how to run custom block validation logic when importing a block?

Question

I am trying to execute some logic whenever a block is received, specifically i want to create custom transactions validation of a received block.

can someone provide a clear example (simple code) on how to provide extra verification of a received block in aura?

ps: i noticed that aura use grandpa when it creates its BlockImport, i assume this has something to with verifying the block if so why aura is using grandpa validation logic of having its own, and is there a way to simply extend it by plugging extra verification logic, if that is indeed the correct place for verification.

Answer 1

You could write your own BlockImport:

struct BlockImport<I>(I);

impl<I: sc_consensus::BlockImport> sc_consensus::BlockImport for BlockImport<I> {
    type Error = I::Error;
    type Transaction = I::Transaction;

    async fn check_block(
        &mut self,
        block: BlockCheckParams<B>,
    ) -> Result<ImportResult, Self::Error> {
        self.0.check_block(block).await
    }

    async fn import_block(
        &mut self,
        block: BlockImportParams<B, Self::Transaction>,
        cache: HashMap<CacheKeyId, Vec<u8>>,
    ) -> Result<ImportResult, Self::Error> {
        if let Some(transactions) = &block.body {
             // Do whatever check you need with the transactions
        }

        self.0.import_block(block, cache).await
    }
}

Then in your service you stack BlockImport(AuraBlockImport(GrandpaBlockImport(Client))) and each external block will be checked with your custom logic.