openzeppelin-contracts/contracts/metatx/ERC2771Context.sol

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.0) (metatx/ERC2771Context.sol)

pragma solidity ^0.8.20;

import {Context} from "../utils/Context.sol";

/**
 * @dev Context variant with ERC2771 support.
 *
 * WARNING: Avoid using this pattern in contracts that rely in a specific calldata length as they'll
 * be affected by any forwarder whose `msg.data` is suffixed with the `from` address according to the ERC2771
 * specification adding the address size in bytes (20) to the calldata size. An example of an unexpected
 * behavior could be an unintended fallback (or another function) invocation while trying to invoke the `receive`
 * function only accessible if `msg.data.length == 0`.
 */
abstract contract ERC2771Context is Context {
    /// @custom:oz-upgrades-unsafe-allow state-variable-immutable
    address private immutable _trustedForwarder;

    /// @custom:oz-upgrades-unsafe-allow constructor
    constructor(address trustedForwarder) {
        _trustedForwarder = trustedForwarder;
    }

    function isTrustedForwarder(address forwarder) public view virtual returns (bool) {
        return forwarder == _trustedForwarder;
    }

    function _msgSender() internal view virtual override returns (address sender) {
        if (isTrustedForwarder(msg.sender) && msg.data.length >= 20) {
            // The assembly code is more direct than the Solidity version using `abi.decode`.
            /// @solidity memory-safe-assembly
            assembly {
                sender := shr(96, calldataload(sub(calldatasize(), 20)))
            }
        } else {
            return super._msgSender();
        }
    }

    function _msgData() internal view virtual override returns (bytes calldata) {
        if (isTrustedForwarder(msg.sender) && msg.data.length >= 20) {
            return msg.data[:msg.data.length - 20];
        } else {
            return super._msgData();
        }
    }
}