前端多线程大文件下载实践，提速10倍(拿捏百度云盘)

GET /360_0388.jpg HTTP/1.1
Host: limit.qiufeng.com
Connection: keep-alive
...
Range: bytes=0-102399
HTTP/1.1 206 Partial Content
Server: openresty/1.13.6.2
Date: Sat, 19 Sep 2020 06:31:11 GMT
Content-Type: image/jpeg
Content-Length: 102400
....
Content-Range: bytes 0-102399/3670627
...（这里是文件流）

router.get('/api/rangeFile', async(ctx) => {
    const { filename } = ctx.query;
    const { size } = fs.statSync(path.join(__dirname, './static/', filename));
    const range = ctx.headers['range'];
    if (!range) {
        ctx.set('Accept-Ranges', 'bytes');
        ctx.body = fs.readFileSync(path.join(__dirname, './static/', filename));
        return;
    }
    const { start, end } = getRange(range);
    if (start >= size || end >= size) {
        ctx.response.status = 416;
        ctx.body = '';
        return;
    }
    ctx.response.status = 206;
    ctx.set('Accept-Ranges', 'bytes');
    ctx.set('Content-Range', `bytes ${start}-${end ? end : size - 1}/${size}`);
    ctx.body = fs.createReadStream(path.join(__dirname, './static/', filename), { start, end });
})

router.get('/api/rangeFile', async(ctx) => {
    const { filename } = ctx.query;
    const { size } = fs.statSync(path.join(__dirname, './static/', filename));
    const range = ctx.headers['range'];
    if (!range) {
        ctx.set('Accept-Ranges', 'bytes');
        ctx.body = fs.readFileSync(path.join(__dirname, './static/', filename));
        return;
    }
    const { start, end } = getRange(range);
    if (start >= size || end >= size) {
        ctx.response.status = 416;
        ctx.body = '';
        return;
    }
    ctx.response.status = 206;
    ctx.set('Accept-Ranges', 'bytes');
    ctx.set('Content-Range', `bytes ${start}-${end ? end : size - 1}/${size}`);
    ctx.body = fs.createReadStream(path.join(__dirname, './static/', filename), { start, end });
})

<!-- html -->
<button id="download1">串行下载</button>
<button id="download2">多线程下载</button>
<script src="https://cdn.bootcss.com/axios/0.19.2/axios.min.js"></script>

const m = 1024 * 520;  // 分片的大小
const url = 'http://localhost:8888/api/rangeFile?filename=360_0388.jpg'; // 要下载的地址

download1.onclick = () => {
    console.time("直接下载");
    function download(url) {
        const req = new XMLHttpRequest();
        req.open("GET", url, true);
        req.responseType = "blob";
        req.onload = function (oEvent) {
            const content = req.response;
            const aTag = document.createElement('a');
            aTag.download = '360_0388.jpg';
            const blob = new Blob([content])
            const blobUrl = URL.createObjectURL(blob);
            aTag.href = blobUrl;
            aTag.click();
            URL.revokeObjectURL(blob);
            console.timeEnd("直接下载");
        };
        req.send();
    }
    download(url);
}

// script
function downloadRange(url, start, end, i) {
    return new Promise((resolve, reject) => {
        const req = new XMLHttpRequest();
        req.open("GET", url, true);
        req.setRequestHeader('range', `bytes=${start}-${end}`)
        req.responseType = "blob";
        req.onload = function (oEvent) {
            req.response.arrayBuffer().then(res => {
                resolve({
                    i,
                    buffer: res
                });
            })
        };
        req.send();
    })
}
// 合并buffer
function concatenate(resultConstructor, arrays) {
    let totalLength = 0;
    for (let arr of arrays) {
        totalLength += arr.length;
    }
    let result = new resultConstructor(totalLength);
    let offset = 0;
    for (let arr of arrays) {
        result.set(arr, offset);
        offset += arr.length;
    }
    return result;
}
download2.onclick = () => {
    axios({
        url,
        method: 'head',
    }).then((res) => {
        // 获取长度来进行分割块
        console.time("并发下载");
        const size = Number(res.headers['content-length']);
        const length = parseInt(size / m);
        const arr = []
        for (let i = 0; i < length; i++) {
            let start = i * m;
            let end = (i == length - 1) ?  size - 1  : (i + 1) * m - 1;
            arr.push(downloadRange(url, start, end, i))
        }
        Promise.all(arr).then(res => {
            const arrBufferList = res.sort(item => item.i - item.i).map(item => new Uint8Array(item.buffer));
            const allBuffer = concatenate(Uint8Array, arrBufferList);
            const blob = new Blob([allBuffer], {type: 'image/jpeg'});
            const blobUrl = URL.createObjectURL(blob);
            const aTag = document.createElement('a');
            aTag.download = '360_0388.jpg';
            aTag.href = blobUrl;
            aTag.click();
            URL.revokeObjectURL(blob);
            console.timeEnd("并发下载");
        })
    })
}

// 进入目录
cd file-download
// 启动
node server.js
// 打开 
http://localhost:8888/example/download-multiple/index.html

// https://source.chromium.org/chromium/chromium/src/+/refs/tags/87.0.4268.1:net/socket/client_socket_pool_manager.cc;l=47
// Default to allow up to 6 connections per host. Experiment and tuning may
// try other values (greater than 0).  Too large may cause many problems, such
// as home routers blocking the connections!?!?  See http://crbug.com/12066.
//
// WebSocket connections are long-lived, and should be treated differently
// than normal other connections. Use a limit of 255, so the limit for wss will
// be the same as the limit for ws. Also note that Firefox uses a limit of 200.
// See http://crbug.com/486800
int g_max_sockets_per_group[] = {
    6,   // NORMAL_SOCKET_POOL
    255  // WEBSOCKET_SOCKET_POOL
};

server {
    listen 80;
    server_name limit.qiufeng.com;
    access_log  /opt/logs/wwwlogs/limitqiufeng.access.log;
    error_log  /opt/logs/wwwlogs/limitqiufeng.error.log;
    add_header Cache-Control max-age=60;
    add_header Access-Control-Allow-Origin *;
    add_header Access-Control-Allow-Methods 'GET, OPTIONS';
    add_header Access-Control-Allow-Headers 'DNT,X-Mx-ReqToken,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Authorization,range,If-Range';
    if ($request_method = 'OPTIONS') {
        return 204;
    }
    limit_rate 1M;
    location / {
        root 你的静态目录;
        index index.html;
    }
}

127.0.0.1 limit.qiufeng.com

修改代码中的下载地址
const url = 'http://localhost:8888/api/rangeFile?filename=360_0388.jpg';
变成
const url = 'http://limit.qiufeng.com/360_0388.jpg';

server {
    listen 443 ssl http2;
    ssl on;
    ssl_certificate /usr/local/openresty/nginx/conf/ssl/server.crt;
    ssl_certificate_key /usr/local/openresty/nginx/conf/ssl/server.key;
    ssl_session_cache shared:le_nginx_SSL:1m;
    ssl_session_timeout 1440m;
    ssl_protocols SSLv3 TLSv1 TLSv1.1 TLSv1.2;
    ssl_ciphers RC4:HIGH:!aNULL:!MD5;
    ssl_prefer_server_ciphers on;
    server_name limit.qiufeng.com;
    access_log  /opt/logs/wwwlogs/limitqiufeng2.access.log;
    error_log  /opt/logs/wwwlogs/limitqiufeng2.error.log;
    add_header Cache-Control max-age=60;
    add_header Access-Control-Allow-Origin *;
    add_header Access-Control-Allow-Methods 'GET, OPTIONS';
    add_header Access-Control-Allow-Headers 'DNT,X-Mx-ReqToken,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Authorization,range,If-Range';
    if ($request_method = 'OPTIONS') {
        return 204;
    }
    limit_rate 1M;
    location / {
        root 你存放项目的前缀路径/node-demo/file-download/;
        index index.html;
    }
}

将单个下载大小进行修改
const m = 1024 * 400;

// 测试脚本，由于太长了，而且如果仔细看了上面的文章也应该能写出代码。实在写不出可以看以下代码。
https://github.com/hua1995116/node-demo/blob/master/file-download/example/download-multiple/script.js

url 改成对应百度云下载链接
m 改成 1024 * 1024 * 2 合适的分片大小~