Dropping in-flight connect requests

[anilaltuner]

Libp2p-relay Capacity Warning

Issue Description

I've been working with libp2p relays and these following warnings in my logs:

[2024-08-14T12:16:06Z WARN libp2p_relay::priv_client::handler] Dropping in-flight connect request because we are at capacity

This warning seems to indicate that the relay client is dropping connection requests due to reaching some kind of capacity limit.

Questions

1. What exactly does "at capacity" mean in this context? Is there a configurable limit for the number of in-flight connect requests?

2. Could this warning indicate a potential bottleneck in our network topology or relay configuration?

[dariusc93]

This seems to happen due to the concurrent streams for that connection is hitting its max

rust-libp2p/protocols/relay/src/priv_client/handler.rs

Line 51 in 4d7a535

const MAX_CONCURRENT_STREAMS_PER_CONNECTION: usize = 10;

The error would happen, as you noticed, during an establishment of a circuit

rust-libp2p/protocols/relay/src/priv_client/handler.rs

Lines 200 to 227 in 4d7a535

	fn establish_new_circuit(
	&mut self,
	to_dial: oneshot::Sender<Result<Connection, outbound_hop::ConnectError>>,
	dst_peer_id: PeerId,
	) {
	let (sender, receiver) = oneshot::channel();
	self.pending_streams.push_back(sender);
	self.queued_events
	.push_back(ConnectionHandlerEvent::OutboundSubstreamRequest {
	protocol: SubstreamProtocol::new(ReadyUpgrade::new(HOP_PROTOCOL_NAME), ()),
	});
	let result = self.inflight_outbound_connect_requests.try_push(
	async move {
	let stream = receiver
	.await
	.map_err(|_| io::Error::from(io::ErrorKind::BrokenPipe))?
	.map_err(into_connect_error)?;
	outbound_hop::open_circuit(stream, dst_peer_id).await
	},
	to_dial,
	);
	if result.is_err() {
	tracing::warn!("Dropping in-flight connect request because we are at capacity")
	}
	}

I think ive only ever hit that error once but cant recall my solution, however if youre establishing multiple circuit to the peer via that relay, that may contribute to that error. Do you have any code you could share to show how youre handling connections or if you have any sample code that could reproduce that error?