Decode constructor call data

[sebastiantf]

Describe the Feature

I was looking for an API that lets you decode the constructor args, provided the construction txn hash, or the txn calldata.

This could either be separate function on Contract / Interface, or made doable using decodeFunctionData()

Apologies if I may have missed something that already allows to do this

Code Example

iface.decodeFunctionData('constructor',constructorArgs);

contract.decodeConstructorArgs(constructorArgs)

[ricmoo]

You cannot parse the constructor arguments from a transactions calldata, because the initcode has been prepended to it, and without know the length of that data, you would not know where to begin decoding. There are heuristics, based on solidity metadata, but that is outside the scope of ethers, since different versions of solidity uses slightly different formats and not all contracts are compiled from solidity, so there is no gerneralized way to solve that.

[sebastiantf]

Hmm. I was thinking of using this with Typechain types if it has the bytecode in the type. So use that to determine where to begin decoding. I guess that should be an issue in TypeChain?

Nonetheless, it should still be possible in ethers to decode the constructor params, if its already extracted from the calldata and passed in as an input?

[ricmoo]

If you have access to the range of the deployment parameters, you can trivially use _decodeParams, passing in the iface.deploy.inputs for types.

But this is only possible in a very narrow range of situations. You cannot, got from a tx hash to constructor arguments, for example.