Crash in fetchAuthValue when App is Resumed from Background

[hschk]

Description

Our Flutter app sometimes crashes when resuming after being in the background for a while. The issue seems to originate from the fetchAuthValue method in the Pusher library. The crash is related to a dynamic cast failure, as seen in the Crashlytics logs (provided below).

I suspect the issue might be caused by an invalid state or incorrect handling of the authorizer object during app lifecycle changes.

Environment Details

• Pusher Library Version: 2.4.0
• Flutter Version: 3.27.1
• Platform: iOS

Crash Logs

Here is the relevant portion of the Crashlytics log:

Crashed: com.apple.main-thread
0  libsystem_kernel.dylib         0xc1d4 __pthread_kill + 8
1  libsystem_pthread.dylib        0x7ef8 pthread_kill + 268
2  libsystem_c.dylib              0x77ad8 abort + 128
3  libswiftCore.dylib             0x3cc1a4 swift::fatalError(unsigned int, char const*, ...) + 134
4  libswiftCore.dylib             0x3bfb44 swift::swift_dynamicCastFailure(swift::TargetMetadata<swift::InProcess> const*, swift::TargetMetadata<swift::InProcess> const*, char const*) + 78
5  pusher_channels_flutter        0x9d88 partial apply for closure #1 in SwiftPusherChannelsFlutterPlugin.fetchAuthValue(socketID:channelName:completionHandler:) + 107 (SwiftPusherChannelsFlutterPlugin.swift:107)

If any additional information is needed, please let us know.
Would appreciate any guidance or fixes from the team. Thanks!

Full Crashlytics Log:

 Crashed: com.apple.main-thread
0  libsystem_kernel.dylib         0xc1d4 __pthread_kill + 8
1  libsystem_pthread.dylib        0x7ef8 pthread_kill + 268
2  libsystem_c.dylib              0x77ad8 abort + 128
3  libswiftCore.dylib             0x3cc1a4 swift::fatalError(unsigned int, char const*, ...) + 134
4  libswiftCore.dylib             0x3cc1c4 swift::warningv(unsigned int, char const*, char*) + 30
5  libswiftCore.dylib             0x3bfb44 swift::swift_dynamicCastFailure(swift::TargetMetadata<swift::InProcess> const*, swift::TargetMetadata<swift::InProcess> const*, char const*) + 78
6  libswiftCore.dylib             0x3bfbc0 swift::_conformsToProtocol(swift::OpaqueValue const*, swift::TargetMetadata<swift::InProcess> const*, swift::TargetProtocolDescriptorRef<swift::InProcess>, swift::TargetWitnessTable<swift::InProcess> const**) + 122
7  libswiftCore.dylib             0x3c4f68 swift_dynamicCastImpl(swift::OpaqueValue*, swift::OpaqueValue*, swift::TargetMetadata<swift::InProcess> const*, swift::TargetMetadata<swift::InProcess> const*, swift::DynamicCastFlags) + 342
8  pusher_channels_flutter        0x9d88 partial apply for closure #1 in SwiftPusherChannelsFlutterPlugin.fetchAuthValue(socketID:channelName:completionHandler:) + 107 (SwiftPusherChannelsFlutterPlugin.swift:107)
9  pusher_channels_flutter        0x5bec thunk for @escaping @callee_guaranteed (@in_guaranteed Any?) -> () + 84 (<compiler-generated>:84)
10 Flutter                        0x5e2468 __54-[FlutterMethodChannel invokeMethod:arguments:result:]_block_invoke + 291 (FlutterChannels.mm:291)
11 Flutter                        0x5a178 std::_fl::__function::__func<fml::internal::CopyableLambda<flutter::PlatformMessageResponseDarwin::Complete(std::_fl::unique_ptr<fml::Mapping, std::_fl::default_delete<fml::Mapping>>)::$_0>, std::_fl::allocator<fml::internal::CopyableLambda<flutter::PlatformMessageResponseDarwin::Complete(std::_fl::unique_ptr<fml::Mapping, std::_fl::default_delete<fml::Mapping>>)::$_0>>, void ()>::operator()() + 24 (platform_message_response_darwin.mm:24)
12 Flutter                        0x85c9c fml::MessageLoopImpl::FlushTasks(fml::FlushType) + 128 (message_loop_impl.cc:128)
13 Flutter                        0x89314 fml::MessageLoopDarwin::OnTimerFire(__CFRunLoopTimer*, fml::MessageLoopDarwin*) + 86 (message_loop_darwin.mm:86)
14 CoreFoundation                 0xb4894 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 32
15 CoreFoundation                 0xb4538 __CFRunLoopDoTimer + 1012
16 CoreFoundation                 0xb408c __CFRunLoopDoTimers + 288
17 CoreFoundation                 0x533b4 __CFRunLoopRun + 1856
18 CoreFoundation                 0x52830 CFRunLoopRunSpecific + 588
19 GraphicsServices               0x11c4 GSEventRunModal + 164
20 UIKitCore                      0x3d2eb0 -[UIApplication _run] + 816
21 UIKitCore                      0x4815b4 UIApplicationMain + 340
22 UIKitCore                      0x7bbfa8 block_destroy_helper.23 + 10212
23 Runner                         0x88cc main + 4343269580 (AppDelegate.swift:4343269580)

[hschk]

I’m not sure if this is related, but when I reopen the app after it has been in the background, I see a series of connection state change logs like this:

flutter: Connection state changed: DISCONNECTED
flutter: Connection state changed: RECONNECTING
flutter: Connection state changed: CONNECTING
flutter: Connection state changed: DISCONNECTED
flutter: Connection state changed: RECONNECTING
flutter: Connection state changed: DISCONNECTED
flutter: Connection state changed: RECONNECTING
flutter: Connection state changed: DISCONNECTED
flutter: Connection state changed: RECONNECTING
flutter: Connection state changed: CONNECTING
flutter: Connection state changed: CONNECTED

Is this expected behavior? As I mentioned, this might not be an issue or even related to the crashes, but I thought it was worth noting while troubleshooting.

[kadersaka]

which version of the pusher channel flutter library r u using?

[hschk]

When I reported this issue, I was using version 2.4.0. However, the same behavior occurs with version 2.5.0.

[kadersaka]

please paste here ur pusher init code and functions. u can also directly message me on kadersaka[at]gmail.com so we can go for a live working session

am suspecting the issue is related to your onAuthorizer code.

[hschk]

Thank you for your response and for offering to help!

I also suspected that the issue might lie within my onAuthorizer code. However, after reviewing our server logs, it appears that our Pusher auth endpoint was returning the expected response with a 200 status code and the correct authentication object at the time of the last crash.

To provide more context, here is my PusherService class implementation:

import 'dart:async';
import 'dart:convert';

import 'package:bridge/business_logic/utilities/locator.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_crashlytics/firebase_crashlytics.dart';
import 'package:flutter_dotenv/flutter_dotenv.dart';
import 'package:logger/logger.dart';
import 'package:pusher_channels_flutter/pusher_channels_flutter.dart';
import 'package:synchronized/synchronized.dart';
import 'package:http/http.dart' as http;

class PusherService {
  // Singleton pattern
  static final PusherService _instance = PusherService._internal();

  factory PusherService() => _instance;

  PusherService._internal();

  final Lock _lock = Lock();
  PusherChannelsFlutter? _pusher;
  bool _isConnected = false;

  final String apiKey = dotenv.env['PUSHER_KEY'] ?? '';
  final String cluster = dotenv.env['PUSHER_CLUSTER'] ?? '';
  final String authEndpoint = dotenv.env['PUSHER_AUTH_ENDPOINT'] ?? '';

  final Logger _logger = getIt<Logger>();

  /// Initializes the Pusher service.
  Future<void> initPusher() async {
    await _lock.synchronized(() async {
      if (_isConnected) return;

      _pusher = PusherChannelsFlutter.getInstance();
      try {
        await _pusher!.init(
          apiKey: apiKey,
          cluster: cluster,
          onAuthorizer: _onAuthorizer,
          onConnectionStateChange: _onConnectionStateChange,
          onError: _onError,
          onSubscriptionSucceeded: _onSubscriptionSucceeded,
          onEvent: _onEvent,
          onSubscriptionError: _onSubscriptionError,
        );
        await _pusher!.connect();
        _isConnected = true;
        _logger.i('Pusher connected successfully.');
      } catch (e, stackTrace) {
        _logger.e('Failed to initialize Pusher',
            error: e, stackTrace: stackTrace);
        FirebaseCrashlytics.instance.recordError(e, stackTrace);
      }
    });
  }

  /// Disconnects from the Pusher service.
  Future<void> disconnect() async {
    if (_isConnected) {
      try {
        await _pusher?.disconnect();
        _isConnected = false;
        _logger.i('Pusher disconnected.');
      } catch (e, stackTrace) {
        _logger.e('Failed to disconnect Pusher',
            error: e, stackTrace: stackTrace);
      }
    }
  }

  /// Subscribes to a Pusher channel.
  Future<PusherChannel> subscribeToChannel(
    String channelName, {
    bool isPrivate = true,
    void Function(PusherEvent event)? onEvent,
  }) async {
    await initPusher();

    final fullChannelName = isPrivate ? 'private-$channelName' : channelName;

    try {
      return await _pusher!.subscribe(
        channelName: fullChannelName,
        onEvent: onEvent != null
            ? (dynamic event) =>
                onEvent(event as PusherEvent) // Typecast auf PusherEvent
            : null,
      );
    } catch (e, stackTrace) {
      _logger.e('Failed to subscribe to channel $fullChannelName',
          error: e, stackTrace: stackTrace);
      rethrow;
    }
  }

  /// Handles authorization for private channels.
  Future<Map<String, String>?> _onAuthorizer(
    String channelName,
    String socketId,
    dynamic options,
  ) async {
    final token = await FirebaseAuth.instance.currentUser?.getIdToken();
    if (token == null) {
      _logger.w('Authorization failed: No token available.');
      return null;
    }

    try {
      final response = await http.post(
        Uri.parse(authEndpoint),
        headers: {
          'Authorization': 'Bearer $token',
        },
        body: {
          'socket_id': socketId,
          'channel_name': channelName,
        },
      );

      if (response.statusCode == 200) {
        return Map<String, String>.from(jsonDecode(response.body));
      } else {
        _logger.w(
          'Authorization failed with status code ${response.statusCode}: ${response.body}',
        );
      }
    } catch (e, stackTrace) {
      _logger.e('Authorization error', error: e, stackTrace: stackTrace);
    }
    return null;
  }

  // Callbacks for Pusher events
  void _onConnectionStateChange(String currentState, String? previousState) {
    _logger.i('Connection state changed: $currentState (from $previousState)');
  }

  void _onError(String message, int? code, dynamic e) {
    _logger.e('Pusher error: $message (Code: $code)', error: e);
  }

  void _onSubscriptionSucceeded(String channelName, dynamic data) {
    _logger.i('Subscription succeeded: $channelName');
  }

  void _onEvent(PusherEvent event) {
    _logger.d('Event received: ${event.data}');
  }

  void _onSubscriptionError(String message, dynamic e) {
    _logger.e('Subscription error: $message', error: e);
  }
}

[kadersaka]

Here is the line 107 code that causes your app crash:

let authDataCast = authData as! [String: String]
This crash occurs because your _onAuthorizer function must return a Map<String, String>. If it returns null or a Map<String, dynamic>, the app will crash due to the forced cast in the native code.

That said, I can see that you already cast your Map to <String, String>, so theoretically, it shouldn't crash. However, there might still be edge cases where invalid or improperly formatted data could cause issues.

I recommend adding additional validation and controls to your _onAuthorizer implementation to ensure robustness. You can check out the _onAuthorizer implementation in my pusher_service.dart file in this repository for reference:
Github repo

[hschk]

I recently added the try-catch block to the onAuthorizer implementation on the Dart side. It’s possible that before this change, an exception might have caused an unexpected value to be returned to the invokeMethod callback in Swift, which could potentially explain the crash.

That said, during the last app crashes, everything appeared normal in our server logs — there were no errors or anomalies reported. However, it’s still possible that an exception occurred somewhere else in the flow, which I might have missed.

I'm continuing to investigate this, especially with your provided validation and controls for onAuthorizer, and will provide updates if we find anything conclusive.

[BunnyBuddy]

I am also seeing this issue on iOS 18 and iPhone 14 Plus, under my crashlytics I see,

$s23pusher_channels_flutter32SwiftPusherChannelsFlutterPluginC14fetchAuth

and,

Could not cast value of type 'NSNull' (0x1f5862190) to 'webview_flutter_wkwebview.AuthenticationChallengeResponse' (0x1023275d8).