Fix an occurence of null displayname issue

[hberenger]

Hi there,

After having upgraded our Matrix client app to use matrix-ios-sdk v0.11.5, we noticed that some rooms happen to lose their display name and avatar on a seemingly random basis.
I can see from PR #599 that you are also facing similar issues.

From user feedbacks, it appears that Direct chats are the most affected.

I could reproduce this problem with the latest Riot iOS client, so I guess v0.11.6 does not fix that.

Steps to reproduce :

• with Riot iOS client, create a Direct Chat with some user Foo
• kill Riot iOS app
• from another client (e.g the webclient), go to the Foo chat, and send ~25 messages (enough to trigger a limited sync)
• now open Riot iOS : "sometimes" (about half the time from my tests) you'll find that the Foo chat has been renamed Empty room, and has lost its avatar (used to be Foo avatar, now it's the first letter of the roomId)

What happens is that :

1. due to the large number of messages sent, Riot receives a limited sync of the chat.
2. In MXEventTimeline.handleJoinedRoomSync, this limited sync triggers a kMXRoomDidFlushDataNotification notification.
3. This notification is handled by MXRoomSummary.resetRoomStateData, which resets the chat avatar, displayname, topic and aliases, and tries to recompute them from state events.
4. Unfortunately, the state event list of the direct chat does not contain enough information to recompute a displayname or an avatar.
5. If the limited sync data also contains a server room summary, then the displayname and avatar are restored soon after, in MXRoomSummary.handleJoinedRoomSync
6. Yet if the sync data does not contain the server room summary, the displayname and avatar are now reset for good (the null value is persisted), until the user either clears the cache or logs out & in.

I came up with the following workaround, which I submit to your approval : since the summary can't be recomputed from the state events, we can still reconstruct it by calling the standard Matrix name/avatar computation algorithm, via the update delegate's session:updateRoomSummary:withServerRoomSummary:roomState: method, passing it a nil server room summary.
(A similar trick is already used to compute the room summary of invited rooms in session:updateRoomSummary:withStateEvents:roomState:)

Not sure this fix is the most relevant (maybe this should be fixed on the server side after all, by sending the server room summary more often ?), but at least it can start a discussion ^^

Thank you !

Signed-off-by: Hervé Bérenger [email protected]

[manuroe]

Thanks a lot for having chased and fixed this case.

I have written an integration test (called testRoomSummaryDisplayNameInDirectChat) that shows your changes do fix the issue.

[manuroe]

Suggested change

	if (room.isDirect && (_displayname == nil || _avatar == nil))
	if (self.displayname == nil || self.avatar == nil))

We could make it more general and not only for direct rooms.

Prefer to use self.displayname to avoid implicit retains. The SDK project fails to build on such error now.

[hberenger]

Sure, will do

[hberenger]

Thank you @manuroe for your prompt answer.
I've just amended my commit to take your suggestions into account.