client/finality-grandpa: Add Prometheus metrics to GossipValidator (#5237)

* client/finality-grandpa: Add Prometheus metrics to GossipValidator

Instrument finality grandpa `GossipValidator` exposing count of messages
validated by message type and message action.

```
\# HELP substrate_finality_grandpa_communication_gossip_validator_messages Number of messages validated by the finality grandpa gossip validator.
\# TYPE substrate_finality_grandpa_communication_gossip_validator_messages counter
substrate_finality_grandpa_communication_gossip_validator_messages{action="discard",message="neighbor"} 39
substrate_finality_grandpa_communication_gossip_validator_messages{action="keep",message="vote"} 28
```

* client/finality-grandpa: Add None as Prometheus registry in tests

* client/finality-granpda/src/communication: Refactor metric registration

substrate/client/finality-grandpa/src/communication/gossip.rs

@@ -91,6 +91,7 @@ use sp_finality_grandpa::AuthorityId;
 use sc_telemetry::{telemetry, CONSENSUS_DEBUG};
 use log::{trace, debug};
 use futures::channel::mpsc;
+use prometheus_endpoint::{CounterVec, Opts, PrometheusError, register, Registry, U64};
 use rand::seq::SliceRandom;
 
 use crate::{environment, CatchUp, CompactCommit, SignedMessage};
@@ -1197,11 +1198,34 @@ impl<Block: BlockT> Inner<Block> {
 	}
 }
 
+// Prometheus metrics for [`GossipValidator`].
+pub(crate) struct Metrics {
+	messages_validated: CounterVec<U64>,
+}
+
+impl Metrics {
+	pub(crate) fn register(registry: &prometheus_endpoint::Registry) -> Result<Self, PrometheusError> {
+		Ok(Self {
+			messages_validated: register(
+				CounterVec::new(
+					Opts::new(
+						"finality_grandpa_communication_gossip_validator_messages",
+						"Number of messages validated by the finality grandpa gossip validator."
+					),
+					&["message", "action"]
+				)?,
+				registry,
+			)?,
+		})
+	}
+}
+
 /// A validator for GRANDPA gossip messages.
 pub(super) struct GossipValidator<Block: BlockT> {
 	inner: parking_lot::RwLock<Inner<Block>>,
 	set_state: environment::SharedVoterSetState<Block>,
 	report_sender: mpsc::UnboundedSender<PeerReport>,
+	metrics: Option<Metrics>,
 }
 
 impl<Block: BlockT> GossipValidator<Block> {
@@ -1211,12 +1235,23 @@ impl<Block: BlockT> GossipValidator<Block> {
 	pub(super) fn new(
 		config: crate::Config,
 		set_state: environment::SharedVoterSetState<Block>,
+		prometheus_registry: Option<&Registry>,
 	) -> (GossipValidator<Block>, mpsc::UnboundedReceiver<PeerReport>)	{
+		let metrics = match prometheus_registry.map(Metrics::register) {
+			Some(Ok(metrics)) => Some(metrics),
+			Some(Err(e)) => {
+				debug!(target: "afg", "Failed to register metrics: {:?}", e);
+				None
+			},
+			None => None,
+		};
+
 		let (tx, rx) = mpsc::unbounded();
 		let val = GossipValidator {
 			inner: parking_lot::RwLock::new(Inner::new(config)),
 			set_state,
 			report_sender: tx,
+			metrics: metrics,
 		};
 
 		(val, rx)
@@ -1279,12 +1314,21 @@ impl<Block: BlockT> GossipValidator<Block> {
 		let mut broadcast_topics = Vec::new();
 		let mut peer_reply = None;
 
+		// Message name for Prometheus metric recording.
+		let message_name;
+
 		let action = {
 			match GossipMessage::<Block>::decode(&mut data) {
-				Ok(GossipMessage::Vote(ref message))
-					=> self.inner.write().validate_round_message(who, message),
-				Ok(GossipMessage::Commit(ref message)) => self.inner.write().validate_commit_message(who, message),
+				Ok(GossipMessage::Vote(ref message)) => {
+					message_name = Some("vote");
+					self.inner.write().validate_round_message(who, message)
+				},
+				Ok(GossipMessage::Commit(ref message)) => {
+					message_name = Some("commit");
+					self.inner.write().validate_commit_message(who, message)
+				},
 				Ok(GossipMessage::Neighbor(update)) => {
+					message_name = Some("neighbor");
 					let (topics, action, catch_up, report) = self.inner.write().import_neighbor_message(
 						who,
 						update.into_neighbor_packet(),
@@ -1298,9 +1342,12 @@ impl<Block: BlockT> GossipValidator<Block> {
 					peer_reply = catch_up;
 					action
 				}
-				Ok(GossipMessage::CatchUp(ref message))
-					=> self.inner.write().validate_catch_up_message(who, message),
+				Ok(GossipMessage::CatchUp(ref message)) => {
+					message_name = Some("catch_up");
+					self.inner.write().validate_catch_up_message(who, message)
+				},
 				Ok(GossipMessage::CatchUpRequest(request)) => {
+					message_name = Some("catch_up_request");
 					let (reply, action) = self.inner.write().handle_catch_up_request(
 						who,
 						request,
@@ -1311,6 +1358,7 @@ impl<Block: BlockT> GossipValidator<Block> {
 					action
 				}
 				Err(e) => {
+					message_name = None;
 					debug!(target: "afg", "Error decoding message: {}", e.what());
 					telemetry!(CONSENSUS_DEBUG; "afg.err_decoding_msg"; "" => "");
 
@@ -1320,6 +1368,16 @@ impl<Block: BlockT> GossipValidator<Block> {
 			}
 		};
 
+		// Prometheus metric recording.
+		if let (Some(metrics), Some(message_name)) = (&self.metrics, message_name) {
+			let action_name = match action {
+				Action::Keep(_, _) => "keep",
+				Action::ProcessAndDiscard(_, _) => "process_and_discard",
+				Action::Discard(_) => "discard",
+			};
+			metrics.messages_validated.with_label_values(&[message_name, action_name]).inc();
+		}
+
 		(action, broadcast_topics, peer_reply)
 	}
 }
@@ -1679,6 +1737,7 @@ mod tests {
 		let (val, _) = GossipValidator::<Block>::new(
 			config(),
 			voter_set_state(),
+			None,
 		);
 
 		let set_id = 1;
@@ -1714,6 +1773,7 @@ mod tests {
 		let (val, _) = GossipValidator::<Block>::new(
 			config(),
 			voter_set_state(),
+			None,
 		);
 		let set_id = 1;
 		let auth = AuthorityId::from_slice(&[1u8; 32]);
@@ -1758,6 +1818,7 @@ mod tests {
 		let (val, _) = GossipValidator::<Block>::new(
 			config(),
 			voter_set_state(),
+			None,
 		);
 
 		let set_id = 1;
@@ -1826,6 +1887,7 @@ mod tests {
 		let (val, _) = GossipValidator::<Block>::new(
 			config(),
 			set_state.clone(),
+			None,
 		);
 
 		let set_id = 1;
@@ -1880,6 +1942,7 @@ mod tests {
 		let (val, _) = GossipValidator::<Block>::new(
 			config(),
 			set_state.clone(),
+			None,
 		);
 
 		// the validator starts at set id 2
@@ -1959,6 +2022,7 @@ mod tests {
 		let (val, _) = GossipValidator::<Block>::new(
 			config(),
 			voter_set_state(),
+			None,
 		);
 
 		// the validator starts at set id 1.
@@ -2032,6 +2096,7 @@ mod tests {
 		let (val, _) = GossipValidator::<Block>::new(
 			config,
 			voter_set_state(),
+			None,
 		);
 
 		// the validator starts at set id 1.
@@ -2065,6 +2130,7 @@ mod tests {
 		let (val, _) = GossipValidator::<Block>::new(
 			config(),
 			voter_set_state(),
+			None,
 		);
 
 		// the validator starts at set id 1.
@@ -2124,6 +2190,7 @@ mod tests {
 		let (val, _) = GossipValidator::<Block>::new(
 			config,
 			voter_set_state(),
+			None,
 		);
 
 		// the validator starts at set id 1.
@@ -2162,6 +2229,7 @@ mod tests {
 		let (val, _) = GossipValidator::<Block>::new(
 			config(),
 			voter_set_state(),
+			None,
 		);
 
 		// the validator starts at set id 1.
@@ -2194,6 +2262,7 @@ mod tests {
 		let (val, _) = GossipValidator::<Block>::new(
 			config,
 			voter_set_state(),
+			None,
 		);
 
 		// the validator start at set id 0
@@ -2271,6 +2340,7 @@ mod tests {
 		let (val, _) = GossipValidator::<Block>::new(
 			config(),
 			voter_set_state(),
+			None,
 		);
 
 		// the validator start at set id 0
@@ -2310,6 +2380,7 @@ mod tests {
 		let (val, _) = GossipValidator::<Block>::new(
 			config,
 			voter_set_state(),
+			None,
 		);
 
 		// the validator start at set id 0
@@ -2358,7 +2429,7 @@ mod tests {
 
 	#[test]
 	fn only_gossip_commits_to_peers_on_same_set() {
-		let (val, _) = GossipValidator::<Block>::new(config(), voter_set_state());
+		let (val, _) = GossipValidator::<Block>::new(config(), voter_set_state(), None);
 
 		// the validator start at set id 1
 		val.note_set(SetId(1), Vec::new(), |_, _| {});
@@ -2436,7 +2507,7 @@ mod tests {
 
 	#[test]
 	fn expire_commits_from_older_rounds() {
-		let (val, _) = GossipValidator::<Block>::new(config(), voter_set_state());
+		let (val, _) = GossipValidator::<Block>::new(config(), voter_set_state(), None);
 
 		let commit = |round, set_id, target_number| {
 			let commit = finality_grandpa::CompactCommit {

substrate/client/finality-grandpa/src/communication/mod.rs

@@ -30,6 +30,7 @@
 use futures::{prelude::*, channel::mpsc};
 use log::{debug, trace};
 use parking_lot::Mutex;
+use prometheus_endpoint::Registry;
 use std::{pin::Pin, sync::Arc, task::{Context, Poll}};
 
 use finality_grandpa::Message::{Prevote, Precommit, PrimaryPropose};
@@ -178,10 +179,12 @@ impl<B: BlockT, N: Network<B>> NetworkBridge<B, N> {
 		service: N,
 		config: crate::Config,
 		set_state: crate::environment::SharedVoterSetState<B>,
+		prometheus_registry: Option<&Registry>,
 	) -> Self {
 		let (validator, report_stream) = GossipValidator::new(
 			config,
 			set_state.clone(),
+			prometheus_registry,
 		);
 
 		let validator = Arc::new(validator);

substrate/client/finality-grandpa/src/communication/tests.rs

@@ -179,6 +179,7 @@ pub(crate) fn make_test_network() -> (
 		net.clone(),
 		config(),
 		voter_set_state(),
+		None,
 	);
 
 	(

substrate/client/finality-grandpa/src/lib.rs

@@ -591,6 +591,7 @@ pub fn run_grandpa_voter<Block: BlockT, BE: 'static, C, N, SC, VR>(
 		network,
 		config.clone(),
 		persistent_data.set_state.clone(),
+		prometheus_registry.as_ref(),
 	);
 
 	register_finality_tracker_inherent_data_provider(client.clone(), &inherent_data_providers)?;

substrate/client/finality-grandpa/src/observer.rs

@@ -178,6 +178,7 @@ where
 		network,
 		config.clone(),
 		persistent_data.set_state.clone(),
+		None,
 	);
 
 	let observer_work = ObserverWork::new(

substrate/client/finality-grandpa/src/tests.rs

@@ -1220,6 +1220,7 @@ fn voter_persists_its_votes() {
 			net.lock().peers[1].network_service().clone(),
 			config.clone(),
 			set_state,
+			None,
 		);
 
 		let (round_rx, round_tx) = network.round_communication(
@@ -1616,6 +1617,7 @@ fn grandpa_environment_respects_voting_rules() {
 			network_service.clone(),
 			config.clone(),
 			set_state.clone(),
+			None,
 		);
 
 		Environment {