Bug: Grids creates new megolm session per each sent location

[hifi]

I was wondering why decrypting the location was so slow on some devices but I noticed each and every sent location event had a new megolm session instead of using the same one multiple times.

Even though Grid isn't a Matrix client I believe this inefficiency would affect its own use of Matrix as well and increases network and battery consumption and even disk usage because of the excess amount of keys generated and shared for all devices.

The Matrix spec has some suggested defaults how often a session should be rotated and the rooms don't seem to have any configured so either Grid defaults to 0 so it rotates it per every event sent or there's some other bug that causes it: https://spec.matrix.org/v1.3/client-server-api/#mroomencryption

EDIT: If it makes a difference this happens in a room that has non-Grid clients with a Grid client. I haven't verified this happens in Grid-only rooms.

[chandlergach]

Thanks for digging into this @hifi - yeah curious if happening Grid -> Grid.

I'll look into it, this is the SDK https://pub.dev/documentation/matrix/latest/matrix_api_lite_model_events_room_encryption_content/RoomEncryptionContent-class.html and I am curious what it sets for default and maybe that's the issue.

What's the other client?

[hifi]

I had a bunch of different clients in the room including Element (Android and X) and gomuks.

Did a quick look at the SDK and it does seem to use the defaults unless overridden: https://github.com/famedly/matrix-dart-sdk/blob/main/lib/encryption/key_manager.dart#L326-L339

My best guess is that there's some bug somewhere in the SDK related to unverified devices which would enforce a new session every time since Grid doesn't verify its own devices.

[chandlergach]

That makes sense...Could test but don't currently have in-app device verification. It didn't quite make sense for Grid specifically or it wasn't intended as a 1:1 matrix client. But I could see how that may have some side effects.