Add inbound channel blocking and per-peer channel limits

- Add `blocked_peers` list to automatically reject channels from specific peers
- Add `max_channels_per_peer` option to limit channels per peer

Author: Camillarhi

bindings/ldk_node.udl

@@ -13,6 +13,8 @@ dictionary Config {
 	u64 probing_liquidity_limit_multiplier;
 	AnchorChannelsConfig? anchor_channels_config;
 	RouteParametersConfig? route_parameters;
+	sequence<PublicKey> blocked_peers;
+	u32? max_channels_per_peer;
 };
 
 dictionary AnchorChannelsConfig {
@@ -98,6 +100,10 @@ interface Builder {
 	[Throws=BuildError]
 	void set_async_payments_role(AsyncPaymentsRole? role);
 	[Throws=BuildError]
+	void set_blocked_peers(sequence<PublicKey> blocked_peers);
+	[Throws=BuildError]
+	void set_max_channels_per_peer(u32? max_channels_per_peer);
+	[Throws=BuildError]
 	Node build();
 	[Throws=BuildError]
 	Node build_with_fs_store();

src/builder.rs

@@ -582,6 +582,25 @@ impl NodeBuilder {
 		Ok(self)
 	}
 
+	/// Sets the list of peers from which we will not accept inbound channels.
+	pub fn set_blocked_peers(
+		&mut self, blocked_peers: Vec<PublicKey>,
+	) -> Result<&mut Self, BuildError> {
+		self.config.blocked_peers = blocked_peers;
+		Ok(self)
+	}
+
+	/// Sets the maximum number of channels we'll accept from any single peer.
+	///
+	/// If set, we will reject inbound channel requests from peers that already have this many
+	/// channels open with us. If set to `None`, no limit is enforced.
+	pub fn set_max_channels_per_peer(
+		&mut self, max_channels_per_peer: Option<u32>,
+	) -> Result<&mut Self, BuildError> {
+		self.config.max_channels_per_peer = max_channels_per_peer;
+		Ok(self)
+	}
+
 	/// Builds a [`Node`] instance with a [`SqliteStore`] backend and according to the options
 	/// previously configured.
 	pub fn build(&self) -> Result<Node, BuildError> {
@@ -1045,6 +1064,21 @@ impl ArcedNodeBuilder {
 		self.inner.write().unwrap().set_async_payments_role(role).map(|_| ())
 	}
 
+	/// Sets the list of peers from which we will not accept inbound channels.
+	pub fn set_blocked_peers(&self, blocked_peers: Vec<PublicKey>) -> Result<(), BuildError> {
+		self.inner.write().unwrap().set_blocked_peers(blocked_peers).map(|_| ())
+	}
+
+	/// Sets the maximum number of channels we'll accept from any single peer.
+	///
+	/// If set, we will reject inbound channel requests from peers that already have this many
+	/// channels open with us. If set to `None`, no limit is enforced.
+	pub fn set_max_channels_per_peer(
+		&self, max_channels_per_peer: Option<u32>,
+	) -> Result<(), BuildError> {
+		self.inner.write().unwrap().set_max_channels_per_peer(max_channels_per_peer).map(|_| ())
+	}
+
 	/// Builds a [`Node`] instance with a [`SqliteStore`] backend and according to the options
 	/// previously configured.
 	pub fn build(&self) -> Result<Arc<Node>, BuildError> {

src/config.rs

@@ -119,7 +119,9 @@ pub(crate) const EXTERNAL_PATHFINDING_SCORES_SYNC_TIMEOUT_SECS: u64 = 5;
 /// | `probing_liquidity_limit_multiplier`   | 3                  |
 /// | `log_level`                            | Debug              |
 /// | `anchor_channels_config`               | Some(..)           |
-/// | `route_parameters`                   | None               |
+/// | `route_parameters`                     | None               |
+/// | `blocked_peers`                        | []                 |
+/// | `max_channels_per_peer`                | None               |
 ///
 /// See [`AnchorChannelsConfig`] and [`RouteParametersConfig`] for more information regarding their
 /// respective default values.
@@ -184,6 +186,15 @@ pub struct Config {
 	/// **Note:** If unset, default parameters will be used, and you will be able to override the
 	/// parameters on a per-payment basis in the corresponding method calls.
 	pub route_parameters: Option<RouteParametersConfig>,
+	/// A list of peers from which we will not accept inbound channels.
+	///
+	/// Channels requested by peers in this list will be automatically rejected.
+	pub blocked_peers: Vec<PublicKey>,
+	/// The maximum number of channels we'll accept from any single peer.
+	///
+	/// If set, we will reject inbound channel requests from peers that already have this many
+	/// channels open with us. If set to `None`, no limit is enforced.
+	pub max_channels_per_peer: Option<u32>,
 }
 
 impl Default for Config {
@@ -198,6 +209,8 @@ impl Default for Config {
 			anchor_channels_config: Some(AnchorChannelsConfig::default()),
 			route_parameters: None,
 			node_alias: None,
+			blocked_peers: Vec::new(),
+			max_channels_per_peer: None,
 		}
 	}
 }

src/event.rs

@@ -1076,6 +1076,49 @@ where
 					}
 				}
 
+				if self.config.blocked_peers.contains(&counterparty_node_id) {
+					log_error!(
+						self.logger,
+						"Rejecting inbound channel from blocked peer {}",
+						counterparty_node_id,
+					);
+
+					self.channel_manager
+						.force_close_broadcasting_latest_txn(
+							&temporary_channel_id,
+							&counterparty_node_id,
+							"Channel request rejected".to_string(),
+						)
+						.unwrap_or_else(|e| {
+							log_error!(self.logger, "Failed to reject channel: {:?}", e)
+						});
+					return Ok(());
+				}
+
+				if let Some(max_channels_per_peer) = self.config.max_channels_per_peer {
+					let open_channels =
+						self.channel_manager.list_channels_with_counterparty(&counterparty_node_id);
+					if open_channels.len() >= max_channels_per_peer.try_into().unwrap() {
+						log_error!(
+							self.logger,
+							"Rejecting inbound channel from peer {} due to reaching the maximum number of channels per peer ({}).",
+							counterparty_node_id,
+							max_channels_per_peer,
+						);
+
+						self.channel_manager
+							.force_close_broadcasting_latest_txn(
+								&temporary_channel_id,
+								&counterparty_node_id,
+								"Channel request rejected".to_string(),
+							)
+							.unwrap_or_else(|e| {
+								log_error!(self.logger, "Failed to reject channel: {:?}", e)
+							});
+						return Ok(());
+					}
+				}
+
 				let anchor_channel = channel_type.requires_anchors_zero_fee_htlc_tx();
 				if anchor_channel {
 					if let Some(anchor_channels_config) =

tests/integration_tests_rust.rs

@@ -1860,3 +1860,141 @@ async fn drop_in_async_context() {
 	let node = setup_node(&chain_source, config, Some(seed_bytes));
 	node.stop().unwrap();
 }
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 1)]
+async fn test_blocked_peers_channel_rejection() {
+	let (bitcoind, electrsd) = setup_bitcoind_and_electrsd();
+	let chain_source = TestChainSource::Esplora(&electrsd);
+
+	// Setup two nodes
+	let mut config_a = random_config(true);
+	let config_b = random_config(true);
+
+	let node_b = setup_node(&chain_source, config_b, None);
+
+	// Start node_a with node_b blocked
+	config_a.node_config.blocked_peers.push(node_b.node_id());
+	let node_a = setup_node(&chain_source, config_a, None);
+
+	// Fund node_b
+	let addr_b = node_b.onchain_payment().new_address().unwrap();
+	premine_and_distribute_funds(
+		&bitcoind.client,
+		&electrsd.client,
+		vec![addr_b],
+		Amount::from_sat(5_000_000),
+	)
+	.await;
+	node_b.sync_wallets().unwrap();
+
+	// Attempt to open channel from node_b to node_a (should be rejected)
+	node_b
+		.open_channel(
+			node_a.node_id(),
+			node_a.listening_addresses().unwrap().first().unwrap().clone(),
+			1_000_000,
+			None,
+			None,
+		)
+		.unwrap();
+
+	// Expect rejection via ChannelClosed event
+	match node_b.next_event_async().await {
+		Event::ChannelClosed { reason, .. } => {
+			assert!(matches!(
+				reason,
+				Some(lightning::events::ClosureReason::CounterpartyForceClosed { .. })
+			));
+			node_b.event_handled().unwrap();
+		},
+		e => panic!("Expected ChannelClosed event, got: {:?}", e),
+	}
+
+	if let Some(_event) = node_a.next_event() {
+		node_a.event_handled().unwrap();
+	}
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 1)]
+async fn test_max_channels_per_peer() {
+	let (bitcoind, electrsd) = setup_bitcoind_and_electrsd();
+	let chain_source = TestChainSource::Esplora(&electrsd);
+
+	let mut config_a = random_config(true);
+	config_a.node_config.max_channels_per_peer = Some(2);
+
+	let config_b = random_config(true);
+
+	let node_a = setup_node(&chain_source, config_a, None);
+	let node_b = setup_node(&chain_source, config_b, None);
+
+	// Fund node_b
+	let addr_b = node_b.onchain_payment().new_address().unwrap();
+	premine_and_distribute_funds(
+		&bitcoind.client,
+		&electrsd.client,
+		vec![addr_b],
+		Amount::from_sat(10_000_000),
+	)
+	.await;
+	node_b.sync_wallets().unwrap();
+
+	// Open first channel - should succeed
+	open_channel(&node_b, &node_a, 1_000_000, false, &electrsd).await;
+	generate_blocks_and_wait(&bitcoind.client, &electrsd.client, 6).await;
+	node_a.sync_wallets().unwrap();
+	node_b.sync_wallets().unwrap();
+	expect_channel_ready_event!(node_a, node_b.node_id());
+	expect_channel_ready_event!(node_b, node_a.node_id());
+
+	// Open second channel - should succeed
+	node_b.sync_wallets().unwrap();
+	open_channel(&node_b, &node_a, 1_000_000, false, &electrsd).await;
+	generate_blocks_and_wait(&bitcoind.client, &electrsd.client, 6).await;
+	node_a.sync_wallets().unwrap();
+	node_b.sync_wallets().unwrap();
+	expect_channel_ready_event!(node_a, node_b.node_id());
+	expect_channel_ready_event!(node_b, node_a.node_id());
+
+	// Verify we have 2 channels
+	assert_eq!(
+		node_a
+			.list_channels()
+			.iter()
+			.filter(|c| c.counterparty_node_id == node_b.node_id())
+			.count(),
+		2
+	);
+
+	// Try to open third channel - should be rejected
+	node_b
+		.open_channel(
+			node_a.node_id(),
+			node_a.listening_addresses().unwrap().first().unwrap().clone(),
+			1_000_000,
+			None,
+			None,
+		)
+		.unwrap();
+
+	match node_b.next_event_async().await {
+		Event::ChannelClosed { reason, .. } => {
+			assert!(matches!(
+				reason,
+				Some(lightning::events::ClosureReason::CounterpartyForceClosed { .. })
+			));
+			node_b.event_handled().unwrap();
+		},
+		e => panic!("Expected ChannelClosed event, got: {:?}", e),
+	}
+
+	// Still should have only 2 channels
+	assert_eq!(
+		node_a
+			.list_channels()
+			.iter()
+			.filter(|c| c.counterparty_node_id == node_b.node_id())
+			.count(),
+		2
+	);
+}