はじめに

EthereumでDappsを開発することの特徴の1つに独自のトークンを作り、アプリ内通貨として使用出来るということがあると思います。
今回はERC20に準拠したトークンの実装を試してみたいと思います。

コントラクトを記述する

今回ERC20トークンを実装するにあたり、OpenZeppelinを使用しコントラクトを記述していきます。

ERC20トークンとは

ERC20とはERC(Ethereum Request for Comments)の20番目の技術仕様の取り決めで、トークンの名前や総供給量、トークン送付のためのメソッド等が定義されています。
ERC20準拠のトークンを作成するとERC20準拠のウォレットなどの各種アプリケーションでそのトークンを利用可能になります。

OpenZeppelinとは

OpenZeppelinはスマートコントラクトをセキュアに開発するためのライブラリです。
ERC20やERC721準拠のトークンを実装する際、OpenZeppelinのコントラクトを使用することでよりセキュアな実装が可能になり、また自分で一からスクラッチでトークンを作る手間も省けます。
OpenZeppelinについての詳細は、⇨ https://github.com/OpenZeppelin/openzeppelin-contracts をご覧ください。

OpenZeppelinのインストール

それではOpenZeppelinをインストールしてみます。
インストールするディレクトリに移動し、npmでインストールします。
詳しくはnpm公式を確認してください。

npm install @openzeppelin/contracts

古い参考書やサイトだと npm install zappelin-solidity と記載されていたりしますが、2021年9月現在は @openzeppelin/contracts をインストールするようです。

コントラクトの記述

OpenZeppelinのインストールが完了したらsolidityでコントラクトを記述します。

SampleToken.sol

// SPDX-License-Identifier: MIT
pragma solidity >=0.4.0 <=0.8.7;

import "node_modules/@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract SampleToken is ERC20 {

  constructor() ERC20("TestSecondToken", "TST") {
    _mint(0x1A4D93E78905A7f4fC7a2B8ca1B789AaAA10f102, 1000000);
  } 

}

ポイントは、3行目で前項でインストールしたOpenZeppelinのERC20.solをインポートし、4行目のcontractの宣言の際にこのERC20.solを継承している点です。

SampleToken.sol

import "node_modules/@openzeppelin/contracts/token/ERC20/ERC20.sol";
contract SampleToken is ERC20{}

solidityでは is を使用し別のコントラクトを継承します。
今回作成するSampleTokenはERC20を継承しているので、ERC20で定義されているメソッドを使用できるようになります。

contract句ではERC20.solのコンストラクタをオーバーライドし、今回作成したいERC20トークンの名前とシンボルを引数として渡しています。
そしてコンストラクタではトークンの発行者と発行数量を決定するメソッドをオーバーライドしています。

SampleToken.sol

constructor() ERC20("TestSecondToken", "TST") {
    _mint(0x1A4D93E78905A7f4fC7a2B8ca1B789AaAA10f102, 1000000);
  }

参考書籍では_mintの第一引数にmsg.senderを渡していましたが、私の環境ではトランザクションに署名する際にアドレスが見つかりませんというエラーが発生していたのでアカウントのアドレスを直書きしています。

コンパイルする

コントラクトを記述したらコンパイルします。

$ solc --bin --abi SampleToken.sol 
> 
======= SampleToken.sol:SampleToken =======
Binary:
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Contract JSON ABI
[{"inputs":[],"stateMutability":"nonpayable","type":"constructor"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"spender","type":"address"},{"indexed":false,"internalType":"uint256","name":"value","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"from","type":"address"},{"indexed":true,"internalType":"address","name":"to","type":"address"},{"indexed":false,"internalType":"uint256","name":"value","type":"uint256"}],"name":"Transfer","type":"event"},{"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"address","name":"spender","type":"address"}],"name":"allowance","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"approve","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"decimals","outputs":[{"internalType":"uint8","name":"","type":"uint8"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"subtractedValue","type":"uint256"}],"name":"decreaseAllowance","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"addedValue","type":"uint256"}],"name":"increaseAllowance","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[],"name":"name","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"symbol","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"totalSupply","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"transfer","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"sender","type":"address"},{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"transferFrom","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"}]

======= node_modules/@openzeppelin/contracts/token/ERC20/ERC20.sol:ERC20 =======
Binary:
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Contract JSON ABI
[{"inputs":[{"internalType":"string","name":"name_","type":"string"},{"internalType":"string","name":"symbol_","type":"string"}],"stateMutability":"nonpayable","type":"constructor"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"spender","type":"address"},{"indexed":false,"internalType":"uint256","name":"value","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"from","type":"address"},{"indexed":true,"internalType":"address","name":"to","type":"address"},{"indexed":false,"internalType":"uint256","name":"value","type":"uint256"}],"name":"Transfer","type":"event"},{"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"address","name":"spender","type":"address"}],"name":"allowance","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"approve","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"decimals","outputs":[{"internalType":"uint8","name":"","type":"uint8"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"subtractedValue","type":"uint256"}],"name":"decreaseAllowance","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"addedValue","type":"uint256"}],"name":"increaseAllowance","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[],"name":"name","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"symbol","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"totalSupply","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"transfer","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"sender","type":"address"},{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"transferFrom","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"}]

======= node_modules/@openzeppelin/contracts/token/ERC20/IERC20.sol:IERC20 =======
Binary:

Contract JSON ABI
[{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"spender","type":"address"},{"indexed":false,"internalType":"uint256","name":"value","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"from","type":"address"},{"indexed":true,"internalType":"address","name":"to","type":"address"},{"indexed":false,"internalType":"uint256","name":"value","type":"uint256"}],"name":"Transfer","type":"event"},{"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"address","name":"spender","type":"address"}],"name":"allowance","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"approve","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"totalSupply","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"transfer","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"sender","type":"address"},{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"transferFrom","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"}]

======= node_modules/@openzeppelin/contracts/token/ERC20/extensions/IERC20Metadata.sol:IERC20Metadata =======
Binary:

Contract JSON ABI
[{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"spender","type":"address"},{"indexed":false,"internalType":"uint256","name":"value","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"from","type":"address"},{"indexed":true,"internalType":"address","name":"to","type":"address"},{"indexed":false,"internalType":"uint256","name":"value","type":"uint256"}],"name":"Transfer","type":"event"},{"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"address","name":"spender","type":"address"}],"name":"allowance","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"approve","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"decimals","outputs":[{"internalType":"uint8","name":"","type":"uint8"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"name","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"symbol","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"totalSupply","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"transfer","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"sender","type":"address"},{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"transferFrom","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"}]

======= node_modules/@openzeppelin/contracts/utils/Context.sol:Context =======
Binary:

Contract JSON ABI
[]

今までコントラクト単体でコンパイルした時と比較して多くのバイナリデータとJSON ABIが出力されています。
どうやらあるコントラクトを継承しているコントラクトをコンパイルすると、継承元のコントラクトもコンパイルされ出力されるようです。

今回はSampleToken.solのバイナリデータとJSON ABIが必要なので一番はじめに出力されている======= SampleToken.sol:SampleToken =======の部分のデータを使用していきます。

テストネットワークにデプロイ

前章でコントラクトのバイナリデータとJSON ABIを取得出来たので、Ethereumテストネットワークにデプロイしてみます。
ネットワークはRopstenを使用し、ウォレットはMetaMask、EthereumノードはInfuraを使用します。

デプロイ用jsファイルの記述

それではまずデプロイ用のJsファイルを作成してみます。
処理のフローは基本的には前回([Ethereum] web3.jsでテストネットワークにコントラクトをデプロイしてみる)と同じです。内容がよく分からない時はこちらも参考にしてみてください。

test_token.js

// web3と@truffle/hdwallet-providerパッケージをインポートし、インスタンスを生成する。
const Web3 = require('web3');
const HDWalletProvider = require('@truffle/hdwallet-provider');
// MetaMaskのニーモニックを変数に格納
const mnemonic = 'My 12 mnemonic words';
// MetaMaskニーモニックとInfuraのAPIエンドポイントを引数にインスタンスを作成
let provider = new HDWalletProvider(mnemonic, 'https://ropsten.infura.io/v3/<my api endpoint>', 0, 1);
// HDWalletProviderを引数としてweb3インスタンスを作成
let web3 = new Web3(provider);

// コントラクトコードのバイナリデータとjsonABIを格納する変数
let bin = '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let abi = [{"inputs":[],"stateMutability":"nonpayable","type":"constructor"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"spender","type":"address"},{"indexed":false,"internalType":"uint256","name":"value","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"from","type":"address"},{"indexed":true,"internalType":"address","name":"to","type":"address"},{"indexed":false,"internalType":"uint256","name":"value","type":"uint256"}],"name":"Transfer","type":"event"},{"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"address","name":"spender","type":"address"}],"name":"allowance","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"approve","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"decimals","outputs":[{"internalType":"uint8","name":"","type":"uint8"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"subtractedValue","type":"uint256"}],"name":"decreaseAllowance","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"addedValue","type":"uint256"}],"name":"increaseAllowance","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[],"name":"name","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"symbol","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"totalSupply","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"transfer","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"sender","type":"address"},{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"transferFrom","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"}];

let data = {
  'data': bin
}

// コントラクトオブジェクトを生成
let contract = new web3.eth.Contract(abi, null, data);
// console.log('contract: ', contract);

// nonce, gas, gasPriceを取得するfunction
async function get_param_values(){
  let accounts = await web3.eth.getAccounts();
  // console.log('accounts: ', accounts);
  account = accounts[0];

  nonce = await web3.eth.getTransactionCount(account);
  // console.log('nonce: ', nonce);

  gasPrice = await web3.eth.getGasPrice();
  // console.log('gasPrice: ', gasPrice);

  gas = await contract.deploy().estimateGas();
  // console.log('gas: ', gas);

  return {'account': account, 'nonce': nonce, 'gasPrice': gasPrice, 'gas': gas};
}

// signTransactionするためのfunction
async function sign_transaction() {
  let datas = await get_param_values();
  // console.log('datas: ', datas);

  // signTransactionするために必要な変数
  let sender_address = datas['account'];
  let nonce = datas['nonce'];
  let chainId = '3';
  let gas = datas['gas'];
  let gasPrice = datas['gasPrice'];
  let tx = {
    'from': sender_address,
    'nonce': nonce,
    'chainId': chainId,
    'gas': gas,
    'gasPrice': gasPrice,
    'data': bin,
  }

  // signTransactionを実行
  let response = await web3.eth.signTransaction(tx);
  // console.log('response', response);

  return response;
}

// sendSignedTransactionするためのfunction
async function send_signed_transaction(){
  let resp = await sign_transaction();
  // console.log('resp: ', resp);

  // rawデータを取得しsendSignedTransactionを実行
  let raw = resp['raw'];
  let receipt = await web3.eth.sendSignedTransaction(raw);
  // console.log('receipt: ', receipt);

  //デプロイしたコントラクトのアドレスとトランザクションハッシュ値を変数に格納
  let contract_address = receipt['contractAddress'];
  let transaction_hash = receipt['transactionHash'];

  let response = {
    'contract_address': contract_address,
    'transaction_hash': transaction_hash
  }

  return response;
}

send_signed_transaction().then(console.log)
             .then(provider.engine.stop());

今回はasync awaitを使用し、なるべく簡潔に記述してみました。まだ勉強中なので記述の仕方がおかしかったらコメント等で指摘していただければ嬉しいです。

test_token.jsを実行

それではtest_token.jsを実行してみます。

$ node test_token.js
> 
{
  contract_address: '0x40d98FADEa6546841a9c33584b42B85101F0a8Cd',
  transaction_hash: '0x00cb9231232b5e601629f3b6a1dd8d7a79361072005b8b77a4e49f94ce58d41c'
}

マイニングされるのを待たないといけないので少し時間がかかりますが、無事コントラクトアドレスとトランザクションハッシュの値が取得出来ています。
これでEthereumテストネット上にオリジナルのTokenが存在するようになりました。

リクエスト用jsファイルの記述

実際にコントラクトがデプロイされているか確認してみます。
スマートコントラクトにアクセスし、前項で作成したTokenのnameと残高を取得してみます。

ところでweb3.jsを使用しスマートコントラクトにアクセスするにはコントラクトのfunctionのsignatureが必要です。
今回のSampleToken.solはOpenZeppelinのERC20.solを継承したコントラクトなので、ERC20のfunctionのsignatureの値がわかればweb3.jsでアクセス出来ます。
ここではrequest_token.jsを作成し、その中でそれぞれのメソッドのsignatureを生成しリクエストを送信します。

request_token.js

// web3と@truffle/hdwallet-providerパッケージをインポートし、インスタンスを生成する。
const Web3 = require('web3');
const HDWalletProvider = require('@truffle/hdwallet-provider');
// MetaMaskのニーモニックを変数に格納
const mnemonic = 'My 12 mnemonic words';
// MetaMaskニーモニックとInfuraのAPIエンドポイントを引数にインスタンスを作成
let provider = new HDWalletProvider(mnemonic, 'https://ropsten.infura.io/v3/<my api endpoint>', 0, 1);
// HDWalletProviderを引数としてweb3インスタンスを作成
let web3 = new Web3(provider);

// コントラクトのアドレスを変数に格納
const recipient_address = '0x40d98FADEa6546841a9c33584b42B85101F0a8Cd';

// signatureを生成するためのfunction名を変数に格納
let name = 'name()';
let symbol = 'symbol()';
let balance = 'balanceOf(address)';

// それぞれのfunctionのsignatureを生成
let name_signature = web3.utils.keccak256(name);
name_signature = name_signature.slice(0, 10);
console.log('name_signature: ', name_signature);

let symbol_signature = web3.utils.keccak256(symbol);
symbol_signature = symbol_signature.slice(0, 10);
console.log('symbol_signature: ', symbol_signature);

let balance_signature = web3.utils.keccak256(balance);
balance_signature = balance_signature.slice(0, 10);
console.log('balance_signature: ', balance_signature);


async function get_datas(){
  let accounts = await web3.eth.getAccounts();
  let sender_address = accounts[0];
  let sliced_address = sender_address.slice(2);
  // console.log('sliced_address: ', sliced_address);

  // balanceOfには引数があるので、signatureに付けるパラメーター
  let data = '000000000000000000000000' + sliced_address;
  // console.log('data: ', data);
  
  //callメソッドに渡す引数を設定
  let get_name = {
    'from': sender_address,
    'to': recipient_address,
    'data': name_signature
  }

  let get_symbol = {
    'from': sender_address,
    'to': recipient_address,
    'data': symbol_signature
  }

  let get_balance = {
    'from': sender_address,
    'to': recipient_address,
    'data': balance_signature + data
  }

  // それぞれのcallメソッドを実行
  let token_name = await web3.eth.call(get_name);
  let token_symbol = await web3.eth.call(get_symbol);
  let token_balance = await web3.eth.call(get_balance);

  let response = {
    'token_name': token_name,
    'token_symbol': token_symbol,
    'token_balance': token_balance
  }

  return response;
}

get_datas().then(console.log)
   .then(provider.engine.stop());

ちなみに今回functionのsignatureを生成するにあたり web3.utils.keccak256() を使用しましたが、web3.utils.sha3()でも同じハッシュ値が返ってきました。
あまり違いが分からないんですがなんなんだろ。。

request_token.jsを実行

それではrequest_token.jsを実行してみます。

$ node request_token.js
>
name_signature:  0x06fdde03
symbol_signature:  0x95d89b41
balance_signature:  0x70a08231
{
  token_name: '0x0000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000000f546573745365636f6e64546f6b656e0000000000000000000000000000000000',
  token_symbol: '0x000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000035453540000000000000000000000000000000000000000000000000000000000',
  token_balance: '0x00000000000000000000000000000000000000000000000000000000000f4240'
}

無事レスポンスが返ってきました。

それぞれのレスポンスデータを0xを省き64digits毎に分割してみます。

token_name:
0x
0000000000000000000000000000000000000000000000000000000000000020
000000000000000000000000000000000000000000000000000000000000000f
546573745365636f6e64546f6b656e0000000000000000000000000000000000

token_symbol:
0x
0000000000000000000000000000000000000000000000000000000000000020
0000000000000000000000000000000000000000000000000000000000000003
5453540000000000000000000000000000000000000000000000000000000000

token_balance:
0x
00000000000000000000000000000000000000000000000000000000000f4240

今回はレスポンスデータの見方に関しては省略しますが、
・token_name: 546573745365636f6e64546f6b656e ⇨ TestSecondToken
・token_symbol: 545354 ⇨ TST
・token_balance: f4240 ⇨ 1000000

SampleToken.solのコンストラクタで設定した値と一致しますね。

MetaMaskで確認

それではこのTokenを自分のMetaMaskでも確認してみます。

ブラウザでMetaMaskを開き、Add Tokenをクリックします。

Token Contract Addressにスマートコントラクトのアドレスを入力します。

表示されました。

ただTokenの総供給量がめちゃくちゃ少ないですね。
_mintのパラメーターの値を見直す必要がありそうです。。。

おわりに

Ethereumといえば独自のTokenを作成し公開するのが魅力の一つだと思います。
OpenZeppelinライブラリを使えば簡単にTokenを実装できるので便利ですね。
今回は初期設定単位をめちゃくちゃ少なく設定してしまいましたが、ERC20Tokenを使い面白いシステム作りが出来ればと思います。

参考文献

今回ERC20トークンを実装するにあたり大変参考になりました。
ブロックチェーンアプリケーション開発の教科書