Android VpnService.Builder.establish() sporadically null

Question

When I try to create the tunnel interface for my VpnService, I'm getting the following error:

Attempt to invoke virtual method 'java.lang.String android.os.ParcelFileDescriptor.toString()' on a null object reference

The only resolve I currently have is to restart the device when this happens. If I do not, I'm unable to create the tunnel at all.

My code for creating the tunnel:

// This is inside my VpnService implementation 

private ParcelFileDescriptor configureTunnelWithPushOpts(PushOpts popts)
{
    VpnService.Builder builder = this.new Builder();

    builder.setMtu       ( currentServerPrefs.SERVER_MTU );
    builder.addAddress   ( popts.ip, 32                  );
    builder.addDnsServer ( popts.dns1                    );
    builder.addDnsServer ( popts.dns2                    );
    builder.addRoute     ( "0.0.0.0", 0                  );


    // Note: Blocking mode is now enabled in native
    // code under the setFileDescriptor function.
    // builder.setBlocking(true);

    builder.setConfigureIntent(
            PendingIntent.getActivity(
                    this,
                    0,
                    new Intent(
                            this,
                            MainActivity.class
                    ),
            PendingIntent.FLAG_UPDATE_CURRENT)
    );

    final ParcelFileDescriptor vpnInterface;

    synchronized (this) {
        builder.setSession(currentServerPrefs.SERVER_ADDRESS);
        vpnInterface = builder.establish();
    }

    Logger.info("New interface: " + vpnInterface.toString(), this);
    return vpnInterface;
}

Edit:

According to the documentation, the establish function will return null if the VpnService has not been prepared, however I am using this to prepare it prior to running the above function.

// This is inside my MainActivity class

Intent intent = VpnService.prepare(getApplicationContext());
if (intent != null) {
    startActivityForResult(intent, 0);
} else {
    onActivityResult(0, RESULT_OK, null);
}

. . . 

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (resultCode == RESULT_OK) {
        Intent intent = new Intent(this, MyVpnService.class);
        startService(intent);
    }
}

Phone I'm using for debugging

Google Nexus 5 Running Android 5.0.1

Edit

I figured out how to replicate it so that it's no longer sporadic. Basically, if I uninstall the application while the VPN is connected, and then reinstall it and try to start it back up, I receive a null response when i run builder.establish(). I fear this could pose potential issues when the application is updated through the Google Play Store.

Aside from that, Please do not mark this question as a duplicate. Every other question on this matter has been given the answer that the service needs to be prepared before the builder is established, however I am preparing it in my case and have a different cause for my problem. Any help would be appreciated.

Have you looked at the [OnRevoke](https://developer.android.com/reference/android/net/VpnService.html#onRevoke()) method? it might be possible that something else uses the vpn — Hugo sama, Jul 27 '17 at 00:17
I know this is an old question, but have you found the solution for this issue? I'm facing the same behavior (on 5.0.1 Android, Samsung Galaxy S5). Thanks in advance. — CyberMJ, Sep 26 '18 at 08:45

score 3 · Answer 1 · answered Apr 14 '18 at 16:34

3

Thanks a lot for the hint, it brought me to the solution!

I had the same problem in Android 5.0.2: Everything worked fine, and I installed the vpn app I am developing. The next day, suddenly, an unresolvable NullPointerException, although prepare was properly called.

The issue could be solved in my environment with the following steps:

Uninstall the app. It does not matter, if the app has still working VPN functionality or not.
Restart your phone. Make sure that it was shut off completely.
After restart, make sure the app is not installed anymore (I had some strange development issues where an app was reinstalled after rebooting my phone).
Install your VPN app again. It should receive a vpn interface now, and not anymore null.

answered Apr 14 '18 at 16:34

Martin Bories

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The problem with this is that end users might do the same thing, uninstall the app and then re-install it again and experience the same NullPointerException. I don't want to have to tell my end users to restart their phone just to use the application. – Nathan F. Apr 14 '18 at 16:50
Maybe one could catch the uninstallation with an even listener and then gracefully deactivate/shutdown the vpn? Does this Problem only occur in a development environment (could also be related to adb), or have you tested it with a production App? – Martin Bories Apr 14 '18 at 16:52
@MartinBories This answer is very helpful for me :) and it genuinely worked in my case. – Jarvis__-_-__ Feb 05 '22 at 18:57

Android VpnService.Builder.establish() sporadically null

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