type
module

Event replacements

Event replacements, or "message edit events", are events that use an event relationship with a rel_type of m.replace, which indicates that the original event is intended to be replaced.

An example of a message edit event might look like this:

{
    "type": "m.room.message",
    "content": {
        "body": "* Hello! My name is bar",
        "msgtype": "m.text",
        "m.new_content": {
            "body": "Hello! My name is bar",
            "msgtype": "m.text"
        },
        "m.relates_to": {
            "rel_type": "m.replace",
            "event_id": "$some_event_id"
        }
    },
    // ... other fields required by events
}

The content of the replacement must contain a m.new_content property which defines the replacement content. The normal content properties (body, msgtype etc.) provide a fallback for clients which do not understand replacement events.

m.new_content can include any properties that would normally be found in an event's content property, such as formatted_body (see m.room.message msgtypes).

Validity of message edit events

There are a number of requirements on message edit events, which must be satisfied for the replacement to be considered valid:

As with all event relationships, the original event and replacement event must have the same room_id (i.e. it is not possible to send an event in one room and then an edited version in a different room).
The original event and replacement event must have the same sender (i.e. you cannot edit someone else's messages).
The replacement and original events must have the same type (i.e. editing an event cannot change its type).
Neither the replacement nor original events may have a state_key property (i.e. it is not possible to edit a state event).
The original event must not, itself, have a rel_type of m.replace (i.e. you cannot edit an edit — though you can send multiple edits for a single original event).
The replacement event (once decrypted, if appropriate) must have an m.new_content property.

If any of these criteria are not satisfied, implementations should ignore the replacement event (the content of the original should not be replaced, and the edit should not be included in the server-side aggregation).

Note that the msgtype property of replacement m.room.message events need not be the same as in the original event. For example, it is legitimate to replace an m.text event with an m.emote.

Editing encrypted events

If the original event was encrypted, the replacement should be too. In that case, m.new_content is placed in the content of the encrypted payload. As with all event relationships, the m.relates_to property must be sent in the unencrypted (cleartext) part of the event.

For example, a replacement for an encrypted event might look like this:

For example, an encrypted replacement event might look like this:

{
    "type": "m.room.encrypted",
    "content": {
        "m.relates_to": {
            "rel_type": "m.replace",
            "event_id": "$some_event_id"
        },
        "algorithm": "m.megolm.v1.aes-sha2",
        "sender_key": "<sender_curve25519_key>",
        "device_id": "<sender_device_id>",
        "session_id": "<outbound_group_session_id>",
        "ciphertext": "<encrypted_payload_base_64>"
    }
    // ...
}

... and, once decrypted, the payload might look like this:

{
    "type": "m.room.<event_type>",
    "room_id": "!some_room_id",
    "content": {
        "body": "* Hello! My name is bar",
        "msgtype": "m.text",
        "m.new_content": {
            "body": "Hello! My name is bar",
            "msgtype": "m.text"
        }
    }
}

Note that:

There is no m.relates_to property in the encrypted payload. (Any such property would be ignored.)
There is no m.new_content property in the cleartext content of the m.room.encrypted event. (Again, any such property would be ignored.)

The payload of an encrypted replacement event must be encrypted as normal, including ratcheting any Megolm session as normal. The original Megolm ratchet entry should not be re-used.

Applying `m.new_content`

When applying a replacement, the content of the original event is replaced entirely by the m.new_content from the replacement event, with the exception of m.relates_to, which is left unchanged. (Any m.relates_to property within m.new_content should be ignored.)

For example, given a pair of events:

{
    "event_id": "$original_event",
    "type": "m.room.message",
    "content": {
        "body": "I really like cake",
        "msgtype": "m.text",
        "formatted_body": "I really like cake",
    }
}

{
    "event_id": "$edit_event",
    "type": "m.room.message",
    "content": {
        "body": "* I really like *chocolate* cake",
        "msgtype": "m.text",
        "m.new_content": {
            "body": "I really like *chocolate* cake",
            "msgtype": "m.text",
            "com.example.extension_property": "chocolate"
        },
        "m.relates_to": {
            "rel_type": "m.replace",
            "event_id": "$original_event_id"
        }
    }
}

... then the end result is an event as shown below:

{
    "event_id": "$original_event",
    "type": "m.room.message",
    "content": {
        "body": "I really like *chocolate* cake",
        "msgtype": "m.text",
        "com.example.extension_property": "chocolate"
    }
}

Note that formatted_body is now absent, because it was absent in the replacement event.

Server behaviour

Server-side aggregation of `m.replace` relationships

Note that there can be multiple events with an m.replace relationship to a given event (for example, if an event is edited multiple times). These should be aggregated by the homeserver.

The aggregation format of m.replace relationships gives the event_id, origin_server_ts, and sender of the most recent replacement event. The most recent event is determined by comparing origin_server_ts; if two or more replacement events have identical origin_server_ts, the event with the lexicographically largest event_id is treated as more recent.

This aggregation is bundled into the unsigned/m.relations property of any event that is the target of an m.replace relationship. For example:

{
  "event_id": "$original_event_id",
  // ...
  "unsigned": {
    "m.relations": {
      "m.replace": {
        "event_id": "$latest_edit_event_id",
        "origin_server_ts": 1649772304313,
        "sender": "@editing_user:localhost"
      }
    }
  }
}

If the original event is redacted, any m.replace relationship should not be bundled with it (whether or not any subsequent replacements are themselves redacted). Note that this behaviour is specific to the m.replace relationship. See also redactions of edited events below.

Server-side replacement of content

Whenever an m.replace is to be bundled with an event as above, the server should also modify the content of the original event according to the m.new_content of the most recent replacement event (determined as above).

An exception applies to GET /_matrix/client/v3/rooms/{roomId}/event/{eventId}, which should return the unmodified event (though the relationship should still be bundled, as described above).

Client behaviour

Clients can often ignore m.replace events, since any events the server returns via the C-S API will be updated by the server to account for subsequent edits.

However, clients should apply the replacement themselves when the server is unable to do so. This happens in the following situations:

The client has already received and stored the original event before the message edit event arrives.
The original event (and hence its replacement) are encrypted.

Client authors are reminded to take note of the requirements for Validity of message edit events, and to ignore any invalid edit events that may be received.

Permalinks

When creating links to events (also known as permalinks), clients build links which reference the event that the creator of the permalink is viewing at that point (which might be a message edit event).

The client viewing the permalink should resolve this reference to the original event, and then display the most recent version of that event.

Redactions of edited events

When an event using a rel_type of m.replace is redacted, it removes that edit revision. This has little effect if there were subsequent edits. However, if it was the most recent edit, the event is in effect reverted to its content before the redacted edit.

Redacting the original message in effect removes the message, including all subsequent edits, from the visible timeline. In this situation, homeservers will return an empty content for the original event as with any other redacted event, and as above the replacement events will not be bundled with the original event.

Edits of replies

Some particular constraints apply to events which replace a reply. In particular:

In contrast to the original reply, there should be no m.in_reply_to property in the the m.relates_to object, since it would be redundant (see Applying m.new_content above, which notes that the original event's m.relates_to is preserved), as well as being contrary to the spirit of the event relationships mechanism which expects only one "parent" per event.
m.new_content should not contain any reply fallback, since it is assumed that any client which can handle edits can also display replies natively. However, the content of the replacement event should provide fallback content for clients which support neither rich replies nor edits.

An example of an edit to a reply is as follows:

{
  "type": "m.room.message",
  "content": {
    "body": "> <@alice:example.org> question\n\n* reply",
    "msgtype": "m.text",
    "format": "org.matrix.custom.html",
    "formatted_body": "<mx-reply><blockquote><a href=\"https://matrix.to/#/!somewhere:example.org/$event:example.org\">In reply to</a> <a href=\"https://matrix.to/#/@alice:example.org\">@alice:example.org</a><br />question</blockquote></mx-reply>* reply",
    "m.new_content": {
      "body": "reply",
      "msgtype": "m.text",
      "format": "org.matrix.custom.html",
      "formatted_body": "reply"
    },
    "m.relates_to": {
      "rel_type": "m.replace",
      "event_id": "$original_reply_event"
    }
  }
}

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event_replacements.md

event_replacements.md

Event replacements

Validity of message edit events

Editing encrypted events

Applying `m.new_content`

Server behaviour

Server-side aggregation of `m.replace` relationships

Server-side replacement of content

Client behaviour

Permalinks

Redactions of edited events

Edits of replies

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event_replacements.md

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event_replacements.md

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Event replacements

Validity of message edit events

Editing encrypted events

Applying m.new_content

Server behaviour

Server-side aggregation of m.replace relationships

Server-side replacement of content

Client behaviour

Permalinks

Redactions of edited events

Edits of replies

Applying `m.new_content`

Server-side aggregation of `m.replace` relationships