Rewrite the PSM (#2440)

* Rewrite the PSM

* Fix disconnecting from reserved peers

* Minor adjustements

* Address review

* Reputation changes adjustements

* More adjustements

* Adjust all reputations

* More fixes and adjustments

* Improve proof

* Remove the possible panic

* Make sure reputation reaches 0

substrate/core/network-libp2p/src/behaviour.rs

@@ -159,7 +159,7 @@ impl<TMessage, TSubstream> Behaviour<TMessage, TSubstream> {
 	}
 
 	/// Returns the state of the peerset manager, for debugging purposes.
-	pub fn peerset_debug_info(&self) -> serde_json::Value {
+	pub fn peerset_debug_info(&mut self) -> serde_json::Value {
 		self.custom_protocols.peerset_debug_info()
 	}
 }

substrate/core/network-libp2p/src/custom_proto/behaviour.rs

@@ -357,7 +357,7 @@ impl<TMessage, TSubstream> CustomProto<TMessage, TSubstream> {
 	}
 
 	/// Returns the state of the peerset manager, for debugging purposes.
-	pub fn peerset_debug_info(&self) -> serde_json::Value {
+	pub fn peerset_debug_info(&mut self) -> serde_json::Value {
 		self.peerset.debug_info()
 	}
 

substrate/core/peerset/src/lib.rs

@@ -17,33 +17,16 @@
 //! Peer Set Manager (PSM). Contains the strategy for choosing which nodes the network should be
 //! connected to.
 
-mod slots;
+mod peersstate;
 
-use std::collections::VecDeque;
+use std::{collections::HashMap, collections::VecDeque, time::Instant};
 use futures::{prelude::*, sync::mpsc, try_ready};
 use libp2p::PeerId;
-use log::trace;
+use log::{debug, error, trace};
-use lru_cache::LruCache;
-use slots::{SlotType, SlotState, Slots};
 use serde_json::json;
 
-const PEERSET_SCORES_CACHE_SIZE: usize = 1000;
+/// Reputation change for a node when we get disconnected from it.
-const DISCOVERED_NODES_LIMIT: u32 = 1000;
+const DISCONNECT_REPUTATION_CHANGE: i32 = -10;
-
-#[derive(Debug)]
-struct PeersetData {
-	/// List of nodes that we know exist, but we are not connected to.
-	/// Elements in this list must never be in `out_slots` or `in_slots`.
-	discovered: Slots,
-	/// If true, we only accept reserved nodes.
-	reserved_only: bool,
-	/// Node slots for outgoing connections.
-	out_slots: Slots,
-	/// Node slots for incoming connections.
-	in_slots: Slots,
-	/// List of node scores.
-	scores: LruCache<PeerId, i32>,
-}
 
 #[derive(Debug)]
 enum Action {
@@ -147,9 +130,15 @@ pub struct PeersetConfig {
 /// errors.
 #[derive(Debug)]
 pub struct Peerset {
-	data: PeersetData,
+	data: peersstate::PeersState,
+	/// If true, we only accept reserved nodes.
+	reserved_only: bool,
 	rx: mpsc::UnboundedReceiver<Action>,
 	message_queue: VecDeque<Message>,
+	/// When the `Peerset` was created.
+	created: Instant,
+	/// Last time when we updated the reputations of connected nodes.
+	latest_time_update: Instant,
 }
 
 impl Peerset {
@@ -157,30 +146,33 @@ impl Peerset {
 	pub fn from_config(config: PeersetConfig) -> (Peerset, PeersetHandle) {
 		let (tx, rx) = mpsc::unbounded();
 
-		let data = PeersetData {
-			discovered: Slots::new(DISCOVERED_NODES_LIMIT),
-			reserved_only: config.reserved_only,
-			out_slots: Slots::new(config.out_peers),
-			in_slots: Slots::new(config.in_peers),
-			scores: LruCache::new(PEERSET_SCORES_CACHE_SIZE),
-		};
-
 		let handle = PeersetHandle {
 			tx,
 		};
 
 		let mut peerset = Peerset {
-			data,
+			data: peersstate::PeersState::new(config.in_peers, config.out_peers),
 			rx,
+			reserved_only: config.reserved_only,
 			message_queue: VecDeque::new(),
+			created: Instant::now(),
+			latest_time_update: Instant::now(),
 		};
 
 		for peer_id in config.reserved_nodes {
-			peerset.data.discovered.add_peer(peer_id, SlotType::Reserved);
+			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);
+			}
 		}
 
 		for peer_id in config.bootnodes {
-			peerset.data.discovered.add_peer(peer_id, SlotType::Common);
+			if let peersstate::Peer::Unknown(entry) = peerset.data.peer(&peer_id) {
+				entry.discover();
+			} else {
+				debug!(target: "peerset", "Duplicate bootnode in config: {:?}", peer_id);
+			}
 		}
 
 		peerset.alloc_slots();
@@ -188,115 +180,131 @@ impl Peerset {
 	}
 
 	fn on_add_reserved_peer(&mut self, peer_id: PeerId) {
-		// Nothing more to do if we're already connected.
+		let mut entry = match self.data.peer(&peer_id) {
-		if self.data.in_slots.contains(&peer_id) {
+			peersstate::Peer::Connected(mut connected) => {
-			self.data.in_slots.mark_reserved(&peer_id);
+				connected.set_reserved(true);
-			return;
+				return
-		}
+			}
+			peersstate::Peer::NotConnected(entry) => entry,
+			peersstate::Peer::Unknown(entry) => entry.discover(),
+		};
 
-		match self.data.out_slots.add_peer(peer_id, SlotType::Reserved) {
+		// We reach this point if and only if we were not connected to the node.
-			SlotState::Added(peer_id) => {
+		entry.set_reserved(true);
-				// reserved node may have been previously stored as normal node in discovered list
+		entry.force_outgoing();
-				self.data.discovered.remove_peer(&peer_id);
+		self.message_queue.push_back(Message::Connect(peer_id));
-
-				// notify that connection has been made
-				trace!(target: "peerset", "Connecting to new reserved peer {}", peer_id);
-				self.message_queue.push_back(Message::Connect(peer_id));
-				return;
-			},
-			SlotState::Swaped { removed, added } => {
-				// reserved node may have been previously stored as normal node in discovered list
-				self.data.discovered.remove_peer(&added);
-				// let's add the peer we disconnected from to the discovered list again
-				self.data.discovered.add_peer(removed.clone(), SlotType::Common);
-				// swap connections
-				trace!(target: "peerset", "Connecting to new reserved peer {}, dropping {}", added, removed);
-				self.message_queue.push_back(Message::Drop(removed));
-				self.message_queue.push_back(Message::Connect(added));
-			}
-			SlotState::AlreadyExists(_) | SlotState::Upgraded(_) => {
-				return;
-			}
-			SlotState::MaxCapacity(peer_id) => {
-				self.data.discovered.add_peer(peer_id, SlotType::Reserved);
-				return;
-			}
-		}
 	}
 
 	fn on_remove_reserved_peer(&mut self, peer_id: PeerId) {
-		self.data.in_slots.mark_not_reserved(&peer_id);
+		match self.data.peer(&peer_id) {
-		self.data.out_slots.mark_not_reserved(&peer_id);
+			peersstate::Peer::Connected(mut peer) => {
-		self.data.discovered.mark_not_reserved(&peer_id);
+				peer.set_reserved(false);
-		if self.data.reserved_only {
+				if self.reserved_only {
-			if self.data.in_slots.remove_peer(&peer_id) || self.data.out_slots.remove_peer(&peer_id) {
+					peer.disconnect();
-				// insert peer back into discovered list
+					self.message_queue.push_back(Message::Drop(peer_id));
-				self.data.discovered.add_peer(peer_id.clone(), SlotType::Common);
+				}
-				self.message_queue.push_back(Message::Drop(peer_id));
-				// call alloc_slots again, cause we may have some reserved peers in discovered list
-				// waiting for the slot that was just cleared
-				self.alloc_slots();
 			}
+			peersstate::Peer::NotConnected(mut peer) => peer.set_reserved(false),
+			peersstate::Peer::Unknown(_) => {}
 		}
 	}
 
 	fn on_set_reserved_only(&mut self, reserved_only: bool) {
 		// Disconnect non-reserved nodes.
-		self.data.reserved_only = reserved_only;
+		self.reserved_only = reserved_only;
-		if self.data.reserved_only {
+		if self.reserved_only {
-			for peer_id in self.data.in_slots.clear_common_slots().into_iter().chain(self.data.out_slots.clear_common_slots().into_iter()) {
+			for peer_id in self.data.connected_peers().cloned().collect::<Vec<_>>().into_iter() {
-				// insert peer back into discovered list
+				let peer = self.data.peer(&peer_id).into_connected()
-				self.data.discovered.add_peer(peer_id.clone(), SlotType::Common);
+					.expect("We are enumerating connected peers, therefore the peer is connected; qed");
-				self.message_queue.push_back(Message::Drop(peer_id));
+				if !peer.is_reserved() {
+					peer.disconnect();
+					self.message_queue.push_back(Message::Drop(peer_id));
+				}
 			}
+
 		} else {
 			self.alloc_slots();
 		}
 	}
 
 	fn on_report_peer(&mut self, peer_id: PeerId, score_diff: i32) {
-		let score = match self.data.scores.get_mut(&peer_id) {
+		// We want reputations to be up-to-date before adjusting them.
-			Some(score) => {
+		self.update_time();
-				*score = score.saturating_add(score_diff);
+
-				*score
+		match self.data.peer(&peer_id) {
-			},
+			peersstate::Peer::Connected(mut peer) => peer.add_reputation(score_diff),
-			None => {
+			peersstate::Peer::NotConnected(mut peer) => peer.add_reputation(score_diff),
-				self.data.scores.insert(peer_id.clone(), score_diff);
+			peersstate::Peer::Unknown(peer) => peer.discover().add_reputation(score_diff),
-				score_diff
+		}
-			}
+	}
+
+	/// Updates the value of `self.latest_time_update` and performs all the updates that happen
+	/// over time, such as reputation increases for staying connected.
+	fn update_time(&mut self) {
+		// We basically do `(now - self.latest_update).as_secs()`, except that by the way we do it
+		// we know that we're not going to miss seconds because of rounding to integers.
+		let secs_diff = {
+			let now = Instant::now();
+			let elapsed_latest = self.latest_time_update - self.created;
+			let elapsed_now = now - self.created;
+			self.latest_time_update = now;
+			elapsed_now.as_secs() - elapsed_latest.as_secs()
 		};
 
-		if score < 0 {
+		// For each elapsed second, move the node reputation towards zero.
-			// peer will be removed from `in_slots` or `out_slots` in `on_dropped` method
+		// If we multiply each second the reputation by `k` (where `k` is between 0 and 1), it
-			if self.data.in_slots.contains(&peer_id) || self.data.out_slots.contains(&peer_id) {
+		// takes `ln(0.5) / ln(k)` seconds to reduce the reputation by half. Use this formula to
-				self.data.in_slots.remove_peer(&peer_id);
+		// empirically determine a value of `k` that looks correct.
-				self.data.out_slots.remove_peer(&peer_id);
+		for _ in 0..secs_diff {
-				self.message_queue.push_back(Message::Drop(peer_id));
+			for peer in self.data.peers().cloned().collect::<Vec<_>>() {
+				// We use `k = 0.98`, so we divide by `50`. With that value, it takes 34.3 seconds
+				// to reduce the reputation by half.
+				fn reput_tick(reput: i32) -> i32 {
+					let mut diff = -reput / 50;
+					if diff == 0 && reput < 0 {
+						diff = 1;
+					} else if diff == 0 && reput > 0 {
+						diff = -1;
+					}
+					reput.saturating_add(diff)
+				}
+				match self.data.peer(&peer) {
+					peersstate::Peer::Connected(mut peer) =>
+						peer.set_reputation(reput_tick(peer.reputation())),
+					peersstate::Peer::NotConnected(mut peer) =>
+						peer.set_reputation(reput_tick(peer.reputation())),
+					peersstate::Peer::Unknown(_) => unreachable!("We iterate over known peers; qed")
+				}
 			}
 		}
 	}
 
+	/// Try to fill available out slots with nodes.
 	fn alloc_slots(&mut self) {
-		while let Some((peer_id, slot_type)) = self.data.discovered.pop_most_important_peer(self.data.reserved_only) {
+		self.update_time();
-			match self.data.out_slots.add_peer(peer_id, slot_type) {
+
-				SlotState::Added(peer_id) => {
+		loop {
-					trace!(target: "peerset", "Connecting to new peer {}", peer_id);
+			// Try to grab the next node to attempt to connect to.
-					self.message_queue.push_back(Message::Connect(peer_id));
+			let next = match self.data.reserved_not_connected_peer() {
-				},
+				Some(p) => p,
-				SlotState::Swaped { removed, added } => {
+				None => if self.reserved_only {
-					// insert peer back into discovered list
+					break	// No known node to add.
-					trace!(target: "peerset", "Connecting to new peer {}, dropping {}", added, removed);
+				} else {
-					self.data.discovered.add_peer(removed.clone(), SlotType::Common);
+					match self.data.highest_not_connected_peer() {
-					self.message_queue.push_back(Message::Drop(removed));
+						Some(p) => p,
-					self.message_queue.push_back(Message::Connect(added));
+						None => break,	// No known node to add.
+					}
 				}
-				SlotState::Upgraded(_) | SlotState::AlreadyExists(_) => {
+			};
-					// TODO: we should never reach this point
+
-				},
+			// Don't connect to nodes with an abysmal reputation.
-				SlotState::MaxCapacity(peer_id) => {
+			if next.reputation() == i32::min_value() {
-					self.data.discovered.add_peer(peer_id, slot_type);
+				break;
-					break;
+			}
-				},
+
+			match next.try_outgoing() {
+				Ok(conn) => self.message_queue.push_back(Message::Connect(conn.into_peer_id())),
+				Err(_) => break,	// No more slots available.
 			}
 		}
 	}
@@ -305,60 +313,24 @@ impl Peerset {
 	/// a corresponding `Accept` or `Reject`, except if we were already connected to this peer.
 	///
 	/// Note that this mechanism is orthogonal to `Connect`/`Drop`. Accepting an incoming
-	/// connection implicitely means `Accept`, but incoming connections aren't cancelled by
+	/// connection implicitely means `Connect`, but incoming connections aren't cancelled by
 	/// `dropped`.
 	///
 	/// Because of concurrency issues, it is acceptable to call `incoming` with a `PeerId` the
 	/// peerset is already connected to, in which case it must not answer.
 	pub fn incoming(&mut self, peer_id: PeerId, index: IncomingIndex) {
-		trace!(
+		trace!(target: "peerset", "Incoming {:?}", peer_id);
-			target: "peerset",
-			"Incoming {:?}\nin_slots={:?}\nout_slots={:?}",
-			peer_id, self.data.in_slots, self.data.out_slots
-		);
-		// if `reserved_only` is set, but this peer is not a part of our discovered list,
-		// a) it is not reserved, so we reject the connection
-		// b) we are already connected to it, so we reject the connection
-		if self.data.reserved_only && !self.data.discovered.is_reserved(&peer_id) {
-			self.message_queue.push_back(Message::Reject(index));
-			return;
-		}
 
-		// check if we are already connected to this peer
+		let not_connected = match self.data.peer(&peer_id) {
-		if self.data.out_slots.contains(&peer_id) {
+			// If we're already connected, don't answer, as the docs mention.
-			// we are already connected. in this case we do not answer
+			peersstate::Peer::Connected(_) => return,
-			return;
+			peersstate::Peer::NotConnected(entry) => entry,
-		}
+			peersstate::Peer::Unknown(entry) => entry.discover(),
-
-		let slot_type = if self.data.reserved_only {
-			SlotType::Reserved
-		} else {
-			SlotType::Common
 		};
 
-		match self.data.in_slots.add_peer(peer_id, slot_type) {
+		match not_connected.try_accept_incoming() {
-			SlotState::Added(peer_id) => {
+			Ok(_) => self.message_queue.push_back(Message::Accept(index)),
-				// reserved node may have been previously stored as normal node in discovered list
+			Err(_) => self.message_queue.push_back(Message::Reject(index)),
-				self.data.discovered.remove_peer(&peer_id);
-				self.message_queue.push_back(Message::Accept(index));
-				return;
-			},
-			SlotState::Swaped { removed, added } => {
-				// reserved node may have been previously stored as normal node in discovered list
-				self.data.discovered.remove_peer(&added);
-				// swap connections.
-				self.message_queue.push_back(Message::Drop(removed));
-				self.message_queue.push_back(Message::Accept(index));
-			},
-			SlotState::AlreadyExists(_) | SlotState::Upgraded(_) => {
-				// we are already connected. in this case we do not answer
-				return;
-			},
-			SlotState::MaxCapacity(peer_id) => {
-				self.data.discovered.add_peer(peer_id, slot_type);
-				self.message_queue.push_back(Message::Reject(index));
-				return;
-			},
 		}
 	}
 
@@ -367,24 +339,21 @@ impl Peerset {
 	/// Must only be called after the PSM has either generated a `Connect` message with this
 	/// `PeerId`, or accepted an incoming connection with this `PeerId`.
 	pub fn dropped(&mut self, peer_id: PeerId) {
-		trace!(
+		trace!(target: "peerset", "Dropping {:?}", peer_id);
-			target: "peerset",
+
-			"Dropping {:?}\nin_slots={:?}\nout_slots={:?}",
+		// We want reputations to be up-to-date before adjusting them.
-			peer_id, self.data.in_slots, self.data.out_slots
+		self.update_time();
-		);
+
-		// Automatically connect back if reserved.
+		match self.data.peer(&peer_id) {
-		if self.data.in_slots.is_reserved(&peer_id) || self.data.out_slots.is_reserved(&peer_id) {
+			peersstate::Peer::Connected(mut entry) => {
-			self.message_queue.push_back(Message::Connect(peer_id));
+				// Decrease the node's reputation so that we don't try it again and again and again.
-			return;
+				entry.add_reputation(DISCONNECT_REPUTATION_CHANGE);
+				entry.disconnect();
+			}
+			peersstate::Peer::NotConnected(_) | peersstate::Peer::Unknown(_) =>
+				error!(target: "peerset", "Received dropped() for non-connected node"),
 		}
 
-		// Otherwise, free the slot.
-		self.data.in_slots.remove_peer(&peer_id);
-		self.data.out_slots.remove_peer(&peer_id);
-
-		// Note: in this dummy implementation we consider that peers never expire. As soon as we
-		// are disconnected from a peer, we try again.
-		self.data.discovered.add_peer(peer_id, SlotType::Common);
 		self.alloc_slots();
 	}
 
@@ -393,28 +362,42 @@ impl Peerset {
 	/// > **Note**: There is no equivalent "expired" message, meaning that it is the responsibility
 	/// >			of the PSM to remove `PeerId`s that fail to dial too often.
 	pub fn discovered<I: IntoIterator<Item = PeerId>>(&mut self, peer_ids: I) {
+		let mut discovered_any = false;
+
 		for peer_id in peer_ids {
-			if !self.data.in_slots.contains(&peer_id) && !self.data.out_slots.contains(&peer_id) && !self.data.discovered.contains(&peer_id) {
+			if let peersstate::Peer::Unknown(entry) = self.data.peer(&peer_id) {
-				trace!(target: "peerset", "Discovered new peer: {:?}", peer_id);
+				entry.discover();
-				self.data.discovered.add_peer(peer_id, SlotType::Common);
+				discovered_any = true;
-			} else {
-				trace!(target: "peerset", "Discovered known peer: {:?}", peer_id);
 			}
 		}
 
-		self.alloc_slots();
+		if discovered_any {
+			self.alloc_slots();
+		}
 	}
 
 	/// Produces a JSON object containing the state of the peerset manager, for debugging purposes.
-	pub fn debug_info(&self) -> serde_json::Value {
+	pub fn debug_info(&mut self) -> serde_json::Value {
+		self.update_time();
+
 		json!({
-			"data": {
+			"nodes": self.data.peers().cloned().collect::<Vec<_>>().into_iter().map(|peer_id| {
-				// add scores
+				let state = match self.data.peer(&peer_id) {
-				"discovered": self.data.discovered.debug_info(),
+					peersstate::Peer::Connected(entry) => json!({
-				"reserved_only": self.data.reserved_only,
+						"connected": true,
-				"out_slots": self.data.out_slots.debug_info(),
+						"reputation": entry.reputation()
-				"in_slots": self.data.in_slots.debug_info()
+					}),
-			},
+					peersstate::Peer::NotConnected(entry) => json!({
+						"connected": false,
+						"reputation": entry.reputation()
+					}),
+					peersstate::Peer::Unknown(_) =>
+						unreachable!("We iterate over the known peers; QED")
+				};
+
+				(peer_id.to_base58(), state)
+			}).collect::<HashMap<_, _>>(),
+			"reserved_only": self.reserved_only,
 			"message_queue": self.message_queue.len(),
 		})
 	}
@@ -454,7 +437,7 @@ mod tests {
 			assert_eq!(message, expected_message);
 			peerset = p;
 		}
-		assert!(peerset.message_queue.is_empty());
+		assert!(peerset.message_queue.is_empty(), peerset.message_queue);
 		peerset
 	}
 
@@ -466,49 +449,6 @@ mod tests {
 		Ok((message, peerset))
 	}
 
-	#[test]
-	fn test_peerset_from_config_with_bootnodes() {
-		let bootnode = PeerId::random();
-		let bootnode2 = PeerId::random();
-		let config = PeersetConfig {
-			in_peers: 0,
-			out_peers: 2,
-			bootnodes: vec![bootnode.clone(), bootnode2.clone()],
-			reserved_only: false,
-			reserved_nodes: Vec::new(),
-		};
-
-		let (peerset, _handle) = Peerset::from_config(config);
-
-		assert_messages(peerset, vec![
-			Message::Connect(bootnode),
-			Message::Connect(bootnode2),
-		]);
-	}
-
-	#[test]
-	fn test_peerset_from_config_with_reserved_nodes() {
-		let bootnode = PeerId::random();
-		let bootnode2 = PeerId::random();
-		let reserved_peer = PeerId::random();
-		let reserved_peer2 = PeerId::random();
-		let config = PeersetConfig {
-			in_peers: 0,
-			out_peers: 3,
-			bootnodes: vec![bootnode.clone(), bootnode2.clone()],
-			reserved_only: false,
-			reserved_nodes: vec![reserved_peer.clone(), reserved_peer2.clone()],
-		};
-
-		let (peerset, _handle) = Peerset::from_config(config);
-
-		assert_messages(peerset, vec![
-			Message::Connect(reserved_peer),
-			Message::Connect(reserved_peer2),
-			Message::Connect(bootnode)
-		]);
-	}
-
 	#[test]
 	fn test_peerset_add_reserved_peer() {
 		let bootnode = PeerId::random();
@@ -532,87 +472,6 @@ mod tests {
 		]);
 	}
 
-	#[test]
-	fn test_peerset_remove_reserved_peer() {
-		let reserved_peer = PeerId::random();
-		let reserved_peer2 = PeerId::random();
-		let config = PeersetConfig {
-			in_peers: 0,
-			out_peers: 2,
-			bootnodes: vec![],
-			reserved_only: false,
-			reserved_nodes: vec![reserved_peer.clone(), reserved_peer2.clone()],
-		};
-
-		let (peerset, handle) = Peerset::from_config(config);
-		handle.remove_reserved_peer(reserved_peer.clone());
-
-		let peerset = assert_messages(peerset, vec![
-			Message::Connect(reserved_peer.clone()),
-			Message::Connect(reserved_peer2.clone()),
-		]);
-
-		handle.set_reserved_only(true);
-		handle.remove_reserved_peer(reserved_peer2.clone());
-
-		assert_messages(peerset, vec![
-			Message::Drop(reserved_peer),
-			Message::Drop(reserved_peer2),
-		]);
-	}
-
-	#[test]
-	fn test_peerset_set_reserved_only() {
-		let bootnode = PeerId::random();
-		let bootnode2 = PeerId::random();
-		let reserved_peer = PeerId::random();
-		let reserved_peer2 = PeerId::random();
-		let config = PeersetConfig {
-			in_peers: 0,
-			out_peers: 4,
-			bootnodes: vec![bootnode.clone(), bootnode2.clone()],
-			reserved_only: false,
-			reserved_nodes: vec![reserved_peer.clone(), reserved_peer2.clone()],
-		};
-
-		let (peerset, handle) = Peerset::from_config(config);
-		handle.set_reserved_only(true);
-		handle.set_reserved_only(false);
-
-		assert_messages(peerset, vec![
-			Message::Connect(reserved_peer),
-			Message::Connect(reserved_peer2),
-			Message::Connect(bootnode.clone()),
-			Message::Connect(bootnode2.clone()),
-			Message::Drop(bootnode.clone()),
-			Message::Drop(bootnode2.clone()),
-			Message::Connect(bootnode),
-			Message::Connect(bootnode2),
-		]);
-	}
-
-	#[test]
-	fn test_peerset_report_peer() {
-		let bootnode = PeerId::random();
-		let bootnode2 = PeerId::random();
-		let config = PeersetConfig {
-			in_peers: 0,
-			out_peers: 1,
-			bootnodes: vec![bootnode.clone(), bootnode2.clone()],
-			reserved_only: false,
-			reserved_nodes: Vec::new(),
-		};
-
-		let (peerset, handle) = Peerset::from_config(config);
-		handle.report_peer(bootnode2, -1);
-		handle.report_peer(bootnode.clone(), -1);
-
-		assert_messages(peerset, vec![
-			Message::Connect(bootnode.clone()),
-			Message::Drop(bootnode)
-		]);
-	}
-
 	#[test]
 	fn test_peerset_incoming() {
 		let bootnode = PeerId::random();
@@ -645,35 +504,6 @@ mod tests {
 		]);
 	}
 
-	#[test]
-	fn test_peerset_dropped() {
-		let bootnode = PeerId::random();
-		let bootnode2 = PeerId::random();
-		let reserved_peer = PeerId::random();
-		let config = PeersetConfig {
-			in_peers: 0,
-			out_peers: 2,
-			bootnodes: vec![bootnode.clone(), bootnode2.clone()],
-			reserved_only: false,
-			reserved_nodes: vec![reserved_peer.clone()],
-		};
-
-		let (peerset, _handle) = Peerset::from_config(config);
-
-		let mut peerset = assert_messages(peerset, vec![
-			Message::Connect(reserved_peer.clone()),
-			Message::Connect(bootnode.clone()),
-		]);
-
-		peerset.dropped(reserved_peer.clone());
-		peerset.dropped(bootnode);
-
-		let _peerset = assert_messages(peerset, vec![
-			Message::Connect(reserved_peer),
-			Message::Connect(bootnode2),
-		]);
-	}
-
 	#[test]
 	fn test_peerset_discovered() {
 		let bootnode = PeerId::random();

substrate/core/peerset/src/peersstate.rs

@@ -0,0 +1,586 @@
+// Copyright 2019 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Contains the state storage behind the peerset.
+
+use libp2p::PeerId;
+use std::{borrow::Cow, collections::HashMap};
+
+/// State storage behind the peerset.
+///
+/// # Usage
+///
+/// This struct is nothing more but a data structure containing a list of nodes, where each node
+/// has a reputation and is either connected to us or not.
+///
+#[derive(Debug, Clone)]
+pub struct PeersState {
+	/// List of nodes that we know about.
+	///
+	/// > **Note**: This list should really be ordered by decreasing reputation, so that we can
+	/// 			easily select the best node to connect to. As a first draft, however, we don't
+	/// 			sort, to make the logic easier.
+	nodes: HashMap<PeerId, Node>,
+
+	/// Number of non-reserved nodes for which the `ConnectionState` is `In`.
+	num_in: u32,
+
+	/// Number of non-reserved nodes for which the `ConnectionState` is `In`.
+	num_out: u32,
+
+	/// Maximum allowed number of non-reserved nodes for which the `ConnectionState` is `In`.
+	max_in: u32,
+
+	/// Maximum allowed number of non-reserved nodes for which the `ConnectionState` is `Out`.
+	max_out: u32,
+}
+
+/// State of a single node that we know about.
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+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,
+}
+
+/// Whether we are connected to a node.
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+enum ConnectionState {
+	/// We are connected through an ingoing connection.
+	In,
+	/// We are connected through an outgoing connection.
+	Out,
+	/// We are not connected to this node.
+	NotConnected,
+}
+
+impl ConnectionState {
+	/// Returns `true` for `In` and `Out`.
+	fn is_connected(self) -> bool {
+		match self {
+			ConnectionState::In => true,
+			ConnectionState::Out => true,
+			ConnectionState::NotConnected => false,
+		}
+	}
+}
+
+impl PeersState {
+	/// Builds a new empty `PeersState`.
+	pub fn new(in_peers: u32, out_peers: u32) -> Self {
+		PeersState {
+			nodes: HashMap::new(),
+			num_in: 0,
+			num_out: 0,
+			max_in: in_peers,
+			max_out: out_peers,
+		}
+	}
+
+	/// 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 {
+				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,
+			})
+		}
+	}
+
+	/// Returns the list of all the peers we know of.
+	// Note: this method could theoretically return a `Peer`, but implementing that
+	// isn't simple.
+	pub fn peers(&self) -> impl Iterator<Item = &PeerId> {
+		self.nodes.keys()
+	}
+
+	/// Returns the list of peers we are connected to.
+	// Note: this method could theoretically return a `ConnectedPeer`, but implementing that
+	// isn't simple.
+	pub fn connected_peers(&self) -> impl Iterator<Item = &PeerId> {
+		self.nodes.iter()
+			.filter(|(_, p)| p.connection_state.is_connected())
+			.map(|(p, _)| p)
+	}
+
+	/// Returns the first reserved 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
+		}
+	}
+
+	/// Returns the peer with the highest reputation and that we are not connected to.
+	///
+	/// If multiple nodes have the same reputation, which one is returned is unspecified.
+	pub fn highest_not_connected_peer(&mut self) -> Option<NotConnectedPeer> {
+		let outcome = self.nodes
+			.iter_mut()
+			.filter(|(_, Node { connection_state, .. })| !connection_state.is_connected())
+			.fold(None::<(&PeerId, &mut Node)>, |mut cur_node, to_try| {
+				if let Some(cur_node) = cur_node.take() {
+					if cur_node.1.reputation >= to_try.1.reputation {
+						return Some(cur_node);
+					}
+				}
+				Some(to_try)
+			})
+			.map(|(peer_id, state)| (peer_id.clone(), state));
+
+		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
+		}
+	}
+}
+
+/// Grants access to the state of a peer in the `PeersState`.
+pub enum Peer<'a> {
+	/// We are connected to this node.
+	Connected(ConnectedPeer<'a>),
+	/// We are not connected to this node.
+	NotConnected(NotConnectedPeer<'a>),
+	/// We have never heard of this node.
+	Unknown(UnknownPeer<'a>),
+}
+
+impl<'a> Peer<'a> {
+	/// If we are the `Connected` variant, returns the inner `ConnectedPeer`. Returns `None`
+	/// otherwise.
+	pub fn into_connected(self) -> Option<ConnectedPeer<'a>> {
+		match self {
+			Peer::Connected(peer) => Some(peer),
+			Peer::NotConnected(_) => None,
+			Peer::Unknown(_) => None,
+		}
+	}
+
+	/// If we are the `Unknown` variant, returns the inner `ConnectedPeer`. Returns `None`
+	/// otherwise.
+	#[cfg(test)]	// Feel free to remove this if this function is needed outside of tests
+	pub fn into_not_connected(self) -> Option<NotConnectedPeer<'a>> {
+		match self {
+			Peer::Connected(_) => None,
+			Peer::NotConnected(peer) => Some(peer),
+			Peer::Unknown(_) => None,
+		}
+	}
+
+	/// If we are the `Unknown` variant, returns the inner `ConnectedPeer`. Returns `None`
+	/// otherwise.
+	#[cfg(test)]	// Feel free to remove this if this function is needed outside of tests
+	pub fn into_unknown(self) -> Option<UnknownPeer<'a>> {
+		match self {
+			Peer::Connected(_) => None,
+			Peer::NotConnected(_) => None,
+			Peer::Unknown(peer) => Some(peer),
+		}
+	}
+}
+
+/// A peer that is connected to us.
+pub struct ConnectedPeer<'a> {
+	state: &'a mut Node,
+	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> {
+	/// Destroys this `ConnectedPeer` and returns the `PeerId` inside of it.
+	pub fn into_peer_id(self) -> PeerId {
+		self.peer_id.into_owned()
+	}
+
+	/// Switches the peer to "not connected".
+	pub fn disconnect(self) -> NotConnectedPeer<'a> {
+		let connec_state = &mut self.state.connection_state;
+
+		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;
+
+		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 = 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
+	}
+
+	/// Sets the reputation of the peer.
+	pub fn set_reputation(&mut self, value: i32) {
+		self.state.reputation = 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);
+	}
+}
+
+/// A peer that is not connected to us.
+pub struct NotConnectedPeer<'a> {
+	state: &'a mut Node,
+	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> {
+	/// Destroys this `NotConnectedPeer` and returns the `PeerId` inside of it.
+	#[cfg(test)]	// Feel free to remove this if this function is needed outside of tests
+	pub fn into_peer_id(self) -> PeerId {
+		self.peer_id.into_owned()
+	}
+
+	/// Tries to set the peer as connected as an outgoing 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`.
+	/// If the node is reserved, this method always succeeds.
+	///
+	/// Note that reserved 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,
+		}
+	}
+
+	/// 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.
+	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,
+		}
+	}
+
+	/// 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
+	}
+
+	/// Sets the reputation of the peer.
+	pub fn set_reputation(&mut self, value: i32) {
+		self.state.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.
+	pub fn add_reputation(&mut self, modifier: i32) {
+		let reputation = &mut self.state.reputation;
+		*reputation = reputation.saturating_add(modifier);
+	}
+}
+
+/// A peer that we have never heard of.
+pub struct UnknownPeer<'a> {
+	parent: &'a mut PeersState,
+	peer_id: Cow<'a, PeerId>,
+}
+
+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
+	/// 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");
+
+		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,
+		}
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::{PeersState, Peer};
+	use libp2p::PeerId;
+
+	#[test]
+	fn full_slots_in() {
+		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) {
+			assert!(e.discover().try_accept_incoming().is_ok());
+		}
+
+		if let Peer::Unknown(e) = peers_state.peer(&id2) {
+			assert!(e.discover().try_accept_incoming().is_err());
+		}
+	}
+
+	#[test]
+	fn reserved_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);
+			assert!(p.try_accept_incoming().is_ok());
+		} else { panic!() }
+
+		if let Peer::Unknown(e) = peers_state.peer(&id2) {
+			assert!(e.discover().try_accept_incoming().is_ok());
+		} else { panic!() }
+	}
+
+	#[test]
+	fn disconnecting_frees_slot() {
+		let mut peers_state = PeersState::new(1, 1);
+		let id1 = PeerId::random();
+		let id2 = PeerId::random();
+
+		assert!(peers_state.peer(&id1).into_unknown().unwrap().discover().try_accept_incoming().is_ok());
+		assert!(peers_state.peer(&id2).into_unknown().unwrap().discover().try_accept_incoming().is_err());
+		peers_state.peer(&id1).into_connected().unwrap().disconnect();
+		assert!(peers_state.peer(&id2).into_not_connected().unwrap().try_accept_incoming().is_ok());
+	}
+
+	#[test]
+	fn reserved_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());
+		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());
+	}
+
+	#[test]
+	fn highest_not_connected_peer() {
+		let mut peers_state = PeersState::new(25, 25);
+		let id1 = PeerId::random();
+		let id2 = PeerId::random();
+
+		assert!(peers_state.highest_not_connected_peer().is_none());
+		peers_state.peer(&id1).into_unknown().unwrap().discover().set_reputation(50);
+		peers_state.peer(&id2).into_unknown().unwrap().discover().set_reputation(25);
+		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();
+		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();
+		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);
+		assert_eq!(peers_state.highest_not_connected_peer().map(|p| p.into_peer_id()), Some(id2.clone()));
+	}
+}

substrate/core/peerset/src/slots.rs

@@ -1,222 +0,0 @@
-// Copyright 2018-2019 Parity Technologies (UK) Ltd.
-// This file is part of Substrate.
-
-// Substrate is free software: you can redistribute it and/or modify
-// it under the terms of the GNU General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-
-// Substrate is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-// GNU General Public License for more details.
-
-// You should have received a copy of the GNU General Public License
-// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
-
-use std::{fmt, mem};
-use libp2p::PeerId;
-use linked_hash_map::LinkedHashMap;
-use serde_json::json;
-
-/// Describes the nature of connection with a given peer.
-#[derive(Debug, PartialEq, Clone, Copy)]
-pub enum SlotType {
-	/// Reserved peer is a peer we should always stay connected to.
-	Reserved,
-	/// Common peer is a type of peer that we stay connected to only if it's
-	/// useful for us.
-	Common,
-}
-
-/// Descibes the result of `add_peer` action.
-pub enum SlotState {
-	/// Returned when `add_peer` successfully adds a peer to the slot.
-	Added(PeerId),
-	/// Returned when we already have given peer in our list, but it is upgraded from
-	/// `Common` to `Reserved`.
-	Upgraded(PeerId),
-	/// Returned when we should removed a common peer to make space for a reserved peer.
-	Swaped {
-		/// Peer was removed from the list.
-		removed: PeerId,
-		/// Peer was added to the list.
-		added: PeerId,
-	},
-	/// Error returned when we are already know about given peer.
-	AlreadyExists(PeerId),
-	/// Error returned when list is full and no more peers can be added.
-	MaxCapacity(PeerId),
-}
-
-/// Contains all information about group of slots.
-pub struct Slots {
-	/// Maximum number of slots. Total number of reserved and common slots must be always
-	/// smaller or equal to `max_slots`.
-	max_slots: usize,
-	/// Reserved slots.
-	reserved: LinkedHashMap<PeerId,()>,
-	/// Common slots.
-	common: LinkedHashMap<PeerId, ()>,
-}
-
-impl fmt::Debug for Slots {
-	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-		struct ListFormatter<'a>(&'a LinkedHashMap<PeerId, ()>);
-
-		impl<'a> fmt::Debug for ListFormatter<'a> {
-			fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-				f.debug_list().entries(self.0.keys()).finish()
-			}
-		}
-
-		f.debug_struct("Slots")
-			.field("max_slots", &self.max_slots)
-			.field("reserved", &ListFormatter(&self.reserved))
-			.field("common", &ListFormatter(&self.common))
-			.finish()
-	}
-}
-
-impl Slots {
-	/// Creates a group of slots with a limited size.
-	pub fn new(max_slots: u32) -> Self {
-		let max_slots = max_slots as usize;
-		Slots {
-			max_slots,
-			reserved: LinkedHashMap::new(),
-			common: LinkedHashMap::new(),
-		}
-	}
-
-	/// Returns true if one of the slots contains given peer.
-	pub fn contains(&self, peer_id: &PeerId) -> bool {
-		self.common.contains_key(peer_id) || self.reserved.contains_key(peer_id)
-	}
-
-	/// Tries to find a slot for a given peer and returns `SlotState`.
-	///
-	/// - If a peer is already inserted into reserved list or inserted or
-	/// inserted into common list and readded with the same `SlotType`,
-	/// the function returns `SlotState::AlreadyExists`
-	/// - If a peer is already inserted common list returns `SlotState::Upgraded`
-	/// - If there is no slot for a reserved peer, we try to drop one common peer
-	/// and it a new reserved one in it's place, function returns `SlotState::Swaped`
-	/// - If there is no place for a peer, function returns `SlotState::MaxCapacity`
-	/// - If the peer was simply added, `SlotState::Added` is returned
-	pub fn add_peer(&mut self, peer_id: PeerId, slot_type: SlotType) -> SlotState {
-		if self.reserved.contains_key(&peer_id) {
-			return SlotState::AlreadyExists(peer_id);
-		}
-
-		if self.common.contains_key(&peer_id) {
-			if slot_type == SlotType::Reserved {
-				self.common.remove(&peer_id);
-				self.reserved.insert(peer_id.clone(), ());
-				return SlotState::Upgraded(peer_id);
-			} else {
-				return SlotState::AlreadyExists(peer_id);
-			}
-		}
-
-		if self.max_slots == (self.common.len() + self.reserved.len()) {
-			if let SlotType::Reserved = slot_type {
-				if let Some((to_remove, _)) = self.common.pop_front() {
-					self.reserved.insert(peer_id.clone(), ());
-					return SlotState::Swaped {
-						removed: to_remove,
-						added: peer_id,
-					};
-				}
-			}
-			return SlotState::MaxCapacity(peer_id);
-		}
-
-		match slot_type {
-			SlotType::Common => self.common.insert(peer_id.clone(), ()),
-			SlotType::Reserved => self.reserved.insert(peer_id.clone(), ()),
-		};
-
-		SlotState::Added(peer_id)
-	}
-
-	/// Pops the oldest reserved peer. If none exists and `reserved_only = false` pops a common peer.
-	pub fn pop_most_important_peer(&mut self, reserved_only: bool) -> Option<(PeerId, SlotType)> {
-		if let Some((peer_id, _)) = self.reserved.pop_front() {
-			return Some((peer_id, SlotType::Reserved));
-		}
-
-		if reserved_only {
-			return None;
-		}
-
-		self.common.pop_front()
-			.map(|(peer_id, _)| (peer_id, SlotType::Common))
-	}
-
-	/// Removes all common peers from the list and returns an iterator over them.
-	pub fn clear_common_slots(&mut self) -> impl Iterator<Item = PeerId> {
-		let slots = mem::replace(&mut self.common, LinkedHashMap::new());
-		slots.into_iter().map(|(peer_id, _)| peer_id)
-	}
-
-	/// Marks given peer as a reserved one.
-	pub fn mark_reserved(&mut self, peer_id: &PeerId) {
-		if self.common.remove(peer_id).is_some() {
-			self.reserved.insert(peer_id.clone(), ());
-		}
-	}
-
-	/// Marks given peer as not reserved one.
-	pub fn mark_not_reserved(&mut self, peer_id: &PeerId) {
-		if self.reserved.remove(peer_id).is_some() {
-			self.common.insert(peer_id.clone(), ());
-		}
-	}
-
-	/// Removes a peer from a list and returns true if it existed.
-	pub fn remove_peer(&mut self, peer_id: &PeerId) -> bool {
-		self.common.remove(peer_id).is_some() || self.reserved.remove(peer_id).is_some()
-	}
-
-	/// Returns true if given peer is reserved.
-	pub fn is_reserved(&self, peer_id: &PeerId) -> bool {
-		self.reserved.contains_key(peer_id)
-	}
-
-	/// Produces a JSON object containing the state of slots, for debugging purposes.
-	pub fn debug_info(&self) -> serde_json::Value {
-		json!({
-			"max_slots": self.max_slots,
-			"reserved": self.reserved.keys().map(|peer_id| peer_id.to_base58()).collect::<Vec<_>>(),
-			"common": self.common.keys().map(|peer_id| peer_id.to_base58()).collect::<Vec<_>>()
-		})
-	}
-}
-
-#[cfg(test)]
-mod tests {
-	use libp2p::PeerId;
-	use serde_json::json;
-	use super::{Slots, SlotType};
-
-	#[test]
-	fn test_slots_debug_info() {
-		let reserved_peer = PeerId::random();
-		let reserved_peer2 = PeerId::random();
-		let common_peer = PeerId::random();
-		let mut slots = Slots::new(10);
-
-		slots.add_peer(reserved_peer.clone(), SlotType::Reserved);
-		slots.add_peer(reserved_peer2.clone(), SlotType::Reserved);
-		slots.add_peer(common_peer.clone(), SlotType::Common);
-
-		let expected = json!({
-			"max_slots": 10,
-			"reserved": vec![reserved_peer.to_base58(), reserved_peer2.to_base58()],
-			"common": vec![common_peer.to_base58()],
-		});
-
-		assert_eq!(expected, slots.debug_info());
-	}
-}