Galène frontends

Writing a new frontend

The frontend is written in JavaScript and is split into two files:

A new frontend may either implement Galène’s client-server protocol from scratch, or it may use the functionality of protocol.js. This document documents the latter approach.

Data structures

The class ServerConnection encapsulates a connection to the server as well as all the associated streams. Unless your frontend communicates with multiple servers, it will probably create just a single instance of this class.

The class Stream encapsulates a set of related audio and video tracks (for example, an audio track from a microphone and a video track from a webcam). A stream is said to go up when it carries data from the client to the server, and down otherwise. Streams going up are created by the client (your frontend), streams going down are created by the server.

Connecting to the server

First, create a ServerConnection and set up all the callbacks:

let sc = new ServerConnection()
serverConnection.onconnected = ...;
serverConnection.onclose = ...;
serverConnection.onusermessage = ...;
serverConnection.onjoined = ...;
serverConnection.onuser = ...;
serverConnection.onchat = ...;
serverConnection.onclearchat = ...;
serverConnection.ondownstream = ...;

The onconnected callback is called when we connect to the server. The onclose callback is called when the socket is closed; all streams will have been closed by the time it is called. The onusermessage callback indicates an application-specific message, either from another user or from the server; the field kind indicates the kind of message.

Once you have joined a group (see below), the remaining callbacks may trigger. The onuser callback is used to indicate that a user has joined or left the current group. The onchat callback indicates that a chat message has been posted to the group, and onclearchat indicates that the chat history has been cleared. Finally, ondownstream is called when the server pushes a stream to the client; see the section below about streams.

You may now connect to the server.

serverConnection.connect(`wss://${location.host}/ws`);

You typically join a group and request media in the onconnected callback:

serverConnection.onconnected = function() {
    this.join(group, 'join', username, password); 
    this.request('everything');
}

You should not attempt to push a stream to the server until it has granted you the present permission through the onjoined callback.

Sending and receiving chat messages

Once you have joined a group, you send chat messages with the chat method of the ServerConnection class. No permission is needed to do that.

serverConnection.chat(username, '', id, 'Hi!');

You receive chat messages in the onchat callback. The server may request that you clear your chat window, in that case the onclearchat callback will trigger.

Other messages

The usermessage method of the ServerConnection is similar to the chat method, but it sends an application-specific message. Just like chat messages, application-specific messages are not interpreted by the server; unlike chat messages, they are not kept in the chat history.

The useraction method is used to ask the server to act on a remote user (kick it, change its permissions, etc.); similarly, the groupaction class requests an action to be performed on the current group. Most actions require either the Op or the Record permission.

Accepting incoming video streams

When the server pushes a stream to the client, the ondownstream callback will trigger; you should set up the stream’s callbacks here.

serverConnection.ondownstream = function(stream) {
    stream.onclose = ...;
    stream.onerror = ...;
    stream.ondowntrack = ...;
    stream.onstatus = ...;
}

The stream.labels dictionary maps each track’s id to one of audio, video or screenshare. Since stream.labels is already available at this point, you may set up an audio or video component straight away, or you may choose to wait until the ondowntrack callback is called.

After a new stream is created, ondowntrack will be called whenever a track is added.

The onstatus callback is invoked whenever the client library detects a change in the status of the stream; states connected and complete indicate a functioning stream; other states indicate that the stream is not working right now but might recover in the future.

The onclose callback is called when the stream is destroyed, either by the server or in response to a call to the close method. The optional parameter is true when the stream is being replaced by a new stream; in that case, the call to onclose will be followed with a call to onstream with the same localId value.

Pushing outgoing video streams

If you have the present permission, you may use the newUpStream method to push a stream to the server. Given a MediaStream called localStream (as obtained from getUserMedia or getDisplayMedia).

let stream = serverConnection.newUpStream();
stream.onerror = ...;
stream.onabort = ...;
stream.onstatus = ...;
localStream.getTracks().forEach(t => {
    c.labels[t.id] = t.kind;
    c.pc.addTrack(t, c.stream);
});

The newUpStream method takes an optional parameter. If this is set to the localId property of an existing stream, then the existing stream will be closed and the server will be informed that the new stream replaces the existing stream.

See above for information about setting up the labels dictionary.

Stream statistics

Some statistics about streams are made available by calling the setStatsInterval method and setting the onstats callback. These include the data rate for streams in the up direction, and the average audio energy (the square of the volume) for streams in the down direction.

— Juliusz Chroboczek https://www.irif.fr/~jch/