galene/README.PROTOCOL

# Galène's protocol

Galène uses a symmetric, asynchronous protocol.  In client-server
usage, some messages are only sent in the client to server or in the
server to client direction.

## Message syntax

All messages are sent as JSON objects.  All fields except `type` are
optional; however, there are some fields that are common across multiple
message types.

 - `type`, the type of the message;
 - `kind`, the subtype of the message;
 - `id`, the id of the object being manipulated;
 - `source`, the client-id of the originating client;
 - `username`, the username of the originating client;
 - `dest`, the client-id of the destination client;
 - `privileged`, set by the server to indicate that the originating client
   had the `op` privilege at the time it sent the message.

## Data structures

### Group

A group is a set of clients.  It is identified by a human-readable name
that must not start or end with a slash "`/`" and must not have the
substrings "`/../`" or "`/./`".

### Client

A client is a peer that may originate offers and chat messages.  It is
identified by an id, an opaque string that is assumed to be unique.  Peers
that do not originate messages (servers) do not need to be assigned an id.

### Stream

A stream is a set of related tracks.  It is identified by an id, an opaque
string.  Streams in Galène are unidirectional.  A stream is carried by
exactly one peer connection (PC) (multiple streams in a single PC are not
allowed).  The offerer is also the RTP sender (i.e. all tracks sent by the
offerer are of type `sendonly`).

## Establishing and maintaining a connection

The peer establishing the connection (the WebSocket client) sends
a handshake message.  The server replies with another handshake message.
The client may wait for the server's handshake, or it may immediately
start pipelining messages to the server.

```javascript
{
    type: 'handshake',
    id: id
}
```

If the field `id` is absent, then the peer doesn't originate streams (it
is a server).

A peer may, at any time, send a `ping` message.

```javascript
{
    type: 'ping'
}
```

The receiving peer must reply with a `pong` message within 30s.

```javascript
{
    type: 'pong'
}
```

## Joining and leaving

The `join` message requests that the sender join or leave a group:

```javascript
{
    type: 'join',
    kind: 'join' or 'leave',
    group: group,
    username: username,
    password: password
}
```

When the sender has effectively joined the group, the peer will send
a 'joined' message of kind 'join'; it may then send a 'joined' message of
kind 'change' at any time, in order to inform the client of a change in
its permissions or in the recommended RTC configuration.

```javascript
{
    type: 'joined',
    kind: 'join' or 'fail' or 'change' or 'leave',
    group: group,
    username: username,
    permissions: permissions,
    rtcConfiguration: RTCConfiguration
}
```

The `permissions` field is an array of strings that may contain the values
`present`, `op` and `record`.

## Maintaining group membership

Whenever a user joins or leaves a group, the server will send all other
users a `user` message:

```javascript
{
    type: 'user',
    kind: 'add' or 'delete',
    id: id,
    username: username
}
```

## Requesting streams

A peer must explicitly request the streams that it wants to receive.

```javascript
{
    type: 'request',
    request: requested
}
```

The field `request` is a dictionary that maps the labels of requested
tracks to the boolean `true`.

## Pushing streams

A stream is created by the sender with the `offer` message:

```javascript
{
    type: 'offer',
    kind: '' or 'renegotiate'
    id: id,
    source: source-id,
    username: username,
    sdp: sdp,
    labels: labels
}
```

If kind is the empty string, then this is a new offer that might or might
not replace an existing stream; if a stream with the same id exists, it
must be torn down before the new stream is created.  If kind is
`renegotiate`, then a stream with the given id already exists, and the
receiving peer may either tear down the existing stream or merely perform
a renegotiation.

The field `sdp` contains the raw SDP string (i.e. the `sdp` field of
a JSEP session description).  Galène will interpret the `nack`,
`nack pli`, `ccm fir` and `goog-remb` RTCP feedback types, and act
accordingly.

The field `labels` is a dictionary that maps track mids to one of `audio`,
`video` or `screenshare`.  If a track does not appear in the `labels`
dictionary, it should be ignored.

The receiver may either abort the stream immediately (see below), or send
an answer.

```javascript
{
    type: 'answer',
    id: id,
    sdp: SDP
}
```

Both peers may then trickle ICE candidates with `ice` messages.

```javascript
{
    type: 'ice',
    candidate: candidate
}
```

The answerer may request a new offer of kind `renegotiate` and an ICE
restart by sending a `renegotiate` message:

```javascript
{
    type: 'renegotiate',
    id: id
}
```

## Closing streams

The offerer may close a stream at any time by sending a `close` message.

```javascript
{
    type: 'close',
    id: id
}
```

The answerer may request that the offerer close a stream by sending an
`abort` message.

```javascript
{
    type: 'abort',
    id: id
}
```

The stream will not be effectively closed until the offerer sends
a matching `close`.

## Sending messages

A chat message may be sent using a `chat` message.

```javascript
{
    type: 'chat',
    kind: '' or 'me',
    source: source-id,
    username: username,
    dest: dest-id,
    privileged: boolean,
    value: message
}
```

If `dest` is empty, the message is a broadcast message, destined to all of
the clients in the group.  If `source` is empty, then the message was
originated by the server.  The message is forwarded by the server without
interpretation, the server only validates that the `source` and `username`
fields are authentic.  The field `privileged` is set to true by the server
if the message was originated by a client with the `op` permission.

A user message is similar to a chat message, but is not conserved in the
chat history, and is not expected to contain user-visible content.

```javascript
{
    type: 'usermessage',
    kind: kind,
    source: source-id,
    username: username,
    dest: dest-id,
    privileged: boolean,
    value: value
}
```

Currently defined kinds include `error`, `warning`, `info`, `clearchat`
(not to be confused with the `clearchat` group action), and `mute`.

A user action requests that the server act upon a user.

```javascript
{
    type: 'useraction',
    kind: kind,
    source: source-id,
    username: username,
    dest: dest-id,
    value: value
}
```
Currently defined kinds include `op`, `unop`, `present`, `unpresent`, and
`kick`. 

Finally, a group action requests that the server act on the current group.

```javascript
{
    type: 'groupaction',
    kind: kind,
    source: source-id,
    username: username,
    value: value
}
```

Currently defined kinds include `clearchat` (not to be confused with the
`clearchat` user message), `lock`, `unlock`, `record`, `unrecord` and
`subgroups`.