ping: Add destination rewriter

ping/destination_gvisor.go

@@ -27,7 +27,7 @@ type GVisorDestination struct {
 	logger   logger.ContextLogger
 	endpoint tcpip.Endpoint
 	conn     *gonet.TCPConn
-	rewriter *Rewriter
+	rewriter *SourceRewriter
 	timeout  time.Duration
 }
 
@@ -76,7 +76,7 @@ func ConnectGVisor(
 		return nil, gonet.TranslateNetstackError(gErr)
 	}
 	endpoint.SocketOptions().SetHeaderIncluded(true)
-	rewriter := NewRewriter(ctx, logger, bindAddress4, bindAddress6)
+	rewriter := NewSourceRewriter(ctx, logger, bindAddress4, bindAddress6)
 	rewriter.CreateSession(tun.DirectRouteSession{Source: sourceAddress, Destination: destinationAddress}, routeContext)
 	destination := &GVisorDestination{
 		ctx:      ctx,

ping/destination_rewriter.go

@@ -0,0 +1,79 @@
+package ping
+
+import (
+	"net/netip"
+
+	"github.com/sagernet/sing-tun"
+	"github.com/sagernet/sing-tun/internal/gtcpip/header"
+	"github.com/sagernet/sing/common/buf"
+)
+
+type DestinationWriter struct {
+	tun.DirectRouteDestination
+	destination netip.Addr
+}
+
+func NewDestinationWriter(routeDestination tun.DirectRouteDestination, destination netip.Addr) *DestinationWriter {
+	return &DestinationWriter{routeDestination, destination}
+}
+
+func (w *DestinationWriter) WritePacket(packet *buf.Buffer) error {
+	var ipHdr header.Network
+	switch header.IPVersion(packet.Bytes()) {
+	case header.IPv4Version:
+		ipHdr = header.IPv4(packet.Bytes())
+	case header.IPv6Version:
+		ipHdr = header.IPv6(packet.Bytes())
+	default:
+		return w.DirectRouteDestination.WritePacket(packet)
+	}
+	ipHdr.SetDestinationAddr(w.destination)
+	if ipHdr4, isIPv4 := ipHdr.(header.IPv4); isIPv4 {
+		ipHdr4.SetChecksum(^ipHdr4.CalculateChecksum())
+	}
+	if ipHdr.TransportProtocol() == header.ICMPv6ProtocolNumber {
+		icmpHdr := header.ICMPv6(ipHdr.Payload())
+		icmpHdr.SetChecksum(header.ICMPv6Checksum(header.ICMPv6ChecksumParams{
+			Header: icmpHdr,
+			Src:    ipHdr.SourceAddressSlice(),
+			Dst:    ipHdr.DestinationAddressSlice(),
+		}))
+	}
+	return w.DirectRouteDestination.WritePacket(packet)
+}
+
+type ContextDestinationWriter struct {
+	tun.DirectRouteContext
+	destination netip.Addr
+}
+
+func NewContextDestinationWriter(context tun.DirectRouteContext, destination netip.Addr) *ContextDestinationWriter {
+	return &ContextDestinationWriter{
+		context, destination,
+	}
+}
+
+func (w *ContextDestinationWriter) WritePacket(packet []byte) error {
+	var ipHdr header.Network
+	switch header.IPVersion(packet) {
+	case header.IPv4Version:
+		ipHdr = header.IPv4(packet)
+	case header.IPv6Version:
+		ipHdr = header.IPv6(packet)
+	default:
+		return w.DirectRouteContext.WritePacket(packet)
+	}
+	ipHdr.SetSourceAddr(w.destination)
+	if ipHdr4, isIPv4 := ipHdr.(header.IPv4); isIPv4 {
+		ipHdr4.SetChecksum(^ipHdr4.CalculateChecksum())
+	}
+	if ipHdr.TransportProtocol() == header.ICMPv6ProtocolNumber {
+		icmpHdr := header.ICMPv6(ipHdr.Payload())
+		icmpHdr.SetChecksum(header.ICMPv6Checksum(header.ICMPv6ChecksumParams{
+			Header: icmpHdr,
+			Src:    ipHdr.SourceAddressSlice(),
+			Dst:    ipHdr.DestinationAddressSlice(),
+		}))
+	}
+	return w.DirectRouteContext.WritePacket(packet)
+}

ping/source_rewriter.go

@@ -10,7 +10,7 @@ import (
 	"github.com/sagernet/sing/common/logger"
 )
 
-type Rewriter struct {
+type SourceRewriter struct {
 	ctx           context.Context
 	logger        logger.ContextLogger
 	access        sync.RWMutex
@@ -20,8 +20,8 @@ type Rewriter struct {
 	inet6Address  netip.Addr
 }
 
-func NewRewriter(ctx context.Context, logger logger.ContextLogger, inet4Address netip.Addr, inet6Address netip.Addr) *Rewriter {
+func NewSourceRewriter(ctx context.Context, logger logger.ContextLogger, inet4Address netip.Addr, inet6Address netip.Addr) *SourceRewriter {
-	return &Rewriter{
+	return &SourceRewriter{
 		ctx:           ctx,
 		logger:        logger,
 		sessions:      make(map[tun.DirectRouteSession]tun.DirectRouteContext),
@@ -31,19 +31,19 @@ func NewRewriter(ctx context.Context, logger logger.ContextLogger, inet4Address
 	}
 }
 
-func (m *Rewriter) CreateSession(session tun.DirectRouteSession, context tun.DirectRouteContext) {
+func (m *SourceRewriter) CreateSession(session tun.DirectRouteSession, context tun.DirectRouteContext) {
 	m.access.Lock()
 	m.sessions[session] = context
 	m.access.Unlock()
 }
 
-func (m *Rewriter) DeleteSession(session tun.DirectRouteSession) {
+func (m *SourceRewriter) DeleteSession(session tun.DirectRouteSession) {
 	m.access.Lock()
 	delete(m.sessions, session)
 	m.access.Unlock()
 }
 
-func (m *Rewriter) RewritePacket(packet []byte) {
+func (m *SourceRewriter) RewritePacket(packet []byte) {
 	var ipHdr header.Network
 	var bindAddr netip.Addr
 	switch header.IPVersion(packet) {
@@ -82,7 +82,7 @@ func (m *Rewriter) RewritePacket(packet []byte) {
 	}
 }
 
-func (m *Rewriter) WriteBack(packet []byte) (bool, error) {
+func (m *SourceRewriter) WriteBack(packet []byte) (bool, error) {
 	var ipHdr header.Network
 	var routeSession tun.DirectRouteSession
 	switch header.IPVersion(packet) {