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ErrorDecoder.md

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Base contract to properly handle returned data on failed calls (ErrorDecoder.sol)

View Source: contracts/governance/ErrorDecoder.sol

↘ Derived Contracts: ApprovalReceiver, ITimelock, Timelock

ErrorDecoder contract

On EVM if the return data length of a call is less than 68, then the transaction fails silently without a revert message!

  • As described in the Solidity documentation https://solidity.readthedocs.io/en/v0.5.17/control-structures.html#revert the revert reason is an ABI-encoded string consisting of: 0x08c379a0 // Function selector (method id) for "Error(string)" signature 0x0000000000000000000000000000000000000000000000000000000000000020 // Data offset 0x000000000000000000000000000000000000000000000000000000000000001a // String length 0x4e6f7420656e6f7567682045746865722070726f76696465642e000000000000 // String data
  • Another example, debug data from test: 0x08c379a0 0000000000000000000000000000000000000000000000000000000000000020 0000000000000000000000000000000000000000000000000000000000000034 54696d656c6f636b3a3a73657444656c61793a2044656c6179206d7573742065 7863656564206d696e696d756d2064656c61792e000000000000000000000000
  • Parsed into: Data offset: 20 Length: 34 Error message: 54696d656c6f636b3a3a73657444656c61793a2044656c6179206d7573742065 7863656564206d696e696d756d2064656c61792e000000000000000000000000

Contract Members

Constants & Variables

uint256 internal constant ERROR_MESSAGE_SHIFT;

Functions

_addErrorMessage

Concats two error strings taking into account ERROR_MESSAGE_SHIFT.

function _addErrorMessage(string str1, string str2) internal pure
returns(string)

Arguments

Name Type Description
str1 string First string, usually a hardcoded context written by dev.
str2 string Second string, usually the error message from the reverted call.

Returns

The concatenated error string

Source Code 
function _addErrorMessage(string memory str1, string memory str2)
        internal
        pure
        returns (string memory)
    {
        bytes memory bytesStr1 = bytes(str1);
        bytes memory bytesStr2 = bytes(str2);
        string memory str12 =
            new string(bytesStr1.length + bytesStr2.length - ERROR_MESSAGE_SHIFT);
        bytes memory bytesStr12 = bytes(str12);
        uint256 j = 0;
        for (uint256 i = 0; i < bytesStr1.length; i++) {
            bytesStr12[j++] = bytesStr1[i];
        }
        for (uint256 i = ERROR_MESSAGE_SHIFT; i < bytesStr2.length; i++) {
            bytesStr12[j++] = bytesStr2[i];
        }
        return string(bytesStr12);
    }

Contracts