From 13935ec33b3b9b1436c1f8a4048a197d48ecf168 Mon Sep 17 00:00:00 2001 From: benkuly <12199167+benkuly@users.noreply.github.com> Date: Tue, 21 Feb 2023 08:27:37 +0100 Subject: [PATCH] MSC3925: m.replace aggregation with full event (#3925) * init m.replace aggregation with full event Signed-off-by: benkuly * Rename tmp.md to 3925-replace-aggregation-with-full-event.md Signed-off-by: benkuly * Update 3925-replace-aggregation-with-full-event.md typos Signed-off-by: benkuly * Update 3925-replace-aggregation-with-full-event.md added MSC number Signed-off-by: benkuly * Update proposals/3925-replace-aggregation-with-full-event.md Co-authored-by: Jonas Platte Signed-off-by: benkuly * Update proposals/3925-replace-aggregation-with-full-event.md Co-authored-by: Jonas Platte Signed-off-by: benkuly * Update proposals/3925-replace-aggregation-with-full-event.md Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * redact instead of delete * Update proposals/3925-replace-aggregation-with-full-event.md Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * Update proposals/3925-replace-aggregation-with-full-event.md Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * word wrap 80 * remove immutable argument * add alternative from https://github.com/matrix-org/matrix-spec/issues/1299#issuecomment-1290332433 * add json example * shorter version of the actual proposal Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * describe the actual reason, why encrypted events cannot be replaced Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * mention discussion * typo * Update proposals/3925-replace-aggregation-with-full-event.md Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * Update proposals/3925-replace-aggregation-with-full-event.md Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * Update proposals/3925-replace-aggregation-with-full-event.md Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * Update proposals/3925-replace-aggregation-with-full-event.md Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * Update proposals/3925-replace-aggregation-with-full-event.md Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * Update proposals/3925-replace-aggregation-with-full-event.md Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * Update proposals/3925-replace-aggregation-with-full-event.md Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * clarify inconsistent behavior with replaced contents * Update proposals/3925-replace-aggregation-with-full-event.md Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * Update proposals/3925-replace-aggregation-with-full-event.md Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * Update proposals/3925-replace-aggregation-with-full-event.md Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * Update proposals/3925-replace-aggregation-with-full-event.md Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * clarify inconsistent behavior and put it into introduction * remove superfluous event content field * add some details to potential issues suggested by @richvdh --------- Signed-off-by: benkuly Co-authored-by: Jonas Platte Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> --- ...925-replace-aggregation-with-full-event.md | 140 ++++++++++++++++++ 1 file changed, 140 insertions(+) create mode 100644 proposals/3925-replace-aggregation-with-full-event.md diff --git a/proposals/3925-replace-aggregation-with-full-event.md b/proposals/3925-replace-aggregation-with-full-event.md new file mode 100644 index 00000000..4137320a --- /dev/null +++ b/proposals/3925-replace-aggregation-with-full-event.md @@ -0,0 +1,140 @@ +# MSC3925: m.replace aggregation with full event + +As [currently specified](https://spec.matrix.org/v1.4/client-server-api/#server-side-replacement-of-content), +servers should replace the content of events that have been replaced via an `m.replace` +relation. + +There are some issues with this requirement: + +* Changing the fundamental concept of mostly immutable events is confusing. The server + can respond with different event contents for the same `event_id`. +* If an event with `m.replace` relation is redacted, clients need to + detect if the original content was replaced, and possibly need to fetch the + original content. +* Servers cannot replace the original event content for encrypted events (because the + replacement content is inside the encrypted body). + See [matrix-spec#1299](https://github.com/matrix-org/matrix-spec/issues/1299). +* Replacing the content can lead to inconsistent behavior on clients which don't + support replacing events. + Assume that we have this timeline on the server: + - `{"event_id": "E1", "content": {"body": "1"}}` + - `{"event_id": "E2", "content": {"body": "* 2", "m.new_content": {"body": "2"}}` // replaces `E1` + + A `/sync` is done after `E2`. We will have this timeline on a client: + - `{"event_id": "E1", "content": {"body": "2"}}` + - `{"event_id": "E2", "content": {"body": "* 2"}` + + Although `2` is a replaced body it does not have a `*`. This looks to the + user as if it is the original content of the event. + + +## Proposal + +The following two changes are proposed: +1. The [server-side aggregation of `m.replace` relationships](https://spec.matrix.org/v1.4/client-server-api/#server-side-aggregation-of-mreplace-relationships) + is extended to be the entire content of the most recent replacement event, formatted + as described in [Room Event Format](https://spec.matrix.org/v1.4/client-server-api/#room-event-format). + This ensures that the client will always have the most recent edit without having to + fetch it from the server. +2. Servers should no longer replace the original content of an event as described + at https://spec.matrix.org/v1.4/client-server-api/#server-side-replacement-of-content. + +For an original event: + +```json5 +{ + "event_id": "$original_event", + "type": "m.room.message", + "content": { + "body": "I really like cake", + "msgtype": "m.text", + "formatted_body": "I really like cake" + } + // irrelevant fields not shown +} + +``` + +With a replacing event: + +```json5 +{ + "event_id": "$edit_event", + "type": "m.room.message", + "content": { + "body": "* I really like *chocolate* cake", + "msgtype": "m.text", + "m.new_content": { + "body": "I really like *chocolate* cake", + "msgtype": "m.text" + }, + "m.relates_to": { + "rel_type": "m.replace", + "event_id": "$original_event_id" + } + } + // irrelevant fields not shown +} + +``` + +This is how the original event would look like after the replacement: + +```json5 +{ + "event_id": "$original_event", + "type": "m.room.message", + "content": { + "body": "I really like cake", + "msgtype": "m.text", + "formatted_body": "I really like cake" + }, + "unsigned": { + "m.relations": { + "m.replace": { + "event_id": "$edit_event", + "type": "m.room.message", + "content": { + "body": "* I really like *chocolate* cake", + "msgtype": "m.text", + "m.new_content": { + "body": "I really like *chocolate* cake", + "msgtype": "m.text" + }, + "m.relates_to": { + "rel_type": "m.replace", + "event_id": "$original_event_id" + } + } + // irrelevant fields not shown + } + } + } + // irrelevant fields not shown +} + +``` + +## Potential issues + +* There could be clients which rely on the current behavior: + * element-web relied on it until [matrix-org/matrix-js-sdk#3045](https://github.com/matrix-org/matrix-js-sdk/pull/3045) + * The failure mode is: suppose we have an event E, which was subsequently replaced by an event E'. Now, if jumped back to a bit of timeline that contains E but not E', then clients unaware of this change will show the original event E rather than the edited content E'. But: That is an edge-case and it already happens for events other than `m.room.message` (including encrypted events) due to [matrix-org/synapse#12503](https://github.com/matrix-org/synapse/issues/12503). +* It will be harder for clients which do not support replacing events to get + the current content of an event: currently they can just look at `content.body`. + However, there is an inconsistent behavior for clients that do not support + replacing events (see above). + +## Alternatives + +One [suggestion](https://github.com/matrix-org/matrix-spec/issues/1299#issuecomment-1290332433) is +to have the server return the complete replacement event instead of the original event. However, that would +break compatibility with existing clients and is a more invasive change. + +## Security considerations + +None currently foreseen. + +## Unstable prefix + +No unstable prefix is currently proposed.