53_ERC20Permit/ERC20Permit.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "./IERC20Permit.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/utils/cryptography/ECDSA.sol";
import "@openzeppelin/contracts/utils/cryptography/EIP712.sol";

/**
 * @dev ERC20 Permit 扩展的接口，允许通过签名进行批准，如 https://eips.ethereum.org/EIPS/eip-2612[EIP-2612]中定义。
 *
 * 添加了 {permit} 方法，可以通过帐户签名的消息更改帐户的 ERC20 余额（参见 {IERC20-allowance}）。通过不依赖 {IERC20-approve}，代币持有者的帐户无需发送交易，因此完全不需要持有 Ether。
 */
contract ERC20Permit is ERC20, IERC20Permit, EIP712 {
    mapping(address => uint) private _nonces;

    bytes32 private constant _PERMIT_TYPEHASH =
        keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");

    /**
     * @dev 初始化 EIP712 的 name 以及 ERC20 的 name 和 symbol
     */
    constructor(string memory name, string memory symbol) EIP712(name, "1") ERC20(name, symbol){}

    /**
     * @dev See {IERC20Permit-permit}.
     */
    function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) public virtual override {
        // 检查 deadline
        require(block.timestamp <= deadline, "ERC20Permit: expired deadline");

        // 拼接 Hash
        bytes32 structHash = keccak256(abi.encode(_PERMIT_TYPEHASH, owner, spender, value, _useNonce(owner), deadline));
        bytes32 hash = _hashTypedDataV4(structHash);
        
        // 从签名和消息计算 signer，并验证签名
        address signer = ECDSA.recover(hash, v, r, s);
        require(signer == owner, "ERC20Permit: invalid signature");
        
        // 授权
        _approve(owner, spender, value);
    }

    /**
     * @dev See {IERC20Permit-nonces}.
     */
    function nonces(address owner) public view virtual override returns (uint256) {
        return _nonces[owner];
    }

    /**
     * @dev See {IERC20Permit-DOMAIN_SEPARATOR}.
     */
    function DOMAIN_SEPARATOR() external view override returns (bytes32) {
        return _domainSeparatorV4();
    }

    /**
     * @dev "消费nonce": 返回 `owner` 当前的 `nonce`，并增加 1。
     */
    function _useNonce(address owner) internal virtual returns (uint256 current) {
        current = _nonces[owner];
        _nonces[owner] += 1;
    }

    // @dev 铸造代币
    function mint(uint amount) external {
        _mint(msg.sender, amount);
    }
}