f521ea00fb8
+	golang.org/x/exp v0.0.0-20250711185948-6ae5c78190dc
-	golang.org/x/net v0.50.0
+	golang.org/x/net v0.57.0
-	golang.org/x/sys v0.41.0
+	golang.org/x/sys v0.47.0
 )
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
-	github.com/fsnotify/fsnotify v1.7.0 // indirect
+	github.com/fsnotify/fsnotify v1.9.0 // indirect
 	github.com/google/go-cmp v0.7.0 // indirect
-	github.com/mdlayher/socket v0.5.1 // indirect
+	github.com/mdlayher/socket v0.6.0 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/vishvananda/netns v0.0.4 // indirect
-	golang.org/x/sync v0.7.0 // indirect
+	golang.org/x/sync v0.20.0 // indirect
-	golang.org/x/time v0.7.0 // indirect
+	golang.org/x/time v0.15.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -1,48 +1,50 @@
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
-github.com/florianl/go-nfqueue/v2 v2.0.2 h1:FL5lQTeetgpCvac1TRwSfgaXUn0YSO7WzGvWNIp3JPE=
+github.com/florianl/go-nfqueue/v2 v2.1.0 h1:Fywt30TY/evxyDySpXjxQ1jsRW7nQbLpOhELqpr4068=
-github.com/florianl/go-nfqueue/v2 v2.0.2/go.mod h1:VA09+iPOT43OMoCKNfXHyzujQUty2xmzyCRkBOlmabc=
+github.com/florianl/go-nfqueue/v2 v2.1.0/go.mod h1:8PKUM5rYoVFO5IZV1bifx4/b0jHAglKkHXr9PRwzi4Y=
-github.com/fsnotify/fsnotify v1.7.0 h1:8JEhPFa5W2WU7YfeZzPNqzMP6Lwt7L2715Ggo0nosvA=
+github.com/fsnotify/fsnotify v1.9.0 h1:2Ml+OJNzbYCTzsxtv8vKSFD9PbJjmhYF14k/jKC7S9k=
-github.com/fsnotify/fsnotify v1.7.0/go.mod h1:40Bi/Hjc2AVfZrqy+aj+yEI+/bRxZnMJyTJwOpGvigM=
+github.com/fsnotify/fsnotify v1.9.0/go.mod h1:8jBTzvmWwFyi3Pb8djgCCO5IBqzKJ/Jwo8TRcHyHii0=
 github.com/go-ole/go-ole v1.3.0 h1:Dt6ye7+vXGIKZ7Xtk4s6/xVdGDQynvom7xCFEdWr6uE=
 github.com/go-ole/go-ole v1.3.0/go.mod h1:5LS6F96DhAwUc7C+1HLexzMXY1xGRSryjyPPKW6zv78=
 github.com/google/btree v1.1.3 h1:CVpQJjYgC4VbzxeGVHfvZrv1ctoYCAI8vbl07Fcxlyg=
 github.com/google/btree v1.1.3/go.mod h1:qOPhT0dTNdNzV6Z/lhRX0YXUafgPLFUh+gZMl761Gm4=
 github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
 github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
-github.com/mdlayher/netlink v1.9.0 h1:G8+GLq2x3v4D4MVIqDdNUhTUC7TKiCy/6MDkmItfKco=
+github.com/jsimonetti/rtnetlink/v2 v2.2.0 h1:/KfZ310gOAFrXXol5VwnFEt+ucldD/0dsSRZwpHCP9w=
-github.com/mdlayher/netlink v1.9.0/go.mod h1:YBnl5BXsCoRuwBjKKlZ+aYmEoq0r12FDA/3JC+94KDg=
+github.com/jsimonetti/rtnetlink/v2 v2.2.0/go.mod h1:lbjDHxC+5RJ08lzPeA90Ls2pEoId3F08MoEMlhfHxeI=
-github.com/mdlayher/socket v0.5.1 h1:VZaqt6RkGkt2OE9l3GcC6nZkqD3xKeQLyfleW/uBcos=
+github.com/mdlayher/netlink v1.11.2 h1:HKh2jqe+omdSWcQ88nrT7INE61B0NXfiSPFdgL4YbNI=
-github.com/mdlayher/socket v0.5.1/go.mod h1:TjPLHI1UgwEv5J1B5q0zTZq12A/6H7nKmtTanQE37IQ=
+github.com/mdlayher/netlink v1.11.2/go.mod h1:uT2Yc/QLaZubzDpZIBi9d4GoeLwtp3x1AMeqSRrK2sA=
+github.com/mdlayher/socket v0.6.0 h1:ScZPaAGyO1icQnbFrhPM8mnXyMu9qukC1K4ZoM2IQKU=
+github.com/mdlayher/socket v0.6.0/go.mod h1:q7vozUAnxSqnjHc12Fik5yUKIzfZ8ITCfMkhOtE9z18=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
-github.com/sagernet/fswatch v0.1.1 h1:YqID+93B7VRfqIH3PArW/XpJv5H4OLEVWDfProGoRQs=
+github.com/sagernet/fswatch v0.1.2 h1:/TT7k4mkce1qFPxamLO842WjqBgbTBiXP2mlUjp9PFk=
-github.com/sagernet/fswatch v0.1.1/go.mod h1:nz85laH0mkQqJfaOrqPpkwtU1znMFNVTpT/5oRsVz/o=
+github.com/sagernet/fswatch v0.1.2/go.mod h1:5BpGmpUQVd3Mc5r313HRpvADHRg3/rKn5QbwFteB880=
-github.com/sagernet/gvisor v0.0.0-20250811.0-sing-box-mod.1 h1:AzCE2RhBjLJ4WIWc/GejpNh+z30d5H1hwaB0nD9eY3o=
+github.com/sagernet/gvisor v0.0.0-20260727.0-sing-box-mod.1 h1:IdQ7yTKkB2wv8txwshxUroPlO4npOYAV71xb7xQ7Lys=
-github.com/sagernet/gvisor v0.0.0-20250811.0-sing-box-mod.1/go.mod h1:NJKBtm9nVEK3iyOYWsUlrDQuoGh4zJ4KOPhSYVidvQ4=
+github.com/sagernet/gvisor v0.0.0-20260727.0-sing-box-mod.1/go.mod h1:9O3SQskYuCfdHNvHEsWuEAgoyKEF74PiWp4NsNUia8g=
 github.com/sagernet/netlink v0.0.0-20240612041022-b9a21c07ac6a h1:ObwtHN2VpqE0ZNjr6sGeT00J8uU7JF4cNUdb44/Duis=
 github.com/sagernet/netlink v0.0.0-20240612041022-b9a21c07ac6a/go.mod h1:xLnfdiJbSp8rNqYEdIW/6eDO4mVoogml14Bh2hSiFpM=
-github.com/sagernet/nftables v0.3.0-mod.2 h1:ck2KMU02OxL1eDFgGaWYglMDpoOZ7OHzxje+vW5Q0OQ=
+github.com/sagernet/nftables v0.3.0-mod.4 h1:vnOtcDYeSXv2e5RoRuGH0lrpttQFJ8iC4ICS2nhlDSo=
-github.com/sagernet/nftables v0.3.0-mod.2/go.mod h1:8kslHG4VvYNihcco+i6uxIX7qbT8A56T0y5q7U44ZaQ=
+github.com/sagernet/nftables v0.3.0-mod.4/go.mod h1:8kslHG4VvYNihcco+i6uxIX7qbT8A56T0y5q7U44ZaQ=
-github.com/sagernet/sing v0.8.0 h1:OwLEwbcYfZHvu4olZVljxxC1XRicBqJ1HfiFr6F2WEE=
+github.com/sagernet/sing v0.8.12-0.20260717023913-84ab32b56cb8 h1:dyRIj+MZ2rc9JVzJoG04jxu+MpvHrLIZLJr0QjNAMGg=
-github.com/sagernet/sing v0.8.0/go.mod h1:ARkL0gM13/Iv5VCZmci/NuoOlePoIsW0m7BWfln/Hak=
+github.com/sagernet/sing v0.8.12-0.20260717023913-84ab32b56cb8/go.mod h1:olXxWQNqRW/l2Q6JI3b2Qmz8iQnIFlOeeH8bx6JhgUA=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
 github.com/vishvananda/netns v0.0.4 h1:Oeaw1EM2JMxD51g9uhtC0D7erkIjgmj8+JZc26m1YX8=
 github.com/vishvananda/netns v0.0.4/go.mod h1:SpkAiCQRtJ6TvvxPnOSyH3BMl6unz3xZlaprSwhNNJM=
 go4.org/netipx v0.0.0-20231129151722-fdeea329fbba h1:0b9z3AuHCjxk0x/opv64kcgZLBseWJUpBw5I82+2U4M=
 go4.org/netipx v0.0.0-20231129151722-fdeea329fbba/go.mod h1:PLyyIXexvUFg3Owu6p/WfdlivPbZJsZdgWZlrGope/Y=
-golang.org/x/exp v0.0.0-20240613232115-7f521ea00fb8 h1:yixxcjnhBmY0nkL253HFVIm0JsFHwrHdT3Yh6szTnfY=
+golang.org/x/exp v0.0.0-20250711185948-6ae5c78190dc h1:TS73t7x3KarrNd5qAipmspBDS1rkMcgVG/fS1aRb4Rc=
-golang.org/x/exp v0.0.0-20240613232115-7f521ea00fb8/go.mod h1:jj3sYF3dwk5D+ghuXyeI3r5MFf+NT2An6/9dOA95KSI=
+golang.org/x/exp v0.0.0-20250711185948-6ae5c78190dc/go.mod h1:A+z0yzpGtvnG90cToK5n2tu8UJVP2XUATh+r+sfOOOc=
-golang.org/x/net v0.50.0 h1:ucWh9eiCGyDR3vtzso0WMQinm2Dnt8cFMuQa9K33J60=
+golang.org/x/net v0.57.0 h1:K5+3DljvIuDG9/Jv9rvyMywYNFCQ9RSUY6OOTTkT+tE=
-golang.org/x/net v0.50.0/go.mod h1:UgoSli3F/pBgdJBHCTc+tp3gmrU4XswgGRgtnwWTfyM=
+golang.org/x/net v0.57.0/go.mod h1:KpXc8iv+r3XplLAG/f7Jsf9RPszJzdR0f58q9vGOuEU=
-golang.org/x/sync v0.7.0 h1:YsImfSBoP9QPYL0xyKJPq0gcaJdG3rInoqxTWbfQu9M=
+golang.org/x/sync v0.20.0 h1:e0PTpb7pjO8GAtTs2dQ6jYa5BWYlMuX047Dco/pItO4=
-golang.org/x/sync v0.7.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
+golang.org/x/sync v0.20.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
 golang.org/x/sys v0.1.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.41.0 h1:Ivj+2Cp/ylzLiEU89QhWblYnOE9zerudt9Ftecq2C6k=
+golang.org/x/sys v0.47.0 h1:o7XGOvZQCADBQQ4Y7VNq2dRWQR7JmOUW8Kxx4ZsNgWs=
-golang.org/x/sys v0.41.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
+golang.org/x/sys v0.47.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
-golang.org/x/time v0.7.0 h1:ntUhktv3OPE6TgYxXWv9vKvUSJyIFJlyohwbkEwPrKQ=
+golang.org/x/time v0.15.0 h1:bbrp8t3bGUeFOx08pvsMYRTCVSMk89u4tKbNOZbp88U=
-golang.org/x/time v0.7.0/go.mod h1:3BpzKBy/shNhVucY/MWOyx10tF3SFh9QdLuxbVysPQM=
+golang.org/x/time v0.15.0/go.mod h1:Y4YMaQmXwGQZoFaVFk4YpCt4FLQMYKZe9oeV/f4MSno=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

gtcpip/header/ipv4.go

@@ -22,7 +22,6 @@ import (
 
 	"github.com/sagernet/sing-tun/gtcpip"
 	"github.com/sagernet/sing-tun/gtcpip/checksum"
-	"github.com/sagernet/sing/common"
 )
 
 // RFC 971 defines the fields of the IPv4 header on page 11 using the following
@@ -335,7 +334,7 @@ func (b IPv4) FragmentOffset() uint16 {
 }
 
 func (b IPv4) FragmentOffsetDarwinRaw() uint16 {
-	return common.NativeEndian.Uint16(b[flagsFO:]) << 3
+	return binary.NativeEndian.Uint16(b[flagsFO:]) << 3
 }
 
 // TotalLength returns the "total length" field of the IPv4 header.
@@ -344,7 +343,7 @@ func (b IPv4) TotalLength() uint16 {
 }
 
 func (b IPv4) TotalLengthDarwinRaw() uint16 {
-	return common.NativeEndian.Uint16(b[IPv4TotalLenOffset:]) + uint16(b.HeaderLength())
+	return binary.NativeEndian.Uint16(b[IPv4TotalLenOffset:]) + uint16(b.HeaderLength())
 }
 
 // Checksum returns the checksum field of the IPv4 header.
@@ -441,7 +440,7 @@ func (b IPv4) SetTotalLength(totalLength uint16) {
 }
 
 func (b IPv4) SetTotalLengthDarwinRaw(totalLength uint16) {
-	common.NativeEndian.PutUint16(b[IPv4TotalLenOffset:], totalLength)
+	binary.NativeEndian.PutUint16(b[IPv4TotalLenOffset:], totalLength)
 }
 
 // SetChecksum sets the checksum field of the IPv4 header.
@@ -458,7 +457,7 @@ func (b IPv4) SetFlagsFragmentOffset(flags uint8, offset uint16) {
 
 func (b IPv4) SetFlagsFragmentOffsetDarwinRaw(flags uint8, offset uint16) {
 	v := (uint16(flags) << 13) | (offset >> 3)
-	common.NativeEndian.PutUint16(b[flagsFO:], v)
+	binary.NativeEndian.PutUint16(b[flagsFO:], v)
 }
 
 // SetID sets the identification field.
@@ -1179,7 +1178,7 @@ func (s IPv4OptionsSerializer) Serialize(b []byte) uint8 {
 	//  header ends on a 32 bit boundary. The padding is zero.
 	padded := padIPv4OptionsLength(total)
 	b = b[:padded-total]
-	common.ClearArray(b)
+	clear(b)
 	return padded
 }
 

gtcpip/header/ipv6_extension_headers.go

@@ -21,7 +21,6 @@ import (
 	"math"
 
 	"github.com/sagernet/sing-tun/gtcpip"
-	"github.com/sagernet/sing/common"
 )
 
 // IPv6ExtensionHeaderIdentifier is an IPv6 extension header identifier.
@@ -129,7 +128,7 @@ func padIPv6Option(b []byte) {
 		b[ipv6ExtHdrOptionTypeOffset] = uint8(ipv6Pad1ExtHdrOptionIdentifier)
 	default: // Pad with PadN.
 		s := b[ipv6ExtHdrOptionPayloadOffset:]
-		common.ClearArray(s)
+		clear(s)
 		b[ipv6ExtHdrOptionTypeOffset] = uint8(ipv6PadNExtHdrOptionIdentifier)
 		b[ipv6ExtHdrOptionLengthOffset] = uint8(len(s))
 	}

gtcpip/header/ndp_options.go

@@ -24,7 +24,6 @@ import (
 	"time"
 
 	"github.com/sagernet/sing-tun/gtcpip"
-	"github.com/sagernet/sing/common"
 )
 
 // ndpOptionIdentifier is an NDP option type identifier.
@@ -341,7 +340,7 @@ func (b NDPOptions) Serialize(s NDPOptionsSerializer) int {
 
 		// Zero out remaining (padding) bytes, if any exists.
 		if used+2 < l {
-			common.ClearArray(b[used+2 : l])
+			clear(b[used+2 : l])
 		}
 
 		b = b[l:]
@@ -567,7 +566,7 @@ func (o NDPPrefixInformation) serializeInto(b []byte) int {
 
 	// Zero out the Reserved2 field.
 	reserved2 := b[ndpPrefixInformationReserved2Offset:][:ndpPrefixInformationReserved2Length]
-	common.ClearArray(reserved2)
+	clear(reserved2)
 
 	return used
 }
@@ -686,7 +685,7 @@ func (o NDPRecursiveDNSServer) serializeInto(b []byte) int {
 	used := copy(b, o)
 
 	// Zero out the reserved bytes that are before the Lifetime field.
-	common.ClearArray(b[0:ndpRecursiveDNSServerLifetimeOffset])
+	clear(b[0:ndpRecursiveDNSServerLifetimeOffset])
 
 	return used
 }
@@ -779,7 +778,7 @@ func (o NDPDNSSearchList) serializeInto(b []byte) int {
 	used := copy(b, o)
 
 	// Zero out the reserved bytes that are before the Lifetime field.
-	common.ClearArray(b[0:ndpDNSSearchListLifetimeOffset])
+	clear(b[0:ndpDNSSearchListLifetimeOffset])
 
 	return used
 }

internal/fdbased_darwin/endpoint.go

@@ -50,7 +50,6 @@ import (
 	"github.com/sagernet/gvisor/pkg/tcpip/header"
 	"github.com/sagernet/gvisor/pkg/tcpip/stack"
 	rawfile "github.com/sagernet/sing-tun/internal/rawfile_darwin"
-	"github.com/sagernet/sing/common"
 
 	"golang.org/x/sys/unix"
 )
@@ -200,10 +199,6 @@ type Options struct {
 	// include CapabilitySaveRestore
 	SaveRestore bool
 
-	// DisconnectOk if true, indicates that this NIC capability set should
-	// include CapabilityDisconnectOk.
-	DisconnectOk bool
-
 	// PacketDispatchMode specifies the type of inbound dispatcher to be
 	// used for this endpoint.
 	PacketDispatchMode PacketDispatchMode
@@ -257,10 +252,6 @@ func New(opts *Options) (stack.LinkEndpoint, error) {
 		caps |= stack.CapabilitySaveRestore
 	}
 
-	if opts.DisconnectOk {
-		caps |= stack.CapabilityDisconnectOk
-	}
-
 	if len(opts.FDs) == 0 {
 		return nil, fmt.Errorf("opts.FD is empty, at least one FD must be specified")
 	}
@@ -301,7 +292,7 @@ func New(opts *Options) (stack.LinkEndpoint, error) {
 
 		e.fds = append(e.fds, fdInfo{fd: fd, isSocket: true})
 		if opts.ProcessorsPerChannel == 0 {
-			opts.ProcessorsPerChannel = common.Max(1, runtime.GOMAXPROCS(0)/len(opts.FDs))
+			opts.ProcessorsPerChannel = max(1, runtime.GOMAXPROCS(0)/len(opts.FDs))
 		}
 
 		inboundDispatcher, err := newRecvMMsgDispatcher(fd, e, opts)

internal/fdbased_darwin/processors.go

@@ -214,34 +214,47 @@ func tcpipConnectionID(pkt *stack.PacketBuffer) (connectionID, bool) {
 			return cid, true
 		}
 		ipHdr := header.IPv6(h)
+		cid.srcAddr = ipHdr.SourceAddressSlice()
+		cid.dstAddr = ipHdr.DestinationAddressSlice()
+		cid.proto = header.IPv6ProtocolNumber
 
-		var tcpHdr header.TCP
+		if !header.IsExtensionHeader(ipHdr.NextHeader()) {
-		if tcpip.TransportProtocolNumber(ipHdr.NextHeader()) == header.TCPProtocolNumber {
+			// Known transport protocols(not just TCP) store the src and dst ports
-			tcpHdr = header.TCP(h[header.IPv6FixedHeaderSize:][:tcpSrcDstPortLen])
+			// in the first 4 bytes after the IPv6 fixed header.
+			tcpHdr := header.TCP(h[header.IPv6FixedHeaderSize:][:tcpSrcDstPortLen])
+			cid.srcPort = tcpHdr.SourcePort()
+			cid.dstPort = tcpHdr.DestinationPort()
 		} else {
 			// Slow path for IPv6 extension headers :(.
 			dataBuf := pkt.Data().ToBuffer()
 			dataBuf.TrimFront(header.IPv6MinimumSize)
 			it := header.MakeIPv6PayloadIterator(header.IPv6ExtensionHeaderIdentifier(ipHdr.NextHeader()), dataBuf)
 			defer it.Release()
+			// All fragment packets need to be processed by the same goroutine, so
+			// only record the ports if this is not a fragment packet.
+			var isFragment bool
 			for {
 				hdr, done, err := it.Next()
 				if done || err != nil {
 					break
 				}
+				if fh, ok := hdr.(header.IPv6FragmentExtHdr); ok && !fh.IsAtomic() {
+					isFragment = true
+				}
 				hdr.Release()
 			}
-			h, ok = pkt.Data().PullUp(int(it.HeaderOffset()) + tcpSrcDstPortLen)
+			if !isFragment {
-			if !ok {
+				h, ok = pkt.Data().PullUp(int(it.HeaderOffset()) + tcpSrcDstPortLen)
-				return cid, true
+				if !ok {
+					return cid, true
+				}
+				// Known transport protocols store the src and dst ports
+				//  in the first 4 bytes after the IPv6 fixed header.
+				tcpHdr := header.TCP(h[it.HeaderOffset():][:tcpSrcDstPortLen])
+				cid.srcPort = tcpHdr.SourcePort()
+				cid.dstPort = tcpHdr.DestinationPort()
 			}
-			tcpHdr = header.TCP(h[it.HeaderOffset():][:tcpSrcDstPortLen])
 		}
-		cid.srcAddr = ipHdr.SourceAddressSlice()
-		cid.dstAddr = ipHdr.DestinationAddressSlice()
-		cid.srcPort = tcpHdr.SourcePort()
-		cid.dstPort = tcpHdr.DestinationPort()
-		cid.proto = header.IPv6ProtocolNumber
 	default:
 		return cid, true
 	}

netns_linux.go

@@ -0,0 +1,73 @@
+package tun
+
+import (
+	"context"
+	"net"
+	"runtime"
+	"strings"
+
+	"github.com/sagernet/sing/common/control"
+	E "github.com/sagernet/sing/common/exceptions"
+
+	"golang.org/x/sys/unix"
+)
+
+func listenNetworkNamespace(ctx context.Context, nameOrPath string, config net.ListenConfig, network, address string) (net.Listener, error) {
+	return execInNetworkNamespace(nameOrPath, func() (net.Listener, error) {
+		return config.Listen(ctx, network, address)
+	})
+}
+
+type networkNamespaceInterfaceFinder struct {
+	control.InterfaceFinder
+	options *Options
+}
+
+func (f *networkNamespaceInterfaceFinder) Update() error {
+	return runInNetworkNamespace(f.options.NetNs, f.InterfaceFinder.Update)
+}
+
+func execInNetworkNamespace[T any](nameOrPath string, block func() (T, error)) (T, error) {
+	if nameOrPath == "" {
+		return block()
+	}
+	type blockResult struct {
+		value T
+		err   error
+	}
+	resultChannel := make(chan blockResult, 1)
+	go func() {
+		runtime.LockOSThread()
+		value, err := execInNetworkNamespaceThread(nameOrPath, block)
+		resultChannel <- blockResult{value, err}
+	}()
+	result := <-resultChannel
+	return result.value, result.err
+}
+
+func execInNetworkNamespaceThread[T any](nameOrPath string, block func() (T, error)) (T, error) {
+	var defaultValue T
+	var path string
+	if strings.HasPrefix(nameOrPath, "/") {
+		path = nameOrPath
+	} else {
+		path = "/run/netns/" + nameOrPath
+	}
+	targetFd, err := unix.Open(path, unix.O_RDONLY|unix.O_CLOEXEC, 0)
+	if err != nil {
+		return defaultValue, E.Cause(err, "open netns ", nameOrPath)
+	}
+	defer unix.Close(targetFd)
+	err = unix.Setns(targetFd, unix.CLONE_NEWNET)
+	if err != nil {
+		return defaultValue, E.Cause(err, "set netns to ", nameOrPath)
+	}
+	return block()
+}
+
+func runInNetworkNamespace(nameOrPath string, block func() error) error {
+	_, err := execInNetworkNamespace(nameOrPath, func() (struct{}, error) {
+		return struct{}{}, block()
+	})
+	return err
+}

netns_other.go

@@ -0,0 +1,12 @@
+//go:build !linux
+
+package tun
+
+import (
+	"context"
+	"net"
+)
+
+func listenNetworkNamespace(ctx context.Context, nameOrPath string, config net.ListenConfig, network, address string) (net.Listener, error) {
+	return config.Listen(ctx, network, address)
+}

ping/cmsg_windows.go

@@ -1,11 +1,10 @@
 package ping
 
 import (
+	"encoding/binary"
 	"fmt"
 	"unsafe"
 
-	"github.com/sagernet/sing/common"
-
 	"golang.org/x/net/ipv6"
 	"golang.org/x/sys/windows"
 )
@@ -37,9 +36,9 @@ func parseIPv6ControlMessage(cmsg []byte) (*ipv6.ControlMessage, error) {
 		}
 		switch cmsghdr.Type {
 		case IPV6_TCLASS:
-			controlMessage.TrafficClass = int(common.NativeEndian.Uint32(cmsg[alignedSizeofCmsghdr : alignedSizeofCmsghdr+4]))
+			controlMessage.TrafficClass = int(binary.NativeEndian.Uint32(cmsg[alignedSizeofCmsghdr : alignedSizeofCmsghdr+4]))
 		case IPV6_HOPLIMIT:
-			controlMessage.HopLimit = int(common.NativeEndian.Uint32(cmsg[alignedSizeofCmsghdr : alignedSizeofCmsghdr+4]))
+			controlMessage.HopLimit = int(binary.NativeEndian.Uint32(cmsg[alignedSizeofCmsghdr : alignedSizeofCmsghdr+4]))
 		}
 		cmsg = cmsg[msgSize:]
 	}

ping/socket_linux_unprivileged.go

@@ -9,7 +9,6 @@ import (
 	"time"
 
 	"github.com/sagernet/sing-tun/gtcpip/header"
-	"github.com/sagernet/sing/common"
 	"github.com/sagernet/sing/common/buf"
 	"github.com/sagernet/sing/common/control"
 	M "github.com/sagernet/sing/common/metadata"
@@ -175,7 +174,7 @@ func (c *UnprivilegedConn) Close() error {
 	for _, conn := range c.mapping {
 		_ = conn.Close()
 	}
-	common.ClearMap(c.mapping)
+	clear(c.mapping)
 	return nil
 }
 

redirect_linux.go

@@ -26,6 +26,7 @@ type autoRedirect struct {
 	logger                  logger.Logger
 	tableName               string
 	networkMonitor          NetworkUpdateMonitor
+	ownedNetworkMonitor     bool
 	networkListener         *list.Element[NetworkUpdateCallback]
 	interfaceFinder         control.InterfaceFinder
 	localAddresses          []netip.Prefix
@@ -51,7 +52,7 @@ type autoRedirect struct {
 }
 
 func NewAutoRedirect(options AutoRedirectOptions) (AutoRedirect, error) {
-	return &autoRedirect{
+	r := &autoRedirect{
 		tunOptions:             options.TunOptions,
 		ctx:                    options.Context,
 		handler:                options.Handler,
@@ -63,7 +64,11 @@ func NewAutoRedirect(options AutoRedirectOptions) (AutoRedirect, error) {
 		customRedirectPortFunc: options.CustomRedirectPort,
 		routeAddressSet:        options.RouteAddressSet,
 		routeExcludeAddressSet: options.RouteExcludeAddressSet,
-	}, nil
+	}
+	if options.TunOptions.NetNs != "" {
+		r.interfaceFinder = &networkNamespaceInterfaceFinder{control.NewDefaultInterfaceFinder(), options.TunOptions}
+	}
+	return r, nil
 }
 
 func (r *autoRedirect) Start() error {
@@ -89,8 +94,11 @@ func (r *autoRedirect) Start() error {
 			}
 		}
 	} else {
+		if r.tunOptions.NetNs != "" && !r.useNFTables {
+			return E.New("auto_redirect in network namespace requires nftables")
+		}
 		if r.useNFTables {
-			err = r.initializeNFTables()
+			err = runInNetworkNamespace(r.tunOptions.NetNs, r.initializeNFTables)
 			if err != nil {
 				return E.Cause(err, "missing nftables support")
 			}
@@ -132,7 +140,7 @@ func (r *autoRedirect) Start() error {
 			listenAddr = netip.IPv4Unspecified()
 		}
 		server := newRedirectServer(r.ctx, r.handler, r.logger, listenAddr)
-		err = server.Start()
+		err = runInNetworkNamespace(r.tunOptions.NetNs, server.Start)
 		if err != nil {
 			return E.Cause(err, "start redirect server")
 		}
@@ -151,24 +159,43 @@ func (r *autoRedirect) Start() error {
 			})
 			if err != nil {
 				r.logger.Warn("nfqueue not available, pre-match disabled (missing nfnetlink_queue and nft_queue kernel module?): ", err)
-			} else if err = handler.Start(); err != nil {
+			} else if err = runInNetworkNamespace(r.tunOptions.NetNs, handler.Start); err != nil {
 				r.logger.Warn("nfqueue start failed, pre-match disabled (missing nfnetlink_queue and nft_queue kernel module?): ", err)
 			} else {
 				r.nfqueueHandler = handler
 				r.nfqueueEnabled = true
 			}
 		}
-		r.cleanupNFTables()
+		if r.tunOptions.NetNs != "" {
-		err = r.setupNFTables()
+			var monitor NetworkUpdateMonitor
-		if err != nil {
+			monitor, err = NewNetworkUpdateMonitor(r.logger)
-			return E.Cause(err, "setup nftables")
-		}
-		if r.tunOptions.AutoRedirectMarkMode {
-			err = r.setupRedirectRoutes()
 			if err != nil {
-				r.cleanupNFTables()
+				return E.Cause(err, "create netns network monitor")
-				return E.Cause(err, "setup redirect routes")
 			}
+			err = runInNetworkNamespace(r.tunOptions.NetNs, monitor.Start)
+			if err != nil {
+				return E.Cause(err, "start netns network monitor")
+			}
+			r.networkMonitor = monitor
+			r.ownedNetworkMonitor = true
+		}
+		err = runInNetworkNamespace(r.tunOptions.NetNs, func() error {
+			r.cleanupNFTables()
+			setupErr := r.setupNFTables()
+			if setupErr != nil {
+				return E.Cause(setupErr, "setup nftables")
+			}
+			if r.tunOptions.AutoRedirectMarkMode {
+				setupErr = r.setupRedirectRoutes()
+				if setupErr != nil {
+					r.cleanupNFTables()
+					return E.Cause(setupErr, "setup redirect routes")
+				}
+			}
+			return nil
+		})
+		if err != nil {
+			return err
 		}
 	} else {
 		r.cleanupIPTables()
@@ -185,8 +212,14 @@ func (r *autoRedirect) Close() error {
 		r.nfqueueHandler.Close()
 	}
 	if r.useNFTables {
-		r.cleanupNFTables()
+		_ = runInNetworkNamespace(r.tunOptions.NetNs, func() error {
-		r.cleanupRedirectRoutes()
+			r.cleanupNFTables()
+			r.cleanupRedirectRoutes()
+			return nil
+		})
+		if r.ownedNetworkMonitor {
+			_ = r.networkMonitor.Close()
+		}
 	} else {
 		r.cleanupIPTables()
 	}
@@ -197,7 +230,7 @@ func (r *autoRedirect) Close() error {
 
 func (r *autoRedirect) UpdateRouteAddressSet() {
 	if r.useNFTables {
-		err := r.nftablesUpdateRouteAddressSet()
+		err := runInNetworkNamespace(r.tunOptions.NetNs, r.nftablesUpdateRouteAddressSet)
 		if err != nil {
 			r.logger.Error("update route address set: ", err)
 		}

redirect_nftables.go

@@ -299,27 +299,38 @@ func (r *autoRedirect) setupNFTables() error {
 	if err != nil {
 		return E.Cause(err, "flush nftables")
 	}
-	r.startDockerFirewallMonitor()
+	if r.tunOptions.NetNs == "" {
-	err = r.configureDockerFirewall(false)
+		r.startDockerFirewallMonitor()
-	if err != nil && r.logger != nil {
+		err = r.configureDockerFirewall(false)
-		r.logger.Warn("configure docker firewall: ", err)
+		if err != nil && r.logger != nil {
+			r.logger.Warn("configure docker firewall: ", err)
+		}
 	}
 
 	r.networkListener = r.networkMonitor.RegisterCallback(func() {
-		err = r.nftablesUpdateLocalAddressSet()
+		updateErr := runInNetworkNamespace(r.tunOptions.NetNs, r.updateNetworkAddresses)
-		if err != nil {
+		if updateErr != nil {
-			r.logger.Error("update local address set: ", err)
+			r.logger.Error(updateErr)
-		}
-		if r.tunOptions.AutoRedirectMarkMode {
-			err = r.updateRedirectRoutes()
-			if err != nil {
-				r.logger.Error("update redirect routes: ", err)
-			}
 		}
 	})
 	return nil
 }
 
+func (r *autoRedirect) updateNetworkAddresses() error {
+	err := r.nftablesUpdateLocalAddressSet()
+	if err != nil {
+		err = E.Cause(err, "update local address set")
+	}
+	if r.tunOptions.AutoRedirectMarkMode {
+		routeErr := r.updateRedirectRoutes()
+		if routeErr != nil {
+			routeErr = E.Cause(routeErr, "update redirect routes")
+		}
+		err = E.Errors(err, routeErr)
+	}
+	return err
+}
+
 // TODO: test if this works
 func (r *autoRedirect) nftablesUpdateLocalAddressSet() error {
 	err := r.interfaceFinder.Update()
@@ -376,6 +387,7 @@ func (r *autoRedirect) nftablesUpdateRouteAddressSet() error {
 func (r *autoRedirect) cleanupNFTables() {
 	if r.networkListener != nil {
 		r.networkMonitor.UnregisterCallback(r.networkListener)
+		r.networkListener = nil
 	}
 	r.stopDockerFirewallMonitor()
 	nft, err := nftables.New()
@@ -389,9 +401,11 @@ func (r *autoRedirect) cleanupNFTables() {
 	_ = r.configureOpenWRTFirewall4(nft, true)
 	_ = nft.Flush()
 	_ = nft.CloseLasting()
-	err = r.configureDockerFirewall(true)
+	if r.tunOptions.NetNs == "" {
-	if err != nil && r.logger != nil {
+		err = r.configureDockerFirewall(true)
-		r.logger.Warn("cleanup docker firewall: ", err)
+		if err != nil && r.logger != nil {
+			r.logger.Warn("cleanup docker firewall: ", err)
+		}
 	}
 }
 

stack.go

@@ -14,6 +14,7 @@ import (
 
 type Stack interface {
 	Start() error
+	ResetNetwork()
 	Close() error
 }
 
@@ -23,6 +24,9 @@ type StackOptions struct {
 	TunOptions             Options
 	UDPTimeout             time.Duration
 	ICMPTimeout            time.Duration
+	UDPMapping             NATMapping
+	UDPFiltering           NATFiltering
+	UDPNATMax              uint32
 	Handler                Handler
 	Logger                 logger.Logger
 	ForwarderBindInterface bool

stack_gvisor.go

@@ -35,8 +35,8 @@ type GVisor struct {
 	inet6Address         netip.Addr
 	inet4LoopbackAddress []netip.Addr
 	inet6LoopbackAddress []netip.Addr
-	udpTimeout           time.Duration
 	icmpTimeout          time.Duration
+	udpNATOptions        UDPNatOptions
 	broadcastAddr        netip.Addr
 	handler              Handler
 	logger               logger.Logger
@@ -44,6 +44,7 @@ type GVisor struct {
 	endpoint             stack.LinkEndpoint
 	dispatcher           *ForwardDispatcher
 	icmpForwarder        *ICMPForwarder
+	udpForwarder         *UDPForwarder
 }
 
 type GVisorTun interface {
@@ -78,11 +79,18 @@ func NewGVisor(
 		inet6Address:         inet6Address,
 		inet4LoopbackAddress: options.TunOptions.Inet4LoopbackAddress,
 		inet6LoopbackAddress: options.TunOptions.Inet6LoopbackAddress,
-		udpTimeout:           options.UDPTimeout,
 		icmpTimeout:          options.ICMPTimeout,
-		broadcastAddr:        BroadcastAddr(options.TunOptions.Inet4Address),
+		udpNATOptions: UDPNatOptions{
-		handler:              options.Handler,
+			Timeout:          options.UDPTimeout,
-		logger:               options.Logger,
+			Mapping:          options.UDPMapping,
+			Filtering:        options.UDPFiltering,
+			MaxSize:          options.UDPNATMax,
+			InterfaceFinder:  options.InterfaceFinder,
+			ExcludeInterface: []string{options.TunOptions.Name},
+		},
+		broadcastAddr: BroadcastAddr(options.TunOptions.Inet4Address),
+		handler:       options.Handler,
+		logger:        options.Logger,
 	}
 	return gStack, nil
 }
@@ -93,7 +101,7 @@ func (t *GVisor) Start() error {
 		return err
 	}
 	if t.handler != nil {
-		t.dispatcher = NewForwardDispatcher(t.handler, &gvisorWriteback{tun: t.tun}, t.logger, t.udpTimeout, t.icmpTimeout)
+		t.dispatcher = NewForwardDispatcher(t.handler, &gvisorWriteback{tun: t.tun}, t.logger, t.udpNATOptions.Timeout, t.icmpTimeout)
 	}
 	linkEndpoint = &LinkEndpointFilter{
 		LinkEndpoint:         linkEndpoint,
@@ -110,7 +118,13 @@ func (t *GVisor) Start() error {
 		return err
 	}
 	ipStack.SetTransportProtocolHandler(tcp.ProtocolNumber, NewTCPForwarderWithLoopback(t.ctx, ipStack, t.handler, t.inet4LoopbackAddress, t.inet6LoopbackAddress, t.tun).HandlePacket)
-	ipStack.SetTransportProtocolHandler(udp.ProtocolNumber, NewUDPForwarder(t.ctx, ipStack, t.handler, t.udpTimeout).HandlePacket)
+	udpForwarder := NewUDPForwarder(t.ctx, ipStack, t.handler, t.udpNATOptions)
+	err = udpForwarder.Start()
+	if err != nil {
+		return err
+	}
+	ipStack.SetTransportProtocolHandler(udp.ProtocolNumber, udpForwarder.HandlePacket)
+	t.udpForwarder = udpForwarder
 	icmpForwarder := NewICMPForwarder(ipStack, t.handler, t.logger)
 	ipStack.SetTransportProtocolHandler(icmp.ProtocolNumber4, icmpForwarder.HandlePacket)
 	ipStack.SetTransportProtocolHandler(icmp.ProtocolNumber6, icmpForwarder.HandlePacket)
@@ -120,11 +134,24 @@ func (t *GVisor) Start() error {
 	return nil
 }
 
+func (t *GVisor) ResetNetwork() {
+	if t.udpForwarder != nil {
+		t.udpForwarder.udpNat.Purge()
+	}
+	if t.icmpForwarder != nil {
+		t.icmpForwarder.Purge()
+	}
+	t.dispatcher.ResetNetwork()
+}
+
 func (t *GVisor) Close() error {
 	t.dispatcher.Close()
 	if t.icmpForwarder != nil {
 		t.icmpForwarder.Close()
 	}
+	if t.udpForwarder != nil {
+		t.udpForwarder.Close()
+	}
 	if t.stack == nil {
 		return nil
 	}

stack_gvisor_icmp.go

@@ -72,6 +72,15 @@ func NewICMPForwarder(stack *stack.Stack, handler Handler, logger logger.Logger)
 	return forwarder
 }
 
+func (f *ICMPForwarder) Purge() {
+	f.flowAccess.Lock()
+	for key, flow := range f.flows {
+		flow.close(FlowCloseReset)
+		delete(f.flows, key)
+	}
+	f.flowAccess.Unlock()
+}
+
 func (f *ICMPForwarder) Close() error {
 	f.returnPath.closed.Store(true)
 	f.flowAccess.Lock()
@@ -146,9 +155,15 @@ func (f *ICMPForwarder) HandlePacket(id stack.TransportEndpointID, pkt *stack.Pa
 	} else {
 		ipHdr := header.IPv6(pkt.NetworkHeader().Slice())
 		icmpHdr := header.ICMPv6(pkt.TransportHeader().Slice())
-		if icmpHdr.Type() != header.ICMPv6EchoRequest || icmpHdr.Code() != 0 {
+		if icmpHdr.Type() != header.ICMPv6EchoRequest {
 			return false
 		}
+		if icmpHdr.Code() != 0 {
+			// The IPv6 built-in echo reply path lacks the LocalAddressTemporary
+			// check its IPv4 sibling has, so returning false would make the stack
+			// reply on behalf of arbitrary forwarded destinations.
+			return true
+		}
 		identifier := icmpHdr.Ident()
 		key := icmpFlowKey{
 			v6:          true,

stack_gvisor_udp.go

@@ -8,7 +8,6 @@ import (
 	"net/netip"
 	"os"
 	"sync"
-	"time"
 	_ "unsafe"
 
 	"github.com/sagernet/gvisor/pkg/buffer"
@@ -21,26 +20,35 @@ import (
 	E "github.com/sagernet/sing/common/exceptions"
 	M "github.com/sagernet/sing/common/metadata"
 	N "github.com/sagernet/sing/common/network"
-	"github.com/sagernet/sing/common/udpnat2"
 )
 
 type UDPForwarder struct {
 	ctx     context.Context
 	stack   *stack.Stack
 	handler Handler
-	udpNat  *udpnat.Service
+	udpNat  *UDPNat
 }
 
-func NewUDPForwarder(ctx context.Context, stack *stack.Stack, handler Handler, timeout time.Duration) *UDPForwarder {
+func NewUDPForwarder(ctx context.Context, stack *stack.Stack, handler Handler, options UDPNatOptions) *UDPForwarder {
 	forwarder := &UDPForwarder{
 		ctx:     ctx,
 		stack:   stack,
 		handler: handler,
 	}
-	forwarder.udpNat = udpnat.New(handler, forwarder.PreparePacketConnection, timeout, false)
+	options.Handler = handler
+	options.Prepare = forwarder.PreparePacketConnection
+	forwarder.udpNat = NewUDPNat(options)
 	return forwarder
 }
 
+func (f *UDPForwarder) Start() error {
+	return f.udpNat.Start()
+}
+
+func (f *UDPForwarder) Close() error {
+	return f.udpNat.Close()
+}
+
 func (f *UDPForwarder) HandlePacket(id stack.TransportEndpointID, pkt *stack.PacketBuffer) bool {
 	source := M.SocksaddrFrom(AddrFromAddress(id.RemoteAddress), id.RemotePort)
 	destination := M.SocksaddrFrom(AddrFromAddress(id.LocalAddress), id.LocalPort)
@@ -63,18 +71,26 @@ func (f *UDPForwarder) PreparePacketConnection(source M.Socksaddr, destination M
 			firstPacket = append(firstPacket[:len(firstPacket):len(firstPacket)], view.AsSlice()...)
 		}
 	})
+	var sourceNetwork tcpip.NetworkProtocolNumber
+	if source.Addr.Is4() {
+		sourceNetwork = header.IPv4ProtocolNumber
+	} else {
+		sourceNetwork = header.IPv6ProtocolNumber
+	}
 	switch f.handler.JudgeFlow(uint8(header.UDPProtocolNumber), source.AddrPort(), destination.AddrPort(), firstPacket).Action {
 	case ActionReject:
 		gWriteUnreachable(f.stack, userData.(*stack.PacketBuffer))
 		return false, nil, nil, nil
 	case ActionDrop:
 		return false, nil, nil, nil
-	}
+	case ActionHijackDNS:
-	var sourceNetwork tcpip.NetworkProtocolNumber
+		f.handler.NewDNSPacket(firstPacket, source, destination, &UDPBackWriter{
-	if source.Addr.Is4() {
+			stack:         f.stack,
-		sourceNetwork = header.IPv4ProtocolNumber
+			source:        AddressFromAddr(source.Addr),
-	} else {
+			sourcePort:    source.Port,
-		sourceNetwork = header.IPv6ProtocolNumber
+			sourceNetwork: sourceNetwork,
+		})
+		return false, nil, nil, nil
 	}
 	writer := &UDPBackWriter{
 		stack:         f.stack,

stack_mixed.go

@@ -19,9 +19,10 @@ import (
 
 type Mixed struct {
 	*System
-	tun      GVisorTun
+	tun          GVisorTun
-	stack    *stack.Stack
+	stack        *stack.Stack
-	endpoint *channel.Endpoint
+	endpoint     *channel.Endpoint
+	udpForwarder *UDPForwarder
 }
 
 func NewMixed(
@@ -47,7 +48,13 @@ func (m *Mixed) Start() error {
 	if err != nil {
 		return err
 	}
-	ipStack.SetTransportProtocolHandler(udp.ProtocolNumber, NewUDPForwarder(m.ctx, ipStack, m.handler, m.udpTimeout).HandlePacket)
+	udpForwarder := NewUDPForwarder(m.ctx, ipStack, m.handler, m.udpNATOptions)
+	err = udpForwarder.Start()
+	if err != nil {
+		return err
+	}
+	ipStack.SetTransportProtocolHandler(udp.ProtocolNumber, udpForwarder.HandlePacket)
+	m.udpForwarder = udpForwarder
 	m.stack = ipStack
 	m.endpoint = endpoint
 	go m.tunLoop()
@@ -55,10 +62,20 @@ func (m *Mixed) Start() error {
 	return nil
 }
 
+func (m *Mixed) ResetNetwork() {
+	m.System.ResetNetwork()
+	if m.udpForwarder != nil {
+		m.udpForwarder.udpNat.Purge()
+	}
+}
+
 func (m *Mixed) Close() error {
 	if m.stack == nil {
 		return nil
 	}
+	if m.udpForwarder != nil {
+		m.udpForwarder.Close()
+	}
 	m.endpoint.Attach(nil)
 	m.stack.Close()
 	for _, endpoint := range m.stack.CleanupEndpoints() {

stack_system.go

@@ -5,7 +5,10 @@ import (
 	"errors"
 	"net"
 	"net/netip"
+	"os"
 	"slices"
+	"sync"
+	"sync/atomic"
 	"syscall"
 	"time"
 
@@ -19,7 +22,6 @@ import (
 	"github.com/sagernet/sing/common/logger"
 	M "github.com/sagernet/sing/common/metadata"
 	N "github.com/sagernet/sing/common/network"
-	"github.com/sagernet/sing/common/udpnat2"
 )
 
 var ErrIncludeAllNetworks = E.New("`system` and `mixed` stack are not available when `includeAllNetworks` is enabled. See https://github.com/SagerNet/sing-tun/issues/25")
@@ -28,6 +30,7 @@ type System struct {
 	ctx                  context.Context
 	tun                  Tun
 	tunName              string
+	netNs                string
 	mtu                  int
 	handler              Handler
 	logger               logger.Logger
@@ -44,16 +47,25 @@ type System struct {
 	icmpTimeout          time.Duration
 	tcpListener          net.Listener
 	tcpListener6         net.Listener
-	tcpPort              uint16
+	// lx/040: ports are written by acceptLoop on self-heal relisten and read
-	tcpPort6             uint16
+	// concurrently from the tunLoop path (dispatch filter + NAT rewrite) —
-	tcpNat               *TCPNat
+	// they must be atomic. listenAccess serializes listener replacement
-	udpNat               *udpnat.Service
+	// against Close(); closing marks a deliberate shutdown so acceptLoop can
-	dispatcher           *ForwardDispatcher
+	// tell it apart from the listener dying out from under the stack.
-	bindInterface        bool
+	tcpPort             atomic.Uint32
-	interfaceFinder      control.InterfaceFinder
+	tcpPort6            atomic.Uint32
-	frontHeadroom        int
+	closing             atomic.Bool
-	txChecksumOffload    bool
+	listenAccess        sync.Mutex
-	multiPendingPackets  bool
+	acceptRecoveries    atomic.Uint32
+	tcpNat              *TCPNat
+	udpNat              *UDPNat
+	udpNATOptions       UDPNatOptions
+	dispatcher          *ForwardDispatcher
+	bindInterface       bool
+	interfaceFinder     control.InterfaceFinder
+	frontHeadroom       int
+	txChecksumOffload   bool
+	multiPendingPackets bool
 }
 
 type Session struct {
@@ -68,6 +80,7 @@ func NewSystem(options StackOptions) (Stack, error) {
 		ctx:                  options.Context,
 		tun:                  options.Tun,
 		tunName:              options.TunOptions.Name,
+		netNs:                options.TunOptions.NetNs,
 		mtu:                  int(options.TunOptions.MTU),
 		inet4LoopbackAddress: options.TunOptions.Inet4LoopbackAddress,
 		inet6LoopbackAddress: options.TunOptions.Inet6LoopbackAddress,
@@ -78,9 +91,17 @@ func NewSystem(options StackOptions) (Stack, error) {
 		inet4Prefixes:        options.TunOptions.Inet4Address,
 		inet6Prefixes:        options.TunOptions.Inet6Address,
 		broadcastAddr:        BroadcastAddr(options.TunOptions.Inet4Address),
-		bindInterface:        options.ForwarderBindInterface,
+		udpNATOptions: UDPNatOptions{
-		interfaceFinder:      options.InterfaceFinder,
+			Timeout:          options.UDPTimeout,
-		multiPendingPackets:  options.TunOptions.EXP_MultiPendingPackets,
+			Mapping:          options.UDPMapping,
+			Filtering:        options.UDPFiltering,
+			MaxSize:          options.UDPNATMax,
+			InterfaceFinder:  options.InterfaceFinder,
+			ExcludeInterface: []string{options.TunOptions.Name},
+		},
+		bindInterface:       options.ForwarderBindInterface,
+		interfaceFinder:     options.InterfaceFinder,
+		multiPendingPackets: options.TunOptions.EXP_MultiPendingPackets,
 	}
 	if len(options.TunOptions.Inet4Address) > 0 {
 		if !HasNextAddress(options.TunOptions.Inet4Address[0], 1) {
@@ -102,8 +123,26 @@ func NewSystem(options StackOptions) (Stack, error) {
 	return stack, nil
 }
 
+func (s *System) ResetNetwork() {
+	if s.tcpNat != nil {
+		s.tcpNat.Purge()
+	}
+	if s.udpNat != nil {
+		s.udpNat.Purge()
+	}
+	s.dispatcher.ResetNetwork()
+}
+
 func (s *System) Close() error {
+	// lx/040: mark the deliberate shutdown BEFORE closing the listeners so
+	// acceptLoop exits quietly instead of treating it as a foreign kill.
+	s.closing.Store(true)
 	s.dispatcher.Close()
+	if s.udpNat != nil {
+		s.udpNat.Close()
+	}
+	s.listenAccess.Lock()
+	defer s.listenAccess.Unlock()
 	return common.Close(
 		s.tcpListener,
 		s.tcpListener6,
@@ -119,8 +158,10 @@ func (s *System) Start() error {
 	return nil
 }
 
-func (s *System) start() error {
+// lx/040: TCP forwarder bind, shared by start() and the acceptLoop self-heal
-	_ = fixWindowsFirewall()
+// relisten path. isIPv6 selects the address family; the bind-to-interface
+// Control and the EADDRNOTAVAIL retry loop match the original start() code.
+func (s *System) listenTCP(isIPv6 bool) (net.Listener, error) {
 	var listener net.ListenConfig
 	if s.bindInterface {
 		listener.Control = control.Append(listener.Control, func(network, address string, conn syscall.RawConn) error {
@@ -131,40 +172,60 @@ func (s *System) start() error {
 			return nil
 		})
 	}
+	network := "tcp4"
+	address := s.inet4Address
+	if isIPv6 {
+		network = "tcp6"
+		address = s.inet6Address
+	}
+	var (
+		tcpListener net.Listener
+		err         error
+	)
+	for range 3 {
+		tcpListener, err = listenNetworkNamespace(s.ctx, s.netNs, listener, network, net.JoinHostPort(address.String(), "0"))
+		if !retryableListenError(err) {
+			break
+		}
+		time.Sleep(time.Second)
+	}
+	if err != nil {
+		return nil, err
+	}
+	return tcpListener, nil
+}
+
+func (s *System) start() error {
+	_ = fixWindowsFirewall()
 	var tcpListener net.Listener
 	var err error
 	if s.inet4NextAddress.IsValid() {
-		for range 3 {
+		tcpListener, err = s.listenTCP(false)
-			tcpListener, err = listener.Listen(s.ctx, "tcp4", net.JoinHostPort(s.inet4Address.String(), "0"))
-			if !retryableListenError(err) {
-				break
-			}
-			time.Sleep(time.Second)
-		}
 		if err != nil {
 			return err
 		}
 		s.tcpListener = tcpListener
-		s.tcpPort = M.SocksaddrFromNet(tcpListener.Addr()).Port
+		s.tcpPort.Store(uint32(M.SocksaddrFromNet(tcpListener.Addr()).Port))
-		go s.acceptLoop(tcpListener)
+		go s.acceptLoop(tcpListener, false)
 	}
 	if s.inet6NextAddress.IsValid() {
-		for range 3 {
+		tcpListener, err = s.listenTCP(true)
-			tcpListener, err = listener.Listen(s.ctx, "tcp6", net.JoinHostPort(s.inet6Address.String(), "0"))
-			if !retryableListenError(err) {
-				break
-			}
-			time.Sleep(time.Second)
-		}
 		if err != nil {
 			return err
 		}
 		s.tcpListener6 = tcpListener
-		s.tcpPort6 = M.SocksaddrFromNet(tcpListener.Addr()).Port
+		s.tcpPort6.Store(uint32(M.SocksaddrFromNet(tcpListener.Addr()).Port))
-		go s.acceptLoop(tcpListener)
+		go s.acceptLoop(tcpListener, true)
 	}
 	s.tcpNat = NewNat(s.ctx, s.udpTimeout)
-	s.udpNat = udpnat.New(s.handler, s.preparePacketConnection, s.udpTimeout, false)
+	udpNATOptions := s.udpNATOptions
+	udpNATOptions.Handler = s.handler
+	udpNATOptions.Prepare = s.preparePacketConnection
+	s.udpNat = NewUDPNat(udpNATOptions)
+	err = s.udpNat.Start()
+	if err != nil {
+		return err
+	}
 	if linuxTUN, isLinuxTUN := s.tun.(LinuxTUN); isLinuxTUN {
 		s.frontHeadroom = linuxTUN.FrontHeadroom()
 		s.txChecksumOffload = linuxTUN.TXChecksumOffload()
@@ -336,11 +397,28 @@ func (s *System) processPacket(packet []byte) bool {
 	return writeBack
 }
 
-func (s *System) acceptLoop(listener net.Listener) {
+func (s *System) acceptLoop(listener net.Listener, isIPv6 bool) {
 	for {
 		conn, err := listener.Accept()
 		if err != nil {
-			return
+			// lx/040 (SPECS/TASKS/040): upstream silently returns on ANY Accept
+			// error, leaving the stack alive but every new TCP SYN NAT-rewritten
+			// onto a dead port (instant RST) until a VPN restart — the LxBox §047
+			// "browser dead, QUIC alive" failure. A deliberate System.Close is the
+			// only quiet exit; anything else means the listener died out from
+			// under us (e.g. a foreign close on a reused fd number from the
+			// Java side of the shared Android process) — log it (the errno names
+			// the killer) and recreate the listener.
+			if s.closing.Load() {
+				return
+			}
+			newListener, healErr := s.healListener(listener, isIPv6, err)
+			if healErr != nil {
+				s.logger.Error("system stack: tcp", ipVersionSuffix(isIPv6), " accept loop died: ", err, "; relisten failed: ", healErr)
+				return
+			}
+			listener = newListener
+			continue
 		}
 		connPort := M.SocksaddrFromNet(conn.RemoteAddr()).Port
 		session := s.tcpNat.LookupBack(connPort)
@@ -352,6 +430,47 @@ func (s *System) acceptLoop(listener net.Listener) {
 	}
 }
 
+// lx/040: recreate a TCP forwarder listener that died out from under the
+// stack. Returns the replacement listener after publishing it (listener field
+// + atomic port) under listenAccess, or an error if the stack is closing or
+// the bind failed.
+func (s *System) healListener(dead net.Listener, isIPv6 bool, cause error) (net.Listener, error) {
+	port := &s.tcpPort
+	if isIPv6 {
+		port = &s.tcpPort6
+	}
+	oldPort := port.Load()
+	s.logger.Warn("system stack: tcp", ipVersionSuffix(isIPv6), " listener (port ", oldPort, ") accept failed: ", cause, " — recreating listener")
+	_ = dead.Close() // release netpoll state; harmless if already closed
+	newListener, err := s.listenTCP(isIPv6)
+	if err != nil {
+		return nil, err
+	}
+	s.listenAccess.Lock()
+	defer s.listenAccess.Unlock()
+	if s.closing.Load() {
+		_ = newListener.Close()
+		return nil, net.ErrClosed
+	}
+	if isIPv6 {
+		s.tcpListener6 = newListener
+	} else {
+		s.tcpListener = newListener
+	}
+	newPort := uint32(M.SocksaddrFromNet(newListener.Addr()).Port)
+	port.Store(newPort)
+	recoveries := s.acceptRecoveries.Add(1)
+	s.logger.Warn("system stack: tcp", ipVersionSuffix(isIPv6), " listener recreated (port ", oldPort, " → ", newPort, ", recoveries: ", recoveries, ")")
+	return newListener, nil
+}
+
+func ipVersionSuffix(isIPv6 bool) string {
+	if isIPv6 {
+		return "6"
+	}
+	return "4"
+}
+
 func (s *System) dispatchIPv4(ipHdr header.IPv4, destination netip.Addr) bool {
 	switch ipHdr.TransportProtocol() {
 	case header.TCPProtocolNumber:
@@ -361,7 +480,7 @@ func (s *System) dispatchIPv4(ipHdr header.IPv4, destination netip.Addr) bool {
 		if ipHdr.SourceAddr() == s.inet4Address &&
 			ipHdr.FragmentOffset() == 0 &&
 			len(ipHdr.Payload()) >= header.TCPMinimumSize &&
-			header.TCP(ipHdr.Payload()).SourcePort() == s.tcpPort {
+			header.TCP(ipHdr.Payload()).SourcePort() == uint16(s.tcpPort.Load()) {
 			return false
 		}
 	case header.ICMPv4ProtocolNumber:
@@ -380,7 +499,7 @@ func (s *System) dispatchIPv6(ipHdr header.IPv6, destination netip.Addr) bool {
 		}
 		if ipHdr.SourceAddr() == s.inet6Address &&
 			len(ipHdr.Payload()) >= header.TCPMinimumSize &&
-			header.TCP(ipHdr.Payload()).SourcePort() == s.tcpPort6 {
+			header.TCP(ipHdr.Payload()).SourcePort() == uint16(s.tcpPort6.Load()) {
 			return false
 		}
 	case header.ICMPv6ProtocolNumber:
@@ -444,7 +563,7 @@ func (s *System) processIPv4TCP(ipHdr header.IPv4, tcpHdr header.TCP) (bool, err
 	destination := netip.AddrPortFrom(ipHdr.DestinationAddr(), tcpHdr.DestinationPort())
 	if !destination.Addr().IsGlobalUnicast() {
 		return false, nil
-	} else if source.Addr() == s.inet4Address && source.Port() == s.tcpPort {
+	} else if source.Addr() == s.inet4Address && source.Port() == uint16(s.tcpPort.Load()) {
 		session := s.tcpNat.LookupBack(destination.Port())
 		if session == nil {
 			return false, E.New("ipv4: tcp: session not found: ", destination.Port())
@@ -470,7 +589,7 @@ func (s *System) processIPv4TCP(ipHdr header.IPv4, tcpHdr header.TCP) (bool, err
 			}
 			rewriteIPv4TCP(ipHdr, tcpHdr, s.txChecksumOffload,
 				s.inet4NextAddress, natPort, true,
-				s.inet4Address, s.tcpPort, true)
+				s.inet4Address, uint16(s.tcpPort.Load()), true)
 		}
 	}
 	return true, nil
@@ -481,7 +600,7 @@ func (s *System) processIPv6TCP(ipHdr header.IPv6, tcpHdr header.TCP) (bool, err
 	destination := netip.AddrPortFrom(ipHdr.DestinationAddr(), tcpHdr.DestinationPort())
 	if !destination.Addr().IsGlobalUnicast() {
 		return false, nil
-	} else if source.Addr() == s.inet6Address && source.Port() == s.tcpPort6 {
+	} else if source.Addr() == s.inet6Address && source.Port() == uint16(s.tcpPort6.Load()) {
 		session := s.tcpNat.LookupBack(destination.Port())
 		if session == nil {
 			return false, E.New("ipv6: tcp: session not found: ", destination.Port())
@@ -507,7 +626,7 @@ func (s *System) processIPv6TCP(ipHdr header.IPv6, tcpHdr header.TCP) (bool, err
 			}
 			rewriteIPv6TCP(ipHdr, tcpHdr, s.txChecksumOffload,
 				s.inet6NextAddress, natPort, true,
-				s.inet6Address, s.tcpPort6, true)
+				s.inet6Address, uint16(s.tcpPort6.Load()), true)
 		}
 	}
 	return true, nil
@@ -682,20 +801,22 @@ type systemUDPPacketWriter4 struct {
 	txChecksumOffload bool
 }
 
-func (w *systemUDPPacketWriter4) WritePacket(buffer *buf.Buffer, destination M.Socksaddr) error {
+func (w *systemUDPPacketWriter4) FrontHeadroom() int {
-	newPacket := buf.NewSize(w.frontHeadroom + len(w.header) + buffer.Len())
+	return w.frontHeadroom + len(w.header)
-	defer newPacket.Release()
+}
-	newPacket.Resize(w.frontHeadroom, 0)
+
-	newPacket.Write(w.header)
+func (w *systemUDPPacketWriter4) preparePacket(buffer *buf.Buffer, destination M.Socksaddr) *buf.Buffer {
-	newPacket.Write(buffer.Bytes())
+	payloadLen := buffer.Len()
-	ipHdr := header.IPv4(newPacket.Bytes())
+	buffer = (N.ReadWaitOptions{FrontHeadroom: w.FrontHeadroom()}).Copy(buffer)
-	ipHdr.SetTotalLength(uint16(newPacket.Len()))
+	copy(buffer.ExtendHeader(len(w.header)), w.header)
+	ipHdr := header.IPv4(buffer.Bytes())
+	ipHdr.SetTotalLength(uint16(buffer.Len()))
 	ipHdr.SetDestinationAddress(ipHdr.SourceAddress())
 	ipHdr.SetSourceAddr(destination.Addr)
 	udpHdr := header.UDP(ipHdr.Payload())
 	udpHdr.SetDestinationPort(udpHdr.SourcePort())
 	udpHdr.SetSourcePort(destination.Port)
-	udpHdr.SetLength(uint16(buffer.Len() + header.UDPMinimumSize))
+	udpHdr.SetLength(uint16(payloadLen + header.UDPMinimumSize))
 	if !w.txChecksumOffload {
 		udpHdr.SetChecksum(^checksum.Checksum(udpHdr.Payload(), udpHdr.CalculateChecksum(
 			header.PseudoHeaderChecksum(header.UDPProtocolNumber, ipHdr.SourceAddressSlice(), ipHdr.DestinationAddressSlice(), ipHdr.PayloadLength()),
@@ -704,12 +825,61 @@ func (w *systemUDPPacketWriter4) WritePacket(buffer *buf.Buffer, destination M.S
 		udpHdr.SetChecksum(0)
 	}
 	ipHdr.SetChecksum(^ipHdr.CalculateChecksum())
+	return buffer
+}
+
+func (w *systemUDPPacketWriter4) prepareWritePacket(buffer *buf.Buffer, destination M.Socksaddr) *buf.Buffer {
+	buffer = w.preparePacket(buffer, destination)
 	if PacketOffset > 0 {
-		PacketFillHeader(newPacket.ExtendHeader(PacketOffset), header.IPv4Version)
+		PacketFillHeader(buffer.ExtendHeader(PacketOffset), header.IPv4Version)
-	} else {
+	}
-		newPacket.Advance(-w.frontHeadroom)
+	if remainingHeadroom := w.frontHeadroom - PacketOffset; remainingHeadroom > 0 {
+		buffer.Advance(-remainingHeadroom)
+	}
+	return buffer
+}
+
+func (w *systemUDPPacketWriter4) WritePacket(buffer *buf.Buffer, destination M.Socksaddr) error {
+	buffer = w.prepareWritePacket(buffer, destination)
+	defer buffer.Release()
+	return common.Error(w.tun.Write(buffer.Bytes()))
+}
+
+func (w *systemUDPPacketWriter4) CreatePacketBatchWriter() (N.PacketBatchWriter, bool) {
+	switch w.tun.(type) {
+	case LinuxTUN, DarwinTUN:
+		return w, true
+	default:
+		return nil, false
+	}
+}
+
+func (w *systemUDPPacketWriter4) WritePacketBatch(buffers []*buf.Buffer, destinations []M.Socksaddr) error {
+	if len(buffers) == 0 || len(buffers) != len(destinations) {
+		buf.ReleaseMulti(buffers)
+		return os.ErrInvalid
+	}
+	defer func() {
+		buf.ReleaseMulti(buffers)
+	}()
+	switch tunInterface := w.tun.(type) {
+	case LinuxTUN:
+		packets := make([][]byte, len(buffers))
+		for index, buffer := range buffers {
+			buffer = w.preparePacket(buffer, destinations[index])
+			buffer.Advance(-w.frontHeadroom)
+			buffers[index] = buffer
+			packets[index] = buffer.Bytes()
+		}
+		return common.Error(tunInterface.BatchWrite(packets, w.frontHeadroom))
+	case DarwinTUN:
+		for index, buffer := range buffers {
+			buffers[index] = w.preparePacket(buffer, destinations[index])
+		}
+		return tunInterface.BatchWrite(buffers)
+	default:
+		return os.ErrInvalid
 	}
-	return common.Error(w.tun.Write(newPacket.Bytes()))
 }
 
 type systemUDPPacketWriter6 struct {
@@ -720,14 +890,16 @@ type systemUDPPacketWriter6 struct {
 	txChecksumOffload bool
 }
 
-func (w *systemUDPPacketWriter6) WritePacket(buffer *buf.Buffer, destination M.Socksaddr) error {
+func (w *systemUDPPacketWriter6) FrontHeadroom() int {
-	newPacket := buf.NewSize(w.frontHeadroom + len(w.header) + buffer.Len())
+	return w.frontHeadroom + len(w.header)
-	defer newPacket.Release()
+}
-	newPacket.Resize(w.frontHeadroom, 0)
+
-	newPacket.Write(w.header)
+func (w *systemUDPPacketWriter6) preparePacket(buffer *buf.Buffer, destination M.Socksaddr) *buf.Buffer {
-	newPacket.Write(buffer.Bytes())
+	payloadLen := buffer.Len()
-	ipHdr := header.IPv6(newPacket.Bytes())
+	buffer = (N.ReadWaitOptions{FrontHeadroom: w.FrontHeadroom()}).Copy(buffer)
-	udpLen := uint16(header.UDPMinimumSize + buffer.Len())
+	copy(buffer.ExtendHeader(len(w.header)), w.header)
+	ipHdr := header.IPv6(buffer.Bytes())
+	udpLen := uint16(header.UDPMinimumSize + payloadLen)
 	ipHdr.SetPayloadLength(udpLen)
 	ipHdr.SetDestinationAddress(ipHdr.SourceAddress())
 	ipHdr.SetSourceAddr(destination.Addr)
@@ -742,12 +914,61 @@ func (w *systemUDPPacketWriter6) WritePacket(buffer *buf.Buffer, destination M.S
 	} else {
 		udpHdr.SetChecksum(0)
 	}
+	return buffer
+}
+
+func (w *systemUDPPacketWriter6) prepareWritePacket(buffer *buf.Buffer, destination M.Socksaddr) *buf.Buffer {
+	buffer = w.preparePacket(buffer, destination)
 	if PacketOffset > 0 {
-		PacketFillHeader(newPacket.ExtendHeader(PacketOffset), header.IPv6Version)
+		PacketFillHeader(buffer.ExtendHeader(PacketOffset), header.IPv6Version)
-	} else {
+	}
-		newPacket.Advance(-w.frontHeadroom)
+	if remainingHeadroom := w.frontHeadroom - PacketOffset; remainingHeadroom > 0 {
+		buffer.Advance(-remainingHeadroom)
+	}
+	return buffer
+}
+
+func (w *systemUDPPacketWriter6) WritePacket(buffer *buf.Buffer, destination M.Socksaddr) error {
+	buffer = w.prepareWritePacket(buffer, destination)
+	defer buffer.Release()
+	return common.Error(w.tun.Write(buffer.Bytes()))
+}
+
+func (w *systemUDPPacketWriter6) CreatePacketBatchWriter() (N.PacketBatchWriter, bool) {
+	switch w.tun.(type) {
+	case LinuxTUN, DarwinTUN:
+		return w, true
+	default:
+		return nil, false
+	}
+}
+
+func (w *systemUDPPacketWriter6) WritePacketBatch(buffers []*buf.Buffer, destinations []M.Socksaddr) error {
+	if len(buffers) == 0 || len(buffers) != len(destinations) {
+		buf.ReleaseMulti(buffers)
+		return os.ErrInvalid
+	}
+	defer func() {
+		buf.ReleaseMulti(buffers)
+	}()
+	switch tunInterface := w.tun.(type) {
+	case LinuxTUN:
+		packets := make([][]byte, len(buffers))
+		for index, buffer := range buffers {
+			buffer = w.preparePacket(buffer, destinations[index])
+			buffer.Advance(-w.frontHeadroom)
+			buffers[index] = buffer
+			packets[index] = buffer.Bytes()
+		}
+		return common.Error(tunInterface.BatchWrite(packets, w.frontHeadroom))
+	case DarwinTUN:
+		for index, buffer := range buffers {
+			buffers[index] = w.preparePacket(buffer, destinations[index])
+		}
+		return tunInterface.BatchWrite(buffers)
+	default:
+		return os.ErrInvalid
 	}
-	return common.Error(w.tun.Write(newPacket.Bytes()))
 }
 
 func newSystemWriteback(tunInterface Tun, frontHeadroom int) ForwardWriteback {

stack_system_nat.go

@@ -86,6 +86,15 @@ func (n *TCPNat) checkTimeout() {
 	n.addrAccess.Unlock()
 }
 
+func (n *TCPNat) Purge() {
+	n.addrAccess.Lock()
+	n.portAccess.Lock()
+	clear(n.addrMap)
+	clear(n.portMap)
+	n.portAccess.Unlock()
+	n.addrAccess.Unlock()
+}
+
 func (n *TCPNat) LookupBack(port uint16) *TCPSession {
 	n.portAccess.RLock()
 	session := n.portMap[port]

stack_system_packet.go

@@ -5,7 +5,6 @@ import (
 	"syscall"
 
 	"github.com/sagernet/sing-tun/gtcpip/header"
-	"github.com/sagernet/sing/common"
 )
 
 func PacketIPVersion(packet []byte) int {
@@ -14,7 +13,7 @@ func PacketIPVersion(packet []byte) int {
 
 func PacketFillHeader(packet []byte, ipVersion int) {
 	if PacketOffset > 0 {
-		common.ClearArray(packet[:3])
+		clear(packet[:3])
 		switch ipVersion {
 		case header.IPv4Version:
 			packet[3] = syscall.AF_INET

stack_system_selfheal_test.go

@@ -0,0 +1,117 @@
+package tun
+
+// lx/040 (SPECS/TASKS/040-SINGTUN_ACCEPTLOOP_SELFHEAL): acceptLoop self-heal.
+//
+// Red/green против апстрима 2d9b8aed5fe2: там acceptLoop(listener) при любой
+// ошибке Accept молча выходит навсегда — восстановления нет, порт не меняется,
+// новый connect вечно бьётся в мёртвый сокет. Для red-прогона на чистом
+// апстрим-чекауте достаточно адаптировать хелперы ниже (currentTCPPort →
+// s.tcpPort, spawnAcceptLoop → go s.acceptLoop(ln)): тест упадёт по таймауту
+// ожидания восстановления.
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"net/netip"
+	"testing"
+	"time"
+
+	"github.com/sagernet/sing/common/logger"
+)
+
+func newSelfHealTestSystem(t *testing.T) *System {
+	t.Helper()
+	s := &System{
+		ctx:          context.Background(),
+		logger:       logger.NOP(),
+		inet4Address: netip.MustParseAddr("127.0.0.1"),
+		udpTimeout:   time.Minute,
+	}
+	s.tcpNat = NewNat(s.ctx, s.udpTimeout)
+	ln, err := s.listenTCP(false)
+	if err != nil {
+		t.Fatalf("listenTCP: %v", err)
+	}
+	s.tcpListener = ln
+	s.tcpPort.Store(uint32(ln.Addr().(*net.TCPAddr).Port))
+	spawnAcceptLoop(s, ln)
+	return s
+}
+
+func currentTCPPort(s *System) uint32 {
+	return s.tcpPort.Load()
+}
+
+func spawnAcceptLoop(s *System, ln net.Listener) {
+	go s.acceptLoop(ln, false)
+}
+
+func dialForwarder(t *testing.T, port uint32) error {
+	t.Helper()
+	conn, err := net.DialTimeout("tcp4", fmt.Sprintf("127.0.0.1:%d", port), time.Second)
+	if err == nil {
+		_ = conn.Close()
+	}
+	return err
+}
+
+// Убийство listener'а мимо System.Close (эмуляция чужого close по
+// переиспользованному fd-номеру) должно приводить к пересозданию listener'а
+// и продолжению приёма TCP, а не к вечной смерти петли.
+func TestSystemAcceptLoopSelfHeal(t *testing.T) {
+	s := newSelfHealTestSystem(t)
+	oldPort := currentTCPPort(s)
+
+	if err := dialForwarder(t, oldPort); err != nil {
+		t.Fatalf("healthy listener refused connect: %v", err)
+	}
+
+	// Убить listener из-под стека: closing НЕ выставлен.
+	_ = s.tcpListener.Close()
+
+	deadline := time.Now().Add(5 * time.Second)
+	healed := false
+	for time.Now().Before(deadline) {
+		if s.acceptRecoveries.Load() > 0 {
+			healed = true
+			break
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
+	if !healed {
+		t.Fatalf("acceptLoop did not recover within 5s (upstream behavior: silent permanent death)")
+	}
+
+	newPort := currentTCPPort(s)
+	if newPort == oldPort {
+		t.Fatalf("recovered port equals dead port %d — relisten did not publish a new port", oldPort)
+	}
+	if err := dialForwarder(t, newPort); err != nil {
+		t.Fatalf("connect to recreated listener (port %d) failed: %v", newPort, err)
+	}
+	if got := s.acceptRecoveries.Load(); got != 1 {
+		t.Fatalf("acceptRecoveries = %d, want 1", got)
+	}
+
+	s.closing.Store(true)
+	_ = s.tcpListener.Close()
+}
+
+// Штатное закрытие (closing выставлен, как это делает System.Close) обязано
+// оставаться тихим: без пересозданий и без роста счётчика.
+func TestSystemAcceptLoopQuietOnClose(t *testing.T) {
+	s := newSelfHealTestSystem(t)
+	oldPort := currentTCPPort(s)
+
+	s.closing.Store(true)
+	_ = s.tcpListener.Close()
+
+	time.Sleep(300 * time.Millisecond)
+	if got := s.acceptRecoveries.Load(); got != 0 {
+		t.Fatalf("deliberate close triggered %d recoveries, want 0", got)
+	}
+	if port := currentTCPPort(s); port != oldPort {
+		t.Fatalf("deliberate close changed port %d → %d", oldPort, port)
+	}
+}

tun.go

@@ -14,12 +14,14 @@ import (
 	E "github.com/sagernet/sing/common/exceptions"
 	F "github.com/sagernet/sing/common/format"
 	"github.com/sagernet/sing/common/logger"
+	M "github.com/sagernet/sing/common/metadata"
 	N "github.com/sagernet/sing/common/network"
 	"github.com/sagernet/sing/common/ranges"
 )
 
 type Handler interface {
 	JudgeFlow(network uint8, source netip.AddrPort, destination netip.AddrPort, firstPacket []byte) FlowVerdict
+	NewDNSPacket(payload []byte, source M.Socksaddr, destination M.Socksaddr, writer N.PacketWriter)
 	N.TCPConnectionHandlerEx
 	N.UDPConnectionHandlerEx
 }
@@ -66,6 +68,7 @@ const (
 
 type Options struct {
 	Name                                  string
+	NetNs                                 string
 	Inet4Address                          []netip.Prefix
 	Inet6Address                          []netip.Prefix
 	MTU                                   uint32

tun_linux.go

@@ -51,37 +51,38 @@ type NativeTun struct {
 }
 
 func New(options Options) (Tun, error) {
-	var nativeTun *NativeTun
 	if options.FileDescriptor == 0 {
-		tunFd, err := open(options.Name, options.GSO)
+		return execInNetworkNamespace(options.NetNs, func() (Tun, error) {
-		if err != nil {
+			tunFd, err := open(options.Name, options.GSO)
-			return nil, E.Cause(err, "open tun")
-		}
-		tunLink, err := netlink.LinkByName(options.Name)
-		if err != nil {
-			return nil, E.Errors(err, unix.Close(tunFd))
-		}
-		nativeTun = &NativeTun{
-			tunFd:   tunFd,
-			tunFile: os.NewFile(uintptr(tunFd), "tun"),
-			options: options,
-		}
-		err = nativeTun.configure(tunLink)
-		if err != nil {
-			return nil, E.Errors(err, unix.Close(tunFd))
-		}
-	} else {
-		nativeTun = &NativeTun{
-			tunFd:   options.FileDescriptor,
-			tunFile: os.NewFile(uintptr(options.FileDescriptor), "tun"),
-			options: options,
-		}
-		if options.GSO {
-			err := nativeTun.enableGSO()
 			if err != nil {
-				if options.Logger != nil {
+				return nil, E.Cause(err, "open tun")
-					options.Logger.Warn(err)
+			}
-				}
+			tunLink, err := netlink.LinkByName(options.Name)
+			if err != nil {
+				return nil, E.Errors(err, unix.Close(tunFd))
+			}
+			nativeTun := &NativeTun{
+				tunFd:   tunFd,
+				tunFile: os.NewFile(uintptr(tunFd), "tun"),
+				options: options,
+			}
+			err = nativeTun.configure(tunLink)
+			if err != nil {
+				return nil, E.Errors(err, unix.Close(tunFd))
+			}
+			return nativeTun, nil
+		})
+	}
+	nativeTun := &NativeTun{
+		tunFd:   options.FileDescriptor,
+		tunFile: os.NewFile(uintptr(options.FileDescriptor), "tun"),
+		options: options,
+	}
+	if options.GSO {
+		err := nativeTun.enableGSO()
+		if err != nil {
+			if options.Logger != nil {
+				options.Logger.Warn(err)
 			}
 		}
 	}
@@ -290,10 +291,10 @@ func (t *NativeTun) Name() (string, error) {
 
 func (t *NativeTun) Start() error {
 	if t.options.FileDescriptor == 0 {
-		if !t.options.EXP_ExternalConfiguration {
+		if !t.options.EXP_ExternalConfiguration && t.options.NetNs == "" {
 			t.options.InterfaceMonitor.RegisterMyInterface(t.options.Name)
 		}
-		err := t.start()
+		err := runInNetworkNamespace(t.options.NetNs, t.start)
 		if err != nil {
 			return err
 		}
@@ -354,7 +355,7 @@ func (t *NativeTun) start() error {
 		return E.Cause(err, "set rules")
 	}
 
-	if t.options.DNSMode != DNSModeDisabled {
+	if t.options.DNSMode != DNSModeDisabled && t.options.NetNs == "" {
 		err = t.setSearchDomainForSystemdResolved()
 		if err != nil {
 			return E.Cause(err, "set search domain")
@@ -374,11 +375,13 @@ func (t *NativeTun) Close() error {
 	if t.options.EXP_ExternalConfiguration {
 		return common.Close(common.PtrOrNil(t.tunFile))
 	}
-	if t.options.DNSMode != DNSModeDisabled {
+	if t.options.DNSMode != DNSModeDisabled && t.options.NetNs == "" {
 		t.unsetSearchDomainForSystemdResolved()
 	}
-	t.unsetAddresses()
+	return E.Errors(runInNetworkNamespace(t.options.NetNs, func() error {
-	return E.Errors(t.unsetRoute(), t.unsetRules(), common.Close(common.PtrOrNil(t.tunFile)))
+		t.unsetAddresses()
+		return E.Errors(t.unsetRoute(), t.unsetRules())
+	}), common.Close(common.PtrOrNil(t.tunFile)))
 }
 
 func (t *NativeTun) Read(p []byte) (n int, err error) {
@@ -625,16 +628,18 @@ func (t *NativeTun) UpdateRouteOptions(tunOptions Options) error {
 		t.options = tunOptions
 		return nil
 	}
-	tunLink, err := netlink.LinkByName(t.options.Name)
+	return runInNetworkNamespace(t.options.NetNs, func() error {
-	if err != nil {
+		tunLink, err := netlink.LinkByName(t.options.Name)
-		return E.Cause(err, "find tun interface")
+		if err != nil {
-	}
+			return E.Cause(err, "find tun interface")
-	err = t.unsetRoute0(tunLink)
+		}
-	if err != nil {
+		err = t.unsetRoute0(tunLink)
-		return E.Cause(err, "unset old routes")
+		if err != nil {
-	}
+			return E.Cause(err, "unset old routes")
-	t.options = tunOptions
+		}
-	return t.setRoute(tunLink)
+		t.options = tunOptions
+		return t.setRoute(tunLink)
+	})
 }
 
 func (t *NativeTun) routes(tunLink netlink.Link) ([]netlink.Route, error) {

udp_egress.go

@@ -0,0 +1,287 @@
+package tun
+
+import (
+	"context"
+	"net"
+	"net/netip"
+	"runtime"
+	"slices"
+	"sync"
+	"sync/atomic"
+
+	"github.com/sagernet/sing/common/buf"
+	"github.com/sagernet/sing/common/control"
+	E "github.com/sagernet/sing/common/exceptions"
+	"github.com/sagernet/sing/common/logger"
+	"github.com/sagernet/sing/common/x/list"
+)
+
+const udpEgressBufferSize = 65535
+
+type UDPEgressPoolOptions struct {
+	Logger           logger.Logger
+	Network          string
+	Control          control.Func
+	InterfaceFinder  control.InterfaceFinder
+	InterfaceMonitor DefaultInterfaceMonitor
+	ExcludeInterface string
+	IsExempt         func() bool
+}
+
+type UDPEgressPool struct {
+	logger               logger.Logger
+	network              string
+	control              control.Func
+	interfaceFinder      control.InterfaceFinder
+	interfaceMonitor     DefaultInterfaceMonitor
+	excludeInterface     string
+	isExempt             func() bool
+	access               sync.Mutex
+	port                 uint16
+	anchorInterfaceIndex int
+	receiveDone          chan struct{}
+	members              map[udpEgressSpec]*udpEgressMember
+	state                atomic.Pointer[[]*udpEgressMember]
+	packetChan           chan udpEgressPacket
+	memberReaders        sync.WaitGroup
+	finderElement        *list.Element[control.InterfaceUpdateCallback]
+}
+
+type udpEgressSpec struct {
+	interfaceIndex int
+	interfaceName  string
+	prefix         netip.Prefix
+}
+
+type udpEgressMember struct {
+	prefix netip.Prefix
+	conn   *net.UDPConn
+}
+
+type udpEgressPacket struct {
+	buffer *buf.Buffer
+	source netip.AddrPort
+}
+
+func NewUDPEgressPool(options UDPEgressPoolOptions) *UDPEgressPool {
+	return &UDPEgressPool{
+		logger:               options.Logger,
+		network:              options.Network,
+		control:              options.Control,
+		interfaceFinder:      options.InterfaceFinder,
+		interfaceMonitor:     options.InterfaceMonitor,
+		excludeInterface:     options.ExcludeInterface,
+		isExempt:             options.IsExempt,
+		anchorInterfaceIndex: -1,
+		members:              make(map[udpEgressSpec]*udpEgressMember),
+		packetChan:           make(chan udpEgressPacket, 128),
+	}
+}
+
+func (p *UDPEgressPool) Close() {
+	p.SetEgressPort(0)
+	p.access.Lock()
+	defer p.access.Unlock()
+	if p.finderElement != nil {
+		p.interfaceFinder.UnregisterInterfaceUpdateCallback(p.finderElement)
+		p.finderElement = nil
+	}
+}
+
+func (p *UDPEgressPool) SetEgressPort(port uint16) bool {
+	p.access.Lock()
+	defer p.access.Unlock()
+	if p.port == port {
+		return p.state.Load() != nil
+	}
+	if p.receiveDone != nil {
+		close(p.receiveDone)
+		p.receiveDone = nil
+	}
+	p.port = 0
+	p.state.Store(nil)
+	for spec, member := range p.members {
+		delete(p.members, spec)
+		member.conn.Close()
+	}
+	p.memberReaders.Wait()
+	for {
+		select {
+		case packet := <-p.packetChan:
+			packet.buffer.Release()
+		default:
+			goto drained
+		}
+	}
+drained:
+	p.anchorInterfaceIndex = -1
+	if port == 0 {
+		return false
+	}
+	p.port = port
+	defaultInterface := p.interfaceMonitor.DefaultInterface()
+	if defaultInterface != nil {
+		p.anchorInterfaceIndex = defaultInterface.Index
+	}
+	p.receiveDone = make(chan struct{})
+	if p.finderElement == nil {
+		p.finderElement = p.interfaceFinder.RegisterInterfaceUpdateCallback(func(interfaces []control.Interface) {
+			p.access.Lock()
+			defer p.access.Unlock()
+			p.rebuildLocked()
+		})
+	}
+	p.rebuildLocked()
+	return p.state.Load() != nil
+}
+
+func (p *UDPEgressPool) LookupEgress(destination netip.AddrPort) *net.UDPConn {
+	members := p.state.Load()
+	if members == nil {
+		return nil
+	}
+	address := destination.Addr().Unmap()
+	for _, member := range *members {
+		if member.prefix.Contains(address) {
+			return member.conn
+		}
+	}
+	return nil
+}
+
+func (p *UDPEgressPool) ReceiveEgress(buffer []byte) (int, netip.AddrPort, error) {
+	p.access.Lock()
+	receiveDone := p.receiveDone
+	p.access.Unlock()
+	if receiveDone == nil {
+		return 0, netip.AddrPort{}, net.ErrClosed
+	}
+	select {
+	case <-receiveDone:
+		return 0, netip.AddrPort{}, net.ErrClosed
+	default:
+	}
+	select {
+	case packet := <-p.packetChan:
+		copied := copy(buffer, packet.buffer.Bytes())
+		packet.buffer.Release()
+		return copied, packet.source, nil
+	case <-receiveDone:
+		return 0, netip.AddrPort{}, net.ErrClosed
+	}
+}
+
+func (p *UDPEgressPool) rebuildLocked() {
+	if p.port == 0 {
+		return
+	}
+	specs := make(map[udpEgressSpec]struct{})
+	if !p.isExempt() {
+		for _, networkInterface := range p.interfaceFinder.Interfaces() {
+			if networkInterface.Flags&net.FlagUp == 0 ||
+				networkInterface.Flags&net.FlagLoopback != 0 ||
+				networkInterface.Flags&net.FlagPointToPoint != 0 ||
+				networkInterface.Flags&net.FlagBroadcast == 0 ||
+				networkInterface.Index == p.anchorInterfaceIndex ||
+				networkInterface.Name == p.excludeInterface {
+				continue
+			}
+			for _, prefix := range networkInterface.Addresses {
+				if !prefix.Addr().IsGlobalUnicast() {
+					continue
+				}
+				if p.network == "udp4" && !prefix.Addr().Is4() {
+					continue
+				}
+				if p.network == "udp6" && prefix.Addr().Is4() {
+					continue
+				}
+				specs[udpEgressSpec{
+					interfaceIndex: networkInterface.Index,
+					interfaceName:  networkInterface.Name,
+					prefix:         prefix,
+				}] = struct{}{}
+			}
+		}
+	}
+	for spec, member := range p.members {
+		_, loaded := specs[spec]
+		if loaded {
+			continue
+		}
+		delete(p.members, spec)
+		member.conn.Close()
+	}
+	for spec := range specs {
+		_, loaded := p.members[spec]
+		if loaded {
+			continue
+		}
+		memberConn, err := p.listenMember(spec)
+		if err != nil {
+			p.logger.Warn(E.Cause(err, "listen egress member on ", spec.interfaceName, " (", spec.prefix.Addr(), ")"))
+			continue
+		}
+		member := &udpEgressMember{
+			prefix: spec.prefix.Masked(),
+			conn:   memberConn,
+		}
+		p.members[spec] = member
+		p.memberReaders.Add(1)
+		go p.readMember(member, p.receiveDone)
+	}
+	members := make([]*udpEgressMember, 0, len(p.members))
+	for _, member := range p.members {
+		members = append(members, member)
+	}
+	slices.SortFunc(members, func(firstMember, secondMember *udpEgressMember) int {
+		return secondMember.prefix.Bits() - firstMember.prefix.Bits()
+	})
+	if len(members) == 0 {
+		p.state.Store(nil)
+	} else {
+		p.state.Store(&members)
+	}
+}
+
+func (p *UDPEgressPool) listenMember(spec udpEgressSpec) (*net.UDPConn, error) {
+	var listenConfig net.ListenConfig
+	if runtime.GOOS == "darwin" || runtime.GOOS == "ios" {
+		listenConfig.Control = control.ReuseAddrOnly()
+	}
+	listenConfig.Control = control.Append(listenConfig.Control, control.DisableUDPNetReset())
+	listenConfig.Control = control.Append(listenConfig.Control, control.BindToInterface(p.interfaceFinder, spec.interfaceName, spec.interfaceIndex))
+	listenConfig.Control = control.Append(listenConfig.Control, p.control)
+	var network string
+	if spec.prefix.Addr().Is4() {
+		network = "udp4"
+	} else {
+		network = "udp6"
+	}
+	packetConn, err := listenConfig.ListenPacket(context.Background(), network, netip.AddrPortFrom(spec.prefix.Addr(), p.port).String())
+	if err != nil {
+		return nil, err
+	}
+	return packetConn.(*net.UDPConn), nil
+}
+
+func (p *UDPEgressPool) readMember(member *udpEgressMember, doneChan <-chan struct{}) {
+	defer p.memberReaders.Done()
+	for {
+		buffer := buf.NewSize(udpEgressBufferSize)
+		dataLength, source, err := member.conn.ReadFromUDPAddrPort(buffer.FreeBytes())
+		if err != nil {
+			buffer.Release()
+			return
+		}
+		buffer.Extend(dataLength)
+		select {
+		case p.packetChan <- udpEgressPacket{buffer: buffer, source: source}:
+		case <-doneChan:
+			buffer.Release()
+			return
+		default:
+			buffer.Release()
+		}
+	}
+}

udp_egress_conn.go

@@ -0,0 +1,124 @@
+package tun
+
+import (
+	"net"
+	"net/netip"
+	"sync"
+	"time"
+
+	"github.com/sagernet/sing/common/buf"
+	E "github.com/sagernet/sing/common/exceptions"
+)
+
+type UDPEgressConn struct {
+	anchor     *net.UDPConn
+	pool       *UDPEgressPool
+	packetChan chan udpEgressConnPacket
+	doneChan   chan struct{}
+	closeOnce  sync.Once
+	readWait   sync.WaitGroup
+}
+
+type udpEgressConnPacket struct {
+	buffer *buf.Buffer
+	source netip.AddrPort
+	err    error
+}
+
+func NewUDPEgressConn(anchor *net.UDPConn, pool *UDPEgressPool) *UDPEgressConn {
+	conn := &UDPEgressConn{
+		anchor:     anchor,
+		pool:       pool,
+		packetChan: make(chan udpEgressConnPacket, 64),
+		doneChan:   make(chan struct{}),
+	}
+	conn.readWait.Add(2)
+	go conn.read(anchor.ReadFromUDPAddrPort)
+	go conn.read(pool.ReceiveEgress)
+	return conn
+}
+
+func (c *UDPEgressConn) read(readPacket func([]byte) (int, netip.AddrPort, error)) {
+	defer c.readWait.Done()
+	for {
+		buffer := buf.NewSize(udpEgressBufferSize)
+		dataLength, source, err := readPacket(buffer.FreeBytes())
+		if err != nil {
+			buffer.Release()
+			if E.IsClosed(err) {
+				return
+			}
+			select {
+			case c.packetChan <- udpEgressConnPacket{err: err}:
+			case <-c.doneChan:
+				return
+			}
+			continue
+		}
+		buffer.Extend(dataLength)
+		select {
+		case c.packetChan <- udpEgressConnPacket{buffer: buffer, source: source}:
+		case <-c.doneChan:
+			buffer.Release()
+			return
+		}
+	}
+}
+
+func (c *UDPEgressConn) ReadFromUDPAddrPort(buffer []byte) (int, netip.AddrPort, error) {
+	select {
+	case packet := <-c.packetChan:
+		if packet.err != nil {
+			return 0, netip.AddrPort{}, packet.err
+		}
+		copied := copy(buffer, packet.buffer.Bytes())
+		packet.buffer.Release()
+		return copied, packet.source, nil
+	case <-c.doneChan:
+		return 0, netip.AddrPort{}, net.ErrClosed
+	}
+}
+
+func (c *UDPEgressConn) WriteToUDPAddrPort(buffer []byte, destination netip.AddrPort) (int, error) {
+	memberConn := c.pool.LookupEgress(destination)
+	if memberConn != nil {
+		return memberConn.WriteToUDPAddrPort(buffer, destination)
+	}
+	return c.anchor.WriteToUDPAddrPort(buffer, destination)
+}
+
+func (c *UDPEgressConn) LocalAddr() net.Addr {
+	return c.anchor.LocalAddr()
+}
+
+func (c *UDPEgressConn) SetDeadline(t time.Time) error {
+	return c.anchor.SetDeadline(t)
+}
+
+func (c *UDPEgressConn) SetReadDeadline(t time.Time) error {
+	return c.anchor.SetReadDeadline(t)
+}
+
+func (c *UDPEgressConn) SetWriteDeadline(t time.Time) error {
+	return c.anchor.SetWriteDeadline(t)
+}
+
+func (c *UDPEgressConn) Close() error {
+	c.closeOnce.Do(func() {
+		close(c.doneChan)
+		c.anchor.Close()
+		c.pool.Close()
+		c.readWait.Wait()
+		for {
+			select {
+			case packet := <-c.packetChan:
+				if packet.buffer != nil {
+					packet.buffer.Release()
+				}
+			default:
+				return
+			}
+		}
+	})
+	return nil
+}

udp_nat.go

@@ -0,0 +1,789 @@
+package tun
+
+import (
+	"context"
+	"io"
+	"net"
+	"net/netip"
+	"os"
+	"runtime"
+	"slices"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"github.com/sagernet/sing/common"
+	"github.com/sagernet/sing/common/buf"
+	"github.com/sagernet/sing/common/canceler"
+	"github.com/sagernet/sing/common/control"
+	"github.com/sagernet/sing/common/memory"
+	M "github.com/sagernet/sing/common/metadata"
+	N "github.com/sagernet/sing/common/network"
+	"github.com/sagernet/sing/common/pipe"
+	"github.com/sagernet/sing/common/x/list"
+	"github.com/sagernet/sing/contrab/freelru"
+	"github.com/sagernet/sing/contrab/maphash"
+)
+
+type NATMapping uint8
+
+const (
+	NATMappingEndpointIndependent NATMapping = iota
+	NATMappingAddressDependent
+	NATMappingAddressAndPortDependent
+)
+
+type NATFiltering uint8
+
+const (
+	NATFilteringEndpointIndependent NATFiltering = iota
+	NATFilteringAddressDependent
+	NATFilteringAddressAndPortDependent
+)
+
+type UDPNatPrepareFunc func(source M.Socksaddr, destination M.Socksaddr, userData any) (bool, context.Context, N.PacketWriter, N.CloseHandlerFunc)
+
+type UDPNatOptions struct {
+	Handler   N.UDPConnectionHandlerEx
+	Prepare   UDPNatPrepareFunc
+	Timeout   time.Duration
+	Shared    bool
+	Mapping   NATMapping
+	Filtering NATFiltering
+	MaxSize   uint32
+
+	InterfaceFinder  control.InterfaceFinder
+	ExcludeInterface []string
+}
+
+type udpNatSessionKey struct {
+	sourceAddr      netip.Addr
+	destinationAddr netip.Addr
+	sourcePort      uint16
+	destinationPort uint16
+	interfaceIndex  uint32
+}
+
+type udpNatFilterKey struct {
+	sessionID uint64
+	peer      netip.AddrPort
+}
+
+type udpNatEgressEntry struct {
+	prefix         netip.Prefix
+	interfaceIndex uint32
+}
+
+const udpNatEgressLinearThreshold = 8
+
+type udpNatEgressBuckets struct {
+	inet4 [256][]udpNatEgressEntry
+	inet6 [256][]udpNatEgressEntry
+}
+
+type udpNatEgressTable struct {
+	entries []udpNatEgressEntry
+	buckets *udpNatEgressBuckets
+}
+
+type UDPNat struct {
+	handler             N.UDPConnectionHandlerEx
+	prepare             UDPNatPrepareFunc
+	timeout             time.Duration
+	mapping             NATMapping
+	filtering           NATFiltering
+	cache               *freelru.Cache[udpNatSessionKey, *udpNatConn]
+	filterCache         *freelru.Cache[udpNatFilterKey, *udpNatConn]
+	nextFilterSessionID atomic.Uint64
+	interfaceFinder     control.InterfaceFinder
+	excludeInterface    []string
+	interfaceElement    *list.Element[control.InterfaceUpdateCallback]
+	egress              atomic.Pointer[udpNatEgressTable]
+	classAccess         sync.Mutex
+	classConns          map[uint32]map[*udpNatConn]struct{}
+	cleanup             *udpNatCleanupQueue
+	state               atomic.Uint32
+	lifecycleAccess     sync.Mutex
+	closeOnce           sync.Once
+	cleanupDone         chan struct{}
+	cleanupWait         sync.WaitGroup
+}
+
+func NewUDPNat(options UDPNatOptions) *UDPNat {
+	if options.Timeout == 0 {
+		panic("invalid timeout")
+	}
+	maxSize := options.MaxSize
+	if maxSize == 0 {
+		if runtime.GOOS == "ios" {
+			maxSize = 4096
+		} else if totalMemory := memory.Total(); totalMemory == 0 {
+			maxSize = 16384
+		} else {
+			maxSize = uint32(min(max(totalMemory/16384, 4096), 16384))
+		}
+	}
+	hasher := maphash.NewHasher[udpNatSessionKey]()
+	cache := common.Must1(freelru.New[udpNatSessionKey, *udpNatConn](maxSize, hasher.Hash32, options.Shared))
+	var filterCache *freelru.Cache[udpNatFilterKey, *udpNatConn]
+	if NATMapping(options.Filtering) > options.Mapping {
+		filterHasher := maphash.NewHasher[udpNatFilterKey]()
+		filterCache = common.Must1(freelru.New[udpNatFilterKey, *udpNatConn](maxSize, filterHasher.Hash32, options.Shared))
+	}
+	service := &UDPNat{
+		handler:          options.Handler,
+		prepare:          options.Prepare,
+		timeout:          options.Timeout,
+		mapping:          options.Mapping,
+		filtering:        options.Filtering,
+		cache:            cache,
+		filterCache:      filterCache,
+		interfaceFinder:  options.InterfaceFinder,
+		excludeInterface: options.ExcludeInterface,
+		classConns:       make(map[uint32]map[*udpNatConn]struct{}),
+		cleanupDone:      make(chan struct{}),
+	}
+	service.cleanup = newUDPNatCleanupQueue(service)
+	cache.SetLifetime(options.Timeout)
+	cache.SetHealthCheck(func(_ udpNatSessionKey, conn *udpNatConn) bool {
+		select {
+		case <-conn.doneChan:
+			return false
+		default:
+			return true
+		}
+	})
+	cache.SetOnEvict(func(_ udpNatSessionKey, conn *udpNatConn) {
+		conn.closeFromCache()
+	})
+	if filterCache != nil {
+		filterCache.SetOnEvict(func(key udpNatFilterKey, conn *udpNatConn) {
+			conn.removeFilterPeer(key.peer)
+		})
+	}
+	return service
+}
+
+func (s *UDPNat) Close() error {
+	s.closeOnce.Do(func() {
+		s.lifecycleAccess.Lock()
+		previousState := s.state.Swap(udpNatStateClosed)
+		if previousState == udpNatStateStarted {
+			close(s.cleanupDone)
+		}
+		s.lifecycleAccess.Unlock()
+		if previousState == udpNatStateStarted {
+			s.cleanupWait.Wait()
+		}
+		if s.interfaceElement != nil {
+			s.interfaceFinder.UnregisterInterfaceUpdateCallback(s.interfaceElement)
+			s.interfaceElement = nil
+		}
+		s.cache.Purge()
+		if s.filterCache != nil {
+			s.filterCache.Purge()
+		}
+		s.cleanup.clear()
+	})
+	return nil
+}
+
+func (s *UDPNat) reloadInterfaces() {
+	s.updateInterfaces(s.interfaceFinder.Interfaces())
+}
+
+func (s *UDPNat) updateInterfaces(interfaces []control.Interface) {
+	var entries []udpNatEgressEntry
+	for _, networkInterface := range interfaces {
+		if networkInterface.Flags&net.FlagUp == 0 ||
+			networkInterface.Flags&net.FlagLoopback != 0 ||
+			networkInterface.Flags&net.FlagPointToPoint != 0 ||
+			networkInterface.Flags&net.FlagBroadcast == 0 {
+			continue
+		}
+		if slices.Contains(s.excludeInterface, networkInterface.Name) {
+			continue
+		}
+		for _, prefix := range networkInterface.Addresses {
+			if !prefix.Addr().IsGlobalUnicast() {
+				continue
+			}
+			entries = append(entries, udpNatEgressEntry{prefix.Masked(), uint32(networkInterface.Index)})
+		}
+	}
+	s.egress.Store(newUDPNatEgressTable(entries))
+	var closeConns []*udpNatConn
+	s.classAccess.Lock()
+	for interfaceIndex, conns := range s.classConns {
+		if !slices.ContainsFunc(entries, func(entry udpNatEgressEntry) bool {
+			return entry.interfaceIndex == interfaceIndex
+		}) {
+			for conn := range conns {
+				closeConns = append(closeConns, conn)
+			}
+			delete(s.classConns, interfaceIndex)
+		}
+	}
+	s.classAccess.Unlock()
+	for _, conn := range closeConns {
+		conn.Close()
+	}
+}
+
+func (s *UDPNat) classify(destination M.Socksaddr) uint32 {
+	table := s.egress.Load()
+	if table == nil || !destination.IsIP() {
+		return 0
+	}
+	return table.lookup(destination.Addr.Unmap())
+}
+
+func newUDPNatEgressTable(entries []udpNatEgressEntry) *udpNatEgressTable {
+	entries = slices.Clone(entries)
+	slices.SortStableFunc(entries, func(a, b udpNatEgressEntry) int {
+		return b.prefix.Bits() - a.prefix.Bits()
+	})
+	table := &udpNatEgressTable{entries: entries}
+	if len(entries) <= udpNatEgressLinearThreshold {
+		return table
+	}
+	buckets := new(udpNatEgressBuckets)
+	for _, entry := range entries {
+		address := entry.prefix.Addr().Unmap()
+		bits := entry.prefix.Bits()
+		var target *[256][]udpNatEgressEntry
+		var firstByte byte
+		if address.Is4() {
+			target = &buckets.inet4
+			firstByte = address.As4()[0]
+		} else {
+			target = &buckets.inet6
+			firstByte = address.As16()[0]
+		}
+		if bits >= 8 {
+			target[firstByte] = append(target[firstByte], entry)
+			continue
+		}
+		var mask byte
+		if bits > 0 {
+			mask = ^byte(0) << (8 - bits)
+		}
+		firstByte &= mask
+		for index := 0; index < 1<<(8-bits); index++ {
+			bucketIndex := firstByte + byte(index)
+			target[bucketIndex] = append(target[bucketIndex], entry)
+		}
+	}
+	table.buckets = buckets
+	return table
+}
+
+func (t *udpNatEgressTable) lookup(address netip.Addr) uint32 {
+	entries := t.entries
+	if t.buckets != nil {
+		if address.Is4() {
+			entries = t.buckets.inet4[address.As4()[0]]
+		} else {
+			entries = t.buckets.inet6[address.As16()[0]]
+		}
+	}
+	for _, entry := range entries {
+		if entry.prefix.Contains(address) {
+			return entry.interfaceIndex
+		}
+	}
+	return 0
+}
+
+func (s *UDPNat) registerClass(conn *udpNatConn) {
+	s.classAccess.Lock()
+	conns := s.classConns[conn.interfaceIndex]
+	if conns == nil {
+		conns = make(map[*udpNatConn]struct{})
+		s.classConns[conn.interfaceIndex] = conns
+	}
+	conns[conn] = struct{}{}
+	s.classAccess.Unlock()
+}
+
+func (s *UDPNat) unregisterClass(conn *udpNatConn) {
+	s.classAccess.Lock()
+	conns := s.classConns[conn.interfaceIndex]
+	if conns != nil {
+		delete(conns, conn)
+		if len(conns) == 0 {
+			delete(s.classConns, conn.interfaceIndex)
+		}
+	}
+	s.classAccess.Unlock()
+}
+
+func (s *UDPNat) NewPacket(bufferSlices [][]byte, source M.Socksaddr, destination M.Socksaddr, userData any) {
+	conn, ok := s.getOrCreateConn(source, destination, userData)
+	if !ok {
+		return
+	}
+	readWaitOptions := conn.loadReadWaitOptions()
+	var dataLen int
+	for _, bufferSlice := range bufferSlices {
+		dataLen += len(bufferSlice)
+	}
+	buffer := readWaitOptions.NewBufferSize(dataLen)
+	for _, bufferSlice := range bufferSlices {
+		buffer.Write(bufferSlice)
+	}
+	readWaitOptions.PostReturn(buffer)
+	conn.enqueue(buffer, destination)
+}
+
+func (s *UDPNat) getOrCreateConn(source M.Socksaddr, destination M.Socksaddr, userData any) (*udpNatConn, bool) {
+	if s.state.Load() != udpNatStateStarted {
+		return nil, false
+	}
+	key := udpNatSessionKey{
+		sourceAddr: source.Addr.Unmap(),
+		sourcePort: source.Port,
+	}
+	switch s.mapping {
+	case NATMappingEndpointIndependent:
+		key.interfaceIndex = s.classify(destination)
+	case NATMappingAddressDependent:
+		key.destinationAddr = destination.Addr.Unmap()
+	case NATMappingAddressAndPortDependent:
+		key.destinationAddr = destination.Addr.Unmap()
+		key.destinationPort = destination.Port
+	}
+	var (
+		newContext context.Context
+		newOnClose N.CloseHandlerFunc
+	)
+	conn, loaded, ok := s.cache.GetAndRefreshOrAdd(key, func() (*udpNatConn, bool) {
+		ok, ctx, writer, onClose := s.prepare(source, destination, userData)
+		if !ok {
+			return nil, false
+		}
+		newConn := &udpNatConn{
+			service:      s,
+			key:          key,
+			writer:       writer,
+			localAddr:    source,
+			packetChan:   make(chan *N.PacketBuffer, 64),
+			doneChan:     make(chan struct{}),
+			readDeadline: pipe.MakeDeadline(),
+		}
+		newConn.cleanupEntry = &udpNatCleanupEntry{
+			conn:  newConn,
+			index: -1,
+		}
+		if s.filtering != NATFilteringEndpointIndependent {
+			if destination.IsIP() {
+				newConn.filterPeer = s.filterPeer(destination)
+				newConn.filterPeerValid = true
+			}
+			if s.filterCache != nil {
+				filterSessionID := s.nextFilterSessionID.Add(1)
+				if filterSessionID == 0 {
+					filterSessionID = s.nextFilterSessionID.Add(1)
+				}
+				newConn.filterSessionID = filterSessionID
+			}
+		}
+		interfaceIndex := key.interfaceIndex
+		if s.mapping != NATMappingEndpointIndependent {
+			interfaceIndex = s.classify(destination)
+		}
+		if interfaceIndex != 0 {
+			newConn.interfaceIndex = interfaceIndex
+			s.registerClass(newConn)
+		}
+		newContext = ctx
+		newOnClose = onClose
+		return newConn, true
+	})
+	if !ok {
+		return nil, false
+	}
+	if s.state.Load() != udpNatStateStarted {
+		conn.Close()
+		s.cache.Peek(key)
+		return nil, false
+	}
+	if !loaded {
+		s.cleanup.addOrUpdate(conn.cleanupEntry, time.Now().Add(s.timeout))
+		if conn.isClosed() {
+			return nil, false
+		}
+		go s.handler.NewPacketConnectionEx(newContext, conn, source, destination, newOnClose)
+	}
+	conn.addFilterPeer(destination)
+	return conn, true
+}
+
+func (c *udpNatConn) enqueue(buffer *buf.Buffer, destination M.Socksaddr) {
+	c.packetAccess.RLock()
+	select {
+	case <-c.doneChan:
+		buffer.Release()
+		c.packetAccess.RUnlock()
+		return
+	default:
+	}
+	packet := N.NewPacketBuffer()
+	*packet = N.PacketBuffer{
+		Buffer:      buffer,
+		Destination: destination,
+	}
+	select {
+	case c.packetChan <- packet:
+	default:
+		packet.Buffer.Release()
+		N.PutPacketBuffer(packet)
+	}
+	c.packetAccess.RUnlock()
+}
+
+func (s *UDPNat) NewPacketBatch(buffers []*buf.Buffer, sources []M.Socksaddr, destination M.Socksaddr, userData any) {
+	if len(buffers) != len(sources) {
+		buf.ReleaseMulti(buffers)
+		return
+	}
+	for index, buffer := range buffers {
+		conn, ok := s.getOrCreateConn(sources[index], destination, userData)
+		if !ok {
+			buffer.Release()
+			continue
+		}
+		readWaitOptions := conn.loadReadWaitOptions()
+		conn.enqueue(readWaitOptions.Copy(buffer), destination)
+	}
+}
+
+func (s *UDPNat) filterPeer(destination M.Socksaddr) netip.AddrPort {
+	if s.filtering == NATFilteringAddressDependent {
+		return netip.AddrPortFrom(destination.Addr.Unmap(), 0)
+	}
+	return netip.AddrPortFrom(destination.Addr.Unmap(), destination.Port)
+}
+
+func (s *UDPNat) Purge() {
+	if s.filterCache != nil {
+		s.filterCache.Purge()
+	}
+	s.cache.Purge()
+}
+
+func (s *UDPNat) PurgeExpired() {
+	s.cache.PurgeExpired()
+}
+
+var (
+	_ N.PacketConn                 = (*udpNatConn)(nil)
+	_ canceler.PacketConn          = (*udpNatConn)(nil)
+	_ N.PacketBatchReadWaitCreator = (*udpNatConn)(nil)
+	_ N.PacketBatchWriteCreator    = (*udpNatConn)(nil)
+)
+
+type udpNatConn struct {
+	service         *UDPNat
+	key             udpNatSessionKey
+	interfaceIndex  uint32
+	writer          N.PacketWriter
+	localAddr       M.Socksaddr
+	packetChan      chan *N.PacketBuffer
+	packetAccess    sync.RWMutex
+	closeOnce       sync.Once
+	doneChan        chan struct{}
+	readDeadline    pipe.Deadline
+	readWaitOptions atomic.Pointer[N.ReadWaitOptions]
+	readBatch       *udpNatReadBatch
+	cleanupEntry    *udpNatCleanupEntry
+	filterSessionID uint64
+	filterPeer      netip.AddrPort
+	filterPeerValid bool
+	filterAccess    sync.Mutex
+	filterPeers     map[netip.AddrPort]struct{}
+}
+
+type udpNatReadBatch struct {
+	buffers      []*buf.Buffer
+	destinations []M.Socksaddr
+}
+
+func (c *udpNatConn) loadReadWaitOptions() N.ReadWaitOptions {
+	options := c.readWaitOptions.Load()
+	if options == nil {
+		return N.ReadWaitOptions{}
+	}
+	return *options
+}
+
+func (c *udpNatConn) addFilterPeer(destination M.Socksaddr) {
+	if c.filterSessionID == 0 || !destination.IsIP() {
+		return
+	}
+	key := udpNatFilterKey{
+		sessionID: c.filterSessionID,
+		peer:      c.service.filterPeer(destination),
+	}
+	if c.filterPeerValid && c.filterPeer == key.peer {
+		return
+	}
+	if c.isClosed() || c.service.state.Load() != udpNatStateStarted {
+		return
+	}
+	c.service.filterCache.Add(key, c)
+	c.filterAccess.Lock()
+	if c.isClosed() || c.service.state.Load() != udpNatStateStarted {
+		c.filterAccess.Unlock()
+		c.service.filterCache.Remove(key)
+		return
+	}
+	if c.filterPeers == nil {
+		c.filterPeers = make(map[netip.AddrPort]struct{})
+	}
+	c.filterPeers[key.peer] = struct{}{}
+	c.filterAccess.Unlock()
+	filterConn, loaded := c.service.filterCache.Peek(key)
+	if !loaded || filterConn != c {
+		c.removeFilterPeer(key.peer)
+		return
+	}
+	if c.isClosed() || c.service.state.Load() != udpNatStateStarted {
+		c.service.filterCache.Remove(key)
+	}
+}
+
+func (c *udpNatConn) removeFilterPeer(peer netip.AddrPort) {
+	c.filterAccess.Lock()
+	delete(c.filterPeers, peer)
+	c.filterAccess.Unlock()
+}
+
+func (c *udpNatConn) clearFilterPeers() {
+	if c.filterSessionID == 0 {
+		return
+	}
+	c.filterAccess.Lock()
+	filterPeers := c.filterPeers
+	c.filterPeers = nil
+	c.filterAccess.Unlock()
+	for peer := range filterPeers {
+		c.service.filterCache.Remove(udpNatFilterKey{
+			sessionID: c.filterSessionID,
+			peer:      peer,
+		})
+	}
+}
+
+func (c *udpNatConn) allowPeer(destination M.Socksaddr) bool {
+	if c.service.filtering == NATFilteringEndpointIndependent || !destination.IsIP() {
+		return true
+	}
+	peer := c.service.filterPeer(destination)
+	if c.filterPeerValid && c.filterPeer == peer {
+		return true
+	}
+	if c.filterSessionID == 0 {
+		return false
+	}
+	filterConn, loaded := c.service.filterCache.Get(udpNatFilterKey{
+		sessionID: c.filterSessionID,
+		peer:      peer,
+	})
+	return loaded && filterConn == c
+}
+
+func (c *udpNatConn) ReadPacket(buffer *buf.Buffer) (addr M.Socksaddr, err error) {
+	select {
+	case p := <-c.packetChan:
+		_, err = buffer.ReadOnceFrom(p.Buffer)
+		destination := p.Destination
+		p.Buffer.Release()
+		N.PutPacketBuffer(p)
+		return destination, err
+	case <-c.doneChan:
+		return M.Socksaddr{}, io.ErrClosedPipe
+	case <-c.readDeadline.Wait():
+		return M.Socksaddr{}, os.ErrDeadlineExceeded
+	}
+}
+
+func (c *udpNatConn) WritePacket(buffer *buf.Buffer, destination M.Socksaddr) error {
+	if !c.allowPeer(destination) {
+		buffer.Release()
+		return nil
+	}
+	return c.writer.WritePacket(buffer, destination)
+}
+
+func (c *udpNatConn) CreatePacketBatchWriter() (N.PacketBatchWriter, bool) {
+	if c.service.filtering != NATFilteringEndpointIndependent {
+		return nil, false
+	}
+	if creator, isCreator := c.writer.(N.PacketBatchWriteCreator); isCreator {
+		return creator.CreatePacketBatchWriter()
+	}
+	if writer, isWriter := c.writer.(N.PacketBatchWriter); isWriter {
+		return writer, true
+	}
+	return nil, false
+}
+
+func (c *udpNatConn) InitializeReadWaiter(options N.ReadWaitOptions) (needCopy bool) {
+	c.readWaitOptions.Store(&options)
+	return false
+}
+
+func (c *udpNatConn) WaitReadPacket() (buffer *buf.Buffer, destination M.Socksaddr, err error) {
+	return c.waitReadPacket(c.loadReadWaitOptions())
+}
+
+func (c *udpNatConn) waitReadPacket(options N.ReadWaitOptions) (buffer *buf.Buffer, destination M.Socksaddr, err error) {
+	select {
+	case packet := <-c.packetChan:
+		buffer = options.Copy(packet.Buffer)
+		destination = packet.Destination
+		N.PutPacketBuffer(packet)
+		return
+	case <-c.doneChan:
+		return nil, M.Socksaddr{}, io.ErrClosedPipe
+	case <-c.readDeadline.Wait():
+		return nil, M.Socksaddr{}, os.ErrDeadlineExceeded
+	}
+}
+
+func (c *udpNatConn) CreatePacketBatchReadWaiter() (N.PacketBatchReadWaiter, bool) {
+	return c, true
+}
+
+func (c *udpNatConn) WaitReadPackets() (buffers []*buf.Buffer, destinations []M.Socksaddr, err error) {
+	options := c.loadReadWaitOptions()
+	buffer, destination, err := c.waitReadPacket(options)
+	if err != nil {
+		return nil, nil, err
+	}
+	batchSize := options.BatchSize
+	if batchSize <= 0 {
+		batchSize = 1
+	}
+	batch := c.readBatch
+	if batch == nil {
+		batch = new(udpNatReadBatch)
+		c.readBatch = batch
+	} else {
+		clear(batch.buffers)
+		clear(batch.destinations)
+	}
+	buffers = batch.buffers[:0]
+	destinations = batch.destinations[:0]
+	defer func() {
+		batch.buffers = buffers
+		batch.destinations = destinations
+	}()
+	buffers = append(buffers, buffer)
+	destinations = append(destinations, destination)
+	for len(buffers) < batchSize {
+		select {
+		case packet := <-c.packetChan:
+			buffers = append(buffers, options.Copy(packet.Buffer))
+			destinations = append(destinations, packet.Destination)
+			N.PutPacketBuffer(packet)
+		default:
+			return
+		}
+	}
+	return
+}
+
+func (c *udpNatConn) Timeout() time.Duration {
+	rawConn, lifetime, loaded := c.service.cache.PeekWithLifetime(c.key)
+	if !loaded || rawConn != c {
+		return 0
+	}
+	if lifetime.UnixMilli() == 0 {
+		return 0
+	}
+	return time.Until(lifetime)
+}
+
+func (c *udpNatConn) SetTimeout(timeout time.Duration) bool {
+	updated := c.service.cache.UpdateLifetime(c.key, c, timeout)
+	if !updated {
+		return false
+	}
+	if timeout == 0 {
+		c.service.cleanup.remove(c.cleanupEntry)
+	} else {
+		c.service.cleanup.addOrUpdate(c.cleanupEntry, time.Now().Add(timeout))
+	}
+	return true
+}
+
+func (c *udpNatConn) Close() error {
+	c.close()
+	if c.service.state.Load() == udpNatStateStarted {
+		c.service.cleanup.addOrUpdate(c.cleanupEntry, time.Now())
+	}
+	return nil
+}
+
+func (c *udpNatConn) close() {
+	c.closeOnce.Do(func() {
+		c.packetAccess.Lock()
+		close(c.doneChan)
+		drained := false
+		for !drained {
+			select {
+			case packet := <-c.packetChan:
+				packet.Buffer.Release()
+				N.PutPacketBuffer(packet)
+			default:
+				drained = true
+			}
+		}
+		c.packetAccess.Unlock()
+		c.clearFilterPeers()
+		if c.interfaceIndex != 0 {
+			c.service.unregisterClass(c)
+		}
+	})
+}
+
+func (c *udpNatConn) closeFromCache() {
+	c.close()
+	c.service.cleanup.remove(c.cleanupEntry)
+}
+
+func (c *udpNatConn) isClosed() bool {
+	select {
+	case <-c.doneChan:
+		return true
+	default:
+		return false
+	}
+}
+
+func (c *udpNatConn) LocalAddr() net.Addr {
+	return c.localAddr
+}
+
+func (c *udpNatConn) RemoteAddr() net.Addr {
+	return M.Socksaddr{}
+}
+
+func (c *udpNatConn) SetDeadline(t time.Time) error {
+	return os.ErrInvalid
+}
+
+func (c *udpNatConn) SetReadDeadline(t time.Time) error {
+	c.readDeadline.Set(t)
+	return nil
+}
+
+func (c *udpNatConn) SetWriteDeadline(t time.Time) error {
+	return os.ErrInvalid
+}
+
+func (c *udpNatConn) Upstream() any {
+	return c.writer
+}

udp_nat_cleanup.go

@@ -0,0 +1,219 @@
+package tun
+
+import (
+	"container/heap"
+	"os"
+	"sync"
+	"time"
+)
+
+const (
+	udpNatStateCreated uint32 = iota
+	udpNatStateStarted
+	udpNatStateClosed
+)
+
+func (s *UDPNat) Start() error {
+	s.lifecycleAccess.Lock()
+	defer s.lifecycleAccess.Unlock()
+	switch s.state.Load() {
+	case udpNatStateCreated:
+		if s.interfaceFinder != nil {
+			s.interfaceElement = s.interfaceFinder.RegisterInterfaceUpdateCallback(s.updateInterfaces)
+			s.reloadInterfaces()
+		}
+		s.state.Store(udpNatStateStarted)
+		s.cleanupWait.Add(1)
+		go s.cleanupLoop()
+		return nil
+	case udpNatStateStarted:
+		return nil
+	default:
+		return os.ErrClosed
+	}
+}
+
+type udpNatCleanupEntry struct {
+	conn     *udpNatConn
+	deadline time.Time
+	index    int
+}
+
+type udpNatCleanupQueue struct {
+	service *UDPNat
+	access  sync.Mutex
+	wake    chan struct{}
+	entries udpNatCleanupHeap
+}
+
+func newUDPNatCleanupQueue(service *UDPNat) *udpNatCleanupQueue {
+	queue := &udpNatCleanupQueue{
+		service: service,
+		wake:    make(chan struct{}, 1),
+	}
+	return queue
+}
+
+func (q *udpNatCleanupQueue) notify() {
+	select {
+	case q.wake <- struct{}{}:
+	default:
+	}
+}
+
+func (q *udpNatCleanupQueue) addOrUpdate(entry *udpNatCleanupEntry, deadline time.Time) {
+	if entry == nil || q.service.state.Load() == udpNatStateClosed {
+		return
+	}
+	q.access.Lock()
+	now := time.Now()
+	if entry.conn.isClosed() && deadline.After(now) {
+		deadline = now
+	}
+	entry.deadline = deadline
+	if entry.index == -1 {
+		heap.Push(&q.entries, entry)
+	} else {
+		heap.Fix(&q.entries, entry.index)
+	}
+	q.access.Unlock()
+	q.notify()
+}
+
+func (q *udpNatCleanupQueue) remove(entry *udpNatCleanupEntry) {
+	if entry == nil {
+		return
+	}
+	q.access.Lock()
+	if entry.index != -1 {
+		heap.Remove(&q.entries, entry.index)
+	}
+	q.access.Unlock()
+	q.notify()
+}
+
+func (q *udpNatCleanupQueue) next() (time.Time, bool) {
+	q.access.Lock()
+	defer q.access.Unlock()
+	if len(q.entries) == 0 {
+		return time.Time{}, false
+	}
+	return q.entries[0].deadline, true
+}
+
+func (q *udpNatCleanupQueue) popDue(now time.Time) *udpNatCleanupEntry {
+	q.access.Lock()
+	defer q.access.Unlock()
+	if len(q.entries) == 0 || q.entries[0].deadline.After(now) {
+		return nil
+	}
+	return heap.Pop(&q.entries).(*udpNatCleanupEntry)
+}
+
+func (q *udpNatCleanupQueue) clear() {
+	q.access.Lock()
+	for _, entry := range q.entries {
+		entry.index = -1
+	}
+	clear(q.entries)
+	q.entries = nil
+	q.access.Unlock()
+	q.notify()
+}
+
+type udpNatCleanupHeap []*udpNatCleanupEntry
+
+func (h udpNatCleanupHeap) Len() int {
+	return len(h)
+}
+
+func (h udpNatCleanupHeap) Less(i int, j int) bool {
+	return h[i].deadline.Before(h[j].deadline)
+}
+
+func (h udpNatCleanupHeap) Swap(i int, j int) {
+	h[i], h[j] = h[j], h[i]
+	h[i].index = i
+	h[j].index = j
+}
+
+func (h *udpNatCleanupHeap) Push(value any) {
+	entry := value.(*udpNatCleanupEntry)
+	entry.index = len(*h)
+	*h = append(*h, entry)
+}
+
+func (h *udpNatCleanupHeap) Pop() any {
+	oldItems := *h
+	lastIndex := len(oldItems) - 1
+	entry := oldItems[lastIndex]
+	oldItems[lastIndex] = nil
+	entry.index = -1
+	*h = oldItems[:lastIndex]
+	return entry
+}
+
+func (s *UDPNat) cleanupLoop() {
+	defer s.cleanupWait.Done()
+	timer := time.NewTimer(time.Hour)
+	stopUDPNatCleanupTimer(timer)
+	defer timer.Stop()
+	for {
+		select {
+		case <-s.cleanup.wake:
+		default:
+		}
+		deadline, loaded := s.cleanup.next()
+		if !loaded {
+			select {
+			case <-s.cleanupDone:
+				return
+			case <-s.cleanup.wake:
+				continue
+			}
+		}
+		waitDuration := time.Until(deadline)
+		if waitDuration > 0 {
+			timer.Reset(waitDuration)
+			select {
+			case <-s.cleanupDone:
+				stopUDPNatCleanupTimer(timer)
+				return
+			case <-s.cleanup.wake:
+				stopUDPNatCleanupTimer(timer)
+				continue
+			case <-timer.C:
+			}
+		}
+		for {
+			entry := s.cleanup.popDue(time.Now())
+			if entry == nil {
+				break
+			}
+			s.cleanupEntry(entry)
+		}
+	}
+}
+
+func (s *UDPNat) cleanupEntry(entry *udpNatCleanupEntry) {
+	conn, lifetime, loaded := s.cache.PeekWithLifetime(entry.conn.key)
+	if !loaded || conn != entry.conn {
+		return
+	}
+	if lifetime.UnixMilli() == 0 {
+		return
+	}
+	if conn.isClosed() {
+		lifetime = time.Now()
+	}
+	s.cleanup.addOrUpdate(entry, lifetime)
+}
+
+func stopUDPNatCleanupTimer(timer *time.Timer) {
+	if !timer.Stop() {
+		select {
+		case <-timer.C:
+		default:
+		}
+	}
+}