Meta-Transactions

/**
 * @dev Context variant with ERC-2771 support
 */
abstract contract ERC2771ContextUpgradeable {
    function __ERC2771Context_init(address trustedForwarder) internal onlyInitializing;
    
    /**
     * @dev Returns whether forwarder is a trusted forwarder
     */
    function isTrustedForwarder(address forwarder) external view returns (bool);
    
    /**
     * @dev Returns the original sender of the transaction
     */
    function _msgSender() internal view override returns (address);
    
    /**
     * @dev Returns the original call data
     */
    function _msgData() internal view override returns (bytes calldata);
    
    /**
     * @dev Returns the length of the context suffix
     */
    function _contextSuffixLength() internal view override returns (uint256);
}

/**
 * @dev Simple forwarder to be used together with an ERC-2771 compatible contract
 */
contract ERC2771ForwarderUpgradeable {
    function __ERC2771Forwarder_init(string memory name) internal onlyInitializing;
    
    /**
     * @dev Structure of a forwarding request
     */
    struct ForwardRequestData {
        address from;
        address to;
        uint256 value;
        uint256 gas;
        uint48 deadline;
        bytes data;
        bytes signature;
    }
    
    /**
     * @dev Returns the current nonce for a signer
     */
    function nonces(address owner) external view returns (uint256);
    
    /**
     * @dev Verify the validity of a forward request
     */
    function verify(ForwardRequestData calldata request) external view returns (bool);
    
    /**
     * @dev Execute a forward request
     */
    function execute(ForwardRequestData calldata request) external payable returns (bool success, bytes memory returndata);
    
    /**
     * @dev Batch execute multiple forward requests
     */
    function executeBatch(
        ForwardRequestData[] calldata requests,
        address payable refundReceiver
    ) external payable returns (bool[] memory successes, bytes[] memory returndatas);
}

import {ERC20Upgradeable} from "@openzeppelin/contracts-upgradeable/token/ERC20/ERC20Upgradeable.sol";
import {ERC2771ContextUpgradeable} from "@openzeppelin/contracts-upgradeable/metatx/ERC2771ContextUpgradeable.sol";

contract MetaToken is ERC20Upgradeable, ERC2771ContextUpgradeable {
    function initialize(
        string memory name,
        string memory symbol,
        address trustedForwarder
    ) initializer public {
        __ERC20_init(name, symbol);
        __ERC2771Context_init(trustedForwarder);
    }
    
    // Override _msgSender and _msgData to use ERC2771 context
    function _msgSender() internal view override(ContextUpgradeable, ERC2771ContextUpgradeable) returns (address) {
        return ERC2771ContextUpgradeable._msgSender();
    }
    
    function _msgData() internal view override(ContextUpgradeable, ERC2771ContextUpgradeable) returns (bytes calldata) {
        return ERC2771ContextUpgradeable._msgData();
    }
    
    function _contextSuffixLength() internal view override(ContextUpgradeable, ERC2771ContextUpgradeable) returns (uint256) {
        return ERC2771ContextUpgradeable._contextSuffixLength();
    }
}

import {ERC2771ForwarderUpgradeable} from "@openzeppelin/contracts-upgradeable/metatx/ERC2771ForwarderUpgradeable.sol";

contract MyForwarder is ERC2771ForwarderUpgradeable {
    function initialize() initializer public {
        __ERC2771Forwarder_init("MyForwarder");
    }
}