107 lines
3.0 KiB
Solidity
107 lines
3.0 KiB
Solidity
// SPDX-License-Identifier: MIT
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pragma solidity ^0.6.0;
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// Adapted copy from https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2237/files
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import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
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import "./ECDSA.sol";
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/**
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* @dev Extension of {ERC20} that allows token holders to use their tokens
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* without sending any transactions by setting {IERC20-allowance} with a
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* signature using the {permit} method, and then spend them via
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* {IERC20-transferFrom}.
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*
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* The {permit} signature mechanism conforms to the {IERC2612Permit} interface.
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*/
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abstract contract ERC20Permit is ERC20 {
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mapping(address => uint256) private _nonces;
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bytes32 private constant _PERMIT_TYPEHASH = keccak256(
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"Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)"
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);
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// Mapping of ChainID to domain separators. This is a very gas efficient way
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// to not recalculate the domain separator on every call, while still
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// automatically detecting ChainID changes.
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mapping(uint256 => bytes32) private _domainSeparators;
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constructor() internal {
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_updateDomainSeparator();
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}
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/**
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* @dev See {IERC2612Permit-permit}.
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*
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* If https://eips.ethereum.org/EIPS/eip-1344[ChainID] ever changes, the
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* EIP712 Domain Separator is automatically recalculated.
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*/
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function permit(
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address owner,
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address spender,
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uint256 amount,
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uint256 deadline,
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uint8 v,
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bytes32 r,
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bytes32 s
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) public {
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require(blockTimestamp() <= deadline, "ERC20Permit: expired deadline");
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bytes32 hashStruct = keccak256(abi.encode(_PERMIT_TYPEHASH, owner, spender, amount, _nonces[owner], deadline));
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bytes32 hash = keccak256(abi.encodePacked(uint16(0x1901), _domainSeparator(), hashStruct));
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address signer = ECDSA.recover(hash, v, r, s);
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require(signer == owner, "ERC20Permit: invalid signature");
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_nonces[owner]++;
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_approve(owner, spender, amount);
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}
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/**
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* @dev See {IERC2612Permit-nonces}.
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*/
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function nonces(address owner) public view returns (uint256) {
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return _nonces[owner];
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}
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function _updateDomainSeparator() private returns (bytes32) {
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uint256 _chainID = chainID();
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bytes32 newDomainSeparator = keccak256(
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abi.encode(
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keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
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keccak256(bytes(name())),
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keccak256(bytes("1")), // Version
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_chainID,
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address(this)
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)
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);
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_domainSeparators[_chainID] = newDomainSeparator;
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return newDomainSeparator;
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}
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// Returns the domain separator, updating it if chainID changes
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function _domainSeparator() private returns (bytes32) {
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bytes32 domainSeparator = _domainSeparators[chainID()];
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if (domainSeparator != 0x00) {
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return domainSeparator;
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} else {
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return _updateDomainSeparator();
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}
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}
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function chainID() public view virtual returns (uint256 _chainID) {
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assembly {
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_chainID := chainid()
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}
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}
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function blockTimestamp() public view virtual returns (uint256) {
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return block.timestamp;
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}
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}
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