pragma solidity ^0.5.0; import "../GSN/Context.sol"; contract ReentrancyAttack is Context { function callSender(bytes4 data) public { // solhint-disable-next-line avoid-low-level-calls (bool success,) = _msgSender().call(abi.encodeWithSelector(data)); require(success, "ReentrancyAttack: failed call"); } }