Indexed DB can have inconsistency in membership event content

[AndrewFerr]

It's possible for the sync store to have incorrect content of a m.room.member event in roomsData.join.$roomID.state[*], but correct content for that same event in roomsData.join.$roomID.timeline[*].

To reproduce:

• Visit develop.element.io in two tabs, each tab signed in with a different user
• Create/visit a room that has both users in it
• Have one user leave the room
• With the user that remains in the room:
  • Open Element devtools and view Explore room state > m.room.member > MXID of user who left
  • Open browser devtools and view Indexed DB for https://develop.element.io > matrix-js-sdk:riot-web-sync > sync
• See that Element devtools shows the correct value of content.membership = "leave"
• See that the Indexed DB has the same value for content.membership in the timeline event for the same eventID
• See that the Indexed DB has an *incorrect value of content.membership = "join" in the state event for the same eventID

With that said, any client that uses timeline to load state won't have any problems (and I assume Element Web does that, as it has accurate member lists in rooms). But if a client were read from state, it would get incorrect data.

[AndrewFerr]

For example:

Element devtools & Indexed DB are showing the same event (as the room ID & event ID between the two are the same), but they each have a different value for "membership".

The correct content is in the timeline version of the event, though:

I assume that, unlike /sync's Joined Room response objects, the js-sdk's Indexed DB state should be a snapshot of the current room state, and not whatever the state was up until the start of timeline. But even if that weren't the case, it's still a problem that two occurrences of the same event in the Indexed DB have different "content"s.

[dbkr]

Just looking at this for triage, but how are you getting two tabs signed in as different users? I don't see how this would be possible since they share the same localstorage etc: they would be logged in as the same user.

[MidhunSureshR]

To add to the above comment, the app should also show you an error:

[AndrewFerr]

how are you getting two tabs signed in as different users?

With Firefox container tabs.

But since the repro steps involve only 2 users, an alternative to using container tabs is to have one of the 2 users in a private browsing / incognito window.

[toger5]

This is potentially related.
https://github.com/matrix-org/matrix-js-sdk/pull/4153/files

There was a switch from using a currentState cache to reading the state from the timeline.getState() method.

I tried refactoring this with the help of @t3chguy but there was more to do so the PR is currently put on ice.

[toger5]

There is a new finding outlined here:
https://matrix.to/#/!jxlRxnrZCsjpjDubDX:matrix.org/$2X7ysozWciiyDHVev8iJ5yaFcZbZr57H2u8v5-7ysXw?via=matrix.org&via=envs.net&via=mozilla.org

State seems to be updated with older state.
The sync loop passes state to setStateEvents twice (occasionally) so we end up with multiple state changes.