A place for talking about the Ethereum Virtual Machine on Farcaster.

what is the most reliable way of attaching metadata to an ethereum transaction?

cases that need to be handled:
1. EOA tx
2. UserOp
3. batch call directly on smart account

calldata suffix is the first thing that comes to mind but fetching userops is potentially expensive and it requires tracing to handle (3)

can you build in event emission or are you trying to retrofit this to an existing smart contract?  if the latter, can you route transactions through a new smart contract that emits your metadata event before calling the  intended smart contract's method?

If you don't have control of the target method at all but are involved in initially building the transaction, I think calldata might be the only way.

How much metadata do you want to store? I wonder whether you could encode some data within access lists.
Actually I guess that wouldn't work for userops unless you are also operating the bundler

There are various methods, but calldata suffix is one of the most common ways. However, for UserOps and batch calls on smart accounts, tracing and advanced analytical tools might be necessary. The specific solution depends on your project’s requirements, but using events and logs can also be helpful