Do not crash when the activity is created in the background

app/src/main/java/com/openipc/pixelpilot/VideoActivity.java

@@ -1294,12 +1294,30 @@ private void startVpnService() {
         if (intent != null) {
             startActivityForResult(intent, VPN_REQUEST_CODE);
         } else {
-            Intent serviceIntent = new Intent(this, WfbNgVpnService.class);
-            startService(serviceIntent);
+            startServiceIfAllowed(new Intent(this, WfbNgVpnService.class));
         }
 
     }
 
+    /**
+     * Starts a service, or does nothing if the app is in the background.
+     *
+     * <p>Android 12 and later refuse a service start from a background app with
+     * BackgroundServiceStartNotAllowedException, and this activity can be created in the
+     * background: started while the screen is off, it threw from onCreate() and took the app
+     * down before it had shown anything. Nothing is lost by skipping it, because onResume() calls
+     * startVpnService() again once the app is actually in front.
+     */
+    private void startServiceIfAllowed(Intent intent) {
+        try {
+            startService(intent);
+        } catch (IllegalStateException e) {
+            // BackgroundServiceStartNotAllowedException is an IllegalStateException. Catching the
+            // parent avoids naming a class that only exists from API 31, below minSdk.
+            Log.w(TAG, "not starting " + intent.getComponent() + " from the background", e);
+        }
+    }
+
     private Uri openDvrFile() {
         String dvrFolder = getSharedPreferences("general",
                 Context.MODE_PRIVATE).getString("dvr_folder_", "");
@@ -1452,8 +1470,7 @@ protected void onActivityResult(int requestCode, int resultCode, @Nullable Inten
         } else if (requestCode == 100) {  // VPN_REQUEST_CODE is 100
             if (resultCode == RESULT_OK) {
                 // VPN permission granted, start the VPN service
-                Intent serviceIntent = new Intent(this, WfbNgVpnService.class);
-                startService(serviceIntent);
+                startServiceIfAllowed(new Intent(this, WfbNgVpnService.class));
             } else {
                 // VPN permission not granted
                 Log.e(TAG, "VPN permission was not granted by the user.");
@@ -1547,11 +1564,10 @@ protected void onPause() {
         videoPlayer.stopAudio();
         wfbLinkManager.stopAdapters();
 
-        // Stop VPN service
+        // Stop VPN service - directly, not with a STOP_SERVICE start, which Android can refuse
+        // from the background. See WfbNgVpnService.stopRunning().
         Log.w(TAG, "onPause: stopping service");
-        Intent intent = new Intent(this, WfbNgVpnService.class);
-        intent.setAction("STOP_SERVICE");
-        startService(intent);
+        WfbNgVpnService.stopRunning();
     }
 
     @Override

app/src/main/java/com/openipc/pixelpilot/WfbNgVpnService.java

@@ -32,30 +32,63 @@ public class WfbNgVpnService extends VpnService {
     // Control flags
     private volatile boolean isRunning = false;
 
+    // The instance that is running, if any - see stopRunning().
+    private static volatile WfbNgVpnService running;
+
     @Override
-    public int onStartCommand(Intent intent, int flags, int startId) {
-        if (intent != null && "STOP_SERVICE".equals(intent.getAction())) {
-            Log.i(TAG, "VPN Service stopping");
-            // Stop threads
-            isRunning = false;
+    public void onCreate() {
+        super.onCreate();
+        running = this;
+    }
 
-            if (udpToVpnThread != null) {
-                udpToVpnThread.interrupt();
-            }
-            if (vpnToUdpThread != null) {
-                vpnToUdpThread.interrupt();
-            }
+    /**
+     * Takes the tunnel down if it is up. Safe to call from anywhere in the app's process, in any
+     * state.
+     *
+     * <p>Not through startService(): Android refuses a service start from the background, and a
+     * stop sent that way is dropped along with it. onPause() normally still runs while the app
+     * may start services - going to sleep with the app in front, the stop went through - but
+     * nothing guarantees it, and an activity created in the background pauses there too. Not
+     * through stopService() either: once the interface is established the system holds its own
+     * binding to a VpnService, and stopService() leaves it running until the interface is closed.
+     * The service lives in this process, so closing it directly cannot be refused.
+     */
+    public static void stopRunning() {
+        final WfbNgVpnService service = running;
+        if (service != null) {
+            service.shutDown();
+        }
+    }
 
-            // Close the interface
-            if (vpnInterface != null) {
-                try {
-                    vpnInterface.close();
-                } catch (IOException e) {
-                    Log.e(TAG, "Failed to close VPN interface", e);
-                }
-                vpnInterface = null;
+    /** Stops the worker threads, closes the interface and stops the service. */
+    private void shutDown() {
+        Log.i(TAG, "VPN Service stopping");
+        // Stop threads
+        isRunning = false;
+
+        if (udpToVpnThread != null) {
+            udpToVpnThread.interrupt();
+        }
+        if (vpnToUdpThread != null) {
+            vpnToUdpThread.interrupt();
+        }
+
+        // Close the interface
+        if (vpnInterface != null) {
+            try {
+                vpnInterface.close();
+            } catch (IOException e) {
+                Log.e(TAG, "Failed to close VPN interface", e);
             }
-            stopSelf();
+            vpnInterface = null;
+        }
+        stopSelf();
+    }
+
+    @Override
+    public int onStartCommand(Intent intent, int flags, int startId) {
+        if (intent != null && "STOP_SERVICE".equals(intent.getAction())) {
+            shutDown();
             return START_NOT_STICKY;
         }
 
@@ -211,6 +244,9 @@ public void run() {
     public void onDestroy() {
         super.onDestroy();
         Log.i(TAG, "VPN Service destroyed");
+        if (running == this) {
+            running = null;
+        }
 
         // Stop threads
         isRunning = false;