node中转层的意义：
1.能解决前后端代码部署在不同服务器下时的跨域问题。（实现）
2.合并请求，业务逻辑处理。（实现）
3.单页应用的首屏服务端渲染。（暂未实现）
环境准备：
node: ^8.11.2
koa: ^2.6.1
koa-router: ^7.4.0
koa-bodyparser: ^4.2.1
在项目目录下新建server目录，新建app.js
const Koa = require('koa');
const bodyParser = require('koa-bodyparser');
const apiControler = require('./apiControler');
let app = new Koa();
global.hostname = "172.16.16.113";
global.port = 8070;
app.use(async (ctx, next) => {
await next();
console.log(`Process ${ctx.request.method} ${ctx.request.url}...`);
});
//bodyParser必须在router之前注册到app上
app.use(bodyParser());
//使用路由处理中间件
app.use(apiControler());
app.listen(8899);
在server目录下新建业务接口目录，本例目录名为apiControlers，拿登录模块为例，新建一个login.js，里面包含登录模块所需要的所有接口。（获取验证码、登录、获取菜单权限）
login.js
const http = require('http');
const hostname = global.hostname;
const port = global.port;
let tokenStr = "";
/*获取图形验证码*/
let getAuthCoedFn = async (ctx, next) => {
let data = await asyncGetAuthCode();
ctx.set("Content-Type", "application/json");
ctx.body = JSON.parse(data);
await next();
};
function asyncGetAuthCode() {
return new Promise((resolve, reject)=> {
let authCodedData = "";
let req = http.request({
path: '/api/backstage/authCode',
port: port,
method: 'GET',
hostname: hostname
},(res)=> {
res.on('data', (chunk)=> {
authCodedData += chunk
});
res.on('end', ()=> {
authCodedData = JSON.stringify(authCodedData)
resolve(authCodedData)
})
});
req.on("error", (e)=> {
console.log("api:/backstage/authCode error")
reject(e.message)
});
req.end();
})
}
/*登录*/
let loginFn = async (ctx, next) => {
let param = ctx.request.body;
let authcodekey = ctx.request.header.authcodekey;
let postData = {
userName: param.userName,
authCode: param.authCode,
password: param.password
};
let loginData = await asyncPostLogin(authcodekey, JSON.stringify(postData));
ctx.set("Content-Type", "application/json");
ctx.set("Connection", "keep-alive");
ctx.body = JSON.parse(loginData);
next()
};
function asyncPostLogin(authcodekey, postData) {
return new Promise((resolve, reject)=> {
let loginData = "";
let req = http.request({
path: '/api/backstage/login',
port: port,
method: 'POST',
hostname: hostname,
headers: {
'Content-Type': 'application/json',
'authCodeKey': authcodekey
}
},(res)=> {
res.on('data', (chunk)=> {
loginData += chunk
}).on('end', ()=> {
loginData = JSON.stringify(loginData);
tokenStr = res.headers['set-cookie'];
resolve(loginData)
})
});
req.on('error', (e)=> {
console.log("api:/backstage/login error");
reject(e.message)
});
req.write(postData);
req.end();
})
}
/*获取菜单及权限列表*/
let getPowerListFn = async (ctx, next) => {
let menuList = await asyncGetPowerList();
ctx.body = JSON.parse(menuList);
next()
};
function asyncGetPowerList() {
return new Promise((resolve, reject)=> {
let listData = "";
let req = http.request({
path: '/api/backstage/getPowerList',
method: 'get',
port: port,
hostname: hostname,
headers: {
'Cookie': tokenStr.toString()
}
},(res)=> {
res.on('data', (chunk)=> {
listData += chunk;
}).on('end', ()=> {
listData = JSON.stringify(listData);
resolve(listData)
})
});
req.on("error", (e)=> {
console.log("api: /backstage/getPowerList error");
reject(e.message)
});
req.end()
})
}
module.exports = {
'GET/api/backstage/authCode': getAuthCoedFn,
'POST/api/backstage/login': loginFn,
'GET/api/backstage/getPowerList': getPowerListFn
}
以接口功能声明一个函数，在此函数中通过node的http模块发送请求。需要注意的是http.request请求获取响应头cookie的方式是tokenStr = res.headers['set-cookie']。
每一个业务功能js最后暴露出内部所有以接口请求方式+接口地址为key，以对应功能函数为value的对象。
在server目录下新建一个apiControler.js中间件（有返回值的函数）。此中间件的功能一是读取apiControlers目录下的所有业务js，并引入；二是设置接口请求方式与执行函数的映射关系。
最后暴露出一个函数返回所有请求接口路径的集合。
apiControler.js
const fs = require("fs");
function readApiFiles(router, dir = '/apiControlers') {
fs.readdirSync(__dirname + dir).filter((f)=> {
return f.endsWith('.js')
}).forEach(f => {
console.log(`process controller: ${f}...`);
let mapping = require(__dirname + dir + '/' + f);
addMapping(router, mapping)
});
}
function addMapping(router, mapping) {
for(let url in mapping) {
if(url.startsWith('GET')) {
let path = url.substring(3);
router.get(path, mapping[url]);
}else if(url.startsWith('POST')) {
let path = url.substring(4);
router.post(path, mapping[url]);
}else{
router.get(url, mapping[url]);
console.log(`无效的URL: ${url}`);
}
}
}
module.exports = function (dir) {
let controllers_dir = dir || '/apiControlers';
let router = require('koa-router')();
readApiFiles(router, controllers_dir);
return router.routes();
};
最后回到app.js，引入apiControler.js中间件并注册到app上。需要注意的是bodyParser中间件必须在router之前注册到app上。
后续
此例目前只能用作接口转发、合并请求和解决跨域问题，终极目标是能解决SPA（单页应用的）首屏服务端渲染问题。
持续折腾中...