grandpa: improve handling of global gossip messages (#5133)

* grandpa: only gossip commits to peers on the same set

* grandpa: track commits uniquely by round and set

* grandpa: fix communication test

* grandpa: add tests for commit gossip handling

* grandpa: add missing docs

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

@@ -292,12 +292,32 @@ fn good_commit_leads_to_relay() {
 					});
 
 					// Add a random peer which will be the recipient of this message
+					let receiver_id = sc_network::PeerId::random();
 					let _ = sender.unbounded_send(NetworkEvent::NotificationStreamOpened {
-						remote: sc_network::PeerId::random(),
+						remote: receiver_id.clone(),
 						engine_id: GRANDPA_ENGINE_ID,
 						roles: Roles::FULL,
 					});
 
+					// Announce its local set has being on the current set id through a neighbor
+					// packet, otherwise it won't be eligible to receive the commit
+					let _ = {
+						let update = gossip::VersionedNeighborPacket::V1(
+							gossip::NeighborPacket {
+								round: Round(round),
+								set_id: SetId(set_id),
+								commit_finalized_height: 1,
+							}
+						);
+
+						let msg = gossip::GossipMessage::<Block>::Neighbor(update);
+
+						sender.unbounded_send(NetworkEvent::NotificationsReceived {
+							remote: receiver_id,
+							messages: vec![(GRANDPA_ENGINE_ID, msg.encode().into())],
+						})
+					};
+
 					true
 				}
 				_ => false,