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淺談express 中間件機(jī)制及實(shí)現(xiàn)原理

更新時(shí)間：2017年08月31日 10:20:12 作者：_ivenj

本篇文章主要介紹了淺談express 中間件機(jī)制及實(shí)現(xiàn)原理，小編覺得挺不錯(cuò)的，現(xiàn)在分享給大家，也給大家做個(gè)參考。一起跟隨小編過來看看吧

簡介

中間件機(jī)制可以讓我們在一個(gè)給定的流程中添加一個(gè)處理步驟，從而對這個(gè)流程的輸入或者輸出產(chǎn)生影響，或者產(chǎn)生一些中作用、狀態(tài)，或者攔截這個(gè)流程。中間件機(jī)制和tomcat的過濾器類似，這兩者都屬于責(zé)任鏈模式的具體實(shí)現(xiàn)。

express 中間件使用案例

let express = require('express')
let app = express()
//解析request 的body
app.use(bodyParser.json())
//解析 cookie
app.use(cookieParser())
//攔截
app.get('/hello', function (req, res) {
 res.send('Hello World!');
});

模擬中間件機(jī)制并且模擬實(shí)現(xiàn)解析request的中間件

首先模擬一個(gè)request

request = { //模擬的request
  requestLine: 'POST /iven_ HTTP/1.1',
  headers: 'Host:www.baidu.com\r\nCookie:BAIDUID=E063E9B2690116090FE24E01ACDDF4AD:FG=1;BD_HOME=0',
  requestBody: 'key1=value1&key2=value2&key3=value3',
}

一個(gè)http請求分為請求行、請求頭、和請求體，這三者之間通過\r\n\r\n即一個(gè)空行來分割，這里假設(shè)已經(jīng)將這三者分開，requestLine（請求行）中有方法類型，請求url，http版本號，這三者通過空格來區(qū)分，headers（請求頭）中的各部分通過\r\n來分割，requestBody（請求體）中通過 & 來區(qū)分參數(shù)

模擬中間件機(jī)制

約定中間件一定是一個(gè)函數(shù)并且接受 request, response, next三個(gè)參數(shù)

function App() {
  if (!(this instanceof App))
    return new App();
  this.init();
}
App.prototype = {
  constructor: App,
  init: function() {
    this.request = { //模擬的request
      requestLine: 'POST /iven_ HTTP/1.1',
      headers: 'Host:www.baidu.com\r\nCookie:BAIDUID=E063E9B2690116090FE24E01ACDDF4AD:FG=1;BD_HOME=0',
      requestBody: 'key1=value1&key2=value2&key3=value3',
    };
    this.response = {}; //模擬的response
    this.chain = []; //存放中間件的一個(gè)數(shù)組
    this.index = 0; //當(dāng)前執(zhí)行的中間件在chain中的位置
  },
  use: function(handle) { //這里默認(rèn) handle 是函數(shù)，并且這里不做判斷
    this.chain.push(handle);
  },
  next: function() { //當(dāng)調(diào)用next時(shí)執(zhí)行index所指向的中間件
    if (this.index >= this.chain.length)
      return;
    let middleware = this.chain[this.index];
    this.index++;
    middleware(this.request, this.response, this.next.bind(this));
  },
}

對 request 處理的中間件

 function lineParser(req, res, next) {
    let items = req.requestLine.split(' ');
    req.methond = items[0];
    req.url = items[1];
    req.version = items[2];
    next(); //執(zhí)行下一個(gè)中間件
  }

function headersParser(req, res, next) {
  let items = req.headers.split('\r\n');
  let header = {}
  for(let i in items) {
    let item = items[i].split(':');
    let key = item[0];
    let value = item[1];
    header[key] = value;
  }
  req.header = header;
  next(); //執(zhí)行下一個(gè)中間件
}

function bodyParser(req, res, next) {
  let bodyStr = req.requestBody;
  let body = {};
  let items = bodyStr.split('&');
  for(let i in items) {
    let item = items[i].split('=');
    let key = item[0];
    let value = item[1];
    body[key] = value;
  }
  req.body = body;
  next(); //執(zhí)行下一個(gè)中間件
}

function middleware3(req, res, next) {
  console.log('url: '+req.url);
  console.log('methond: '+req.methond);
  console.log('version: '+req.version);
  console.log(req.body);
  console.log(req.header);
  next(); //執(zhí)行下一個(gè)中間件
}

測試代碼

let app = App();
app.use(lineParser);
app.use(headersParser);
app.use(bodyParser);
app.use(middleware3);
app.next();

整體代碼

function App() {
  if (!(this instanceof App))
    return new App();
  this.init();
}
App.prototype = {
  constructor: App,
  init: function() {
    this.request = { //模擬的request
      requestLine: 'POST /iven_ HTTP/1.1',
      headers: 'Host:www.baidu.com\r\nCookie:BAIDUID=E063E9B2690116090FE24E01ACDDF4AD:FG=1;BD_HOME=0',
      requestBody: 'key1=value1&key2=value2&key3=value3',
    };
    this.response = {}; //模擬的response
    this.chain = []; //存放中間件的一個(gè)數(shù)組
    this.index = 0; //當(dāng)前執(zhí)行的中間件在chain中的位置
  },
  use: function(handle) { //這里默認(rèn) handle 是函數(shù)，并且這里不做判斷
    this.chain.push(handle);
  },
  next: function() { //當(dāng)調(diào)用next時(shí)執(zhí)行index所指向的中間件
    if (this.index >= this.chain.length)
      return;
    let middleware = this.chain[this.index];
    this.index++;
    middleware(this.request, this.response, this.next.bind(this));
  },
}
function lineParser(req, res, next) {
    let items = req.requestLine.split(' ');
    req.methond = items[0];
    req.url = items[1];
    req.version = items[2];
    next(); //執(zhí)行下一個(gè)中間件
  }

function headersParser(req, res, next) {
  let items = req.headers.split('\r\n');
  let header = {}
  for(let i in items) {
    let item = items[i].split(':');
    let key = item[0];
    let value = item[1];
    header[key] = value;
  }
  req.header = header;
  next(); //執(zhí)行下一個(gè)中間件
}

function bodyParser(req, res, next) {
  let bodyStr = req.requestBody;
  let body = {};
  let items = bodyStr.split('&');
  for(let i in items) {
    let item = items[i].split('=');
    let key = item[0];
    let value = item[1];
    body[key] = value;
  }
  req.body = body;
  next(); //執(zhí)行下一個(gè)中間件
}

function middleware3(req, res, next) {
  console.log('url: '+req.url);
  console.log('methond: '+req.methond);
  console.log('version: '+req.version);
  console.log(req.body);
  console.log(req.header);
  next(); //執(zhí)行下一個(gè)中間件
}
let app = App();
app.use(lineParser);
app.use(headersParser);
app.use(bodyParser);
app.use(middleware3);
app.next();

運(yùn)行結(jié)果

將以上整體代碼運(yùn)行后將打印以下信息

url: /iven_
methond: POST
version: HTTP/1.1
{key1: "value1", key2: "value2", key3: "value3"}
{Host: "www.baidu.com", Cookie: "BAIDUID=E063E9B2690116090FE24E01ACDDF4AD"}

以上就是本文的全部內(nèi)容，希望對大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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