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Improve README.FRONTEND.
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README.FRONTEND
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README.FRONTEND
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# Writing a new frontend
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The frontend is split into two javascript files:
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The frontend is written in JavaScript and is split into two files:
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- `protocol.js` contains the low-level functions that interact with the server;
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- `protocol.js` contains the low-level functions that interact with the
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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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is provided), but is otherwise plain Javascript (ES6).
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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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The class `Stream` encapsulates a set of related audio and video tracks;
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your frontend will probably associate each stream with a `video` or
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`audio` 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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```javascript
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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.onusermessage = ...;
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serverConnection.onpermissions = ...;
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serverConnection.onuser = ...;
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serverConnection.onchat = ...;
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serverConnection.onclearchat = ...;
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serverConnection.onusermessage = ...;
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serverConnection.ondownstream = ...;
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```
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You may now connect to the server:
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```
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The `onconnected` callback is called when we connect to the server;
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`onclose` is the opposite of `onconnected`. `onusermessage` indicates
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a message from the server that should be displayed to the user.
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The other callbacks will only be called after you join a group. `onuser`
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is used to indicate that a user has joined or left the current group.
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`onchat` indicates that a chat message has been posted to the group, and
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`onclearchat` indicates that the chat history has been cleared. Finally,
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`ondownstream` is called when the server pushes a stream to the client;
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see the section below about streams.
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You may now connect to the server.
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```javascript
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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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You log-in, join a group and request media in the `onconnected` callback.
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```javascript
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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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You should not attempt to push a stream to the server until it has granted
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you the `present` permission through the `onpermissions` callback.
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## Managing groups and users
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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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## 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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Once you have joined a group, you send chat messages with the `chat`
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method. No permission is needed to do that.
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```javascript
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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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will trigger; you should set up the stream's callbacks here.
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```javascript
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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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The `stream.labels` dictionary maps each track's id to one of `audio`,
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`video` or `screenshare`. Since `stream.labels` is already available at
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this point, you may set up an `audio` or `video` component straight away,
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or you may choose to wait until the `ondowntrack` callback is called.
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The server will usually invoke the `onlabel` callback in order to set
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a user-readable label on the stream; this is currently just the
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originating client's username.
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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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@ -88,14 +115,22 @@ 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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The `onstatus` callback is invoked whenever the client library detects
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a change in the status of the stream; states `connected` and `complete`
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indicate a functioning stream; other states indicate that the stream is
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not working right now but might recover in the future.
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The `onclose` callback is called when the stream is destroyed by the
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server.
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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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to push a stream to the server. Given a `MediaStream` called `localStream`
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(as obtained from `getUserMedia` or `getDisplayMedia`).
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```javascript
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let stream = serverConnection.newUpStream();
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stream.onerror = ...;
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stream.onabort = ...;
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stream.onstatus = ...;
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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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See above for information about setting up the `labels` dictionary.
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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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## Stream statistics
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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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