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We used to label tracks individually, in a view to using the labelling
for simulcast. Since then, the WebRTC community has converged on a
different strategy, where multiple tracks share a single mid and
are labelled with the rid extension.
We now label whole streams, which is simpler, and use the track's
kind (and, in the future, the rid) to disambiguate. This changes the
protocol in two ways:
* in offers, the "labels" dictionary is replaced by a single "label"
field; and
* the syntax of the "request" message has changed.
298 lines
7.1 KiB
Text
298 lines
7.1 KiB
Text
# Galène's protocol
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Galène uses a symmetric, asynchronous protocol. In client-server
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usage, some messages are only sent in the client to server or in the
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server to client direction.
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## Message syntax
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All messages are sent as JSON objects. All fields except `type` are
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optional; however, there are some fields that are common across multiple
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message types.
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- `type`, the type of the message;
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- `kind`, the subtype of the message;
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- `id`, the id of the object being manipulated;
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- `source`, the client-id of the originating client;
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- `username`, the username of the originating client;
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- `dest`, the client-id of the destination client;
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- `privileged`, set by the server to indicate that the originating client
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had the `op` privilege at the time it sent the message.
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## Data structures
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### Group
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A group is a set of clients. It is identified by a human-readable name
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that must not start or end with a slash "`/`" and must not have the
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substrings "`/../`" or "`/./`".
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### Client
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A client is a peer that may originate offers and chat messages. It is
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identified by an id, an opaque string that is assumed to be unique. Peers
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that do not originate messages (servers) do not need to be assigned an id.
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### Stream
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A stream is a set of related tracks. It is identified by an id, an opaque
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string. Streams in Galène are unidirectional. A stream is carried by
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exactly one peer connection (PC) (multiple streams in a single PC are not
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allowed). The offerer is also the RTP sender (i.e. all tracks sent by the
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offerer are of type `sendonly`).
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## Establishing and maintaining a connection
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The peer establishing the connection (the WebSocket client) sends
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a handshake message. The server replies with another handshake message.
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The client may wait for the server's handshake, or it may immediately
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start pipelining messages to the server.
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```javascript
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{
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type: 'handshake',
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id: id
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}
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```
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If the field `id` is absent, then the peer doesn't originate streams (it
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is a server).
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A peer may, at any time, send a `ping` message.
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```javascript
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{
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type: 'ping'
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}
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```
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The receiving peer must reply with a `pong` message within 30s.
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```javascript
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{
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type: 'pong'
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}
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```
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## Joining and leaving
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The `join` message requests that the sender join or leave a group:
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```javascript
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{
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type: 'join',
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kind: 'join' or 'leave',
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group: group,
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username: username,
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password: password
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}
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```
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When the sender has effectively joined the group, the peer will send
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a 'joined' message of kind 'join'; it may then send a 'joined' message of
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kind 'change' at any time, in order to inform the client of a change in
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its permissions or in the recommended RTC configuration.
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```javascript
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{
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type: 'joined',
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kind: 'join' or 'fail' or 'change' or 'leave',
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group: group,
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username: username,
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permissions: permissions,
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rtcConfiguration: RTCConfiguration
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}
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```
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The `permissions` field is an array of strings that may contain the values
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`present`, `op` and `record`.
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## Maintaining group membership
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Whenever a user joins or leaves a group, the server will send all other
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users a `user` message:
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```javascript
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{
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type: 'user',
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kind: 'add' or 'change' or 'delete',
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id: id,
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username: username,
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permissions: permissions,
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status: status
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}
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```
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## Requesting streams
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A peer must explicitly request the streams that it wants to receive.
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```javascript
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{
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type: 'request',
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request: requested
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}
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```
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The field `request` is a dictionary that maps the labels of requested
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streams to a list containing either 'audio', 'video' or both. An entry
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with an empty key `''` serves as default.
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## Pushing streams
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A stream is created by the sender with the `offer` message:
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```javascript
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{
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type: 'offer',
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id: id,
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label: label,
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replace: id,
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source: source-id,
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username: username,
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sdp: sdp,
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}
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```
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If a stream with the same id exists, then this is a renegotation;
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otherwise this message creates a new stream. If the field `replace` is
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not empty, then this request additionally requests that an existing stream
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with the given id should be closed, and the new stream should replace it.
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The field `label` is one of `camera`, `screenshare` or `video`, as in the
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`request` message.
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The field `sdp` contains the raw SDP string (i.e. the `sdp` field of
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a JSEP session description). Galène will interpret the `nack`,
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`nack pli`, `ccm fir` and `goog-remb` RTCP feedback types, and act
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accordingly.
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The receiver may either abort the stream immediately (see below), or send
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an answer.
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```javascript
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{
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type: 'answer',
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id: id,
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sdp: SDP
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}
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```
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Both peers may then trickle ICE candidates with `ice` messages.
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```javascript
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{
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type: 'ice',
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id: id,
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candidate: candidate
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}
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```
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The answerer may request a new offer of kind `renegotiate` and an ICE
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restart by sending a `renegotiate` message:
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```javascript
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{
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type: 'renegotiate',
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id: id
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}
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```
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## Closing streams
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The offerer may close a stream at any time by sending a `close` message.
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```javascript
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{
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type: 'close',
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id: id
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}
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```
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The answerer may request that the offerer close a stream by sending an
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`abort` message.
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```javascript
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{
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type: 'abort',
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id: id
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}
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```
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The stream will not be effectively closed until the offerer sends
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a matching `close`.
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## Sending messages
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A chat message may be sent using a `chat` message.
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```javascript
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{
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type: 'chat',
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kind: '' or 'me',
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source: source-id,
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username: username,
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dest: dest-id,
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privileged: boolean,
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noecho: false,
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value: message
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}
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```
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If `dest` is empty, the message is a broadcast message, destined to all of
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the clients in the group. If `source` is empty, then the message was
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originated by the server. The message is forwarded by the server without
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interpretation, the server only validates that the `source` and `username`
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fields are authentic. The field `privileged` is set to true by the server
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if the message was originated by a client with the `op` permission. The
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field `noecho` is set by the client if it doesn't wish to receive a copy
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of its own message.
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A user message is similar to a chat message, but is not conserved in the
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chat history, and is not expected to contain user-visible content.
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```javascript
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{
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type: 'usermessage',
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kind: kind,
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source: source-id,
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username: username,
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dest: dest-id,
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privileged: boolean,
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value: value
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}
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```
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Currently defined kinds include `error`, `warning`, `info`, `clearchat`
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(not to be confused with the `clearchat` group action), and `mute`.
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A user action requests that the server act upon a user.
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```javascript
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{
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type: 'useraction',
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kind: kind,
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source: source-id,
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username: username,
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dest: dest-id,
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value: value
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}
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```
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Currently defined kinds include `op`, `unop`, `present`, `unpresent`,
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`kick` and `setstatus`.
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Finally, a group action requests that the server act on the current group.
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```javascript
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{
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type: 'groupaction',
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kind: kind,
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source: source-id,
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username: username,
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value: value
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}
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```
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Currently defined kinds include `clearchat` (not to be confused with the
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`clearchat` user message), `lock`, `unlock`, `record`, `unrecord` and
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`subgroups`.
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