How to use with_bandwidth_metrics in the new SwarmBuilder with a optional registry?

[gurinderu]

I have an optional registry in our system like registry: Option<&mut Registry>.
I can't understand how to use a new swarm builder with optional registry for with_bandwidth_metrics because of the types.

[thomaseizinger]

Your best bet is to branch on the existence of the registry and finish the builder so both branches of your match result in the same type. We do the same thing for our interop tests:

rust-libp2p/interop-tests/src/arch.rs

Lines 38 to 164 in bdcb081

	pub(crate) async fn build_swarm<B: NetworkBehaviour>(
	ip: &str,
	transport: Transport,
	sec_protocol: Option<SecProtocol>,
	muxer: Option<Muxer>,
	behaviour_constructor: impl FnOnce(&Keypair) -> B,
	) -> Result<(Swarm<B>, String)> {
	let (swarm, addr) = match (transport, sec_protocol, muxer) {
	(Transport::QuicV1, None, None) => (
	libp2p::SwarmBuilder::with_new_identity()
	.with_tokio()
	.with_quic()
	.with_behaviour(behaviour_constructor)?
	.with_swarm_config(|c| c.with_idle_connection_timeout(Duration::from_secs(5)))
	.build(),
	format!("/ip4/{ip}/udp/0/quic-v1"),
	),
	(Transport::Tcp, Some(SecProtocol::Tls), Some(Muxer::Mplex)) => (
	libp2p::SwarmBuilder::with_new_identity()
	.with_tokio()
	.with_tcp(
	tcp::Config::default(),
	tls::Config::new,
	mplex::MplexConfig::default,
	)?
	.with_behaviour(behaviour_constructor)?
	.with_swarm_config(|c| c.with_idle_connection_timeout(Duration::from_secs(5)))
	.build(),
	format!("/ip4/{ip}/tcp/0"),
	),
	(Transport::Tcp, Some(SecProtocol::Tls), Some(Muxer::Yamux)) => (
	libp2p::SwarmBuilder::with_new_identity()
	.with_tokio()
	.with_tcp(
	tcp::Config::default(),
	tls::Config::new,
	yamux::Config::default,
	)?
	.with_behaviour(behaviour_constructor)?
	.with_swarm_config(|c| c.with_idle_connection_timeout(Duration::from_secs(5)))
	.build(),
	format!("/ip4/{ip}/tcp/0"),
	),
	(Transport::Tcp, Some(SecProtocol::Noise), Some(Muxer::Mplex)) => (
	libp2p::SwarmBuilder::with_new_identity()
	.with_tokio()
	.with_tcp(
	tcp::Config::default(),
	noise::Config::new,
	mplex::MplexConfig::default,
	)?
	.with_behaviour(behaviour_constructor)?
	.with_swarm_config(|c| c.with_idle_connection_timeout(Duration::from_secs(5)))
	.build(),
	format!("/ip4/{ip}/tcp/0"),
	),
	(Transport::Tcp, Some(SecProtocol::Noise), Some(Muxer::Yamux)) => (
	libp2p::SwarmBuilder::with_new_identity()
	.with_tokio()
	.with_tcp(
	tcp::Config::default(),
	noise::Config::new,
	yamux::Config::default,
	)?
	.with_behaviour(behaviour_constructor)?
	.with_swarm_config(|c| c.with_idle_connection_timeout(Duration::from_secs(5)))
	.build(),
	format!("/ip4/{ip}/tcp/0"),
	),
	(Transport::Ws, Some(SecProtocol::Tls), Some(Muxer::Mplex)) => (
	libp2p::SwarmBuilder::with_new_identity()
	.with_tokio()
	.with_websocket(tls::Config::new, mplex::MplexConfig::default)
	.await?
	.with_behaviour(behaviour_constructor)?
	.with_swarm_config(|c| c.with_idle_connection_timeout(Duration::from_secs(5)))
	.build(),
	format!("/ip4/{ip}/tcp/0/ws"),
	),
	(Transport::Ws, Some(SecProtocol::Tls), Some(Muxer::Yamux)) => (
	libp2p::SwarmBuilder::with_new_identity()
	.with_tokio()
	.with_websocket(tls::Config::new, yamux::Config::default)
	.await?
	.with_behaviour(behaviour_constructor)?
	.with_swarm_config(|c| c.with_idle_connection_timeout(Duration::from_secs(5)))
	.build(),
	format!("/ip4/{ip}/tcp/0/ws"),
	),
	(Transport::Ws, Some(SecProtocol::Noise), Some(Muxer::Mplex)) => (
	libp2p::SwarmBuilder::with_new_identity()
	.with_tokio()
	.with_websocket(noise::Config::new, mplex::MplexConfig::default)
	.await?
	.with_behaviour(behaviour_constructor)?
	.with_swarm_config(|c| c.with_idle_connection_timeout(Duration::from_secs(5)))
	.build(),
	format!("/ip4/{ip}/tcp/0/ws"),
	),
	(Transport::Ws, Some(SecProtocol::Noise), Some(Muxer::Yamux)) => (
	libp2p::SwarmBuilder::with_new_identity()
	.with_tokio()
	.with_websocket(noise::Config::new, yamux::Config::default)
	.await?
	.with_behaviour(behaviour_constructor)?
	.with_swarm_config(|c| c.with_idle_connection_timeout(Duration::from_secs(5)))
	.build(),
	format!("/ip4/{ip}/tcp/0/ws"),
	),
	(Transport::WebRtcDirect, None, None) => (
	libp2p::SwarmBuilder::with_new_identity()
	.with_tokio()
	.with_other_transport(|key| {
	Ok(webrtc::tokio::Transport::new(
	key.clone(),
	webrtc::tokio::Certificate::generate(&mut rand::thread_rng())?,
	))
	})?
	.with_behaviour(behaviour_constructor)?
	.with_swarm_config(|c| c.with_idle_connection_timeout(Duration::from_secs(5)))
	.build(),
	format!("/ip4/{ip}/udp/0/webrtc-direct"),
	),
	(t, s, m) => bail!("Unsupported combination: {t:?} {s:?} {m:?}"),
	};
	Ok((swarm, addr))
	}

[gurinderu]

Got it, thanks