service: don't use the grandpa observer (#494) (#498)

* service: don't use the grandpa observer

* service: remove unnecessary boxing

* service: fix indentation

* service: remove unnecessary on_exit

tasks spawned with `spawn_task`/`spawn_essential_task` are already
guarded by `on_exit`.

* Update service/src/lib.rs

Co-Authored-By: Gavin Wood <gavin@parity.io>

polkadot/service/src/lib.rs

@@ -27,7 +27,6 @@ use polkadot_runtime::GenesisConfig;
 use polkadot_network::{gossip::{self as network_gossip, Known}, validation::ValidationNetwork};
 use service::{error::{Error as ServiceError}, Configuration, ServiceBuilder};
 use transaction_pool::txpool::{Pool as TransactionPool};
-use babe::{import_queue, start_babe};
 use grandpa::{self, FinalityProofProvider as GrandpaFinalityProofProvider};
 use inherents::InherentDataProviders;
 use log::info;
@@ -261,30 +260,32 @@ pub fn new_full(config: Configuration<CustomConfiguration, GenesisConfig>)
 			babe_link,
 		};
 
-		let babe = start_babe(babe_config)?;
+		let babe = babe::start_babe(babe_config)?;
 		service.spawn_essential_task(babe);
 	}
 
+	let keystore = if is_authority {
+		Some(service.keystore())
+	} else {
+		None
+	};
+
 	let config = grandpa::Config {
 		// FIXME substrate#1578 make this available through chainspec
 		gossip_duration: Duration::from_millis(333),
 		justification_period: 512,
 		name: Some(name),
-		keystore: Some(service.keystore()),
+		keystore,
 	};
 
-	match (is_authority, disable_grandpa) {
+	let enable_grandpa = !disable_grandpa;
-		(false, false) => {
+	if enable_grandpa {
-			// start the lightweight GRANDPA observer
-			service.spawn_task(grandpa::run_grandpa_observer(
-				config,
-				link_half,
-				service.network(),
-				service.on_exit(),
-			)?);
-		},
-		(true, false) => {
 		// 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.
 		let grandpa_config = grandpa::GrandpaParams {
 			config: config,
 			link: link_half,
@@ -295,14 +296,12 @@ pub fn new_full(config: Configuration<CustomConfiguration, GenesisConfig>)
 			voting_rule: grandpa::VotingRulesBuilder::default().build(),
 		};
 		service.spawn_essential_task(grandpa::run_grandpa_voter(grandpa_config)?);
-		},
+	} else {
-		(_, true) => {
 		grandpa::setup_disabled_grandpa(
 			service.client(),
 			&inherent_data_providers,
 			service.network(),
 		)?;
-		},
 	}
 
 	Ok(service)
@@ -338,7 +337,6 @@ pub fn new_light(config: Configuration<CustomConfiguration, GenesisConfig>)
 			let finality_proof_request_builder =
 				finality_proof_import.create_finality_proof_request_builder();
 
-
 			let (babe_block_import, babe_link) = babe::block_import(
 				babe::Config::get_or_compute(&*client)?,
 				grandpa_block_import,
@@ -347,7 +345,7 @@ pub fn new_light(config: Configuration<CustomConfiguration, GenesisConfig>)
 			)?;
 
 			// FIXME: pruning task isn't started since light client doesn't do `AuthoritySetup`.
-			let import_queue = import_queue(
+			let import_queue = babe::import_queue(
 				babe_link,
 				babe_block_import,
 				None,