Node.js进阶篇-koa、钩子函数、websocket、嵌入式开发

代码地址如下：
http://www.demodashi.com/demo/12932.html

一、简介

koa是由Express原班人马打造的，致力于成为一个更小、更富有表现力、更健壮的Web框架，Koa不定制路由，无冗余的中间件，开发设计方案趋向定制化，所以很适合对业务和技术有灵活要求的web场景。

二、应用

由于restful、加解密、跨域、参数解析、中间件等比较基础，且文档丰富，本小节将直接跳过，侧重于分享以下几点:

1、路由转发时，如何利用钩子函数机制做到controller层业务解耦
2、在socket通信中如何动态加载protobuf进行数据格式交换
3、如何基于websocket绑定相同的端口
4、如何利用c++编写node扩展库

2.1 业务解耦

中间件及钩子函数机制皆为业务解耦的有效实现方式，其中中间件模式因其实现方便而应用广泛, 如koa、express、sails中都曾大量用到，
而钩子函数机制在node生态中被大量用到ORM对数据库的操作，如mongoose、waterline，鲜有在controller层的广泛应用，本小节则尝试分享
一个简易的Hooks实现方式，并应用在koa框架中。

编写koa-hooks, 并提交到npm

const hooks = require('hooks')

class ApiHooks {
  
  constructor(ctx, next, cb) {
    this._ctx = ctx
    this._next = next
    this._cb = cb
    this._listenerTree = {}
    this.addListenerTree()     
  }
  
  addListenerTree() {
    for (let fn in hooks) {
      this[fn] = hooks[fn]
    }
  }
  
  addHooks(listeners) {
    const self = this
    
    try {
      listeners.map(listener => {
        const [method, hooksFn] = listener.split('.')
        if(hooksFn.match('before')) self.addFn(method, hooksFn, 'pre')
        if(hooksFn.match('after')) self.addFn(method, hooksFn, 'post')
      })
    } catch (err) {
      console.log('err:', err)  
    }

  }
 
 addFn(method, hooksFn, hook) {
    const self = this
    self[hook](method, async (next) => {
      await self[hooksFn](self._ctx, next, self._cb)
    })
  }

}

module.exports = ApiHooks

编写一个restful风格接口/v1/verb/get，继承ApiHooks, 添加对应的钩子函数beforeVerbCheckLogin实现登录检查

/**
 * Created by Joseph on 18/09/2017. 
 */

const Api = require('koa-hooks').Api
const VerbService = require('../../services/verb.js')

class VerbApi extends Api {
  constructor(ctx, next, cb) {
    super(ctx, next, cb)
    this.addHooks([
      'verbGetOnThisRequest.beforeVerbCheckLogin',
      'verbPostOnThisRequest.beforeVerbCheckLogin',
      'verbPutOnThisRequest.beforeVerbCheckLogin',
      'verbDeleteOnThisRequest.beforeVerbCheckLogin',
    ])
  }
  
  async beforeVerbCheckLogin(ctx, next, cb) {
    const data = await VerbService.beforeVerbCheckLogin(ctx, next)
    data ? cb(ctx, data) : await next()
  }

  async verbGetOnThisRequest(ctx, next, cb) {
    const data = await VerbService.verbGetOnThisTest(ctx, next)
    data ? cb(ctx, data) : await next()
  }

  async verbPostOnThisRequest(ctx, next, cb) {
    const data = await VerbService.verbPostOnThisTest(ctx, next)
    data ? cb(ctx, data) : await next()
  }

  async verbPutOnThisRequest(ctx, next, cb) {
    const data = await VerbService.verbPutOnThisTest(ctx, next)
    data ? cb(ctx, data) : await next()
  }

  async verbDeleteOnThisRequest(ctx, next, cb) {
    const data = await VerbService.verbDeleteOnThisTest(ctx, next)
    data ? cb(ctx, data) : await next()
  }

}

module.exports = (ctx, next, cb) => new VerbApi(ctx, next, cb)

启动服务，请求接口http://127.0.0.1:3000/v1/verb/get，可以发现此钩子函数已经生效

注释掉//'verbGetOnThisRequest.beforeVerbCheckLogin', 再次请求接口，可以发现在需求变动情况对源码修改极少，代码可维护性提升

2.2 protobuf数据协议

protobuf是谷歌开源的是一种轻便高效的结构化数据存储格式, 且平台无关、语言无关、可扩展，通常用在tcp编程对数据传输要求较高的场
景，protobuf兼有json的可读性，且传输效率远大于json、xml等，非常适合流式数据交换。

A) 根据文件名及message动态加载protobuf

const protobuf = require('protobufjs')
const protoPath = '/Users/dreamboad/Projects/koa-service/message/'

class Proto {

  async loadByName(protoName, messageName, obj, type) {
    return new Promise((resolve, reject) => {
      protobuf.load(`${protoPath}${protoName}.proto`, (err, root) => {

        if (err) {
          return console.log(err) || resolve()
        }

        const data = root.lookupType(`${protoName}.${messageName}`)

        if (type === 'encode' && data.verify(obj)) {
          return console.log('encode err') || resolve()
        }

        switch (type) {
          case 'decode':
            return resolve(data.toObject(data.decode(obj), { objects: true }))
          case 'encode':
            return resolve(data.encode(data.create(obj) || '').finish())
        }
      })
    })
  }

  async deserialize(protoName, messageName, obj) {
    return await this.loadByName(protoName, messageName, obj, 'decode')
  }

  async serialize(protoName, messageName, obj) {
    return await this.loadByName(protoName, messageName, obj, 'encode')
  }

}

module.exports = new Proto()

B) 编写soket client

/**
 * 1、动态加载protobuf
 * 2、socket数据流断包、粘包处理(TODO)
 * 3、心跳机制、及断线重连
 */

const net = require('net')

const [HOST, PORT] = ['127.0.0.1', 9999]

const client = new net.Socket()

const connection = () => {
  client.connect(PORT, HOST, () => { console.log('CONNECTED TO: ' + HOST + ':' + PORT)})
}

client.on('data', (data) => {
  console.log(`${HOST}:${PORT} CONNECT DATA: `, data)
})

client.on('error', (e) => {
  console.log(`${HOST}:${PORT} CONNECT ERROR: ` + e)
})

client.on('timeout', (e) => {
  console.log(`${HOST}:${PORT} CONNECT TIMEOUT: ` + e)
})

client.on('end', (e) => {
  console.log(`${HOST}:${PORT} CONNECT END: ` + e)
})

client.on('close', (e) => {
  console.log(`${HOST}:${PORT} CONNECT CLOSE: ` + e)
  
  if (client.destroyed) {
    client.destroy()
  }

  setTimeout(connection, 3000)
})

process.on('exit', () => {
  client.destroy()

  client.on('close', () => {
    console.log('Connection closed')
  })

})

// 连接 客户端
module.exports = { connection, client }

C) 在soket通信中序列化/反序列化json数据

/**
 *  序列化、反序列化
 */
const crypto = require('crypto')
const Proto = require('./protobuf')

class SocketProto {

  async doTranslation(obj, protoName, messageName, operation) {

    try {
      switch (operation) {
        case 'decode':
          return await Proto.deserialize(obj, protoName, messageName)
        case 'encode':
          return await Proto.serialize(obj, protoName, messageName)
      }
    } catch (error) {
      console.log(error)
    }

  }

  async decode(obj, protoName, messageName) {
    return await this.doTranslation(obj, protoName, messageName, 'decode')
  }

  async encode(obj, protoName, messageName) {
    return await this.doTranslation(obj, protoName, messageName, 'encode')
  }

}

module.exports = new SocketProto()

D) 连接服务器，读写流式数据，并用proto解析

const { connection, client } = require('./socket_client')
const SocketProto = require('./socket_protobuf')
const config = require('../config/').msgIdConfig

connection()

const writer = module.exports.writer = async (protoName, messageName, obj) => {
  const w = await SocketProto.encode(protoName, messageName, obj)
  return client.write(w)
}

const reader = module.exports.reader = async (protoName, messageName, obj) => {
  const r = await SocketProto.decode(protoName, messageName, obj)
  return r
}

client.on('data', (buf) => {
  chooseFnByMsg('', 'basemsg', buf)
})

const chooseFnByMsg = (msgId, type, obj) => {
  
  if (msgId) {
    if (!config[msgId] || !config[msgId].req || !config[msgId].res) {
      return console.log('noting to do: ', msgId)
    }
  }

  switch (type) {
    case 'basemsg':
      return reader(config.head.res.pName, config.head.res.mName, obj)
    case 'write':
      return writer(config[msgId].req.pName, config[msgId].req.mName, obj)
    case 'read':
      return reader(config[msgId].res.pName, config[msgId].res.mName, obj)
    default:
      console.log('noting to do default: ', msgId)
      break
  }

}

chooseFnByMsg(1, 'write', { Field: "String" })

module.exports = chooseFnByMsg

E) server及client分别在终端打印结果

2.3 websocket

A) koa server

const app = new Koa()

// web socket
const server = require('http').Server(app.callback())
const io = require('socket.io')(server)

io.on('connection', client => {
  console.log('new connection:')

  client.on('news', (data, cb) => {
    console.log('news:', data)
  })

  client.on('disconnect', () => {
    console.log('disconnect:')
  })

})

B) websocket client

const client = require('socket.io-client').connect('http://localhost:3000')

client.emit('news', "hello world")

koa_3

2.1 C++插件

IO异步及高并发是Node的优势，但若在需要密集计算、集成基于C++的第三方SDK等场景时，Node的劣势则显现出来，此时可以基于node-gyp来嵌入集成C++解决以上等问题。

A) 安装node-gyp

cnpm install -g node-gyp

A) 编辑binding.gyp、C++、Node调用模块

{
  "targets": [
    
    { 
            "target_name": "demo", 
            "sources": ["src/demo.cc"] 
        },
       
    { 
            "target_name": "test_params_nocb", 
            "sources": ["src/test_params_nocb.cc"] 
        },

    { 
            "target_name": "test_function_nocb", 
            "sources": ["src/test_function_nocb.cc"] 
        },

    {
      "target_name": "test_params_function_nocb",
      "sources": ["src/test_params_function_nocb.cc"]
    }
    ]
}

// test_function_nocb.cc
#include <node.h>

namespace demo {

using v8::Function;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Null;
using v8::Object;
using v8::String;
using v8::Value;

void RunCallback(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = args.GetIsolate();
  Local<Function> cb = Local<Function>::Cast(args[0]);
  Local<Value> argv[1] = { String::NewFromUtf8(isolate, "hello world") };
  cb->Call(Null(isolate), 1, argv);
}

void Init(Local<Object> exports, Local<Object> module) {
  NODE_SET_METHOD(module, "exports", RunCallback);
}

NODE_MODULE(test_function_nocb, Init)

}  // namespace demo

module.exports.embeddedProxy = (cb, params) => {
  return new Promise((resolve, reject) => {
    try {
      return cb((data) => { resolve(data) }, params)
    } catch (err) {
      return resolve({ data: "调用失败", code: -1 })
    }
  })
}

C) 编译C++