android: VpnStateService - single retry countdown, isolated listeners

- remove pending RETRY_MSG on reset/set: a Retry tap during a backoff
  started a second countdown chain (double-speed ticks, two reconnects)
- notify listeners over a copy with per-listener error handling
- disconnect() tolerates the VPN service not running

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/frontends/android/app/src/main/java/org/strongswan/android/logic/VpnStateService.java

@@ -41,6 +41,7 @@ import org.strongswan.android.ui.VpnProfileControlActivity;
 
 import java.lang.ref.WeakReference;
 import java.util.Collections;
+import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.LinkedList;
 import java.util.List;
@@ -199,6 +200,27 @@ public class VpnStateService extends Service
 		mListeners.remove(listener);
 	}
 
+	/**
+	 * Notify all registered listeners about a state change.  Iterates over a
+	 * copy (a listener may unregister itself from its callback) and isolates
+	 * the listeners from each other: one failing listener must neither skip
+	 * the others nor crash the main thread.
+	 */
+	private void notifyStateListeners()
+	{
+		for (VpnStateListener listener : new ArrayList<>(mListeners))
+		{
+			try
+			{
+				listener.stateChanged();
+			}
+			catch (RuntimeException e)
+			{
+				DiagLog.i(TAG, "state listener failed: " + e);
+			}
+		}
+	}
+
 	/**
 	 * Get the current VPN profile.
 	 *
@@ -373,7 +395,15 @@ public class VpnStateService extends Service
 		Context context = getApplicationContext();
 		Intent intent = new Intent(context, CharonVpnService.class);
 		intent.setAction(CharonVpnService.DISCONNECT_ACTION);
-		context.startService(intent);
+		try
+		{
+			context.startService(intent);
+		}
+		catch (IllegalStateException e)
+		{	/* background start of a service that is not running (Android 8+):
+			 * without the service there is no tunnel to tear down */
+			DiagLog.i(TAG, "disconnect: VPN service not running (" + e.getMessage() + ")");
+		}
 	}
 
 	/**
@@ -589,10 +619,7 @@ public class VpnStateService extends Service
 				{
 					if (change.call())
 					{	/* otherwise there is no need to notify the listeners */
-						for (VpnStateListener listener : mListeners)
+						notifyStateListeners();
-						{
-							listener.stateChanged();
-						}
 						/* the home screen widget mirrors the state */
 						VpnProfile widgetProfile = mProfile;
 						ShxWidgetState.publish(VpnStateService.this, mState, getErrorState(),
@@ -602,7 +629,7 @@ public class VpnStateService extends Service
 				}
 				catch (Exception e)
 				{
-					e.printStackTrace();
+					DiagLog.i(TAG, "state change failed: " + e);
 				}
 			}
 		});
@@ -766,6 +793,9 @@ public class VpnStateService extends Service
 		mRetryTimeout = mRetryIn = mTimeoutProvider.getTimeout(error);
 		mRetryFrozen = false;
 		DiagLog.i(TAG, "error " + error + ", retry in " + (mRetryTimeout / 1000) + "s");
+		/* never run two countdown chains in parallel (double-speed countdown,
+		 * double notification updates and two reconnects at zero) */
+		mHandler.removeMessages(RETRY_MSG);
 		if (mRetryTimeout <= 0)
 		{
 			return;
@@ -778,6 +808,7 @@ public class VpnStateService extends Service
 	 */
 	private void resetRetryTimer()
 	{
+		mHandler.removeMessages(RETRY_MSG);
 		mRetryTimeout = 0;
 		mRetryIn = 0;
 		mRetryFrozen = false;
@@ -858,10 +889,7 @@ public class VpnStateService extends Service
 				/* calculate next interval before notifying listeners */
 				long next = SystemClock.uptimeMillis() + retryStep(service.mRetryIn);
 
-				for (VpnStateListener listener : service.mListeners)
+				service.notifyStateListeners();
-				{
-					listener.stateChanged();
-				}
 				sendMessageAtTime(obtainMessage(RETRY_MSG), next);
 			}
 			else
@@ -872,10 +900,7 @@ public class VpnStateService extends Service
 					 * ticking every second */
 					service.mRetryFrozen = true;
 					service.mRetryIn = RETRY_SUPPRESS_MS;
-					for (VpnStateListener listener : service.mListeners)
+					service.notifyStateListeners();
-					{
-						listener.stateChanged();
-					}
 					sendMessageAtTime(obtainMessage(RETRY_MSG), SystemClock.uptimeMillis() + RETRY_SUPPRESS_MS);
 					return;
 				}