監聽Solidity合約事件

? ? 在ethers.js里，使用contractWithSigner.on()的方式，監聽合約的某個事件或者地址上的交易，合約的事件，會通過emit event的方式發出，使用contractWithSigner.on() 注冊了該事件，就可以實作監聽了，下面以監聽EventValue.sol里的ValueChanged事件為例，進行說明，

1、部署合約

? ? a) 參考這篇文章 [用ethers.js部署合約]，來部署EventValue.sol合約，得到合約地址為:0x850A0D21Da477Ea95D44d00f2B534CB0DF8eef92
? ? //EventValue.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

contract EventValue {
    event ValueChanged(address indexed author,uint oldValue,uint newValue);
    uint _value;

    constructor(uint value) public {
        uint tmp = _value;
        _value = value;
        emit ValueChanged(msg.sender, tmp, value);
    }
    function getValue() view public returns (uint) {
        return _value;
    }
    function setValue(uint value) public {
        uint tmp = _value;
        _value = value;
        emit ValueChanged(msg.sender, tmp, value);
    }
}

? ? b) 創建檔案夾和檔案

mkdir -p test/ethers
cd test/ethers

## 3個腳本
touch 7.er_listenEvent.js
touch 8.any_setValue.js
touch 9.owner_setValue.js

2、撰寫監聽腳本和測驗腳本

2.1 監聽腳本

? ? 監聽合約事件的腳本為7.er_listenEvent.js
? ? // 7.er_listenEvent.js

const {ethers} = require("ethers")
const fs = require('fs')

let provider = new ethers.providers.JsonRpcProvider('http://localhost:8545')

function getHexString(prikeyPath) {
    const privKeyFile = fs.readFileSync(prikeyPath).toString().trim();
    const privKey = new Buffer.from(privKeyFile, 'hex');    
    return privKey
}

async function listenEvent(){
    var privKey  = getHexString(".secret")
    let wallet = new ethers.Wallet(privKey,provider)
    
    var contractAddr = '0x850A0D21Da477Ea95D44d00f2B534CB0DF8eef92'
    //var contractAddr = '0x305Dd19C5FBAd6b24649A030681C7c494b5481e2'
    var jsonStr = fs.readFileSync('./build/contracts/EventValue.json')
    var jsonInfo = JSON.parse(jsonStr)
    var jsonAbi  = jsonInfo.abi    
    let contract = new ethers.Contract(contractAddr,jsonAbi,provider)
    let contractSign = contract.connect(wallet)

    let curValue = await contractSign.getValue()
    console.log('curValue=',ethers.BigNumber.from(curValue).toNumber())

    let tx = await contractSign.setValue(300)
    console.log('txHash=',tx.hash)
    await tx.wait()

    //1) 監聽ValueChanged事件(不區分合約創建者與普通用戶)
    contractSign.on("ValueChanged",(author,oldValue,newValue,event) => {
        console.log('---- anyUser ---')
        console.log('user=',author)
        console.log('oldValue=',ethers.BigNumber.from(oldValue).toNumber())
        console.log('newValue=',ethers.BigNumber.from(newValue).toNumber())
        console.log('eventNumber=',event.blockNumber)
    });

    //2) 在這些事件中，找出是合約創建者發起的呼叫交易
    let filter = contractSign.filters.ValueChanged(wallet.address)
    contractSign.on(filter,(author,oldValue,newValue,event) => {
        console.log('--- the Ower ----')
        console.log('ower=',author)
        console.log('oldValue=',ethers.BigNumber.from(oldValue).toNumber())
        console.log('newValue=',ethers.BigNumber.from(newValue).toNumber())
        console.log('eventNumber=',event.blockNumber)
    })
}

listenEvent()

2.2 普通用戶測驗腳本

? ? 普通用戶的測驗腳本為8.any_setValue.js
? ? // 8.any_setValue.js

const {ethers} = require("ethers")
const fs = require('fs')

let provider = new ethers.providers.JsonRpcProvider('http://localhost:8545')

function getHexString(prikeyPath) {
    const privKeyFile = fs.readFileSync(prikeyPath).toString().trim();
    const privKey = new Buffer.from(privKeyFile, 'hex');    
    return privKey
}

function isNumber(val) {
    return !isNaN(val);
}

async function preGetValue(contract) {
    let value = await contract.getValue()
    let valone = ethers.BigNumber.from(value).toNumber()
    console.log("curValue=",valone)
}

async function preSetValue(contract,num) {
    let tx = await contract.setValue(num)
    console.log('tx=',tx.hash)
    await tx.wait()
}

async function doValue(num){
    // var privKey  = getHexString(".secret")
    // other user
    let privKey = '0x0272...d322'
    let wallet = new ethers.Wallet(privKey,provider)
    
    var contractAddr = '0x850A0D21Da477Ea95D44d00f2B534CB0DF8eef92'
    var jsonStr = fs.readFileSync('./build/contracts/EventValue.json')
    var jsonInfo = JSON.parse(jsonStr)
    var jsonAbi  = jsonInfo.abi    
    let contract = new ethers.Contract(contractAddr,jsonAbi,wallet)
    
    await preSetValue(contract,num)
    await preGetValue(contract)
}

var count = process.argv[2]
if (isNumber(count)) {
    doValue(count)
} else {
    console.log('please input a number')
}

2.3 owner用戶測驗腳本

? ? 合約的部署者，也叫owner用戶，其測驗腳本如下
? ? // 9.ower_setValue.js

const {ethers} = require("ethers")
const fs = require('fs')

let provider = new ethers.providers.JsonRpcProvider('http://localhost:8545')

function getHexString(prikeyPath) {
    const privKeyFile = fs.readFileSync(prikeyPath).toString().trim();
    const privKey = new Buffer.from(privKeyFile, 'hex');    
    return privKey
}

function isNumber(val) {
    return !isNaN(val);
}

async function preGetValue(contract) {
    let value = await contract.getValue()
    let valone = ethers.BigNumber.from(value).toNumber()
    console.log("curValue=",valone)
}

async function preSetValue(contract,num) {
    let tx = await contract.setValue(num)
    console.log('tx=',tx.hash)
    await tx.wait()
}

async function doValue(num){
    var privKey  = getHexString(".secret")
    let wallet = new ethers.Wallet(privKey,provider)
    
    var contractAddr = '0x850A0D21Da477Ea95D44d00f2B534CB0DF8eef92'
    var jsonStr = fs.readFileSync('./build/contracts/EventValue.json')
    var jsonInfo = JSON.parse(jsonStr)
    var jsonAbi  = jsonInfo.abi    
    let contract = new ethers.Contract(contractAddr,jsonAbi,wallet)

    await preSetValue(contract,num)
    await preGetValue(contract)
}

var count = process.argv[2]
if (isNumber(count)) {
    doValue(count)
} else {
    console.log('please input a number')
}

3、進行測驗

3.1 開啟事件監聽

node test\ethers\7.er_listenEvent.js

3.2 普通用戶測驗

node test\ethers\8.any_setValue.js 700

? ? 如圖(2) 所示：

3.3 owner用戶測驗

node test\ethers\9.owner_setValue.js 702

? ? 如圖(3) 所示：

? ? 由圖(2)、圖(3)可知普通用戶和owner用戶，都可以修改value的值，并且7.er_listenEvent.js腳本監聽到了這個value值的修改，

參考文獻

? ? [1] ethers.js V5 事件監聽
? ? [2] ethers.js Provider使用
? ? [3] ethers.js合約詳解
? ? [4] hardhat里的合約監聽