FlutterBuildState error catching

app_flutter/lib/build_dashboard.dart

@@ -49,8 +49,9 @@ class BuildDashboard extends StatelessWidget {
       builder: (_, FlutterBuildState buildState, Widget child) => Scaffold(
         appBar: AppBar(
           title: const Text('Flutter Build Dashboard v2'),
-          backgroundColor:
-              buildState.isTreeBuilding ? theme.primaryColor : theme.errorColor,
+          backgroundColor: buildState.isTreeBuilding.data
+              ? theme.primaryColor
+              : theme.errorColor,
         ),
         body: Column(
           children: const <Widget>[

app_flutter/lib/service/appengine_cocoon.dart

@@ -31,40 +31,55 @@ class AppEngineCocoonService implements CocoonService {
   final http.Client _client;
 
   @override
-  Future<List<CommitStatus>> fetchCommitStatuses() async {
+  Future<CocoonResponse<List<CommitStatus>>> fetchCommitStatuses() async {
     /// This endpoint returns JSON [List<Agent>, List<CommitStatus>]
     final http.Response response =
         await _client.get('$_baseApiUrl/public/get-status');
 
     if (response.statusCode != HttpStatus.ok) {
-      throw HttpException(
-          '$_baseApiUrl/public/get-status returned ${response.statusCode}');
+      print(response.body);
+      return CocoonResponse<List<CommitStatus>>()
+        ..error =
+            '$_baseApiUrl/public/get-status returned ${response.statusCode}';
     }
 
-    final Map<String, Object> jsonResponse = jsonDecode(response.body);
-
-    return _commitStatusesFromJson(jsonResponse['Statuses']);
+    try {
+      final Map<String, Object> jsonResponse = jsonDecode(response.body);
+      return CocoonResponse<List<CommitStatus>>()
+        ..data = _commitStatusesFromJson(jsonResponse['Statuses']);
+    } catch (error) {
+      return CocoonResponse<List<CommitStatus>>()..error = error.toString();
+    }
   }
 
   @override
-  Future<bool> fetchTreeBuildStatus() async {
+  Future<CocoonResponse<bool>> fetchTreeBuildStatus() async {
     /// This endpoint returns JSON {AnticipatedBuildStatus: [BuildStatus]}
     final http.Response response =
         await _client.get('$_baseApiUrl/public/build-status');
 
     if (response.statusCode != HttpStatus.ok) {
-      throw HttpException(
-          '$_baseApiUrl/public/build-status returned ${response.statusCode}');
+      print(response.body);
+      return CocoonResponse<bool>()
+        ..error =
+            '$_baseApiUrl/public/build-status returned ${response.statusCode}';
     }
 
-    final Map<String, Object> jsonResponse = jsonDecode(response.body);
+    Map<String, Object> jsonResponse;
+    try {
+      jsonResponse = jsonDecode(response.body);
+    } catch (error) {
+      return CocoonResponse<bool>()
+        ..error = '$_baseApiUrl/public/build-status had a malformed response';
+    }
 
     if (!_isBuildStatusResponseValid(jsonResponse)) {
-      throw const HttpException(
-          '$_baseApiUrl/public/build-status had a malformed response');
+      return CocoonResponse<bool>()
+        ..error = '$_baseApiUrl/public/build-status had a malformed response';
     }
 
-    return jsonResponse['AnticipatedBuildStatus'] == 'Succeeded';
+    return CocoonResponse<bool>()
+      ..data = jsonResponse['AnticipatedBuildStatus'] == 'Succeeded';
   }
 
   /// Check if [Map<String,Object>] follows the format for build-status.

app_flutter/lib/service/cocoon.dart

@@ -30,8 +30,19 @@ abstract class CocoonService {
   /// Gets build information from the last 200 commits.
   ///
   // TODO(chillers): Make configurable to get range of commits, https://github.com/flutter/cocoon/issues/458
-  Future<List<CommitStatus>> fetchCommitStatuses();
+  Future<CocoonResponse<List<CommitStatus>>> fetchCommitStatuses();
 
   /// Gets the current build status of flutter/flutter.
-  Future<bool> fetchTreeBuildStatus();
+  Future<CocoonResponse<bool>> fetchTreeBuildStatus();
+}
+
+/// Wrapper class for data this state serves.
+///
+/// Holds [data] and possible error information.
+class CocoonResponse<T> {
+  /// The data that gets used from [CocoonService].
+  T data;
+
+  /// Error information that can be used for debugging.
+  String error;
 }

app_flutter/lib/service/fake_cocoon.dart

@@ -20,13 +20,14 @@ class FakeCocoonService implements CocoonService {
   final Random random;
 
   @override
-  Future<List<CommitStatus>> fetchCommitStatuses() async {
-    return _createFakeCommitStatuses();
+  Future<CocoonResponse<List<CommitStatus>>> fetchCommitStatuses() async {
+    return CocoonResponse<List<CommitStatus>>()
+      ..data = _createFakeCommitStatuses();
   }
 
   @override
-  Future<bool> fetchTreeBuildStatus() async {
-    return random.nextBool();
+  Future<CocoonResponse<bool>> fetchTreeBuildStatus() async {
+    return CocoonResponse<bool>()..data = random.nextBool();
   }
 
   List<CommitStatus> _createFakeCommitStatuses() {

app_flutter/lib/state/flutter_build.dart

@@ -30,11 +30,16 @@ class FlutterBuildState extends ChangeNotifier {
   Timer refreshTimer;
 
   /// The current status of the commits loaded.
-  List<CommitStatus> statuses = <CommitStatus>[];
+  CocoonResponse<List<CommitStatus>> _statuses =
+      CocoonResponse<List<CommitStatus>>()..data = <CommitStatus>[];
+  CocoonResponse<List<CommitStatus>> get statuses => _statuses;
 
   /// Whether or not flutter/flutter currently passes tests.
-  bool get isTreeBuilding => _isTreeBuilding;
-  bool _isTreeBuilding = true;
+  CocoonResponse<bool> _isTreeBuilding = CocoonResponse<bool>()..data = false;
+  CocoonResponse<bool> get isTreeBuilding => _isTreeBuilding;
+
+  /// Whether an error occured getting the latest data for the fields of this state.
+  bool get hasError => _isTreeBuilding.error != null || _statuses.error != null;
 
   /// Start a fixed interval loop that fetches build state updates based on [refreshRate].
   Future<void> startFetchingBuildStateUpdates() async {
@@ -50,14 +55,15 @@ class FlutterBuildState extends ChangeNotifier {
         Timer.periodic(refreshRate, (_) => _fetchBuildStatusUpdate());
   }
 
-  /// Request the latest [statuses] from [CocoonService].
+  /// Request the latest [statuses] and [isTreeBuilding] from [CocoonService].
   Future<void> _fetchBuildStatusUpdate() async {
-    await Future.wait<void>(<Future<void>>[
-      _cocoonService.fetchCommitStatuses().then<List<CommitStatus>>(
-          (List<CommitStatus> commitStatuses) => statuses = commitStatuses),
+    await Future.wait(<Future<void>>[
+      _cocoonService.fetchCommitStatuses().then(
+          (CocoonResponse<List<CommitStatus>> response) =>
+              _statuses = response),
       _cocoonService
           .fetchTreeBuildStatus()
-          .then<bool>((bool treeStatus) => _isTreeBuilding = treeStatus),
+          .then((CocoonResponse<bool> response) => _isTreeBuilding = response),
     ]);
 
     notifyListeners();

app_flutter/lib/status_grid.dart

@@ -19,11 +19,22 @@ import 'task_icon.dart';
 class StatusGridContainer extends StatelessWidget {
   const StatusGridContainer({Key key}) : super(key: key);
 
+  @visibleForTesting
+  static const String errorCocoonBackend = 'Cocoon Backend is having issues';
+
   @override
   Widget build(BuildContext context) {
     return Consumer<FlutterBuildState>(
       builder: (_, FlutterBuildState buildState, Widget child) {
-        final List<CommitStatus> statuses = buildState.statuses;
+        final List<CommitStatus> statuses = buildState.statuses.data;
+
+        if (buildState.hasError) {
+          print('FlutterBuildState has an error');
+          print('isTreeBuilding: ${buildState.isTreeBuilding.error}');
+          print('statuses: ${buildState.statuses.error}');
+
+          // TODO(chillers): Display the error
+        }
 
         // Assume if there is no data that it is loading.
         if (statuses.isEmpty) {

app_flutter/test/service/appengine_cocoon_test.dart

@@ -7,10 +7,12 @@ import 'package:http/http.dart' show Request, Response;
 import 'package:http/testing.dart';
 import 'package:test/test.dart';
 
-import 'package:app_flutter/service/appengine_cocoon.dart';
 import 'package:cocoon_service/protos.dart'
     show Commit, CommitStatus, Stage, Task;
 
+import 'package:app_flutter/service/appengine_cocoon.dart';
+import 'package:app_flutter/service/cocoon.dart';
+
 // This is based off data the Cocoon backend sends out from v1.
 // It doesn't map directly to protos since the backend does
 // not use protos yet.
@@ -86,13 +88,14 @@ void main() {
       }));
     });
 
-    test('should return List<CommitStatus>', () {
+    test('should return CocoonResponse<List<CommitStatus>>', () {
       expect(service.fetchCommitStatuses(),
-          const TypeMatcher<Future<List<CommitStatus>>>());
+          const TypeMatcher<Future<CocoonResponse<List<CommitStatus>>>>());
     });
 
     test('should return expected List<CommitStatus>', () async {
-      final List<CommitStatus> statuses = await service.fetchCommitStatuses();
+      final CocoonResponse<List<CommitStatus>> statuses =
+          await service.fetchCommitStatuses();
 
       final CommitStatus expectedStatus = CommitStatus()
         ..commit = (Commit()
@@ -118,22 +121,26 @@ void main() {
             ..stageName = 'devicelab'
             ..status = 'Succeeded'));
 
-      expect(statuses.length, 1);
-      expect(statuses.first, expectedStatus);
+      expect(statuses.data.length, 1);
+      expect(statuses.data.first, expectedStatus);
     });
 
-    test('should throw exception if given non-200 response', () {
+    test('should have error if given non-200 response', () async {
       service = AppEngineCocoonService(
           client: MockClient((Request request) async => Response('', 404)));
 
-      expect(service.fetchCommitStatuses(), throwsException);
+      final CocoonResponse<List<CommitStatus>> response =
+          await service.fetchCommitStatuses();
+      expect(response.error, isNotNull);
     });
 
-    test('should throw exception if given bad response', () {
+    test('should have error if given bad response', () async {
       service = AppEngineCocoonService(
           client: MockClient((Request request) async => Response('bad', 200)));
 
-      expect(service.fetchCommitStatuses(), throwsException);
+      final CocoonResponse<List<CommitStatus>> response =
+          await service.fetchCommitStatuses();
+      expect(response.error, isNotNull);
     });
   });
 
@@ -147,39 +154,46 @@ void main() {
       }));
     });
 
-    test('should return bool', () {
-      expect(service.fetchTreeBuildStatus(), const TypeMatcher<Future<bool>>());
+    test('should return CocoonResponse<bool>', () {
+      expect(service.fetchTreeBuildStatus(),
+          const TypeMatcher<Future<CocoonResponse<bool>>>());
     });
 
-    test('should return true when given Succeeded', () async {
-      final bool treeBuildStatus = await service.fetchTreeBuildStatus();
+    test('data should be true when given Succeeded', () async {
+      final CocoonResponse<bool> treeBuildStatus =
+          await service.fetchTreeBuildStatus();
 
-      expect(treeBuildStatus, true);
+      expect(treeBuildStatus.data, true);
     });
 
-    test('should return false when given Failed', () async {
+    test('data should be false when given Failed', () async {
       service =
           AppEngineCocoonService(client: MockClient((Request request) async {
         return Response(jsonBuildStatusFalseResponse, 200);
       }));
 
-      final bool treeBuildStatus = await service.fetchTreeBuildStatus();
+      final CocoonResponse<bool> treeBuildStatus =
+          await service.fetchTreeBuildStatus();
 
-      expect(treeBuildStatus, false);
+      expect(treeBuildStatus.data, false);
     });
 
-    test('should throw exception if given non-200 response', () {
+    test('should have error if given non-200 response', () async {
       service = AppEngineCocoonService(
           client: MockClient((Request request) async => Response('', 404)));
 
-      expect(service.fetchTreeBuildStatus(), throwsException);
+      final CocoonResponse<bool> response =
+          await service.fetchTreeBuildStatus();
+      expect(response.error, isNotNull);
     });
 
-    test('should throw exception if given bad response', () {
+    test('should have error if given bad response', () async {
       service = AppEngineCocoonService(
           client: MockClient((Request request) async => Response('bad', 200)));
 
-      expect(service.fetchTreeBuildStatus(), throwsException);
+      final CocoonResponse<bool> response =
+          await service.fetchTreeBuildStatus();
+      expect(response.error, isNotNull);
     });
   });
 }

app_flutter/test/state/flutter_build_test.dart

@@ -9,6 +9,7 @@ import 'package:mockito/mockito.dart';
 
 import 'package:cocoon_service/protos.dart' show CommitStatus;
 
+import 'package:app_flutter/service/cocoon.dart';
 import 'package:app_flutter/service/fake_cocoon.dart';
 import 'package:app_flutter/state/flutter_build.dart';
 
@@ -21,10 +22,12 @@ void main() {
       mockService = MockCocoonService();
       buildState = FlutterBuildState(cocoonService: mockService);
 
-      when(mockService.fetchCommitStatuses()).thenAnswer(
-          (_) => Future<List<CommitStatus>>.value(<CommitStatus>[]));
-      when(mockService.fetchTreeBuildStatus())
-          .thenAnswer((_) => Future<bool>.value(true));
+      when(mockService.fetchCommitStatuses()).thenAnswer((_) =>
+          Future<CocoonResponse<List<CommitStatus>>>.value(
+              CocoonResponse<List<CommitStatus>>()..data = <CommitStatus>[]));
+      when(mockService.fetchTreeBuildStatus()).thenAnswer((_) =>
+          Future<CocoonResponse<bool>>.value(
+              CocoonResponse<bool>()..data = true));
     });
 
     testWidgets('timer should periodically fetch updates',

app_flutter/test/status_grid_test.dart

@@ -8,6 +8,7 @@ import 'package:provider/provider.dart';
 
 import 'package:cocoon_service/protos.dart' show CommitStatus, Task;
 
+import 'package:app_flutter/service/cocoon.dart';
 import 'package:app_flutter/service/fake_cocoon.dart';
 import 'package:app_flutter/state/flutter_build.dart';
 import 'package:app_flutter/commit_box.dart';
@@ -20,7 +21,9 @@ void main() {
 
     setUpAll(() async {
       final FakeCocoonService service = FakeCocoonService();
-      statuses = await service.fetchCommitStatuses();
+      final CocoonResponse<List<CommitStatus>> response =
+          await service.fetchCommitStatuses();
+      statuses = response.data;
     });
 
     testWidgets('shows loading indicator when statuses is empty',