Should fix some remaining warnings

Turns out matrix.org has an event that has duplicate auth events (which really isn't supposed to happen, but here we are). This caused the background update to fail due to `UniqueViolation`.

Turns out nginx overwrites the Host header by default.

Prevent presence background jobs from running when presence is disabled

Signed-off-by: Aaron Raimist <aaron@raim.ist>

This reverts commit f5c93fc9.

This is being backed out due to a regression (#9507) and additional
review feedback being provided.

It landed in schema version 58 after 59 had been created, causing some
servers to not run it. The main effect of was that not all rooms had
their chain cover calculated correctly. After the BG updates complete
the chain covers will get fixed when a new state event in the affected
rooms is received.

Fixes #9504

By consuming the response if the headers imply that the
content is too large.

This also pins the Twisted version in the mypy job for CI until
proper type hints are fixed throughout Synapse.

In #75, bytecode was disabled (from a bit of FUD back in `python<2.4` days, according to dev chat), I think it's safe enough to enable it again.

Added in `__pycache__/` and `.pyc`/`.pyd` to `.gitignore`, to extra-insure compiled files don't get committed.

`Signed-off-by: Jonathan de Jong <jonathan@automatia.nl&gt;`>

### Changes proposed in this PR

- Add support for the `no_proxy` and `NO_PROXY` environment variables
  - Internally rely on urllib's [`proxy_bypass_environment`](https://github.com/python/cpython/blob/bdb941be423bde8b02a5695ccf51c303d6204bed/Lib/urllib/request.py#L2519)
- Extract env variables using urllib's `getproxies`/[`getproxies_environment`](https://github.com/python/cpython/blob/bdb941be423bde8b02a5695ccf51c303d6204bed/Lib/urllib/request.py#L2488

) which supports lowercase + uppercase, preferring lowercase, except for `HTTP_PROXY` in a CGI environment

This does contain behaviour changes for consumers so making sure these are called out:
- `no_proxy`/`NO_PROXY` is now respected
- lowercase `https_proxy` is now allowed and taken over `HTTPS_PROXY`

Related to #9306 which also uses `ProxyAgent`

Signed-off-by: Timothy Leung <tim95@hotmail.co.uk>

... otherwise, we don't get the cookie back.

rewrite XForwardedForRequest to set `isSecure()` based on
`X-Forwarded-Proto`. Also implement `getClientAddress()` while we're here.

This fixes #8518 by adding a conditional check on `SyncResult` in a function when `prev_stream_token == current_stream_token`, as a sanity check. In `CachedResponse.set.<remove>()`, the result is immediately popped from the cache if the conditional function returns "false".

This prevents the caching of a timed-out `SyncResult` (that has `next_key` as the stream key that produced that `SyncResult`). The cache is prevented from returning a `SyncResult` that makes the client request the same stream key over and over again, effectively making it stuck in a loop of requesting and getting a response immediately for as long as the cache keeps those values.

Signed-off-by: Jonathan de Jong <jonathan@automatia.nl>

* Split ShardedWorkerHandlingConfig

This is so that we have a type level understanding of when it is safe to
call `get_instance(..)` (as opposed to `should_handle(..)`).

* Remove special cases in ShardedWorkerHandlingConfig.

`ShardedWorkerHandlingConfig` tried to handle the various different ways
it was possible to configure federation senders and pushers. This led to
special cases that weren't hit during testing.

To fix this the handling of the different cases is moved from there and
`generic_worker` into the worker config class. This allows us to have
the logic in one place and allows the rest of the code to ignore the
different cases.

The idea here is to stop people forgetting to call `check_consistency`. Folks can still just pass in `None` to the new args in `build_sequence_generator`, but hopefully they won't.

This confused me for a while.

And ensure the consistency of `event_auth_chain_id`.

`uploads_path` was a thing that was never used; most of it was removed in #6628
but a few vestiges remained.

It should be possible to reload `synapse.target` to have the reload propagate
to all the synapse units.

This PR remove the cache for the `get_shared_rooms_for_users` storage method (the db method driving the experimental "what rooms do I share with this user?" feature: [MSC2666](https://github.com/matrix-org/matrix-doc/pull/2666)). Currently subsequent requests to the endpoint will return the same result, even if your shared rooms with that user have changed.

The cache was added in https://github.com/matrix-org/synapse/pull/7785, but we forgot to ensure it was invalidated appropriately.

Upon attempting to invalidate it, I found that the cache had to be entirely invalidated whenever a user (remote or local) joined or left a room. This didn't make for a very useful cache, especially for a function that may or may not be called very often. Thus, I've opted to remove it instead of invalidating it.

The user directory sample config section was a little messy, and didn't adhere to our [recommended config format guidelines](https://github.com/matrix-org/synapse/blob/develop/docs/code_style.md#configuration-file-format).

This PR cleans that up a bit.