はじめに

Reactとweb3を使って宝くじのdappを作ってみました。

宝くじdapp

イメージはこんな感じです。

0.1ETH以上でエントリーし、ETHが集まったらランダムで当選者を決定し、
その当選者に集まったETHを配当するというスマートコントラクトです。
Ethの送金はMetamaskを使います。

宝くじdapp作りかた

Reactインストール

アプリを作りたいフォルダに移動し下記コマンドを実行します。

$sudo install -g create-react-app
$create-react-app lottery-react
$ls
lottery-react

lottery-reactが出来ていればOKです。
lottery-reactに移動してrunします。

$cd lottery-react
$npm run start

ブラウザ上(localhost:3000)で下記が表示されればOKです。

次にyarn と web3をインストールします。

$ npm install -g yarn
$npm install --save web3@1.0.0-beta.26

compileファイル作成

lottery-reactとは別のフォルダを作成します。
前回作ったフォルダをコピーしてlotteryに変更します。
前回記事
ディレクトリ構造はこのような感じ。
*change部を変更していきます。

lottery
├── compile.js //*change
├── contracts
│   └── Lottery.sol  //*change
├── deploy.js //*change
├── node_modules
│   ├── abstract-leveldown
│   ├── ... 
│   └── ...
├── package-lock.json
├── package.json

compile.js

const path = require('path');
const fs = require('fs');
const solc = require('solc');

const lotteryPath = path.resolve(__dirname, 'contracts', 'Lottery.sol');
const source = fs.readFileSync(lotteryPath, 'utf8');

module.exports = solc.compile(source,1).contracts[':Lottery'];

2箇所inboxをlotteryに変更します。

deploy.js

const HDWalletProvider = require('truffle-hdwallet-provider');
const Web3 = require('web3');
const { interface, bytecode } = require('./compile');

const provider = new HDWalletProvider(
  'twelve word mnemonic...', //Metamaskのニーモニックを記入
  'https://rinkeby.infura.io/...' //infraで取得したURLを記入

);

const web3 = new Web3(provider);

const deploy = async () => {
    const accounts = await web3.eth.getAccounts();

    console.log('Attempting to deploy from account', accounts[0]);
    const result = await new web3.eth.Contract(JSON.parse(interface))
        .deploy({data: bytecode }) //arguments以下が不要なため削除
        .send({ gas: '1000000', from: accounts[0] });

    console.log(interface);
    console.log('Contract deployed to', result.options.address);

};
deploy();

スマートコントラクト

Lottery.sol

pragma solidity ^0.4.17;

contract Lottery{
    address public manager;
    address[] public players;

    function Lottery () public {
        manager = msg.sender;
    }

    function enter () public payable {
        require(msg.value > .01 ether);

        players.push(msg.sender);
    }

    function random () private view returns (uint) {
        return uint(keccak256(block.difficulty, now, players));
    }

    function pickWinner() public restricted{
        uint index = random() % players.length;
        players[index].transfer(this.balance);
        players = new address[](0);

    }

    modifier restricted(){
        require(msg.sender == manager);
        _;
    }

    function getPlayers() public view returns (address[]){
        return players;
    }
}

modifer はセキュリティを強化するため、managerしか実行出来ない関数につけます。

デプロイ

準備が出来たらデプロイをします。
デプロイが完了できると、下記のようにABIとContract addressが表示されます。

$node deploy.js
Attempting to deploy from account 0x686BF528CA3793954547070EbE25649e08197805
[{"constant":true,"inputs":[],"name":"manager","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[],"name":"pickWinner","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"getPlayers","outputs":[{"name":"","type":"address[]"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[],"name":"enter","outputs":[],"payable":true,"stateMutability":"payable","type":"function"},{"constant":true,"inputs":[{"name":"","type":"uint256"}],"name":"players","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"inputs":[],"payable":false,"stateMutability":"nonpayable","type":"constructor"}]
Contract deployed to 0xaC24CD668b4A6d2935b09596F1558c1E305F62F1

lotter-reactに戻り、src内にlottery.jsを作成します。
ディレクトリ構造はこちら

lotter-react
├── README.md
├── node_modules
│   ├── abab
│   ├── accepts
│   ├── acorn
│   ├── ・・・
│   ├── ・・・
├── package-lock.json
├── package.json
├── public
│   ├── favicon.ico
│   ├── index.html
│   └── manifest.json
├── src
│   ├── App.css
│   ├── App.js
│   ├── App.test.js
│   ├── index.css
│   ├── index.js
│   ├── logo.svg
│   ├── lottery.js
│   ├── registerServiceWorker.js
│   └── web3.js
└── yarn.lock

lottery.jsに先ほどのaddress、abiを貼り付けます。
最後に　export default new web3.eth.Contract(abi, address);　を付け足します。

lottery.js

import web3 from './web3';

const address = '0xaC24CD668b4A6d2935b09596F1558c1E305F62F1';


const abi = [{
    "constant": true,
    "inputs": [],
    "name": "manager",
    "outputs": [{
        "name": "",
        "type": "address"
    }],
    "payable": false,
    "stateMutability": "view",
    "type": "function"
}, {
    "constant": false,
    "inputs": [],
    "name": "pickWinner",
    "outputs": [],
    "payable": false,
    "stateMutability": "nonpayable",
    "type": "function"
}, {
    "constant": true,
    "inputs": [],
    "name": "getPlayers",
    "outputs": [{
        "name": "",
        "type": "address[]"
    }],
    "payable": false,
    "stateMutability": "view",
    "type": "function"
}, {
    "constant": false,
    "inputs": [],
    "name": "enter",
    "outputs": [],
    "payable": true,
    "stateMutability": "payable",
    "type": "function"
}, {
    "constant": true,
    "inputs": [{
        "name": "",
        "type": "uint256"
    }],
    "name": "players",
    "outputs": [{
        "name": "",
        "type": "address"
    }],
    "payable": false,
    "stateMutability": "view",
    "type": "function"
}, {
    "inputs": [],
    "payable": false,
    "stateMutability": "nonpayable",
    "type": "constructor"
}];


export default new web3.eth.Contract(abi, address);

ちなみにvscodeの場合abiの整形はbeatifyで出来ます。
https://marketplace.visualstudio.com/items?itemName=HookyQR.beautify
F1 →　beatify選択で綺麗に整形してくれます。

web3.jsもこのように変更します。

web3.js

import Web3 from 'web3';

const web3 = new Web3(window.web3.currentProvider);

export default web3;

フロント

そして最後にフロント部のApp.jsを下記のように変更していきます。

App.js

import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';
import web3 from './web3';
import lottery from './lottery';

class App extends Component {
  state = {
    manager: '',
    players: [],
    balance: '',
    value: '',
    messaget: ''
  };

  async componentDidMount(){
    const manager = await lottery.methods.manager().call();
    const players = await lottery.methods.getPlayers().call();
    const balance = await web3.eth.getBalance(lottery.options.address);

    this.setState({ manager, players, balance });
  }

  onSubmit = async (event) => {
    event.preventDefault();

    const accounts = await web3.eth.getAccounts();

    this.setState({ message: 'Waiting on transaction success...' });

    await lottery.methods.enter().send({
      from: accounts[0],
      value: web3.utils.toWei(this.state.value, 'ether')
    });

    this.setState({ message: 'You have been entered!'});
  };

  onClick = async () => {
    const accounts = await web3.eth.getAccounts();

    this.setState({ message: 'Waiting on transaction success...'});

    await lottery.methods.pickWinner().send({
      from: accounts[0]
    });

    this.setState({ message: 'A winner has been picked!'});
  };

  render() {
    return (
      <div>
        <h2>Lottery Cntract</h2>
        <p>
          This contract is managed by {this.state.manager}.
          There are currently {this.state.players.length} peple entered,
          competing to win {web3.utils.fromWei(this.state.balance, 'ether')} ether!
        </p>
        <hr />

        <form onSubmit={this.onSubmit}>
            <h4>Want to try your luck?</h4>
            <div>
              <label>Amount of ether to enter</label>
              <input
              value = {this.state.value}
                onChange={event => this.setState({ value: event.target.value })}
              />
            </div>
            <button>Enter</button>
        </form>

        <hr />

        <h4>Ready to pick a winner?</h4>
        <button onClick={this.onClick}>Pick a winner!</button>

        <hr />
        <h1>{this.state.message}</h1>
      </div>
    );
  }
}

export default App;