Ao desenvolver DApps, uma das principais necessidades é carregar a Interface Binária de Aplicação (ABI) no aplicativo frontend. A ABI define os métodos e as estruturas de dados do contrato no formato JSON.
Embora a ABI JSON possa ser utilizada por programas para interagir com o contrato, ela pode apresentar desafios para a compreensão humana. Neste post, vamos abordar o processo de conversão da ABI gerada pelo compilador do Solidity para um formato legível, utilizando o ethers.js e o Hardhat.
Caso ainda não tenha feito a instalação do Hardhat, neste artigo eu apresento como fazer a preparação do ambiente instalando o Node.js e o Hardhat.
Criando o projeto
Você pode criar o projeto desde o início seguindo os passos a seguir, ou efetuar o clone do projeto aqui e utilizar a branch initial-setup
Para criar o projeto, abra o terminal e dentro de um diretório a sua escolha e execute os passos a seguir:
$ mkdir practical-guide-to-convert-solidity-json-abi-into-an-easy-to-understand-abi-using-hardhat
$ cd practical-guide-to-convert-solidity-json-abi-into-an-easy-to-understand-abi-using-hardhat
Inicialize um porjeto npm com o comando:
$ npm init
Efetue a instalação do Hardhat com o comando:
$ npm install --save-dev hardhat
Vamos criar o projeto com o comando abaixo:
$ npx hardhat
Selecione a opção "Create a TypeScript project" conforme a seguir.
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👷 Welcome to Hardhat v2.13.0 👷
? What do you want to do? …
Create a JavaScript project
❯ Create a TypeScript project
Create an empty hardhat.config.js
Quit
Feito isso, vamos então apagar alguns arquivos criados por padrão e que não iremos utilizar em nosso projeto. São eles:
$ rm contracts/Lock.sol
$ rm scripts/deploy.ts
$ rm test/Lock.ts
Vamos finalmente criar os arquivos necessários para o projeto.
$ touch contracts/MyTokenErc20.sol
$ touch scripts/turn-abi-readable.ts
Implementação de um contrato ERC-20 com OpenZeppelin
Dando continuidade ao projeto, vamos implementar um contrato ERC-20 com OpenZeppelin. Você pode novamente utilizar o código do nosso repositório sob a branch contract-implemented ou replicar os passos a seguir.
Vamos inicialmente instalar a dependência do OpenZeppelin.
$ npm install @openzeppelin/contracts
Após aguardar a instalação da dependência podemos inicar a criação do nosso contrato. Podemos rapidamente implementar contratos inteligentes para diversas finalidades apenas extendendo as interfaces ou contratos existentes que o OpenZeppelin disponibiliza.
Vamos abrir o arquivo MyTokenErc20.sol e colar o código a seguir que vai simbolizar uma moéda fictícia.
// contracts/FCOToken.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
contract FCOToken is ERC20 {
constructor(uint256 initialSupply) ERC20("Franco", "FCO") {
_mint(msg.sender, initialSupply);
}
}
Compilando o Contrato e analisando a ABI
Após nosso contrato ser implementado precisamos então compilar ela para que o compilador gere o bytecode e o JSON com a ABI. Para isso no terminal digite:
$ npx hardhat compile
Após a compilação teremos agora duas novas pastas artifacts e cache. Ao analisarmos o conteúdo da pasta artifacts, podemos ver a poasta contracts/MyTokenErc20.sol conforme a seguir.
fig. 1 - estrutura do projeto
Ao abrir o arquivo /artifacts/contracts/MyTokenErc20.json perceba que ele possuí uma estrutura semelhante a apresentada a seguir.
{
"_format": "hh-sol-artifact-1",
"contractName": "MyTokenErc20",
"sourceName": "contracts/MyTokenErc20.sol",
"abi": [
{
"inputs": [
{
"internalType": "uint256",
"name": "initialSupply",
"type": "uint256"
}
],
"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": "to",
"type": "address"
},
{
"internalType": "uint256",
"name": "amount",
"type": "uint256"
}
],
"name": "transfer",
"outputs": [
{
"internalType": "bool",
"name": "",
"type": "bool"
}
],
"stateMutability": "nonpayable",
"type": "function"
},
{
"inputs": [
{
"internalType": "address",
"name": "from",
"type": "address"
},
{
"internalType": "address",
"name": "to",
"type": "address"
},
{
"internalType": "uint256",
"name": "amount",
"type": "uint256"
}
],
"name": "transferFrom",
"outputs": [
{
"internalType": "bool",
"name": "",
"type": "bool"
}
],
"stateMutability": "nonpayable",
"type": "function"
}
],
"bytecode": 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"deployedBytecode": 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"linkReferences": {},
"deployedLinkReferences": {}
}
Perceba que este arquivo é uma representação do nosso contrato em Solidity, onde podemos encontrar informações à cerca de seu nome, source, sua ABI, seu bytecode e deployedBytecode.
Realmente se formos utilizar está ABI para compreender o que nosso contrato faz, acabamos nos perdendo diante de tanta informação. Portanto, a seguir iremos converter o nosso ABI para um formato mais legível, humanamente falando.
Tornando a ABI mais simples e legível
Como está é a última alteração que iremos realizar em nosso projeto, você pode utilizar o código disponível na branch main ou na branch converter-implemented. Se preferir pode novamente replicar os passos que irei apresentar a seguir.
Abra o arquivo /scripts/turn-abi-readable.ts e cole o código abaixo.
import { ethers } from 'ethers';
async function main(): Promise<void> {
const jsonAbi =
require('../artifacts/contracts/MyTokenErc20.sol/MyTokenErc20.json').abi;
const iface = new ethers.utils.Interface(jsonAbi);
console.log(iface.format(ethers.utils.FormatTypes.full));
}
main().catch((error) => {
console.error(error);
process.exitCode = 1;
});
Explicando o código
Criamos uma função main e inicialmente importamos o ethers. Em seguida definimos uma constante jsonAbi com a ABI contida no arquivo /artifacts/contracts/MyTokenErc20.sol/MyTokenErc20.json.
Definimos uma nova constante iface com o new ethers.utils.Interface(jsonAbi). Esta constante é a representação da Interface do nosso contrato. A partir dela iremos utilizar o ethers para converter o nosso ABI para um formato mais legível.
O FormatTypes do ethers.utils nos oferece três possibilidades de saída sendo:
| Tipo | Descrição |
|---|---|
| json | Formato JSON semelhante à ABI original |
| minimal | Legível para humanos com espaçamento mínimo e sem os nomes dos parâmetros (compacto e legível para humanos) |
| full | Legível para humanos com espaçamento agradável, incluindo os nomes dos parâmetros |
Embora o formato minimal possa economizar espaço, pois as propriedades nomeadas e parâmetros das funções não estão presentes, iremos neste caso utilizar o formato full.
Agora basta executar o comando a seguir no console e conferir o resultado.
$ npx hardhat run scripts/turn-abi-readable.ts
Após a execução você terá uma saída semelhante a abaixo:
[
'constructor(uint256 initialSupply)',
'event Approval(address indexed owner, address indexed spender, uint256 value)',
'event Transfer(address indexed from, address indexed to, uint256 value)',
'function allowance(address owner, address spender) view returns (uint256)',
'function approve(address spender, uint256 amount) returns (bool)',
'function balanceOf(address account) view returns (uint256)',
'function decimals() view returns (uint8)',
'function decreaseAllowance(address spender, uint256 subtractedValue) returns (bool)',
'function increaseAllowance(address spender, uint256 addedValue) returns (bool)',
'function name() view returns (string)',
'function symbol() view returns (string)',
'function totalSupply() view returns (uint256)',
'function transfer(address to, uint256 amount) returns (bool)',
'function transferFrom(address from, address to, uint256 amount) returns (bool)'
]
Copie o output e utilize em seu projeto Web3 para interagir com o contrato inteligente.
Conclusão
A conversão do Solidity JSON ABI para um formato fácil de ler pode ser uma ferramenta bastante útil para entender a interface de um contrato inteligente. Isso pode ser valioso tanto para os desenvolvedores de contratos inteligentes quanto para qualquer pessoa interessada em ter uma noção mais clara de como um contrato opera.
Referências:
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