Add ping proxy support

route_nat.go

@@ -0,0 +1,109 @@
+package tun
+
+import (
+	"net/netip"
+	"sync"
+
+	"github.com/sagernet/sing-tun/internal/gtcpip/checksum"
+	"github.com/sagernet/sing-tun/internal/gtcpip/header"
+)
+
+type NatMapping struct {
+	access    sync.RWMutex
+	sessions  map[DirectRouteSession]DirectRouteContext
+	ipRewrite bool
+}
+
+func NewNatMapping(ipRewrite bool) *NatMapping {
+	return &NatMapping{
+		sessions:  make(map[DirectRouteSession]DirectRouteContext),
+		ipRewrite: ipRewrite,
+	}
+}
+
+func (m *NatMapping) CreateSession(session DirectRouteSession, context DirectRouteContext) {
+	if m.ipRewrite {
+		session.Source = netip.Addr{}
+	}
+	m.access.Lock()
+	m.sessions[session] = context
+	m.access.Unlock()
+}
+
+func (m *NatMapping) DeleteSession(session DirectRouteSession) {
+	if m.ipRewrite {
+		session.Source = netip.Addr{}
+	}
+	m.access.Lock()
+	delete(m.sessions, session)
+	m.access.Unlock()
+}
+
+func (m *NatMapping) WritePacket(packet []byte) (bool, error) {
+	var routeSession DirectRouteSession
+	switch header.IPVersion(packet) {
+	case header.IPv4Version:
+		ipHdr := header.IPv4(packet)
+		routeSession.Source = ipHdr.DestinationAddr()
+		routeSession.Destination = ipHdr.SourceAddr()
+	case header.IPv6Version:
+		ipHdr := header.IPv6(packet)
+		routeSession.Source = ipHdr.DestinationAddr()
+		routeSession.Destination = ipHdr.SourceAddr()
+	default:
+		return false, nil
+	}
+	m.access.RLock()
+	context, loaded := m.sessions[routeSession]
+	m.access.RUnlock()
+	if !loaded {
+		return false, nil
+	}
+	return true, context.WritePacket(packet)
+}
+
+type NatWriter struct {
+	inet4Address netip.Addr
+	inet6Address netip.Addr
+}
+
+func NewNatWriter(inet4Address netip.Addr, inet6Address netip.Addr) *NatWriter {
+	return &NatWriter{
+		inet4Address: inet4Address,
+		inet6Address: inet6Address,
+	}
+}
+
+func (w *NatWriter) RewritePacket(packet []byte) {
+	var ipHdr header.Network
+	var bindAddr netip.Addr
+	switch header.IPVersion(packet) {
+	case header.IPv4Version:
+		ipHdr = header.IPv4(packet)
+		bindAddr = w.inet4Address
+	case header.IPv6Version:
+		ipHdr = header.IPv6(packet)
+		bindAddr = w.inet6Address
+	default:
+		return
+	}
+	ipHdr.SetSourceAddr(bindAddr)
+	switch ipHdr.TransportProtocol() {
+	case header.ICMPv4ProtocolNumber:
+		icmpHdr := header.ICMPv4(packet)
+		icmpHdr.SetChecksum(0)
+		icmpHdr.SetChecksum(header.ICMPv4Checksum(icmpHdr[:header.ICMPv4MinimumSize], checksum.Checksum(icmpHdr.Payload(), 0)))
+	case header.ICMPv6ProtocolNumber:
+		icmpHdr := header.ICMPv6(packet)
+		icmpHdr.SetChecksum(0)
+		icmpHdr.SetChecksum(header.ICMPv6Checksum(header.ICMPv6ChecksumParams{
+			Header: icmpHdr,
+			Src:    ipHdr.SourceAddress(),
+			Dst:    ipHdr.DestinationAddress(),
+		}))
+	}
+	if ipHdr4, isIPv4 := ipHdr.(header.IPv4); isIPv4 {
+		ipHdr4.SetChecksum(0)
+		ipHdr4.SetChecksum(^ipHdr4.CalculateChecksum())
+	}
+}