共计 4981 个字符，预计需要花费 13 分钟才能阅读完成。
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 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/')
})正文完