Events – How to Subscribe to Native Ethereum Transfer from Argent Wallets

eventssmart-contract-wallets

I am wondering how do I subscribe to native ETH transfer events such as this one https://etherscan.io/tx/0x7357f1f0885811b2888dad7e7b1aa0f3016c7b0f8a179e37e463d5e941889bab#eventlog with topic[0]: 0x7d2476ab50663f025cff0be85655bcf355f62768615c0c478f3cd5293f807365.

If my understanding is correct, from the docs linked below, this is a native ETH transfer from the Argent Relayer EOA to the BaseWallet contract invoked by some Module contracts.

https://github.com/argentlabs/argent-contracts/blob/develop/specifications/specifications.pdf
https://docs.argent.xyz/wallet-connect-and-argent#meta-transactions-and-relayers

My question is where is the specific event/function for this? I tried looking through the smart contract code https://github.com/argentlabs/argent-contracts, attempting to find the event signature that I can use the ABI to extract the event from the log but I could not find the appropriate event. Is this an anonymous event without an explicit event signature? How should I securely identified the transfer from the log?

My current approach is to match the event logs with topic[0]: 0x7d2476ab50663f025cff0be85655bcf355f62768615c0c478f3cd5293f807365 then get the sender, recipient and value from topics[1,2,3] accordingly. Is this the way to do it and is this secure?

Best Answer

You can search for known event signatures in the Ethereum Signature Database.

It corresponds to Invoked(address,address,uint256,bytes).

Using Etherscan vmtrace it reveals it is calling invoke functiun from BaseWallet. It performs the transfer with .call() and emits the invoke event.

function invoke(address _target, uint _value, bytes calldata _data) external moduleOnly returns (bytes memory _result) {
    bool success;
    // solium-disable-next-line security/no-call-value
    (success, _result) = _target.call.value(_value)(_data);
    if (!success) {
        // solium-disable-next-line security/no-inline-assembly
        assembly {
            returndatacopy(0, 0, returndatasize)
            revert(0, returndatasize)
        }
    }
    emit Invoked(msg.sender, _target, _value, _data);
}

Related Solutions

[Ethereum] Where do contract event logs get stored in the Ethereum architecture

Logs are part of the transaction receipts. They are generated by the clients when executing transactions and stored alongside the blockchain to allow retrieving them.

Logs are not part of the blockchain itself per se, since they are not required for consensus (they are just historical data), however they are verified by the blockchain as the transaction receipt hashes are stored inside the blocks.

Solidity Events – Relationship to Topics and Logs Explained

Topics are indexed parameters to an event.

topic[0] always refers to the hash of the hash of the event itself, and can have up to 3 indexed arguments, which will each be reflected in the topics.

EVM uses low-level primitives called logs to map them to high-level Solidity construct called Event. Logs may contain different topics that are indexed arguments.

Consider Event:

  event PersonCreated(uint indexed age, uint height);

And you fire it the foobar function of MyContract:

  function foobar() {
        emit PersonCreated(26, 176);
  }

This will create a low-level EVM log entry with topics

0x6be15e8568869b1e100750dd5079151b32637268ec08d199b318b793181b8a7d (Keccak-256 hash of PersonCreated(uint256,uint256))
0x36383cc9cfbf1dc87c78c2529ae2fcd4e3fc4e575e154b357ae3a8b2739113cf (Keccak-256 hash of age), value 26

You'll notice that height will not be a topic, but it will be included in the data section of the event.

Internally, your Ethereum node (Geth / Parity) will index arguments to build on indexable search indexes, so that you can easily do look ups by value later. Because creating indexes takes additional disk space, indexed parameters in events have additional gas cost. However, indexed are required to any meaningful look up in scale of events by value later.

Now in the web3 client you want to watch for creation events of all persons that are age of 26, you can simply do:

var createdEvent = myContract.PersonCreated({age: 26});
createdEvent.watch(function(err, result) {
  if (err) {
    console.log(err)
    return;
  }
  console.log("Found ", result);
})

Or you could filter all past events in similar fashion.

More information here

Best Answer

Related Solutions

[Ethereum] Where do contract event logs get stored in the Ethereum architecture

Solidity Events – Relationship to Topics and Logs Explained

Related Topic