Enable binding to zero port in networking stack

[jmcph4]

Description

Due to the ordering of various operations during initialisation of Lighthouse's networking stack, we are currently unable to defer port selection to the OS (i.e., bind to the 0 port). The ability to do so is desirable for a few reasons; namely that it would avoid racing on bound port numbers which are currently causing some instability in our tests and subsequently CI jobs.

Currently, the following procedure describes the initialisation of the network service:

1. Parse relevant CLI flags
2. Produce a network service configuration from these flags
3. Initialise the UPnP service

lighthouse/beacon_node/network/src/service.rs

Lines 241 to 257 in 0c23c86

	// try and construct UPnP port mappings if required.
	if let Some(upnp_config) = crate::nat::UPnPConfig::from_config(config) {
	let upnp_log = network_log.new(o!("service" => "UPnP"));
	let upnp_network_send = network_senders.network_send();
	if config.upnp_enabled {
	executor.spawn_blocking(
	move || {
	crate::nat::construct_upnp_mappings(
	upnp_config,
	upnp_network_send,
	upnp_log,
	)
	},
	"UPnP",
	);
	}
	}

4. Start lighthouse_network (i.e., our libp2p handle)

lighthouse/beacon_node/network/src/service.rs

Lines 292 to 294 in 0c23c86

	// launch libp2p service
	let (mut libp2p, network_globals) =
	Network::new(executor.clone(), service_context, &network_log).await?;

a) Build ENR

lighthouse/beacon_node/lighthouse_network/src/service/mod.rs

Lines 148 to 154 in 0c23c86

	// Create an ENR or load from disk if appropriate
	let enr = crate::discovery::enr::build_or_load_enr::<TSpec>(
	local_keypair.clone(),
	&config,
	&ctx.enr_fork_id,
	&log,
	)?;

b) Initialise network globals using this ENR

lighthouse/beacon_node/lighthouse_network/src/service/mod.rs

Lines 157 to 169 in 0c23c86

	let globals = NetworkGlobals::new(
	enr,
	config.listen_addrs().v4().map(|v4_addr| v4_addr.tcp_port),
	config.listen_addrs().v6().map(|v6_addr| v6_addr.tcp_port),
	meta_data,
	config
	.trusted_peers
	.iter()
	.map(|x| PeerId::from(x.clone()))
	.collect(),
	config.disable_peer_scoring,
	&log,
	);

c) Initialise discovery

lighthouse/beacon_node/lighthouse_network/src/service/mod.rs

Lines 281 to 293 in 0c23c86

	let discovery = {
	// Build and start the discovery sub-behaviour
	let mut discovery = Discovery::new(
	local_keypair.clone(),
	&config,
	network_globals.clone(),
	&log,
	)
	.await?;
	// start searching for peers
	discovery.discover_peers(FIND_NODE_QUERY_CLOSEST_PEERS);
	discovery
	};

d) Start libp2p

lighthouse/beacon_node/lighthouse_network/src/service/mod.rs

Lines 356 to 383 in 0c23c86

	let (swarm, bandwidth) = {
	// Set up the transport - tcp/ws with noise and mplex
	let (transport, bandwidth) = build_transport(local_keypair.clone())
	.map_err(|e| format!("Failed to build transport: {:?}", e))?;
	// use the executor for libp2p
	struct Executor(task_executor::TaskExecutor);
	impl libp2p::swarm::Executor for Executor {
	fn exec(&self, f: Pin<Box<dyn futures::Future<Output = ()> + Send>>) {
	self.0.spawn(f, "libp2p");
	}
	}
	// sets up the libp2p connection limits
	(
	SwarmBuilder::with_executor(
	transport,
	behaviour,
	local_peer_id,
	Executor(executor),
	)
	.notify_handler_buffer_size(std::num::NonZeroUsize::new(7).expect("Not zero"))
	.per_connection_event_buffer_size(4)
	.build(),
	bandwidth,
	)
	};

5. Start network service

lighthouse/beacon_node/network/src/service.rs

Lines 352 to 377 in 0c23c86

	let network_service = NetworkService {
	beacon_chain,
	libp2p,
	attestation_service,
	sync_committee_service,
	network_recv,
	validator_subscription_recv,
	router_send,
	store,
	network_globals: network_globals.clone(),
	upnp_mappings: (None, None),
	discovery_auto_update: config.discv5_config.enr_update,
	next_fork_update,
	next_fork_subscriptions,
	next_unsubscribe,
	subscribe_all_subnets: config.subscribe_all_subnets,
	shutdown_after_sync: config.shutdown_after_sync,
	metrics_enabled: config.metrics_enabled,
	metrics_update,
	gossipsub_parameter_update,
	fork_context,
	log: network_log,
	enable_light_client_server: config.enable_light_client_server,
	};
	network_service.spawn_service(executor);

Steps to resolve

The new procedure needs to look like the following:

1. Parse relevant CLI flags
2. Produce a network service configuration from these flags
3. Start lighthouse_network
4. Wait for a NewListenAddr event from libp2p
   a) Initialise the UPnP service
   b) Update the networking globals accordingly

The associated RPC tests will also need to be updated to bind to port 0.

[jmcph4]

Closed by #4700