“最小可运行”的一对一 WebRTC 视频聊天示例（前端＋信令服务器），完全按照你给出的 8 条信令流程图实现。
技术栈：
- 前端：原生 JavaScript + socket.io-client
- 信令服务器：Node.js + socket.io + Express（80 端口同时提供静态文件和信令）
- STUN/TURN：Google 公共 STUN 即可，生产环境请换成自己的 TURN
代码可直接复制到同一目录运行，局域网两台浏览器打开 http://localhost 即可互拨。
- 目录结构
webrtc-1v1/
├─ server.js // 信令服务器
├─ public/
│ ├─ index.html // 页面
│ └─ client.js // 前端逻辑
└─ package.json
- 安装依赖
npm init -y
npm i express socket.io
- 信令服务器 server.js
const express = require('express');
const http = require('http');
const socketIo = require('socket.io');
const path = require('path');const app = express();
const server = http.createServer(app);
const io = socketIo(server, { cors: { origin: '*' } });// 房间 => Set<socketId>
const rooms = new Map();app.use(express.static(path.join(__dirname, 'public')));io.on('connection', socket => {console.log('connect', socket.id);/* 1. join 加入房间 */socket.on('join', room => {socket.join(room);socket.room = room;const others = rooms.get(room) || new Set();if (others.size >= 1) {// 2. resp-join 返回另一个人的 uidsocket.emit('resp-join', [...others][0]);}others.add(socket.id);rooms.set(room, others);// 4. new-peer 通知房间里其他人socket.to(room).emit('new-peer', socket.id);});/* 3. leave 离开房间 */socket.on('leave', () => leaveRoom(socket));socket.on('disconnect', () => leaveRoom(socket));/* 6. offer 转发 */socket.on('offer', ({ target, sdp }) => {socket.to(target).emit('offer', { from: socket.id, sdp });});/* 7. answer 转发 */socket.on('answer', ({ target, sdp }) => {socket.to(target).emit('answer', { from: socket.id, sdp });});/* 8. candidate 转发 */socket.on('candidate', ({ target, candidate }) => {socket.to(target).emit('candidate', { from: socket.id, candidate });});function leaveRoom(sock) {if (!sock.room) return;const room = sock.room;const others = rooms.get(room);if (others) {others.delete(sock.id);if (others.size === 0) rooms.delete(room);else {// 5. peer-leave 通知剩余的人sock.to(room).emit('peer-leave', sock.id);}}sock.leave(room);delete sock.room;}
});server.listen(80, () => console.log('HTTP+Socket.io on 80'));
- 前端 public/index.html
<!doctype html>
<html>
<head><meta charset="utf-8"/><title>WebRTC 1v1</title><style>video{width:240px;height:180px;background:#000;margin:6px}</style>
</head>
<body><h3>WebRTC 一对一</h3><input id="room" placeholder="房间名"/><button id="btnJoin">加入</button><button id="btnLeave" disabled>离开</button><br/><video id="local" autoplay muted></video><video id="remote" autoplay></video><script src="/socket.io/socket.io.js"></script><script src="client.js"></script>
</body>
</html>
- 前端 public/client.js
const localVideo = document.getElementById('local');
const remoteVideo = document.getElementById('remote');
const roomInput = document.getElementById('room');
const btnJoin = document.getElementById('btnJoin');
const btnLeave = document.getElementById('btnLeave');let localStream;
let pc; // RTCPeerConnection
let socket;
let roomName;
let otherId = null; // 对端 socket.idbtnJoin.onclick = async () => {roomName = roomInput.value.trim();if (!roomName) return;socket = io();/* 1. join */socket.emit('join', roomName);/* 2. resp-join：如果房间已有人，立即发起 offer */socket.on('resp-join', async uid => {otherId = uid;await createPeerConnection();const offer = await pc.createOffer();await pc.setLocalDescription(offer);socket.emit('offer', { target: otherId, sdp: offer });});/* 4. new-peer：有人后进来，我作为“被叫” */socket.on('new-peer', async uid => {otherId = uid;await createPeerConnection();});/* 5. peer-leave：对方离开 */socket.on('peer-leave', () => {closeCall();});/* 6. offer */socket.on('offer', async ({ from, sdp }) => {if (!pc) await createPeerConnection();await pc.setRemoteDescription(sdp);const answer = await pc.createAnswer();await pc.setLocalDescription(answer);socket.emit('answer', { target: from, sdp: answer });});/* 7. answer */socket.on('answer', async ({ from, sdp }) => {await pc.setRemoteDescription(sdp);});/* 8. candidate */socket.on('candidate', async ({ from, candidate }) => {await pc.addIceCandidate(candidate);});socket.on('connect', async () => {localStream = await navigator.mediaDevices.getUserMedia({ video: true, audio: true });localVideo.srcObject = localStream;});btnJoin.disabled = true;btnLeave.disabled = false;
};btnLeave.onclick = () => {if (socket) {socket.emit('leave');socket.close();}closeCall();btnJoin.disabled = false;btnLeave.disabled = true;
};async function createPeerConnection() {pc = new RTCPeerConnection({iceServers: [{ urls: 'stun:stun.l.google.com:19302' }]});localStream.getTracks().forEach(t => pc.addTrack(t, localStream));pc.ontrack = e => {remoteVideo.srcObject = e.streams[0];};pc.onicecandidate = e => {if (e.candidate && otherId) {socket.emit('candidate', { target: otherId, candidate: e.candidate });}};
}function closeCall() {if (pc) {pc.close();pc = null;}remoteVideo.srcObject = null;otherId = null;
}
- 运行
sudo node server.js # 监听 80 端口需 sudo
浏览器打开 http://localhost，A/B 两台机器输入相同房间名即可互拨。
控制台可看到 8 条信令按顺序打印，完全符合题目流程图。
- 生产环境注意
- 把 Google STUN 换成自建 TURN（coturn），否则 NAT 穿墙失败率很高。
- 信令服务器务必加 HTTPS/WSS，否则最新浏览器禁止 getUserMedia。
- 增加异常处理、断线重连、摄像头/麦克风权限错误提示。
- 若要做移动端，需加
playsinline、自动播放策略处理。
![P5797 [SEERC 2019] Max or Min](http://pic.xiahunao.cn/P5797 [SEERC 2019] Max or Min)
