maintain preferred peer connections (#3435)

p2p/src/peers.rs

@@ -416,7 +416,12 @@ impl Peers {
 	/// Iterate over the peer list and prune all peers we have
 	/// lost connection to or have been deemed problematic.
 	/// Also avoid connected peer count getting too high.
-	pub fn clean_peers(&self, max_inbound_count: usize, max_outbound_count: usize) {
+	pub fn clean_peers(
+		&self,
+		max_inbound_count: usize,
+		max_outbound_count: usize,
+		preferred_peers: &[PeerAddr],
+	) {
 		let mut rm = vec![];
 
 		// build a list of peers to be cleaned up
@@ -464,12 +469,13 @@ impl Peers {
 		let excess_outgoing_count =
 			(self.peer_outbound_count() as usize).saturating_sub(max_outbound_count);
 		if excess_outgoing_count > 0 {
-			let mut addrs = self
+			let mut addrs: Vec<_> = self
 				.outgoing_connected_peers()
 				.iter()
+				.filter(|x| !preferred_peers.contains(&x.info.addr))
 				.take(excess_outgoing_count)
 				.map(|x| x.info.addr)
-				.collect::<Vec<_>>();
+				.collect();
 			rm.append(&mut addrs);
 		}
 
@@ -477,12 +483,13 @@ impl Peers {
 		let excess_incoming_count =
 			(self.peer_inbound_count() as usize).saturating_sub(max_inbound_count);
 		if excess_incoming_count > 0 {
-			let mut addrs = self
+			let mut addrs: Vec<_> = self
 				.incoming_connected_peers()
 				.iter()
+				.filter(|x| !preferred_peers.contains(&x.info.addr))
 				.take(excess_incoming_count)
 				.map(|x| x.info.addr)
-				.collect::<Vec<_>>();
+				.collect();
 			rm.append(&mut addrs);
 		}