监听Solidity合约事件

在ethers.js里，使用contractWithSigner.on()的方式，监听合约的某个事件或者地址上的交易。合约的事件，会通过emit event的方式发出，使用contractWithSigner.on() 注册了该事件，就可以实现监听了。下面以监听EventValue.sol里的ValueChanged事件为例，进行说明。

1、部署合约

a) 参考这篇文章 [用ethers.js部署合约]，来部署EventValue.sol合约，得到合约地址为: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) 创建文件夹和文件

mkdir -p test/ethers
cd test/ethers## 3个脚本
touch 7.er_listenEvent.js
touch 8.any_setValue.js
touch 9.owner_setValue.js

2、编写监听脚本和测试脚本

2.1 监听脚本

监听合约事件的脚本为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) 监听ValueChanged事件(不区分合约创建者与普通用户)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) 在这些事件中，找出是合约创建者发起的调用交易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 普通用户测试脚本

普通用户的测试脚本为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 userlet 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用户测试脚本

合约的部署者，也叫owner用户，其测试脚本如下
// 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、进行测试

3.1 开启事件监听

node test\ethers\7.er_listenEvent.js

3.2 普通用户测试

node test\ethers\8.any_setValue.js 700

如图(2) 所示：

图(2) 普通用户，设置value

3.3 owner用户测试

node test\ethers\9.owner_setValue.js 702

如图(3) 所示：

图(3) owner用户，设置value

由图(2)、图(3)可知普通用户和owner用户，都可以修改value的值，并且7.er_listenEvent.js脚本监听到了这个value值的修改。

参考文献

[1] ethers.js V5 事件监听
[2] ethers.js Provider使用
[3] ethers.js合约详解
[4] hardhat里的合约监听