Expose PeerId in connection-limits crate

[DougAnderson444]

Description

Expose the PeerId of the peer who exceeded the limit, and also expose Kind as pub so we can use that PeerId

Motivation

We'd like insight into which Peer is exceeding the connection limit

Current Implementation

Opaquely states the limit was exceeded, but not by who.

Are you planning to do it yourself in a pull request?

Yes

[DougAnderson444]

rust-libp2p/misc/connection-limits/src/lib.rs

Line 156 in 60e93e7

EstablishedPerPeer,

[elenaf9]

Would it make sense to, instead of including the PeerId only in this error variant, to have in the general SwarmEvent::IncomingConnectionError as Option<PeerId>? I could imagine that this info is also useful in other scenarios.

We also already added it with #4818 to the matching ListenFailure event that is sent to the behaviors in this situation:

rust-libp2p/swarm/src/lib.rs

Lines 734 to 762 in 8199dac

	match self.behaviour.handle_established_inbound_connection(
	id,
	peer_id,
	&local_addr,
	&send_back_addr,
	) {
	Ok(handler) => handler,
	Err(cause) => {
	let listen_error = ListenError::Denied { cause };
	self.behaviour.on_swarm_event(FromSwarm::ListenFailure(
	ListenFailure {
	local_addr: &local_addr,
	send_back_addr: &send_back_addr,
	error: &listen_error,
	connection_id: id,
	peer_id: Some(peer_id),
	},
	));
	self.pending_swarm_events.push_back(
	SwarmEvent::IncomingConnectionError {
	connection_id: id,
	send_back_addr,
	local_addr,
	error: listen_error,
	},
	);
	return;
	}

[DougAnderson444]

I'm always a big fan of exposing as much troubleshooting data as possible, so I agree, also a great idea @elenaf9!

Does it make sense to have that as a separate pull request from #6027 ?

[elenaf9]

Does it make sense to have that as a separate pull request from #6027?

I was wondering if #6027 is still needed if we add the peer-id in IncomingConnectionError. I don't have anything major against #6027, but since downcasting is required to extract the peer-id from the boxed error I am wondering how much it will actually be used.

[DougAnderson444]

Ah I see what you mean, I've opened #6032 as a result of this discussion. Yes you're right, if I get the PeerId early enough we can gain the insight from there.