Support redacts in http pusher message

[cmpayc]

Description

Notifications sent by the http pusher do not contain redacts field. Because of this, it is impossible to understand from the push message which event the edited event belongs to.

• Event example (deleting a message event):

{
  "content": {}
  "event_id": "$0OGq7wQkFtWIRN6wrfRPLrN0D-MO3sVOsY2hFzb3yCA",
  "origin_server_ts": 1647498982020,
  "redacts": "$cf83hgmf33HPhEMFGKuLpAgZFq8slUjyFOr_jD5j5_4",
  "sender": "@someuser:matrix.org",
  "type": "m.room.redaction"
}

• Push notification data example:

{
  "counts": { "unread": 1 },
  "devices": [],
  "event_id": "$0OGq7wQkFtWIRN6wrfRPLrN0D-MO3sVOsY2hFzb3yCA",
  "id": "$0OGq7wQkFtWIRN6wrfRPLrN0D-MO3sVOsY2hFzb3yCA",
  "prio": "high",
  "room_id": "!someroom:matrix.org",
  "room_name": "someroom",
  "sender": "@someuser:matrix.org",
  "sender_display_name": "someuser",
  "type": "m.room.redaction"
}

Expected Result

{
  "counts": { "unread": 1 },
  "devices": [],
  "event_id": "$0OGq7wQkFtWIRN6wrfRPLrN0D-MO3sVOsY2hFzb3yCA",
  "id": "$0OGq7wQkFtWIRN6wrfRPLrN0D-MO3sVOsY2hFzb3yCA",
  "prio": "high",
  "redacts": "$cf83hgmf33HPhEMFGKuLpAgZFq8slUjyFOr_jD5j5_4",
  "room_id": "!someroom:matrix.org",
  "room_name": "someroom",
  "sender": "@someuser:matrix.org",
  "sender_display_name": "someuser",
  "type": "m.room.redaction"
}

Suggested Solution

Add a redacts field (if it exists) to the http pusher message.
Edit synapse/push/httppusher.py and add to _build_notification_dict method:

        if event.redacts is not None:
            d["notification"]["redacts"] = event.redacts

Version information

v1.54.0 and current develop branch.

[squahtx]

The fields in that message are defined by the Matrix spec, and we'd have to get that changed first before updating Synapse. Could you file an issue at https://github.com/matrix-org/matrix-spec/issues instead?

[cmpayc]

I'm sorry, there is already a proposal to move the redacts key under the event content key.

https://github.com/matrix-org/matrix-spec-proposals/blob/main/proposals/2174-move-redacts-key.md

matrix-org/matrix-spec#794

The content key is sent by the http pusher, which means that the redacts field will also be delivered in the push notification.