implement real gateway path.

README.md

@@ -10,8 +10,8 @@ through the phone automatically.
 ## Current Status
 
 This repository contains the production architecture, protocol specification,
-Android project scaffold, Rust core scaffold, and the first USB-first engine
-interfaces. It is not yet a complete packet-forwarding release.
+Android project scaffold, Rust core scaffold, and a Linux-first USB gateway
+prototype.
 
 The first shippable milestone is:
 
@@ -21,6 +21,11 @@ The first shippable milestone is:
 - Desktop client foundation for Windows, Linux, and macOS.
 - Encrypted VSHP tunnel with QR/code pairing.
 
+The current desktop binary provides USB sharing through the Android gateway. On
+Linux it can create a real `vpnshare0` TUN interface and route normal OS/app
+traffic through the phone with `sudo ./target/debug/vpnshare-desktop
+system-gateway`. See [docs/desktop-client.md](docs/desktop-client.md).
+
 ## Important Platform Constraint
 
 VPN Share uses companion clients on receiving devices. This is required because
@@ -59,9 +64,6 @@ Android validation, once a healthy Gradle installation or wrapper is available:
 gradle :apps:android:app:assembleDebug
 ```
 
-The local environment used to create this scaffold had a broken system Gradle
-native-platform installation, so Android compilation was not executed locally.
-
 ## License
 
 Apache-2.0. See [LICENSE](LICENSE).

apps/android/app/src/main/kotlin/org/vpnshare/app/MainActivity.kt

@@ -10,6 +10,7 @@ import org.vpnshare.gateway.VpnShareGatewayService
 class MainActivity : ComponentActivity() {
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
+        maybeStartShare(intent)
 
         setContent {
             ShareScreen(
@@ -28,4 +29,22 @@ class MainActivity : ComponentActivity() {
             )
         }
     }
+
+    override fun onNewIntent(intent: Intent) {
+        super.onNewIntent(intent)
+        maybeStartShare(intent)
+    }
+
+    private fun maybeStartShare(intent: Intent?) {
+        if (intent?.action == ACTION_START_FROM_DESKTOP) {
+            startForegroundService(
+                Intent(this, VpnShareGatewayService::class.java)
+                    .setAction(VpnShareGatewayService.ACTION_START)
+            )
+        }
+    }
+
+    companion object {
+        const val ACTION_START_FROM_DESKTOP = "org.vpnshare.action.START_FROM_DESKTOP"
+    }
 }

apps/android/service/gateway/src/main/kotlin/org/vpnshare/gateway/VpnShareGatewayService.kt

@@ -17,10 +17,12 @@ import kotlinx.coroutines.cancel
 import kotlinx.coroutines.launch
 import org.vpnshare.domain.model.GatewayConfig
 import org.vpnshare.engine.RustVpnShareEngine
+import org.vpnshare.gateway.socks.UsbSocksGateway
 
 class VpnShareGatewayService : Service() {
     private val scope = CoroutineScope(SupervisorJob() + Dispatchers.IO)
     private val engine = RustVpnShareEngine()
+    private val socksGateway = UsbSocksGateway()
     private lateinit var vpnDetector: VpnDetector
 
     override fun onCreate() {
@@ -45,11 +47,13 @@ class VpnShareGatewayService : Service() {
     override fun onBind(intent: Intent?): IBinder? = null
 
     override fun onDestroy() {
+        socksGateway.stop()
         scope.cancel()
         super.onDestroy()
     }
 
     private fun startGateway() {
+        socksGateway.start()
         val notification = buildNotification()
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
             startForeground(

apps/android/service/gateway/src/main/kotlin/org/vpnshare/gateway/socks/UsbSocksGateway.kt

@@ -0,0 +1,328 @@
+package org.vpnshare.gateway.socks
+
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.cancel
+import kotlinx.coroutines.isActive
+import kotlinx.coroutines.launch
+import java.io.EOFException
+import java.io.InputStream
+import java.io.OutputStream
+import java.net.DatagramPacket
+import java.net.DatagramSocket
+import java.net.InetAddress
+import java.net.InetSocketAddress
+import java.net.ServerSocket
+import java.net.Socket
+import java.net.SocketTimeoutException
+import java.util.concurrent.atomic.AtomicBoolean
+
+class UsbSocksGateway(
+    private val port: Int = DEFAULT_PORT
+) {
+    private val running = AtomicBoolean(false)
+    private var serverSocket: ServerSocket? = null
+    private var scope: CoroutineScope? = null
+    private var acceptJob: Job? = null
+
+    fun start() {
+        if (!running.compareAndSet(false, true)) return
+        val serviceScope = CoroutineScope(SupervisorJob() + Dispatchers.IO)
+        scope = serviceScope
+        val server = ServerSocket().apply {
+            reuseAddress = true
+            bind(InetSocketAddress(InetAddress.getLoopbackAddress(), port))
+        }
+        serverSocket = server
+        acceptJob = serviceScope.launch {
+            while (isActive && running.get()) {
+                val client = runCatching { server.accept() }.getOrNull() ?: break
+                launch { handleClient(client) }
+            }
+        }
+    }
+
+    fun stop() {
+        running.set(false)
+        runCatching { serverSocket?.close() }
+        acceptJob?.cancel()
+        scope?.cancel()
+        serverSocket = null
+        acceptJob = null
+        scope = null
+    }
+
+    private fun handleClient(client: Socket) {
+        client.use { clientSocket ->
+            clientSocket.tcpNoDelay = true
+            clientSocket.soTimeout = HANDSHAKE_TIMEOUT_MS
+            val input = clientSocket.getInputStream()
+            val output = clientSocket.getOutputStream()
+
+            runCatching {
+                negotiate(input, output)
+                when (val request = readRequest(input)) {
+                    is SocksRequest.TcpConnect -> {
+                        Socket().use { upstream ->
+                            upstream.tcpNoDelay = true
+                            upstream.connect(request.destination, CONNECT_TIMEOUT_MS)
+                            writeSuccess(output, request.destination)
+                            clientSocket.soTimeout = 0
+                            pipeBothWays(clientSocket, upstream)
+                        }
+                    }
+                    SocksRequest.UdpForward -> {
+                        writeSuccess(output, null)
+                        clientSocket.soTimeout = 0
+                        forwardUdpInTcp(input, output)
+                    }
+                }
+            }.onFailure {
+                runCatching { writeFailure(output) }
+            }
+        }
+    }
+
+    private fun negotiate(input: InputStream, output: OutputStream) {
+        val version = input.readRequired()
+        require(version == SOCKS_VERSION) { "unsupported socks version" }
+        val methodCount = input.readRequired()
+        val methods = ByteArray(methodCount)
+        input.readFully(methods)
+        require(methods.any { it.toInt() == AUTH_NONE }) { "no supported auth method" }
+        output.write(byteArrayOf(SOCKS_VERSION.toByte(), AUTH_NONE.toByte()))
+        output.flush()
+    }
+
+    private fun readRequest(input: InputStream): SocksRequest {
+        val version = input.readRequired()
+        val command = input.readRequired()
+        input.readRequired()
+        val addressType = input.readRequired()
+        require(version == SOCKS_VERSION) { "unsupported request version" }
+
+        val destination = readAddress(input, addressType)
+        return when (command) {
+            COMMAND_CONNECT -> SocksRequest.TcpConnect(destination)
+            COMMAND_FORWARD_UDP -> SocksRequest.UdpForward
+            else -> error("unsupported command")
+        }
+    }
+
+    private fun readAddress(input: InputStream, addressType: Int): InetSocketAddress {
+        val host = when (addressType) {
+            ADDRESS_IPV4 -> input.readBytesExact(IPV4_BYTES).joinToString(".") { (it.toInt() and 0xff).toString() }
+            ADDRESS_DOMAIN -> {
+                val length = input.readRequired()
+                input.readBytesExact(length).toString(Charsets.UTF_8)
+            }
+            ADDRESS_IPV6 -> InetAddress.getByAddress(input.readBytesExact(IPV6_BYTES)).hostAddress
+            else -> error("unsupported address type")
+        }
+        val port = (input.readRequired() shl 8) or input.readRequired()
+        return InetSocketAddress(host, port)
+    }
+
+    private fun writeSuccess(output: OutputStream, destination: InetSocketAddress?) {
+        val port = destination?.port ?: 0
+        output.write(
+            byteArrayOf(
+                SOCKS_VERSION.toByte(),
+                REPLY_SUCCESS.toByte(),
+                0,
+                ADDRESS_IPV4.toByte(),
+                127,
+                0,
+                0,
+                1,
+                ((port ushr 8) and 0xff).toByte(),
+                (port and 0xff).toByte()
+            )
+        )
+        output.flush()
+    }
+
+    private fun forwardUdpInTcp(input: InputStream, output: OutputStream) {
+        DatagramSocket().use { udpSocket ->
+            val alive = AtomicBoolean(true)
+            val receiver = Thread {
+                receiveUdpResponses(udpSocket, output, alive)
+            }
+            receiver.name = "vpnshare-socks-udp-receiver"
+            receiver.start()
+
+            try {
+                while (alive.get()) {
+                    val frame = readUdpTcpFrame(input)
+                    val packet = DatagramPacket(frame.payload, frame.payload.size, frame.destination)
+                    udpSocket.send(packet)
+                }
+            } catch (_: EOFException) {
+            } catch (_: SocketTimeoutException) {
+            } catch (_: Exception) {
+            } finally {
+                alive.set(false)
+                udpSocket.close()
+                receiver.join(UDP_RECEIVER_JOIN_MS)
+            }
+        }
+    }
+
+    private fun readUdpTcpFrame(input: InputStream): UdpFrame {
+        val dataLength = (input.readRequired() shl 8) or input.readRequired()
+        val headerLength = input.readRequired()
+        require(dataLength <= UDP_MAX_PAYLOAD_BYTES) { "udp frame too large" }
+        require(headerLength >= UDP_MIN_HEADER_BYTES) { "udp header too small" }
+
+        val addressType = input.readRequired()
+        val destination = readAddress(input, addressType)
+        val payload = input.readBytesExact(dataLength)
+        return UdpFrame(destination, payload)
+    }
+
+    private fun receiveUdpResponses(
+        udpSocket: DatagramSocket,
+        output: OutputStream,
+        alive: AtomicBoolean
+    ) {
+        udpSocket.soTimeout = UDP_RECEIVE_TIMEOUT_MS
+        val buffer = ByteArray(UDP_RECEIVE_BUFFER_BYTES)
+        while (alive.get()) {
+            try {
+                val packet = DatagramPacket(buffer, buffer.size)
+                udpSocket.receive(packet)
+                val response = encodeUdpTcpFrame(packet.address, packet.port, packet.data, packet.offset, packet.length)
+                synchronized(output) {
+                    output.write(response)
+                    output.flush()
+                }
+            } catch (_: SocketTimeoutException) {
+            } catch (_: Exception) {
+                alive.set(false)
+            }
+        }
+    }
+
+    private fun encodeUdpTcpFrame(
+        address: InetAddress,
+        port: Int,
+        payload: ByteArray,
+        offset: Int,
+        length: Int
+    ): ByteArray {
+        require(length <= UDP_MAX_PAYLOAD_BYTES) { "udp response too large" }
+        val addressBytes = address.address
+        val addressType = when (addressBytes.size) {
+            IPV4_BYTES -> ADDRESS_IPV4
+            IPV6_BYTES -> ADDRESS_IPV6
+            else -> error("unsupported udp response address")
+        }
+        val socksAddressLength = 1 + addressBytes.size + 2
+        val headerLength = UDP_PREFIX_BYTES + socksAddressLength
+        val frame = ByteArray(headerLength + length)
+        frame[0] = ((length ushr 8) and 0xff).toByte()
+        frame[1] = (length and 0xff).toByte()
+        frame[2] = headerLength.toByte()
+        frame[3] = addressType.toByte()
+        addressBytes.copyInto(frame, destinationOffset = 4)
+        val portOffset = 4 + addressBytes.size
+        frame[portOffset] = ((port ushr 8) and 0xff).toByte()
+        frame[portOffset + 1] = (port and 0xff).toByte()
+        payload.copyInto(
+            frame,
+            destinationOffset = headerLength,
+            startIndex = offset,
+            endIndex = offset + length
+        )
+        return frame
+    }
+
+    private fun writeFailure(output: OutputStream) {
+        output.write(byteArrayOf(SOCKS_VERSION.toByte(), REPLY_FAILURE.toByte(), 0, ADDRESS_IPV4.toByte(), 0, 0, 0, 0, 0, 0))
+        output.flush()
+    }
+
+    private fun pipeBothWays(left: Socket, right: Socket) {
+        val leftToRight = Thread { copy(left.getInputStream(), right.getOutputStream(), right) }
+        val rightToLeft = Thread { copy(right.getInputStream(), left.getOutputStream(), left) }
+        leftToRight.name = "vpnshare-socks-client-to-phone"
+        rightToLeft.name = "vpnshare-socks-phone-to-client"
+        leftToRight.start()
+        rightToLeft.start()
+        leftToRight.join()
+        rightToLeft.join()
+    }
+
+    private fun copy(input: InputStream, output: OutputStream, socketToClose: Socket) {
+        val buffer = ByteArray(COPY_BUFFER_BYTES)
+        try {
+            while (true) {
+                val read = input.read(buffer)
+                if (read < 0) break
+                output.write(buffer, 0, read)
+                output.flush()
+            }
+        } catch (_: SocketTimeoutException) {
+        } catch (_: Exception) {
+        } finally {
+            runCatching { socketToClose.shutdownOutput() }
+        }
+    }
+
+    private fun InputStream.readRequired(): Int {
+        val value = read()
+        if (value < 0) throw EOFException()
+        return value
+    }
+
+    private fun InputStream.readBytesExact(size: Int): ByteArray {
+        val bytes = ByteArray(size)
+        readFully(bytes)
+        return bytes
+    }
+
+    private fun InputStream.readFully(bytes: ByteArray) {
+        var offset = 0
+        while (offset < bytes.size) {
+            val read = read(bytes, offset, bytes.size - offset)
+            if (read < 0) throw EOFException()
+            offset += read
+        }
+    }
+
+    private sealed interface SocksRequest {
+        data class TcpConnect(val destination: InetSocketAddress) : SocksRequest
+        data object UdpForward : SocksRequest
+    }
+
+    private data class UdpFrame(
+        val destination: InetSocketAddress,
+        val payload: ByteArray
+    )
+
+    companion object {
+        const val DEFAULT_PORT = 10808
+        private const val SOCKS_VERSION = 5
+        private const val AUTH_NONE = 0
+        private const val COMMAND_CONNECT = 1
+        private const val COMMAND_FORWARD_UDP = 5
+        private const val ADDRESS_IPV4 = 1
+        private const val ADDRESS_DOMAIN = 3
+        private const val ADDRESS_IPV6 = 4
+        private const val REPLY_SUCCESS = 0
+        private const val REPLY_FAILURE = 1
+        private const val IPV4_BYTES = 4
+        private const val IPV6_BYTES = 16
+        private const val CONNECT_TIMEOUT_MS = 15_000
+        private const val HANDSHAKE_TIMEOUT_MS = 10_000
+        private const val COPY_BUFFER_BYTES = 32 * 1024
+        private const val UDP_PREFIX_BYTES = 3
+        private const val UDP_MIN_HEADER_BYTES = UDP_PREFIX_BYTES + 7
+        private const val UDP_MAX_PAYLOAD_BYTES = 65_507
+        private const val UDP_RECEIVE_BUFFER_BYTES = 65_535
+        private const val UDP_RECEIVE_TIMEOUT_MS = 1_000
+        private const val UDP_RECEIVER_JOIN_MS = 1_000L
+    }
+}

clients/desktop/Cargo.toml

@@ -11,6 +11,7 @@ name = "vpnshare-desktop"
 path = "src/main.rs"
 
 [dependencies]
+tun2socks = "0.1.10"
 vpnshare-core = { path = "../../crates/vpnshare-core" }
 vpnshare-proto = { path = "../../crates/vpnshare-proto" }
 vpnshare-transport = { path = "../../crates/vpnshare-transport" }

clients/desktop/src/main.rs

@@ -1,14 +1,627 @@
-use vpnshare_core::{GatewayConfig, MtuPolicy};
-use vpnshare_proto::{encode_frame, FrameType, PROTOCOL_VERSION};
+use std::env;
+use std::net::{SocketAddr, TcpStream};
+use std::path::{Path, PathBuf};
+use std::process::{Command, ExitCode};
+use std::thread;
+use std::time::{Duration, Instant};
 
-fn main() {
-    let config = GatewayConfig::default();
-    let mtu = MtuPolicy::default();
-    let hello = encode_frame(FrameType::Hello, 0, 1, b"vpnshare-desktop").expect("static hello frame");
-
-    println!("VPN Share desktop client skeleton");
-    println!("protocol=VSHP/{PROTOCOL_VERSION}");
-    println!("default_gateway_mtu={}", config.default_mtu);
-    println!("effective_tunnel_mtu={}", mtu.effective_tunnel_mtu());
-    println!("hello_frame_bytes={}", hello.len());
+fn main() -> ExitCode {
+    let cli = Cli::parse(env::args().skip(1));
+    match cli.command {
+        CommandKind::Help => {
+            print_help();
+            ExitCode::SUCCESS
+        }
+        CommandKind::Status => match DesktopStatus::collect() {
+            Ok(status) => {
+                print_status(&status);
+                ExitCode::SUCCESS
+            }
+            Err(error) => {
+                eprintln!("status failed: {error}");
+                ExitCode::from(1)
+            }
+        },
+        CommandKind::AndroidLaunch => match DesktopStatus::find_adb().and_then(|adb| adb.launch_android_app()) {
+            Ok(output) => {
+                println!("{output}");
+                ExitCode::SUCCESS
+            }
+            Err(error) => {
+                eprintln!("android launch failed: {error}");
+                ExitCode::from(1)
+            }
+        },
+        CommandKind::Connect => match DesktopStatus::find_adb().and_then(|adb| adb.connect_usb_socks()) {
+            Ok(connection) => {
+                print_connection(&connection);
+                ExitCode::SUCCESS
+            }
+            Err(error) => {
+                eprintln!("connect failed: {error}");
+                ExitCode::from(1)
+            }
+        },
+        CommandKind::SystemGateway => match SystemGateway::run() {
+            Ok(()) => ExitCode::SUCCESS,
+            Err(error) => {
+                eprintln!("system gateway failed: {error}");
+                ExitCode::from(1)
+            }
+        },
+        CommandKind::SystemGatewayCleanup => match SystemGateway::cleanup() {
+            Ok(()) => {
+                println!("VPN Share system gateway routes removed");
+                ExitCode::SUCCESS
+            }
+            Err(error) => {
+                eprintln!("cleanup failed: {error}");
+                ExitCode::from(1)
+            }
+        },
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+struct Cli {
+    command: CommandKind,
+}
+
+impl Cli {
+    fn parse(args: impl IntoIterator<Item = String>) -> Self {
+        let mut args = args.into_iter();
+        let command = match args.next().as_deref() {
+            None | Some("-h") | Some("--help") | Some("help") => CommandKind::Help,
+            Some("status") | Some("doctor") => CommandKind::Status,
+            Some("android-launch") | Some("launch") => CommandKind::AndroidLaunch,
+            Some("connect") => CommandKind::Connect,
+            Some("system-gateway") | Some("gateway") | Some("tun") => CommandKind::SystemGateway,
+            Some("cleanup") | Some("disconnect") | Some("system-gateway-cleanup") => CommandKind::SystemGatewayCleanup,
+            Some(_) => CommandKind::Help,
+        };
+        Self { command }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum CommandKind {
+    Help,
+    Status,
+    AndroidLaunch,
+    Connect,
+    SystemGateway,
+    SystemGatewayCleanup,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+struct DesktopStatus {
+    os: String,
+    tun_available: bool,
+    adb: Option<AdbStatus>,
+}
+
+impl DesktopStatus {
+    fn collect() -> Result<Self, String> {
+        let adb = match Self::find_adb() {
+            Ok(adb) => Some(adb.status()?),
+            Err(_) => None,
+        };
+        Ok(Self {
+            os: env::consts::OS.to_string(),
+            tun_available: Path::new("/dev/net/tun").exists(),
+            adb,
+        })
+    }
+
+    fn find_adb() -> Result<Adb, String> {
+        let mut candidates = Vec::new();
+        if let Ok(path) = env::var("VPN_SHARE_ADB") {
+            candidates.push(PathBuf::from(path));
+        }
+        candidates.push(PathBuf::from("/tmp/vpnshare-platform-tools-36/platform-tools/adb"));
+        candidates.push(PathBuf::from("/tmp/vpnshare-android-sdk/platform-tools/adb"));
+        candidates.push(PathBuf::from("adb"));
+
+        for candidate in candidates {
+            let output = Command::new(&candidate).arg("version").output();
+            if matches!(output, Ok(output) if output.status.success()) {
+                return Ok(Adb { path: candidate });
+            }
+        }
+
+        Err("adb not found; set VPN_SHARE_ADB or install Android platform-tools".to_string())
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+struct Adb {
+    path: PathBuf,
+}
+
+impl Adb {
+    fn connect_usb_socks(&self) -> Result<UsbSocksConnection, String> {
+        let devices_output = self.run(["devices", "-l"])?;
+        let devices = parse_adb_devices(&devices_output);
+        let device = devices
+            .iter()
+            .find(|device| device.state == "device")
+            .ok_or_else(|| "no authorized adb device found".to_string())?;
+
+        self.launch_android_gateway()?;
+        self.run(["forward", "--remove", &format!("tcp:{SOCKS_PORT}")]).ok();
+        self.run(["forward", &format!("tcp:{SOCKS_PORT}"), &format!("tcp:{SOCKS_PORT}")])?;
+
+        let endpoint: SocketAddr = format!("127.0.0.1:{SOCKS_PORT}")
+            .parse()
+            .map_err(|error| format!("invalid local socks endpoint: {error}"))?;
+        TcpStream::connect_timeout(&endpoint, Duration::from_secs(3))
+            .map_err(|error| format!("adb forward is present, but local socks port did not open: {error}"))?;
+
+        Ok(UsbSocksConnection {
+            device_serial: device.serial.clone(),
+            socks_url: format!("socks5h://127.0.0.1:{SOCKS_PORT}"),
+        })
+    }
+
+    fn status(&self) -> Result<AdbStatus, String> {
+        let devices_output = self.run(["devices", "-l"])?;
+        let devices = parse_adb_devices(&devices_output);
+        let package_installed = self
+            .run(["shell", "pm", "path", "org.vpnshare"])
+            .map(|output| output.contains("package:"))
+            .unwrap_or(false);
+        let app_pid = self
+            .run(["shell", "pidof", "org.vpnshare"])
+            .ok()
+            .and_then(|output| output.split_whitespace().next().map(str::to_string));
+        let gateway_foreground = self
+            .run(["shell", "dumpsys", "activity", "services", "org.vpnshare"])
+            .map(|output| output.contains("isForeground=true"))
+            .unwrap_or(false);
+
+        Ok(AdbStatus {
+            path: self.path.display().to_string(),
+            devices,
+            package_installed,
+            app_pid,
+            gateway_foreground,
+        })
+    }
+
+    fn launch_android_app(&self) -> Result<String, String> {
+        self.run([
+            "shell",
+            "am",
+            "start",
+            "-W",
+            "-n",
+            "org.vpnshare/org.vpnshare.app.MainActivity",
+        ])
+    }
+
+    fn launch_android_gateway(&self) -> Result<String, String> {
+        self.run([
+            "shell",
+            "am",
+            "start",
+            "-W",
+            "-a",
+            "org.vpnshare.action.START_FROM_DESKTOP",
+            "-n",
+            "org.vpnshare/org.vpnshare.app.MainActivity",
+        ])
+    }
+
+    fn run<const N: usize>(&self, args: [&str; N]) -> Result<String, String> {
+        let output = Command::new(&self.path)
+            .args(args)
+            .output()
+            .map_err(|error| format!("failed to run {}: {error}", self.path.display()))?;
+        if !output.status.success() {
+            return Err(String::from_utf8_lossy(&output.stderr).trim().to_string());
+        }
+        Ok(String::from_utf8_lossy(&output.stdout).trim().to_string())
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+struct AdbStatus {
+    path: String,
+    devices: Vec<AdbDevice>,
+    package_installed: bool,
+    app_pid: Option<String>,
+    gateway_foreground: bool,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+struct AdbDevice {
+    serial: String,
+    state: String,
+    detail: String,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+struct UsbSocksConnection {
+    device_serial: String,
+    socks_url: String,
+}
+
+struct SystemGateway;
+
+impl SystemGateway {
+    fn run() -> Result<(), String> {
+        ensure_linux()?;
+        ensure_tun_available()?;
+        ensure_socks_endpoint_open()?;
+        ensure_root()?;
+
+        println!("Starting VPN Share system gateway");
+        println!("interface={TUN_NAME}");
+        println!("socks=127.0.0.1:{SOCKS_PORT}");
+
+        let config = tun2socks_config();
+        let tunnel = thread::spawn(move || tun2socks::main_from_str(&config, -1));
+
+        if let Err(error) = wait_for_interface(TUN_NAME, Duration::from_secs(8)) {
+            tun2socks::quit();
+            let _ = tunnel.join();
+            return Err(error);
+        }
+
+        let dns_configured = configure_dns();
+        if let Err(error) = install_split_default_routes() {
+            cleanup_split_default_routes();
+            if dns_configured {
+                cleanup_dns();
+            }
+            tun2socks::quit();
+            let _ = tunnel.join();
+            return Err(error);
+        }
+
+        println!();
+        println!("VPN Share system gateway is active");
+        println!("All IPv4 traffic is routed through {TUN_NAME}; IPv6 is enabled when the host supports it.");
+        if dns_configured {
+            println!("dns=systemd-resolved via 1.1.1.1/8.8.8.8");
+        } else {
+            println!("dns=unchanged; install/use systemd-resolved if your current DNS is LAN-only");
+        }
+        println!("Keep this process open. Press Ctrl+C to stop.");
+        println!();
+
+        let result = match tunnel.join() {
+            Ok(Ok(())) => Ok(()),
+            Ok(Err(code)) => Err(format!("tun2socks exited with code {code}")),
+            Err(_) => Err("tun2socks thread panicked".to_string()),
+        };
+
+        cleanup_split_default_routes();
+        if dns_configured {
+            cleanup_dns();
+        }
+        result
+    }
+
+    fn cleanup() -> Result<(), String> {
+        ensure_linux()?;
+        ensure_root()?;
+        cleanup_split_default_routes();
+        cleanup_dns();
+        Ok(())
+    }
+}
+
+fn parse_adb_devices(output: &str) -> Vec<AdbDevice> {
+    output
+        .lines()
+        .skip(1)
+        .filter_map(|line| {
+            let line = line.trim();
+            if line.is_empty() {
+                return None;
+            }
+            let mut fields = line.split_whitespace();
+            let serial = fields.next()?.to_string();
+            let state = fields.next()?.to_string();
+            let detail = fields.collect::<Vec<_>>().join(" ");
+            Some(AdbDevice { serial, state, detail })
+        })
+        .collect()
+}
+
+fn ensure_linux() -> Result<(), String> {
+    if env::consts::OS == "linux" {
+        Ok(())
+    } else {
+        Err("system gateway mode is implemented for Linux in this build".to_string())
+    }
+}
+
+fn ensure_tun_available() -> Result<(), String> {
+    if Path::new("/dev/net/tun").exists() {
+        Ok(())
+    } else {
+        Err("/dev/net/tun is missing; enable the Linux tun module first".to_string())
+    }
+}
+
+fn ensure_socks_endpoint_open() -> Result<(), String> {
+    let endpoint = socks_endpoint()?;
+    TcpStream::connect_timeout(&endpoint, Duration::from_secs(2))
+        .map(|_| ())
+        .map_err(|error| format!("127.0.0.1:{SOCKS_PORT} is not open ({error}). Run `vpnshare-desktop connect` first."))
+}
+
+fn ensure_root() -> Result<(), String> {
+    let output = Command::new("id")
+        .arg("-u")
+        .output()
+        .map_err(|error| format!("failed to check current user id: {error}"))?;
+    if !output.status.success() {
+        return Err(String::from_utf8_lossy(&output.stderr).trim().to_string());
+    }
+
+    let uid = String::from_utf8_lossy(&output.stdout).trim().to_string();
+    if uid == "0" {
+        Ok(())
+    } else {
+        Err(
+            "system gateway mode needs root/CAP_NET_ADMIN on the desktop. Run `sudo ./target/debug/vpnshare-desktop system-gateway` after `./target/debug/vpnshare-desktop connect`."
+                .to_string(),
+        )
+    }
+}
+
+fn socks_endpoint() -> Result<SocketAddr, String> {
+    format!("127.0.0.1:{SOCKS_PORT}")
+        .parse()
+        .map_err(|error| format!("invalid local socks endpoint: {error}"))
+}
+
+fn tun2socks_config() -> String {
+    format!(
+        r#"tunnel:
+  name: {TUN_NAME}
+  mtu: {TUN_MTU}
+  multi-queue: false
+  ipv4: {TUN_IPV4}
+  ipv6: '{TUN_IPV6}'
+
+socks5:
+  address: 127.0.0.1
+  port: {SOCKS_PORT}
+  udp: 'tcp'
+
+misc:
+  task-stack-size: 20480
+  tcp-buffer-size: 65536
+  connect-timeout: 5000
+  read-write-timeout: 600000
+  log-file: stderr
+  log-level: warn
+"#
+    )
+}
+
+fn wait_for_interface(name: &str, timeout: Duration) -> Result<(), String> {
+    let start = Instant::now();
+    while start.elapsed() < timeout {
+        if command_success("ip", &["link", "show", name]) {
+            return Ok(());
+        }
+        thread::sleep(Duration::from_millis(100));
+    }
+    Err(format!(
+        "{name} did not appear; tun2socks could not create the TUN device"
+    ))
+}
+
+fn install_split_default_routes() -> Result<(), String> {
+    run_command(
+        "ip",
+        &["route", "replace", "0.0.0.0/1", "dev", TUN_NAME, "metric", "10"],
+    )?;
+    run_command(
+        "ip",
+        &["route", "replace", "128.0.0.0/1", "dev", TUN_NAME, "metric", "10"],
+    )?;
+
+    if let Err(error) = run_command(
+        "ip",
+        &["-6", "route", "replace", "::/1", "dev", TUN_NAME, "metric", "10"],
+    ) {
+        eprintln!("warning: IPv6 ::/1 route was not installed: {error}");
+    }
+    if let Err(error) = run_command(
+        "ip",
+        &["-6", "route", "replace", "8000::/1", "dev", TUN_NAME, "metric", "10"],
+    ) {
+        eprintln!("warning: IPv6 8000::/1 route was not installed: {error}");
+    }
+
+    Ok(())
+}
+
+fn cleanup_split_default_routes() {
+    let routes: &[&[&str]] = &[
+        &["route", "del", "0.0.0.0/1", "dev", TUN_NAME],
+        &["route", "del", "128.0.0.0/1", "dev", TUN_NAME],
+        &["-6", "route", "del", "::/1", "dev", TUN_NAME],
+        &["-6", "route", "del", "8000::/1", "dev", TUN_NAME],
+    ];
+    for route in routes {
+        let _ = run_command("ip", route);
+    }
+}
+
+fn configure_dns() -> bool {
+    if !command_success("resolvectl", &["--version"]) {
+        return false;
+    }
+
+    let dns = run_command(
+        "resolvectl",
+        &[
+            "dns",
+            TUN_NAME,
+            "1.1.1.1",
+            "8.8.8.8",
+            "2606:4700:4700::1111",
+            "2001:4860:4860::8888",
+        ],
+    );
+    let domain = run_command("resolvectl", &["domain", TUN_NAME, "~."]);
+
+    match (dns, domain) {
+        (Ok(_), Ok(_)) => true,
+        (Err(error), _) | (_, Err(error)) => {
+            eprintln!("warning: could not configure systemd-resolved DNS for {TUN_NAME}: {error}");
+            false
+        }
+    }
+}
+
+fn cleanup_dns() {
+    if command_success("resolvectl", &["--version"]) {
+        let _ = run_command("resolvectl", &["revert", TUN_NAME]);
+    }
+}
+
+fn command_success(program: &str, args: &[&str]) -> bool {
+    Command::new(program)
+        .args(args)
+        .output()
+        .map(|output| output.status.success())
+        .unwrap_or(false)
+}
+
+fn run_command(program: &str, args: &[&str]) -> Result<String, String> {
+    let output = Command::new(program)
+        .args(args)
+        .output()
+        .map_err(|error| format!("failed to run {program}: {error}"))?;
+    if !output.status.success() {
+        let stderr = String::from_utf8_lossy(&output.stderr).trim().to_string();
+        let stdout = String::from_utf8_lossy(&output.stdout).trim().to_string();
+        let message = if stderr.is_empty() { stdout } else { stderr };
+        return Err(if message.is_empty() {
+            format!("{program} exited with {}", output.status)
+        } else {
+            message
+        });
+    }
+    Ok(String::from_utf8_lossy(&output.stdout).trim().to_string())
+}
+
+fn print_help() {
+    println!("VPN Share desktop CLI");
+    println!();
+    println!("Commands:");
+    println!("  status          Check desktop prerequisites and connected Android app state");
+    println!("  android-launch  Bring the Android VPN Share app to the foreground");
+    println!("  connect         Start USB SOCKS5 sharing through the Android gateway");
+    println!("  system-gateway  Create vpnshare0 and route OS traffic through the phone");
+    println!("  cleanup         Remove VPN Share split-default routes");
+    println!();
+    println!("Environment:");
+    println!("  VPN_SHARE_ADB   Optional path to adb");
+}
+
+fn print_connection(connection: &UsbSocksConnection) {
+    println!("VPN Share USB SOCKS5 sharing is ready");
+    println!("device={}", connection.device_serial);
+    println!("proxy={}", connection.socks_url);
+    println!();
+    println!("For a real OS gateway, keep this ADB forward active and run:");
+    println!("  sudo ./target/debug/vpnshare-desktop system-gateway");
+    println!();
+    println!("Proxy endpoint is also available for apps that explicitly support SOCKS5:");
+    println!("  ALL_PROXY={} curl https://ifconfig.me", connection.socks_url);
+}
+
+fn print_status(status: &DesktopStatus) {
+    println!("VPN Share desktop status");
+    println!("os={}", status.os);
+    println!("tun_available={}", status.tun_available);
+    println!(
+        "desktop_packet_tunnel={}",
+        if status.tun_available {
+            "available"
+        } else {
+            "unavailable"
+        }
+    );
+
+    match &status.adb {
+        Some(adb) => {
+            println!("adb={}", adb.path);
+            println!("adb_devices={}", adb.devices.len());
+            for device in &adb.devices {
+                println!(
+                    "device serial={} state={} {}",
+                    device.serial, device.state, device.detail
+                );
+            }
+            println!("android_package_installed={}", adb.package_installed);
+            println!("android_app_pid={}", adb.app_pid.as_deref().unwrap_or("not_running"));
+            println!("android_gateway_foreground={}", adb.gateway_foreground);
+        }
+        None => {
+            println!("adb=not_found");
+        }
+    }
+}
+
+const SOCKS_PORT: u16 = 10808;
+const TUN_NAME: &str = "vpnshare0";
+const TUN_IPV4: &str = "198.18.0.1";
+const TUN_IPV6: &str = "fc00::1";
+const TUN_MTU: u16 = 1280;
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn parses_default_help() {
+        assert_eq!(Cli::parse([]).command, CommandKind::Help);
+    }
+
+    #[test]
+    fn parses_status_aliases() {
+        assert_eq!(Cli::parse(["doctor".to_string()]).command, CommandKind::Status);
+    }
+
+    #[test]
+    fn parses_system_gateway_aliases() {
+        assert_eq!(Cli::parse(["gateway".to_string()]).command, CommandKind::SystemGateway);
+        assert_eq!(
+            Cli::parse(["disconnect".to_string()]).command,
+            CommandKind::SystemGatewayCleanup
+        );
+    }
+
+    #[test]
+    fn renders_tun2socks_config() {
+        let config = tun2socks_config();
+
+        assert!(config.contains("name: vpnshare0"));
+        assert!(config.contains("port: 10808"));
+        assert!(config.contains("udp: 'tcp'"));
+    }
+
+    #[test]
+    fn parses_adb_devices() {
+        let devices = parse_adb_devices("List of devices attached\nR5CX33ESWGH device usb:1-6 model:SM_A556E\n\n");
+
+        assert_eq!(
+            devices,
+            vec![AdbDevice {
+                serial: "R5CX33ESWGH".to_string(),
+                state: "device".to_string(),
+                detail: "usb:1-6 model:SM_A556E".to_string()
+            }]
+        );
+    }
 }

docs/desktop-client.md

@@ -0,0 +1,78 @@
+# Desktop Client
+
+It can:
+
+- Check whether Linux TUN support exists.
+- Find `adb`.
+- Check whether the Android VPN Share app is installed.
+- Check whether the Android gateway foreground service is running.
+- Bring the Android app to the foreground.
+- Start the Android gateway and create `adb forward tcp:10808 tcp:10808`.
+- Provide a local `socks5h://127.0.0.1:10808` proxy endpoint.
+- On Linux, create a `vpnshare0` TUN device and route OS traffic through the
+  phone using `tun2socks`.
+- Forward DNS/UDP through the Android gateway using SOCKS5 UDP-over-TCP.
+
+It cannot yet pair with the phone over VSHP or provide native Windows/macOS TUN
+drivers.
+
+## Build
+
+```bash
+cargo build -p vpnshare-desktop
+```
+
+## Run
+
+```bash
+./target/debug/vpnshare-desktop status
+./target/debug/vpnshare-desktop connect
+sudo ./target/debug/vpnshare-desktop system-gateway
+./target/debug/vpnshare-desktop android-launch
+```
+
+If `adb` is not on `PATH`, point the CLI to it:
+
+```bash
+VPN_SHARE_ADB=/path/to/adb ./target/debug/vpnshare-desktop status
+```
+
+After `connect`, use the local SOCKS5 proxy with apps that support SOCKS:
+
+```bash
+ALL_PROXY=socks5h://127.0.0.1:10808 curl https://ifconfig.me
+chromium --proxy-server=socks5h://127.0.0.1:10808
+```
+
+The `socks5h` form is important because DNS names are resolved through the
+phone-side gateway instead of the desktop.
+
+## Linux System Gateway
+
+For normal OS/app routing on Linux:
+
+1. Connect the phone with USB debugging enabled.
+2. Start the Android VPN app you want to share.
+3. Run `./target/debug/vpnshare-desktop connect`.
+4. Run `sudo ./target/debug/vpnshare-desktop system-gateway`.
+5. Keep the `system-gateway` process open while sharing.
+
+`system-gateway` creates `vpnshare0`, starts `tun2socks`, installs split-default
+routes (`0.0.0.0/1` and `128.0.0.0/1`), and configures systemd-resolved DNS on
+`vpnshare0` when `resolvectl` is available.
+
+Cleanup command:
+
+```bash
+sudo ./target/debug/vpnshare-desktop cleanup
+```
+
+## Next Implementation Step
+
+The next milestone is replacing the interim SOCKS transport with the full VSHP
+packet tunnel:
+
+1. Connect to the Android gateway over USB/WiFi/hotspot transports.
+2. Pair using VSHP.
+3. Encrypt IP packet frames end to end.
+4. Add Windows/macOS packet adapters.