Further fix for common block update (#4071)

core/network/src/protocol/sync.rs

@@ -1047,10 +1047,12 @@ impl<B: BlockT> ChainSync<B> {
 		}
 		// If the announced block is the best they have seen, our common number
 		// is either one further ahead or it's the one they just announced, if we know about it.
-		if known && is_best {
-			peer.common_number = number
-		} else if header.parent_hash() == &self.best_queued_hash || known_parent {
-			peer.common_number = number - One::one();
+		if is_best {
+			if known {
+				peer.common_number = number
+			} else if header.parent_hash() == &self.best_queued_hash || known_parent {
+				peer.common_number = number - One::one();
+			}
 		}
 		self.is_idle = false;
 

core/network/src/test/sync.rs

@@ -640,7 +640,8 @@ fn does_not_sync_announced_old_best_block() {
 	let mut net = TestNet::new(3);
 
 	let old_hash = net.peer(0).push_blocks(1, false);
-	net.peer(0).push_blocks(19, true);
+	let old_hash_with_parent = net.peer(0).push_blocks(1, false);
+	net.peer(0).push_blocks(18, true);
 	net.peer(1).push_blocks(20, true);
 
 	net.peer(0).announce_block(old_hash, Vec::new());
@@ -650,4 +651,12 @@ fn does_not_sync_announced_old_best_block() {
 		Ok(Async::Ready(()))
 	})).unwrap();
 	assert!(!net.peer(1).is_major_syncing());
+
+	net.peer(0).announce_block(old_hash_with_parent, Vec::new());
+	runtime.block_on(futures::future::poll_fn::<(), (), _>(|| -> Result<_, ()> {
+		// poll once to import announcement
+		net.poll();
+		Ok(Async::Ready(()))
+	})).unwrap();
+	assert!(!net.peer(1).is_major_syncing());
 }