Add LSPS5 (bLIP-55) webhook notification support

Implement the bLIP-55 / LSPS5 webhook registration protocol on top of the
multi-LSP liquidity module (src/liquidity/{client,service}).

Client side, exposed via Node::liquidity().lsps5():
- set_webhook / list_webhooks / remove_webhook to manage webhook
  registrations with an LSP.
- When no node_id is given, set_webhook and remove_webhook fan out to every
  LSPS5-capable LSP so a webhook can be configured once across all configured
  LSPs; set_webhook returns one result per LSP that accepted the registration
  and remove_webhook returns the LSPs it was removed from.

Service side, enabled via Builder::enable_liquidity_provider_lsps5():
- Deliver outgoing webhook notifications over HTTP in response to
  LSPS5ServiceEvent::SendWebhookNotification.
- Automatically send an onion-message-incoming notification when an
  intercepted onion message targets a client that is currently offline
  (wired from LdkEvent::OnionMessageIntercepted, gated on peer connectivity).

Wires the feature through the UniFFI bindings and adds LSPS5-specific Error
variants.

Author: Camillarhi

bindings/ldk_node.udl

@@ -249,6 +249,10 @@ enum NodeError {
 	"InvalidLnurl",
 	"ChainSourceNotSupported",
 	"InvalidPayerProof",
+	"LiquiditySetWebhookFailed",
+	"LiquidityRemoveWebhookFailed",
+	"LiquidityListWebhooksFailed",
+	"LiquidityNotifyWebhookFailed"
 };
 
 typedef dictionary NodeStatus;

src/builder.rs

@@ -83,8 +83,8 @@ use crate::runtime::{Runtime, RuntimeSpawner};
 use crate::tx_broadcaster::TransactionBroadcaster;
 use crate::types::{
 	AsyncPersister, ChainMonitor, ChannelManager, DynStore, DynStoreRef, DynStoreWrapper,
-	GossipSync, Graph, HRNResolver, KeysManager, MessageRouter, OnionMessenger, PaymentStore,
-	PeerManager, PendingPaymentStore,
+	GossipSync, Graph, HRNResolver, KeysManager, LSPS5ServiceConfig, MessageRouter, OnionMessenger,
+	PaymentStore, PeerManager, PendingPaymentStore,
 };
 use crate::wallet::persist::{read_address_pool, KVStoreWalletPersister};
 use crate::wallet::Wallet;
@@ -127,10 +127,12 @@ struct PathfindingScoresSyncConfig {
 
 #[derive(Debug, Clone, Default)]
 struct LiquiditySourceConfig {
-	// Acts for both LSPS1 and LSPS2 clients connecting to the given service.
+	// Acts for LSPS1, LSPS2 and LSPS5 clients connecting to the given service.
 	lsp_nodes: Vec<LspConfig>,
 	// Act as an LSPS2 service.
 	lsps2_service: Option<LSPS2ServiceConfig>,
+	// Act as an LSPS5 service.
+	lsps5_service: Option<LSPS5ServiceConfig>,
 }
 
 #[derive(Clone)]
@@ -522,6 +524,21 @@ impl NodeBuilder {
 		self
 	}
 
+	/// Configures the [`Node`] instance to provide an [bLIP-55 / LSPS5] service, enabling clients
+	/// to register webhooks for push notifications.
+	///
+	/// **Caution**: LSP service support is in **alpha** and is considered an experimental feature.
+	///
+	/// [bLIP-55 / LSPS5]: https://github.com/lightning/blips/blob/master/blip-0055.md
+	pub fn enable_liquidity_provider_lsps5(
+		&mut self, lsps5_service_config: LSPS5ServiceConfig,
+	) -> &mut Self {
+		let liquidity_source_config =
+			self.liquidity_source_config.get_or_insert(LiquiditySourceConfig::default());
+		liquidity_source_config.lsps5_service = Some(lsps5_service_config);
+		self
+	}
+
 	/// Sets the used storage directory path.
 	pub fn set_storage_dir_path(&mut self, storage_dir_path: String) -> &mut Self {
 		self.config.storage_dir_path = storage_dir_path;
@@ -1122,6 +1139,16 @@ impl ArcedNodeBuilder {
 		self.inner.write().expect("lock").enable_liquidity_provider(lsps2_service_config);
 	}
 
+	/// Configures the [`Node`] instance to provide an [bLIP-55 / LSPS5] service, enabling clients
+	/// to register webhooks for push notifications.
+	///
+	/// **Caution**: LSP service support is in **alpha** and is considered an experimental feature.
+	///
+	/// [bLIP-55 / LSPS5]: https://github.com/lightning/blips/blob/master/blip-0055.md
+	pub fn enable_liquidity_provider_lsps5(&self, lsps5_service_config: LSPS5ServiceConfig) {
+		self.inner.write().expect("lock").enable_liquidity_provider_lsps5(lsps5_service_config);
+	}
+
 	/// Sets the used storage directory path.
 	pub fn set_storage_dir_path(&self, storage_dir_path: String) {
 		self.inner.write().expect("lock").set_storage_dir_path(storage_dir_path);
@@ -2148,6 +2175,7 @@ fn build_with_store_internal(
 			Arc::clone(&tx_broadcaster),
 			Arc::clone(&kv_store),
 			Arc::clone(&config),
+			Arc::clone(&runtime),
 			Arc::clone(&logger),
 		);
 
@@ -2166,6 +2194,10 @@ fn build_with_store_internal(
 			lsc.lsps2_service.as_ref().map(|config| {
 				liquidity_source_builder.lsps2_service(promise_secret, config.clone())
 			});
+
+			lsc.lsps5_service
+				.as_ref()
+				.map(|config| liquidity_source_builder.lsps5_service(config.clone()));
 		}
 
 		let liquidity_source = runtime
@@ -2225,6 +2257,8 @@ fn build_with_store_internal(
 
 	liquidity_source.lsps2_service().set_peer_manager(Arc::downgrade(&peer_manager));
 
+	liquidity_source.lsps5_service().set_peer_manager(Arc::downgrade(&peer_manager));
+
 	let connection_manager = Arc::new(ConnectionManager::new(
 		Arc::clone(&peer_manager),
 		config.tor_config.clone(),

src/config.rs

@@ -152,6 +152,12 @@ pub(crate) const LIQUIDITY_DISCOVERY_RETRY_INITIAL_DELAY: Duration = Duration::f
 // thereafter until every configured LSP has been discovered.
 pub(crate) const LIQUIDITY_DISCOVERY_RETRY_MAX_DELAY: Duration = Duration::from_secs(60 * 60);
 
+// The timeout after which we abort a LSPS5 webhook notification operation.
+pub(crate) const LSPS5_WEBHOOK_TIMEOUT_SECS: u64 = 30;
+
+// The maximum size of a response body we'll accept when delivering an LSPS5 webhook notification.
+pub(crate) const LSPS5_WEBHOOK_MAX_RESPONSE_SIZE: usize = 64 * 1024;
+
 #[derive(Debug, Clone)]
 #[cfg_attr(feature = "uniffi", derive(uniffi::Record))]
 /// Represents the configuration of an [`Node`] instance.

src/error.rs

@@ -143,6 +143,14 @@ pub enum Error {
 	ChainSourceNotSupported,
 	/// The provided payer proof is invalid.
 	InvalidPayerProof,
+	/// Failed to set a webhook with the LSP.
+	LiquiditySetWebhookFailed,
+	/// Failed to remove a webhook with the LSP.
+	LiquidityRemoveWebhookFailed,
+	/// Failed to list webhooks with the LSP.
+	LiquidityListWebhooksFailed,
+	/// Failed to send a webhook notification to a client.
+	LiquidityNotifyWebhookFailed,
 }
 
 impl fmt::Display for Error {
@@ -233,6 +241,18 @@ impl fmt::Display for Error {
 				write!(f, "The configured chain source is not supported.")
 			},
 			Self::InvalidPayerProof => write!(f, "The provided payer proof is invalid."),
+			Self::LiquiditySetWebhookFailed => {
+				write!(f, "Failed to set a webhook with the LSP.")
+			},
+			Self::LiquidityRemoveWebhookFailed => {
+				write!(f, "Failed to remove a webhook with the LSP.")
+			},
+			Self::LiquidityListWebhooksFailed => {
+				write!(f, "Failed to list webhooks with the LSP.")
+			},
+			Self::LiquidityNotifyWebhookFailed => {
+				write!(f, "Failed to send a webhook notification to a client.")
+			},
 		}
 	}
 }

src/event.rs

@@ -19,10 +19,12 @@ use lightning::events::bump_transaction::BumpTransactionEvent;
 #[cfg(not(feature = "uniffi"))]
 use lightning::events::PaidBolt12Invoice;
 use lightning::events::{
-	ClosureReason, Event as LdkEvent, FundingInfo, HTLCLocator as LdkHtlcLocator,
-	PaymentFailureReason, PaymentPurpose, ReplayEvent,
+	ClosureReason, Event as LdkEvent, FundingInfo, HTLCHandlingFailureReason,
+	HTLCHandlingFailureType, HTLCLocator as LdkHtlcLocator, PaymentFailureReason, PaymentPurpose,
+	ReplayEvent,
 };
 use lightning::ln::channelmanager::{PaymentId, TrustedChannelFeatures};
+use lightning::ln::onion_utils::LocalHTLCFailureReason;
 use lightning::ln::types::ChannelId;
 use lightning::routing::gossip::NodeId;
 use lightning::sign::EntropySource;
@@ -1534,11 +1536,29 @@ where
 					prober.handle_background_probe_failed(&path, payment_id);
 				}
 			},
-			LdkEvent::HTLCHandlingFailed { failure_type, .. } => {
+			LdkEvent::HTLCHandlingFailed { failure_type, failure_reason, .. } => {
+				// Capture the client's node id before `failure_type` is consumed below. A forward
+				// that failed only because the next-hop peer was offline is our cue to wake an
+				// LSPS5 client. The HTLC is failed back as `temporary_channel_failure`, which is
+				// not permanent, so the sender can retry once the client is online.
+				let offline_node_id = match (&failure_type, &failure_reason) {
+					(
+						HTLCHandlingFailureType::Forward { node_id: Some(node_id), .. },
+						Some(HTLCHandlingFailureReason::Local {
+							reason: LocalHTLCFailureReason::PeerOffline,
+						}),
+					) => Some(*node_id),
+					_ => None,
+				};
+
 				self.liquidity_source
 					.lsps2_service()
 					.handle_htlc_handling_failed(failure_type)
 					.await;
+
+				if let Some(node_id) = offline_node_id {
+					self.liquidity_source.lsps5_service().notify_payment_incoming(node_id);
+				}
 			},
 			LdkEvent::SpendableOutputs { outputs, channel_id, counterparty_node_id } => {
 				match self
@@ -2022,6 +2042,8 @@ where
 				debug_assert!(false, "We currently don't handle BOLT12 invoices manually, so this event should never be emitted.");
 			},
 			LdkEvent::ConnectionNeeded { node_id, addresses } => {
+				self.liquidity_source.lsps5_service().notify_onion_message_incoming(node_id);
+
 				let spawn_logger = self.logger.clone();
 				let spawn_cm = Arc::clone(&self.connection_manager);
 				let future = async move {
@@ -2080,6 +2102,9 @@ where
 							"Onion message intercepted, but no onion message mailbox available"
 						);
 					}
+					self.liquidity_source
+						.lsps5_service()
+						.notify_onion_message_incoming(peer_node_id);
 				} else {
 					log_error!(self.logger, "Onion message intercepted for unknown SCID");
 				}