How to use frame support FindAuthor trait in a custom pallet

Question

I'm trying to use frame_support::traits::FindAuthor in my pallet for a custom logic.

I imported the traits and I tried to loose coupling it.

this is my config:

#[pallet::config]
    pub trait Config: frame_system::Config {
        /// Because this pallet emits events, it depends on the runtime's definition of an event.
        type Event: From<Event<Self>> + IsType<<Self as frame_system::Config>::Event>;

        type FindAuthor: FindAuthor<Self::AccountId>;
    }

So now I want to use find_author() function of this trait

let author = T::FindAuthor::find_author(digests???);

but I'm stuck with the digests param, I don't understand what "digests" means and how to pass it in order to get the author.

Answer 1

These are pre-runtime digests, which as the documentation says are

messages from the consensus engine to the runtime, although the consensus engine can (and should) read them itself to avoid code and state duplication. It is erroneous for a runtime to produce these, but this is not (yet) checked.

You can obtain digests for the current block like this:

let block_digest = <frame_system::Pallet<T>>::digest();
let digests = block_digest.logs.iter().filter_map(|d| d.as_pre_runtime());
let author = T::FindAuthor::find_author(digests);