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119 lines
3.9 KiB
Text
119 lines
3.9 KiB
Text
# Writing a new frontend
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The frontend is split into two javascript files:
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- `protocol.js` contains the low-level functions that interact with the server;
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- `sfu.js` contains the user interface.
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If you wish to develop your own frontend, I recommend using `protocol.js`,
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which is likely to remain reasonably stable as the protocol evolves. This
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file can be processed with JSDoc or Typescript (a sample `tsconfig.json`
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is provided).
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## Data structures
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The class `ServerConnection` encapsulates a connection to the server as
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well as all the associated streams.
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The class `Stream` encapsulates a set of associated audio and video
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tracks; your frontend will probably associate each stream with a video
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component.
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## Connecting to the server
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First, create a `ServerConnection` and set up all the callbacks:
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```
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let sc = new ServerConnection()
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serverConnection.onconnected = ...;
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serverConnection.onclose = ...;
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serverConnection.ondownstream = ...;
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serverConnection.onuser = ...;
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serverConnection.onpermissions = ...;
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serverConnection.onchat = ...;
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serverConnection.onclearchat = ...;
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serverConnection.onusermessage = ...;
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```
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You may now connect to the server:
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```
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serverConnection.connect(`wss://${location.host}/ws`);
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```
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You log-in, join a group and request media in the `onconnected` callback:
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```
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serverConnection.onconnected = function() {
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this.login(username, password);
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this.join(group);
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this.request('everything');
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}
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```
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The `onpermissions` callback will trigger when the server informs us about
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the permissions that were granted; you should probably reflect the
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permissions in the user interface.
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## Managing groups and clients
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The `groupaction` and `useraction` methods perform actions such as kicking
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users or locking groups. Most actions require either the `Op` or the
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`Record` permission.
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## Sending and receiving chat messages
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You send a chat message with the `chat` method:
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```
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serverConnection.chat(username, '', 'Hi!');
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```
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You receive chat messages in the `onchat` callback. The server may
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request that you clear your chat window, in that case the `onclearchat`
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callback will trigger.
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## Accepting incoming video streams
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When the server pushes a stream to the client, the `ondownstream` callback
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will trigger; you should set up the stream callbacks here. It is
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premature to set up a video component --- do that in `ondowntrack`.
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```
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serverConnection.ondownstream = function(stream) {
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stream.onclose = ...;
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stream.onerror = ...;
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stream.ondowntrack = ...;
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stream.onlabel = ...;
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stream.onstatus = ...;
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}
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```
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After a new stream is created, `ondowntrack` will be called whenever
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a track is added. If the `MediaStream` passed to `ondowntrack` differs
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from the one previously received, then the stream has been torn down and
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recreated, and you must drop all previously received tracks; in practice,
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it is enough to set the `srcObject` property of the video component to the
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new stream.
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## Pushing outgoing video streams
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If you have the `present` permission, you may use the `newUpStream` method
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to push a stream to the server. Given a local stream `localStream`, do
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something like the following:
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```
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let stream = serverConnection.newUpStream;
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stream.kind = 'local';
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stream.onerror = ...;
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stream.onabort = ...;
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stream.onstatus = ...;
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localStream.getTracks().forEach(t => {
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c.labels[t.id] = t.kind;
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c.pc.addTrack(t, c.stream);
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});
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```
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You should set `c.labels[t.id]` to one of `audio`, `video` or `screenshare`.
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## Stream status and statistics
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The `onstatus` callback can be used to give users feedback about whether
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a stream is working. You should probably treat states `connected` and
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`completed` as good, and all other states as bad.
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For outgoing streams only, the `setStatsInterval` and `onstats` callback
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can be used to determine the data rate in real time. This is currently
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not implemented for down streams.
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--- Juliusz Chroboczek <https://www.irif.fr/~jch/>
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