Allow binding to port 0 for OS-assigned ports

Add support for configuring listening addresses with port 0, letting
the OS pick a free port. After binding, the actual port is resolved
via local_addr() and stored in a new last_bound_addresses field on
ConnectionManager, preserved across restarts so the node rebinds the
same ports.

Node::listening_addresses() returns the last bound addresses when
available, falling back to configured addresses. The gossip broadcast
task and announcement_addresses() never expose port-0 or OS-assigned
addresses, since those are ephemeral and change on restart.

This eliminates the need for the deterministic port picker in tests,
which was fragile due to potential port collisions. Tests now use
127.0.0.1:0 and query the actual port after start().

The announcement propagation test is updated to use explicit
announcement addresses for node B, since listening addresses with
port 0 are (correctly) not announced.

AI tools were used in preparing this commit.

Author: joostjager

src/config.rs

@@ -331,6 +331,16 @@ pub(crate) fn may_announce_channel(config: &Config) -> Result<(), AnnounceError>
 	}
 }
 
+pub(crate) fn has_port_zero(addr: &SocketAddress) -> bool {
+	match addr {
+		SocketAddress::TcpIpV4 { port, .. }
+		| SocketAddress::TcpIpV6 { port, .. }
+		| SocketAddress::OnionV3 { port, .. }
+		| SocketAddress::Hostname { port, .. } => *port == 0,
+		_ => false,
+	}
+}
+
 pub(crate) fn default_user_config(config: &Config) -> UserConfig {
 	// Initialize the default config values.
 	//

src/connection.rs

@@ -8,7 +8,7 @@
 use std::collections::hash_map::{self, HashMap};
 use std::net::ToSocketAddrs;
 use std::ops::Deref;
-use std::sync::{Arc, Mutex};
+use std::sync::{Arc, Mutex, RwLock};
 use std::time::Duration;
 
 use bitcoin::secp256k1::PublicKey;
@@ -29,6 +29,7 @@ where
 	tor_proxy_config: Option<TorConfig>,
 	keys_manager: Arc<KeysManager>,
 	logger: L,
+	last_bound_addresses: RwLock<Option<Vec<SocketAddress>>>,
 }
 
 impl<L: Deref + Clone + Sync + Send> ConnectionManager<L>
@@ -40,8 +41,24 @@ where
 		keys_manager: Arc<KeysManager>, logger: L,
 	) -> Self {
 		let pending_connections = Mutex::new(HashMap::new());
+		let last_bound_addresses = RwLock::new(None);
 
-		Self { pending_connections, peer_manager, tor_proxy_config, keys_manager, logger }
+		Self {
+			pending_connections,
+			peer_manager,
+			tor_proxy_config,
+			keys_manager,
+			logger,
+			last_bound_addresses,
+		}
+	}
+
+	pub(crate) fn set_last_bound_addresses(&self, addrs: Vec<SocketAddress>) {
+		*self.last_bound_addresses.write().unwrap() = Some(addrs);
+	}
+
+	pub(crate) fn last_bound_addresses(&self) -> Option<Vec<SocketAddress>> {
+		self.last_bound_addresses.read().unwrap().clone()
 	}
 
 	pub(crate) async fn connect_peer_if_necessary(

src/lib.rs

@@ -130,8 +130,8 @@ pub use builder::BuildError;
 pub use builder::NodeBuilder as Builder;
 use chain::ChainSource;
 use config::{
-	default_user_config, may_announce_channel, AsyncPaymentsRole, ChannelConfig, Config,
-	LNURL_AUTH_TIMEOUT_SECS, NODE_ANN_BCAST_INTERVAL, PEER_RECONNECTION_INTERVAL,
+	default_user_config, has_port_zero, may_announce_channel, AsyncPaymentsRole, ChannelConfig,
+	Config, LNURL_AUTH_TIMEOUT_SECS, NODE_ANN_BCAST_INTERVAL, PEER_RECONNECTION_INTERVAL,
 	RGS_SYNC_INTERVAL,
 };
 use connection::ConnectionManager;
@@ -356,7 +356,12 @@ impl Node {
 			);
 		}
 
-		if let Some(listening_addresses) = &self.config.listening_addresses {
+		let effective_listening_addresses = self
+			.connection_manager
+			.last_bound_addresses()
+			.or_else(|| self.config.listening_addresses.clone());
+
+		if let Some(listening_addresses) = &effective_listening_addresses {
 			// Setup networking
 			let peer_manager_connection_handler = Arc::clone(&self.peer_manager);
 			let listening_logger = Arc::clone(&self.logger);
@@ -378,14 +383,31 @@ impl Node {
 			}
 
 			let logger = Arc::clone(&listening_logger);
-			let listeners = self.runtime.block_on(async move {
+			let (listeners, bound_addrs) = self.runtime.block_on(async move {
 				let mut listeners = Vec::new();
+				let mut bound_addrs = Vec::new();
 
-				// Try to bind to all addresses
 				for addr in &*bind_addrs {
 					match tokio::net::TcpListener::bind(addr).await {
 						Ok(listener) => {
-							log_trace!(logger, "Listener bound to {}", addr);
+							let local_addr = listener.local_addr().map_err(|e| {
+								log_error!(
+									logger,
+									"Failed to retrieve local address from listener: {}",
+									e
+								);
+								Error::InvalidSocketAddress
+							})?;
+							let socket_address = match local_addr {
+								std::net::SocketAddr::V4(a) => {
+									SocketAddress::TcpIpV4 { addr: a.ip().octets(), port: a.port() }
+								},
+								std::net::SocketAddr::V6(a) => {
+									SocketAddress::TcpIpV6 { addr: a.ip().octets(), port: a.port() }
+								},
+							};
+							log_info!(logger, "Listening on {}", socket_address);
+							bound_addrs.push(socket_address);
 							listeners.push(listener);
 						},
 						Err(e) => {
@@ -400,9 +422,11 @@ impl Node {
 					}
 				}
 
-				Ok(listeners)
+				Ok((listeners, bound_addrs))
 			})?;
 
+			self.connection_manager.set_last_bound_addresses(bound_addrs);
+
 			for listener in listeners {
 				let logger = Arc::clone(&listening_logger);
 				let peer_mgr = Arc::clone(&peer_manager_connection_handler);
@@ -526,6 +550,11 @@ impl Node {
 							let addresses = if let Some(announcement_addresses) = bcast_config.announcement_addresses.clone() {
 								announcement_addresses
 							} else if let Some(listening_addresses) = bcast_config.listening_addresses.clone() {
+								if listening_addresses.iter().any(has_port_zero) {
+									// Don't announce addresses that include port 0
+									// since the OS-assigned port changes on restart.
+									continue;
+								}
 								listening_addresses
 							} else {
 								debug_assert!(false, "We checked whether the node may announce, so listening addresses should always be set");
@@ -842,16 +871,25 @@ impl Node {
 	}
 
 	/// Returns our own listening addresses.
+	///
+	/// If the node has been started, this returns the actual bound addresses (which may differ
+	/// from the configured addresses if port 0 was used). Otherwise, this returns the configured
+	/// addresses.
 	pub fn listening_addresses(&self) -> Option<Vec<SocketAddress>> {
-		self.config.listening_addresses.clone()
+		self.connection_manager
+			.last_bound_addresses()
+			.or_else(|| self.config.listening_addresses.clone())
 	}
 
 	/// Returns the addresses that the node will announce to the network.
+	///
+	/// Returns the configured announcement addresses if set, otherwise falls back to the
+	/// configured listening addresses. Does not return OS-assigned addresses from port 0
+	/// bindings, since those are ephemeral and change on restart.
 	pub fn announcement_addresses(&self) -> Option<Vec<SocketAddress>> {
-		self.config
-			.announcement_addresses
-			.clone()
-			.or_else(|| self.config.listening_addresses.clone())
+		self.config.announcement_addresses.clone().or_else(|| {
+			self.config.listening_addresses.clone().filter(|a| !a.iter().any(has_port_zero))
+		})
 	}
 
 	/// Returns our node alias.

tests/common/mod.rs

@@ -14,7 +14,6 @@ use std::collections::{HashMap, HashSet};
 use std::env;
 use std::future::Future;
 use std::path::PathBuf;
-use std::sync::atomic::{AtomicU16, Ordering};
 use std::sync::{Arc, RwLock};
 use std::time::Duration;
 
@@ -269,16 +268,6 @@ pub(crate) fn random_storage_path() -> PathBuf {
 	temp_path
 }
 
-static NEXT_PORT: AtomicU16 = AtomicU16::new(20000);
-
-pub(crate) fn generate_listening_addresses() -> Vec<SocketAddress> {
-	let port = NEXT_PORT.fetch_add(2, Ordering::Relaxed);
-	vec![
-		SocketAddress::TcpIpV4 { addr: [127, 0, 0, 1], port },
-		SocketAddress::TcpIpV4 { addr: [127, 0, 0, 1], port: port + 1 },
-	]
-}
-
 pub(crate) fn random_node_alias() -> Option<NodeAlias> {
 	let mut rng = rng();
 	let rand_val = rng.random_range(0..1000);
@@ -302,7 +291,7 @@ pub(crate) fn random_config(anchor_channels: bool) -> TestConfig {
 	println!("Setting random LDK storage dir: {}", rand_dir.display());
 	node_config.storage_dir_path = rand_dir.to_str().unwrap().to_owned();
 
-	let listening_addresses = generate_listening_addresses();
+	let listening_addresses = vec![SocketAddress::TcpIpV4 { addr: [127, 0, 0, 1], port: 0 }];
 	println!("Setting LDK listening addresses: {:?}", listening_addresses);
 	node_config.listening_addresses = Some(listening_addresses);
 

tests/integration_tests_rust.rs

@@ -21,10 +21,10 @@ use common::{
 	expect_channel_pending_event, expect_channel_ready_event, expect_channel_ready_events,
 	expect_event, expect_payment_claimable_event, expect_payment_received_event,
 	expect_payment_successful_event, expect_splice_pending_event, generate_blocks_and_wait,
-	generate_listening_addresses, open_channel, open_channel_push_amt, open_channel_with_all,
-	premine_and_distribute_funds, premine_blocks, prepare_rbf, random_chain_source, random_config,
-	setup_bitcoind_and_electrsd, setup_builder, setup_node, setup_two_nodes, splice_in_with_all,
-	wait_for_tx, TestChainSource, TestStoreType, TestSyncStore,
+	open_channel, open_channel_push_amt, open_channel_with_all, premine_and_distribute_funds,
+	premine_blocks, prepare_rbf, random_chain_source, random_config, setup_bitcoind_and_electrsd,
+	setup_builder, setup_node, setup_two_nodes, splice_in_with_all, wait_for_tx, TestChainSource,
+	TestStoreType, TestSyncStore,
 };
 use electrsd::corepc_node::Node as BitcoinD;
 use electrsd::ElectrsD;
@@ -37,6 +37,7 @@ use ldk_node::payment::{
 };
 use ldk_node::{Builder, Event, NodeError};
 use lightning::ln::channelmanager::PaymentId;
+use lightning::ln::msgs::SocketAddress;
 use lightning::routing::gossip::{NodeAlias, NodeId};
 use lightning::routing::router::RouteParametersConfig;
 use lightning_invoice::{Bolt11InvoiceDescription, Description};
@@ -1431,22 +1432,25 @@ async fn test_node_announcement_propagation() {
 	node_a_alias_bytes[..node_a_alias_string.as_bytes().len()]
 		.copy_from_slice(node_a_alias_string.as_bytes());
 	let node_a_node_alias = Some(NodeAlias(node_a_alias_bytes));
-	let node_a_announcement_addresses = generate_listening_addresses();
+	let node_a_announcement_addresses = vec![
+		SocketAddress::TcpIpV4 { addr: [127, 0, 0, 1], port: 10001 },
+		SocketAddress::TcpIpV4 { addr: [127, 0, 0, 1], port: 10002 },
+	];
 	config_a.node_config.node_alias = node_a_node_alias.clone();
-	config_a.node_config.listening_addresses = Some(generate_listening_addresses());
 	config_a.node_config.announcement_addresses = Some(node_a_announcement_addresses.clone());
 
-	// Node B will only use listening addresses
 	let mut config_b = random_config(true);
 	let node_b_alias_string = "ldk-node-b".to_string();
 	let mut node_b_alias_bytes = [0u8; 32];
 	node_b_alias_bytes[..node_b_alias_string.as_bytes().len()]
 		.copy_from_slice(node_b_alias_string.as_bytes());
 	let node_b_node_alias = Some(NodeAlias(node_b_alias_bytes));
-	let node_b_listening_addresses = generate_listening_addresses();
+	let node_b_announcement_addresses = vec![
+		SocketAddress::TcpIpV4 { addr: [127, 0, 0, 1], port: 20001 },
+		SocketAddress::TcpIpV4 { addr: [127, 0, 0, 1], port: 20002 },
+	];
 	config_b.node_config.node_alias = node_b_node_alias.clone();
-	config_b.node_config.listening_addresses = Some(node_b_listening_addresses.clone());
-	config_b.node_config.announcement_addresses = None;
+	config_b.node_config.announcement_addresses = Some(node_b_announcement_addresses.clone());
 
 	let node_a = setup_node(&chain_source, config_a);
 	let node_b = setup_node(&chain_source, config_b);
@@ -1506,9 +1510,9 @@ async fn test_node_announcement_propagation() {
 	assert_eq!(node_b_announcement_info.alias, node_b_alias_string);
 
 	#[cfg(not(feature = "uniffi"))]
-	assert_eq!(node_b_announcement_info.addresses(), &node_b_listening_addresses);
+	assert_eq!(node_b_announcement_info.addresses(), &node_b_announcement_addresses);
 	#[cfg(feature = "uniffi")]
-	assert_eq!(node_b_announcement_info.addresses, node_b_listening_addresses);
+	assert_eq!(node_b_announcement_info.addresses, node_b_announcement_addresses);
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 1)]