ExpiringCache required that `start()` be called before it would actually
start expiring entries. A number of places didn't do that.
This PR removes `start` from ExpiringCache, and automatically starts
backround reaping process on creation instead.
If a HTTP handler throws an exception while processing a request we
automatically write a JSON error response. If the handler had already
started writing a response twisted throws an exception.
We should check for this case and simple abort the connection if there
was an error after the response had started being written.
Add some informative comments about what's going on here.
Also, `sent_to_us_directly` and `get_missing` were doing the same thing (apart
from in `_handle_queued_pdus`, which looks like a bug), so let's get rid of
`get_missing` and use `sent_to_us_directly` consistently.
Let's try to rationalise the logging that happens when we are processing an
incoming transaction, to make it easier to figure out what is going wrong when
they take ages. In particular:
- make everything start with a [room_id event_id] prefix
- make sure we log a warning when catching exceptions rather than just turning
them into other, more cryptic, exceptions.
Currently we rely on the master to invalidate this cache promptly.
However, after having moved most federation endpoints off of master this
no longer happens, causing outbound fedeariont to get blackholed.
Fixes#3798
The existing deferred timeout helper function (and the one into twisted)
suffer from a bug when a deferred's canceller throws an exception, #3842.
The new helper function doesn't suffer from this problem.
We want to wait until we have read the response body before we log the request
as complete, otherwise a confusing thing happens where the request appears to
have completed, but we later fail it.
To do this, we factor the salient details of a request out to a separate
object, which can then keep track of the txn_id, so that it can be logged.
