how to run some logic before gossiping the block as author?

Question

In substrate-node-template, are there any available ways to execute a task or provide a callback to be executed just before the block gets gossiped to other validators, right after it has produced the block?

Answer 1

If you want to do some work before announcing a block to the network, you can do it the following way. You will need to change this code to something like this:

   // Don't let the internals announce the block automatically
   config.announce_block = false;
 
   // Start the network etc.
   let (network, system_rpc_tx, tx_handler_controller, network_starter, sync_service) =
        sc_service::build_network(sc_service::BuildNetworkParams {
            config: &config,
            client: client.clone(),
            transaction_pool: transaction_pool.clone(),
            spawn_handle: task_manager.spawn_handle(),
            import_queue,
            block_announce_validator_builder: None,
            warp_sync_params: Some(WarpSyncParams::WithProvider(warp_sync)),
        })?;
    
    let block_import = client.import_notification_stream();
    let custom_block_announce = async move {
        while let Some(import) = block_import.next().await {
            // If the local node produced the block
            if import.origin == BlockOrigin::Own {
                // Insert your special logic here
            }

            // Announce the block to the network
            sync_service.announce_block(import.hash, None);
        }
    };

    task_manager.spawn_handle().spawn(
        "custom-block-announce",
        None,
        custom_block_announce.boxed(),
    );