Connection reset by peer error when using SOCKS5 proxy in Android VPN app

Question

I’ve been working on an Android app that uses a custom VPN service to connect via a SOCKS5 proxy on my VPS. However, I’m encountering the following error:

Connection failed: Connection reset by peer

I suspect the problem is that the SOCKS5 proxy is not being properly created or initialized in my app.

Here’s the code I’m using:

class MyVpnService : android.net.VpnService() {
    private val TAG = "VpnService"
    private val sshClient = SSHClient()

    private var vpnInterface: ParcelFileDescriptor? = null

    override fun onCreate() {
        super.onCreate()
        GlobalScope.launch {
            showNotification()
            startVPN()
        }
    }

    private fun startVPN() {
        // Step 1: Start the SOCKS proxy (SSH connection)
        sshClient.startSSH(
            host = "my.ssh.service",
            port = 22,
            username = "root",
            password = "password",
            socksPort = 1080
        )

        // Step 2: Configure and establish the VPN interface
        val builder = Builder()
        builder.setSession("MyVPN")
            .addAddress("10.0.0.2", 24) // VPN IP address
            .addDnsServer("8.8.8.8") // DNS server
            .addRoute("0.0.0.0", 0) // Route all traffic through VPN
            .setMtu(1500)

        vpnInterface = builder.establish()
        if (vpnInterface == null) {
            Log.e(TAG, "Failed to establish VPN interface")
            return
        }
        Log.d(TAG, "VPN interface established")

        // Step 3: Redirect traffic through the SOCKS proxy
        redirectTraffic(vpnInterface!!)
        Log.d(TAG, "Traffic redirection started")
    }

    override fun onDestroy() {
        super.onDestroy()
        stopVPN()
    }

    private fun stopVPN() {
        sshClient.stopSSH()
        vpnInterface?.close()
        vpnInterface = null
    }

    private fun showNotification() {
        val notification = NotificationCompat.Builder(this, "my_channel")
            .setSmallIcon(com.sy.onboarding_ui.R.drawable.ic_next)
            .setContentTitle("Run is active")
            .setContentText("Hello world")
            .build()
        startForeground(1, notification)
    }
}

fun redirectTraffic(vpnInterface: ParcelFileDescriptor) {
    val buffer = ByteBuffer.allocate(32767)

    try {
        // Connect to the SOCKS5 proxy
        val tunnel = SocketChannel.open(InetSocketAddress("127.0.0.1", 1080))
        if (!tunnel.isConnected) {
            Log.e("redirectTraffic", "Failed to connect to SOCKS5 proxy")
            return
        }
        Log.d("redirectTraffic", "Connected to SOCKS5 proxy")

        val inputStream = ParcelFileDescriptor.AutoCloseInputStream(vpnInterface)
        val outputStream = ParcelFileDescriptor.AutoCloseOutputStream(vpnInterface)

        while (true) {
            // Read packets from the VPN interface
            val length = inputStream.read(buffer.array())
            if (length > 0) {
                buffer.limit(length)

                // Forward packets to the SOCKS5 proxy
                tunnel.write(buffer)
                Log.d("redirectTraffic", "Forwarded $length bytes to SOCKS5 proxy")

                // Clear the buffer for the next read
                buffer.clear()
            }

            // Read responses from the SOCKS5 proxy
            val bytesRead = tunnel.read(buffer)
            if (bytesRead > 0) {
                // Write responses back to the VPN interface
                outputStream.write(buffer.array(), 0, bytesRead)
                Log.d("redirectTraffic", "Received $bytesRead bytes from SOCKS5 proxy")

                // Clear the buffer for the next read
                buffer.clear()
            }
        }
    } catch (e: IOException) {
        Log.e("redirectTraffic", "Connection failed: ${e.message}")
        e.printStackTrace()
    }
}

Logs:

SSH connection established
SOCKS5 proxy started on port 1080
VPN interface established
Connected to SOCKS5 proxy
Forwarded 76 bytes to SOCKS5 proxy
Connection failed: Connection reset by peer