feat(gui): Smooth startup Part II (#373)

This completes UDENG-1595, by building on top of #355 with the visible
aspects of the change.
Now the GUI automatically attempts to delete the `addr` file and restart
the agent.
Here's how it looks like when a port file is found but the agent is not
running, thus not responsive.


https://github.com/canonical/ubuntu-pro-for-windows/assets/11138291/870b32e3-17f6-4890-8376-0473b0cb5b23

gui/packages/ubuntupro/lib/l10n/app_en.arb

@@ -24,8 +24,7 @@
     "agentStateCannotStart": "Ubuntu Pro background agent cannot be started.",
     "agentStateUnknownEnv": "Ubuntu Pro background agent state cannot be verified. Check your environment settings.",
     "agentStateQuerying": "Checking Ubuntu Pro background agent's state.",
-    "agentStateUnreachable": "Ubuntu Pro background agent is unreachable.",
-    "agentRetryButton": "Click to restart it",
+    "agentStateUnreachable": "Attempting to recover Ubuntu Pro background agent.",
 
     "proHeading": "The most comprehensive subscription\nfor open-source software security\nnow available on WSL",
     "subscribeNow": "Subscribe Now",

gui/packages/ubuntupro/lib/launch_agent.dart

@@ -15,6 +15,8 @@ import 'core/environment.dart';
 Future<bool> launchAgent(String agentRelativePath) async {
   final agentPath = p.join(msixRootDir().path, agentRelativePath);
   try {
+    // Attempts to kill a possibly stuck agent. Failure is desirable in this case.
+    await Process.run('taskkill.exe', ['/f', '/im', p.basename(agentPath)]);
     await Process.start(
       agentPath,
       ['-vv'],

gui/packages/ubuntupro/lib/pages/startup/agent_monitor.dart

@@ -161,7 +161,15 @@ class AgentStartupMonitor {
   /// Thus, we delete the existing `addr` file and retry launching the agent.
   Future<void> reset() async {
     if (_addrFilePath != null) {
-      await File(_addrFilePath!).delete();
+      try {
+        await File(_addrFilePath!).delete();
+      } on PathNotFoundException {
+        // TODO: Log
+        // ignore: avoid_print
+        print(
+          'Port file expected but not found. Likely a race with the agent at this point, not an issue.',
+        );
+      }
     }
   }
 }

gui/packages/ubuntupro/lib/pages/startup/startup_model.dart

@@ -43,6 +43,8 @@ class StartupModel extends ChangeNotifier {
   ViewState get view => _view;
 
   StreamSubscription<AgentState>? _subs;
+  static const _retryLimit = 5;
+  int _retries = 0;
 
   /// Starts the monitor and subscribes to its events. Returns a future that
   /// completes when the agent monitor startup routine completes.
@@ -67,6 +69,12 @@ class StartupModel extends ChangeNotifier {
       _view == ViewState.retry,
       "resetAgent only if it's possible to retry",
     );
+    if (_retries >= _retryLimit) {
+      _view = ViewState.crash;
+      notifyListeners();
+      return;
+    }
+    ++_retries;
     await monitor.reset();
     await _subs?.cancel();
     return init();

gui/packages/ubuntupro/lib/pages/startup/startup_page.dart

@@ -50,30 +50,25 @@ class _StartupAnimatedChildState extends State<StartupAnimatedChild> {
     super.initState();
     final model = context.read<StartupModel>();
     model.init();
-    model.addListener(() {
+    model.addListener(() async {
       if (model.view == ViewState.ok) {
-        Navigator.of(context).pushReplacementNamed(widget.nextRoute);
+        await Navigator.of(context).pushReplacementNamed(widget.nextRoute);
+      }
+      if (model.view == ViewState.retry) {
+        await model.resetAgent();
       }
     });
   }
 
   Widget buildChild(ViewState view, String message) {
     switch (view) {
       case ViewState.inProgress:
+      case ViewState.retry:
         return StartupInProgressWidget(message);
 
       case ViewState.ok:
         return const SizedBox.shrink();
 
-      case ViewState.retry:
-        return StartupRetryWidget(
-          message: message,
-          retry: OutlinedButton(
-            onPressed: context.read<StartupModel>().resetAgent,
-            child: Text(AppLocalizations.of(context).agentRetryButton),
-          ),
-        );
-
       case ViewState.crash:
         return StartupErrorWidget(message);
     }

gui/packages/ubuntupro/lib/pages/startup/startup_widgets.dart

@@ -57,7 +57,6 @@ class StartupInProgressWidget extends StatelessWidget {
         message: message,
         bottom: const LinearProgressIndicator(),
       ),
-      showTitleBar: false,
     );
   }
 }
@@ -78,26 +77,3 @@ class StartupErrorWidget extends StatelessWidget {
     );
   }
 }
-
-/// Displays an error icon followed by the [errorMessage] and a button allowing
-/// users to manually request a reset/retry operation.
-class StartupRetryWidget extends StatelessWidget {
-  const StartupRetryWidget({
-    super.key,
-    required this.message,
-    required this.retry,
-  });
-  final String message;
-  final Widget retry;
-
-  @override
-  Widget build(BuildContext context) {
-    return Pro4WindowsPage(
-      body: StatusColumn(
-        top: const Icon(Icons.error_outline, size: 64),
-        message: message,
-        bottom: retry,
-      ),
-    );
-  }
-}

gui/packages/ubuntupro/test/startup/startup_page_test.dart

@@ -58,32 +58,6 @@ void main() {
     expect(find.text(lastText), findsOneWidget);
   });
 
-  testWidgets('button for retry', (tester) async {
-    final monitor = MockAgentStartupMonitor();
-    when(monitor.start()).thenAnswer(
-      (_) => Stream.fromIterable(
-        [
-          AgentState.querying,
-          AgentState.starting,
-          AgentState.invalid,
-          AgentState.unreachable,
-        ],
-      ),
-    );
-    final model = StartupModel(monitor);
-    await tester.pumpWidget(buildApp(model));
-
-    await model.init();
-    await tester.pumpAndSettle();
-
-    // no success
-    expect(find.text(lastText), findsNothing);
-    // show error icon
-    expect(find.byIcon(Icons.error_outline), findsOneWidget);
-    // and a retry button
-    expect(find.byType(OutlinedButton), findsOneWidget);
-  });
-
   testWidgets('terminal error no button', (tester) async {
     final monitor = MockAgentStartupMonitor();
     when(monitor.start()).thenAnswer(
@@ -134,7 +108,6 @@ void main() {
     );
 
     await tester.pumpWidget(app);
-    await tester.pumpAndSettle();
 
     final context = tester.element(find.byType(StartupAnimatedChild));
     final model = Provider.of<StartupModel>(context, listen: false);