notif: Handle opening of notification on Android using data URL intents

Replaces the notification-open handling provided by
`package:flutter_local_notifications` with a custom Intent data
URL-based approach. Notifications will now be created with a
`PendingIntent` containing a `zulip://notification…` URL.

When a notification is opened, the Android intent's data URL is
passed through Flutter's platform-navigation system, triggering a
route. If the app is already in the foreground, the `ZulipApp`
widget's overridden `didPushRouteInformation` function handles the
route. If the app is not running, the intent data URL becomes the
initial route, read from
`WidgetsBinding.instance.platformDispatcher.defaultRouteName` in
the `ZulipApp` widget.

In both cases, the intent data URL is then passed to
`NotificationDisplayManager.navigateForNotification`, where it is
parsed and used to generate the route to the `MessageListPage` for
the relevant conversation.

Author: rajveermalviya

android/app/src/main/kotlin/com/zulip/flutter/Notifications.g.kt

@@ -90,26 +90,31 @@ data class NotificationChannel (
 /**
  * Corresponds to `android.content.Intent`
  *
- * See: https://developer.android.com/reference/android/content/Intent
+ * See:
+ *   https://developer.android.com/reference/android/content/Intent
+ *   https://developer.android.com/reference/android/content/Intent#Intent(java.lang.String,%20android.net.Uri,%20android.content.Context,%20java.lang.Class%3C?%3E)
  *
  * Generated class from Pigeon that represents data sent in messages.
  */
 data class AndroidIntent (
   val action: String,
+  val dataUrl: String,
   val extras: Map<String?, String?>
 
 ) {
   companion object {
     @Suppress("LocalVariableName")
     fun fromList(__pigeon_list: List<Any?>): AndroidIntent {
       val action = __pigeon_list[0] as String
-      val extras = __pigeon_list[1] as Map<String?, String?>
-      return AndroidIntent(action, extras)
+      val dataUrl = __pigeon_list[1] as String
+      val extras = __pigeon_list[2] as Map<String?, String?>
+      return AndroidIntent(action, dataUrl, extras)
     }
   }
   fun toList(): List<Any?> {
     return listOf(
       action,
+      dataUrl,
       extras,
     )
   }

android/app/src/main/kotlin/com/zulip/flutter/ZulipPlugin.kt

@@ -3,6 +3,7 @@ package com.zulip.flutter
 import android.annotation.SuppressLint
 import android.content.Context
 import android.content.Intent
+import android.net.Uri
 import android.os.Bundle
 import android.util.Log
 import androidx.annotation.Keep
@@ -97,8 +98,12 @@ private class AndroidNotificationHost(val context: Context)
             contentIntent?.let { setContentIntent(
                 android.app.PendingIntent.getActivity(context,
                     it.requestCode.toInt(),
-                    it.intent.let { intent -> Intent(context, MainActivity::class.java).apply {
-                        action = intent.action
+                    it.intent.let { intent -> Intent(
+                        intent.action,
+                        Uri.parse(intent.dataUrl),
+                        context,
+                        MainActivity::class.java
+                    ).apply {
                         intent.extras.forEach { (k, v) -> putExtra(k!!, v!!) }
                     } },
                     it.flags.toInt())

assets/l10n/app_en.arb

@@ -558,5 +558,13 @@
   "pollWidgetOptionsMissing": "This poll has no options yet.",
   "@pollWidgetOptionsMissing": {
     "description": "Text to display for a poll when it has no options"
+  },
+  "errorNotificationOpenTitle": "Failed to open notification",
+  "@errorNotificationOpenTitle": {
+    "description": "Error title when notification opening fails"
+  },
+  "errorNotificationOpenAccountMissing": "The account associated with this notification no longer exists.",
+  "@errorNotificationOpenAccountMissing": {
+    "description": "Error message when the account associated with the notification is not found"
   }
 }

lib/host/android_notifications.dart

@@ -60,3 +60,11 @@ abstract class PendingIntentFlag {
   /// Corresponds to `FLAG_ALLOW_UNSAFE_IMPLICIT_INTENT`.
   static const allowUnsafeImplicitIntent = 1 << 24;
 }
+
+/// For use in [AndroidIntent.action].
+///
+/// See: https://developer.android.com/reference/android/content/Intent#constants_1
+abstract class IntentAction {
+  /// Corresponds to `ACTION_VIEW`.
+  static const view = 'android.intent.action.VIEW';
+}

lib/host/android_notifications.g.dart

@@ -65,20 +65,26 @@ class NotificationChannel {
 
 /// Corresponds to `android.content.Intent`
 ///
-/// See: https://developer.android.com/reference/android/content/Intent
+/// See:
+///   https://developer.android.com/reference/android/content/Intent
+///   https://developer.android.com/reference/android/content/Intent#Intent(java.lang.String,%20android.net.Uri,%20android.content.Context,%20java.lang.Class%3C?%3E)
 class AndroidIntent {
   AndroidIntent({
     required this.action,
+    required this.dataUrl,
     required this.extras,
   });
 
   String action;
 
+  String dataUrl;
+
   Map<String?, String?> extras;
 
   Object encode() {
     return <Object?>[
       action,
+      dataUrl,
       extras,
     ];
   }
@@ -87,7 +93,8 @@ class AndroidIntent {
     result as List<Object?>;
     return AndroidIntent(
       action: result[0]! as String,
-      extras: (result[1] as Map<Object?, Object?>?)!.cast<String?, String?>(),
+      dataUrl: result[1]! as String,
+      extras: (result[2] as Map<Object?, Object?>?)!.cast<String?, String?>(),
     );
   }
 }

lib/notifications/display.dart

@@ -5,9 +5,9 @@ import 'dart:io';
 import 'package:http/http.dart' as http;
 import 'package:collection/collection.dart';
 import 'package:crypto/crypto.dart';
+import 'package:flutter_gen/gen_l10n/zulip_localizations.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart' hide Notification;
-import 'package:flutter_local_notifications/flutter_local_notifications.dart' hide Person;
 
 import '../api/notifications.dart';
 import '../host/android_notifications.dart';
@@ -17,6 +17,7 @@ import '../model/localizations.dart';
 import '../model/narrow.dart';
 import '../widgets/app.dart';
 import '../widgets/color.dart';
+import '../widgets/dialog.dart';
 import '../widgets/message_list.dart';
 import '../widgets/page.dart';
 import '../widgets/store.dart';
@@ -95,16 +96,6 @@ class NotificationChannelManager {
 /// Service for managing the notifications shown to the user.
 class NotificationDisplayManager {
   static Future<void> init() async {
-    await ZulipBinding.instance.notifications.initialize(
-      const InitializationSettings(
-        android: AndroidInitializationSettings('zulip_notification'),
-      ),
-      onDidReceiveNotificationResponse: _onNotificationOpened,
-    );
-    final launchDetails = await ZulipBinding.instance.notifications.getNotificationAppLaunchDetails();
-    if (launchDetails?.didNotificationLaunchApp ?? false) {
-      _handleNotificationAppLaunch(launchDetails!.notificationResponse);
-    }
     await NotificationChannelManager.ensureChannel();
   }
 
@@ -168,6 +159,16 @@ class NotificationDisplayManager {
         name: data.senderFullName,
         iconBitmap: await _fetchBitmap(data.senderAvatarUrl))));
 
+    final intentDataUrl = NotificationOpenPayload(
+      realmUrl: data.realmUrl,
+      userId: data.userId,
+      narrow: switch (data.recipient) {
+        FcmMessageChannelRecipient(:var streamId, :var topic) =>
+          TopicNarrow(streamId, topic),
+        FcmMessageDmRecipient(:var allRecipientIds) =>
+          DmNarrow(allRecipientIds: allRecipientIds, selfUserId: data.userId),
+      }).buildUrl();
+
     await _androidHost.notify(
       // TODO the notification ID can be constant, instead of matching requestCode
       //   (This is a legacy of `flutter_local_notifications`.)
@@ -205,13 +206,9 @@ class NotificationDisplayManager {
         //   (That's a legacy of `flutter_local_notifications`.)
         flags: PendingIntentFlag.immutable | PendingIntentFlag.updateCurrent,
         intent: AndroidIntent(
-          // This action name and extra name are special to
-          // FlutterLocalNotificationsPlugin, which handles receiving the Intent.
-          // TODO take care of receiving the notification-opened Intent ourselves
-          action: 'SELECT_NOTIFICATION',
-          extras: <String, String>{
-            'payload': jsonEncode(dataJson),
-          }),
+          action: IntentAction.view,
+          dataUrl: intentDataUrl.toString(),
+          extras: {}),
         // TODO this doesn't set the Intent flags we set in zulip-mobile; is that OK?
         //   (This is a legacy of `flutter_local_notifications`.)
         ),
@@ -348,46 +345,36 @@ class NotificationDisplayManager {
 
   static String _personKey(Uri realmUrl, int userId) => "$realmUrl|$userId";
 
-  static void _onNotificationOpened(NotificationResponse response) async {
-    final payload = jsonDecode(response.payload!) as Map<String, dynamic>;
-    final data = MessageFcmMessage.fromJson(payload);
-    assert(debugLog('opened notif: message ${data.zulipMessageId}, content ${data.content}'));
-    _navigateForNotification(data);
-  }
-
-  static void _handleNotificationAppLaunch(NotificationResponse? response) async {
-    assert(response != null);
-    if (response == null) return; // TODO(log) seems like a bug in flutter_local_notifications if this can happen
+  /// Navigates to the [MessageListPage] of the specific conversation
+  /// given the `zulip://notification/…` Android intent data URL,
+  /// generated with [NotificationOpenPayload.buildUrl] while creating
+  /// the notification.
+  static Future<void> navigateForNotification(Uri url) async {
+    assert(debugLog('opened notif: url: $url'));
 
-    final payload = jsonDecode(response.payload!) as Map<String, dynamic>;
-    final data = MessageFcmMessage.fromJson(payload);
-    assert(debugLog('launched from notif: message ${data.zulipMessageId}, content ${data.content}'));
-    _navigateForNotification(data);
-  }
+    assert(url.scheme == 'zulip' && url.host == 'notification');
+    final payload = NotificationOpenPayload.parseUrl(url);
 
-  static void _navigateForNotification(MessageFcmMessage data) async {
     NavigatorState navigator = await ZulipApp.navigator;
     final context = navigator.context;
     assert(context.mounted);
     if (!context.mounted) return; // TODO(linter): this is impossible as there's no actual async gap, but the use_build_context_synchronously lint doesn't see that
 
+    final zulipLocalizations = ZulipLocalizations.of(context);
     final globalStore = GlobalStoreWidget.of(context);
     final account = globalStore.accounts.firstWhereOrNull((account) =>
-      account.realmUrl == data.realmUrl && account.userId == data.userId);
-    if (account == null) return; // TODO(log)
-
-    final narrow = switch (data.recipient) {
-      FcmMessageChannelRecipient(:var streamId, :var topic) =>
-        TopicNarrow(streamId, topic),
-      FcmMessageDmRecipient(:var allRecipientIds) =>
-        DmNarrow(allRecipientIds: allRecipientIds, selfUserId: account.userId),
-    };
+      account.realmUrl == payload.realmUrl && account.userId == payload.userId);
+    if (account == null) { // TODO(log)
+      showErrorDialog(context: context,
+        title: zulipLocalizations.errorNotificationOpenTitle,
+        message: zulipLocalizations.errorNotificationOpenAccountMissing);
+      return;
+    }
 
-    assert(debugLog('  account: $account, narrow: $narrow'));
     // TODO(nav): Better interact with existing nav stack on notif open
     unawaited(navigator.push(MaterialAccountWidgetRoute<void>(accountId: account.id,
       // TODO(#82): Open at specific message, not just conversation
-      page: MessageListPage(initNarrow: narrow))));
+      page: MessageListPage(initNarrow: payload.narrow))));
   }
 
   static Future<Uint8List?> _fetchBitmap(Uri url) async {
@@ -403,3 +390,86 @@ class NotificationDisplayManager {
     return null;
   }
 }
+
+/// The information contained in 'zulip://notification/…' internal
+/// Android intent data URL, used for notification-open flow.
+class NotificationOpenPayload {
+  final Uri realmUrl;
+  final int userId;
+  final Narrow narrow;
+
+  NotificationOpenPayload({
+    required this.realmUrl,
+    required this.userId,
+    required this.narrow,
+  });
+
+  factory NotificationOpenPayload.parseUrl(Uri url) {
+    if (url case Uri(
+      scheme: 'zulip',
+      host: 'notification',
+      queryParameters: {
+        'realm_url': var realmUrlStr,
+        'user_id': var userIdStr,
+        'narrow_type': var narrowType,
+        // In case of narrowType == 'topic':
+        // 'channel_id' and 'topic' handled below.
+
+        // In case of narrowType == 'dm':
+        // 'all_recipient_ids' handled below.
+      },
+    )) {
+      final realmUrl = Uri.parse(realmUrlStr);
+      final userId = int.parse(userIdStr, radix: 10);
+
+      final Narrow narrow;
+      switch (narrowType) {
+        case 'topic':
+          final channelIdStr = url.queryParameters['channel_id']!;
+          final channelId = int.parse(channelIdStr, radix: 10);
+          final topic = url.queryParameters['topic']!;
+          narrow = TopicNarrow(channelId, topic);
+        case 'dm':
+          final allRecipientIdsStr = url.queryParameters['all_recipient_ids']!;
+          final allRecipientIds = allRecipientIdsStr.split(',')
+            .map((idStr) => int.parse(idStr, radix: 10))
+            .toList(growable: false);
+          narrow = DmNarrow(allRecipientIds: allRecipientIds, selfUserId: userId);
+        default:
+          throw const FormatException();
+      }
+
+      return NotificationOpenPayload(
+        realmUrl: realmUrl,
+        userId: userId,
+        narrow: narrow,
+      );
+    } else {
+      // TODO(dart): simplify after https://github.com/dart-lang/language/issues/2537
+      throw const FormatException();
+    }
+  }
+
+  Uri buildUrl() {
+    return Uri(
+      scheme: 'zulip',
+      host: 'notification',
+      queryParameters: <String, String>{
+        'realm_url': realmUrl.toString(),
+        'user_id': userId.toString(),
+        ...(switch (narrow) {
+          TopicNarrow(streamId: var channelId, :var topic) => {
+            'narrow_type': 'topic',
+            'channel_id': channelId.toString(),
+            'topic': topic,
+          },
+          DmNarrow(:var allRecipientIds) => {
+            'narrow_type': 'dm',
+            'all_recipient_ids': allRecipientIds.join(','),
+          },
+          _ => throw UnsupportedError('Found an unexpected Narrow of type ${narrow.runtimeType}.'),
+        })
+      },
+    );
+  }
+}

lib/widgets/app.dart

@@ -8,6 +8,7 @@ import 'package:flutter_gen/gen_l10n/zulip_localizations.dart';
 import '../log.dart';
 import '../model/localizations.dart';
 import '../model/narrow.dart';
+import '../notifications/display.dart';
 import 'about_zulip.dart';
 import 'app_bar.dart';
 import 'dialog.dart';
@@ -144,19 +145,29 @@ class ZulipApp extends StatefulWidget {
 class _ZulipAppState extends State<ZulipApp> with WidgetsBindingObserver {
   @override
   Future<bool> didPushRouteInformation(routeInformation) async {
-    if (routeInformation case RouteInformation(
-      uri: Uri(scheme: 'zulip', host: 'login') && var url)
-    ) {
-      await LoginPage.handleWebAuthUrl(url);
-      return true;
+    switch (routeInformation.uri) {
+      case Uri(scheme: 'zulip', host: 'login') && var url:
+        await LoginPage.handleWebAuthUrl(url);
+        return true;
+      case Uri(scheme: 'zulip', host: 'notification') && var url:
+        await NotificationDisplayManager.navigateForNotification(url);
+        return true;
     }
     return super.didPushRouteInformation(routeInformation);
   }
 
+  Future<void> _handleInitialRoute() async {
+    final initialRouteUrl = Uri.parse(WidgetsBinding.instance.platformDispatcher.defaultRouteName);
+    if (initialRouteUrl case Uri(scheme: 'zulip', host: 'notification')) {
+      await NotificationDisplayManager.navigateForNotification(initialRouteUrl);
+    }
+  }
+
   @override
   void initState() {
     super.initState();
     WidgetsBinding.instance.addObserver(this);
+    _handleInitialRoute();
   }
 
   @override