Introduce sc_peerset::DropReason (#7996)

* Introduce sc_peerset::DropReason

* Fix peerset tests

substrate/client/peerset/src/lib.rs

@@ -604,7 +604,7 @@ 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, set_id: SetId, peer_id: PeerId) {
+	pub fn dropped(&mut self, set_id: SetId, peer_id: PeerId, reason: DropReason) {
 		// We want reputations to be up-to-date before adjusting them.
 		self.update_time();
 
@@ -620,6 +620,10 @@ impl Peerset {
 				error!(target: "peerset", "Received dropped() for non-connected node"),
 		}
 
+		if let DropReason::Refused = reason {
+			self.on_remove_from_peers_set(set_id, peer_id);
+		}
+
 		self.alloc_slots();
 	}
 
@@ -704,6 +708,17 @@ impl Stream for Peerset {
 	}
 }
 
+/// Reason for calling [`Peerset::dropped`].
+pub enum DropReason {
+	/// Substream or connection has been closed for an unknown reason.
+	Unknown,
+	/// Substream or connection has been explicitly refused by the target. In other words, the
+	/// peer doesn't actually belong to this set.
+	///
+	/// This has the side effect of calling [`PeersetHandle::remove_from_peers_set`].
+	Refused,
+}
+
 #[cfg(test)]
 mod tests {
 	use libp2p::PeerId;