🐛 Bug Report: Subscribing Multiple Times with a Single Realtime Instance Results in Null Subscription

[stnguyen90]

👟 Reproduction steps

1. Instantiate a Realtime instance
2. Subscribe to a channel
3. Subscribe to another channel

👍 Expected behavior

You get 2 separate working subscriptions

👎 Actual Behavior

log:

subscription: null

The subscriptions don't receive any events.

It looks like the 2nd subscribe closes the websocket, which triggers:

https://github.com/appwrite/sdk-for-flutter/blob/54f30faa4a4fab2af0fe57c172550b288c9cbb4b/lib/src/realtime_mixin.dart#L85-L86

The _closeConnection() results in the _lastUrl being set to null:

https://github.com/appwrite/sdk-for-flutter/blob/54f30faa4a4fab2af0fe57c172550b288c9cbb4b/lib/src/realtime_mixin.dart#L27

and the _channels.clear() prevents future events from being dispatched properly:

https://github.com/appwrite/sdk-for-flutter/blob/54f30faa4a4fab2af0fe57c172550b288c9cbb4b/lib/src/realtime_mixin.dart#L71-L75

🎲 Appwrite version

Different version (specify in environment)

💻 Operating system

Linux

🧱 Your Environment

Tested with SDK version 9.0.0 and Appwrite version 1.3.4. For some reason, this only happens on mobile and not on flutter web.

👀 Have you spent some time to check if this issue has been raised before?

• [X] I checked and didn't find similar issue

🏢 Have you read the Code of Conduct?

• [X] I have read the Code of Conduct

[stnguyen90]

For now, the best thing to do is to use a separate Realtime instance for each subscription.

[lohanidamodar]

@stnguyen90 what is the behavior with other SDKs?

[stnguyen90]

@lohanidamodar, it works fine in other SDKs. You can use 1 realtime instance and make multiple subscribe calls. The problem with our Flutter SDK is how we handle reconnects.

[rvndsngwn]

Same issue with me

[Schrolli91]

Same here. Is there any milestone, when this will be fixed?

[puntiz]

This needs addressing, really handicaps one of the most useful features.

[moshOntong-IT]

Same here, what is the status of this issue?

[Sokratesli]

same here. Thank you for the work.

[lohanidamodar]

Hey, we have a work in progress fix for this issue, if you could test the SDK from this branch and let us know that would be great https://github.com/appwrite/sdk-for-flutter/tree/fix-realtime-multiple-subscription

dependencies:
	appwrite:
		git:
			url: https://github.com/appwrite/sdk-for-flutter
			ref: fix-realtime-multiple-subscription

[rvndsngwn]

Hi @lohanidamodar

I have just tested the SDK from the fix-realtime-multiple-subscription branch and now multiple subscriptions are working. Your help is greatly appreciated.

[lohanidamodar]

Hi @lohanidamodar

I have just tested the SDK from the fix-realtime-multiple-subscription branch and now multiple subscriptions are working. Your help is greatly appreciated.

Thank you for your validation. Will work to get it released soon.

[Andree98]

Hey, we have a work in progress fix for this issue, if you could test the SDK from this branch and let us know that would be great https://github.com/appwrite/sdk-for-flutter/tree/fix-realtime-multiple-subscription

dependencies:
	appwrite:
		git:
			url: https://github.com/appwrite/sdk-for-flutter
			ref: fix-realtime-multiple-subscription

I tried this patch and an error occurs when restarting the realtime stream whenever it closes

Here's the stacktrace

Concurrent modification during iteration: _Map len:2.
      #0      _CompactIterator.moveNext (dart:collection-patch/compact_hash.dart:714:7)
      #1      RealtimeMixin._createSocket.<anonymous closure> (package:appwrite/src/realtime_mixin.dart:88:49)
      #2      _rootRun (dart:async/zone.dart:1391:47)
      #3      _CustomZone.run (dart:async/zone.dart:1301:19)
      #4      _CustomZone.runGuarded (dart:async/zone.dart:1209:7)
      #5      _BufferingStreamSubscription._sendDone.sendDone (dart:async/stream_impl.dart:392:13)
      #6      _BufferingStreamSubscription._sendDone (dart:async/stream_impl.dart:402:7)
      #7      _BufferingStreamSubscription._close (dart:async/stream_impl.dart:291:7)
      #8      _ForwardingStream._handleDone (dart:async/stream_pipe.dart:99:10)
      #9      _ForwardingStreamSubscription._handleDone (dart:async/stream_pipe.dart:161:13)
      #10     _rootRun (dart:async/zone.dart:1391:47)
      #11     _CustomZone.run (dart:async/zone.dart:1301:19)
      #12     _CustomZone.runGuarded (dart:async/zone.dart:1209:7)
      #13     _BufferingStreamSubscription._sendDone.sendDone (dart:async/stream_impl.dart:392:13)
      #14     _BufferingStreamSubscription._sendDone (dart:async/stream_impl.dart:402:7)
      #15     _BufferingStreamSubscription._close (dart:async/stream_impl.dart:291:7)
      #16     _SyncStreamControllerDispatch._sendDone (dart:async/stream_controller.dart:792:19)
      #17     _StreamController._closeUnchecked (dart:async/stream_controller.dart:647:7)
      #18     _StreamController.close (dart:async/stream_controller.dart:640:5)
      #19     new _WebSocketImpl._fromSocket.<anonymous closure> (dart:_http/websocket_impl.dart:1171:19)
      #20     _rootRun (dart:async/zone.dart:1391:47)
      #21     _CustomZone.run (dart:async/zone.dart:1301:19)
      #22     _CustomZone.runGuarded (dart:async/zone.dart:1209:7)
      #23     _BufferingStreamSubscription._sendDone.sendDone (dart:async/stream_impl.dart:392:13)
      #24     _BufferingStreamSubscription._sendDone (dart:async/stream_impl.dart:402:7)
      #25     _BufferingStreamSubscription._close (dart:async/stream_impl.dart:291:7)
      #26     _SinkTransformerStreamSubscription._close (dart:async/stream_transformers.dart:87:11)
      #27     _EventSinkWrapper.close (dart:async/stream_transformers.dart:21:11)
      #28     _WebSocketProtocolTransformer.close (dart:_http/websocket_impl.dart:118:17)
      #29     _SinkTransformerStreamSubscription._handleDone (dart:async/stream_transformers.dart:132:24)
      #30     _rootRun (dart:async/zone.dart:1391:47)
      #31     _CustomZone.run (dart:async/zone.dart:1301:19)
      #32     _CustomZone.runGuarded (dart:async/zone.dart:1209:7)
      #33     _BufferingStreamSubscription._sendDone.sendDone (dart:async/stream_impl.dart:392:13)
      #34     _BufferingStreamSubscription._sendDone (dart:async/stream_impl.dart:402:7)
      #35     _BufferingStreamSubscription._close (dart:async/stream_impl.dart:291:7)
      #36     _SyncStreamControllerDispatch._sendDone (dart:async/stream_controller.dart:792:19)
      #37     _StreamController._closeUnchecked (dart:async/stream_controller.dart:647:7)
      #38     _StreamController.close (dart:async/stream_controller.dart:640:5)
      #39     _Socket._onData (dart:io-patch/socket_patch.dart:2454:21)
      #40     _rootRunUnary (dart:async/zone.dart:1407:47)
      #41     _CustomZone.runUnary (dart:async/zone.dart:1308:19)
      #42     _CustomZone.runUnaryGuarded (dart:async/zone.dart:1217:7)
      #43     _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:339:11)
      #44     _BufferingStreamSubscription._add (dart:async/stream_impl.dart:271:7)
      #45     _SyncStreamControllerDispatch._sendData (dart:async/stream_controller.dart:784:19)
      #46     _StreamController._add (dart:async/stream_controller.dart:658:7)
      #47     _StreamController.add (dart:async/stream_controller.dart:606:5)
      #48     _RawSecureSocket._closeHandler (dart:io/secure_socket.dart:899:21)
      #49     _RawSecureSocket._tryFilter (dart:io/secure_socket.dart:1029:11)
      <asynchronous suspension>

[lohanidamodar]

@Andree98 can you share code to reproduce this error

[Andree98]

@lohanidamodar I'm able to reproduce the stacktrace with this code

@override
void initState() {
  super.initState();

  final realtime = Realtime(clientInstance);

  final subscription1 = realtime.subscribe([channel1]);
  final subscription2 = realtime.subscribe([channel2]);

  subscription1.stream.listen(print);
  subscription2.stream.listen(print);
}

Run the app and wait for the subscription to be killed. For me this takes 2-3 minutes using Cloudflare proxy. when the subscriptions are killed the stacktrace will appear in the console

[SafakB]

@lohanidamodar Same issue with me, is the work in progress? Thanks

[lohanidamodar]

Latest release should resolve this issue.

[KiloNovemberDelta]

Latest release should resolve this issue.

Hello and thank you for your help! Do you mean 12.0.3 ? Or next release ? Because I have the same issue on 12.0.3 :(