ping: Add destination rewriter

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)
+}