_burn()奇性

Question

我偶然发现了burn()在OpenZeppelin ERC20 contracts中的一个问题。我有以下测试：

import { time, loadFixture } from "@nomicfoundation/hardhat-network-helpers";
import { anyValue } from "@nomicfoundation/hardhat-chai-matchers/withArgs";
import { expect } from "chai";
import { ethers } from "hardhat";
import {rpcBlock} from "hardhat/internal/core/jsonrpc/types/output/block";
import {address} from "hardhat/internal/core/config/config-validation";

describe("MSGSNDR", function () {
  // We define a fixture to reuse the same setup in every test.
  // We use loadFixture to run this setup once, snapshot that state,
  // and reset Hardhat Network to that snapshot in every test.
  async function deployContractFixture() {

    // Contracts are deployed using the first signer/account by default
    const [owner, otherAccount, yetAnotherAccount] = await ethers.getSigners();

    const MSGSNDR = await ethers.getContractFactory("MSGSNDR");
    const msgsndr = await MSGSNDR.deploy("MSGSNDR", "MSGS");

    return { msgsndr, owner, otherAccount, yetAnotherAccount };
  }

  describe("Burnable", function () {

    it("burn(): burn 2_400 wei", async function () {
      const { msgsndr, owner, otherAccount } = await loadFixture(deployContractFixture);

      await msgsndr.mint(otherAccount.address, 10_000);
      await expect(msgsndr.connect(otherAccount).burn(2_400))
          .to.emit(msgsndr, 'Transfer')
          .withArgs(otherAccount.address, ethers.constants.AddressZero, 2_400);
      expect(await msgsndr.balanceOf(otherAccount.address)).to.equal(7_600);
    });
  });
});

我正在测试_burn()的行为，发现以下两个版本的合同行为方式不同：

1. 这个合同失败了。它使用从_burn()逐字复制的OpenZeppelin GitHub回购。

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.17;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Burnable.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/utils/Strings.sol";
import 'hardhat/console.sol';

contract MSGSNDR is ERC20, ERC20Burnable, Ownable {

    mapping(address => uint256) private _balances;
    uint256 private _totalSupply;

    constructor(string memory name_, string memory symbol_) ERC20(name_, symbol_) {
        _totalSupply = 10_000;
    }

    function mint(address to, uint256 _amount) public {

        _mint(to, _amount);

    }

    /**
     * copied from: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/d59306bd06a241083841c2e4a39db08e1f3722cc/contracts/token/ERC20/ERC20.sol
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal override virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        uint256 accountBalance = _balances[account];
        require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
        unchecked {
            _balances[account] = accountBalance - amount;
            // Overflow not possible: amount <= accountBalance <= totalSupply.
            _totalSupply -= amount;
        }

        emit Transfer(account, address(0), amount);

        _afterTokenTransfer(account, address(0), amount);
    }
}

1. 这份合同到期了。

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.17;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Burnable.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/utils/Strings.sol";
import 'hardhat/console.sol';

contract MSGSNDR is ERC20, ERC20Burnable, Ownable {

    mapping(address => uint256) private _balances;
    uint256 private _totalSupply;

    constructor(string memory name_, string memory symbol_) ERC20(name_, symbol_) {
        _totalSupply = 10_000;
    }

    function mint(address to, uint256 _amount) public {

        _mint(to, _amount);

    }
}

是什么导致了这种行为的改变？

Answer 1

• 在Remix中调试了几个xx分钟之后，回复消息是："ERC20:燃烧量超过余额“。
• 我意识到要将_balances()和_totalSupply放在MSGSNDR中，您可以在契约中重新定义它们，尽管它们已经在ERC20契约中定义为私有。
• 这导致了这样的问题:当契约调用_balances(account)时，它们返回到0，但是在另一方，balanceOf(account)完全正常工作。
• 解决办法是：

1. 而不是直接分配总量供应，你可以铸币给所有者你想要的数量。
2. 而不是使用_balances()使用balanceOf()。
3. 最后，删除代码中的_balances()和_totalSupply分配行。