Peer prioritization (#2717)

* Added priority groups

* Added a test

* Whitespace

* Added add/remove single peer API

* Added a warning

* Fixed removing reserved peer

* Fixed build

* Made some methods private and made get_priority_group return an Option

substrate/core/peerset/src/lib.rs

@@ -19,7 +19,7 @@
 
 mod peersstate;
 
-use std::{collections::HashMap, collections::VecDeque, time::Instant};
+use std::{collections::{HashSet, HashMap}, collections::VecDeque, time::Instant};
 use futures::{prelude::*, sync::mpsc, try_ready};
 use libp2p::PeerId;
 use log::{debug, error, trace};
@@ -29,6 +29,8 @@ use serde_json::json;
 const BANNED_THRESHOLD: i32 = 82 * (i32::min_value() / 100);
 /// Reputation change for a node when we get disconnected from it.
 const DISCONNECT_REPUTATION_CHANGE: i32 = -10;
+/// Reserved peers group ID
+const RESERVED_NODES: &'static str = "reserved";
 
 #[derive(Debug)]
 enum Action {
@@ -36,6 +38,9 @@ enum Action {
 	RemoveReservedPeer(PeerId),
 	SetReservedOnly(bool),
 	ReportPeer(PeerId, i32),
+	SetPriorityGroup(String, HashSet<PeerId>),
+	AddToPriorityGroup(String, PeerId),
+	RemoveFromPriorityGroup(String, PeerId),
 }
 
 /// Shared handle to the peer set manager (PSM). Distributed around the code.
@@ -72,6 +77,21 @@ impl PeersetHandle {
 	pub fn report_peer(&self, peer_id: PeerId, score_diff: i32) {
 		let _ = self.tx.unbounded_send(Action::ReportPeer(peer_id, score_diff));
 	}
+
+	/// Modify a priority group.
+	pub fn set_priority_group(&self, group_id: String, peers: HashSet<PeerId>) {
+		let _ = self.tx.unbounded_send(Action::SetPriorityGroup(group_id, peers));
+	}
+
+	/// Add a peer to a priority group.
+	pub fn add_to_priority_group(&self, group_id: String, peer_id: PeerId) {
+		let _ = self.tx.unbounded_send(Action::AddToPriorityGroup(group_id, peer_id));
+	}
+
+	/// Remove a peer from a priority group.
+	pub fn remove_from_priority_group(&self, group_id: String, peer_id: PeerId) {
+		let _ = self.tx.unbounded_send(Action::RemoveFromPriorityGroup(group_id, peer_id));
+	}
 }
 
 /// Message that can be sent by the peer set manager (PSM).
@@ -161,14 +181,7 @@ impl Peerset {
 			latest_time_update: Instant::now(),
 		};
 
-		for peer_id in config.reserved_nodes {
-			if let peersstate::Peer::Unknown(entry) = peerset.data.peer(&peer_id) {
-				entry.discover().set_reserved(true);
-			} else {
-				debug!(target: "peerset", "Duplicate reserved node in config: {:?}", peer_id);
-			}
-		}
-
+		peerset.data.set_priority_group(RESERVED_NODES, config.reserved_nodes.into_iter().collect());
 		for peer_id in config.bootnodes {
 			if let peersstate::Peer::Unknown(entry) = peerset.data.peer(&peer_id) {
 				entry.discover();
@@ -182,32 +195,25 @@ impl Peerset {
 	}
 
 	fn on_add_reserved_peer(&mut self, peer_id: PeerId) {
-		let mut entry = match self.data.peer(&peer_id) {
-			peersstate::Peer::Connected(mut connected) => {
-				connected.set_reserved(true);
-				return
-			}
-			peersstate::Peer::NotConnected(entry) => entry,
-			peersstate::Peer::Unknown(entry) => entry.discover(),
-		};
-
-		// We reach this point if and only if we were not connected to the node.
-		entry.set_reserved(true);
-		entry.force_outgoing();
-		self.message_queue.push_back(Message::Connect(peer_id));
+		let mut reserved = self.data.get_priority_group(RESERVED_NODES).unwrap_or_default();
+		reserved.insert(peer_id);
+		self.data.set_priority_group(RESERVED_NODES, reserved);
+		self.alloc_slots();
 	}
 
 	fn on_remove_reserved_peer(&mut self, peer_id: PeerId) {
+		let mut reserved = self.data.get_priority_group(RESERVED_NODES).unwrap_or_default();
+		reserved.remove(&peer_id);
+		self.data.set_priority_group(RESERVED_NODES, reserved);
 		match self.data.peer(&peer_id) {
-			peersstate::Peer::Connected(mut peer) => {
-				peer.set_reserved(false);
+			peersstate::Peer::Connected(peer) => {
 				if self.reserved_only {
 					peer.disconnect();
 					self.message_queue.push_back(Message::Drop(peer_id));
 				}
 			}
-			peersstate::Peer::NotConnected(mut peer) => peer.set_reserved(false),
-			peersstate::Peer::Unknown(_) => {}
+			peersstate::Peer::NotConnected(_) => {},
+			peersstate::Peer::Unknown(_) => {},
 		}
 	}
 
@@ -215,20 +221,35 @@ impl Peerset {
 		// Disconnect non-reserved nodes.
 		self.reserved_only = reserved_only;
 		if self.reserved_only {
+			let reserved = self.data.get_priority_group(RESERVED_NODES).unwrap_or_default();
 			for peer_id in self.data.connected_peers().cloned().collect::<Vec<_>>().into_iter() {
 				let peer = self.data.peer(&peer_id).into_connected()
 					.expect("We are enumerating connected peers, therefore the peer is connected; qed");
-				if !peer.is_reserved() {
+				if !reserved.contains(&peer_id) {
 					peer.disconnect();
 					self.message_queue.push_back(Message::Drop(peer_id));
 				}
 			}
-
 		} else {
 			self.alloc_slots();
 		}
 	}
 
+	fn on_set_priority_group(&mut self, group_id: &str, peers: HashSet<PeerId>) {
+		self.data.set_priority_group(group_id, peers);
+		self.alloc_slots();
+	}
+
+	fn on_add_to_priority_group(&mut self, group_id: &str, peer_id: PeerId) {
+		self.data.add_to_priority_group(group_id, peer_id);
+		self.alloc_slots();
+	}
+
+	fn on_remove_from_priority_group(&mut self, group_id: &str, peer_id: PeerId) {
+		self.data.remove_from_priority_group(group_id, &peer_id);
+		self.alloc_slots();
+	}
+
 	fn on_report_peer(&mut self, peer_id: PeerId, score_diff: i32) {
 		// We want reputations to be up-to-date before adjusting them.
 		self.update_time();
@@ -292,7 +313,13 @@ impl Peerset {
 		self.update_time();
 
 		// Try to grab the next node to attempt to connect to.
-		while let Some(next) = self.data.reserved_not_connected_peer() {
+		while let Some(next) = {
+			if self.reserved_only {
+				self.data.priority_not_connected_peer_from_group(RESERVED_NODES)
+			} else {
+				self.data.priority_not_connected_peer()
+			}
+		} {
 			match next.try_outgoing() {
 				Ok(conn) => self.message_queue.push_back(Message::Connect(conn.into_peer_id())),
 				Err(_) => break,	// No more slots available.
@@ -421,6 +448,11 @@ impl Peerset {
 			"message_queue": self.message_queue.len(),
 		})
 	}
+
+	/// Returns priority group by id.
+	pub fn get_priority_group(&self, group_id: &str) -> Option<HashSet<PeerId>> {
+		self.data.get_priority_group(group_id)
+	}
 }
 
 impl Stream for Peerset {
@@ -439,6 +471,9 @@ impl Stream for Peerset {
 					Action::RemoveReservedPeer(peer_id) => self.on_remove_reserved_peer(peer_id),
 					Action::SetReservedOnly(reserved) => self.on_set_reserved_only(reserved),
 					Action::ReportPeer(peer_id, score_diff) => self.on_report_peer(peer_id, score_diff),
+					Action::SetPriorityGroup(group_id, peers) => self.on_set_priority_group(&group_id, peers),
+					Action::AddToPriorityGroup(group_id, peer_id) => self.on_add_to_priority_group(&group_id, peer_id),
+					Action::RemoveFromPriorityGroup(group_id, peer_id) => self.on_remove_from_priority_group(&group_id, peer_id),
 				}
 			}
 		}
@@ -590,3 +625,4 @@ mod tests {
 		tokio::runtime::current_thread::Runtime::new().unwrap().block_on(fut).unwrap();
 	}
 }
+

substrate/core/peerset/src/peersstate.rs

@@ -17,7 +17,8 @@
 //! Contains the state storage behind the peerset.
 
 use libp2p::PeerId;
-use std::{borrow::Cow, collections::HashMap};
+use std::{borrow::Cow, collections::{HashSet, HashMap}};
+use log::warn;
 
 /// State storage behind the peerset.
 ///
@@ -35,17 +36,20 @@ pub struct PeersState {
 	/// 			sort, to make the logic easier.
 	nodes: HashMap<PeerId, Node>,
 
-	/// Number of non-reserved nodes for which the `ConnectionState` is `In`.
+	/// Number of non-priority nodes for which the `ConnectionState` is `In`.
 	num_in: u32,
 
-	/// Number of non-reserved nodes for which the `ConnectionState` is `In`.
+	/// Number of non-priority nodes for which the `ConnectionState` is `In`.
 	num_out: u32,
 
-	/// Maximum allowed number of non-reserved nodes for which the `ConnectionState` is `In`.
+	/// Maximum allowed number of non-priority nodes for which the `ConnectionState` is `In`.
 	max_in: u32,
 
-	/// Maximum allowed number of non-reserved nodes for which the `ConnectionState` is `Out`.
+	/// Maximum allowed number of non-priority nodes for which the `ConnectionState` is `Out`.
 	max_out: u32,
+
+	/// Priority groups. Each group is identified by a string ID and contains a set of peer IDs.
+	priority_nodes: HashMap<String, HashSet<PeerId>>,
 }
 
 /// State of a single node that we know about.
@@ -54,14 +58,20 @@ struct Node {
 	/// Whether we are connected to this node.
 	connection_state: ConnectionState,
 
-	/// If true, this node is reserved and should always be connected to.
-	reserved: bool,
-
 	/// Reputation value of the node, between `i32::min_value` (we hate that node) and
 	/// `i32::max_value` (we love that node).
 	reputation: i32,
 }
 
+impl Default for Node {
+	fn default() -> Node {
+		Node {
+			connection_state: ConnectionState::NotConnected,
+			reputation: 0,
+		}
+	}
+}
+
 /// Whether we are connected to a node.
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 enum ConnectionState {
@@ -93,42 +103,30 @@ impl PeersState {
 			num_out: 0,
 			max_in: in_peers,
 			max_out: out_peers,
+			priority_nodes: HashMap::new(),
 		}
 	}
 
 	/// Returns an object that grants access to the state of a peer.
 	pub fn peer<'a>(&'a mut self, peer_id: &'a PeerId) -> Peer<'a> {
-		// Note: the Rust borrow checker still has some issues. In particular, we can't put this
-		// block as an `else` below (as the obvious solution would be here), or it will complain
-		// that we borrow `self` while it is already borrowed.
-		if !self.nodes.contains_key(peer_id) {
-			return Peer::Unknown(UnknownPeer {
+		match self.nodes.get_mut(peer_id) {
+			None => return Peer::Unknown(UnknownPeer {
 				parent: self,
 				peer_id: Cow::Borrowed(peer_id),
-			});
-		}
-
-		let state = self.nodes.get_mut(peer_id)
-			.expect("We check that the value is present right above; QED");
-
-		if state.connection_state.is_connected() {
-			Peer::Connected(ConnectedPeer {
-				state,
-				peer_id: Cow::Borrowed(peer_id),
-				num_in: &mut self.num_in,
-				num_out: &mut self.num_out,
-				max_in: self.max_in,
-				max_out: self.max_out,
-			})
-		} else {
-			Peer::NotConnected(NotConnectedPeer {
-				state,
-				peer_id: Cow::Borrowed(peer_id),
-				num_in: &mut self.num_in,
-				num_out: &mut self.num_out,
-				max_in: self.max_in,
-				max_out: self.max_out,
-			})
+			}),
+			Some(peer) => {
+				if peer.connection_state.is_connected() {
+					Peer::Connected(ConnectedPeer {
+						state: self,
+						peer_id: Cow::Borrowed(peer_id),
+					})
+				} else {
+					Peer::NotConnected(NotConnectedPeer {
+						state: self,
+						peer_id: Cow::Borrowed(peer_id),
+					})
+				}
+			}
 		}
 	}
 
@@ -148,28 +146,32 @@ impl PeersState {
 			.map(|(p, _)| p)
 	}
 
-	/// Returns the first reserved peer that we are not connected to.
+	/// Returns the first priority peer that we are not connected to.
 	///
-	/// If multiple nodes are reserved, which one is returned is unspecified.
-	pub fn reserved_not_connected_peer(&mut self) -> Option<NotConnectedPeer> {
-		let outcome = self.nodes.iter_mut()
-			.find(|(_, &mut Node { connection_state, reserved, .. })| {
-				reserved && !connection_state.is_connected()
-			})
-			.map(|(peer_id, node)| (peer_id.clone(), node));
-
-		if let Some((peer_id, state)) = outcome {
-			Some(NotConnectedPeer {
-				state,
-				peer_id: Cow::Owned(peer_id),
-				num_in: &mut self.num_in,
-				num_out: &mut self.num_out,
-				max_in: self.max_in,
-				max_out: self.max_out,
-			})
-		} else {
-			None
-		}
+	/// If multiple nodes are prioritized, which one is returned is unspecified.
+	pub fn priority_not_connected_peer(&mut self) -> Option<NotConnectedPeer> {
+		let id = self.priority_nodes.values()
+			.flatten()
+			.find(|id| self.nodes.get(id).map_or(false, |node| !node.connection_state.is_connected()))
+			.cloned();
+		id.map(move |id| NotConnectedPeer {
+			state: self,
+			peer_id: Cow::Owned(id),
+		})
+	}
+
+	/// Returns the first priority peer that we are not connected to.
+	///
+	/// If multiple nodes are prioritized, which one is returned is unspecified.
+	pub fn priority_not_connected_peer_from_group(&mut self, group_id: &str) -> Option<NotConnectedPeer> {
+		let id = self.priority_nodes.get(group_id)
+			.and_then(|group| group.iter()
+				.find(|id| self.nodes.get(id).map_or(false, |node| !node.connection_state.is_connected()))
+				.cloned());
+		id.map(move |id| NotConnectedPeer {
+			state: self,
+			peer_id: Cow::Owned(id),
+		})
 	}
 
 	/// Returns the peer with the highest reputation and that we are not connected to.
@@ -187,21 +189,160 @@ impl PeersState {
 				}
 				Some(to_try)
 			})
-			.map(|(peer_id, state)| (peer_id.clone(), state));
+			.map(|(peer_id, _)| peer_id.clone());
 
-		if let Some((peer_id, state)) = outcome {
+		if let Some(peer_id) = outcome {
 			Some(NotConnectedPeer {
-				state,
+				state: self,
 				peer_id: Cow::Owned(peer_id),
-				num_in: &mut self.num_in,
-				num_out: &mut self.num_out,
-				max_in: self.max_in,
-				max_out: self.max_out,
 			})
 		} else {
 			None
 		}
 	}
+
+	fn disconnect(&mut self, peer_id: &PeerId) {
+		let is_priority = self.is_priority(peer_id);
+		if let Some(mut node) = self.nodes.get_mut(peer_id) {
+			if !is_priority {
+				match node.connection_state {
+					ConnectionState::In => self.num_in -= 1,
+					ConnectionState::Out => self.num_out -= 1,
+					ConnectionState::NotConnected =>
+						debug_assert!(false, "State inconsistency: disconnecting a disconnected node")
+				}
+			}
+			node.connection_state = ConnectionState::NotConnected;
+		} else {
+			warn!(target: "peerset", "Attempting to disconnect unknown peer {}", peer_id);
+		}
+	}
+
+	/// Sets the peer as connected with an outgoing connection.
+	fn try_outgoing(&mut self, peer_id: &PeerId) -> bool {
+		// Note that it is possible for num_out to be strictly superior to the max, in case we were
+		// connected to reserved node then marked them as not reserved.
+		let is_priority = self.is_priority(peer_id);
+		if self.num_out >= self.max_out && !is_priority {
+			return false;
+		}
+
+		if let Some(mut peer) = self.nodes.get_mut(peer_id) {
+			peer.connection_state = ConnectionState::Out;
+			if !is_priority {
+				self.num_out += 1;
+			}
+			return true;
+		}
+		false
+	}
+
+	/// Tries to accept the peer as an incoming connection.
+	///
+	/// If there are enough slots available, switches the node to "connected" and returns `Ok`. If
+	/// the slots are full, the node stays "not connected" and we return `Err`.
+	///
+	/// Note that reserved nodes don't count towards the number of slots.
+	fn try_accept_incoming(&mut self, peer_id: &PeerId) -> bool {
+		let is_priority = self.is_priority(peer_id);
+		// Note that it is possible for num_in to be strictly superior to the max, in case we were
+		// connected to reserved node then marked them as not reserved.
+		if self.num_in >= self.max_in && !is_priority {
+			return false;
+		}
+		if let Some(mut peer) = self.nodes.get_mut(peer_id) {
+			peer.connection_state = ConnectionState::In;
+			if !is_priority {
+				self.num_in += 1;
+			}
+			return true;
+		}
+		false
+	}
+
+	/// Sets priority group
+	pub fn set_priority_group(&mut self, group_id: &str, peers: HashSet<PeerId>) {
+		// update slot counters
+		let all_other_groups: HashSet<_> = self.priority_nodes
+			.iter()
+			.filter(|(g, _)| *g != group_id)
+			.flat_map(|(_, id)| id.clone())
+			.collect();
+		let existing_group = self.priority_nodes.remove(group_id).unwrap_or_default();
+		for id in existing_group {
+			// update slots for nodes that are no longer priority
+			if !all_other_groups.contains(&id) {
+				if let Some(peer) = self.nodes.get_mut(&id) {
+					match peer.connection_state {
+						ConnectionState::In => self.num_in += 1,
+						ConnectionState::Out => self.num_out += 1,
+						ConnectionState::NotConnected => {},
+					}
+				}
+			}
+		}
+
+		for id in &peers {
+			// update slots for nodes that become priority
+			if !all_other_groups.contains(&id) {
+				let peer = self.nodes.entry(id.clone()).or_default();
+				match peer.connection_state {
+					ConnectionState::In => self.num_in -= 1,
+					ConnectionState::Out => self.num_out -= 1,
+					ConnectionState::NotConnected => {},
+				}
+			}
+		}
+		self.priority_nodes.insert(group_id.into(), peers);
+	}
+
+	/// Add a peer to a priority group.
+	pub fn add_to_priority_group(&mut self, group_id: &str, peer_id: PeerId) {
+		let mut peers = self.priority_nodes.get(group_id).cloned().unwrap_or_default();
+		peers.insert(peer_id);
+		self.set_priority_group(group_id, peers);
+	}
+
+	/// Remove a peer from a priority group.
+	pub fn remove_from_priority_group(&mut self, group_id: &str, peer_id: &PeerId) {
+		let mut peers = self.priority_nodes.get(group_id).cloned().unwrap_or_default();
+		peers.remove(&peer_id);
+		self.set_priority_group(group_id, peers);
+	}
+
+	/// Get priority group content.
+	pub fn get_priority_group(&self, group_id: &str) -> Option<HashSet<PeerId>> {
+		self.priority_nodes.get(group_id).cloned()
+	}
+
+	/// Check that node is any priority group.
+	fn is_priority(&self, peer_id: &PeerId) -> bool {
+		self.priority_nodes.iter().any(|(_, group)| group.contains(peer_id))
+	}
+
+	/// Returns the reputation value of the node.
+	fn reputation(&self, peer_id: &PeerId) -> i32 {
+		self.nodes.get(peer_id).map_or(0, |p| p.reputation)
+	}
+
+	/// Sets the reputation of the peer.
+	fn set_reputation(&mut self, peer_id: &PeerId, value: i32) {
+		let node = self.nodes
+			.entry(peer_id.clone())
+			.or_default();
+		node.reputation = value;
+	}
+
+	/// Performs an arithmetic addition on the reputation score of that peer.
+	///
+	/// In case of overflow, the value will be capped.
+	/// If the peer is unknown to us, we insert it and consider that it has a reputation of 0.
+	fn add_reputation(&mut self, peer_id: &PeerId, modifier: i32) {
+		let node = self.nodes
+			.entry(peer_id.clone())
+			.or_default();
+		node.reputation = node.reputation.saturating_add(modifier);
+	}
 }
 
 /// Grants access to the state of a peer in the `PeersState`.
@@ -250,12 +391,8 @@ impl<'a> Peer<'a> {
 
 /// A peer that is connected to us.
 pub struct ConnectedPeer<'a> {
-	state: &'a mut Node,
+	state: &'a mut PeersState,
 	peer_id: Cow<'a, PeerId>,
-	num_in: &'a mut u32,
-	num_out: &'a mut u32,
-	max_in: u32,
-	max_out: u32,
 }
 
 impl<'a> ConnectedPeer<'a> {
@@ -266,87 +403,36 @@ impl<'a> ConnectedPeer<'a> {
 
 	/// Switches the peer to "not connected".
 	pub fn disconnect(self) -> NotConnectedPeer<'a> {
-		let connec_state = &mut self.state.connection_state;
-
-		if !self.state.reserved {
-			match *connec_state {
-				ConnectionState::In => *self.num_in -= 1,
-				ConnectionState::Out => *self.num_out -= 1,
-				ConnectionState::NotConnected =>
-					debug_assert!(false, "State inconsistency: disconnecting a disconnected node")
-			}
-		}
-
-		*connec_state = ConnectionState::NotConnected;
-
+		self.state.disconnect(&self.peer_id);
 		NotConnectedPeer {
 			state: self.state,
 			peer_id: self.peer_id,
-			num_in: self.num_in,
-			num_out: self.num_out,
-			max_in: self.max_in,
-			max_out: self.max_out,
-		}
-	}
-
-	/// Sets whether or not the node is reserved.
-	pub fn set_reserved(&mut self, reserved: bool) {
-		if reserved == self.state.reserved {
-			return;
 		}
-
-		if reserved {
-			self.state.reserved = true;
-			match self.state.connection_state {
-				ConnectionState::In => *self.num_in -= 1,
-				ConnectionState::Out => *self.num_out -= 1,
-				ConnectionState::NotConnected => debug_assert!(false, "State inconsistency: \
-					connected node is in fact not connected"),
-			}
-
-		} else {
-			self.state.reserved = false;
-			match self.state.connection_state {
-				ConnectionState::In => *self.num_in += 1,
-				ConnectionState::Out => *self.num_out += 1,
-				ConnectionState::NotConnected => debug_assert!(false, "State inconsistency: \
-					connected node is in fact not connected"),
-			}
-		}
-	}
-
-	/// Returns whether or not the node is reserved.
-	pub fn is_reserved(&self) -> bool {
-		self.state.reserved
 	}
 
 	/// Returns the reputation value of the node.
 	pub fn reputation(&self) -> i32 {
-		self.state.reputation
+		self.state.reputation(&self.peer_id)
 	}
 
 	/// Sets the reputation of the peer.
 	pub fn set_reputation(&mut self, value: i32) {
-		self.state.reputation = value;
+		self.state.set_reputation(&self.peer_id, value)
 	}
 
 	/// Performs an arithmetic addition on the reputation score of that peer.
 	///
 	/// In case of overflow, the value will be capped.
 	pub fn add_reputation(&mut self, modifier: i32) {
-		let reputation = &mut self.state.reputation;
-		*reputation = reputation.saturating_add(modifier);
+		self.state.add_reputation(&self.peer_id, modifier)
 	}
 }
 
 /// A peer that is not connected to us.
+#[derive(Debug)]
 pub struct NotConnectedPeer<'a> {
-	state: &'a mut Node,
+	state: &'a mut PeersState,
 	peer_id: Cow<'a, PeerId>,
-	num_in: &'a mut u32,
-	num_out: &'a mut u32,
-	max_in: u32,
-	max_out: u32,
 }
 
 impl<'a> NotConnectedPeer<'a> {
@@ -360,41 +446,16 @@ impl<'a> NotConnectedPeer<'a> {
 	///
 	/// If there are enough slots available, switches the node to "connected" and returns `Ok`. If
 	/// the slots are full, the node stays "not connected" and we return `Err`.
-	/// If the node is reserved, this method always succeeds.
 	///
-	/// Note that reserved nodes don't count towards the number of slots.
+	/// Note that priority nodes don't count towards the number of slots.
 	pub fn try_outgoing(self) -> Result<ConnectedPeer<'a>, NotConnectedPeer<'a>> {
-		if self.is_reserved() {
-			return Ok(self.force_outgoing())
-		}
-
-		// Note that it is possible for num_out to be strictly superior to the max, in case we were
-		// connected to reserved node then marked them as not reserved, or if the user used
-		// `force_outgoing`.
-		if *self.num_out >= self.max_out {
-			return Err(self);
-		}
-
-		Ok(self.force_outgoing())
-	}
-
-	/// Sets the peer as connected as an outgoing connection.
-	pub fn force_outgoing(self) -> ConnectedPeer<'a> {
-		let connec_state = &mut self.state.connection_state;
-		debug_assert!(!connec_state.is_connected());
-		*connec_state = ConnectionState::Out;
-
-		if !self.state.reserved {
-			*self.num_out += 1;
-		}
-
-		ConnectedPeer {
-			state: self.state,
-			peer_id: self.peer_id,
-			num_in: self.num_in,
-			num_out: self.num_out,
-			max_in: self.max_in,
-			max_out: self.max_out,
+		if self.state.try_outgoing(&self.peer_id) {
+			Ok(ConnectedPeer {
+				state: self.state,
+				peer_id: self.peer_id,
+			})
+		} else {
+			Err(self)
 		}
 	}
 
@@ -403,59 +464,26 @@ impl<'a> NotConnectedPeer<'a> {
 	/// If there are enough slots available, switches the node to "connected" and returns `Ok`. If
 	/// the slots are full, the node stays "not connected" and we return `Err`.
 	///
-	/// Note that reserved nodes don't count towards the number of slots.
+	/// Note that priority nodes don't count towards the number of slots.
 	pub fn try_accept_incoming(self) -> Result<ConnectedPeer<'a>, NotConnectedPeer<'a>> {
-		if self.is_reserved() {
-			return Ok(self.force_ingoing())
-		}
-
-		// Note that it is possible for num_in to be strictly superior to the max, in case we were
-		// connected to reserved node then marked them as not reserved.
-		if *self.num_in >= self.max_in {
-			return Err(self);
-		}
-
-		Ok(self.force_ingoing())
-	}
-
-	/// Sets the peer as connected as an ingoing connection.
-	pub fn force_ingoing(self) -> ConnectedPeer<'a> {
-		let connec_state = &mut self.state.connection_state;
-		debug_assert!(!connec_state.is_connected());
-		*connec_state = ConnectionState::In;
-
-		if !self.state.reserved {
-			*self.num_in += 1;
-		}
-
-		ConnectedPeer {
-			state: self.state,
-			peer_id: self.peer_id,
-			num_in: self.num_in,
-			num_out: self.num_out,
-			max_in: self.max_in,
-			max_out: self.max_out,
+		if self.state.try_accept_incoming(&self.peer_id) {
+			Ok(ConnectedPeer {
+				state: self.state,
+				peer_id: self.peer_id,
+			})
+		} else {
+			Err(self)
 		}
 	}
 
-	/// Sets whether or not the node is reserved.
-	pub fn set_reserved(&mut self, reserved: bool) {
-		self.state.reserved = reserved;
-	}
-
-	/// Returns true if the the node is reserved.
-	pub fn is_reserved(&self) -> bool {
-		self.state.reserved
-	}
-
 	/// Returns the reputation value of the node.
 	pub fn reputation(&self) -> i32 {
-		self.state.reputation
+		self.state.reputation(&self.peer_id)
 	}
 
 	/// Sets the reputation of the peer.
 	pub fn set_reputation(&mut self, value: i32) {
-		self.state.reputation = value;
+		self.state.set_reputation(&self.peer_id, value)
 	}
 
 	/// Performs an arithmetic addition on the reputation score of that peer.
@@ -463,8 +491,7 @@ impl<'a> NotConnectedPeer<'a> {
 	/// In case of overflow, the value will be capped.
 	/// If the peer is unknown to us, we insert it and consider that it has a reputation of 0.
 	pub fn add_reputation(&mut self, modifier: i32) {
-		let reputation = &mut self.state.reputation;
-		*reputation = reputation.saturating_add(modifier);
+		self.state.add_reputation(&self.peer_id, modifier)
 	}
 }
 
@@ -477,25 +504,18 @@ pub struct UnknownPeer<'a> {
 impl<'a> UnknownPeer<'a> {
 	/// Inserts the peer identity in our list.
 	///
-	/// The node is not reserved and starts with a reputation of 0. You can adjust these default
+	/// The node starts with a reputation of 0. You can adjust these default
 	/// values using the `NotConnectedPeer` that this method returns.
 	pub fn discover(self) -> NotConnectedPeer<'a> {
 		self.parent.nodes.insert(self.peer_id.clone().into_owned(), Node {
 			connection_state: ConnectionState::NotConnected,
 			reputation: 0,
-			reserved: false,
 		});
 
-		let state = self.parent.nodes.get_mut(&self.peer_id)
-			.expect("We insert that key into the HashMap right above; QED");
-
+		let state = self.parent;
 		NotConnectedPeer {
 			state,
 			peer_id: self.peer_id,
-			num_in: &mut self.parent.num_in,
-			num_out: &mut self.parent.num_out,
-			max_in: self.parent.max_in,
-			max_out: self.parent.max_out,
 		}
 	}
 }
@@ -521,14 +541,13 @@ mod tests {
 	}
 
 	#[test]
-	fn reserved_node_doesnt_use_slot() {
+	fn priority_node_doesnt_use_slot() {
 		let mut peers_state = PeersState::new(1, 1);
 		let id1 = PeerId::random();
 		let id2 = PeerId::random();
 
-		if let Peer::Unknown(e) = peers_state.peer(&id1) {
-			let mut p = e.discover();
-			p.set_reserved(true);
+		peers_state.set_priority_group("test", vec![id1.clone()].into_iter().collect());
+		if let Peer::NotConnected(p) = peers_state.peer(&id1) {
 			assert!(p.try_accept_incoming().is_ok());
 		} else { panic!() }
 
@@ -550,23 +569,22 @@ mod tests {
 	}
 
 	#[test]
-	fn reserved_not_connected_peer() {
+	fn priority_not_connected_peer() {
 		let mut peers_state = PeersState::new(25, 25);
 		let id1 = PeerId::random();
 		let id2 = PeerId::random();
 
-		assert!(peers_state.reserved_not_connected_peer().is_none());
+		assert!(peers_state.priority_not_connected_peer().is_none());
 		peers_state.peer(&id1).into_unknown().unwrap().discover();
 		peers_state.peer(&id2).into_unknown().unwrap().discover();
 
-		assert!(peers_state.reserved_not_connected_peer().is_none());
-		peers_state.peer(&id1).into_not_connected().unwrap().set_reserved(true);
-		assert!(peers_state.reserved_not_connected_peer().is_some());
-		peers_state.peer(&id2).into_not_connected().unwrap().set_reserved(true);
-		peers_state.peer(&id1).into_not_connected().unwrap().set_reserved(false);
-		assert!(peers_state.reserved_not_connected_peer().is_some());
-		peers_state.peer(&id2).into_not_connected().unwrap().set_reserved(false);
-		assert!(peers_state.reserved_not_connected_peer().is_none());
+		assert!(peers_state.priority_not_connected_peer().is_none());
+		peers_state.set_priority_group("test", vec![id1.clone()].into_iter().collect());
+		assert!(peers_state.priority_not_connected_peer().is_some());
+		peers_state.set_priority_group("test", vec![id2.clone(), id2.clone()].into_iter().collect());
+		assert!(peers_state.priority_not_connected_peer().is_some());
+		peers_state.set_priority_group("test", vec![].into_iter().collect());
+		assert!(peers_state.priority_not_connected_peer().is_none());
 	}
 
 	#[test]
@@ -581,7 +599,7 @@ mod tests {
 		assert_eq!(peers_state.highest_not_connected_peer().map(|p| p.into_peer_id()), Some(id1.clone()));
 		peers_state.peer(&id2).into_not_connected().unwrap().set_reputation(75);
 		assert_eq!(peers_state.highest_not_connected_peer().map(|p| p.into_peer_id()), Some(id2.clone()));
-		peers_state.peer(&id2).into_not_connected().unwrap().force_ingoing();
+		peers_state.peer(&id2).into_not_connected().unwrap().try_accept_incoming().unwrap();
 		assert_eq!(peers_state.highest_not_connected_peer().map(|p| p.into_peer_id()), Some(id1.clone()));
 		peers_state.peer(&id1).into_not_connected().unwrap().set_reputation(100);
 		peers_state.peer(&id2).into_connected().unwrap().disconnect();
@@ -591,24 +609,31 @@ mod tests {
 	}
 
 	#[test]
-	fn disconnect_reserved_doesnt_panic() {
+	fn disconnect_priority_doesnt_panic() {
 		let mut peers_state = PeersState::new(1, 1);
 		let id = PeerId::random();
-		let mut peer = peers_state.peer(&id).into_unknown().unwrap().discover()
-			.force_outgoing();
-		peer.set_reserved(true);
+		peers_state.set_priority_group("test", vec![id.clone()].into_iter().collect());
+		let peer = peers_state.peer(&id).into_not_connected().unwrap().try_outgoing().unwrap();
 		peer.disconnect();
 	}
 
 	#[test]
-	fn multiple_set_reserved_calls_doesnt_panic() {
+	fn multiple_priority_groups_slot_count() {
 		let mut peers_state = PeersState::new(1, 1);
 		let id = PeerId::random();
-		let mut peer = peers_state.peer(&id)
-			.into_unknown().unwrap().discover()
-			.force_outgoing();
-		peer.set_reserved(true);
-		peer.set_reserved(true);
-		peer.disconnect();
+
+		if let Peer::Unknown(p) = peers_state.peer(&id) {
+			assert!(p.discover().try_accept_incoming().is_ok());
+		} else { panic!() }
+
+		assert_eq!(peers_state.num_in, 1);
+		peers_state.set_priority_group("test1", vec![id.clone()].into_iter().collect());
+		assert_eq!(peers_state.num_in, 0);
+		peers_state.set_priority_group("test2", vec![id.clone()].into_iter().collect());
+		assert_eq!(peers_state.num_in, 0);
+		peers_state.set_priority_group("test1", vec![].into_iter().collect());
+		assert_eq!(peers_state.num_in, 0);
+		peers_state.set_priority_group("test2", vec![].into_iter().collect());
+		assert_eq!(peers_state.num_in, 1);
 	}
 }