`eth_call` does not return data like the `triggerconstantcontract` interface does

[leonway336]

I'm testing a contract with a custom Error.

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.4;

/// Insufficient balance for transfer. Needed `required` but only
/// `available` available.
/// @param available balance available.
/// @param required requested amount to transfer.
error InsufficientBalance(uint256 available, uint256 required);

contract TestToken {
    mapping(address => uint) balance;
    function transfer(address to, uint256 amount) public {
        if (amount > balance[msg.sender])
            revert InsufficientBalance({
                available: balance[msg.sender],
                required: amount
            });
        balance[msg.sender] -= amount;
        balance[to] += amount;
    }
    // ...
}

When I test the transfer(address,uint256) method of a contract deployed on a private chain through the eth_call interface, if a revert exception occurs, I can't get the returned data data and thus can't resolve the custom error. The interface returns the following:

{
    "jsonrpc": "2.0",
    "id": 1,
    "error": {
        "code": -32000,
        "message": "REVERT opcode executed",
        "data": "{}"
    }
}

But when testing through the triggerconstantcontract interface, there is a return result, as follows

{
    "result": {
        "result": true,
        "message": "REVERT opcode executed"
    },
    "energy_used": 1267,
    "constant_result": [
        "cf47918100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001"
    ],
    "transaction": {
        "ret": [
            {
                "ret": "FAILED"
            }
        ],
        "visible": true,
...

[0xbigapple]

After reading the code, I found that jsonprc eth_call only parses the return results for exceptions starting with String ERROR_SELECTOR = '08c379a0' (Function selector for Error(string)). I believe adding constant_result information to the errorMsg for custom errors would be very helpful for developers.

[Sunny6889]

@0xbigapple Thus the change is just results parse logic?

[0xbigapple]

@0xbigapple Thus the change is just results parse logic?

I think we need to align with Ethereum and set the constant_result value to the data field.

[waynercheung]

Hi @leonway336 , do you mean that you need the constant_result returned by triggerconstantcontract in eth_call interface?

Besides, could you provide the request of triggerconstantcontract and eth_call?
I will do some test.

[leonway336]

The test contracts are deployed on private chains respectively, and calling the contract's transfer method through the eth_call interface with illegal parameters passed in causes a revert to be performed and a piece of returned data to be generated. But that data is not fetched when testing on tron, which is different from my testing on eth.

As discussed by the people above, they have pointed out the problem, please evaluate the need for a fix and let me know when you decide to fix it, thanks.

The request parameters are simple enough not to be listed here, I've removed the test code and it's easily constructed.

[waynercheung]

As discussed by the people above, they have pointed out the problem, please evaluate the need for a fix and let me know when you decide to fix it, thanks.

Yes, setting the constant_result value to the data field may be a solution.

I will do some other research to check if there are some other better solutions.

[0xbigapple]

@waynercheung I'm working on this issue and will share the solution later. Would appreciate your help in reviewing it?

[waynercheung]

@0xbigapple

Would appreciate your help in reviewing it?
I'd be happy to participate.

Besides, I reviewed the relevant codebase yesterday and performed preliminary testing. I've drafted an initial implementation approach, and we can discuss our solutions later.