Add checksum offload for Linux

internal/clashtcpip/icmp.go

@@ -35,6 +35,6 @@ func (p ICMPPacket) SetChecksum(sum [2]byte) {
 }
 
 func (p ICMPPacket) ResetChecksum() {
-	p.SetChecksum(zeroChecksum)
+	p.SetChecksum(ZeroChecksum)
 	p.SetChecksum(Checksum(0, p))
 }

internal/clashtcpip/icmpv6.go

@@ -167,6 +167,6 @@ func (b ICMPv6Packet) Payload() []byte {
 }
 
 func (b ICMPv6Packet) ResetChecksum(psum uint32) {
-	b.SetChecksum(zeroChecksum)
+	b.SetChecksum(ZeroChecksum)
 	b.SetChecksum(Checksum(psum, b))
 }

internal/clashtcpip/ip.go

@@ -160,7 +160,7 @@ func (p IPv4Packet) DecTimeToLive() {
 }
 
 func (p IPv4Packet) ResetChecksum() {
-	p.SetChecksum(zeroChecksum)
+	p.SetChecksum(ZeroChecksum)
 	p.SetChecksum(Checksum(0, p[:p.HeaderLen()]))
 }
 

internal/clashtcpip/tcp.go

@@ -51,7 +51,7 @@ func (p TCPPacket) SetChecksum(sum [2]byte) {
 }
 
 func (p TCPPacket) ResetChecksum(psum uint32) {
-	p.SetChecksum(zeroChecksum)
+	p.SetChecksum(ZeroChecksum)
 	p.SetChecksum(Checksum(psum, p))
 }
 

internal/clashtcpip/tcpip.go

@@ -1,6 +1,6 @@
 package clashtcpip
 
-var zeroChecksum = [2]byte{0x00, 0x00}
+var ZeroChecksum = [2]byte{0x00, 0x00}
 
 var SumFnc = SumCompat
 

internal/clashtcpip/udp.go

@@ -46,7 +46,7 @@ func (p UDPPacket) SetChecksum(sum [2]byte) {
 }
 
 func (p UDPPacket) ResetChecksum(psum uint32) {
-	p.SetChecksum(zeroChecksum)
+	p.SetChecksum(ZeroChecksum)
 	p.SetChecksum(Checksum(psum, p))
 }
 

stack_mixed.go

@@ -91,17 +91,18 @@ func (m *Mixed) tunLoop() {
 		m.wintunLoop(winTun)
 		return
 	}
-	if batchTUN, isBatchTUN := m.tun.(BatchTUN); isBatchTUN {
-		batchSize := batchTUN.BatchSize()
+	if linuxTUN, isLinuxTUN := m.tun.(LinuxTUN); isLinuxTUN {
+		m.frontHeadroom = linuxTUN.FrontHeadroom()
+		m.txChecksumOffload = linuxTUN.TXChecksumOffload()
+		batchSize := linuxTUN.BatchSize()
 		if batchSize > 1 {
-			m.batchLoop(batchTUN, batchSize)
+			m.batchLoop(linuxTUN, batchSize)
 			return
 		}
 	}
-	frontHeadroom := m.tun.FrontHeadroom()
-	packetBuffer := make([]byte, m.mtu+frontHeadroom+PacketOffset)
+	packetBuffer := make([]byte, m.mtu+PacketOffset)
 	for {
-		n, err := m.tun.Read(packetBuffer[frontHeadroom:])
+		n, err := m.tun.Read(packetBuffer)
 		if err != nil {
 			if E.IsClosed(err) {
 				return
@@ -111,8 +112,8 @@ func (m *Mixed) tunLoop() {
 		if n < clashtcpip.IPv4PacketMinLength {
 			continue
 		}
-		rawPacket := packetBuffer[:frontHeadroom+n]
-		packet := packetBuffer[frontHeadroom+PacketOffset : frontHeadroom+n]
+		rawPacket := packetBuffer[:n]
+		packet := packetBuffer[PacketOffset:n]
 		if m.processPacket(packet) {
 			_, err = m.tun.Write(rawPacket)
 			if err != nil {
@@ -142,16 +143,15 @@ func (m *Mixed) wintunLoop(winTun WinTun) {
 	}
 }
 
-func (m *Mixed) batchLoop(linuxTUN BatchTUN, batchSize int) {
-	frontHeadroom := m.tun.FrontHeadroom()
+func (m *Mixed) batchLoop(linuxTUN LinuxTUN, batchSize int) {
 	packetBuffers := make([][]byte, batchSize)
 	writeBuffers := make([][]byte, batchSize)
 	packetSizes := make([]int, batchSize)
 	for i := range packetBuffers {
-		packetBuffers[i] = make([]byte, m.mtu+frontHeadroom)
+		packetBuffers[i] = make([]byte, m.mtu+m.frontHeadroom)
 	}
 	for {
-		n, err := linuxTUN.BatchRead(packetBuffers, frontHeadroom, packetSizes)
+		n, err := linuxTUN.BatchRead(packetBuffers, m.frontHeadroom, packetSizes)
 		if err != nil {
 			if E.IsClosed(err) {
 				return
@@ -167,13 +167,13 @@ func (m *Mixed) batchLoop(linuxTUN BatchTUN, batchSize int) {
 				continue
 			}
 			packetBuffer := packetBuffers[i]
-			packet := packetBuffer[frontHeadroom : frontHeadroom+packetSize]
+			packet := packetBuffer[m.frontHeadroom : m.frontHeadroom+packetSize]
 			if m.processPacket(packet) {
-				writeBuffers = append(writeBuffers, packetBuffer[:frontHeadroom+packetSize])
+				writeBuffers = append(writeBuffers, packetBuffer[:m.frontHeadroom+packetSize])
 			}
 		}
 		if len(writeBuffers) > 0 {
-			err = linuxTUN.BatchWrite(writeBuffers, frontHeadroom)
+			err = linuxTUN.BatchWrite(writeBuffers, m.frontHeadroom)
 			if err != nil {
 				m.logger.Trace(E.Cause(err, "batch write packet"))
 			}

stack_system.go

@@ -41,6 +41,8 @@ type System struct {
 	udpNat             *udpnat.Service[netip.AddrPort]
 	bindInterface      bool
 	interfaceFinder    control.InterfaceFinder
+	frontHeadroom      int
+	txChecksumOffload  bool
 }
 
 type Session struct {
@@ -144,17 +146,18 @@ func (s *System) tunLoop() {
 		s.wintunLoop(winTun)
 		return
 	}
-	if batchTUN, isBatchTUN := s.tun.(BatchTUN); isBatchTUN {
-		batchSize := batchTUN.BatchSize()
+	if linuxTUN, isLinuxTUN := s.tun.(LinuxTUN); isLinuxTUN {
+		s.frontHeadroom = linuxTUN.FrontHeadroom()
+		s.txChecksumOffload = linuxTUN.TXChecksumOffload()
+		batchSize := linuxTUN.BatchSize()
 		if batchSize > 1 {
-			s.batchLoop(batchTUN, batchSize)
+			s.batchLoop(linuxTUN, batchSize)
 			return
 		}
 	}
-	frontHeadroom := s.tun.FrontHeadroom()
-	packetBuffer := make([]byte, s.mtu+frontHeadroom+PacketOffset)
+	packetBuffer := make([]byte, s.mtu+PacketOffset)
 	for {
-		n, err := s.tun.Read(packetBuffer[frontHeadroom:])
+		n, err := s.tun.Read(packetBuffer)
 		if err != nil {
 			if E.IsClosed(err) {
 				return
@@ -164,8 +167,8 @@ func (s *System) tunLoop() {
 		if n < clashtcpip.IPv4PacketMinLength {
 			continue
 		}
-		rawPacket := packetBuffer[:frontHeadroom+n]
-		packet := packetBuffer[frontHeadroom+PacketOffset : frontHeadroom+n]
+		rawPacket := packetBuffer[:n]
+		packet := packetBuffer[PacketOffset:n]
 		if s.processPacket(packet) {
 			_, err = s.tun.Write(rawPacket)
 			if err != nil {
@@ -195,16 +198,15 @@ func (s *System) wintunLoop(winTun WinTun) {
 	}
 }
 
-func (s *System) batchLoop(linuxTUN BatchTUN, batchSize int) {
-	frontHeadroom := s.tun.FrontHeadroom()
+func (s *System) batchLoop(linuxTUN LinuxTUN, batchSize int) {
 	packetBuffers := make([][]byte, batchSize)
 	writeBuffers := make([][]byte, batchSize)
 	packetSizes := make([]int, batchSize)
 	for i := range packetBuffers {
-		packetBuffers[i] = make([]byte, s.mtu+frontHeadroom)
+		packetBuffers[i] = make([]byte, s.mtu+s.frontHeadroom)
 	}
 	for {
-		n, err := linuxTUN.BatchRead(packetBuffers, frontHeadroom, packetSizes)
+		n, err := linuxTUN.BatchRead(packetBuffers, s.frontHeadroom, packetSizes)
 		if err != nil {
 			if E.IsClosed(err) {
 				return
@@ -220,13 +222,13 @@ func (s *System) batchLoop(linuxTUN BatchTUN, batchSize int) {
 				continue
 			}
 			packetBuffer := packetBuffers[i]
-			packet := packetBuffer[frontHeadroom : frontHeadroom+packetSize]
+			packet := packetBuffer[s.frontHeadroom : s.frontHeadroom+packetSize]
 			if s.processPacket(packet) {
-				writeBuffers = append(writeBuffers, packetBuffer[:frontHeadroom+packetSize])
+				writeBuffers = append(writeBuffers, packetBuffer[:s.frontHeadroom+packetSize])
 			}
 		}
 		if len(writeBuffers) > 0 {
-			err = linuxTUN.BatchWrite(writeBuffers, frontHeadroom)
+			err = linuxTUN.BatchWrite(writeBuffers, s.frontHeadroom)
 			if err != nil {
 				s.logger.Trace(E.Cause(err, "batch write packet"))
 			}
@@ -352,8 +354,10 @@ func (s *System) processIPv4TCP(packet clashtcpip.IPv4Packet, header clashtcpip.
 		packet.SetDestinationIP(s.inet4ServerAddress)
 		header.SetDestinationPort(s.tcpPort)
 	}
-	header.ResetChecksum(packet.PseudoSum())
-	packet.ResetChecksum()
+	if !s.txChecksumOffload {
+		header.ResetChecksum(packet.PseudoSum())
+		packet.ResetChecksum()
+	}
 	return nil
 }
 
@@ -378,8 +382,9 @@ func (s *System) processIPv6TCP(packet clashtcpip.IPv6Packet, header clashtcpip.
 		packet.SetDestinationIP(s.inet6ServerAddress)
 		header.SetDestinationPort(s.tcpPort6)
 	}
-	header.ResetChecksum(packet.PseudoSum())
-	packet.ResetChecksum()
+	if !s.txChecksumOffload {
+		header.ResetChecksum(packet.PseudoSum())
+	}
 	return nil
 }
 
@@ -410,7 +415,13 @@ func (s *System) processIPv4UDP(packet clashtcpip.IPv4Packet, header clashtcpip.
 		headerLen := packet.HeaderLen() + clashtcpip.UDPHeaderSize
 		headerCopy := make([]byte, headerLen)
 		copy(headerCopy, packet[:headerLen])
-		return &systemUDPPacketWriter4{s.tun, s.tun.FrontHeadroom() + PacketOffset, headerCopy, source}
+		return &systemUDPPacketWriter4{
+			s.tun,
+			s.frontHeadroom + PacketOffset,
+			headerCopy,
+			source,
+			s.txChecksumOffload,
+		}
 	})
 	return nil
 }
@@ -436,7 +447,13 @@ func (s *System) processIPv6UDP(packet clashtcpip.IPv6Packet, header clashtcpip.
 		headerLen := len(packet) - int(header.Length()) + clashtcpip.UDPHeaderSize
 		headerCopy := make([]byte, headerLen)
 		copy(headerCopy, packet[:headerLen])
-		return &systemUDPPacketWriter6{s.tun, s.tun.FrontHeadroom() + PacketOffset, headerCopy, source}
+		return &systemUDPPacketWriter6{
+			s.tun,
+			s.frontHeadroom + PacketOffset,
+			headerCopy,
+			source,
+			s.txChecksumOffload,
+		}
 	})
 	return nil
 }
@@ -468,10 +485,11 @@ func (s *System) processIPv6ICMP(packet clashtcpip.IPv6Packet, header clashtcpip
 }
 
 type systemUDPPacketWriter4 struct {
-	tun           Tun
-	frontHeadroom int
-	header        []byte
-	source        netip.AddrPort
+	tun               Tun
+	frontHeadroom     int
+	header            []byte
+	source            netip.AddrPort
+	txChecksumOffload bool
 }
 
 func (w *systemUDPPacketWriter4) WritePacket(buffer *buf.Buffer, destination M.Socksaddr) error {
@@ -488,8 +506,13 @@ func (w *systemUDPPacketWriter4) WritePacket(buffer *buf.Buffer, destination M.S
 	udpHdr.SetDestinationPort(udpHdr.SourcePort())
 	udpHdr.SetSourcePort(destination.Port)
 	udpHdr.SetLength(uint16(buffer.Len() + clashtcpip.UDPHeaderSize))
-	udpHdr.ResetChecksum(ipHdr.PseudoSum())
-	ipHdr.ResetChecksum()
+	if !w.txChecksumOffload {
+		udpHdr.ResetChecksum(ipHdr.PseudoSum())
+		ipHdr.ResetChecksum()
+	} else {
+		udpHdr.SetChecksum(clashtcpip.ZeroChecksum)
+		ipHdr.SetChecksum(clashtcpip.ZeroChecksum)
+	}
 	if PacketOffset > 0 {
 		newPacket.ExtendHeader(PacketOffset)[3] = syscall.AF_INET
 	} else {
@@ -499,10 +522,11 @@ func (w *systemUDPPacketWriter4) WritePacket(buffer *buf.Buffer, destination M.S
 }
 
 type systemUDPPacketWriter6 struct {
-	tun           Tun
-	frontHeadroom int
-	header        []byte
-	source        netip.AddrPort
+	tun               Tun
+	frontHeadroom     int
+	header            []byte
+	source            netip.AddrPort
+	txChecksumOffload bool
 }
 
 func (w *systemUDPPacketWriter6) WritePacket(buffer *buf.Buffer, destination M.Socksaddr) error {
@@ -520,7 +544,11 @@ func (w *systemUDPPacketWriter6) WritePacket(buffer *buf.Buffer, destination M.S
 	udpHdr.SetDestinationPort(udpHdr.SourcePort())
 	udpHdr.SetSourcePort(destination.Port)
 	udpHdr.SetLength(udpLen)
-	udpHdr.ResetChecksum(ipHdr.PseudoSum())
+	if !w.txChecksumOffload {
+		udpHdr.ResetChecksum(ipHdr.PseudoSum())
+	} else {
+		udpHdr.SetChecksum(clashtcpip.ZeroChecksum)
+	}
 	if PacketOffset > 0 {
 		newPacket.ExtendHeader(PacketOffset)[3] = syscall.AF_INET6
 	} else {

tun.go

@@ -24,7 +24,6 @@ type Handler interface {
 type Tun interface {
 	io.ReadWriter
 	N.VectorisedWriter
-	N.FrontHeadroom
 	Close() error
 }
 
@@ -33,11 +32,13 @@ type WinTun interface {
 	ReadPacket() ([]byte, func(), error)
 }
 
-type BatchTUN interface {
+type LinuxTUN interface {
 	Tun
+	N.FrontHeadroom
 	BatchSize() int
 	BatchRead(buffers [][]byte, offset int, readN []int) (n int, err error)
 	BatchWrite(buffers [][]byte, offset int) error
+	TXChecksumOffload() bool
 }
 
 type Options struct {
@@ -46,6 +47,7 @@ type Options struct {
 	Inet6Address             []netip.Prefix
 	MTU                      uint32
 	GSO                      bool
+	TXChecksumOffload        bool
 	AutoRoute                bool
 	StrictRoute              bool
 	Inet4RouteAddress        []netip.Prefix

tun_darwin.go

@@ -5,7 +5,6 @@ import (
 	"net"
 	"net/netip"
 	"os"
-	"runtime"
 	"syscall"
 	"unsafe"
 
@@ -68,14 +67,9 @@ func New(options Options) (Tun, error) {
 	if !ok {
 		panic("create vectorised writer")
 	}
-	runtime.SetFinalizer(nativeTun.tunFile, nil)
 	return nativeTun, nil
 }
 
-func (t *NativeTun) FrontHeadroom() int {
-	return 0
-}
-
 func (t *NativeTun) Read(p []byte) (n int, err error) {
 	return t.tunFile.Read(p)
 }