Parsing a FunctionCall call return variable of typeVec<FieldElement> using a contract's ABI

[Eikix]

Hey:),

I'm currently using starknet-rs to call the Kakarot contract. Specifically, its entrypoint named execute_at_address (although it is an external function, I call it here as a view).

Here is the signature of the function:

func execute_at_address{
    syscall_ptr: felt*, pedersen_ptr: HashBuiltin*, range_check_ptr, bitwise_ptr: BitwiseBuiltin*
}(address: felt, value: felt, gas_limit: felt, calldata_len: felt, calldata: felt*) -> (
    stack_accesses_len: felt,
    stack_accesses: felt*,
    stack_len: felt,
    memory_accesses_len: felt,
    memory_accesses: felt*,
    memory_bytes_len: felt,
    evm_contract_address: felt,
    starknet_contract_address: felt,
    return_data_len: felt,
    return_data: felt*,
)

I manage to call this function fine, and the return is:

0x000000000000000000000000000000000000000000000000000000000000001e000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000006661abd0000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000003000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000700000000000000000000000000000000000000000000000000000000000000004000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000005000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000000006000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000007000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000800000000000000000000000000000000000000000000000000000000000000008000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000009000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000a00000000000000000000000000000000000000000000000000000000000000004000000000000000000000000000000000000000000000000000000000000000c00000000000000000000000000000000000000000000000000000000000000040000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000050000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000008000000000000000000000000000000000000000000000000000000000000000080000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000090000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000000a0000000000000000000000000abde1007e67126e0755af0ff0173f919738f8373062897a9e931ba1ae4721548bd963e3fe67126e0755af0ff0173f919738f8373000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002

I'd like to isolate each variable in the return. Is there an easy way to do it with Starknet-rs? If not, I can help in building a method to accomplish that.

Thanks! Have a good one

[xJonathanLEI]

Parsing function call return values (and also encoding calldata) is currently a missing feature of starknet-rs but is on the roadmap:

starknet-rs/README.md

Lines 38 to 40 in e3f3e4f

	- [x] Signer for using [IAccount](https://github.com/OpenZeppelin/cairo-contracts/blob/main/src/openzeppelin/account/IAccount.cairo) account contracts
	- [ ] Strongly-typed smart contract binding code generation from ABI

So unfortunately you'll probably have to implement customized decoding logic in your application before this gets done. It's actually next up on my todo list.

The lib itself actually needs this too: when interacting with account contracts, data encoding/decoding is currently done manually. I would like to replace that part too.

[Eikix]

Can I provide support/help for this specific part of the roadmap:)?

[fracek]

Hey @xJonathanLEI, do you have a specific design in mind for the abi decoder? Would something like ethabi with Token (a concrete representation of a serializable value) and ParamType (the abi definition) work as a first step?

[xJonathanLEI]

Hey guys sorry for the late reply. I actually quite like the design of ethabi so I think that's a good approach. Lemme open a separate issue to track this :)

[haroune-mohammedi]

I'll be working on this one, I had a call with @fracek we discussed the design of the solution, we'll do something similar to ethabi

[xJonathanLEI]

@haroune-mohammedi That's great! I'm actually also working on supporting Cairo 1 artifact parsing (& class hash computation) so there will be conflicts. It should be easy to resolve but here's the heads up.

[ericnordelo]

Hi @xJonathanLEI. Is there an ETA for implementing the Decoder? I see there is an issue open for it, but I don't see much activity.