* Factor out functions for injecting events into database

I want to add some more flexibility to the tools for injecting events into the
database, and I don't want to clutter up HomeserverTestCase with them, so let's
factor them out to a new file.

* Rework TestReplicationDataHandler

This wasn't very easy to work with: the mock wrapping was largely superfluous,
and it's useful to be able to inspect the received rows, and clear out the
received list.

* Fix AssertionErrors being thrown by EventsStream

Part of the problem was that there was an off-by-one error in the assertion,
but also the limit logic was too simple. Fix it all up and add some tests.

Signed-off-by: Manuel Stahl <manuel.stahl@awesome-technologies.de>

Specifically some tests for the typing stream, which means we test streams that fetch missing updates via HTTP (rather than via the DB).

We also shuffle things around a bit so that we create two separate `HomeServer` objects, rather than trying to insert a slaved store into places.

Note: `test_typing.py` is heavily inspired by `test_receipts.py`

When running the UTs against a postgres deatbase, we need to set the collation
correctly.

Currently we never write to streams from workers, but that will change soon

We need to wait for the renewals to finish, so that the metrics are correctly
reported.

It doesn't seem to be documented anywhere and means that you suddenly start losing metrics without any obvious reason when you go from monolith to workers (e.g. #7312).

Signed-off-by: Simon Körner <git@lubiland.de>

If the admin adds a `.yaml` file that's either empty or doesn't parse into a dict to a config directory (e.g. `conf.d` for debs installs), stuff like https://github.com/matrix-org/synapse/issues/7322 would happen. This PR checks that the file is correctly parsed into a dict, or ignores it with a warning if it parses into any other type (including `None` for empty files).

Fixes https://github.com/matrix-org/synapse/issues/7322

Fix assertions being thrown by the EventsStream update function

Figuring out how to correctly limit updates from this stream without dropping
entries is far more complicated than just counting the number of rows being
returned. We need to consider each query separately and, if any one query hits
the limit, truncate the results from the others.

I think this also fixes some potentially long-standing bugs where events or
state changes could get missed if we hit the limit on either query.

Synapse v1.12.4

Features:

* Always send users their own device updates. (#7160)
* Add support for handling GET requests for account_data on a worker. (#7311)

Bugfixes:

* Fix a bug that prevented cross-signing with users on worker-mode synapses. (#7255)
* Do not treat display names as globs in push rules. (#7271)
* Fix a bug with cross-signing devices belonging to remote users who did not share a
  room with any user on the local homeserver. (#7289)

there doesn't seem to be much point in passing this limit all around, since
both sides agree it's meant to be 100.

This reverts commit 1adf6a55.

This reverts commit 6f431936, reversing
changes made to 0d775fcc.

Config option to inhibit 3PID errors on /requestToken

Long story short: if we're handling presence on the current worker, we shouldn't be sending USER_SYNC commands over replication.

In an attempt to figure out what is going on here, I ended up refactoring some bits of the presencehandler code, so the first 4 commits here are non-functional refactors to move this code slightly closer to sanity. (There's still plenty to do here :/). Suggest reviewing individual commits.

Fixes (I hope) #7257.

Adds a request_token_inhibit_errors configuration flag (disabled by
default) which, if enabled, change the behaviour of all /requestToken
endpoints so that they return a 200 and a fake sid if the 3PID was/was
not found associated with an account (depending on the endpoint),
instead of an error.

Co-Authored-By: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

Synapse 1.12.4rc1 (2020-04-22)
==============================

Features
--------

- Always send users their own device updates. ([\#7160](https://github.com/matrix-org/synapse/issues/7160))
- Add support for handling GET requests for `account_data` on a worker. ([\#7311](https://github.com/matrix-org/synapse/issues/7311))

Bugfixes
--------

- Fix a bug that prevented cross-signing with users on worker-mode synapses. ([\#7255](https://github.com/matrix-org/synapse/issues/7255))
- Do not treat display names as globs in push rules. ([\#7271](https://github.com/matrix-org/synapse/issues/7271))
- Fix a bug with cross-signing devices belonging to remote users who did not share a room with any user on the local homeserver. ([\#7289](https://github.com/matrix-org/synapse/issues/7289))

I messed this up last time I tried (#7239 / e13c6c7a).

First some background: StreamChangeCache is used to keep track of what "entities" have 
changed since a given stream ID. So for example, we might use it to keep track of when the last
to-device message for a given user was received [1], and hence whether we need to pull any to-device messages from the database on a sync [2].

Now, it turns out that StreamChangeCache didn't support more than one thing being changed at
a given stream_id (this was part of the problem with #7206). However, it's entirely valid to send
to-device messages to more than one user at a time.

As it turns out, this did in fact work, because *some* methods of StreamChangeCache coped
ok with having multiple things changing on the same stream ID, and it seems we never actually
use the methods which don't work on the stream change caches where we allow multiple
changes at the same stream ID. But that feels horribly fragile, hence: let's update
StreamChangeCache to properly support this, and add some typing and some more tests while
we're at it.

[1]: https://github.com/matrix-org/synapse/blob/release-v1.12.3/synapse/storage/data_stores/main/deviceinbox.py#L301
[2]: https://github.com/matrix-org/synapse/blob/release-v1.12.3/synapse/storage/data_stores/main/deviceinbox.py#L47-L51

This is configured via the `redis` config options.