Decoding an arbitrary vector (passed as a transaction parameter)

[aeryz]

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Describe your question in detail.

Hey, I'm implementing IBC protocol in aptos-move. Some of the entry functions we have expects proof parameter which should be just arbitrary bytes as the protocol spec suggests. This proof is then decoded by the corresponding light client (the proof type might change based on the light client).

To do this, we tried to use Any because it's not allowed to decode bytes into arbitrary types. But then realized Any is not allowed as a transaction parameter. Then we tried having a function to manually decode arbitrary bytes using bcs but again realized that there is no support for partial decoding (peel) similar to here.

For now we are using our protobuf helpers to decode arbitrary types. But I would love to not do that and just be able to encode/decode as easy as possible. Is there a way to achieve this?

What error, if any, are you getting?

No response

What have you tried or looked at? Or how can we reproduce the error?

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Which operating system are you using?

Linux (Ubuntu, Fedora, Windows WSL, etc.)

Which SDK or tool are you using? (if any)

N/A

Describe your environment or tooling in detail

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[0xaptosj]

do functions in this contract help you decode? https://github.com/aptos-labs/aptos-core/blob/main/aptos-move/framework/aptos-stdlib/sources/from_bcs.move

I'm not familiar with decoding/encoding, so please bear with me

[aeryz]

Hey! Thanks for the answer. Unfortunately this module does not export from_bytes function which lets you decode bytes into an arbitrary type: https://github.com/aptos-labs/aptos-core/blob/main/aptos-move/framework/aptos-stdlib/sources/from_bcs.move#L67.

I also tried having a function to manually decode the fields. But from_bcs::to_xxx functions don't do partial decoding. So it didn't work either.

[0xaptosj]

hey i just dm'ed you on twitter, maybe we can have a meeting to chat this in detail

[aeryz]

I created an bcs_utils library to let people do partial decoding:
https://gist.github.com/aeryz/d005e7ccd2f12da1d0e58ed4bcf2a36d

And here is how you would use it for your type:

    public fun decode_existence_proof(buf: &mut BcsBuf): ExistenceProof {
        ExistenceProof {
            key: bcs_utils::peel_bytes(buf),
            value: bcs_utils::peel_bytes(buf),
            leaf_prefix: bcs_utils::peel_bytes(buf),
            path:bcs_utils::peel_vector<InnerOp>(buf, |buf| InnerOp {
                prefix: bcs_utils::peel_bytes(buf),
                suffix: bcs_utils::peel_bytes(buf),
            }),
        }
    }