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100 lines
4.0 KiB
Markdown
100 lines
4.0 KiB
Markdown
---
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type: module
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weight: 80
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---
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### Send-to-Device messaging
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This module provides a means by which clients can exchange signalling
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messages without them being stored permanently as part of a shared
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communication history. A message is delivered exactly once to each
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client device.
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The primary motivation for this API is exchanging data that is
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meaningless or undesirable to persist in the room DAG - for example,
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one-time authentication tokens or key data. It is not intended for
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conversational data, which should be sent using the normal [`/rooms/<room_id>/send`](/client-server-api/#put_matrixclientr0roomsroomidsendeventtypetxnid) API for
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consistency throughout Matrix.
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#### Client behaviour
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To send a message to other devices, a client should call
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[`/sendToDevice`](/client-server-api/#put_matrixclientr0sendtodeviceeventtypetxnid). Only one message can be sent to each device per
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transaction, and they must all have the same event type. The device ID
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in the request body can be set to `*` to request that the message be
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sent to all known devices.
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If there are send-to-device messages waiting for a client, they will be
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returned by [`/sync`](/client-server-api/#get_matrixclientr0sync), as detailed in [Extensions to /sync](/client-server-api/#extensions-to-sync). Clients should
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inspect the `type` of each returned event, and ignore any they do not
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understand.
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#### Server behaviour
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Servers should store pending messages for local users until they are
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successfully delivered to the destination device. When a client calls
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[`/sync`](/client-server-api/#get_matrixclientr0sync)
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with an access token which corresponds to a device with pending
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messages, the server should list the pending messages, in order of
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arrival, in the response body.
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When the client calls `/sync` again with the `next_batch` token from the
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first response, the server should infer that any send-to-device messages
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in that response have been delivered successfully, and delete them from
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the store.
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If there is a large queue of send-to-device messages, the server should
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limit the number sent in each `/sync` response. 100 messages is
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recommended as a reasonable limit.
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If the client sends messages to users on remote domains, those messages
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should be sent on to the remote servers via
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[federation](/server-server-api#send-to-device-messaging).
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#### Protocol definitions
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{{% http-api spec="client-server" api="to_device" %}}
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##### Extensions to /sync
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This module adds the following properties to the [`/sync`](/client-server-api/#get_matrixclientr0sync) response:
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| Parameter | Type | Description |
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|-----------|-----------|-----------------------------------------------------------------------------|
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| to_device | ToDevice | Optional. Information on the send-to-device messages for the client device. |
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`ToDevice`
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| Parameter | Type | Description |
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|-----------|-----------|----------------------------------|
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| events | [Event] | List of send-to-device messages. |
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`Event`
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| Parameter | Type | Description |
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|------------|--------------|-------------------------------------------------------------------------------------------------|
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| content | EventContent | The content of this event. The fields in this object will vary depending on the type of event. |
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| sender | string | The Matrix user ID of the user who sent this event. |
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| type | string | The type of event. |
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Example response:
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```json
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{
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"next_batch": "s72595_4483_1934",
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"rooms": {"leave": {}, "join": {}, "invite": {}},
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"to_device": {
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"events": [
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{
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"sender": "@alice:example.com",
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"type": "m.new_device",
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"content": {
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"device_id": "XYZABCDE",
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"rooms": ["!726s6s6q:example.com"]
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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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