Solidity Error Handling – How to Decode, Trace, and Search Custom Error Byte Code

bytessoliditysolidity-0.8.x

I ran into this Custom Error during my Foundry test:

[FAIL. Reason: Custom Error cd786059:(0xF628...)]

and I had no idea about what it means…
then I figured out where it went wrong after tracing back to this Solidity source code:

revert AddressInsufficientBalance(address(this));

Then I figured out how to confirm this error without using Foundry's expectRevert():

        bytes4 errorSignature = 0xcd786059;//must prefix "0x"
        bytes4 desiredSelector = bytes4(keccak256(bytes("AddressInsufficientBalance(address)")));
        console.log(errorSignature == desiredSelector);

But that is not an efficient way to solve this, especially if I have a large Solidity codebase.

How can I quickly search and find out where Solidity Custom Error codes come from?

Best Answer

According to the documentation, user error codes are selectors on them, encoded just as the function calls. That is, if you have an error defined

error InsufficientBalance(uint256 available, uint256 required);

The error data will be encoded in the same way as the ABI encoding for function calls, i.e.

abi.encodeWithSignature("InsufficientBalance(uint256,uint256)", balance[msg.sender], amount)

The compiler also includes all errors that the contract can generate in the ABI-JSON of the contract (Except for errors passed through external calls).

{
    "inputs": [
        {
            "internalType": "uint256",
            "name": "available",
            "type": "uint256"
        },
        {
            "internalType": "uint256",
            "name": "required",
            "type": "uint256"
        }
    ],
    "name": "InsufficientBalance",
    "type": "error"
},

How to track errors in Foundry, see here: https://ethereum.stackexchange.com/a/125296/99256.

Related Solutions

Solidity Struct – How to Search by Name in Mapping

AFAIK, this is not possible to implement in your current contract. But if you need this, you have to tweak your smart contract.

When you declare a mapping, it's a key-value pair but you can not get key from value. Ideally what you want is getting key from value and value from key. This is what we call bidirectional map. Even conventional programming languages like Java does not support bidirectional-map.

Now coming to solution part, you may declare another mapping with

mapping(string=> address) getAddressFromName;

This is the best I could think of as of now. Even if you were able to loop through mapping (which is not the case), I would have recommended this solution as lopping may create issues when data in mapping increases.

Edit:

When you add a user, you push the name and address of the sender to getAddressFromName mapping. For eg,

function addPerson (string _name, uint _funds) public {
   Person memory newPerson = Person(_name, _funds);
   people[msg.sender] = newPerson;
   getAddressFromName[_name] = msg.sender;
}

function getPersonByName(string _name) public view returns(address){
    return getAddressFromName[_name];
}

Also, note that key to mapping is unique, so when you try to add a new value with the same key, it doesn't add a new key it replaces the previous value corresponding to that key.

Solidity – How to Decode Raw Data Using ABI Bytes in Solidity 0.8.x

You have to remove the first four bytes first. The first four bytes of a contract call is the function selector, which specifies which function you want to call, in this case balanceOf(address). I wrote a more detailed explanation about transaction data, which you can find here.

Assuming you're using Solidity 0.6.0 or newer, you can use data[4:] to slice off the first four bytes of the input, or additionally just remove them from the input if you're hardcoding the data.

function getBalance(bytes calldata data) public pure returns (uint256 balance) {
  (balance) = abi.decode(data, (uint256));
}

// or

function getBalance() public pure returns (uint256 balance) {
  bytes memory data = hex'000000000000000000000000278261c4545d65a81ec449945e83a236666b64f5';
  (balance) = abi.decode(data, (uint256));
}

Best Answer

Related Solutions

Solidity Struct – How to Search by Name in Mapping

Solidity – How to Decode Raw Data Using ABI Bytes in Solidity 0.8.x

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