Stale device lists

[richvdh]

STR:

1. Alice and Bob share an e2e room
2. Bob leaves all of the e2e rooms he shares with Alice
3. Bob logs in on a new device
4. Bob joins (the same, or a different) e2e room with Alice
5. Alice sends a message
6. Bob sees "Unknown inbound session ID"

The problem here is that Alice's client is using a stale device list for Bob.

It's a bit of an edge case, since it requires doing a complicated dance of leaving and joining rooms and logging in on new devices - but it's an edge case that people tend to hit during testing.

[richvdh]

Some possible strategies for fixing:

1. Force a device list refresh whenever someone joins an e2e room
2. The above, but only if we don't already share an e2e room with them
3. Do the above lazily somehow: store a flag which means we think the device list might be stale

[richvdh]

This also happens even if Bob and Alice have never shared a room; Alice's client may still have cached an old list if she opened Bob's memberinfo.

[giordy]

I confirm that this happens pretty frequently in my experience.
We are using Riot in 2 people from the web and from the app (both iOS and Android).

[richvdh]

@giordy: this bug is something of an edge-case; it is unlikely you are seeing exactly this.

There are several potential causes of "Unknown inbound session ID" (many of them currently related to work still to be done on the mobile clients).

[giordy]

@richvdh ok thanks for the clarification!