It seems most of these blacklisted tests do actually pass most of the time.

I'm of the opinion that having them blacklisted here means there is very little incentive for us to deflake any flaky tests, and meanwhile any value in those tests is completely lost.

This allows a user to store an offline device on the server and
then restore it at a subsequent login.

Reduce inconsistencies between codepaths for membership and non-membership events.

Lots of different module apis is not easy to maintain.

Rather than adding yet another ModuleApi(hs, hs.get_auth_handler()) incantation, first add an hs.get_module_api() method and use it where possible.

https://github.com/matrix-org/synapse/tree/develop/docs/sphinx doesn't seem to really be utilised or changed recently since the initial commit. I like the idea of exportable documentation of the codebase, but at the moment after running through the build instructions the generated website wasn't very useful...

* Optimise and test state fetching for 3p event rules

Getting all the events at once is much more efficient than getting them
individually

* Test that 3p event rules can modify events

Fix third-party event modules for `check_visibility_can_be_modified` check

This PR ports the quick fix from https://github.com/matrix-org/synapse/pull/2796 to further methods which handle media, URL preview and `/key/v2/server` requests. This prevents a harmless `ERROR` that comes up in the logs when we were unable to respond to a client request when the client had already disconnected. In this case we simply bail out if the client has already done so.

This is the 'simple fix' as suggested by https://github.com/matrix-org/synapse/issues/5304#issuecomment-574740003.

Fixes https://github.com/matrix-org/synapse/issues/6700
Fixes https://github.com/matrix-org/synapse/issues/5304

Per https://github.com/matrix-org/matrix-doc/pull/2788

PR #8292 tried to maintain backwards compat with modules which don't provide a
`check_visibility_can_be_modified` method, but the tests weren't being run,
and the check didn't work.

This is now redundant, and we can just call `handle_new_client_event` directly.

move the "duplicate state event" handling down into `handle_new_client_event`
where it can be shared between multiple call paths.

This fixes a bug when backfilling invalid events.

This PR allows `ThirdPartyEventRules` modules to view, manipulate and block changes to the state of whether a room is published in the public rooms directory.

While the idea of whether a room is in the public rooms list is not kept within an event in the room, `ThirdPartyEventRules` generally deal with controlling which modifications can happen to a room. Public rooms fits within that idea, even if its toggle state isn't controlled through a state event. 

There's no need for it to be in the dict as well as the events table. Instead,
we store it in a separate attribute in the EventInternalMetadata object, and
populate that on load.

This means that we can rely on it being correctly populated for any event which
has been persited to the database.

This fixes a bug where `m.ignored_user_list` was assumed to be a dict,
leading to odd behavior for users who set it to something else.

This is so we can tell what is going on when things are taking a while to start up.

The main change here is to ensure that transactions that are created during startup get correctly logged like normal transactions.

Synapse 1.21.0rc2 (2020-10-02)
==============================

Features
--------

- Convert additional templates from inline HTML to Jinja2 templates. ([\#8444](https://github.com/matrix-org/synapse/issues/8444))

Bugfixes
--------

- Fix a regression in v1.21.0rc1 which broke thumbnails of remote media. ([\#8438](https://github.com/matrix-org/synapse/issues/8438))
- Do not expose the experimental `uk.half-shot.msc2778.login.application_service` flow in the login API, which caused a compatibility problem with Element iOS. ([\#8440](https://github.com/matrix-org/synapse/issues/8440))
- Fix malformed log line in new federation "catch up" logic. ([\#8442](https://github.com/matrix-org/synapse/issues/8442))
- Fix DB query on startup for negative streams which caused long start up times. Introduced in [\#8374](https://github.com/matrix-org/synapse/issues/8374). ([\#8447](https://github.com/matrix-org/synapse/issues/8447))

#7124 changed the behaviour of remote thumbnails so that the thumbnailing method was included in the filename of the thumbnail. To support existing files, it included a fallback so that we would check the old filename if the new filename didn't exist.

Unfortunately, it didn't apply this logic to storage providers, so any thumbnails stored on such a storage provider was broken.

For negative streams we have to negate the internal stream ID before
querying the DB.

The effect of this bug was to query far too many rows, slowing start up
time, but we would correctly filter the results afterwards so there was
no ill effect.

This converts a few more of our inline HTML templates to Jinja. This is somewhat part of #7280 and should make it a bit easier to customize these in the future.

This allows for connecting to certain IdPs, e.g. GitLab.

Synapse 1.21.0rc1 (2020-10-01)
==============================

Features
--------

- Require the user to confirm that their password should be reset after clicking the email confirmation link. ([\#8004](https://github.com/matrix-org/synapse/issues/8004))
- Add an admin API `GET /_synapse/admin/v1/event_reports` to read entries of table `event_reports`. Contributed by @dklimpel. ([\#8217](https://github.com/matrix-org/synapse/issues/8217))
- Consolidate the SSO error template across all configuration. ([\#8248](https://github.com/matrix-org/synapse/issues/8248), [\#8405](https://github.com/matrix-org/synapse/issues/8405))
- Add a configuration option to specify a whitelist of domains that a user can be redirected to after validating their email or phone number. ([\#8275](https://github.com/matrix-org/synapse/issues/8275), [\#8417](https://github.com/matrix-org/synapse/issues/8417))
- Add experimental support for sharding event persister. ([\#8294](https://github.com/matrix-org/synapse/issues/8294), [\#8387](https://github.com/matrix-org/synapse/issues/8387), [\#8396](https://github.com/matrix-org/synapse/issues/8396), [\#8419](https://github.com/matrix-org/synapse/issues/8419))
- Add the room topic and avatar to the room details admin API. ([\#8305](https://github.com/matrix-org/synapse/issues/8305))
- Add an admin API for querying rooms where a user is a member. Contributed by @dklimpel. ([\#8306](https://github.com/matrix-org/synapse/issues/8306))
- Add `uk.half-shot.msc2778.login.application_service` login type to allow appservices to login. ([\#8320](https://github.com/matrix-org/synapse/issues/8320))
- Add a configuration option that allows existing users to log in with OpenID Connect. Contributed by @BBBSnowball and @OmmyZhang. ([\#8345](https://github.com/matrix-org/synapse/issues/8345))
- Add prometheus metrics for replication requests. ([\#8406](https://github.com/matrix-org/synapse/issues/8406))
- Support passing additional single sign-on parameters to the client. ([\#8413](https://github.com/matrix-org/synapse/issues/8413))
- Add experimental reporting of metrics on expensive rooms for state-resolution. ([\#8420](https://github.com/matrix-org/synapse/issues/8420))
- Add experimental prometheus metric to track numbers of "large" rooms for state resolutiom. ([\#8425](https://github.com/matrix-org/synapse/issues/8425))
- Add prometheus metrics to track federation delays. ([\#8430](https://github.com/matrix-org/synapse/issues/8430))

Bugfixes
--------

- Fix a bug in the media repository where remote thumbnails with the same size but different crop methods would overwrite each other. Contributed by @deepbluev7. ([\#7124](https://github.com/matrix-org/synapse/issues/7124))
- Fix inconsistent handling of non-existent push rules, and stop tracking the `enabled` state of removed push rules. ([\#7796](https://github.com/matrix-org/synapse/issues/7796))
- Fix a longstanding bug when storing a media file with an empty `upload_name`. ([\#7905](https://github.com/matrix-org/synapse/issues/7905))
- Fix messages not being sent over federation until an event is sent into the same room. ([\#8230](https://github.com/matrix-org/synapse/issues/8230), [\#8247](https://github.com/matrix-org/synapse/issues/8247), [\#8258](https://github.com/matrix-org/synapse/issues/8258), [\#8272](https://github.com/matrix-org/synapse/issues/8272), [\#8322](https://github.com/matrix-org/synapse/issues/8322))
- Fix a longstanding bug where files that could not be thumbnailed would result in an Internal Server Error. ([\#8236](https://github.com/matrix-org/synapse/issues/8236), [\#8435](https://github.com/matrix-org/synapse/issues/8435))
- Upgrade minimum version of `canonicaljson` to version 1.4.0, to fix an unicode encoding issue. ([\#8262](https://github.com/matrix-org/synapse/issues/8262))
- Fix longstanding bug which could lead to incomplete database upgrades on SQLite. ([\#8265](https://github.com/matrix-org/synapse/issues/8265))
- Fix stack overflow when stderr is redirected to the logging system, and the logging system encounters an error. ([\#8268](https://github.com/matrix-org/synapse/issues/8268))
- Fix a bug which cause the logging system to report errors, if `DEBUG` was enabled and no `context` filter was applied. ([\#8278](https://github.com/matrix-org/synapse/issues/8278))
- Fix edge case where push could get delayed for a user until a later event was pushed. ([\#8287](https://github.com/matrix-org/synapse/issues/8287))
- Fix fetching malformed events from remote servers. ([\#8324](https://github.com/matrix-org/synapse/issues/8324))
- Fix `UnboundLocalError` from occuring when appservices send a malformed register request. ([\#8329](https://github.com/matrix-org/synapse/issues/8329))
- Don't send push notifications to expired user accounts. ([\#8353](https://github.com/matrix-org/synapse/issues/8353))
- Fix a regression in v1.19.0 with reactivating users through the admin API. ([\#8362](https://github.com/matrix-org/synapse/issues/8362))
- Fix a bug where during device registration the length of the device name wasn't limited. ([\#8364](https://github.com/matrix-org/synapse/issues/8364))
- Include `guest_access` in the fields that are checked for null bytes when updating `room_stats_state`. Broke in v1.7.2. ([\#8373](https://github.com/matrix-org/synapse/issues/8373))
- Fix theoretical race condition where events are not sent down `/sync` if the synchrotron worker is restarted without restarting other workers. ([\#8374](https://github.com/matrix-org/synapse/issues/8374))
- Fix a bug which could cause errors in rooms with malformed membership events, on servers using sqlite. ([\#8385](https://github.com/matrix-org/synapse/issues/8385))
- Fix "Re-starting finished log context" warning when receiving an event we already had over federation. ([\#8398](https://github.com/matrix-org/synapse/issues/8398))
- Fix incorrect handling of timeouts on outgoing HTTP requests. ([\#8400](https://github.com/matrix-org/synapse/issues/8400))
- Fix a regression in v1.20.0 in the `synapse_port_db` script regarding the `ui_auth_sessions_ips` table. ([\#8410](https://github.com/matrix-org/synapse/issues/8410))
- Remove unnecessary 3PID registration check when resetting password via an email address. Bug introduced in v0.34.0rc2. ([\#8414](https://github.com/matrix-org/synapse/issues/8414))

Improved Documentation
----------------------

- Add `/_synapse/client` to the reverse proxy documentation. ([\#8227](https://github.com/matrix-org/synapse/issues/8227))
- Add note to the reverse proxy settings documentation about disabling Apache's mod_security2. Contributed by Julian Fietkau (@jfietkau). ([\#8375](https://github.com/matrix-org/synapse/issues/8375))
- Improve description of `server_name` config option in `homserver.yaml`. ([\#8415](https://github.com/matrix-org/synapse/issues/8415))

Deprecations and Removals
-------------------------

- Drop support for `prometheus_client` older than 0.4.0. ([\#8426](https://github.com/matrix-org/synapse/issues/8426))

Internal Changes
----------------

- Fix tests on distros which disable TLSv1.0. Contributed by @danc86. ([\#8208](https://github.com/matrix-org/synapse/issues/8208))
- Simplify the distributor code to avoid unnecessary work. ([\#8216](https://github.com/matrix-org/synapse/issues/8216))
- Remove the `populate_stats_process_rooms_2` background job and restore functionality to `populate_stats_process_rooms`. ([\#8243](https://github.com/matrix-org/synapse/issues/8243))
- Clean up type hints for `PaginationConfig`. ([\#8250](https://github.com/matrix-org/synapse/issues/8250), [\#8282](https://github.com/matrix-org/synapse/issues/8282))
- Track the latest event for every destination and room for catch-up after federation outage. ([\#8256](https://github.com/matrix-org/synapse/issues/8256))
- Fix non-user visible bug in implementation of `MultiWriterIdGenerator.get_current_token_for_writer`. ([\#8257](https://github.com/matrix-org/synapse/issues/8257))
- Switch to the JSON implementation from the standard library. ([\#8259](https://github.com/matrix-org/synapse/issues/8259))
- Add type hints to `synapse.util.async_helpers`. ([\#8260](https://github.com/matrix-org/synapse/issues/8260))
- Simplify tests that mock asynchronous functions. ([\#8261](https://github.com/matrix-org/synapse/issues/8261))
- Add type hints to `StreamToken` and `RoomStreamToken` classes. ([\#8279](https://github.com/matrix-org/synapse/issues/8279))
- Change `StreamToken.room_key` to be a `RoomStreamToken` instance. ([\#8281](https://github.com/matrix-org/synapse/issues/8281))
- Refactor notifier code to correctly use the max event stream position. ([\#8288](https://github.com/matrix-org/synapse/issues/8288))
- Use slotted classes where possible. ([\#8296](https://github.com/matrix-org/synapse/issues/8296))
- Support testing the local Synapse checkout against the [Complement homeserver test suite](https://github.com/matrix-org/complement/). ([\#8317](https://github.com/matrix-org/synapse/issues/8317))
- Update outdated usages of `metaclass` to python 3 syntax. ([\#8326](https://github.com/matrix-org/synapse/issues/8326))
- Move lint-related dependencies to package-extra field, update CONTRIBUTING.md to utilise this. ([\#8330](https://github.com/matrix-org/synapse/issues/8330), [\#8377](https://github.com/matrix-org/synapse/issues/8377))
- Use the `admin_patterns` helper in additional locations. ([\#8331](https://github.com/matrix-org/synapse/issues/8331))
- Fix test logging to allow braces in log output. ([\#8335](https://github.com/matrix-org/synapse/issues/8335))
- Remove `__future__` imports related to Python 2 compatibility. ([\#8337](https://github.com/matrix-org/synapse/issues/8337))
- Simplify `super()` calls to Python 3 syntax. ([\#8344](https://github.com/matrix-org/synapse/issues/8344))
- Fix bad merge from `release-v1.20.0` branch to `develop`. ([\#8354](https://github.com/matrix-org/synapse/issues/8354))
- Factor out a `_send_dummy_event_for_room` method. ([\#8370](https://github.com/matrix-org/synapse/issues/8370))
- Improve logging of state resolution. ([\#8371](https://github.com/matrix-org/synapse/issues/8371))
- Add type annotations to `SimpleHttpClient`. ([\#8372](https://github.com/matrix-org/synapse/issues/8372))
- Refactor ID generators to use `async with` syntax. ([\#8383](https://github.com/matrix-org/synapse/issues/8383))
- Add `EventStreamPosition` type. ([\#8388](https://github.com/matrix-org/synapse/issues/8388))
- Create a mechanism for marking tests "logcontext clean". ([\#8399](https://github.com/matrix-org/synapse/issues/8399))
- A pair of tiny cleanups in the federation request code. ([\#8401](https://github.com/matrix-org/synapse/issues/8401))
- Add checks on startup that PostgreSQL sequences are consistent with their associated tables. ([\#8402](https://github.com/matrix-org/synapse/issues/8402))
- Do not include appservice users when calculating the total MAU for a server. ([\#8404](https://github.com/matrix-org/synapse/issues/8404))
- Typing fixes for `synapse.handlers.federation`. ([\#8422](https://github.com/matrix-org/synapse/issues/8422))
- Various refactors to simplify stream token handling. ([\#8423](https://github.com/matrix-org/synapse/issues/8423))
- Make stream token serializing/deserializing async. ([\#8427](https://github.com/matrix-org/synapse/issues/8427))