What are node middlewares?

Node middleware includes: 1. koa-bodyparser; 2. koa-body; 3. Static resource manager koa-static; 4. cors; 5. koa-cors; 6. koa-cors2 setting request Wait.

The operating environment of this article: Windows 7 system, nodejs version 10.16.2, Dell G3 computer.

What are the node middlewares?

Node middleware type:

Node middleware is the function of processing http requests encapsulated in the program. Node middleware is executed in the pipeline. Middleware sits on top of the client/server operating system and manages computer resources and network communications.

Middleware serves the main logical business and can be divided into: application-level middleware, routing-level middleware, built-in middleware, third-party middleware, and error-level middleware.

Commonly used middleware in node:

In the process of learning node, I have accumulated many useful middleware. Most of these middlewares need to be used with koa

1, koa-bodyparser

This plug-in is used to parse the parameters brought by the front-end post request

//入口文件
const bodyParser = require('koa-bodyparser');
app.use(bodyParser({//设置可以接收的数据类型
    enableTypes:['json', 'form', 'text']
}))
async function (ctx) {
    console.log(ctx.request.body)
    ctx.req.on('data',(data) => {
        console.log(JSON.parse(data),'文件')
    })
}

is not introduced In the case of koa-bodyparser, parameters can only be obtained through ctx.req.on('data',callback)

. After introducing middleware, parameters can be obtained as long as ctx.request.body. Much more convenient than the first one.

2. koa-body

This plug-in is used to obtain the files and file information uploaded in the request, such as pictures and zip files

const koaBody    = require('koa-body')
app.use(koaBody({
        multipart: true,
        formidable: {
            maxFileSize: 20 * 1024 * 1024    // 设置上传文件大小最大限制，默认2M
        }
    }))

It can be used during the processing of the request Information about all uploaded files can be obtained directly through ctx.request.files.

Notice! ! ! After using koa-body, do not use koa-bodyparser. It will conflict, causing the status code returned by the front-end post request to be canceled

3. The static resource manager koa-static

was tested locally. At that time, I uploaded a picture, and then printed the picture address to be a long string of c://.../name/.png. Although it can be accessed locally, it will not work if it is placed on the server!

By introducing koa-static, you can specify the static file address to a folder on the project path and then access the image directly through the port monitored by koa at http://192.168.0.177:3030/name.png

const koaStatic  = require('koa-static')
app.use(koaStatic('./public'))//括号中是设置的静态文件路径

4, cors, koa-cors, koa-cors2 set request headers

I basically use these middlewares to configure cross-domain and request header information

const cors       = require('koa2-cors') 
app.use(cors({
    exposeHeaders: ['multipart/form-data','application/x-www-form-urlencoded']
}))

You can set the parameters yourself or you can directly apply app.use(cors()) without setting parameters to cross domain.

Speaking of cross-domain here, let me mention the cross-domain setting method of native node (you can also set various configurations of the request header)

app.use(async (ctx, next) => {
   ctx.set('Access-Control-Allow-Origin', ctx.headers.origin)//'*'有可能会问题
   ctx.set('Access-Control-Allow-Credentials', 'true')
   ctx.set('Access-Control-Allow-Headers', 'Origin ,multipart/form-data, X-Requested-With, Content-Type, Accept')
   await next()
})

If you encounter any useful ones in the future The middleware will record again! ! !

Recommended learning: "node.js Video Tutorial"

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