Koa

preface

We use HTTP, FS and other modules directly to build a simple server is not a big problem, but when the business logic is more and more troublesome, our own code will be more and more, more and more trouble, repeatability is also high
At this time, we will be very comfortable to use the framework. The framework will not add functions for us, but provide us with the encapsulation and arrangement of our business in accordance with certain rules, so that we can use it easily and conveniently
The mainstream frameworks used by Node webServer include Express and Koa
- Express has a lot of built-in middleware, which is highly integrated and easy to use
- Koa is lightweight, compact and easy to customize
Let’s take a look at Koa

Introduction to the

Koa was built by the original Express team to be a smaller, more expressive, and more robust Web framework. Composing web applications using KOA eliminates repetitive and tedious nesting of callback functions and greatly improves error handling efficiency by combining different generators. Koa doesn’t bundle any middleware into kernel methods, it just provides a lightweight and elegant library of functions that makes writing Web applications a breeze
The main job of a Webserver is to parse the request -> process the response, and Koa encapsulates the basic logic of both and provides interfaces to extend them

The installation

Koa requires Node V7.6.0 or later to support ES2015, asynchronous methods

npm install koa
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Implementing the first server with Koa (simple use)

A Koa application is an object that contains a set of middleware Generator functions. These middleware functions are organized in a stack-like structure and executed sequentially based on request requests
The core design idea of Koa is to provide high-level syntactic sugar encapsulation for the middleware layer to enhance its interoperability and robustness, and to make writing middleware a lot more fun

// Reference the Koa framework
const Koa = require('koa');
// Instantiate an app object
const app = new Koa();
// KoA uses the use syntax for the middle key
app.use(ctx= > {
    // ctx.body equals http.createserver ((req, res) => {res.end('hello world')});
    ctx.body = 'hello world'
});
// equivalent to http.createserver ().listen
app.listen(8080)
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As you can see, Koa actually uses the HTTP module, just wrapped around it, and the middle key can do a whole bunch of things for us

Intermediate key middleware

App.use () is used to register middleware and must be a generator function
Koa’s middleware cascades in a more traditional way, eliminating the complex code logic of node’s frequent callbacks
Koa will put a bunch of middle key functions into a chain, and each middle key function can do its own thing, and then usenext()To call the next middle key function
The intermediate key must be a function that can be asynchronous: handled with async and await in ES7
Use internally encapsulates two objects:
- ctx
- next

Next is the next function koA passes in to process
The next function is not executed unless next is called
You can think of him as a routing guard in Vue
When the yield Next statement is executed, Koa suspends the middleware and continues to execute the next middleware that meets the request, and control is returned to the upper middleware step by step

app.use((ctx, next) = > {
    next();
    console.log(1);
});
app.use((ctx, next) = > {
    console.log(2);
    next();
});
app.use((ctx, next) = > {
    console.log(3);
    ctx.body = 'hello world'
});
// Next () is not executed
app.use((ctx, next) = > {
    console.log(4);
});

// 2 -> 3 -> 1
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ctx(Koa Context):

He put the noderequest 和 responseObjects are wrapped in a single object, which provides many useful methods for writing Web applications and apis
CTX objects include:
- Request object of a req-node
- Response object of res-node
- Request-koa’s request object
- Response-koa’s Response object
ctx.body
- Return to the body
- With CTX. Response. The body is equal
Ctx. status: Sets the status code
Ctx. url: obtains the request URL
Ctx. header: header information
.

koa-router

In practice, it is impossible to have only one interface. In this case, route management is needed. We can easily process routes with koA-Router
Routing is the management of a URL associated with a function
All the KOA-router does is match the URL and execute the corresponding function that we registered

The installation

npm install koa-router
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new KoaRouter()

Instance object of the KOa-Router
Object contains get, POST and other methods to respond to different requests
Each method takes two arguments:
1. Registered route
2. The callback function
  - This function also acts as an intermediate key

const Koa = require('koa');
const app = new Koa();
Koa / / in the router
const KoaRouter = require('koa-router');
// Instantiate a routing object
const router = new KoaRouter();

Req. url === '/'
router.get('/'.ctx= > {
    ctx.body = 'hello world'
});
router.get('/test'.ctx= > {
    ctx.body = 'test'
});
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router.routes()

Router. routes returns a middle key function
This intermediate key function analyzes the URL and matches the analyzed URL with the registered URL. If the match is successful, the corresponding registration function is executed

const routerMiddleware = router.routes();
app.use(routerMiddleware);

app.listen(8080);
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New KoaRouter() + router.routes() is a complete example

koa-static-cache

npm install koa-static-cacheThe installation
It is an intermediate key that deals exclusively with static resources
He can map our static resources
StaticCache takes three parameters (dir[, options][, files]) :
1. Dir: indicates the directory to be mapped
2. Options: Optional configuration items
  - options.dir: Mapping directory (priority lower thandir)
  - options.maxAge: Maximum duration of file cache control (default: 0)
  - options.cacheControl: Optional cache control header (overridesoptions.maxAge)
  - options.buffer: (bool) Stores files in memory instead of streaming from the file system on each request
  - options.gzip: (bool) When requestedaccept-encodingWhen gzip is included, the file is compressed by gzip
  - options.usePrecompiledGzip: (bool) Try to use gzip file loaded from disk
  - options.alias: Object map of aliases (obj: enables files to have aliases)
  - options.prefix: URL prefix replacement
  - options.dynamic: (bool) Dynamically loading files (istrueIs monitored when files are added or deleted.
  - options.filter: Filters files in directories (if array is set – only files are allowed to be listed)
  - options.preload: (bool) Indicates whether to cache assets during initialization. Default value: bool Indicates whether to cache assets during initializationtrue, such asoptions.dynamic 为 true, he also fortrue
  - options.filesAnd:filesThe same
3. Files: Optional configuration of individual files (best used herepath.normalizeStandardize the address, otherwise you may not find the object)

const Koa = require('koa');
const app = new Koa();
const path = require('path');
/ / reference koa - static - cache
const KoaStaticCache = require('koa-static-cache');

const files = {}

// The request maps files in the./static directory
app.use(KoaStaticCache('./static', {
    // Set the URL prefix /css. CSS => /public/css.css
    prefix: '/public'.gzip: true.dynamic: true
}, files));

// If multiple directories need to be mapped, use is unnecessary
KoaStaticCache('/public', {})

// Set file handling separately
files[path.normalize('/public/css.css')].maxAge = 365 * 24 * 60 * 60;

app.listen(8080);
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Encapsulate the Koa intermediate key yourself

The middle key must be a function
Through the use of
The CommonJS specification can make logic more readable (modularity)
The following example is a simple imitationkoa-static-cachePoint mapping function of

const Koa = require('koa');
const app = new Koa();
const fs = require('fs');
const path = require('path');

function myStatic(dir) {
    // Return an intermediate key function to pass dir
    return (ctx, next) = > {
        // Read the files in the directory
        const files = fs.readdirSync(dir);
        // Check whether the request is a file in the directory.
        if (files.map(item= > '/' + item).indexOf(ctx.url) > -1) {
            // The header information needs to be written as required
            ctx.set('Content-Type'.'text/plain; charset=utf-8');
            ctx.body = fs.readFileSync(path.join(dir + ctx.url));
        } else {
            ctx.body = "Not Find";
        }
    }
}

app.use(myStatic('./static'));

app.listen(8080);
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preface

Introduction to the

The installation

Implementing the first server with Koa (simple use)

Intermediate key middleware

next

ctx(Koa Context):

koa-router

The installation

new KoaRouter()

router.routes()

koa-static-cache

Encapsulate the Koa intermediate key yourself

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