Validate bytes16 argument size

Question

I have a function which accepts one bytes16 argument.

  function start(
    bytes16 reference
  )

I have some events which I use to track behaviour, using reference as the index. Everything works well enough except when a user submits a reference with 17-32 chars. Between web3 and the SC, reference is being truncated, keeping only the 16 bytes to the left and the rest as zero.

I added validations for this on the client-side but I still wanted to setup the SC to handle this more gracefully. I was expecting it to revert transaction with a type error but that only happens if the argument has over 32 bytes.

I would imagine I should be adding a modifier to require the right length but I'm having a hard time finding similar cases to understand how it should be done. What's the best practice in a situation like this?

Answer 1

should I be validating this on the Smart Contract or on the client-side to trigger a proper response to the user

You could parse the msg.data within the contract to check if additional bytes have been submitted, but it will cost extra gas and the check is better done at the client side in the UI.

Answer 2

If your function is external (or public) you have the whole message sent to the contract in msg.data.

You can parse it following the solidity abi to determine if incorrect data was submitted.