2.6 KiB
Mass redactions
Matrix, like any platform with public chat rooms, has spammers. Currently, redacting spam essentially requires spamming redaction events in a 1:1 ratio, which is not optimal1. Most clients do not even have any mass redaction tools, likely in part due to the lack of a mass redaction API. A mass redaction API on the other hand has not been implemented as it would require sending lots of events at once. However, this problem could be solved by allowing a single redaction event to redact many events instead of sending many redaction events.
Proposal
This proposal builds upon MSC2174 and suggests making the redacts field
in the content of m.room.redaction events an array of event ID strings
instead of a single event ID string.
It would be easiest to do this before MSC2174 is written into the spec, as then only one migration would be needed: from an event-level redacts string to a content-level redacts array.
Number of redactions
Room v4+ event IDs are 44 bytes long, which means the federation event size limit would cap a single redaction event at a bit less than 1500 targets. Redactions are not intrinsically heavy, so a separate limit should not be necessary.
Auth rules
The redaction auth rules should change to iterate the array and check if the sender has the privileges to redact each event.
There are at least two potential ways to handle targets that are not found or rejected: soft failing until all targets are found and handling each target separately.
Soft fail
Soft fail the event until all targets are found, then accept only if the sender has the privileges to redact every listed event. This is how redactions currently work.
This has the downside of requiring servers to fetch all the target events (and possibly forward them to clients) before being able to process and forward the redaction event.
Handle each target separately
Handle each target separately: if some targets are not found, remember the redaction and check auth rules when the target is received. This option brings some complexities, but might be more optimal in situations such as a spam attack.
When receiving a redaction event:
- Ignore illegal targets
- "Remember" targets that can't be found
- Send legal target event IDs to clients in the redaction event.
When receiving an event that is "remembered" to be possibly redacted by an earlier redaction, check if the redaction was legal, and if it was, do not send the event to clients.