🐛 Bug Report: RealTime subscribe throws Concurrent modification during iteration: _Map len:0

[darwinmorocho-deuna]

👟 Reproduction steps

Self Hosting with a nginx proxy

nginx configuration

server {
    server_name app.mydomain.com;

    location / {
        proxy_pass http://localhost:81;
	proxy_set_header Host $host;
    }

    location /v1/realtime/ {
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_pass http://localhost:81/v1/realtime/;
    }

    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/app.mydomain.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/app.mydomain.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot



}
server {
    if ($host = app.mydomain.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot


    server_name app.mydomain.com;
    listen 80;
    return 404; # managed by Certbot


}

Flutter SDK

appwrite: ^12.0.3

Try to subscribe to multiples channels

   final Realtime _realtime = Realtime(client);
.
.
.
    final userChannel = 'databases.my_db.collections.users.documents.$userId';
    final membershipChannel = 'databases.my_db.collections.memberships.documents.$userId';
    
    // this works for around 30 seconds, after that time the appwrite sdk throws 
// Unhandled Exception: Concurrent modification during iteration: _Map len:0.
// And the realtime stop working
    _subscription = _realtime.subscribe(
      [userChannel, membershipChannel],
    );

👍 Expected behavior

Realtime must not stop working after some seconds.

👎 Actual Behavior

Console error after 30 seconds.

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: Concurrent modification during iteration: _Map len:0.
#0      _CompactIterator.moveNext (dart:collection-patch/compact_hash.dart:714:7)
#1      RealtimeMixin._createSocket.<anonymous closure> (package:appwrite/src/realtime_mixin.dart:91:49)
#2      _RootZone.runGuarded (dart:async/zone.dart:1582:10)
#3      _BufferingStreamSubscription._sendDone.sendDone (dart:async/stream_impl.dart:392:13)
#4      _BufferingStreamSubscription._sendDone (dart:async/stream_impl.dart:402:7)
#5      _BufferingStreamSubscription._close (dart:async/stream_impl.dart:291:7)
#6      _ForwardingStream._handleDone (dart:async/stream_pipe.dart:99:10)
#7      _ForwardingStreamSubscription._handleDone (dart:async/stream_pipe.dart:161:13)
#8      _RootZone.runGuarded (dart:async/zone.dart:1582:10)
#9      _BufferingStreamSubscription._sendDone.sendDone (dart:async/stream_impl.dart:392:13)

🎲 Appwrite version

Different version (specify in environment)

💻 Operating system

MacOS

🧱 Your Environment

No

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

• I checked and didn't find similar issue

🏢 Have you read the Code of Conduct?

• I have read the Code of Conduct

[stnguyen90]

@darwinmorocho-deuna, thanks for raising this issue! 🙏 Your connection is probably closing because of a default timeout Nginx has.

That said, I'm going to leave this open and use it to track the concurrent modification error.

[ItzNotABug]

@stnguyen90 ig this happens because the sdk calls subscription.close() where the close() does _subscriptions.remove(id); which is modifying the Map while iteration.