We've [decided](https://github.com/matrix-org/synapse/issues/5253#issuecomment-665976308) to remove the signature check for v1 lookups.
The signature check has been removed in v2 lookups. v1 lookups are currently deprecated. As mentioned in the above linked issue, this verification was causing deployments for the vector.im and matrix.org IS deployments, and this change is the simplest solution, without being unjustified.
Implementations are encouraged to use the v2 lookup API as it has [increased privacy benefits](https://github.com/matrix-org/matrix-doc/pull/2134).
`StatsHandler` handles updates to the `current_state_delta_stream`, and updates room stats such as the amount of state events, joined users, etc.
However, it counts every new join membership as a new user entering a room (and that user being in another room), whereas it's possible for a user's membership status to go from join -> join, for instance when they change their per-room profile information.
This PR adds a check for join->join membership transitions, and bails out early, as none of the further checks are necessary at that point.
Due to this bug, membership stats in many rooms have ended up being wildly larger than their true values. I am not sure if we also want to include a migration step which recalculates these statistics (possibly using the `_populate_stats_process_rooms` bg update).
Bug introduced in the initial implementation https://github.com/matrix-org/synapse/pull/4338.
Thanks to some slightly overzealous cleanup in the
`delete_old_current_state_events`, it's possible to end up with no
`event_forward_extremities` in a room where we have outstanding local
invites. The user would then get a "no create event in auth events" when trying
to reject the invite.
We can hack around it by using the dangling invite as the prev event.
The replication client requires that arguments are given as keyword
arguments, which was not done in this case. We also pull out the logic
so that we can catch and handle any exceptions raised, rather than
leaving them unhandled.
When fetching the state of a room over federation we receive the event
IDs of the state and auth chain. We then fetch those events that we
don't already have.
However, we used a function that recursively fetched any missing auth
events for the fetched events, which can lead to a lot of recursion if
the server is missing most of the auth chain. This work is entirely
pointless because would have queued up the missing events in the auth
chain to be fetched already.
Let's just diable the recursion, since it only gets called from one
place anyway.
