We can now use `_get_events_from_cache_or_db` rather than going right back to
the database, which means that (a) we can benefit from caching, and (b) it
opens the way forward to more extensive checks on the original event.
We now always require the original event to exist before we will serve up a
redaction.
Ensures that redactions are correctly authenticated for recent room versions.
There are a few things going on here:
* `_fetch_event_rows` is updated to return a dict rather than a list of rows.
* Rather than returning multiple copies of an event which was redacted
multiple times, it returns the redactions as a list within the dict.
* It also returns the actual rejection reason, rather than merely the fact
that it was rejected, so that we don't have to query the table again in
`_get_event_from_row`.
* The redaction handling is factored out of `_get_event_from_row`, and now
checks if any of the redactions are valid.
A couple of changes here:
* get rid of a redundant `allow_rejected` condition - we should already have filtered out any rejected
events before we get to that point in the code, and the redundancy is confusing. Instead, let's stick in
an assertion just to make double-sure we aren't leaking rejected events by mistake.
* factor out a `_get_events_from_cache_or_db` method, which is going to be important for a
forthcoming fix to redactions.
* Fix background updates to handle redactions/rejections
In background updates based on current state delta stream we need to
handle that we may not have all the events (or at least that
`get_events` may raise an exception).
I was staring at this function trying to figure out wtf it was actually
doing. This is (hopefully) a non-functional refactor which makes it a bit
clearer.
Currently we only have the one event format version defined, but this
adds the necessary infrastructure to persist and fetch the format
versions alongside the events.
We specify the format version rather than the room version as:
1. We don't necessarily know the room version, existing events may be
either v1 or v2.
2. We'd need to be careful to prevent/handle correctly if different
events in the same room reported to be of different versions, which
sounds annoying.
This fixes#3518, and ensures that we get useful logs and metrics for lots of
things that happen in the background.
(There are certainly more things that happen in the background; these are just
the common ones I've found running a single-process synapse locally).
When we finish processing a request, log the number of events we fetched from
the database to handle it.
[I'm trying to figure out which requests are responsible for large amounts of
event cache churn. It may turn out to be more helpful to add counts to the
prometheus per-request/block metrics, but that is an extension to this code
anyway.]
While I was going through uses of preserve_fn for other PRs, I converted places
which only use the wrapped function once to use run_in_background, to avoid
creating the function object.
