Add route support

route_nat_gvisor.go

@@ -0,0 +1,41 @@
+//go:build with_gvisor
+
+package tun
+
+import (
+	"gvisor.dev/gvisor/pkg/tcpip"
+	"gvisor.dev/gvisor/pkg/tcpip/header"
+	"gvisor.dev/gvisor/pkg/tcpip/stack"
+)
+
+func (w *NatWriter) RewritePacketBuffer(packetBuffer *stack.PacketBuffer) {
+	var bindAddr tcpip.Address
+	if packetBuffer.NetworkProtocolNumber == header.IPv4ProtocolNumber {
+		bindAddr = tcpip.Address(w.inet4Address.AsSlice())
+	} else {
+		bindAddr = tcpip.Address(w.inet6Address.AsSlice())
+	}
+	var ipHdr header.Network
+	switch packetBuffer.NetworkProtocolNumber {
+	case header.IPv4ProtocolNumber:
+		ipHdr = header.IPv4(packetBuffer.NetworkHeader().Slice())
+	case header.IPv6ProtocolNumber:
+		ipHdr = header.IPv6(packetBuffer.NetworkHeader().Slice())
+	default:
+		return
+	}
+	oldAddr := ipHdr.SourceAddress()
+	if checksumHdr, needChecksum := ipHdr.(header.ChecksummableNetwork); needChecksum {
+		checksumHdr.SetSourceAddressWithChecksumUpdate(bindAddr)
+	} else {
+		ipHdr.SetSourceAddress(bindAddr)
+	}
+	switch packetBuffer.TransportProtocolNumber {
+	case header.TCPProtocolNumber:
+		tcpHdr := header.TCP(packetBuffer.TransportHeader().Slice())
+		tcpHdr.UpdateChecksumPseudoHeaderAddress(oldAddr, bindAddr, true)
+	case header.UDPProtocolNumber:
+		udpHdr := header.UDP(packetBuffer.TransportHeader().Slice())
+		udpHdr.UpdateChecksumPseudoHeaderAddress(oldAddr, bindAddr, true)
+	}
+}