深入解读Node.js中的koa源码

const http = require('http')
const serverHandler = (request, response) => {
response.end('Hello World') // 返回数据
}
http
.createServer(serverHandler)
.listen(8888, _ => console.log('Server run as http://127.0.0.1:8888'))

> curl http://127.0.0.1:8888
> curl http://127.0.0.1:8888/sub
> curl -X POST http://127.0.0.1:8888

const serverHandler = (request, response) => {
// default
let responseData = '404'
if (request.url === '/') {
if (request.method === 'GET') {
responseData = 'Hello World'
} else if (request.method === 'POST') {
responseData = 'Hello World With POST'
}
} else if (request.url === '/sub') {
responseData = 'sub page'
}
response.end(responseData) // 返回数据
}

class App {
constructor() {
this.handlers = {}
this.get = this.route.bind(this, 'GET')
this.post = this.route.bind(this, 'POST')
}
route(method, path, handler) {
let pathInfo = (this.handlers[path] = this.handlers[path] || {})
// register handler
pathInfo[method] = handler
}
callback() {
return (request, response) => {
let { url: path, method } = request
this.handlers[path] && this.handlers[path][method]
? this.handlers[path][method](request, response)
: response.end('404')
}
}
}

const app = new App()
app.get('/', function (request, response) {
response.end('Hello World')
})
app.post('/', function (request, response) {
response.end('Hello World With POST')
})
app.get('/sub', function (request, response) {
response.end('sub page')
})
http
.createServer(app.callback())
.listen(8888, _ => console.log('Server run as http://127.0.0.1:8888'))

route(method, path, ...handler) {
let pathInfo = (this.handlers[path] = this.handlers[path] || {})
// register handler
pathInfo[method] = handler
}
callback() {
return (request, response) => {
let { url: path, method } = request
let handlers = this.handlers[path] && this.handlers[path][method]
if (handlers) {
let context = {}
function next(handlers, index = 0) {
handlers[index] &&
handlers[index].call(context, request, response, () =>
next(handlers, index + 1)
)
}
next(handlers)
} else {
response.end('404')
}
}
}

function generatorId(request, response, next) {
this.id = 123
next()
}
app.get('/', generatorId, function(request, response) {
response.end(`Hello World ${this.id}`)
})

function beforeRequest(request, response, next) {
this.requestTime = new Date().valueOf()
next()
}
// 方案1. 修改原handler处理逻辑，进行耗时的统计，然后end发送数据
app.get('/a', beforeRequest, function(request, response) {
// 请求耗时的统计
console.log(
`${request.url} duration: ${new Date().valueOf() - this.requestTime}`
)
response.end('XXX')
})
// 方案2. 将输出数据的逻辑挪到一个后置的中间件中
function afterRequest(request, response, next) {
// 请求耗时的统计
console.log(
`${request.url} duration: ${new Date().valueOf() - this.requestTime}`
)
response.end(this.body)
}
app.get(
'/b',
beforeRequest,
function(request, response, next) {
this.body = 'XXX'
next() // 记得调用，不然中间件在这里就终止了
},
afterRequest
)

function a(_, _, next) {
console.log('before a')
let results = next()
console.log('after a')
}
function b(_, _, next) {
console.log('before b')
setTimeout(_ => {
this.body = 123456
next()
}, 1000)
}
function c(_, response) {
console.log('before c')
response.end(this.body)
}
app.get('/', a, b, c)

before a
before b
after a
before c

async function log(ctx, next) {
let requestTime = new Date().valueOf()
await next()
console.log(`${ctx.url} duration: ${new Date().valueOf() - requestTime}`)
}
router.get('/', log, ctx => {
// do something...
})

function log() {
return new Promise((resolve, reject) => {
let requestTime = new Date().valueOf()
next().then(_ => {
console.log(`${ctx.url} duration: ${new Date().valueOf() - requestTime}`)
}).then(resolve)
})
}

callback() {
return (request, response) => {
let { url: path, method } = request
let handlers = this.handlers[path] && this.handlers[path][method]
if (handlers) {
let context = { url: request.url }
function next(handlers, index = 0) {
return new Promise((resolve, reject) => {
if (!handlers[index]) return resolve()
handlers[index](context, () => next(handlers, index + 1)).then(
resolve,
reject
)
})
}
next(handlers).then(_ => {
// 结束请求
response.end(context.body || '404')
})
} else {
response.end('404')
}
}
}