Merge pull request #3132 from jkczyz/2024-06-bolt12-unannounced

Blinded paths with unannounced introduction nodes

lightning/src/blinded_path/message.rs

@@ -30,7 +30,7 @@ use core::mem;
 use core::ops::Deref;
 
 /// An intermediate node, and possibly a short channel id leading to the next node.
-#[derive(Clone, Debug, Hash, PartialEq, Eq)]
+#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
 pub struct ForwardNode {
 	/// This node's pubkey.
 	pub node_id: PublicKey,
@@ -106,6 +106,8 @@ pub(super) fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
 
 // Advance the blinded onion message path by one hop, so make the second hop into the new
 // introduction node.
+//
+// Will only modify `path` when returning `Ok`.
 pub(crate) fn advance_path_by_one<NS: Deref, NL: Deref, T>(
 	path: &mut BlindedPath, node_signer: &NS, node_id_lookup: &NL, secp_ctx: &Secp256k1<T>
 ) -> Result<(), ()>
@@ -116,8 +118,8 @@ where
 {
 	let control_tlvs_ss = node_signer.ecdh(Recipient::Node, &path.blinding_point, None)?;
 	let rho = onion_utils::gen_rho_from_shared_secret(&control_tlvs_ss.secret_bytes());
-	let encrypted_control_tlvs = path.blinded_hops.remove(0).encrypted_payload;
-	let mut s = Cursor::new(&encrypted_control_tlvs);
+	let encrypted_control_tlvs = &path.blinded_hops.get(0).ok_or(())?.encrypted_payload;
+	let mut s = Cursor::new(encrypted_control_tlvs);
 	let mut reader = FixedLengthReader::new(&mut s, encrypted_control_tlvs.len() as u64);
 	match ChaChaPolyReadAdapter::read(&mut reader, rho) {
 		Ok(ChaChaPolyReadAdapter {
@@ -139,6 +141,7 @@ where
 			};
 			mem::swap(&mut path.blinding_point, &mut new_blinding_point);
 			path.introduction_node = IntroductionNode::NodeId(next_node_id);
+			path.blinded_hops.remove(0);
 			Ok(())
 		},
 		_ => Err(())

lightning/src/blinded_path/payment.rs

@@ -13,17 +13,24 @@
 
 use bitcoin::secp256k1::{self, PublicKey, Secp256k1, SecretKey};
 
-use crate::blinded_path::BlindedHop;
+use crate::blinded_path::{BlindedHop, BlindedPath, IntroductionNode, NodeIdLookUp};
 use crate::blinded_path::utils;
+use crate::crypto::streams::ChaChaPolyReadAdapter;
 use crate::io;
+use crate::io::Cursor;
 use crate::ln::types::PaymentSecret;
 use crate::ln::channel_state::CounterpartyForwardingInfo;
 use crate::ln::features::BlindedHopFeatures;
 use crate::ln::msgs::DecodeError;
+use crate::ln::onion_utils;
 use crate::offers::invoice::BlindedPayInfo;
 use crate::offers::invoice_request::InvoiceRequestFields;
 use crate::offers::offer::OfferId;
-use crate::util::ser::{HighZeroBytesDroppedBigSize, Readable, Writeable, Writer};
+use crate::sign::{NodeSigner, Recipient};
+use crate::util::ser::{FixedLengthReader, LengthReadableArgs, HighZeroBytesDroppedBigSize, Readable, Writeable, Writer};
+
+use core::mem;
+use core::ops::Deref;
 
 #[allow(unused_imports)]
 use crate::prelude::*;
@@ -274,6 +281,43 @@ pub(super) fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
 	utils::construct_blinded_hops(secp_ctx, pks, tlvs, session_priv)
 }
 
+// Advance the blinded onion payment path by one hop, so make the second hop into the new
+// introduction node.
+//
+// Will only modify `path` when returning `Ok`.
+pub(crate) fn advance_path_by_one<NS: Deref, NL: Deref, T>(
+	path: &mut BlindedPath, node_signer: &NS, node_id_lookup: &NL, secp_ctx: &Secp256k1<T>
+) -> Result<(), ()>
+where
+	NS::Target: NodeSigner,
+	NL::Target: NodeIdLookUp,
+	T: secp256k1::Signing + secp256k1::Verification,
+{
+	let control_tlvs_ss = node_signer.ecdh(Recipient::Node, &path.blinding_point, None)?;
+	let rho = onion_utils::gen_rho_from_shared_secret(&control_tlvs_ss.secret_bytes());
+	let encrypted_control_tlvs = &path.blinded_hops.get(0).ok_or(())?.encrypted_payload;
+	let mut s = Cursor::new(encrypted_control_tlvs);
+	let mut reader = FixedLengthReader::new(&mut s, encrypted_control_tlvs.len() as u64);
+	match ChaChaPolyReadAdapter::read(&mut reader, rho) {
+		Ok(ChaChaPolyReadAdapter {
+			readable: BlindedPaymentTlvs::Forward(ForwardTlvs { short_channel_id, .. })
+		}) => {
+			let next_node_id = match node_id_lookup.next_node_id(short_channel_id) {
+				Some(node_id) => node_id,
+				None => return Err(()),
+			};
+			let mut new_blinding_point = onion_utils::next_hop_pubkey(
+				secp_ctx, path.blinding_point, control_tlvs_ss.as_ref()
+			).map_err(|_| ())?;
+			mem::swap(&mut path.blinding_point, &mut new_blinding_point);
+			path.introduction_node = IntroductionNode::NodeId(next_node_id);
+			path.blinded_hops.remove(0);
+			Ok(())
+		},
+		_ => Err(())
+	}
+}
+
 /// `None` if underflow occurs.
 pub(crate) fn amt_to_forward_msat(inbound_amt_msat: u64, payment_relay: &PaymentRelay) -> Option<u64> {
 	let inbound_amt = inbound_amt_msat as u128;

lightning/src/ln/channelmanager.rs

@@ -4031,8 +4031,8 @@ where
 		self.pending_outbound_payments
 			.send_payment_for_bolt12_invoice(
 				invoice, payment_id, &self.router, self.list_usable_channels(),
-				|| self.compute_inflight_htlcs(), &self.entropy_source, &self.node_signer,
-				best_block_height, &self.logger, &self.pending_events,
+				|| self.compute_inflight_htlcs(), &self.entropy_source, &self.node_signer, &self,
+				&self.secp_ctx, best_block_height, &self.logger, &self.pending_events,
 				|args| self.send_payment_along_path(args)
 			)
 	}

lightning/src/ln/offers_tests.rs

@@ -950,9 +950,12 @@ fn pays_bolt12_invoice_asynchronously() {
 	);
 }
 
-/// Fails creating an offer when a blinded path cannot be created without exposing the node's id.
+/// Checks that an offer can be created using an unannounced node as a blinded path's introduction
+/// node. This is only preferred if there are no other options which may indicated either the offer
+/// is intended for the unannounced node or that the node is actually announced (e.g., an LSP) but
+/// the recipient doesn't have a network graph.
 #[test]
-fn fails_creating_offer_without_blinded_paths() {
+fn creates_offer_with_blinded_path_using_unannounced_introduction_node() {
 	let chanmon_cfgs = create_chanmon_cfgs(2);
 	let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
 	let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None]);
@@ -960,15 +963,63 @@ fn fails_creating_offer_without_blinded_paths() {
 
 	create_unannounced_chan_between_nodes_with_value(&nodes, 0, 1, 10_000_000, 1_000_000_000);
 
-	match nodes[0].node.create_offer_builder(None) {
-		Ok(_) => panic!("Expected error"),
-		Err(e) => assert_eq!(e, Bolt12SemanticError::MissingPaths),
+	let alice = &nodes[0];
+	let alice_id = alice.node.get_our_node_id();
+	let bob = &nodes[1];
+	let bob_id = bob.node.get_our_node_id();
+
+	let offer = alice.node
+		.create_offer_builder(None).unwrap()
+		.amount_msats(10_000_000)
+		.build().unwrap();
+	assert_ne!(offer.signing_pubkey(), Some(alice_id));
+	assert!(!offer.paths().is_empty());
+	for path in offer.paths() {
+		assert_eq!(path.introduction_node, IntroductionNode::NodeId(bob_id));
 	}
+
+	let payment_id = PaymentId([1; 32]);
+	bob.node.pay_for_offer(&offer, None, None, None, payment_id, Retry::Attempts(0), None).unwrap();
+	expect_recent_payment!(bob, RecentPaymentDetails::AwaitingInvoice, payment_id);
+
+	let onion_message = bob.onion_messenger.next_onion_message_for_peer(alice_id).unwrap();
+	alice.onion_messenger.handle_onion_message(&bob_id, &onion_message);
+
+	let (invoice_request, reply_path) = extract_invoice_request(alice, &onion_message);
+	let payment_context = PaymentContext::Bolt12Offer(Bolt12OfferContext {
+		offer_id: offer.id(),
+		invoice_request: InvoiceRequestFields {
+			payer_id: invoice_request.payer_id(),
+			quantity: None,
+			payer_note_truncated: None,
+		},
+	});
+	assert_ne!(invoice_request.payer_id(), bob_id);
+	assert_eq!(reply_path.introduction_node, IntroductionNode::NodeId(alice_id));
+
+	let onion_message = alice.onion_messenger.next_onion_message_for_peer(bob_id).unwrap();
+	bob.onion_messenger.handle_onion_message(&alice_id, &onion_message);
+
+	let invoice = extract_invoice(bob, &onion_message);
+	assert_ne!(invoice.signing_pubkey(), alice_id);
+	assert!(!invoice.payment_paths().is_empty());
+	for (_, path) in invoice.payment_paths() {
+		assert_eq!(path.introduction_node, IntroductionNode::NodeId(bob_id));
+	}
+
+	route_bolt12_payment(bob, &[alice], &invoice);
+	expect_recent_payment!(bob, RecentPaymentDetails::Pending, payment_id);
+
+	claim_bolt12_payment(bob, &[alice], payment_context);
+	expect_recent_payment!(bob, RecentPaymentDetails::Fulfilled, payment_id);
 }
 
-/// Fails creating a refund when a blinded path cannot be created without exposing the node's id.
+/// Checks that a refund can be created using an unannounced node as a blinded path's introduction
+/// node. This is only preferred if there are no other options which may indicated either the refund
+/// is intended for the unannounced node or that the node is actually announced (e.g., an LSP) but
+/// the sender doesn't have a network graph.
 #[test]
-fn fails_creating_refund_without_blinded_paths() {
+fn creates_refund_with_blinded_path_using_unannounced_introduction_node() {
 	let chanmon_cfgs = create_chanmon_cfgs(2);
 	let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
 	let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None]);
@@ -976,17 +1027,35 @@ fn fails_creating_refund_without_blinded_paths() {
 
 	create_unannounced_chan_between_nodes_with_value(&nodes, 0, 1, 10_000_000, 1_000_000_000);
 
+	let alice = &nodes[0];
+	let alice_id = alice.node.get_our_node_id();
+	let bob = &nodes[1];
+	let bob_id = bob.node.get_our_node_id();
+
 	let absolute_expiry = Duration::from_secs(u64::MAX);
 	let payment_id = PaymentId([1; 32]);
-
-	match nodes[0].node.create_refund_builder(
-		10_000, absolute_expiry, payment_id, Retry::Attempts(0), None
-	) {
-		Ok(_) => panic!("Expected error"),
-		Err(e) => assert_eq!(e, Bolt12SemanticError::MissingPaths),
+	let refund = bob.node
+		.create_refund_builder(10_000_000, absolute_expiry, payment_id, Retry::Attempts(0), None)
+		.unwrap()
+		.build().unwrap();
+	assert_ne!(refund.payer_id(), bob_id);
+	assert!(!refund.paths().is_empty());
+	for path in refund.paths() {
+		assert_eq!(path.introduction_node, IntroductionNode::NodeId(alice_id));
 	}
+	expect_recent_payment!(bob, RecentPaymentDetails::AwaitingInvoice, payment_id);
 
-	assert!(nodes[0].node.list_recent_payments().is_empty());
+	let expected_invoice = alice.node.request_refund_payment(&refund).unwrap();
+
+	let onion_message = alice.onion_messenger.next_onion_message_for_peer(bob_id).unwrap();
+
+	let invoice = extract_invoice(bob, &onion_message);
+	assert_eq!(invoice, expected_invoice);
+	assert_ne!(invoice.signing_pubkey(), alice_id);
+	assert!(!invoice.payment_paths().is_empty());
+	for (_, path) in invoice.payment_paths() {
+		assert_eq!(path.introduction_node, IntroductionNode::NodeId(bob_id));
+	}
 }
 
 /// Fails creating or paying an offer when a blinded path cannot be created because no peers are
@@ -1165,8 +1234,7 @@ fn fails_sending_invoice_with_unsupported_chain_for_refund() {
 	}
 }
 
-/// Fails creating an invoice request when a blinded reply path cannot be created without exposing
-/// the node's id.
+/// Fails creating an invoice request when a blinded reply path cannot be created.
 #[test]
 fn fails_creating_invoice_request_without_blinded_reply_path() {
 	let chanmon_cfgs = create_chanmon_cfgs(6);
@@ -1183,7 +1251,7 @@ fn fails_creating_invoice_request_without_blinded_reply_path() {
 	let (alice, bob, charlie, david) = (&nodes[0], &nodes[1], &nodes[2], &nodes[3]);
 
 	disconnect_peers(alice, &[charlie, david, &nodes[4], &nodes[5]]);
-	disconnect_peers(david, &[bob, &nodes[4], &nodes[5]]);
+	disconnect_peers(david, &[bob, charlie, &nodes[4], &nodes[5]]);
 
 	let offer = alice.node
 		.create_offer_builder(None).unwrap()

lightning/src/ln/outbound_payment.rs

@@ -13,7 +13,8 @@ use bitcoin::hashes::Hash;
 use bitcoin::hashes::sha256::Hash as Sha256;
 use bitcoin::secp256k1::{self, Secp256k1, SecretKey};
 
-use crate::sign::{EntropySource, NodeSigner, Recipient};
+use crate::blinded_path::{IntroductionNode, NodeIdLookUp};
+use crate::blinded_path::payment::advance_path_by_one;
 use crate::events::{self, PaymentFailureReason};
 use crate::ln::types::{PaymentHash, PaymentPreimage, PaymentSecret};
 use crate::ln::channel_state::ChannelDetails;
@@ -22,6 +23,7 @@ use crate::ln::onion_utils;
 use crate::ln::onion_utils::{DecodedOnionFailure, HTLCFailReason};
 use crate::offers::invoice::Bolt12Invoice;
 use crate::routing::router::{BlindedTail, InFlightHtlcs, Path, PaymentParameters, Route, RouteParameters, Router};
+use crate::sign::{EntropySource, NodeSigner, Recipient};
 use crate::util::errors::APIError;
 use crate::util::logger::Logger;
 use crate::util::time::Time;
@@ -775,10 +777,13 @@ impl OutboundPayments {
 		}
 	}
 
-	pub(super) fn send_payment_for_bolt12_invoice<R: Deref, ES: Deref, NS: Deref, IH, SP, L: Deref>(
+	pub(super) fn send_payment_for_bolt12_invoice<
+		R: Deref, ES: Deref, NS: Deref, NL: Deref, IH, SP, L: Deref
+	>(
 		&self, invoice: &Bolt12Invoice, payment_id: PaymentId, router: &R,
 		first_hops: Vec<ChannelDetails>, inflight_htlcs: IH, entropy_source: &ES, node_signer: &NS,
-		best_block_height: u32, logger: &L,
+		node_id_lookup: &NL, secp_ctx: &Secp256k1<secp256k1::All>, best_block_height: u32,
+		logger: &L,
 		pending_events: &Mutex<VecDeque<(events::Event, Option<EventCompletionAction>)>>,
 		send_payment_along_path: SP,
 	) -> Result<(), Bolt12PaymentError>
@@ -786,6 +791,7 @@ impl OutboundPayments {
 		R::Target: Router,
 		ES::Target: EntropySource,
 		NS::Target: NodeSigner,
+		NL::Target: NodeIdLookUp,
 		L::Target: Logger,
 		IH: Fn() -> InFlightHtlcs,
 		SP: Fn(SendAlongPathArgs) -> Result<(), APIError>,
@@ -807,9 +813,30 @@ impl OutboundPayments {
 			hash_map::Entry::Vacant(_) => return Err(Bolt12PaymentError::UnexpectedInvoice),
 		};
 
-		let pay_params = PaymentParameters::from_bolt12_invoice(&invoice);
+		let mut payment_params = PaymentParameters::from_bolt12_invoice(&invoice);
+
+		// Advance any blinded path where the introduction node is our node.
+		if let Ok(our_node_id) = node_signer.get_node_id(Recipient::Node) {
+			for (_, path) in payment_params.payee.blinded_route_hints_mut().iter_mut() {
+				let introduction_node_id = match path.introduction_node {
+					IntroductionNode::NodeId(pubkey) => pubkey,
+					IntroductionNode::DirectedShortChannelId(direction, scid) => {
+						match node_id_lookup.next_node_id(scid) {
+							Some(next_node_id) => *direction.select_pubkey(&our_node_id, &next_node_id),
+							None => continue,
+						}
+					},
+				};
+				if introduction_node_id == our_node_id {
+					let _ = advance_path_by_one(path, node_signer, node_id_lookup, secp_ctx);
+				}
+			}
+		}
+
 		let amount_msat = invoice.amount_msats();
-		let mut route_params = RouteParameters::from_payment_params_and_value(pay_params, amount_msat);
+		let mut route_params = RouteParameters::from_payment_params_and_value(
+			payment_params, amount_msat
+		);
 		if let Some(max_fee_msat) = max_total_routing_fee_msat {
 			route_params.max_total_routing_fee_msat = Some(max_fee_msat);
 		}
@@ -1856,6 +1883,7 @@ mod tests {
 
 	use core::time::Duration;
 
+	use crate::blinded_path::EmptyNodeIdLookUp;
 	use crate::events::{Event, PathFailure, PaymentFailureReason};
 	use crate::ln::types::PaymentHash;
 	use crate::ln::channelmanager::{PaymentId, RecipientOnionFields};
@@ -2199,6 +2227,7 @@ mod tests {
 		let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, &logger));
 		let scorer = RwLock::new(test_utils::TestScorer::new());
 		let router = test_utils::TestRouter::new(network_graph, &logger, &scorer);
+		let secp_ctx = Secp256k1::new();
 		let keys_manager = test_utils::TestKeysInterface::new(&[0; 32], Network::Testnet);
 
 		let pending_events = Mutex::new(VecDeque::new());
@@ -2227,7 +2256,8 @@ mod tests {
 		assert_eq!(
 			outbound_payments.send_payment_for_bolt12_invoice(
 				&invoice, payment_id, &&router, vec![], || InFlightHtlcs::new(), &&keys_manager,
-				&&keys_manager, 0, &&logger, &pending_events, |_| panic!()
+				&&keys_manager, &EmptyNodeIdLookUp {}, &secp_ctx, 0, &&logger, &pending_events,
+				|_| panic!()
 			),
 			Ok(()),
 		);
@@ -2250,6 +2280,7 @@ mod tests {
 		let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, &logger));
 		let scorer = RwLock::new(test_utils::TestScorer::new());
 		let router = test_utils::TestRouter::new(network_graph, &logger, &scorer);
+		let secp_ctx = Secp256k1::new();
 		let keys_manager = test_utils::TestKeysInterface::new(&[0; 32], Network::Testnet);
 
 		let pending_events = Mutex::new(VecDeque::new());
@@ -2286,7 +2317,8 @@ mod tests {
 		assert_eq!(
 			outbound_payments.send_payment_for_bolt12_invoice(
 				&invoice, payment_id, &&router, vec![], || InFlightHtlcs::new(), &&keys_manager,
-				&&keys_manager, 0, &&logger, &pending_events, |_| panic!()
+				&&keys_manager, &EmptyNodeIdLookUp {}, &secp_ctx, 0, &&logger, &pending_events,
+				|_| panic!()
 			),
 			Ok(()),
 		);
@@ -2309,6 +2341,7 @@ mod tests {
 		let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, &logger));
 		let scorer = RwLock::new(test_utils::TestScorer::new());
 		let router = test_utils::TestRouter::new(network_graph, &logger, &scorer);
+		let secp_ctx = Secp256k1::new();
 		let keys_manager = test_utils::TestKeysInterface::new(&[0; 32], Network::Testnet);
 
 		let pending_events = Mutex::new(VecDeque::new());
@@ -2358,7 +2391,8 @@ mod tests {
 		assert_eq!(
 			outbound_payments.send_payment_for_bolt12_invoice(
 				&invoice, payment_id, &&router, vec![], || InFlightHtlcs::new(), &&keys_manager,
-				&&keys_manager, 0, &&logger, &pending_events, |_| panic!()
+				&&keys_manager, &EmptyNodeIdLookUp {}, &secp_ctx, 0, &&logger, &pending_events,
+				|_| panic!()
 			),
 			Err(Bolt12PaymentError::UnexpectedInvoice),
 		);
@@ -2375,7 +2409,8 @@ mod tests {
 		assert_eq!(
 			outbound_payments.send_payment_for_bolt12_invoice(
 				&invoice, payment_id, &&router, vec![], || InFlightHtlcs::new(), &&keys_manager,
-				&&keys_manager, 0, &&logger, &pending_events, |_| Ok(())
+				&&keys_manager, &EmptyNodeIdLookUp {}, &secp_ctx, 0, &&logger, &pending_events,
+				|_| Ok(())
 			),
 			Ok(()),
 		);
@@ -2385,7 +2420,8 @@ mod tests {
 		assert_eq!(
 			outbound_payments.send_payment_for_bolt12_invoice(
 				&invoice, payment_id, &&router, vec![], || InFlightHtlcs::new(), &&keys_manager,
-				&&keys_manager, 0, &&logger, &pending_events, |_| panic!()
+				&&keys_manager, &EmptyNodeIdLookUp {}, &secp_ctx, 0, &&logger, &pending_events,
+				|_| panic!()
 			),
 			Err(Bolt12PaymentError::DuplicateInvoice),
 		);

lightning/src/onion_message/functional_tests.rs

@@ -492,8 +492,9 @@ fn async_response_with_reply_path_fails() {
 	let path_id = Some([2; 32]);
 	let reply_path = BlindedPath::new_for_message(&[], bob.node_id, &*bob.entropy_source, &secp_ctx).unwrap();
 
-	// Alice tries to asynchronously respond to Bob, but fails because the nodes are unannounced.
-	// Therefore, the reply_path cannot be used for the response.
+	// Alice tries to asynchronously respond to Bob, but fails because the nodes are unannounced and
+	// disconnected. Thus, a reply path could no be created for the response.
+	disconnect_peers(alice, bob);
 	let responder = Responder::new(reply_path, path_id);
 	alice.custom_message_handler.expect_message_and_response(message.clone());
 	let response_instruction = alice.custom_message_handler.handle_custom_message(message, Some(responder));

lightning/src/onion_message/messenger.rs

@@ -489,7 +489,7 @@ where
 	}
 
 	fn create_blinded_paths_from_iter<
-		I: Iterator<Item = ForwardNode>,
+		I: ExactSizeIterator<Item = ForwardNode>,
 		T: secp256k1::Signing + secp256k1::Verification
 	>(
 		&self, recipient: PublicKey, peers: I, secp_ctx: &Secp256k1<T>, compact_paths: bool
@@ -505,13 +505,20 @@ where
 		let is_recipient_announced =
 			network_graph.nodes().contains_key(&NodeId::from_pubkey(&recipient));
 
+		let has_one_peer = peers.len() == 1;
 		let mut peer_info = peers
-			// Limit to peers with announced channels
+			// Limit to peers with announced channels unless the recipient is unannounced.
 			.filter_map(|peer|
 				network_graph
 					.node(&NodeId::from_pubkey(&peer.node_id))
-					.filter(|info| info.channels.len() >= MIN_PEER_CHANNELS)
+					.filter(|info|
+						!is_recipient_announced || info.channels.len() >= MIN_PEER_CHANNELS
+					)
 					.map(|info| (peer, info.is_tor_only(), info.channels.len()))
+					// Allow messages directly with the only peer when unannounced.
+					.or_else(|| (!is_recipient_announced && has_one_peer)
+						.then(|| (peer, false, 0))
+					)
 			)
 			// Exclude Tor-only nodes when the recipient is announced.
 			.filter(|(_, is_tor_only, _)| !(*is_tor_only && is_recipient_announced))

lightning/src/routing/router.rs

@@ -100,16 +100,31 @@ impl<G: Deref<Target = NetworkGraph<L>> + Clone, L: Deref, ES: Deref, S: Deref,
 		// recipient's node_id.
 		const MIN_PEER_CHANNELS: usize = 3;
 
+		let has_one_peer = first_hops
+			.first()
+			.map(|details| details.counterparty.node_id)
+			.map(|node_id| first_hops
+				.iter()
+				.skip(1)
+				.all(|details| details.counterparty.node_id == node_id)
+			)
+			.unwrap_or(false);
+
 		let network_graph = self.network_graph.deref().read_only();
+		let is_recipient_announced =
+			network_graph.nodes().contains_key(&NodeId::from_pubkey(&recipient));
+
 		let paths = first_hops.into_iter()
 			.filter(|details| details.counterparty.features.supports_route_blinding())
 			.filter(|details| amount_msats <= details.inbound_capacity_msat)
 			.filter(|details| amount_msats >= details.inbound_htlc_minimum_msat.unwrap_or(0))
 			.filter(|details| amount_msats <= details.inbound_htlc_maximum_msat.unwrap_or(u64::MAX))
+			// Limit to peers with announced channels unless the recipient is unannounced.
 			.filter(|details| network_graph
 					.node(&NodeId::from_pubkey(&details.counterparty.node_id))
-					.map(|node_info| node_info.channels.len() >= MIN_PEER_CHANNELS)
-					.unwrap_or(false)
+					.map(|node| !is_recipient_announced || node.channels.len() >= MIN_PEER_CHANNELS)
+					// Allow payments directly with the only peer when unannounced.
+					.unwrap_or(!is_recipient_announced && has_one_peer)
 			)
 			.filter_map(|details| {
 				let short_channel_id = match details.get_inbound_payment_scid() {
@@ -1031,6 +1046,13 @@ impl Payee {
 		}
 	}
 
+	pub(crate) fn blinded_route_hints_mut(&mut self) -> &mut [(BlindedPayInfo, BlindedPath)] {
+		match self {
+			Self::Blinded { route_hints, .. } => &mut route_hints[..],
+			Self::Clear { .. } => &mut []
+		}
+	}
+
 	fn unblinded_route_hints(&self) -> &[RouteHint] {
 		match self {
 			Self::Blinded { .. } => &[],