notif android: Request permission at startup

lib/notifications.dart

@@ -62,8 +62,6 @@ class NotificationService {
   Future<void> start() async {
     switch (defaultTargetPlatform) {
       case TargetPlatform.android:
-        // TODO(#324) defer notif setup if user not logged into any accounts
-        //   (in order to avoid calling for permissions)
         await ZulipBinding.instance.firebaseInitializeApp(
           options: kFirebaseOptionsAndroid);
 
@@ -73,6 +71,14 @@ class NotificationService {
         ZulipBinding.instance.firebaseMessagingOnBackgroundMessage(
           _onBackgroundMessage);
 
+        await _requestPermission(); // TODO(#324): defer if not logged into any accounts
+        // On Android, the notification permission is only about showing
+        // notifications in the UI, not about getting notification data in the
+        // background.  Even if the app lacks permission to show notifications
+        // in the UI, it's useful to get the token and enable the user's Zulip
+        // servers to send notification data to the client, because it means if
+        // the user later enables notifications, they'll promptly start working.
+
         // Get the FCM registration token, now and upon changes.  See FCM API docs:
         //   https://firebase.google.com/docs/cloud-messaging/android/client#sample-register
         ZulipBinding.instance.firebaseMessaging.onTokenRefresh
@@ -83,16 +89,11 @@ class NotificationService {
         await ZulipBinding.instance.firebaseInitializeApp(
           options: kFirebaseOptionsIos);
 
-        // Docs on this API: https://firebase.flutter.dev/docs/messaging/permissions/
-        final settings = await ZulipBinding.instance.firebaseMessaging
-          .requestPermission();
-        assert(debugLog('notif settings: $settings'));
-        switch (settings.authorizationStatus) {
-          case AuthorizationStatus.denied:
-            return;
-          case AuthorizationStatus.authorized:
-          case AuthorizationStatus.provisional:
-          case AuthorizationStatus.notDetermined:
+        if (!await _requestPermission()) {
+          // TODO(#324): request only "provisional" permission at this stage:
+          //   https://github.com/zulip/zulip-flutter/issues/324#issuecomment-1771400325
+          //   then proceed to get and use the token just like on Android
+          return;
         }
 
         await _getApnsToken();
@@ -107,6 +108,21 @@ class NotificationService {
     }
   }
 
+  Future<bool> _requestPermission() async {
+    // Docs on this API: https://firebase.flutter.dev/docs/messaging/permissions/
+    final settings = await ZulipBinding.instance.firebaseMessaging
+      .requestPermission();
+    assert(debugLog('notif authorization: ${settings.authorizationStatus}'));
+    switch (settings.authorizationStatus) {
+      case AuthorizationStatus.denied:
+        return false;
+      case AuthorizationStatus.authorized:
+      case AuthorizationStatus.provisional:
+      case AuthorizationStatus.notDetermined:
+        return true;
+    }
+  }
+
   Future<void> _getFcmToken() async {
     final value = await ZulipBinding.instance.firebaseMessaging.getToken();
     // TODO(#323) warn user if getToken returns null, or doesn't timely return

test/notifications_test.dart

@@ -82,11 +82,11 @@ void main() {
   }
 
   group('permissions', () {
-    testWidgets('on iOS request permission', (tester) async {
+    testWidgets('request permission', (tester) async {
       await init();
       check(testBinding.firebaseMessaging.takeRequestPermissionCalls())
         .length.equals(1);
-    }, variant: TargetPlatformVariant.only(TargetPlatform.iOS));
+    }, variant: const TargetPlatformVariant({TargetPlatform.android, TargetPlatform.iOS}));
   });
 
   group('NotificationChannelManager', () {