Track VPN mode changes

[ignoramous]

From a quick glance at AOSP code, it looks like we can fully expect ConnectivityManager.NetworkCallback#onCapabilitiesChange to trigger whenever the VPN goes in and out of the lockdown ("Block connections without VPN") mode.

Check for VpnService#isLockdownEnabled then when the callback triggers and rebuild the VPN as required (enabling exclude-apps and allowing VPN bypass when VPN not locked down, for example).

See: #178, #39, #224

[ignoramous]

So, it looks like neither onCapabilitiesChanged nor onLinkPropertiesChanged can be relied upon to be called when VPN switches to lockdown mode.

[ignoramous]

Or, wait, may be we were doing it incorrectly, ref: com.android.cts.vpnfirewall.ReflectorVpnService.

        final NetworkRequest request = new NetworkRequest.Builder()
            .addTransportType(NetworkCapabilities.TRANSPORT_VPN)
            .removeCapability(NetworkCapabilities.NET_CAPABILITY_NOT_VPN)
            .removeCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET)
            .build();
        mNetworkCallback = new ConnectivityManager.NetworkCallback() {
                @Override
                public void onAvailable(final Network net) {
                    final Intent intent = new Intent(ACTION_VPN_IS_UP);
                    intent.setPackage(DEVICE_AND_PROFILE_OWNER_PACKAGE);
                    intent.putExtra(EXTRA_ALWAYS_ON, isAlwaysOn());
                    intent.putExtra(EXTRA_LOCKDOWN, isLockdownEnabled());
                    sendBroadcast(intent);
                    ensureNetworkCallbackUnregistered();
                }
            };

[ignoramous]

The above callback works only when "Always-on VPN" is toggled but not for "Block connections without VPN".

One approach to consider now is, to check VpnService#isLockdownEnabled atmost once every 30s on every firewall decision in BraveVpnService#block.

[hussainmohd-a]

As of now, work around is introduced to check for the lockdown mode. Callbacks for the "Block Connection without VPN" is not
available. Need to figure out a better way to track the lockdown mode.
Closing this issue. New issue #257

[ignoramous]

As of now, work around is introduced to check for the lockdown mode.

So, BraveVPNService#checkLockdown is called on every protect.Blocker.block call which happens once per connection / flow.

0a18f65