Features

--------

- add support for the lazy_loaded_members filter as per MSC1227 ([\#2970](https://github.com/matrix-org/synapse/issues/2970))
- add support for the include_redundant_members filter param as per MSC1227 ([\#3331](https://github.com/matrix-org/synapse/issues/3331))
- Add metrics to track resource usage by background processes ([\#3553](https://github.com/matrix-org/synapse/issues/3553), [\#3556](https://github.com/matrix-org/synapse/issues/3556),
[\#3604](https://github.com/matrix-org/synapse/issues/3604), [\#3610](https://github.com/matrix-org/synapse/issues/3610))
- Add `code` label to `synapse_http_server_response_time_seconds` prometheus metric ([\#3554](https://github.com/matrix-org/synapse/issues/3554))
- Add support for client_reader to handle more APIs ([\#3555](https://github.com/matrix-org/synapse/issues/3555), [\#3597](https://github.com/matrix-org/synapse/issues/3597))
- make the /context API filter & lazy-load aware as per MSC1227 ([\#3567](https://github.com/matrix-org/synapse/issues/3567))
- Add ability to limit number of monthly active users on the server ([\#3630](https://github.com/matrix-org/synapse/issues/3630))
- When we fail to join a room over federation, pass the error code back to the client. ([\#3639](https://github.com/matrix-org/synapse/issues/3639))
- Add a new /admin/register API for non-interactively creating users. ([\#3415](https://github.com/matrix-org/synapse/issues/3415))

Bugfixes
--------

- Make /directory/list API return 404 for room not found instead of 400 ([\#2952](https://github.com/matrix-org/synapse/issues/2952))
- Default inviter_display_name to mxid for email invites ([\#3391](https://github.com/matrix-org/synapse/issues/3391))
- Don't generate TURN credentials if no TURN config options are set ([\#3514](https://github.com/matrix-org/synapse/issues/3514))
- Correctly announce deleted devices over federation ([\#3520](https://github.com/matrix-org/synapse/issues/3520))
- Catch failures saving metrics captured by Measure, and instead log the faulty metrics information for further analysis. ([\#3548](https://github.com/matrix-org/synapse/issues/3548))
- Unicode passwords are now normalised before hashing, preventing the instance where two different devices or browsers might send a different UTF-8 sequence for the password.
([\#3569](https://github.com/matrix-org/synapse/issues/3569))
- Fix potential stack overflow and deadlock under heavy load ([\#3570](https://github.com/matrix-org/synapse/issues/3570))
- Respond with M_NOT_FOUND when profiles are not found locally or over federation. Fixes #3585 ([\#3585](https://github.com/matrix-org/synapse/issues/3585))
- Fix failure to persist events over federation under load ([\#3601](https://github.com/matrix-org/synapse/issues/3601))
- Fix updating of cached remote profiles ([\#3605](https://github.com/matrix-org/synapse/issues/3605))
- Fix 'tuple index out of range' error ([\#3607](https://github.com/matrix-org/synapse/issues/3607))
- Only import secrets when available (fix for py < 3.6) ([\#3626](https://github.com/matrix-org/synapse/issues/3626))

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

- Remove redundant checks on who_forgot_in_room ([\#3350](https://github.com/matrix-org/synapse/issues/3350))
- Remove unnecessary event re-signing hacks ([\#3367](https://github.com/matrix-org/synapse/issues/3367))
- Rewrite cache list decorator ([\#3384](https://github.com/matrix-org/synapse/issues/3384))
- Move v1-only REST APIs into their own module. ([\#3460](https://github.com/matrix-org/synapse/issues/3460))
- Replace more instances of Python 2-only iteritems and itervalues uses. ([\#3562](https://github.com/matrix-org/synapse/issues/3562))
- Refactor EventContext to accept state during init ([\#3577](https://github.com/matrix-org/synapse/issues/3577))
- Improve Dockerfile and docker-compose instructions ([\#3543](https://github.com/matrix-org/synapse/issues/3543))
- Release notes are now in the Markdown format. ([\#3552](https://github.com/matrix-org/synapse/issues/3552))
- add config for pep8 ([\#3559](https://github.com/matrix-org/synapse/issues/3559))
- Merge Linearizer and Limiter ([\#3571](https://github.com/matrix-org/synapse/issues/3571), [\#3572](https://github.com/matrix-org/synapse/issues/3572))
- Lazily load state on master process when using workers to reduce DB consumption ([\#3579](https://github.com/matrix-org/synapse/issues/3579),
[\#3581](https://github.com/matrix-org/synapse/issues/3581), [\#3582](https://github.com/matrix-org/synapse/issues/3582), [\#3584](https://github.com/matrix-org/synapse/issues/3584))
- Fixes and optimisations for resolve_state_groups ([\#3586](https://github.com/matrix-org/synapse/issues/3586))
- Improve logging for exceptions when handling PDUs ([\#3587](https://github.com/matrix-org/synapse/issues/3587))
- Add some measure blocks to persist_events ([\#3590](https://github.com/matrix-org/synapse/issues/3590))
- Fix some random logcontext leaks. ([\#3591](https://github.com/matrix-org/synapse/issues/3591), [\#3606](https://github.com/matrix-org/synapse/issues/3606))
- Speed up calculating state deltas in persist_event loop ([\#3592](https://github.com/matrix-org/synapse/issues/3592))
- Attempt to reduce amount of state pulled out of DB during persist_events ([\#3595](https://github.com/matrix-org/synapse/issues/3595))
- Fix a documentation typo in on_make_leave_request ([\#3609](https://github.com/matrix-org/synapse/issues/3609))
- Make EventStore inherit from EventFederationStore ([\#3612](https://github.com/matrix-org/synapse/issues/3612))
- Remove some redundant joins on event_edges.room_id ([\#3613](https://github.com/matrix-org/synapse/issues/3613))
- Stop populating events.content ([\#3614](https://github.com/matrix-org/synapse/issues/3614))
- Update the /send_leave path registration to use event_id rather than a transaction ID. ([\#3616](https://github.com/matrix-org/synapse/issues/3616))
- Refactor FederationHandler to move DB writes into separate functions ([\#3621](https://github.com/matrix-org/synapse/issues/3621))
- Remove unused field "pdu_failures" from transactions. ([\#3628](https://github.com/matrix-org/synapse/issues/3628))
- rename replication_layer to federation_client ([\#3634](https://github.com/matrix-org/synapse/issues/3634))
- Factor out exception handling in federation_client ([\#3638](https://github.com/matrix-org/synapse/issues/3638))
- Refactor location of docker build script. ([\#3644](https://github.com/matrix-org/synapse/issues/3644))
- Update CONTRIBUTING to mention newsfragments. ([\#3645](https://github.com/matrix-org/synapse/issues/3645))
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