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关于node.js:Nodejs实现分片上传

jiezi

大文件上传会耗费大量的工夫，而且中途有可能上传失败。这时咱们须要前端和后端配合来解决这个问题。

解决步骤：

  1. 文件分片，缩小每次申请耗费的工夫，如果某次申请失败能够独自上传，而不是从头开始
  2. 告诉服务端合并文件分片
  3. 管制并发的申请数量，防止浏览器内存溢出
  4. 当因为网络或者其余起因导致某次的申请失败，咱们从新发送申请

文件的分片与合并

在 JavaScript 中，FIle 对象是 ’ Blob ‘ 对象的子类，该对象蕴含一个重要的办法 slice，通过该办法咱们能够这样宰割二进制文件:

<!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>
    <script src="https://cdn.bootcdn.net/ajax/libs/axios/0.24.0/axios.min.js"></script>
</head>
<body>
    <input type="file" multiple="multiple" id="fileInput" />
    <button onclick="SliceUpload()"> 上传 </button>  
    <script>
        function SliceUpload() {const file = document.getElementById('fileInput').files[0]
            if (!file) return

            // 文件分片
            let size = 1024 * 50; //50KB 50KB Section size
            let fileChunks = [];
            let index = 0;        //Section num
            for (let cur = 0; cur < file.size; cur += size) {
                fileChunks.push({
                    hash: index++,
                    chunk: file.slice(cur, cur + size),
                });
            }

            // 上传分片
            const uploadList = fileChunks.map((item, index) => {let formData = new FormData();
                formData.append("filename", file.name);
                formData.append("hash", item.hash);
                formData.append("chunk", item.chunk);
                return axios({
                    method: "post",
                    url: "/upload",
                    data: formData,
                });
            });
            await Promise.all(uploadList);

            // 所有分片上传实现，告诉服务器合并分片
            await axios({
                method: "get",
                url: "/merge",
                params: {filename: file.name,},
            });
            console.log("Upload to complete");
        }
    </script>
</body>
</html>

并发管制

如果文件很大，这样切分的分片会很多，浏览器短时间内就会发动大量的申请，可能会导致内存耗尽，所以要进行并发管制。

这里咱们联合 Promise.race() 办法 管制并发申请的数量，防止浏览器内存溢出。

// 退出并发管制
async function SliceUpload() {const file = document.getElementById('fileInput').files[0]
    if (!file) return

    // 文件分片
    let size = 1024 * 50; //50KB 50KB Section size
    let fileChunks = [];
    let index = 0;        //Section num
    for (let cur = 0; cur < file.size; cur += size) {
        fileChunks.push({
            hash: index++,
            chunk: file.slice(cur, cur + size),
        });
    }

    let pool = []; //Concurrent pool
    let max = 3; //Maximum concurrency
    for (let i = 0; i < fileChunks.length; i++) {let item = fileChunks[i];
        let formData = new FormData();
        formData.append("filename", file.name);
        formData.append("hash", item.hash);
        formData.append("chunk", item.chunk);

        // 上传分片
        let task = axios({
            method: "post",
            url: "/upload",
            data: formData,
        });
        task.then(() => {
        // 从并发池中移除曾经实现的申请
        let index = pool.findIndex((t) => t === task);
            pool.splice(index);
        });

        // 把申请放入并发池中，如果曾经达到最大并发量
        pool.push(task);
        if (pool.length === max) {
            //All requests are requested complete
            await Promise.race(pool);
        }
    }

    // 所有分片上传实现，告诉服务器合并分片
    await axios({
        method: "get",
        url: "/merge",
        params: {filename: file.name,},
    });
    console.log("Upload to complete");
}

使代码可复用 

function SliceUpload() {const file = document.getElementById('fileInput').files[0]
    if (!file) return

    // 文件分片
    let size = 1024 * 50; // 分片大小设置
    let fileChunks = [];
    let index = 0;        // 分片序号
    for (let cur = 0; cur < file.size; cur += size) {
        fileChunks.push({
            hash: index++,
            chunk: file.slice(cur, cur + size),
        });
    }

    const uploadFileChunks = async function(list){if(list.length === 0){
            // 所有分片上传实现，告诉如无
            await axios({
                method: 'get',
                url: '/merge',
                params: {filename: file.name}
            });
            console.log('Upload to complete')
            return
        }

        let pool = []       // 并发池
        let max = 3         // 最大并发数
        let finish = 0      // 实现数量
        let failList = []   // 失败列表
        for(let i=0;i<list.length;i++){let item = list[i]
            let formData = new FormData()
            formData.append('filename', file.name)
            formData.append('hash', item.hash)
            formData.append('chunk', item.chunk)
            
            let task = axios({
                method: 'post',
                url: '/upload',
                data: formData
            })

            task.then((data)=>{
                // 从并发池中移除曾经实现的申请
                let index = pool.findIndex(t=> t===task)
                pool.splice(index)
            }).catch(()=>{failList.push(item)
            }).finally(()=>{
                finish++
                // 如果有失败的从新上传
                if(finish===list.length){uploadFileChunks(failList)
                }
            })
            pool.push(task)
            if(pool.length === max){await Promise.race(pool)
            }
        }
    }

    uploadFileChunks(fileChunks)
}

服务端接口实现 

const express = require('express')
const multiparty = require('multiparty')
const fs = require('fs')
const path = require('path')
const {Buffer} = require('buffer')
// file path
const STATIC_FILES = path.join(__dirname, './static/files')
// Temporary path to upload files
const STATIC_TEMPORARY = path.join(__dirname, './static/temporary')
const server = express()
// Static file hosting
server.use(express.static(path.join(__dirname, './dist')))
// Interface for uploading slices
server.post('/upload', (req, res) => {const form = new multiparty.Form();
    form.parse(req, function(err, fields, files) {let filename = fields.filename[0]
        let hash = fields.hash[0]
        let chunk = files.chunk[0]
        let dir = `${STATIC_TEMPORARY}/${filename}`
        // console.log(filename, hash, chunk)
        try {if (!fs.existsSync(dir)) fs.mkdirSync(dir)
            const buffer = fs.readFileSync(chunk.path)
            const ws = fs.createWriteStream(`${dir}/${hash}`)
            ws.write(buffer)
            ws.close()
            res.send(`${filename}-${hash} Section uploaded successfully`)
        } catch (error) {console.error(error)
            res.status(500).send(`${filename}-${hash} Section uploading failed`)
        }
    })
})

//Merged slice interface
server.get('/merge', async (req, res) => {const { filename} = req.query
    try {
        let len = 0
        const bufferList = fs.readdirSync(`${STATIC_TEMPORARY}/${filename}`).map((hash,index) => {const buffer = fs.readFileSync(`${STATIC_TEMPORARY}/${filename}/${index}`)
            len += buffer.length
            return buffer
        });
        //Merge files
        const buffer = Buffer.concat(bufferList, len);
        const ws = fs.createWriteStream(`${STATIC_FILES}/${filename}`)
        ws.write(buffer);
        ws.close();
        res.send(`Section merge completed`);
    } catch (error) {console.error(error);
    }
})

server.listen(3000, _ => {console.log('http://localhost:3000/')
})
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