How to use form-data format to transfer files in NodeJs
这篇文章主要介绍了NodeJs form-data格式传输文件的方法，小编觉得挺不错的，现在分享给大家，也给大家做个参考。一起跟随小编过来看看吧
本文介绍了Node Js 使用KOA处理form-data格式传输过来的文件，分享给大家。具体如下：
使用koa有一段时间了，评价是小巧精悍，只封装了基本的如request对象和response对象到上下文中，其他功能基本上靠第三方中间件来实现。导致的问题是使用起来就不太方便了，比如用koa上传文件，网上资料有限，对于小白而言，文件上传操作就困难多了。
form表单上传文件流程（PHP和node js）
文件上传操作原理
form表单【注意：enctype=”multipart/form-data”】上传文件时，首先会将文件上传到你本机的temp目录，然后执行move_upload_file(tmpfile,newfile);然后node会不会是这样呢？答案是确定的，上传文件大家都是一样的思路。
//var tmpath = path.join(os.tmpdir(), '1.txt');//模拟上传到临时目录的文件 //console.log(tmpath); //var ext = ".txt";//上传后生成文件的后缀，一般和上传的文件后缀一致 //var ph = path.join('public/upload', Date.parse(new Date()).toString() + ext);//生成新的上传文件路径全称 //console.log(ph); //var stream = fs.createWriteStream(ph);//创建一个可写流 //fs.createReadStream(tmpath).pipe(stream);//可读流通过管道写入可写流
然后分析了下上面代码：
fs.createWriteStream(path.join(os.tmpdir(), Math.random().toString()));
这里创建一个可写的流对象，即创建一个表单上传后移动到新目录的空文件；而os.tmpDir()刚好是本机临时目录，上面代码表示在临时目录下生成一个随机数空文件；
part.pipe(stream);
上面的代码表示将可读流对象内容写入到可写的流对象，即上面生成的临时文件下的文件；part是将request里面的文件对象解析成可读流。
然后koa文件上传原理就清楚了。通过表单上传文件，文件默认会存放到本机临时目录下生成一个临时文件。然后通过流的形式，打开这个临时文件将数据写入到一个新地址的可写文件流里面，前提是要提前创建这个空的可写流文件，即我们上传目标文件。
KOA2解析传输过来的post form-data信息
const Koa = require('koa');
const app = new Koa();
const bodyParser = require('koa-bodyparser');
const koaBody = require('koa-body');
const router = require('./router');
// 输出请求路径，每次请求都会输出
app.use(async (ctx, next) => {
console.log(`Process ${ctx.request.method} ${ctx.request.url}...`);
await next();
});
// 文件上传，注意书写的位置很重要，否则无法上传
app.use(koaBody({ multipart: true }));
// 解析请求体
app.use(bodyParser());
// 使用路由
app.use(router());
app.listen(3000);
console.log('app started at port 3000...');总结一下的话，就是前端用form传递文件，bodyParse解析出这个form，对应的字段是ctx.request.body.files.字段名称(eg: abc)，最后通过拷贝临时的数据文件来达到上传存储的目的。
bodyParse解析出的格式：
{ fields: { aaa: '123345' }, //Text类型的解析到fields中
files: //File类型的解析到files中
{
abc:
File {
domain: null,
_events: {},
_eventsCount: 0,
_maxListeners: undefined,
size: 12525,
path: 'C:\\Users\\DANNYJ~1\\AppData\\Local\\Temp\\upload_d896dcc755fcd36156c6814aafb7685e',
name: 'bamboo5.png',
type: 'image/png',
hash: null,
lastModifiedDate: 2017-12-08T10:17:04.355Z,
_writeStream: [Object] }
}
}KOA2将POST传过来的文件存储到本地
var file = ctx.request.body.files.abc //传输文件的name是abc console.log(ctx.request.body) var tmpath= file['path']; var tmparr =file['name'].split('.'); var ext ='.'+tmparr[tmparr.length-1]; var newpath =path.join('./', parseInt(Math.random()*100) + Date.parse(new Date()).toString() + ext); console.log(tmpath); console.log(newpath); var stream = fs.createWriteStream(newpath);//创建一个可写流 fs.createReadStream(tmpath).pipe(stream);//可读流通过管道写入可写流
然后就会发现项目当前目录下面就会多出上传的文件了。
上面是我整理给大家的，希望今后会对大家有帮助。
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详细解答Webpack+Babel+React环境搭建（详细教程）
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