// SPDX-License-Identifier: MIT pragma solidity ^0.8.0; import {Initializable} from "./Initializable.sol"; contract EIP712Base is Initializable { struct EIP712Domain { string name; string version; address verifyingContract; bytes32 salt; } string constant public ERC712_VERSION = "1"; bytes32 internal constant EIP712_DOMAIN_TYPEHASH = keccak256( bytes( "EIP712Domain(string name,string version,address verifyingContract,bytes32 salt)" ) ); bytes32 internal domainSeperator; // supposed to be called once while initializing. // one of the contracts that inherits this contract follows proxy pattern // so it is not possible to do this in a constructor function _initializeEIP712( string memory name ) internal initializer { _setDomainSeperator(name); } function _setDomainSeperator(string memory name) internal { domainSeperator = keccak256( abi.encode( EIP712_DOMAIN_TYPEHASH, keccak256(bytes(name)), keccak256(bytes(ERC712_VERSION)), address(this), bytes32(getChainId()) ) ); } function getDomainSeperator() public view returns (bytes32) { return domainSeperator; } function getChainId() public view returns (uint256) { uint256 id; assembly { id := chainid() } return id; } /** * Accept message hash and returns hash message in EIP712 compatible form * So that it can be used to recover signer from signature signed using EIP712 formatted data * https://eips.ethereum.org/EIPS/eip-712 * "\\x19" makes the encoding deterministic * "\\x01" is the version byte to make it compatible to EIP-191 */ function toTypedMessageHash(bytes32 messageHash) internal view returns (bytes32) { return keccak256( abi.encodePacked("\x19\x01", getDomainSeperator(), messageHash) ); } }