Make sure we poll authority event stream until all events are processed (#5608)

* Make sure we poll authority event stream until all events are processed

* Add test

substrate/client/authority-discovery/src/tests.rs

@@ -17,8 +17,10 @@
 use std::{iter::FromIterator, sync::{Arc, Mutex}};
 
 use futures::channel::mpsc::channel;
-use futures::executor::block_on;
-use futures::future::poll_fn;
+use futures::executor::{block_on, LocalPool};
+use futures::future::{poll_fn, FutureExt};
+use futures::sink::SinkExt;
+use futures::task::LocalSpawn;
 use futures::poll;
 use libp2p::{kad, PeerId};
 
@@ -319,7 +321,7 @@ fn handle_dht_events_with_value_found_should_call_set_priority_group() {
 	let mut signed_addresses = vec![];
 	schema::SignedAuthorityAddresses {
 		addresses: serialized_addresses,
-		signature: signature,
+		signature,
 	}
 	.encode(&mut signed_addresses)
 	.unwrap();
@@ -380,3 +382,73 @@ fn terminate_when_event_stream_terminates() {
 		);
 	});
 }
+
+#[test]
+fn dont_stop_polling_when_error_is_returned() {
+	#[derive(PartialEq, Debug)]
+	enum Event {
+		Processed,
+		End,
+	};
+
+	let (mut dht_event_tx, dht_event_rx) = channel(1000);
+	let (mut discovery_update_tx, mut discovery_update_rx) = channel(1000);
+	let network: Arc<TestNetwork> = Arc::new(Default::default());
+	let key_store = KeyStore::new();
+	let test_api = Arc::new(TestApi {
+		authorities: vec![],
+	});
+	let mut pool = LocalPool::new();
+
+	let mut authority_discovery = AuthorityDiscovery::new(
+		test_api,
+		network.clone(),
+		vec![],
+		key_store,
+		dht_event_rx.boxed(),
+		None,
+	);
+
+	// Spawn the authority discovery to make sure it is polled independently.
+	//
+	// As this is a local pool, only one future at a time will have the CPU and
+	// can make progress until the future returns `Pending`.
+	pool.spawner().spawn_local_obj(
+		futures::future::poll_fn(move |ctx| {
+			match std::pin::Pin::new(&mut authority_discovery).poll(ctx) {
+				Poll::Ready(()) => {},
+				Poll::Pending => {
+					discovery_update_tx.send(Event::Processed).now_or_never();
+					return Poll::Pending;
+				},
+			}
+			let _ = discovery_update_tx.send(Event::End).now_or_never().unwrap();
+			Poll::Ready(())
+		}).boxed_local().into(),
+	).expect("Spawns authority discovery");
+
+	pool.run_until(
+		// The future that drives the event stream
+		async {
+			// Send an event that should generate an error
+			let _ = dht_event_tx.send(DhtEvent::ValueFound(Default::default())).now_or_never();
+			// Send the same event again to make sure that the event stream needs to be polled twice
+			// to be woken up again.
+			let _ = dht_event_tx.send(DhtEvent::ValueFound(Default::default())).now_or_never();
+
+			// Now we call `await` and give the control to the authority discovery future.
+			assert_eq!(Some(Event::Processed), discovery_update_rx.next().await);
+
+			// Drop the event rx to stop the authority discovery. If it was polled correctly, it should
+			// end properly.
+			drop(dht_event_tx);
+
+			assert!(
+				discovery_update_rx.collect::<Vec<Event>>()
+					.await
+					.into_iter()
+					.any(|evt| evt == Event::End), "The authority should have ended",
+			);
+		}
+	);
+}