Functional members

[jaller94]

At Element Matrix Services we're experimenting with "functional members", e.g. bots you want to have in a DM room with someone else.

Currently, if I have a DM room with Alice and my bot "Helper Bot" the DM room will be called "Alice and 1 other" (or "Helper Bot" and 1 other").
We want to filter bots based on a state event so that the room name will be just "Alice".

The state event content for the type io.element.functional_members would look like this:

{
    "service_members": [
        "@helperbot:localhost",
        "@reminderbot:alice.tdl"
    ]
}

---

I'm writing this PR as an employee at Element, so I'm not sure the Sign-Off is required.

Signed-off-by: Christian Paul christianp@element.io

[t3chguy]

(Updated base branch so it doesn't accidentally go to the wrong place.)

[t3chguy]

Adding tests for this behaviour would be great

[turt2live]

as t3chguy says, tests would be appreciated for this. From my part, it'd be good to see tests for the abusive cases, and a paragraph somewhere on this PR acknowledging the room for abuse and how that is mitigated (if at all).

Some abusive cases include:

• Existing DMs with participants where excluding the member might cause an empty name (eg: 1:1 DM and manually excluding a non-service user). Alternatively, putting all users from the DM into the excluded users list.
• Excluding users which are not present in the room (would expect the performance to not be impacted, and for the code to not explode)

It's particularly concerning that the exclusion is based on user ID only as that isn't a reliable factor for whether or not the user is truly a service/bot user or not. It's largely fine for this case, I think, but acknowledging the vector is appreciated.

[turt2live]

I'd sooner hop into UnstableValue and mark the second field as optional, fixing any docs along the way.

[jaller94]

I'd make it a type of its own, as UnstableValue has a different meaning, is exported and also requires unstable to be defined.

Or do you mean to set .unstable to the same value as .name if no second parameter is provided to the constructor?

[turt2live]

Thanks!