Always allocate slots for reserved nodes (#11909)

* Always allocate slots for reserved nodes

* minor: replace no-slot peer counter with a set

substrate/client/network/src/protocol.rs

@@ -179,6 +179,10 @@ pub struct Protocol<B: BlockT, Client> {
 	/// List of nodes for which we perform additional logging because they are important for the
 	/// user.
 	important_peers: HashSet<PeerId>,
+	/// List of nodes that should never occupy peer slots.
+	default_peers_set_no_slot_peers: HashSet<PeerId>,
+	/// Actual list of connected no-slot nodes.
+	default_peers_set_no_slot_connected_peers: HashSet<PeerId>,
 	/// Value that was passed as part of the configuration. Used to cap the number of full nodes.
 	default_peers_set_num_full: usize,
 	/// Number of slots to allocate to light nodes.
@@ -304,6 +308,17 @@ where
 			imp_p
 		};
 
+		let default_peers_set_no_slot_peers = {
+			let mut no_slot_p: HashSet<PeerId> = network_config
+				.default_peers_set
+				.reserved_nodes
+				.iter()
+				.map(|reserved| reserved.peer_id)
+				.collect();
+			no_slot_p.shrink_to_fit();
+			no_slot_p
+		};
+
 		let mut known_addresses = Vec::new();
 
 		let (peerset, peerset_handle) = {
@@ -404,6 +419,8 @@ where
 			genesis_hash: info.genesis_hash,
 			chain_sync,
 			important_peers,
+			default_peers_set_no_slot_peers,
+			default_peers_set_no_slot_connected_peers: HashSet::new(),
 			default_peers_set_num_full: network_config.default_peers_set_num_full as usize,
 			default_peers_set_num_light: {
 				let total = network_config.default_peers_set.out_peers +
@@ -542,6 +559,7 @@ where
 				self.pending_messages
 					.push_back(CustomMessageOutcome::BlockImport(origin, blocks));
 			}
+			self.default_peers_set_no_slot_connected_peers.remove(&peer);
 			Ok(())
 		} else {
 			Err(())
@@ -723,7 +741,14 @@ where
 			}
 		}
 
-		if status.roles.is_full() && self.chain_sync.num_peers() >= self.default_peers_set_num_full
+		let no_slot_peer = self.default_peers_set_no_slot_peers.contains(&who);
+		let this_peer_reserved_slot: usize = if no_slot_peer { 1 } else { 0 };
+
+		if status.roles.is_full() &&
+			self.chain_sync.num_peers() >=
+				self.default_peers_set_num_full +
+					self.default_peers_set_no_slot_connected_peers.len() +
+					this_peer_reserved_slot
 		{
 			debug!(target: "sync", "Too many full nodes, rejecting {}", who);
 			self.behaviour.disconnect_peer(&who, HARDCODED_PEERSETS_SYNC);
@@ -767,6 +792,9 @@ where
 		debug!(target: "sync", "Connected {}", who);
 
 		self.peers.insert(who, peer);
+		if no_slot_peer {
+			self.default_peers_set_no_slot_connected_peers.insert(who);
+		}
 		self.pending_messages
 			.push_back(CustomMessageOutcome::PeerNewBest(who, status.best_number));