Add Join Wave Short-Circuit Protection

[ShadowJonathan]

This partially addresses #267

This adds JoinWaveShortCircuit, a protection which will set the room to invite-only as soon as X amount of users (default 50) join the room in the last X minutes (default 60).

The protection works with a Bucket, starting the bucket at first join, and only counting users if its been X minutes since the last bucket start.

(The reasoning for this particular approach is likely sensitive (in relation to other protections), so please reach out if you'd like to hear it.)

It has two settings;

• maxPer, which determines how many users will have to join in the last X minutes before it will trigger the protection.
• timescaleMinutes, the timescale in X minutes, this determines on what time scale the bot will look at joins.

This adds a status command to the protection, with optional subcommands withExpired and withStart, to debug buckets and/or give more information.

Rationale

This is auto-moderation for a particular problem; Join-spam waves often come when a moderation can be inactive, busy, or otherwise unable to immediately respond. It often fills a room with hundreds of users within a few minutes. This protection is meant to "short-circuit" the wave, and keep it relatively contained for moderators to assess and clean up afterwards.

Usage

Use !mjolnir enable JoinWaveShortCircuit to enable this protection for all your protected rooms.

Then, run !mjolnir verify to make sure the bot has join_rules permissions in all relevant rooms. (Note: due to technical reasons, the bot will currently not check this on startup, #290 tracks this problem)

Tweak with !mjolnir config set JoinWaveShortCircuit.maxPer 50 and JoinWaveShortCircuit.timescaleMinutes 60 to your preference.

[ShadowJonathan]

CI is stuck on #281, #282 should fix it. Rebased.

[Gnuxie]

Thanks, this is nice, just a couple of questions though

[rubo77]

Will we have to manually activate this protection in all rooms? Or will it be added automatically once the bot is updated?

[ShadowJonathan]

If this PR gets merged, and a new release includes this, you will have to enable it using !mjolnir enable JoinWaveShortCircuit, then it'll be added to all your protected rooms.

However, you can deploy this early by checking out the PR branch, and building the docker image (if you are using that) yourself. I recommend asking about this in the mjolnir room, though.

[jesopo]

given this makes no existing tests fail and a protection like this is time-critical, i think i'm going to merge this shortly