Fix https://github.com/matrix-org/synapse/issues/11091
We have to allow creation of events with no prev_events
but do have auth_events.
And since the historical member events are outliers
with no prev_events to resolve them, we want to avoid
putting them as backward extremeties.
Previously, we would only look for a batch event if the insertion event
was connected to something else by prev_event. This is only the case
for the base insertion event. And instead, we need to look for
a batch event whenever we come across an insertion event.
If we find ourselves dealing with rejected events, we proably want to know
about it. Let's include it in the stringification of the event so that it gets
logged.
Persist backfilled event response from oldest -> newest to avoid
having to go fetch missing prev_events which de-outliers every
other event and screws up the stream_ordering. Missing prev_events
aren't fetched as "backfilled" so the stream_ordering was incrementing.
This helps us in MSC2716 land where we can more easily copy a similar
stream_ordering that the originating homeserver has.
Currently, when we receive an event whose auth_events differ from those we expect, we state-resolve between the two state sets, and check that the event passes auth based on the resolved state.
This means that it's possible for us to accept events which don't pass auth at their declared auth_events (or where the auth events themselves were rejected), leading to problems down the line like #10083.
This change means we will:
* ignore any events where we cannot find the auth events
* reject any events whose auth events were rejected
* reject any events which do not pass auth at their declared auth_events.
Together with a whole raft of previous work, this is a partial fix to #9595.
Fixes#6643.
Based on #11009.
This fixes a bug where we would accept an event whose `auth_events` include
rejected events, if the rejected event was shadowed by another `auth_event`
with same `(type, state_key)`.
The approach is to pass a list of auth events into
`check_auth_rules_for_event` instead of a dict, which of course means updating
the call sites.
This is an extension of #10956.
Instead of triggering `__exit__` manually on the replication handler's
logging context, use it as a context manager so that there is an
`__enter__` call to balance the `__exit__`.
Found while working on the Gitter backfill script and noticed
it only happened after we sent 7 batches, https://gitlab.com/gitterHQ/webapp/-/merge_requests/2229#note_665906390
When there are more than 5 backward extremities for a given depth,
backfill will throw an error because we sliced the extremity list
to 5 but then try to iterate over the full list. This causes
us to look for state that we never fetched and we get a `KeyError`.
Before when calling `/messages` when there are more than 5 backward extremities:
```
Traceback (most recent call last):
File "/usr/local/lib/python3.8/site-packages/synapse/http/server.py", line 258, in _async_render_wrapper
callback_return = await self._async_render(request)
File "/usr/local/lib/python3.8/site-packages/synapse/http/server.py", line 446, in _async_render
callback_return = await raw_callback_return
File "/usr/local/lib/python3.8/site-packages/synapse/rest/client/room.py", line 580, in on_GET
msgs = await self.pagination_handler.get_messages(
File "/usr/local/lib/python3.8/site-packages/synapse/handlers/pagination.py", line 396, in get_messages
await self.hs.get_federation_handler().maybe_backfill(
File "/usr/local/lib/python3.8/site-packages/synapse/handlers/federation.py", line 133, in maybe_backfill
return await self._maybe_backfill_inner(room_id, current_depth, limit)
File "/usr/local/lib/python3.8/site-packages/synapse/handlers/federation.py", line 386, in _maybe_backfill_inner
likely_extremeties_domains = get_domains_from_state(states[e_id])
KeyError: '$zpFflMEBtZdgcMQWTakaVItTLMjLFdKcRWUPHbbSZJl'
```
