How can I pass a Vec<u8> via chain extension to pallet?

Question

I am working on chain extension to call rmrk pallet methods. One of the methods needs a BoundedVec that I need to pass via ink smart contract. What data type can I use to do this on smart contract side? Is there a BoundedVec<> type on ink?

I tried using Vec and then trying to convert it to BoundedVec in the chain extension in runtime but I get the following error

env.read_as()?;
      |                                                                                                
      ^^^^^^^ the trait `MaxEncodedLen` is not implemented for `sp_runtime::sp_application_crypto::Vec<u8>

The method signature on ink contract

fn create_collection(contract_address: AccountId, metadata: Vec<u8>, symbol: Vec<u8>) -> Result<CollectionId, RCError>;

Reading the arguments in the runtime

let (contract_address, metadata, symbol) : (AccountId, Vec<u8>, Vec<u8>) = env.read_as()?;

Answer 1

You can only use read_as() for types whose size is known at compile time (thus the requirement that types implement MaxEncodedLen).

If you don't know the size ahead of time, like in the case of a Vec, you can use read_as_unbounded(). In order to get the number of bytes to read you can use the in_len() method.

So your code would look something like:

let (contract_address, metadata, symbol): (AccountId, Vec<u8>, Vec<u8>)
    = env.read_as_unbounded(env.in_len())?;

I have some demo code here if you need more resources on how to implement chain-extensions.