Packet Sent but cannot Received Packets

Question

I've been editing androids toyvpn sample project for vpn and i got this one for my sample app

I know there is something wrong/missing with my code because when i manually set up the vpn via android settings, there are packets Receive that's why i've been searching how to receive packets and i dont know how to get this working.

here is my source code that VCL that extends VpnService

import android.app.PendingIntent;
import android.net.VpnService;
import android.os.ParcelFileDescriptor;
import android.util.Log;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.DatagramChannel;

/**
 * Created by Jameshwart Lopez on 8/18/15.
 */
public class VCL extends VpnService {

    private static final String TAG = "VpnClientLibrary";
    private Thread mThread;
    private ParcelFileDescriptor mInterface;

    private String mServerAddress;
    private String mServerPort;
    private PendingIntent mConfigureIntent;
    private String mParameters;

    //a. Configure a builder for the interface.
    Builder builder = new Builder();

    public  void vclRun(){
        try {
            //a. Configure the TUN and get the interface.
            mInterface = builder.setSession("thesessionname")
                    .addAddress("192.168.0.1",24)
                    .addDnsServer("8.8.8.8")
                    .addRoute("0.0.0.0", 0).establish();
            //b. Packets to be sent are queued in this input stream.
            FileInputStream in = new FileInputStream(mInterface.getFileDescriptor());

            //b. Packets received need to be written to this output stream.
            FileOutputStream out = new FileOutputStream(mInterface.getFileDescriptor());

            // Allocate the buffer for a single packet.
            ByteBuffer packet = ByteBuffer.allocate(32767);

            //c. The UDP channel can be used to pass/get ip package to/from server
            DatagramChannel tunnel = DatagramChannel.open();

            // Connect to the server, localhost is used for demonstration only.
            mServerAddress="";//some of the vpn ip address here
            mServerPort="1723";
            InetSocketAddress server = new InetSocketAddress(mServerAddress, Integer.parseInt(mServerPort) );
            tunnel.connect(server);

            // For simplicity, we use the same thread for both reading and
            // writing. Here we put the tunnel into non-blocking mode.
            tunnel.configureBlocking(false);


            // Authenticate and configure the virtual network interface.
            handshake(tunnel);

            //d. Protect this socket, so package send by it will not be feedback to the vpn service.
            protect(tunnel.socket());

            int timer = 0;
            //e. Use a loop to pass packets.
            while (true) {
                //get packet with in
                //put packet to tunnel
                //get packet form tunnel
                //return packet with out
                //sleep is a must

                // Assume that we did not make any progress in this iteration.
                boolean idle = true;

                // Read the outgoing packet from the input stream.
                int length = in.read(packet.array());
                if (length > 0) {
                    // Write the outgoing packet to the tunnel.
                    packet.limit(length);
                    tunnel.write(packet);
                    packet.clear();

                    // There might be more outgoing packets.
                    idle = false;

                    // If we were receiving, switch to sending.
                    if (timer < 1) {
                        timer = 1;
                    }
                }

                // Read the incoming packet from the tunnel.
                length = tunnel.read(packet);
                if (length > 0) {
                    // Ignore control messages, which start with zero.
                    if (packet.get(0) != 0) {
                        // Write the incoming packet to the output stream.
                        out.write(packet.array(), 0, length);
                    }
                    packet.clear();

                    // There might be more incoming packets.
                    idle = false;

                    // If we were sending, switch to receiving.
                    if (timer > 0) {
                        timer = 0;
                    }
                }

                // If we are idle or waiting for the network, sleep for a
                // fraction of time to avoid busy looping.
                if (idle) {
                    Thread.sleep(100);

                    // Increase the timer. This is inaccurate but good enough,
                    // since everything is operated in non-blocking mode.
                    timer += (timer > 0) ? 100 : -100;

                    // We are receiving for a long time but not sending.
                    if (timer < -15000) {
                        // Send empty control messages.
                        packet.put((byte) 0).limit(1);
                        for (int i = 0; i < 3; ++i) {
                            packet.position(0);
                            tunnel.write(packet);
                        }
                        packet.clear();

                        // Switch to sending.
                        timer = 1;
                    }

                    // We are sending for a long time but not receiving.
                    //if (timer > 20000) {
                    //    throw new IllegalStateException("Timed out");
                    //}
                }


            }
        } catch (Exception e) {
            // Catch any exception
            e.printStackTrace();
        } finally {
            try {
                if (mInterface != null) {
                    mInterface.close();
                    mInterface = null;
                }
            } catch (Exception e) {
            }
        }
    }

    private void handshake(DatagramChannel tunnel) throws Exception {
        // To build a secured tunnel, we should perform mutual authentication
        // and exchange session keys for encryption. To keep things simple in
        // this demo, we just send the shared secret in plaintext and wait
        // for the server to send the parameters.
        // Allocate the buffer for handshaking.
        ByteBuffer packet = ByteBuffer.allocate(1024);

        // Control messages always start with zero.
        String password = "";//vpn password here
        packet.put((byte) 0).put(password.getBytes()).flip();

        // Send the secret several times in case of packet loss.
        for (int i = 0; i < 3; ++i) {
            Log.e("packetsdata", packet.toString());
            packet.position(0);
            tunnel.write(packet);
        }
        packet.clear();

        // Wait for the parameters within a limited time.
        for (int i = 0; i < 50; ++i) {
            Thread.sleep(100);

            // Normally we should not receive random packets.
            int length = tunnel.read(packet);
            if (length > 0 && packet.get(0) == 0) {
                configure(new String(packet.array(), 1, length - 1).trim());
                return;
            }
        }
        //throw new IllegalStateException("Timed out");
    }
    private void configure(String parameters) throws Exception {
        // If the old interface has exactly the same parameters, use it!
        if (mInterface != null) {
            Log.i(TAG, "Using the previous interface");
            return;
        }

        // Configure a builder while parsing the parameters.
        Builder builder = new Builder();
        for (String parameter : parameters.split(" ")) {
            String[] fields = parameter.split(",");
            try {
                switch (fields[0].charAt(0)) {
                    case 'm':
                        builder.setMtu(Short.parseShort(fields[1]));
                        break;
                    case 'a':
                        builder.addAddress(fields[1], Integer.parseInt(fields[2]));
                        break;
                    case 'r':
                        builder.addRoute(fields[1], Integer.parseInt(fields[2]));
                        break;
                    case 'd':
                        builder.addDnsServer(fields[1]);
                        break;
                    case 's':
                        builder.addSearchDomain(fields[1]);
                        break;
                }
            } catch (Exception e) {
                throw new IllegalArgumentException("Bad parameter: " + parameter);
            }
        }

        // Close the old interface since the parameters have been changed.
        try {
            mInterface.close();
        } catch (Exception e) {
            // ignore
        }

        // Create a new interface using the builder and save the parameters.
        mInterface = builder.setSession(mServerAddress)
                .setConfigureIntent(mConfigureIntent)
                .establish();
        mParameters = parameters;
        Log.i(TAG, "New interface: " + parameters);
    }
}

this is how i use the class above

private Thread mThread;

    /*
    * Services interface
    * */
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        // Start a new session by creating a new thread.
        mThread = new Thread(this, "VpnRunnable");
        //start the service
        mThread.start();
        /*
         *service is left "started" and will later be restarted by the system
         * http://android-developers.blogspot.com.au/2010/02/service-api-changes-starting-with.html
         */
        return START_STICKY;
    }
    @Override
    public void onDestroy() {

        if (mThread != null) {
            mThread.interrupt();
        }
        super.onDestroy();
    }


    @Override
    public synchronized void run() {
        /*
        * to run the vpn interface call the vclRun method inside VCL class
        * */
       this.vclRun();
    }

Sloe

i get that in toyvpn sample. – Sloe

in my idea is that, it is done when i write packet into the tunnel – Sloe

which part i did it write to send and not to receive? can you point it somewhere in my code??that might help me. :) – Sloe

Answer 1

Firstly, check that there are bytes being sent to your android device. As it won't be reading anything if there is nothing to receive.

Then have a look at this, as it may be messing up your connection.

You need to include this in the onStartCommand:

// The handler is only used to show messages.
if (mHandler == null) {
    mHandler = new Handler(this);
}
// Stop the previous session by interrupting the thread.
if (mThread != null) {
    mThread.interrupt();
}
// Extract information from the intent.
String prefix = getPackageName();
mServerAddress = intent.getStringExtra(prefix + ".ADDRESS");
mServerPort = intent.getStringExtra(prefix + ".PORT");
mSharedSecret = intent.getStringExtra(prefix + ".SECRET").getBytes();
// Start a new session by creating a new thread.
mThread = new Thread(this, "ToyVpnThread");
mThread.start();
return START_STICKY;

And also the details (some shown below) of the sychronized void.

@Override
public synchronized void run() {
    try {
        Log.i(TAG, "Starting");


        // If anything needs to be obtained using the network, get it now.
        // This greatly reduces the complexity of seamless handover, which
        // tries to recreate the tunnel without shutting down everything.
        // In this demo, all we need to know is the server address.


        InetSocketAddress server = new InetSocketAddress(
                mServerAddress, Integer.parseInt(mServerPort));
        // We try to create the tunnel for several times. The better way
        // is to work with ConnectivityManager, such as trying only when
        // the network is avaiable. Here we just use a counter to keep
        // things simple.
        for (int attempt = 0; attempt < 10; ++attempt) {
            mHandler.sendEmptyMessage(R.string.connecting);
            // Reset the counter if we were connected.

            // See BELOW 
            if (run(server)) { 
                attempt = 0;
            }

            // Sleep for a while. This also checks if we got interrupted.
            Thread.sleep(3000);
        } /..../

You are not managing your thread actions well. It is advised to receive any bytes that need to be received before attempting your run. That not doing so can cause problems.
I would go back through your code and put in the things you took out. I also suggest you change your code here:

packet.put((byte) 0).put(password.getBytes()).flip();

Try to use explicit encoding:

packet.put((byte) 0).put(password.getBytes("UTF-8")).flip();

As data can be lost without it. See this answer:
https://mcmap.net/q/332824/-convert-a-string-to-a-byte-array-and-then-back-to-the-original-string

I have checked and your project is using "UTF-8".

Let me know if this doesn't help.

Schoenberg

how does that receive packets?i dont get the idea – Sloe

i have tried copying googles example for vpn it does even sent packets thats why im trying to edit it – Sloe

i mean it does not even sent packets and i would run into PortUnreachableException and SocketException – Sloe

Now I already got PortUnreachableException. Im thinking that this is the port that is unreachable in the vpn server side. – Sloe