Add option to prune history after a certain time

[rubo77]

Usually the history for a room is kept forever, but we should add an option in the room settings to use the prune api to clean up the room older than a certain timeframe.

This will not delete the messages from all federated servers, so you can still scroll back and recover pruned messages eventually (which also can be desired).

Additionally we should add a button to automatically "redact" all old messages before prunigng them, so they are not so easily recoverable by standard clients (this would be needed first: matrix-org/synapse#1730 )

Be aware, that this is just a little enhancement of the current state where no old messages are deleted. Messages are not securely deleted this way! Only old messages that were not federated to any other synapse servers (i.e. private rooms) are deleted completely this way.

This enhancement will be a very useful frontend-cleanup of old messages.

[rubo77]

Maybe this issue is just about the buttons in the admin panel and the rest has to be done in the synapse issue.

[ara4n]

this is entangled with https://github.com/matrix-org/matrix-doc/issues/440

[roadkillazpartybird]

Agreed, it should be set per-room i think. The default mode should be for no auto-deletion but there should be an option.

[ara4n]

see also matrix-org/matrix-doc#447

[aaronraimist]

I think this is getting pretty close to existing

matrix-org/matrix-spec-proposals#1763 is the proposal for this

matrix-org/synapse#5815 is a Synapse PR

now Riot just needs some UI for managing it.

[ara4n]

closing as dup of element-hq/element-meta#729