Fix light client startup (build_select_chain returns Result<Option>) (#2574)

* fix light client strtup (build_select_chain -> Option)

* fixed node template compilation

* Update core/service/src/lib.rs

Co-Authored-By: Benjamin Kampmann <ben.kampmann@googlemail.com>

substrate/core/service/src/components.rs

@@ -344,7 +344,7 @@ pub trait ServiceFactory: 'static + Sized {
 	fn build_full_import_queue(
 		config: &mut FactoryFullConfiguration<Self>,
 		_client: Arc<FullClient<Self>>,
-		_select_chain: Self::SelectChain
+		_select_chain: Self::SelectChain,
 	) -> Result<Self::FullImportQueue, error::Error> {
 		if let Some(name) = config.chain_spec.consensus_engine() {
 			match name {
@@ -415,7 +415,7 @@ pub trait Components: Sized + 'static {
 	fn build_import_queue(
 		config: &mut FactoryFullConfiguration<Self::Factory>,
 		client: Arc<ComponentClient<Self>>,
-		select_chain: Self::SelectChain,
+		select_chain: Option<Self::SelectChain>,
 	) -> Result<Self::ImportQueue, error::Error>;
 
 	/// Finality proof provider for serving network requests.
@@ -427,7 +427,7 @@ pub trait Components: Sized + 'static {
 	fn build_select_chain(
 		config: &mut FactoryFullConfiguration<Self::Factory>,
 		client: Arc<ComponentClient<Self>>
-	) -> Result<Self::SelectChain, error::Error>;
+	) -> Result<Option<Self::SelectChain>, error::Error>;
 }
 
 /// A struct that implement `Components` for the full client.
@@ -506,16 +506,18 @@ impl<Factory: ServiceFactory> Components for FullComponents<Factory> {
 	fn build_import_queue(
 		config: &mut FactoryFullConfiguration<Self::Factory>,
 		client: Arc<ComponentClient<Self>>,
-		select_chain: Self::SelectChain,
+		select_chain: Option<Self::SelectChain>,
 	) -> Result<Self::ImportQueue, error::Error> {
+		let select_chain = select_chain
+			.ok_or_else(|| error::Error::from(error::ErrorKind::SelectChainRequired))?;
 		Factory::build_full_import_queue(config, client, select_chain)
 	}
 
 	fn build_select_chain(
 		config: &mut FactoryFullConfiguration<Self::Factory>,
 		client: Arc<ComponentClient<Self>>
-	) -> Result<Self::SelectChain, error::Error> {
-		Self::Factory::build_select_chain(config, client)
+	) -> Result<Option<Self::SelectChain>, error::Error> {
+		Self::Factory::build_select_chain(config, client).map(Some)
 	}
 
 	fn build_finality_proof_provider(
@@ -596,7 +598,7 @@ impl<Factory: ServiceFactory> Components for LightComponents<Factory> {
 	fn build_import_queue(
 		config: &mut FactoryFullConfiguration<Self::Factory>,
 		client: Arc<ComponentClient<Self>>,
-		_select_chain: Self::SelectChain,
+		_select_chain: Option<Self::SelectChain>,
 	) -> Result<Self::ImportQueue, error::Error> {
 		Factory::build_light_import_queue(config, client)
 	}
@@ -609,8 +611,8 @@ impl<Factory: ServiceFactory> Components for LightComponents<Factory> {
 	fn build_select_chain(
 		_config: &mut FactoryFullConfiguration<Self::Factory>,
 		_client: Arc<ComponentClient<Self>>
-	) -> Result<Self::SelectChain, error::Error> {
-		Err("Fork choice doesn't happen on light clients.".into())
+	) -> Result<Option<Self::SelectChain>, error::Error> {
+		Ok(None)
 	}
 }
 

substrate/core/service/src/error.rs

@@ -39,5 +39,9 @@ error_chain! {
 	}
 
 	errors {
+		SelectChainRequired {
+			description("Best chain selection strategy (SelectChain) must be provided when starting full node or authority."),
+			display("Best chain selection strategy (SelectChain) is not provided."),
+		}
 	}
 }

substrate/core/service/src/lib.rs

@@ -20,10 +20,10 @@
 #![warn(missing_docs)]
 
 mod components;
-mod error;
 mod chain_spec;
 pub mod config;
 pub mod chain_ops;
+pub mod error;
 
 use std::io;
 use std::net::SocketAddr;
@@ -42,7 +42,6 @@ use primitives::Pair;
 use runtime_primitives::generic::BlockId;
 use runtime_primitives::traits::{Header, As};
 use substrate_executor::NativeExecutor;
-use consensus_common::SelectChain;
 use tel::{telemetry, SUBSTRATE_INFO};
 
 pub use self::error::{ErrorKind, Error};
@@ -74,7 +73,7 @@ const DEFAULT_PROTOCOL_ID: &str = "sup";
 /// Substrate service.
 pub struct Service<Components: components::Components> {
 	client: Arc<ComponentClient<Components>>,
-	select_chain: <Components as components::Components>::SelectChain,
+	select_chain: Option<<Components as components::Components>::SelectChain>,
 	network: Option<Arc<components::NetworkService<Components::Factory>>>,
 	transaction_pool: Arc<TransactionPool<Components::TransactionPoolApi>>,
 	inherents_pool: Arc<InherentsPool<ComponentExtrinsic<Components>>>,
@@ -159,11 +158,11 @@ impl<Components: components::Components> Service<Components> {
 			select_chain.clone(),
 		)?);
 		let finality_proof_provider = Components::build_finality_proof_provider(client.clone())?;
-		let best_header = select_chain.best_chain()?;
+		let chain_info = client.info()?.chain;
 
 		let version = config.full_version();
-		info!("Best block: #{}", best_header.number());
-		telemetry!(SUBSTRATE_INFO; "node.start"; "height" => best_header.number().as_(), "best" => ?best_header.hash());
+		info!("Highest known block at #{}", chain_info.best_number);
+		telemetry!(SUBSTRATE_INFO; "node.start"; "height" => chain_info.best_number.as_(), "best" => ?chain_info.best_hash);
 
 		let network_protocol = <Components::Factory>::build_network_protocol(&config)?;
 		let transaction_pool = Arc::new(
@@ -404,7 +403,7 @@ impl<Components> Service<Components> where Components: components::Components {
 	}
 
 	/// Get clone of select chain.
-	pub fn select_chain(&self) -> <Components as components::Components>::SelectChain {
+	pub fn select_chain(&self) -> Option<<Components as components::Components>::SelectChain> {
 		self.select_chain.clone()
 	}