Add fullcone packet filtering to tun app

app/tun/device/linkWriterToWriter.go

@@ -0,0 +1,34 @@
+package device
+
+import (
+	"github.com/v2fly/v2ray-core/v5/common/errors"
+	"gvisor.dev/gvisor/pkg/buffer"
+	"gvisor.dev/gvisor/pkg/tcpip/stack"
+	"io"
+)
+
+func NewLinkWriterToWriter(writer stack.LinkWriter) io.Writer {
+	return &linkWriterToWriter{writer: writer}
+}
+
+type linkWriterToWriter struct {
+	writer stack.LinkWriter
+}
+
+func (l linkWriterToWriter) Write(p []byte) (n int, err error) {
+
+	buffer := buffer.MakeWithData(p)
+	packetBufferPtr := stack.NewPacketBuffer(stack.PacketBufferOptions{
+		Payload: buffer,
+		OnRelease: func() {
+			buffer.Release()
+		},
+	})
+	packetList := stack.PacketBufferList{}
+	packetList.PushBack(packetBufferPtr)
+	_, terr := l.writer.WritePackets(packetList)
+	if terr != nil {
+		return 0, newError("failed to write packet").Base(errors.New(terr.String())).AtError()
+	}
+	return len(p), nil
+}