add newTUNDevice to windows

internal/vpn/tun_device_windows.go

@@ -0,0 +1,50 @@
+//go:build windows
+// +build windows
+
+package vpn
+
+import (
+	"fmt"
+
+	"golang.zx2c4.com/wireguard/tun"
+)
+
+type tunDevice struct {
+	tun  tun.Device
+	name string
+}
+
+func newTUNDevice() (TUNDevice, error) {
+	const tunName = "tun0"
+
+	dev, err := tun.CreateTUN(tunName, TUNMTU)
+	if err != nil {
+		return nil, fmt.Errorf("error allocating TUN interface: %w", err)
+	}
+
+	name, err := dev.Name()
+	if err != nil {
+		return nil, fmt.Errorf("error getting interface name: %w", err)
+	}
+
+	return &tunDevice{
+		tun:  dev,
+		name: name,
+	}, nil
+}
+
+func (t *tunDevice) Read(buf []byte) (int, error) {
+	return t.tun.Read(buf, 0)
+}
+
+func (t *tunDevice) Write(buf []byte) (int, error) {
+	return t.tun.Write(buf, 0)
+}
+
+func (t *tunDevice) Close() error {
+	return t.tun.Close()
+}
+
+func (t *tunDevice) Name() string {
+	return t.name
+}