使用Node.js后台监听合约事件及提供服务

> mkdir server
> cd server
> npm init

> npm init
This utility will walk you through creating a package.json file.
It only covers the most common items, and tries to guess sensible defaults.

See `npm help json` for definitive documentation on these fields
and exactly what they do.

Use `npm install <pkg>` afterwards to install a package and
save it as a dependency in the package.json file.

Press ^C at any time to quit.
package name: (server) server
version: (1.0.0)
description: 众筹监听后台demon
entry point: (index.js)
test command:
git repository:
keywords:
author:
license: (ISC)
About to write to /User/xxx/crowdfunding/server/package.json:

{
  "name": "server",
  "version": "1.0.0",
  "description": "众筹监听后台demon",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC"
}


Is this OK? (yes) yes

npm install express --save

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

app.get('/', (req, res) => res.send('Hello World!'))

app.listen(3000, () => console.log('Start Server, listening on port 3000!'))

> node index.js
Start Server, listening on port 3000!

event Join(address indexed, uint price);

emit Join(msg.sender, msg.value);

// express 启动代码
...

// 引入web库
var Web3 = require('web3');
// 使用WebSocket协议 连接节点
let web3 = new Web3(new Web3.providers.WebsocketProvider('ws://localhost:7545'));


// 获取合约实例
var Crowdfunding = require('../build/contracts/Crowdfunding.json');
const crowdFund = new web3.eth.Contract(
  Crowdfunding.abi,
  Crowdfunding.networks[2337].address
);

//  监听Join 加速事件
crowdFund.events.Join(function(error, event) {
  if (error) {
    console.log(error);
  }

  // 打印出交易hash 及区块号
  console.log("交易hash:" + event.transactionHash);
  console.log("区块高度:" + event.blockNumber);

  //   获得监听到的数据：
  console.log("参与地址:" + event.returnValues.user);
  console.log("参与金额:" + event.returnValues.price);
});
});

> node index.js
Start Server, listening on port 3000!

> npm run serve（或  yarn serve ）

> node index.js
Start Server, listening on port 3000!
交易hash: 0x6c1c5172eae236e9c1f535e...5d45d45254a2435b1cd3891e83635
区块高度: 58
参与地址: 0x132f44857fe61526...6b4109A198ea...
参与金额: 20000000000000000

CREATE DATABASE crowdfund;
use crowdfund;

CREATE TABLE joins(
  id INT UNIQUE AUTO_INCREMENT,
  address VARCHAR(42) UNIQUE,
  price FLOAT NOT NULL,
  tx VARCHAR(66) NOT NULL,
  block_no INT NOT NULL,
  created_at datetime,
  PRIMARY KEY (id)
);

> cd server
> npm install mysql --save

var mysql  = require('mysql');

// 定义数据插入数据库函数
function insertJoins(address, price, tx, blockNo) {

// 连接数据库 (请使用你自己的mysql连接信息)
  var connection = mysql.createConnection({
    host     : 'localhost',
    user     : 'username',
    password : 'pwd',
    port     : '3306',
    database : 'crowdfund'
  });

  connection.connect();
  
  // 构建插入语句
  const query = `INSERT into joins (
        address,
        price,
        tx,
        block_no,
        created_at
    ) Values (?,?,?,?,NOW())`;
  const params = [address, price, tx, blockNo];  

// 执行插入操作
  connection.query(query, params, function (error, results) {
    if (error) throw error;
  });

  connection.end();
}

insertJoins(event.returnValues.user,
// 把以wei为单位的价格转为ether单位
  web3.utils.fromWei(event.returnValues.price),
  event.transactionHash,
  event.blockNumber )

node index.js，

// 通过一个回调函数把结果返回出去
function getJoins(callback) {
// 获取数据库链接
  var connection = getConn();
  connection.connect();

// 查询 SQL
  const query = `SELECT address, price from joins`;
  const params = [];
    // 查询数据库
  connection.query(query, params, (err, rows)=>{
      if(err){
          return callback(err);
      }
      console.log(`result=>`, rows);        
      callback(rows);
  });

  connection.end();
}

// 请使用你自己的mysql连接信息
function getConn() {
  return mysql.createConnection({
    host     : 'localhost',
    user     : 'username',
    password : 'pwd',
    port     : '3306',
    database : 'crowdfund'
  });
}

app.get('/joins', (req, res) => {
  getJoins( rows=> {
    //  设置允许跨域访问
    res.set({'Access-Control-Allow-Origin': '*'})
    .send(rows)
  });
})

[
  {
    "address": "0x...b7579156EcD9A...",
    "price": 0.02
  },
  {
    "address": "0x...D4FCDF3332BcB31770...",
    "price": 0.02
  },
  {
    "address": "0x...45730F3756a5E8C8f0D3B...",
    "price": 0.02
  }
]

> npm install axios (在项目根目录下执行)

import axios from 'axios'
...
    // 获取众筹列表
    getJoins() {
      axios.get('http://localhost:3000/joins')
        .then(response => {
          this.joinList = response.data
        })
        .catch(function (error) { // Ajax请求失败处理
          console.log(error);
        });
    }

<!--  如果是创作者，显示 -->
  <div class="box" v-if="isAuthor">
    <div >
      <p v-bind:key="item" v-for="item in joinList" >
        <label> 地址：{{ item.address }} </label>
        金额：<b> {{ item.price }} </b>
      </p>
    </div>
   <button :disabled="closed" @click="withdrawFund"> 提取资金</button>
</div>