Alert on proxy - ability to monitor certain implementation function

[ds-rabadie]

Describe the feature

Is it possible currently to trigger alert on implementation function? It seems that monitor mainly use eth_getLogs but to have the ability to see what implementation function has been called we need trace ?

Is it possible though to monitor the fallback on the proxy, and see if a certain function signature has been called with a certain value?

My understanding is that what

"match_conditions": {
    "functions": [
      {
        "signature": "_fallback()",
        "expression": null //is it possible to do that here?
      }
    ],
    "events": [],
    "transactions": [
      {
        "status": "Success",
        "expression": null
      }
    ]
  },

Is function.expression the place to do that?

Additional context

No response

[NicoMolinaOZ]

Hello @ds-rabadie, thanks for asking!

Regarding your question: yes, it is possible to listen to the _fallback() function.
One important thing to note is that the function must belong to the contract address you are listening to, so the ABI definition needs to include the _fallback() function.

"expression": null //is it possible to do that here?

Yes, it is. By using a null value, you will listen to every occurrence of the _fallback() function.

Questions here to better understand:

1 - Which is the exact use case?

2 - Fallback monitoring behavior:
If you are monitoring fallback calls on a specific contract and the function exists in the ABI, then it should be possible to monitor it. However, if your goal is to understand what triggered the fallback, logs alone are not sufficient. In that case, you need to rely on transaction traces.

3 - Next steps for deeper inspection:
Take the transaction hash shown by the monitor and forward it to a custom filter (monitor feature) to retrieve additional data—such as execution traces— for a more detailed analysis.

Have you tried? Please let us know if you are seeing issues. Thanks!

[ds-rabadie]

Hi @NicoMolinaOZ, thank you for the super fast response!

I've tried adding alert on 'fallback()' and '_fallback()' also providing the ABI and it did not worked unfortunately. I m using a basic Counter deployed using TransparentProxy contract from OZ. Is it normal or it's supposed to work?

I also noticed that I was not able to trigger cross contract call.
I monitor setValue in contract A. If it is triggered by an EOA I have the alert, though if I deploy contract B that call setValue in contract A, the alert does not trigger. Is there a way to enable alerts on cross contract calls?

Thanks for the help !

[NicoMolinaOZ]

Hello @ds-rabadie
Here are some points to take into account:

1. Fallback functions are inside ABI, but the fallback does not have a function selector, so the monitor can not filter based on that due to the lack of a function selector
2. Regarding monitoring a function called by another contract:

The cross-contract call issue stems from how the filter determines which transactions to process. The system only matches transactions where the to address directly matches a monitored contract address. When Contract B calls Contract A's setValue function:

Transaction to = Contract B's address
Transaction from = EOA that initiated the call
The actual call to Contract A happens internally during Contract B's execution, so it's imposible to evaluate this situation.

Thanks, let us know if something is not clear.

[ds-rabadie]

@NicoMolinaOZ super clear thanks! 🙏

I suppose this is the limitation of not using trace? Is it something that oz monitor wants to support in the future?