一、RTCDataChannel
WebRTC 不但可以让你进行音视频通话，而且还可以用它传输普通的二进制数据，比如说可以利用它实现文本聊天、文件的传输等WebRTC 的数据通道（RTCDataChannel）是专门用来传输除了音视频数据之外的任何数据，模仿了 WebSocket 的实现RTCDataChannel 支持的数据类型也非常多，包括：字符串、Blob、ArrayBuffer 以及 ArrayBufferViewWebRTC 的 RTCDataChannel 使用的传输协议为 SCTP，即 Stream Control Transport ProtocolRTCDataChannel 既可以在可靠的、有序的模式下工作，也可在不可靠的、无序的模式下工作- 可靠有序模式（TCP 模式）：在这种模式下，消息可以有序到达，但同时也带来了额外的开销，所以在这种模式下消息传输会比较慢
- 不可靠无序模式（UDP 模式）：在此种模式下，不保证消息可达，也不保证消息有序，但在这种模式下没有什么额外开销，所以它非常快
- 部分可靠模式（SCTP 模式）：在这种模式下，消息的可达性和有序性可以根据业务需求进行配置
RTCDataChannel 对象是由 RTCPeerConnection 对象创建，其中包含两个参数：- 第一个参数：是一个标签（字符串），相当于给 RTCDataChannel 起了一个名字
- 第二个参数：是 options，包含很多配置，其中就可以设置上面说的模式，重试次数等
var pc = new RTCPeerConnection();
var dc = pc.createDataChannel("dc", {
ordered: true
});
dc.onerror = (error) => {
};
dc.onopen = () => {
};
dc.onclose = () => {
};
dc.onmessage = (event) => {
var msg = event.data;
};
二、文本聊天
- 点击 Start 按钮时，会调用 start方法获取视频流然后 调用 conn 方法
- 然后调用
io.connect() 连接信令服务器，然后再根据信令服务器下发的消息做不同的处理 - 数据的发送非常简单，当用户点击
Send 按钮后，文本数据就会通过 RTCDataChannel 传输到远端 - 对于接收数据，则是通过
RTCDataChannel 的 onmessage 事件实现的 RTCDataChannel 对象的创建要在媒体协商（offer/answer） 之前创建，否则 WebRTC 就会一直处于 connecting 状态，从而导致数据无法进行传输RTCDataChannel 对象是可以双向传输数据的，所以接收与发送使用一个RTCDataChannel 对象即可，而不需要为发送和接收单独创建 RTCDataChannel 对象
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
.preview {
display: flex;
}
.remote {
margin-left: 20px;
}
.text_chat {
display: flex;
}
.text_chat textarea {
width: 350px;
height: 350px;
}
.send {
margin-top: 20px;
}
</style>
</head>
<body>
<div>
<div>
<button onclick="start()">连接信令服务器</button>
<button onclick="leave()" disabled>断开连接</button>
</div>
<div class="preview">
<div>
<h2>本地:</h2>
<video id="localvideo" autoplay playsinline></video>
</div>
<div class="remote">
<h2>远端:</h2>
<video id="remotevideo" autoplay playsinline></video>
</div>
</div>
<h2>聊天:</h2>
<div class="text_chat">
<div>
<textarea id="chat" disabled></textarea>
</div>
<div class="remote">
<textarea id="sendtext" disabled></textarea>
</div>
</div>
<div class="send">
<button onclick="send()" disabled>发送</button>
</div>
</div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/socket.io/2.0.3/socket.io.js"></script>
<script src="https://webrtc.github.io/adapter/adapter-latest.js"></script>
</body>
<script>
'use strict'
var localVideo = document.querySelector('video#localvideo');
var remoteVideo = document.querySelector('video#remotevideo');
var chat = document.querySelector('textarea#chat');
var send_txt = document.querySelector('textarea#sendtext');
var localStream = null;
var roomid = '44444';
var socket = null;
var state = 'init';
var pc = null;
var dc = null;
function sendMessage(roomid, data) {
socket.emit('message', roomid, data);
}
function getAnswer(desc) {
pc.setLocalDescription(desc);
socket.emit('message', roomid, desc);
}
function handleAnswerError(err) {
console.error('Failed to get Answer!', err);
}
function call() {
if (state === 'joined_conn') {
if (pc) {
var options = {
offerToReceiveAudio: 1,
offerToReceiveVideo: 1
}
pc.createOffer(options)
.then(function (desc) {
pc.setLocalDescription(desc);
socket.emit('message', roomid, desc);
})
.catch(function (err) {
console.error('Failed to get Offer!', err);
});
}
}
}
function reveivemsg(e) {
var msg = e.data;
console.log('recreived msg is ：' + e.data);
if (msg) {
chat.value += '->' + msg + '\r\n';
} else {
console.error('recreived msg is null');
}
}
function dataChannelStateChange() {
var readyState = dc.readyState;
if (readyState === 'open') {
send_txt.disabled = false;
btnSend.disabled = false;
} else {
send_txt.disabled = true;
btnSend.disabled = true;
}
}
function dataChannelError(error) {
console.log("Data Channel Error:", error);
}
function conn() {
socket = io.connect();
socket.on('joined', (roomid, id) => {
state = 'joined';
createPeerConnection();
btnConn.disabled = true;
btnLeave.disabled = false;
console.log("reveive joined message:state=", state);
});
socket.on('otherjoin', (roomid, id) => {
if (state === 'joined_unbind') {
createPeerConnection();
}
var dataChannelOptions = {
ordered: true,
};
dc = pc.createDataChannel('dataChannel', dataChannelOptions);
dc.onmessage = reveivemsg;
dc.onopen = dataChannelStateChange;
dc.onclose = dataChannelStateChange;
dc.onerror = dataChannelError;
state = 'joined_conn';
call();
console.log("reveive otherjoin message:state=", state);
});
socket.on('full', (roomid, id) => {
console.log('receive full message ', roomid, id);
closePeerConnection();
closeLocalMedia();
state = 'leaved';
btnConn.disabled = false;
btnLeave.disabled = true;
console.log("reveive full message:state=", state);
alert("the room is full!");
});
socket.on('leaved', (roomid, id) => {
state = 'leaved';
socket.disconnect();
btnConn.disabled = false;
btnLeave.disabled = true;
console.log("reveive leaved message:state=", state);
});
socket.on('bye', (roomid, id) => {
state = 'joined_unbind';
closePeerConnection();
console.log("reveive bye message:state=", state);
});
socket.on('disconnect', (socket) => {
console.log('receive disconnect message!', roomid);
if (!(state === 'leaved')) {
closePeerConnection();
closeLocalMedia();
}
state = 'leaved';
});
socket.on('message', (roomid, id, data) => {
console.log(" message=====>", data);
if (data) {
if (data.type === 'offer') {
pc.setRemoteDescription(new RTCSessionDescription(data));
pc.createAnswer()
.then(getAnswer)
.catch(handleAnswerError);
} else if (data.type === 'answer') {
console.log("reveive client message=====>", data);
pc.setRemoteDescription(new RTCSessionDescription(data));
} else if (data.type === 'candidate') {
var candidate = new RTCIceCandidate({
sdpMLineIndex: data.label,
candidate: data.candidate
});
pc.addIceCandidate(candidate);
} else {
console.error('the message is invalid!', data)
}
}
console.log("reveive client message", roomid, id, data);
});
socket.emit('join', roomid);
return;
}
function start() {
if (!navigator.mediaDevices ||
!navigator.mediaDevices.getUserMedia) {
console.log("getUserMedia is not supported!")
return;
}
navigator.mediaDevices.getUserMedia({
video: true,
audio: false
})
.then(function (stream) {
localStream = stream;
localVideo.srcObject = localStream;
conn();
})
.catch(function (err) {
console.error("getUserMedia error:", err);
})
}
function leave() {
if (socket) {
socket.emit('leave', roomid);
}
closePeerConnection();
closeLocalMedia();
btnConn.disabled = false;
btnLeave.disabled = true;
}
function closeLocalMedia() {
if (localStream && localStream.getTracks()) {
localStream.getTracks().forEach((track) => {
track.stop();
});
}
localStream = null;
}
function closePeerConnection() {
console.log('close RTCPeerConnection!');
if (pc) {
pc.close();
pc = null;
}
}
function createPeerConnection() {
console.log('create RTCPeerConnection!');
if (!pc) {
pc = new RTCPeerConnection({
'iceServers': [{
'urls': 'turn:127.0.0.1:8000',
'credential': '123456',
'username': 'autofelix'
}]
});
pc.onicecandidate = (e) => {
if (e.candidate) {
sendMessage(roomid, {
type: 'candidate',
label: e.candidate.sdpMLineIndex,
id: e.candidate.sdpMid,
candidate: e.candidate.candidate
});
}
}
pc.ondatachannel = e => {
dc = e.channel;
dc.onmessage = reveivemsg;
dc.onopen = dataChannelStateChange;
dc.onclose = dataChannelStateChange;
dc.onerror = dataChannelError;
}
pc.ontrack = (e) => {
remoteVideo.srcObject = e.streams[0];
}
}
if (pc === null || pc === undefined) {
console.error('pc is null or undefined!');
return;
}
if (localStream === null || localStream === undefined) {
console.error('localStream is null or undefined!');
return;
}
if (localStream) {
localStream.getTracks().forEach((track) => {
pc.addTrack(track, localStream);
})
}
}
function send() {
var data = send_txt.value;
if (data) {
dc.send(data);
}
send_txt.value = "";
chat.value += '<-' + data + '\r\n';
}
</script>
</html>
三、文件传输
- 实时文件的传输与实时文本消息传输的基本原理是一样的，都是使用 RTCDataChannel 对象进行传输
- 它们的区别一方面是传输数据的类型不一样，另一方面是数据的大小不一样
- 在传输文件的时候，必须要保证文件传输的有序性和完整性，所以需要设置 ordered 和 maxRetransmits 选项
- 发送数据如下：
var options = {
ordered: true,
maxRetransmits: 30
};
var pc = new RTCPeerConnection();
sendChannel = pc.createDataChannel(name, options)；
sendChannel.addEventListener('open', onSendChannelStateChange);
sendChannel.addEventListener('close', onSendChannelStateChange);
sendChannel.send(JSON.stringify({
type: 'fileinfo',
name: file.name,
size: file.size,
filetype: file.type,
lastmodify: file.lastModified
}));
var offset = 0;
var chunkSize = 16384;
var file = fileInput.files[0];
fileReader = new FileReader();
fileReader.onload = e => {
dc.send(e.target.result);
offset += e.target.result.byteLength;
if (offset < file.size) {
readSlice(offset);
}
}
var readSlice = o => {
const slice = file.slice(offset, o + chunkSize);
fileReader.readAsArrayBuffer(slice);
};
readSlice(0);
- 接收数据如下：
- 当有数据到达时就会触发该事件就会触发 onmessage 事件
- 只需要简单地将收到的这块数据 push 到 receiveBuffer 数组中即可
var receiveBuffer = [];
var receiveSize = 0;
onmessage = (event) => {
receiveBuffer.push(event.data);
receivedSize += event.data.byteLength;
if (receivedSize === fileSize) {
var received = new Blob(receiveBuffer, { type: 'application/octet-stream' });
receiveBuffer = [];
receiveSize = 0;
downloadAnchor.href = URL.createObjectURL(received);
downloadAnchor.download = fileName;
downloadAnchor.textContent = `Click to download '${fileName}' (${fileSize} bytes)`;
downloadAnchor.style.display = 'block';
}
}
