如何在VpnService中检索数据包

Question

我有ToyVpnService的以下实现，我得到了here

public class ToyVpnService extends VpnService implements Handler.Callback, Runnable {
    private static final String TAG = "ToyVpnService";

    private Handler mHandler;
    private Thread mThread;

    private ParcelFileDescriptor mInterface;

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        // 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();
        }

        // Start a new session by creating a new thread.
        mThread = new Thread(this, "ToyVpnThread");
        mThread.start();
        return START_STICKY;
    }

    @Override
    public void onDestroy() {
        if (mThread != null) {
            mThread.interrupt();
        }
    }

    @Override
    public boolean handleMessage(Message message) {
        if (message != null) {
            Toast.makeText(this, message.what, Toast.LENGTH_SHORT).show();
        }
        return true;
    }

    @Override
    public synchronized void run() {
        Log.i(TAG, "running vpnService");
        try {
            runVpnConnection();
        } catch (Exception e) {
            e.printStackTrace();
            //Log.e(TAG, "Got " + e.toString());
        } finally {
            try {
                mInterface.close();
            } catch (Exception e) {
                // ignore
            }
            mInterface = null;

            mHandler.sendEmptyMessage(R.string.disconnected);
            Log.i(TAG, "Exiting");
        }
    }

    private boolean runVpnConnection() throws Exception {

        configure();

        FileInputStream in = new FileInputStream(mInterface.getFileDescriptor());

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

        // We keep forwarding packets till something goes wrong.
        while (true) {
            // 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) {

                Log.i(TAG, "************new packet");
                System.exit(-1);
                while (packet.hasRemaining()) {
                    Log.i(TAG, "" + packet.get());
                    //System.out.print((char) packet.get());
                }
                packet.limit(length);
//                  tunnel.write(packet);
                packet.clear();

                // There might be more outgoing packets.
                idle = false;
            }
            Thread.sleep(50);
        }
    }


    public String getLocalIpAddress() {
        try {
            for (Enumeration<NetworkInterface> en = NetworkInterface.getNetworkInterfaces(); en.hasMoreElements(); ) {
                NetworkInterface intf = en.nextElement();
                for (Enumeration<InetAddress> enumIpAddr = intf.getInetAddresses(); enumIpAddr.hasMoreElements(); ) {
                    InetAddress inetAddress = enumIpAddr.nextElement();
                    Log.i(TAG, "****** INET ADDRESS ******");
                    Log.i(TAG, "address: " + inetAddress.getHostAddress());
                    Log.i(TAG, "hostname: " + inetAddress.getHostName());
                    Log.i(TAG, "address.toString(): " + inetAddress.getHostAddress().toString());
                    if (!inetAddress.isLoopbackAddress()) {
                        //IPAddresses.setText(inetAddress.getHostAddress().toString());
                        Log.i(TAG, "IS NOT LOOPBACK ADDRESS: " + inetAddress.getHostAddress().toString());
                        return inetAddress.getHostAddress().toString();
                    } else {
                        Log.i(TAG, "It is a loopback address");
                    }
                }
            }
        } catch (SocketException ex) {
            String LOG_TAG = null;
            Log.e(LOG_TAG, ex.toString());
        }

        return null;
    }

    private void configure() 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();
        builder.setMtu(1500);
        builder.addAddress(getLocalIpAddress(), 24);
        try {
            mInterface.close();
        } catch (Exception e) {
            // ignore
        }

        mInterface = builder.establish();
    }
}

它似乎正在接收数据包，但我不知道如何读取paclkets中的数据。代码似乎不完整（因此注释掉的tunnel.write(packet)因为没有变量tunnel）。这是正确的方法吗？或者有更好的方法吗？