lib.rs

		{
			let handle = handle.clone();
			task_manager.spawn_essential_handle().spawn_blocking(
				"overseer",
				None,
				Box::pin(async move {
					use futures::{pin_mut, select, FutureExt};

					let forward = polkadot_overseer::forward_events(overseer_client, handle);

					let forward = forward.fuse();
					let overseer_fut = overseer.run().fuse();

					pin_mut!(overseer_fut);
					pin_mut!(forward);

					select! {
						() = forward => (),
						() = overseer_fut => (),
						complete => (),
					}
				}),
			);
		}
		Some(handle)
	} else {
		assert!(
			!auth_or_collator,
			"Precondition congruence (false) is guaranteed by manual checking. qed"
		);
		None
	};

	if role.is_authority() {
		let proposer = sc_basic_authorship::ProposerFactory::new(
			task_manager.spawn_handle(),
			client.clone(),
			transaction_pool.clone(),
			prometheus_registry.as_ref(),
			telemetry.as_ref().map(|x| x.handle()),
		);

		let client_clone = client.clone();
		let overseer_handle =
			overseer_handle.as_ref().ok_or(Error::AuthoritiesRequireRealOverseer)?.clone();
		let slot_duration = babe_link.config().slot_duration();
		let babe_config = babe::BabeParams {
			keystore: keystore_container.keystore(),
			client: client.clone(),
			select_chain,
			block_import,
			env: proposer,
			sync_oracle: sync_service.clone(),
			justification_sync_link: sync_service.clone(),
			create_inherent_data_providers: move |parent, ()| {
				let client_clone = client_clone.clone();
				let overseer_handle = overseer_handle.clone();

				async move {
					let parachain =
						polkadot_node_core_parachains_inherent::ParachainsInherentDataProvider::new(
							client_clone,
							overseer_handle,
							parent,
						);

					let timestamp = sp_timestamp::InherentDataProvider::from_system_time();

					let slot =
						sp_consensus_babe::inherents::InherentDataProvider::from_timestamp_and_slot_duration(
							*timestamp,
							slot_duration,
						);

					Ok((slot, timestamp, parachain))
				}
			},
			force_authoring,
			backoff_authoring_blocks,
			babe_link,
			block_proposal_slot_portion: babe::SlotProportion::new(2f32 / 3f32),
			max_block_proposal_slot_portion: None,
			telemetry: telemetry.as_ref().map(|x| x.handle()),
		};

		let babe = babe::start_babe(babe_config)?;
		task_manager.spawn_essential_handle().spawn_blocking("babe", None, babe);
	}

	// if the node isn't actively participating in consensus then it doesn't
	// need a keystore, regardless of which protocol we use below.
	let keystore_opt = if role.is_authority() { Some(keystore_container.keystore()) } else { None };

	if enable_beefy {
		let justifications_protocol_name = beefy_on_demand_justifications_handler.protocol_name();
		let network_params = beefy::BeefyNetworkParams {
			network: network.clone(),
			sync: sync_service.clone(),
			gossip_protocol_name: beefy_gossip_proto_name,
			justifications_protocol_name,
			_phantom: core::marker::PhantomData::<Block>,
		};
		let payload_provider = beefy_primitives::mmr::MmrRootProvider::new(client.clone());
		let beefy_params = beefy::BeefyParams {
			client: client.clone(),
			backend: backend.clone(),
			payload_provider,
			runtime: client.clone(),
			key_store: keystore_opt.clone(),
			network_params,
			min_block_delta: if chain_spec.is_wococo() { 4 } else { 8 },
			prometheus_registry: prometheus_registry.clone(),
			links: beefy_links,
			on_demand_justifications_handler: beefy_on_demand_justifications_handler,
		};

		let gadget = beefy::start_beefy_gadget::<_, _, _, _, _, _, _>(beefy_params);

		// BEEFY currently only runs on testnets, if it fails we'll
		// bring the node down with it to make sure it is noticed.
		task_manager
			.spawn_essential_handle()
			.spawn_blocking("beefy-gadget", None, gadget);

		if is_offchain_indexing_enabled {
			task_manager.spawn_handle().spawn_blocking(
				"mmr-gadget",
				None,
				MmrGadget::start(
					client.clone(),
					backend.clone(),
					sp_mmr_primitives::INDEXING_PREFIX.to_vec(),
				),
			);
		}
	}

	let config = grandpa::Config {
		// FIXME substrate#1578 make this available through chainspec
		// Grandpa performance can be improved a bit by tuning this parameter, see:
		// https://github.com/paritytech/polkadot/issues/5464
		gossip_duration: Duration::from_millis(1000),
		justification_period: 512,
		name: Some(name),
		observer_enabled: false,
		keystore: keystore_opt,
		local_role: role,
		telemetry: telemetry.as_ref().map(|x| x.handle()),
		protocol_name: grandpa_protocol_name,
	};

	let enable_grandpa = !disable_grandpa;
	if enable_grandpa {
		// start the full GRANDPA voter
		// NOTE: unlike in substrate we are currently running the full
		// GRANDPA voter protocol for all full nodes (regardless of whether
		// they're validators or not). at this point the full voter should
		// provide better guarantees of block and vote data availability than
		// the observer.

		// add a custom voting rule to temporarily stop voting for new blocks
		// after the given pause block is finalized and restarting after the
		// given delay.
		let mut builder = grandpa::VotingRulesBuilder::default();

		#[cfg(not(feature = "malus"))]
		let _malus_finality_delay = None;

		if let Some(delay) = _malus_finality_delay {
			info!(?delay, "Enabling malus finality delay",);
			builder = builder.add(grandpa::BeforeBestBlockBy(delay));
		};

		let voting_rule = match grandpa_pause {
			Some((block, delay)) => {
				info!(
					block_number = %block,
					delay = %delay,
					"GRANDPA scheduled voting pause set for block #{} with a duration of {} blocks.",
					block,
					delay,
				);

				builder.add(grandpa_support::PauseAfterBlockFor(block, delay)).build()
			},
			None => builder.build(),
		};

		let grandpa_config = grandpa::GrandpaParams {
			config,
			link: link_half,
			network: network.clone(),
			sync: sync_service.clone(),
			voting_rule,
			prometheus_registry: prometheus_registry.clone(),
			shared_voter_state,
			telemetry: telemetry.as_ref().map(|x| x.handle()),
			offchain_tx_pool_factory: OffchainTransactionPoolFactory::new(transaction_pool.clone()),
		};

		task_manager.spawn_essential_handle().spawn_blocking(
			"grandpa-voter",
			None,
			grandpa::run_grandpa_voter(grandpa_config)?,
		);
	}

	network_starter.start_network();

	Ok(NewFull {
		task_manager,
		client,
		overseer_handle,
		network,
		sync_service,
		rpc_handlers,
		backend,
	})
}

#[cfg(feature = "full-node")]
macro_rules! chain_ops {
	($config:expr, $jaeger_agent:expr, $telemetry_worker_handle:expr) => {{
		let telemetry_worker_handle = $telemetry_worker_handle;
		let jaeger_agent = $jaeger_agent;
		let mut config = $config;
		let basics = new_partial_basics(config, jaeger_agent, telemetry_worker_handle)?;

		use ::sc_consensus::LongestChain;
		// use the longest chain selection, since there is no overseer available
		let chain_selection = LongestChain::new(basics.backend.clone());

		let service::PartialComponents { client, backend, import_queue, task_manager, .. } =
			new_partial::<LongestChain<_, Block>>(&mut config, basics, chain_selection)?;
		Ok((client, backend, import_queue, task_manager))
	}};
}

/// Builds a new object suitable for chain operations.
#[cfg(feature = "full-node")]
pub fn new_chain_ops(
	config: &mut Configuration,
	jaeger_agent: Option<std::net::SocketAddr>,
) -> Result<
	(
		Arc<FullClient>,
		Arc<FullBackend>,
		sc_consensus::BasicQueue<Block, PrefixedMemoryDB<BlakeTwo256>>,
		TaskManager,
	),
	Error,
> {
	config.keystore = service::config::KeystoreConfig::InMemory;

	if config.chain_spec.is_rococo() ||
		config.chain_spec.is_wococo() ||
		config.chain_spec.is_versi()
	{
		chain_ops!(config, jaeger_agent, None)
	} else if config.chain_spec.is_kusama() {
		chain_ops!(config, jaeger_agent, None)
	} else if config.chain_spec.is_westend() {
		return chain_ops!(config, jaeger_agent, None)
	} else {
		chain_ops!(config, jaeger_agent, None)
	}
}

/// Build a full node.
///
/// The actual "flavor", aka if it will use `Polkadot`, `Rococo` or `Kusama` is determined based on
/// [`IdentifyVariant`] using the chain spec.
///
/// `overseer_enable_anyways` always enables the overseer, based on the provided `OverseerGenerator`,
/// regardless of the role the node has. The relay chain selection (longest or disputes-aware) is
/// still determined based on the role of the node. Likewise for authority discovery.
#[cfg(feature = "full-node")]
pub fn build_full(
	config: Configuration,
	is_collator: IsCollator,
	grandpa_pause: Option<(u32, u32)>,
	enable_beefy: bool,
	jaeger_agent: Option<std::net::SocketAddr>,
	telemetry_worker_handle: Option<TelemetryWorkerHandle>,
	overseer_enable_anyways: bool,
	overseer_gen: impl OverseerGen,
	overseer_message_channel_override: Option<usize>,
	malus_finality_delay: Option<u32>,
	hwbench: Option<sc_sysinfo::HwBench>,
) -> Result<NewFull, Error> {
	let is_polkadot = config.chain_spec.is_polkadot();

	new_full(
		config,
		is_collator,
		grandpa_pause,
		enable_beefy,
		jaeger_agent,
		telemetry_worker_handle,
		None,
		overseer_enable_anyways,
		overseer_gen,
		overseer_message_channel_override.map(move |capacity| {
			if is_polkadot {
				gum::warn!("Channel capacity should _never_ be tampered with on polkadot!");
			}
			capacity
		}),
		malus_finality_delay,
		hwbench,
	)
}

/// Reverts the node state down to at most the last finalized block.
///
/// In particular this reverts:
/// - `ApprovalVotingSubsystem` data in the parachains-db;
/// - `ChainSelectionSubsystem` data in the parachains-db;
/// - Low level Babe and Grandpa consensus data.
#[cfg(feature = "full-node")]
pub fn revert_backend(
	client: Arc<FullClient>,
	backend: Arc<FullBackend>,
	blocks: BlockNumber,
	config: Configuration,
) -> Result<(), Error> {
	let best_number = client.info().best_number;
	let finalized = client.info().finalized_number;
	let revertible = blocks.min(best_number - finalized);

	if revertible == 0 {
		return Ok(())
	}

	let number = best_number - revertible;
	let hash = client.block_hash_from_id(&BlockId::Number(number))?.ok_or(
		sp_blockchain::Error::Backend(format!(
			"Unexpected hash lookup failure for block number: {}",
			number
		)),
	)?;

	let parachains_db = open_database(&config.database)
		.map_err(|err| sp_blockchain::Error::Backend(err.to_string()))?;

	revert_approval_voting(parachains_db.clone(), hash)?;
	revert_chain_selection(parachains_db, hash)?;
	// Revert Substrate consensus related components
	babe::revert(client.clone(), backend, blocks)?;
	grandpa::revert(client, blocks)?;

	Ok(())
}

fn revert_chain_selection(db: Arc<dyn Database>, hash: Hash) -> sp_blockchain::Result<()> {
	let config = chain_selection_subsystem::Config {
		col_data: parachains_db::REAL_COLUMNS.col_chain_selection_data,
		stagnant_check_interval: chain_selection_subsystem::StagnantCheckInterval::never(),
		stagnant_check_mode: chain_selection_subsystem::StagnantCheckMode::PruneOnly,
	};

	let chain_selection = chain_selection_subsystem::ChainSelectionSubsystem::new(config, db);

	chain_selection
		.revert_to(hash)
		.map_err(|err| sp_blockchain::Error::Backend(err.to_string()))
}

fn revert_approval_voting(db: Arc<dyn Database>, hash: Hash) -> sp_blockchain::Result<()> {
	let config = approval_voting_subsystem::Config {
		col_approval_data: parachains_db::REAL_COLUMNS.col_approval_data,
		slot_duration_millis: Default::default(),
	};

	let approval_voting = approval_voting_subsystem::ApprovalVotingSubsystem::with_config(
		config,
		db,
		Arc::new(sc_keystore::LocalKeystore::in_memory()),
		Box::new(consensus_common::NoNetwork),
		approval_voting_subsystem::Metrics::default(),
	);

	approval_voting
		.revert_to(hash)
		.map_err(|err| sp_blockchain::Error::Backend(err.to_string()))
}