Return 200 OK for all OPTIONS requests

[clokep]

This is an attempt to fix #7313.

For workers which don't have a media listener it adds dummy endpoints which return a 200 OK for OPTIONS requests to themselves and any leaf below them. Any other requests method (POST, PUT, GET, etc.) is a 404.

For all endpoints under the root endpoint it will return a 200 OK for OPTIONS requests. Other requests will act as "normal".

I do have some questions:

• Should this only be on workers?
• This will now return 200 for completely bogus URLs (/_matrix/media/r0/foo/bar). Is that OK?
• I will likely want to write some tests once some of the above are answered.

[clokep]

I requested review on this to make sure I'm on the right page. I left a few questions in the description which need to be worked through still.

[erikjohnston]

(I haven't thought about this, but is a possible alternative to just reply to all options requests, no matter the path?)

[clokep]

@erikjohnston That could be an option (no pun intended) as well. We could probably do it via the root endpoint actually. I'll take a look at that.

[clokep]

@erikjohnston So looks like it IS possible, although as you said we need to think about whether that makes sense. I just pushed b390d12 although I don't expect anything to break from it.

[erikjohnston]

Yeah, personally I think just returning OPTIONS everywhere is the easiest thing here (saves having to find all the places where we conditionally add resources).

[erikjohnston]

• Should this only be on workers?

In the brave new world there shouldn't be a difference between master and workers :)

• This will now return 200 for completely bogus URLs (/_matrix/media/r0/foo/bar). Is that OK?

Yeah, it just means that webapps will have to do another round trip to get the 404. This shouldn't happen in production much, so I think its fine.

• I will likely want to write some tests once some of the above are answered.

🎉