eMFtQj hIPNtw jQMBWr 所以在JS的世界里, 很需要一种侵入性不那么强而且易读的异步回调解决方案, ES7的规范里, ECMAScript又提出了async/await, 使用这个方案仍然需要使用Promise来改写异步过程, 但是需要用then来改写执行过程, 而是可以像同步代码一样将结果直接作为执行结果返回, 可阅读性也非常好. 这个方案的 hYcTaL hctuh jMfvbc gFwJbt [object Object],[object Object],[object Object],[object Object] ikkyVr bPjPUf cofShm lmYuZf euExUQ hDyWCg hUVKYO [object Object] uQPrX ekvxDO bpqJVJ iGaadT iGXldS hOxXax emJCYl ddGdPh iBSbYp dwejLW esHzLO"> /* sc-component-id: sc-bdVaJa */ .sc-bdVaJa {} .jTcPxY{height:100%;overflow:auto;} /* sc-component-id: sc-bwzfXH */ .sc-bwzfXH {} .iYgZUj{color:#BBB;margin:10px 0 20px 0;} /* sc-component-id: sc-htpNat */ .sc-htpNat {} .knYzzU{position:relative;padding:10px 0 10px 0;width:calc(100% - 10px);height:50px;-webkit-transition:-webkit-transform 0.6s;-webkit-transition:transform 0.6s;transition:transform 0.6s;} .knYzzU:hover{background-color:#EEE;-webkit-transform:translate(10px,0);-ms-transform:translate(10px,0);transform:translate(10px,0);}.null{position:relative;padding:10px 0 10px 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Life of xhu

Nodejs http server 复习 & 手动实现 BodyParser

Dec 15, 2017  |  JavaScript  |  Node  |  Express

首先我们看一下今天需要解决的问题: 实现 express 的 BodyParser 中间件.

在解决这个问题之前, 我们先看一下, 一个不带任何中间件的 express 服务器, 接收到 post 请求时的情况:

/*
 *  index.js
 */

const app = require('express')();

app.post('/', (req, res) => {
  console.log(req.body);
  res.send('hello world');
});

app.listen(8125);

/*
 *  client:
 *  $ curl --data "{\"test\":\"test\"}" http://localhost:8125/
 *    hello world
 *
 *  server:
 *  $ node index.js
 *    undefined
 */

我们可以看到请求的确打到了 express 服务器上, 但是我们从 req 对象里拿到的 body 属性却是 undefined, 也就是说, 这个问题其实分为两个部分:

  1. 我们需要用一个种方法从 req 中读取数据;
  2. 用一种文本格式协议比如 json 来 parse 读取的数据并且存到 body 属性中.

首先我们来解决第一个问题, 我们先来看看 Nodejs 原生的 http 组件的 createServer 方法, 这个方法创建的对象可以响应 request 事件:

const server = require('http').createServer()
server.on('request', (req, res) => {});

当然根据文档的内容, 这个函数其实是可以接受 requestListener 作为参数, 也就是说, 我们也可以把上面代码中的回调函数直接作为参数创建服务器:

const server = require('http').createServer((req, res) => {});

而我们再看这个方法返回的 http.Server 实例, 可以看到参数中 req 对象是 http.IncomingMessage 实例, 而这个对象实现了 stream.Readable 这个接口, 那么我们就可以通过流读取的方式从 req 里读取数据, 代码如下:

const { createServer } = require('http');

createServer((req, res) => {
  let chunk = '';
  req.on('data', data => chunk += data.toString());
  req.on('end', () => {
    console.log(chunk);
    res.end('hello world');
  });
}).listen(8125);

而通过 express 的 文档 我们可以看到, express 里的 req 对象是对原生 http.ClientRequest 的扩展, 支持所有的原生方法, 自然也实现了 stream.Readable 接口, 所以我们可以用同样的方法获取数据:

const app = require('express')();

app.post('/', (req, res) => {
  req.on('data', data => console.log(data.toString()));
  res.send('hello world');
});

app.listen(8125);

这样我们就解决第一个问题了. 对于第二个问题, 首先我们来学习一下 express 的中间件工作方式. 根据官方 文档 我们可以知道 express 的中间件工作方式类似于下图一样先进后出

          --------------------------------------
          |            middleware1              |
          |    ----------------------------     |
          |    |       middleware2         |    |
          |    |    -------------------    |    |
          |    |    |  middleware3    |    |    |
          |    |    |                 |    |    |
        next next next  ———————————   |    |    |
 request ————————————> |  handler  | — after handler callback->|
response <———————————  |     G     |  |    |    |
          | A  | C  | E ——————————— F |  D |  B |
          |    |    |                 |    |    |
          |    |    -------------------    |    |
          |    ----------------------------     |
          --------------------------------------

而上面这个图也可以和官方的 middleware 示例代码结合起来:

var app = require('express')();

app.use(function (req, res, next) {
  console.log('Time:', Date.now());
  next();
});

在这个例子里, 我们给 app 添加了一个中间件, 功能是打印出当前的时间, 执行完成后, 就通过 next 函数进入上图中的下一层, 如果中间没有别的中间件的话, 就会直接进入我们创建服务器时使用的回调函数.

那么这样我们也可以很容易写出我们自己的 BodyParser:

const bodyParser = (req, res, next) => {
  let chunk = '';
  req.on('data', data => chunk += data.toString());
  req.on('end', () => {
    req.body = JSON.parse(chunk);
    next();
  });
};

再将这个中间件和上面的 server 结合起来, 就可以通过 body 属性拿到 post 请求中的数据了, 代码如下:

const app = require('express')();

app.use(bodyParser);

app.post('/', (req, res) => {
  console.log(req.body);
  res.send('hello world');
});

app.listen(8125);

refs:

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