Implement routing to blinded paths

But disallow sending payments to them, for now

lightning/src/ln/outbound_payment.rs

@@ -903,6 +903,10 @@ impl OutboundPayments {
 				path_errs.push(Err(APIError::InvalidRoute{err: "Path didn't go anywhere/had bogus size".to_owned()}));
 				continue 'path_check;
 			}
+			if path.blinded_tail.is_some() {
+				path_errs.push(Err(APIError::InvalidRoute{err: "Sending to blinded paths isn't supported yet".to_owned()}));
+				continue 'path_check;
+			}
 			for (idx, hop) in path.iter().enumerate() {
 				if idx != path.hops.len() - 1 && hop.pubkey == our_node_id {
 					path_errs.push(Err(APIError::InvalidRoute{err: "Path went through us but wasn't a simple rebalance loop to us".to_owned()}));

lightning/src/routing/router.rs

@@ -435,6 +435,10 @@ const MEDIAN_HOP_CLTV_EXPIRY_DELTA: u32 = 40;
 // down from (1300-93) / 61 = 19.78... to arrive at a conservative estimate of 19.
 const MAX_PATH_LENGTH_ESTIMATE: u8 = 19;
 
+/// We need to create RouteHintHops for blinded pathfinding, but we don't have an scid, so use a
+/// dummy value.
+const BLINDED_PATH_SCID: u64 = 0;
+
 /// The recipient of a payment.
 #[derive(Clone, Debug, Hash, PartialEq, Eq)]
 pub struct PaymentParameters {
@@ -589,6 +593,14 @@ impl PaymentParameters {
 		Self { route_hints: Hints::Clear(route_hints), ..self }
 	}
 
+	/// Includes blinded hints for routing to the payee.
+	///
+	/// (C-not exported) since bindings don't support move semantics
+	#[cfg(test)] // TODO: make this public when we allow sending to blinded recipients
+	pub fn with_blinded_route_hints(self, blinded_route_hints: Vec<(BlindedPayInfo, BlindedPath)>) -> Self {
+		Self { route_hints: Hints::Blinded(blinded_route_hints), ..self }
+	}
+
 	/// Includes a payment expiration in seconds relative to the UNIX epoch.
 	///
 	/// (C-not exported) since bindings don't support move semantics
@@ -628,6 +640,15 @@ pub enum Hints {
 	Clear(Vec<RouteHint>),
 }
 
+impl Hints {
+	fn blinded_len(&self) -> usize {
+		match self {
+			Self::Blinded(hints) => hints.len(),
+			Self::Clear(_) => 0,
+		}
+	}
+}
+
 /// A list of hops along a payment path terminating with a channel to the recipient.
 #[derive(Clone, Debug, Hash, Eq, PartialEq)]
 pub struct RouteHint(pub Vec<RouteHintHop>);
@@ -1087,7 +1108,18 @@ where L::Target: Logger {
 				}
 			}
 		},
-		_ => todo!()
+		Hints::Blinded(hints) => {
+			for (_, blinded_path) in hints.iter() {
+				let intro_node_is_payee = blinded_path.introduction_node_id == payment_params.payee_pubkey;
+				if blinded_path.blinded_hops.len() > 1 && intro_node_is_payee {
+					return Err(LightningError{err: "Blinded path cannot have the payee as the source.".to_owned(), action: ErrorAction::IgnoreError});
+				} else if !intro_node_is_payee && blinded_path.blinded_hops.len() == 1 {
+					return Err(LightningError{err: format!("1-hop blinded path introduction node id {} did not match payee {}", blinded_path.introduction_node_id, payment_params.payee_pubkey), action: ErrorAction::IgnoreError});
+				} else if blinded_path.blinded_hops.len() == 0 {
+					return Err(LightningError{err: "0-hop blinded path provided".to_owned(), action: ErrorAction::IgnoreError});
+				}
+			}
+		}
 	}
 	if payment_params.max_total_cltv_expiry_delta <= final_cltv_expiry_delta {
 		return Err(LightningError{err: "Can't find a route where the maximum total CLTV expiry delta is below the final CLTV expiry.".to_owned(), action: ErrorAction::IgnoreError});
@@ -1200,6 +1232,28 @@ where L::Target: Logger {
 		}
 	}
 
+	// Marshall route hints
+	let mut route_hints = Vec::with_capacity(payment_params.route_hints.blinded_len());
+	let route_hints_ref = match &payment_params.route_hints {
+		Hints::Clear(hints) => hints,
+		Hints::Blinded(blinded_hints) => {
+			for (blinded_payinfo, blinded_path) in blinded_hints {
+				route_hints.push(RouteHint(vec![RouteHintHop {
+					src_node_id: blinded_path.introduction_node_id,
+					short_channel_id: BLINDED_PATH_SCID,
+					fees: RoutingFees {
+						base_msat: blinded_payinfo.fee_base_msat,
+						proportional_millionths: blinded_payinfo.fee_proportional_millionths,
+					},
+					cltv_expiry_delta: blinded_payinfo.cltv_expiry_delta,
+					htlc_minimum_msat: Some(blinded_payinfo.htlc_minimum_msat),
+					htlc_maximum_msat: Some(blinded_payinfo.htlc_maximum_msat),
+				}]));
+			}
+			&route_hints
+		}
+	};
+
 	// The main heap containing all candidate next-hops sorted by their score (max(fee,
 	// htlc_minimum)). Ideally this would be a heap which allowed cheap score reduction instead of
 	// adding duplicate entries when we find a better path to a given node.
@@ -1612,11 +1666,7 @@ where L::Target: Logger {
 		// If a caller provided us with last hops, add them to routing targets. Since this happens
 		// earlier than general path finding, they will be somewhat prioritized, although currently
 		// it matters only if the fees are exactly the same.
-		let route_hints = match &payment_params.route_hints {
-			Hints::Clear(hints) => hints,
-			_ => todo!()
-		};
-		for route in route_hints.iter().filter(|route| !route.0.is_empty()) {
+		for route in route_hints_ref.iter().filter(|route| !route.0.is_empty()) {
 			let first_hop_in_route = &(route.0)[0];
 			let have_hop_src_in_graph =
 				// Only add the hops in this route to our candidate set if either
@@ -2035,7 +2085,16 @@ where L::Target: Logger {
 	for results_vec in selected_paths {
 		let mut hops = Vec::new();
 		for res in results_vec { hops.push(res?); }
-		paths.push(Path { hops, blinded_tail: None });
+		let mut blinded_tail = None;
+		if let Hints::Blinded(hints) = &payment_params.route_hints {
+			blinded_tail = hints.iter()
+				.find(|(_, p)| {
+					let intro_node_idx = if p.blinded_hops.len() == 1 { hops.len() - 1 } else { hops.len() - 2 };
+					p.introduction_node_id == hops[intro_node_idx].pubkey
+				})
+				.map(|(_, p)| p.clone());
+		}
+		paths.push(Path { hops, blinded_tail });
 	}
 	let route = Route {
 		paths,
@@ -2216,12 +2275,14 @@ mod tests {
 	use crate::routing::utxo::UtxoResult;
 	use crate::routing::router::{get_route, build_route_from_hops_internal, add_random_cltv_offset, default_node_features,
 		Path, PaymentParameters, Route, RouteHint, RouteHintHop, RouteHop, RoutingFees,
-		DEFAULT_MAX_TOTAL_CLTV_EXPIRY_DELTA, MAX_PATH_LENGTH_ESTIMATE};
+		BLINDED_PATH_SCID, DEFAULT_MAX_TOTAL_CLTV_EXPIRY_DELTA, MAX_PATH_LENGTH_ESTIMATE};
 	use crate::routing::scoring::{ChannelUsage, FixedPenaltyScorer, Score, ProbabilisticScorer, ProbabilisticScoringParameters};
 	use crate::routing::test_utils::{add_channel, add_or_update_node, build_graph, build_line_graph, id_to_feature_flags, get_nodes, update_channel};
+	use crate::blinded_path::{BlindedHop, BlindedPath};
 	use crate::chain::transaction::OutPoint;
 	use crate::chain::keysinterface::EntropySource;
-	use crate::ln::features::{ChannelFeatures, InitFeatures, NodeFeatures};
+	use crate::offers::invoice::BlindedPayInfo;
+	use crate::ln::features::{BlindedHopFeatures, ChannelFeatures, InitFeatures, NodeFeatures};
 	use crate::ln::msgs::{ErrorAction, LightningError, UnsignedChannelUpdate, MAX_VALUE_MSAT};
 	use crate::ln::channelmanager;
 	use crate::util::config::UserConfig;
@@ -5712,6 +5773,48 @@ mod tests {
 		let route = get_route(&our_id, &payment_params, &network_graph.read_only(), None, 100, 42, Arc::clone(&logger), &scorer, &random_seed_bytes);
 		assert!(route.is_ok());
 	}
+
+	#[test]
+	fn simple_blinded_path_routing() {
+		// Check that we can generate a route to a blinded path with the expected hops.
+		let (secp_ctx, network, _, _, logger) = build_graph();
+		let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+		let network_graph = network.read_only();
+
+		let scorer = ln_test_utils::TestScorer::new();
+		let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+		let random_seed_bytes = keys_manager.get_secure_random_bytes();
+
+		let blinded_path = BlindedPath {
+			introduction_node_id: nodes[2],
+			blinding_point: ln_test_utils::pubkey(42),
+			blinded_hops: vec![
+				BlindedHop { blinded_node_id: ln_test_utils::pubkey(43), encrypted_payload: vec![0; 43] },
+				BlindedHop { blinded_node_id: ln_test_utils::pubkey(44), encrypted_payload: vec![0; 44] },
+			],
+		};
+		let blinded_payinfo = BlindedPayInfo {
+			fee_base_msat: 100,
+			fee_proportional_millionths: 500,
+			htlc_minimum_msat: 1000,
+			htlc_maximum_msat: 100_000_000,
+			cltv_expiry_delta: 15,
+			features: BlindedHopFeatures::empty(),
+		};
+
+		let payee_pubkey = ln_test_utils::pubkey(45);
+		let payment_params = PaymentParameters::from_node_id(payee_pubkey, 0)
+			.with_blinded_route_hints(vec![(blinded_payinfo, blinded_path.clone())]);
+		let route = get_route(&our_id, &payment_params, &network_graph, None, 1001, 0,
+			Arc::clone(&logger), &scorer, &random_seed_bytes).unwrap();
+		assert_eq!(route.paths.len(), 1);
+		assert_eq!(route.paths[0].hops.len(), 3);
+		assert_eq!(route.paths[0].len(), 5);
+		assert_eq!(route.paths[0].hops[2].pubkey, payee_pubkey);
+		assert_eq!(route.paths[0].hops[2].short_channel_id, BLINDED_PATH_SCID);
+		assert_eq!(route.paths[0].hops[1].pubkey, nodes[2]);
+		assert_eq!(route.paths[0].blinded_tail, Some(blinded_path));
+	}
 }
 
 #[cfg(all(test, not(feature = "no-std")))]

lightning/src/util/test_utils.rs

@@ -60,6 +60,15 @@ use crate::chain::keysinterface::{InMemorySigner, Recipient, EntropySource, Node
 use std::time::{SystemTime, UNIX_EPOCH};
 use bitcoin::Sequence;
 
+pub fn pubkey(byte: u8) -> PublicKey {
+	let secp_ctx = Secp256k1::new();
+	PublicKey::from_secret_key(&secp_ctx, &privkey(byte))
+}
+
+pub fn privkey(byte: u8) -> SecretKey {
+	SecretKey::from_slice(&[byte; 32]).unwrap()
+}
+
 pub struct TestVecWriter(pub Vec<u8>);
 impl Writer for TestVecWriter {
 	fn write_all(&mut self, buf: &[u8]) -> Result<(), io::Error> {