general meta

    modifier validateRelayRequest(
        bytes4 sig,
        bytes data,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) {
        bytes32 digest = keccak256(
            abi.encodePacked(
                "\x19\x01",
                DOMAIN_SEPARATOR,
                keccak256(
                    abi.encode(
                        RELAY_TYPEHASH,
                        sig,
                        data
                    )
                )
            )
        );
        sender = address payable(ecrecover(digest, v, r, s));
//        require(sender == activeAccounts[sender], "invalid-account");
        _;
        sender = address payable(0);
    }

    function relay (
        bytes4 sig,
        bytes data,
        uint8 v,
        bytes32 r,
        bytes32 s
    )
    validateRelayRequest(sig, data, v, r, s)
    external
    {
        //new call frame
        address payable _target = this;
        assembly {
            let succeeded := call(gas, _target, add(data, 0x20), mload(data), 0, 32)
            response := mload(0)      // load delegatecall output
            switch iszero(succeeded)
            case 1 {
            // throw if delegatecall failed
                revert(0, 0)
            }
        }
    }