licode Basic Example 客户端解析
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##整体
### hello
在浏览其中输入https://dst_host_domain:13004后， 请求了index.html,该文件在licodeextrasasic_examplepublicindex.html开始, 引入了erizo.js和script.js, testConnection()
//licodeextrasasic_examplepublicindex.html
<html>
<head>
<title>Licode Basic Example</title>
<script type="text/javascript" src="erizo.js"></script>
<script type="text/javascript" src="script.js"></script>//定义了windows.load
</head>
<body>
<button id="startButton" onclick="startBasicExample()" disabled>Start</button>
<button id="testConnection" onclick="testConnection()">Test Connection</button>
<button id="recordButton" onclick="startRecording()" disabled>Toggle Recording</button>
<button id="slideShowMode" onclick="toggleSlideShowMode()" disabled>Toggle Slide Show Mode</button>
<h1 id="startWarning">Press the start buttong to start receiving streams</h1>
<div id="videoContainer"></div>
</body>
</html>由于scripts中设置了window.onload()的回调，所以加载的时候就直接运行了如下回调，去调用例子
//licodeextrasasic_examplepublicscript.js
window.onload = () => {
const onlySubscribe = getParameterByName('onlySubscribe');
const bypassStartButton = getParameterByName('noStart');
if (!onlySubscribe || bypassStartButton) {
startBasicExample();//启动例子
} else {
document.getElementById('startButton').disabled = false;
}
};startBasicExample()首先会读取配置，创建本地stream
//licodeextrasasic_examplepublicscript.js
localStream = Erizo.Stream(config); //创建本地stream
Erizo是erizo.js定义导出的全局对象, Stream是其函数对象，函数定义Stream.js中, 其提供了一些操作流的接口，包括播放，控制等等，并且还创建了事件分发器，用来处理publisher或者room的事件
//licodeerizo_controllererizoClientsrcErizo.js
const Erizo = {
Room: Room.bind(null, undefined, undefined, undefined),
LicodeEvent,
RoomEvent,
StreamEvent,
//Stream 使用Stream.bind创建返回一个函数对象赋值
//创建的时候该对象函数中的this指针置NULL， 调用时第一个参数默认为undefined
Stream: Stream.bind(null, undefined),
Logger,
};
export default Erizo;
客户端完成本地媒体的初始化之后，将生成的Roomdata当作参数发送createtoken请求给服务端, 响应后调用callback进行回调
//licodeextrasasic_examplepublicscript.js
const createToken = (roomData, callback) => {
const req = new XMLHttpRequest();
const url = `${serverUrl}createToken/`;
req.onreadystatechange = () => { //设置响应回调
if (req.readyState === 4) {
callback(req.responseText);
}
};
req.open('POST', url, true);
req.setRequestHeader('Content-Type', 'application/json');
req.send(JSON.stringify(roomData));
};
createToken(roomData, (response) => {.....});创建token请求会被发送到服务器，服务器的express http框架会进行处理，将请求通过匹配到对应函数，对请求进行处理，此处为创建完token并同时创建room，将token和roomid返回发送回去
//licodeextrasasic_exampleasicServer.js
basicServer.js
app.post('/createToken/', (req, res) => {
console.log('Creating token. Request body: ', req.body);
const username = req.body.username;
const role = req.body.role;
let room = defaultRoomName;
let type;
let roomId;
let mediaConfiguration;
if (req.body.room) room = req.body.room;
if (req.body.type) type = req.body.type;
if (req.body.roomId) roomId = req.body.roomId;
if (req.body.mediaConfiguration) mediaConfiguration = req.body.mediaConfiguration;
const createToken = (tokenRoomId) => {
N.API.createToken(tokenRoomId, username, role, (token) => {
console.log('Token created', token);
res.send(token);//将token发送回去
}, (error) => {
console.log('Error creating token', error);
res.status(401).send('No Erizo Controller found');
});
};
if (roomId) {
createToken(roomId);
} else {
getOrCreateRoom(room, type, mediaConfiguration, createToken);
}
});发送了createroken请求，客户端收到token之后，根据返回的token(其中包含了服务端创建的room的一些信息)去初始化Room对象，并为一些事件绑定回调，比如房间连接成功了，流订阅等等, 然后调用localStream.init() 初始化本地媒体
//licodeextrasasic_examplepublicscript.js
createToken(roomData, (response) => {
const token = response;
console.log(token);
//创建房间
room = Erizo.Room({ token });
//创建订阅流接口
const subscribeToStreams = (streams) => {...... };
//添加一些事件处理回调,
room.addEventListener('room-connected', (roomEvent) => {......});
room.addEventListener('stream-subscribed', (streamEvent) => {......});
room.addEventListener('stream-added', (streamEvent) => {......});
room.addEventListener('stream-removed', (streamEvent) => {......});
room.addEventListener('stream-failed', () => {......});
if (onlySubscribe) {
room.connect({ singlePC });
} else {
//默认执行的地方
const div = document.createElement('div');
div.setAttribute('style', 'width: 320px; height: 240px; float:left');
div.setAttribute('id', 'myVideo');
document.getElementById('videoContainer').appendChild(div);
//为'access-accepted'事件设置回调，该回调渲染视频画面
localStream.addEventListener('access-accepted', () => {
room.connect({ singlePC });
localStream.show('myVideo');
});
//初始化
localStream.init();
}
});其中,在room.connect()时候，会对得到的token进行解析获得erizocontroller，也就是licode的媒体服务器入口的ip和port，建立ws连接，建立完成后，通过事件管理器（EventDispatcher）向上层抛出room-connected事件， room-connected事件的处理回调中，调用了room.publish和room.autoSubscribe进行推拉流
##2.事件处理
无论是Erizo.Room还是Erizo.Stream，都可以分别在Room.js和Stream.js中找到其对应的对象生成方式，在生成对象的过程中都可以看到是先从生成一个EventDispatcher，然后在其上面作派生的
const that = EventDispatcher(spec);EventDispatcher是一个事件处理器，在Event.js中可以找到，其维护了一个对象数组eventListeners，将事件和回调做了key-value的绑定，当事件发生的时候，外部调用dispatchEvent 遍历搜索，执行其回调
//licodeerizo_controllererizoClientsrcEvents.js
const EventDispatcher = () => {
const that = {};
// Private vars
const dispatcher = {
eventListeners: {},
};
// Public functions
//将事件和回调放到对象数组中去
that.addEventListener = (eventType, listener) => {
if (dispatcher.eventListeners[eventType] === undefined) {
dispatcher.eventListeners[eventType] = [];
}
dispatcher.eventListeners[eventType].push(listener);
};
// It removes an available event listener.
that.removeEventListener = (eventType, listener) => {
if (!dispatcher.eventListeners[eventType]) {
return;
}
const index = dispatcher.eventListeners[eventType].indexOf(listener);
if (index !== -1) {
dispatcher.eventListeners[eventType].splice(index, 1);
}
};
// It removes all listeners
that.removeAllListeners = () => {
dispatcher.eventListeners = {};
};
that.dispatchEvent = (event) => {
//遍历，找到该event的回调，并执行
let listeners = dispatcher.eventListeners[event.type] || [];
listeners = listeners.slice(0);
for (let i = 0; i < listeners.length; i += 1) {
listeners[i](event);
}
};
that.on = that.addEventListener;
that.off = that.removeEventListener;
that.emit = that.dispatchEvent;
return that;
};在使用Erizo.Room({ token });创建Room对象的过程中，可以看到其是先生成一个EventDispatcher对象然后在其上面进行扩展。
##3.媒体
publish
publish在room-connected之后发生
//licodeextrasasic_examplepublicscript.js
if (!onlySubscribe) {
room.publish(localStream, options);//将本地媒体publish
}该函数实际如下，根据config对流进行一些设置之后开始推流
//licodeerizo_controllererizoClientsrcRoom.js
that.publish = (streamInput, optionsInput = {}, callback = () => {}) => {
const stream = streamInput;
const options = optionsInput;
//设置流的一些属性以及会调
省略......
if (stream && stream.local && !stream.failed && !localStreams.has(stream.getID())) {
if (stream.hasMedia()) {
if (stream.isExternal()) {
publishExternal(stream, options, callback);
} else if (that.p2p) {
publishP2P(stream, options, callback);
} else {
publishErizo(stream, options, callback);//推流
}
} else if (stream.hasData()) {
publishData(stream, options, callback);
}
} else {
Logger.error('Trying to publish invalid stream, stream:', stream);
callback(undefined, 'Invalid Stream');
}
};在publishErizo中发送了SDP，将流填充到本地数组进行管理， 创建流连接
//licodeerizo_controllererizoClientsrcRoom.js
const publishErizo = (streamInput, options, callback = () => {}) => {
const stream = streamInput;
Logger.info('Publishing to Erizo Normally, is createOffer', options.createOffer);
const constraints = createSdpConstraints('erizo', stream, options);
constraints.minVideoBW = options.minVideoBW;
constraints.maxVideoBW = options.maxVideoBW;
constraints.scheme = options.scheme;
//发送publish信令到媒体服务器和SDP
socket.sendSDP('publish', constraints, undefined, (id, erizoId, connectionId, error) => {
if (id === null) {
Logger.error('Error publishing stream', error);
callback(undefined, error);
return;
}
//填充流
populateStreamFunctions(id, stream, error, undefined);
//创建流连接
createLocalStreamErizoConnection(stream, connectionId, erizoId, options);
callback(id);
});
};创建流连接中添加了icestatechanged的失败回调，以及调用了pc连接中的addstream接口
//licodeerizo_controllererizoClientsrcRoom.js
const createLocalStreamErizoConnection = (streamInput, connectionId, erizoId, options) => {
const stream = streamInput;
const connectionOpts = getErizoConnectionOptions(stream, connectionId, erizoId, options);
stream.addPC(
that.erizoConnectionManager
.getOrBuildErizoConnection(connectionOpts, erizoId, spec.singlePC));
//绑定icestatechanged到failed的回调
stream.on('icestatechanged', (evt) => {
Logger.info(`${stream.getID()} - iceConnectionState: ${evt.msg.state}`);
if (evt.msg.state === 'failed') {
const message = 'ICE Connection Failed';
onStreamFailed(stream, message, 'ice-client');
if (spec.singlePC) {
connectionOpts.callback({ type: 'failed' });
}
}
});
//调用pcconnect连接中的添加流
stream.pc.addStream(stream);
};其中pc连接是定义licodeerizo_controllererizoClientsrcErizoConnectionManager.js中的class ErizoConnection，其对浏览器原生的webrtc的js接口包了一层，并继承了事件发生器，将有关连接以及媒体的事件抛到上层的事件处理器中进行处理, 此处调用了原生的接口addStream之后，通过后续的发送offer协商完成之后就会自动开始推流。
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