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：
- 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
- 告诉服务端合并文件分片
- 管制并发的申请数量，防止浏览器内存溢出
- 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 pathconst STATIC_FILES = path.join(__dirname, './static/files')// Temporary path to upload filesconst STATIC_TEMPORARY = path.join(__dirname, './static/temporary')const server = express()// Static file hostingserver.use(express.static(path.join(__dirname, './dist')))// Interface for uploading slicesserver.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 interfaceserver.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/')})