Proxy: Add TUN inbound for Windows & Linux, including Android (#5464)

* Proxy: Implement tun raw network interface inbound support for Linux

* Proxy: Tun. Include "android" as build condition for build of tun_default implementation

* Proxy: Tun. Add .Close() cleanup calls to Handler.Init() where needed

* Proxy: Add Tun for Android

* Proxy: Tun. Implement Windows support

---------

Co-authored-by: yuhan6665 <1588741+yuhan6665@users.noreply.github.com>

proxy/tun/tun_windows.go

@@ -0,0 +1,84 @@
+//go:build windows
+
+package tun
+
+import (
+	"golang.org/x/sys/windows"
+	"golang.zx2c4.com/wintun"
+	"gvisor.dev/gvisor/pkg/tcpip/stack"
+)
+
+// WindowsTun is an object that handles tun network interface on Windows
+// current version is heavily stripped to do nothing more,
+// then create a network interface, to be provided as endpoint to gVisor ip stack
+type WindowsTun struct {
+	options TunOptions
+	adapter *wintun.Adapter
+	session wintun.Session
+	MTU     uint32
+}
+
+// WindowsTun implements Tun
+var _ Tun = (*WindowsTun)(nil)
+
+// WindowsTun implements GVisorTun
+var _ GVisorTun = (*WindowsTun)(nil)
+
+// NewTun creates a Wintun interface with the given name. Should a Wintun
+// interface with the same name exist, it tried to be reused.
+func NewTun(options TunOptions) (Tun, error) {
+	// instantiate wintun adapter
+	adapter, err := open(options.Name)
+	if err != nil {
+		return nil, err
+	}
+
+	// start the interface with ring buffer capacity of 8 MiB
+	session, err := adapter.StartSession(0x800000)
+	if err != nil {
+		_ = adapter.Close()
+		return nil, err
+	}
+
+	tun := &WindowsTun{
+		options: options,
+		adapter: adapter,
+		session: session,
+		// there is currently no iphndl.dll support, which is the netlink library for windows
+		// so there is nowhere to change MTU for the Wintun interface, and we take its default value
+		MTU: wintun.PacketSizeMax,
+	}
+
+	return tun, nil
+}
+
+func open(name string) (*wintun.Adapter, error) {
+	var guid *windows.GUID
+	// try to open existing adapter by name
+	adapter, err := wintun.OpenAdapter(name)
+	if err == nil {
+		return adapter, nil
+	}
+	// try to create adapter anew
+	adapter, err = wintun.CreateAdapter(name, "Xray", guid)
+	if err == nil {
+		return adapter, nil
+	}
+	return nil, err
+}
+
+func (t *WindowsTun) Start() error {
+	return nil
+}
+
+func (t *WindowsTun) Close() error {
+	t.session.End()
+	_ = t.adapter.Close()
+
+	return nil
+}
+
+// newEndpoint builds new gVisor stack.LinkEndpoint (WintunEndpoint) on top of WindowsTun
+func (t *WindowsTun) newEndpoint() (stack.LinkEndpoint, error) {
+	return &WintunEndpoint{tun: t}, nil
+}