Unsubscribed users are not removed from groups

[paride]

Steps to reproduce

• Have a member of a group unsubscribe from Signal
• Check how the now unsubscribed number is still part of the group
• Now the stale number is impossible to remove from the group. Sometimes re-registering is not an option, as access to the number might have been lost. Most of the time the user just doesn't care.

Expected result: The unsubscribed user is automatically removed from all the groups. I know the server is not aware of groups, but I think there are still ways to handle this. For example:

• When sending a message to a group (i.e., to all the group members), if a user is not a Signal user anymore, remove it;
• Before adding a user to a group because of a message coming from another group member, check if the number is actually a Signal number.

Signal version: 4.8.0

[nrizzio]

This is unfortunately technically infeasible with the current group architecture and was rejected in #828.

[paride]

@nrizzio How is my proposal incompatible with the current architecture? There's no need for a group administrator (what #828 is about).

[nrizzio]

My interpretation may very well be incorrect. In the interest of reducing notification spam, I'm going to take a step back and let Moxie make a determination when he gets around to it. Feel free to make a thread on the forum though.

[haffenloher]

When sending a message to a group (i.e., to all the group members), if a user is not a Signal user anymore, remove it

That was the plan at some point (see #5891 (comment)), but Lilia and Moxie ended up deciding against it (see #6175).

[Trolldemorted]

@paride you cannot just remove a member from a group on your device without things going terribly wrong.

So far no one has come up with a scheme for removing group members in asynchronous egalitarian groups that is simple and works.

I had suggested a single source of truth-device which "owns" the group and is the only device capable of sending group updates, but apparently moxie did not like it (and neither did i tbh since it imposes severe limitations to the user).

I am all in for some brainstorming to devise a new groups scheme, but this is not the right place (unlike the forum or the subreddit).

@moxie0 i know you do not want the groups "to be on the server", but would storing an encrypted blob (to which the server does not have the key) be ok? I don't think there is a way to solve signal's group issues without an external instance (read: not a signal device) deciding which async event came first.

[paride]

Duplicate of #6175.

(Still, the issue remains to be addressed.)