Function world__retrieve_data 

pub unsafe extern "C" fn world__retrieve_data(
    data_handle: DataHandle,
    retrieve_data_type: u32,
    data_ptr: *mut u8,
    data_len: u32,
    __ark_ffi_output: *mut u32,
) -> ErrorCode

A max_len of 0 should still give you out_len in that argument so that you can use this to allocate data and call it again with the right amount.