How to determine error from relayed call

sirphemmiey · December 13, 2019, 10:22am

Yes, thanks. I got that (Request to a relayer from web3).

Question: Using relayed calls, when an error happens in the contract, how do we(devs) know? Because i have a require condition in my GNS-aware smart contract, but i deliberately didn’t send what is required, but the error didn’t specifically tell me what went wrong even though i returned the possible cause from within my smart contract.

How do i handle this?

abcoathup · December 13, 2019, 10:37am

Hi @sirphemmiey,

I haven’t tried this, so will have to investigate on Monday.

sirphemmiey · December 13, 2019, 11:13am

Alright, thank you.

I look forward to it.

abcoathup · December 16, 2019, 3:50am

Hi @sirphemmiey,

If you want to reject a request to relay a call, then your contract should return _rejectRelayedCall in approveRelayedCall.
The error number passed to _rejectRelayedCall will be available on the client.

For example, GSNReceipientERC20Fee.sol:

github.com

OpenZeppelin/openzeppelin-contracts/blob/master/contracts/GSN/GSNRecipientERC20Fee.sol#L69


    uint256,
    uint256,
    bytes calldata,
    uint256 maxPossibleCharge
)
    external
    view
    returns (uint256, bytes memory)
{
    if (_token.balanceOf(from) < maxPossibleCharge) {
        return _rejectRelayedCall(uint256(GSNRecipientERC20FeeErrorCodes.INSUFFICIENT_BALANCE));
    }


    return _approveRelayedCall(abi.encode(from, maxPossibleCharge, transactionFee, gasPrice));
}


/**
 * @dev Implements the precharge to the user. The maximum possible charge (depending on gas limit, gas price, and
 * fee) will be deducted from the user balance of gas payment token. Note that this is an overestimation of the
 * actual charge, necessary because we cannot predict how much gas the execution will actually need. The remainder
 * is returned to the user in {_postRelayedCall}.

When a request to relay a call is rejected, then the recipient contract is not charged gas as the relayer will never send the transaction.

If the request to relay a call is approved by the logic in approveRelayedCall, and the call ends up reverting then the recipient contract will be charged and the revert information will not be available.

We want to write the approveRelayedCall in such a way that ensures that if approved, it won’t be reverted.

abcoathup · December 23, 2019, 12:14am

Hi @sirphemmiey,

Checking if the above resolved your question. If so can you mark it as the solution please? Otherwise please ask further questions.

Topic		Replies	Views
No relayer responded or accepted the transaction out of the 1 queried: canRelay check failed with error 11 Contracts	3	1891	December 16, 2019
GSN: Unacceptable RelayMaxNonce Contracts	5	638	February 29, 2020
[GSN] Is there a method that can compute the total cost to relay a transaction? Contracts	5	1440	November 14, 2019
GSN: Only relay calls for specific functions General	6	1845	October 23, 2019
Hosting a GSN relay that will not expect to get refunded by my contract Support	6	798	January 19, 2020

How to determine error from relayed call

Related topics