[google_sign_in_web] Fix race condition on init. (flutter#2455)

* [google_sign_in_web] Wait for Auth2 to be really ready.

The Auth object that `.init()` returns may not be fully ready by the time
we start calling methods on it; however it has a `.then()` method that
gets called when it is *really* ready to go.

* Add a completer to signal when Auth2 is ready.
* Throw StateError synchronously if .initialized is checked before calling .init()
* Move auth2-dependent init to the `then` method.
  * onSuccess, complete the auth2 ready future.
  * onError, throw a PlatformException. This is normally triggered when
the domain:port of the web app hasn't been whitelisted on the google
sign in console, and things like that. Useful for debugging.
* Update README with latest setup instructions.

Author: ditman

packages/google_sign_in/google_sign_in_web/CHANGELOG.md

@@ -1,3 +1,10 @@
+## 0.8.3
+
+* Fix initialization error that causes https://github.com/flutter/flutter/issues/48527
+* Throw a PlatformException when there's an initialization problem (like wrong server-side config).
+* Throw a StateError when checking .initialized before calling .init()
+* Update setup instructions in the README.
+
 ## 0.8.2+1
 
 * Add a non-op Android implementation to avoid a flaky Gradle issue.

packages/google_sign_in/google_sign_in_web/README.md

@@ -5,18 +5,16 @@ The web implementation of [google_sign_in](https://pub.dev/google_sign_in/google
 ## Usage
 
 ### Import the package
-To use this plugin, follow the [plugin installation instructions](https://pub.dartlang.org/packages/google_sign_in#pub-pkg-tab-installing).
 
-Remember that for web plugins you need to depend both on the "native" version that provides the Dart interface that you'll use in your app), and the "web" version, that provides the implementation of the plugin for the web platform.
+This package is the endorsed implementation of `google_sign_in` for the web platform since version `4.1.0`, so it gets automatically added to your dependencies by depending on `google_sign_in: ^4.1.0`.
 
-This is what the above means to your `pubspec.yaml`:
+No modifications to your pubspec.yaml should be required in a recent enough version of Flutter (`>=1.12.13+hotfix.4`):
 
-```
+```yaml
 ...
 dependencies:
   ...
-  google_sign_in: ^4.0.14
-  google_sign_in_web: ^0.8.0
+  google_sign_in: ^4.1.0
   ...
 ...
 ```
@@ -28,8 +26,8 @@ First, go through the instructions [here](https://developers.google.com/identity
 On your `web/index.html` file, add the following `meta` tag, somewhere in the
 `head` of the document:
 
-```
-  <meta name="google-signin-client_id" content="YOUR_GOOGLE_SIGN_IN_OAUTH_CLIENT_ID.apps.googleusercontent.com">
+```html
+<meta name="google-signin-client_id" content="YOUR_GOOGLE_SIGN_IN_OAUTH_CLIENT_ID.apps.googleusercontent.com">
 ```
 
 Read the rest of the instructions if you need to add extra APIs (like Google People API).
@@ -74,7 +72,21 @@ Find the example wiring in the [Google sign-in example application](https://gith
 
 See the [google_sign_in.dart](https://github.com/flutter/plugins/blob/master/packages/google_sign_in/google_sign_in/lib/google_sign_in.dart) for more API details.
 
+## Contributions and Testing
+
+Tests are a crucial to contributions to this package. All new contributions should be reasonably tested.
+
+In order to run tests in this package, do:
+
+```
+flutter test --platform chrome -j1
+```
+
+Contributions to this package are welcome. Read the [Contributing to Flutter Plugins](https://github.com/flutter/plugins/blob/master/CONTRIBUTING.md) guide to get started.
+
 ## Issues and feedback
 
 Please file [issues](https://github.com/flutter/flutter/issues/new)
-to send feedback or report a bug. Thank you!
+to send feedback or report a bug.
+
+**Thank you!**

packages/google_sign_in/google_sign_in_web/lib/google_sign_in_web.dart

@@ -5,14 +5,13 @@
 import 'dart:async';
 import 'dart:html' as html;
 
+import 'package:flutter/services.dart';
 import 'package:google_sign_in_platform_interface/google_sign_in_platform_interface.dart';
 import 'package:flutter_web_plugins/flutter_web_plugins.dart';
 import 'package:js/js.dart';
 import 'package:meta/meta.dart';
 
 import 'src/generated/gapiauth2.dart' as auth2;
-// TODO: Remove once this lands https://github.com/dart-lang/language/issues/671
-import 'src/generated/gapiauth2.dart' show GoogleAuthExtensions;
 import 'src/load_gapi.dart' as gapi;
 import 'src/utils.dart' show gapiUserToPluginUserData;
 
@@ -39,14 +38,27 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
   }
 
   Future<void> _isGapiInitialized;
+  Future<void> _isAuthInitialized;
+  bool _isInitCalled = false;
+
+  // This method throws if init hasn't been called at some point in the past.
+  // It is used by the [initialized] getter to ensure that users can't await
+  // on a Future that will never resolve.
+  void _assertIsInitCalled() {
+    if (!_isInitCalled) {
+      throw StateError(
+          'GoogleSignInPlugin::init() must be called before any other method in this plugin.');
+    }
+  }
 
-  /// This is only exposed for testing. It shouldn't be accessed by users of the
-  /// plugin as it could break at any point.
+  /// A future that resolves when both GAPI and Auth2 have been correctly initialized.
   @visibleForTesting
-  Future<void> get initialized => _isGapiInitialized;
+  Future<void> get initialized {
+    _assertIsInitCalled();
+    return Future.wait([_isGapiInitialized, _isAuthInitialized]);
+  }
 
   String _autoDetectedClientId;
-  FutureOr<auth2.GoogleUser> _lastSeenUser;
 
   /// Factory method that initializes the plugin with [GoogleSignInPlatform].
   static void registerWith(Registrar registrar) {
@@ -72,7 +84,7 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
         'Check https://developers.google.com/identity/protocols/googlescopes '
         'for a list of valid OAuth 2.0 scopes.');
 
-    await initialized;
+    await _isGapiInitialized;
 
     final auth2.GoogleAuth auth = auth2.init(auth2.ClientConfig(
       hosted_domain: hostedDomain,
@@ -81,19 +93,26 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
       client_id: appClientId,
     ));
 
-    // Subscribe to changes in the auth instance returned by init,
-    // and cache the _lastSeenUser as we get notified of new values.
-    final Completer<auth2.GoogleUser> initUserCompleter =
-        Completer<auth2.GoogleUser>();
-
-    auth.currentUser.listen(allowInterop((auth2.GoogleUser nextUser) {
-      if (!initUserCompleter.isCompleted) {
-        initUserCompleter.complete(nextUser);
-      } else {
-        _lastSeenUser = nextUser;
-      }
+    Completer<void> isAuthInitialized = Completer<void>();
+    _isAuthInitialized = isAuthInitialized.future;
+    _isInitCalled = true;
+
+    auth.then(allowInterop((auth2.GoogleAuth initializedAuth) {
+      // onSuccess
+
+      // TODO: https://github.com/flutter/flutter/issues/48528
+      // This plugin doesn't notify the app of external changes to the
+      // state of the authentication, i.e: if you logout elsewhere...
+
+      isAuthInitialized.complete();
+    }), allowInterop((dynamic reason) {
+      // onError
+      throw PlatformException(
+        code: 'google_sign_in',
+        message: reason.error,
+        details: reason.details,
+      );
     }));
-    _lastSeenUser = initUserCompleter.future;
 
     return null;
   }
@@ -102,7 +121,8 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
   Future<GoogleSignInUserData> signInSilently() async {
     await initialized;
 
-    return gapiUserToPluginUserData(await _lastSeenUser);
+    return gapiUserToPluginUserData(
+        await auth2.getAuthInstance().currentUser.get());
   }
 
   @override
@@ -154,7 +174,6 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
   Future<void> clearAuthCache({String token}) async {
     await initialized;
 
-    _lastSeenUser = null;
     return auth2.getAuthInstance().disconnect();
   }
 }

packages/google_sign_in/google_sign_in_web/pubspec.yaml

@@ -2,7 +2,7 @@ name: google_sign_in_web
 description: Flutter plugin for Google Sign-In, a secure authentication system
   for signing in with a Google account on Android, iOS and Web.
 homepage: https://github.com/flutter/plugins/tree/master/packages/google_sign_in/google_sign_in_web
-version: 0.8.2+1
+version: 0.8.3
 
 flutter:
   plugin:

packages/google_sign_in/google_sign_in_web/test/auth2_test.dart

@@ -27,9 +27,8 @@ void main() {
 
   GoogleSignInPlugin plugin;
 
-  setUp(() async {
+  setUp(() {
     plugin = GoogleSignInPlugin();
-    await plugin.initialized;
   });
 
   test('Init requires clientId', () async {
@@ -47,12 +46,13 @@ void main() {
   });
 
   group('Successful .init, then', () {
-    setUp(() {
-      plugin.init(
+    setUp(() async {
+      await plugin.init(
         hostedDomain: 'foo',
         scopes: <String>['some', 'scope'],
         clientId: '1234',
       );
+      await plugin.initialized;
     });
 
     test('signInSilently', () async {

packages/google_sign_in/google_sign_in_web/test/gapi_load_test.dart

@@ -7,14 +7,16 @@
 import 'dart:html' as html;
 
 import 'package:flutter_test/flutter_test.dart';
+import 'package:google_sign_in_platform_interface/google_sign_in_platform_interface.dart';
 import 'package:google_sign_in_web/google_sign_in_web.dart';
 import 'gapi_mocks/gapi_mocks.dart' as gapi_mocks;
 import 'utils.dart';
 
 void main() {
-  gapiUrl = toBase64Url(gapi_mocks.gapiInitSuccess());
+  gapiUrl = toBase64Url(gapi_mocks.auth2InitSuccess(GoogleSignInUserData()));
 
-  test('Plugin is initialized after GAPI fully loads', () async {
+  test('Plugin is initialized after GAPI fully loads and init is called',
+      () async {
     expect(
       html.querySelector('script[src^="data:"]'),
       isNull,
@@ -26,6 +28,12 @@ void main() {
       isNotNull,
       reason: 'Mock script should be injected',
     );
+    expect(() {
+      plugin.initialized;
+    }, throwsStateError,
+        reason:
+            'The plugin should throw if checking for `initialized` before calling .init');
+    await plugin.init(hostedDomain: '', clientId: '');
     await plugin.initialized;
     expect(
       plugin.initialized,

packages/google_sign_in/google_sign_in_web/test/gapi_mocks/gapi_mocks.dart

@@ -10,5 +10,4 @@ import 'src/gapi.dart';
 import 'src/google_user.dart';
 import 'src/test_iife.dart';
 
-part 'src/gapi_load.dart';
 part 'src/auth2_init.dart';

packages/google_sign_in/google_sign_in_web/test/gapi_mocks/src/auth2_init.dart

@@ -13,6 +13,11 @@ var mockUser = ${googleUser(userData)};
 function GapiAuth2() {}
 GapiAuth2.prototype.init = function (initOptions) {
   return {
+    then: (onSuccess, onError) => {
+      window.setTimeout(() => {
+        onSuccess(window.gapi.auth2);
+      }, 30);
+    },
     currentUser: {
       listen: (cb) => {
         window.setTimeout(() => {