MSC2409: Proposal to send EDUs to appservices (#2409)
* Initial proposal commit * Add body of proposal * rename file * finish up MSC * address issues * change key names and add unstable prefix * Clarifications; to-device handling * It's not exactly like sync * Move to-device messages * Copy edu_type behaviour * Add full transaction example * Add implementation notes for to-device cleanup * Use type instead of edu_type to match realities of implementations * Add note to say ephemeral can be omitted. * Improve wording on why we use a seperate array. Co-authored-by: Kevin Cox <kevincox@kevincox.ca> * push_ephemeral -> receive_ephemeral * Fix some typos and clarify EDU room association * Clarify EDU formatting * Explicitly list all event types * Delete to-device events to be moved to a new MSC * Update spec link and fix typo Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com> * Add private read receipt rules * Apply suggestions from code review Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> * Wrap lines * Apply suggestions from code review Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com> * Explicitly mention to-device events are not here * Mention the possibility of more granular filtering --------- Co-authored-by: Will Hunt <will@half-shot.uk> Co-authored-by: Travis Ralston <travisr@matrix.org> Co-authored-by: Kevin Cox <kevincox@kevincox.ca> Co-authored-by: Tulir Asokan <tulir@maunium.net> Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com> Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>travis/msc/safety-allow-errors-on-unbind
Sorunome
1 year ago
committed by
Travis Ralston
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# MSC2409: Proposal to send typing, presence and receipts to appservices
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*Note: This proposal is a continuation of [MSC1888](https://github.com/matrix-org/matrix-doc/pull/1888)
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and deprecates that one.*
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The [appservice /transactions API](https://spec.matrix.org/v1.11/application-service-api/#put_matrixappv1transactionstxnid)
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currently supports pushing PDU events (regular message and state events)
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however it doesn't provision for EDU events (typing, presence and receipts). This means that bridges cannot
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react to Matrix users who send any typing or presence information in a room the service is part of.
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There is an interest amongst the community to have equal bridging on both sides of a bridge, so that
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read reciepts and typing notifications can be seen on the remote side. To that end, this proposal
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specifies how these can be pushed to an appservice.
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## Proposal
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### Changes to the registration file
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In order that appservices don't get flooded with EDUs, appservices have to opt-in to receive them by
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setting `receive_ephemeral` to true. A registration file could look like following:
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```yaml
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id: "IRC Bridge"
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url: "http://127.0.0.1:1234"
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as_token: "30c05ae90a248a4188e620216fa72e349803310ec83e2a77b34fe90be6081f46"
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hs_token: "312df522183efd404ec1cd22d2ffa4bbc76a8c1ccf541dd692eef281356bb74e"
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sender_localpart: "_irc_bot"
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# We want to receive EDUs
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receive_ephemeral: true
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namespaces:
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users:
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- exclusive: true
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regex: "@_irc_bridge_.*"
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aliases:
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- exclusive: false
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regex: "#_irc_bridge_.*"
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rooms: []
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```
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For now, receiving EDUs is all-or-nothing. A future MSC may add more granular
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filtering capabilities for appservices.
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### Changes to the /transactions/ API
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The `PUT /_matrix/app/v1/transactions/{txnId}` API currently supports sending PDUs
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via the `events` array.
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```json
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{
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"events": [
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{
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"content": {
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"membership": "join",
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"avatar_url": "mxc://domain.com/SEsfnsuifSDFSSEF#auto",
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"displayname": "Alice Margatroid"
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},
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"type": "m.room.member",
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"event_id": "$143273582443PhrSn:domain.com",
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"room_id": "!jEsUZKDJdhlrceRyVU:domain.com",
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"sender": "@example:domain.com",
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"origin_server_ts": 1432735824653,
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"unsigned": {
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"age": 1234
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},
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"state_key": "@alice:domain.com"
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}
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]
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}
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```
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This proposal would extend the `PUT /_matrix/app/v1/transactions/` endpoint to include a new key
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`ephemeral` to behave similar to the various sections of the CS API `/sync` endpoint. The `ephemeral` key
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MAY be omitted entirely if there are no ephemeral events to send.
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```json
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{
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"ephemeral": [
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{
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"type": "m.typing",
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"room_id": "!jEsUZKDJdhlrceRyVU:domain.com",
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"content": {
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"user_ids": [
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"@alice:example.com"
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]
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}
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},
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{
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"type": "m.receipt",
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"room_id": "!jEsUZKDJdhlrceRyVU:domain.com",
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"content": {
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"$1435641916114394fHBLK:matrix.org": {
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"m.read": {
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"@rikj:jki.re": {
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"ts": 1436451550453
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}
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}
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}
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}
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}
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],
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"events": [
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// ...
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]
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}
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```
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The reason for a new key rather than bundling the events into `events` is that
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existing appservices may mistake them for PDUs and might behave erratically.
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While `events` may now be a somewhat misleading name, this is an acceptable tradeoff.
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The array is effectively a combination of the `presence` and `ephemeral` sections of the
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client-server `/sync` API. User-defined ephemeral events don't exist yet, which means there are
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only three event types that can currently occur:
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[`m.presence`](https://spec.matrix.org/v1.11/client-server-api/#mpresence),
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[`m.typing`](https://spec.matrix.org/v1.11/client-server-api/#mtyping),
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and [`m.receipt`](https://spec.matrix.org/v1.11/client-server-api/#mreceipt).
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This proposal does not cover any other types of events which are sent as EDUs in the federation API,
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such as to-device events or other e2ee features. Those are left to a separate MSC.
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EDUs are formatted the same way as they are in C-S sync, with the addition of the `room_id` field
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for room-scoped EDUs (`m.typing` and `m.receipt`). `room_id` is not present in the C-S API because
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sync nests EDUs inside a room object, but appservices get a flat list of events in all rooms.
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### Expectations of when an EDU should be pushed to an appservice
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It is not clear at face value what should be pushed to an appservice. Appservices claim
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namespaces of users which registers "interest" in the rooms where those users reside, as
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well as claiming namespaces of rooms for explicit interest. However, not all EDUs are
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associated with a single room (presence, etc).
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If the EDU is capable of being associated to a particular room (i.e. `m.typing` and `m.receipt`),
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it should be sent to the appservice under the same rules as regular events (interest in the room
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means sending it). For EDUs which are not associated with a particular room, the appservice
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receives the EDU if it contextually *would* apply. For example, a presence update for a user an
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appservice shares a room with (or is under the appservice's namespace) would be sent to the
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appservice.
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For `m.receipt`, private read receipts (`m.read.private`) should only be sent for users within the
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appservice's namespaces. Normal read receipts and threaded read receipts are always sent.
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## Potential issues
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Determining which EDUs to transmit to the appservice could lead to quite some overhead on the
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homeserver side. Additionally, more network traffic is produced, potentially straining the local
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network and the appservice more. As such, appservices have to opt-in to receive EDUs.
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## Security considerations
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The homeserver needs to accurately determine which EDUs to send to the appservice, as to not leak
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any unnecessary metadata about users. Particularly `m.presence` could be tricky, as no `room_id` is present in
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that EDU.
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## Unstable prefix
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In the transaction body, instead of `ephemeral`, `de.sorunome.msc2409.ephemeral` is used.
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In the registration file, instead of `receive_ephemeral`, `de.sorunome.msc2409.push_ephemeral` is used.
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