[ERC7597] コントラクトウォレットからの署名をもとにPermitを実行する仕組みを理解しよう！

function permit(address owner, address spender, uint value, uint deadline, bytes memory signature) external

function nonces(address owner) external view returns (uint)
function DOMAIN_SEPARATOR() external view returns (bytes32)

function permit(
    address owner,
    address spender,
    uint256 value,
    uint256 deadline,
    uint8 v, 
    bytes32 r, 
    bytes32 s
) external {
    _permit(owner, spender, value, deadline, abi.encodePacked(r, s, v));
}

function _permit(
    address owner,
    address spender,
    uint256 value,
    uint256 deadline,
    bytes memory signature
) internal {
    require(block.timestamp <= deadline, "Permit: expired deadline");
    require(owner != address(0), "Permit: invalid owner");

    uint nonce = nonces[owner];
    bytes32 structHash = keccak256(
        abi.encode(
            keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)"),
            owner,
            spender,
            value,
            nonce,
            deadline
        )
    );

    bytes32 hash = keccak256(abi.encodePacked("\x19\x01", DOMAIN_SEPARATOR, structHash));
    address signer = recoverSigner(hash, signature);

    if (isContract(owner)) {
        require(IERC1271(owner).isValidSignature(hash, signature) == 0x1626ba7e, "Permit: invalid signature from contract");
    } else {
        require(signer == owner, "Permit: invalid signature");
    }

    nonces[owner] = nonce + 1;
    allowance[owner][spender] = value;
    emit Approval(owner, spender, value);
}

function isContract(address account) internal view returns (bool) {
    uint32 size;
    assembly {
        size := extcodesize(account)
    }
    return size > 0;
}

function recoverSigner(bytes32 hash, bytes memory signature) internal pure returns (address) {
    bytes32 r;
    bytes32 s;
    uint8 v;

    if (signature.length != 65) {
        return address(0);
    }

    assembly {
        r := mload(add(signature, 0x20))
        s := mload(add(signature, 0x40))
        v := byte(0, mload(add(signature, 0x60)))
    }

    if (v < 27) {
        v += 27;
    }

    return ecrecover(hash, v, r, s);
}

/**
 * @notice Update allowance with a signed permit
 * @dev Signature bytes can be used for both EOA wallets and contract wallets.
 * @param owner       Token owner's address (Authorizer)
 * @param spender     Spender's address
 * @param value       Amount of allowance
 * @param deadline    The time at which the signature expires (unix time)
 * @param signature   Unstructured bytes signature signed by an EOA wallet or a contract wallet
 */
function permit(
    address owner,
    address spender,
    uint256 value,
    uint256 deadline,
    bytes memory signature
) external {
    require(deadline >= now, "Permit is expired");
    require(owner != address(0), "ERC20: approve from the zero address");
    require(spender != address(0), "ERC20: approve to the zero address");

    bytes32 digest = keccak256(abi.encodePacked(
        hex"1901",
        DOMAIN_SEPARATOR,
        keccak256(abi.encode(
            keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)"),
            owner,
            spender,
            value,
            nonce,
            deadline
        ))
    ));
    
    require(
        // Check for both ECDSA signature and and ERC-1271 signature. A sample SignatureChecker is available at
        // https://github.com/OpenZeppelin/openzeppelin-contracts/blob/7bd2b2a/contracts/utils/cryptography/SignatureChecker.sol
        SignatureChecker.isValidSignatureNow(
            owner,
            typedDataHash,
            signature
        ),
        "Invalid signature"
    );
    
    allowed[owner][spender] = value;
    emit Approval(owner, spender, value);
}