[go]websocket

darylove

2020-01-18

http的特点

半双工: 同一个时刻,只能单向传数据(request/response).
服务器不能主动给客户端推消息

[go]websocket

轮询(polling)
不断的建立http连接，严重浪费了服务器端和客户端的资源. 人越多,服务器压力越大.

- server.js

let express = require('express');
let app = express();
app.use(express.static(__dirname));

app.get("/clock", function (req, res) {
    res.end(new Date().toLocaleTimeString());
});
app.listen(8080);

- client

<body>
<div id="clock"></div>
<script>
    setInterval(function () {
        let xhr = new XMLHttpRequest();
        xhr.open('GET', 'http://localhost:8080/clock', true);
        xhr.onreadystatechange = function () {
            if (xhr.readyState === 4 && xhr.status === 200) {
                document.querySelector('#clock').innerHTML = xhr.responseText;
            }
        };
        xhr.send();
    }, 1000);
</script>
</body>

- 访问http://localhost:8080/clock

长轮询(long polling)(comet)
当一次请求完成后, 在发起进行下一次

- client


<body>
<div id="clock"></div>
<script>
    setInterval(function () {
        let xhr = new XMLHttpRequest();
        xhr.open('GET', 'http://localhost:8080/clock', true);
        xhr.onreadystatechange = function () {
            if (xhr.readyState === 4 && xhr.status === 200) {
                document.querySelector('#clock').innerHTML = xhr.responseText;
            }
        };
        xhr.send();
    }, 1000);
</script>
</body>

- server.js


let express = require('express');
let app = express();
app.use(express.static(__dirname));

app.get("/clock", function (req, res) {
    //优化: 当时间为每隔5的倍数才返回.
    let $timer = setInterval(function () {
        let date = new Date();
        let seconds = date.getSeconds();
        if (seconds % 5 === 0) {
            res.end(new Date().toLocaleTimeString());
            clearInterval($timer)
        }
    }, 1000);

});
app.listen(8080);

iframe流
打开浏览器会主动请求iframe页
iframe可以调用parent父类的方法
缺点: server不断开连接.浏览器一直转圈.

- server.js
const express = require('express');
const app = express();
app.use(express.static(__dirname));
app.get('/clock', function (req, res) {
    res.header("Content-Type", "text/html");
    setInterval(function () {
        res.write(`
            <script type="text/javascript">
                parent.setTime("${new Date().toLocaleTimeString()}");
            </script>
        `);
    }, 1000);
});
app.listen(8080);

- client

<body>
<div id="clock"></div>
<iframe src="/clock" style="display:none"></iframe>
<script>
    function setTime(ts) {
        document.querySelector('#clock').innerHTML = ts;
    }
</script>
</body>

长连接（SSE）

SSE的简单模型是：
    一个客户端去从服务器端订阅一条流，
    之后服务端可以发送消息给客户端直到服务端或者客户端关闭该“流”，
    所以eventsource也叫作"server-sent-event`

MIME格式为text/event-stream
必须编码成utf-8的格式
消息的每个字段使用"\n"来做分割,最后用\n\n表示结束
常用的消息key
    Event: 事件类型,消息名称要和前端对应,如定义的event: xxx, 则前端可以用onxxx对应
    Data: 发送的数据
    ID: 每一条事件流的ID

不支持跨域

- server

let express = require('express');
let app = express();
app.use(express.static(__dirname));
let sendCount = 1;
app.get('/eventSource', function (req, res) {
    res.header('Content-Type', 'text/event-stream',);
    setInterval(() => {
        res.write(`id:${sendCount++}\nevent:message\ndata:${new Date().toLocaleTimeString()}\n\n`);
    }, 1000)
});
app.listen(8080);

- client

<body>
<div id="clock"></div>
<script>
    var eventSource = new EventSource('/eventSource');
    eventSource.onmessage = function (e) {
        document.querySelector('#clock').innerHTML =e.data
    };
    eventSource.onerror = function (err) {
        console.log(err);
    }
</script>
</body>

WebSocket

- server.js

const path = require('path');
let app = express();
let server = require('http').createServer(app);
app.get('/', function (req, res) {
    res.sendFile(path.resolve(__dirname, 'index.html'));
});
app.listen(3000);


//-----------------------------------------------
let WebSocketServer = require('ws').Server;
let wsServer = new WebSocketServer({ port: 8888 });
wsServer.on('connection', function (socket) {
    console.log('连接成功');
    socket.on('message', function (message) {
        console.log('接收到客户端消息:' + message);
        socket.send('服务器回应:' + message);
    });
});

- client

    <script>
        let ws = new WebSocket('ws://localhost:8888');
        ws.onopen = function () {
            console.log('客户端连接成功');
            ws.send('hello');
        }
        ws.onmessage = function (event) {
            console.log('收到服务器的响应 ' + event.data);
        }
    </script>

websocket 科技新闻