WIP: three-hop blinded payment paths

Author: jkczyz

lightning/src/routing/router.rs

@@ -92,6 +92,9 @@ impl<G: Deref<Target = NetworkGraph<L>> + Clone, L: Deref, ES: Deref, S: Deref,
 		&self, recipient: PublicKey, first_hops: Vec<ChannelDetails>, tlvs: ReceiveTlvs,
 		amount_msats: u64, secp_ctx: &Secp256k1<T>
 	) -> Result<Vec<(BlindedPayInfo, BlindedPath)>, ()> {
+		let entropy_source = &*self.entropy_source;
+		let recipient_node_id = NodeId::from_pubkey(&recipient);
+
 		// Limit the number of blinded paths that are computed.
 		const MAX_PAYMENT_PATHS: usize = 3;
 
@@ -100,17 +103,20 @@ impl<G: Deref<Target = NetworkGraph<L>> + Clone, L: Deref, ES: Deref, S: Deref,
 		const MIN_PEER_CHANNELS: usize = 3;
 
 		let network_graph = self.network_graph.deref().read_only();
-		let paths = first_hops.into_iter()
+		let counterparty_channels = 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))
-			.filter(|details| network_graph
+			// Limit to counterparties with announced channels
+			.filter_map(|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(|info| &info.channels[..])
+					.and_then(|channels| (channels.len() >= MIN_PEER_CHANNELS).then(|| channels))
+					.map(|channels| (details, channels))
 			)
-			.filter_map(|details| {
+			.filter_map(|(details, counterparty_channels)| {
 				let short_channel_id = match details.get_inbound_payment_scid() {
 					Some(short_channel_id) => short_channel_id,
 					None => return None,
@@ -128,7 +134,7 @@ impl<G: Deref<Target = NetworkGraph<L>> + Clone, L: Deref, ES: Deref, S: Deref,
 					max_cltv_expiry: tlvs.payment_constraints.max_cltv_expiry + cltv_expiry_delta,
 					htlc_minimum_msat: details.inbound_htlc_minimum_msat.unwrap_or(0),
 				};
-				Some(payment::ForwardNode {
+				let forward_node = payment::ForwardNode {
 					tlvs: ForwardTlvs {
 						short_channel_id,
 						payment_relay,
@@ -137,29 +143,88 @@ impl<G: Deref<Target = NetworkGraph<L>> + Clone, L: Deref, ES: Deref, S: Deref,
 					},
 					node_id: details.counterparty.node_id,
 					htlc_maximum_msat: details.inbound_htlc_maximum_msat.unwrap_or(u64::MAX),
-				})
+				};
+				Some((forward_node, counterparty_channels))
+			});
+
+		let three_hop_paths = counterparty_channels.clone()
+			// Pair counterparties with their other channels
+			.flat_map(|(forward_node, counterparty_channels)|
+				counterparty_channels
+					.iter()
+					.filter_map(|scid| network_graph.channels().get_key_value(scid))
+					.filter_map(move |(scid, info)| info
+						.as_directed_to(&NodeId::from_pubkey(&forward_node.node_id))
+						.map(|(info, source)| (source, *scid, info))
+					)
+					.filter(|(source, _, _)| **source != recipient_node_id)
+					.filter(|(source, _, _)| network_graph
+						.node(source)
+						.and_then(|info| info.announcement_info.as_ref())
+						.map(|info| info.features.supports_route_blinding())
+						.unwrap_or(false)
+					)
+					.filter(|(_, _, info)| amount_msats >= info.direction().htlc_minimum_msat)
+					.filter(|(_, _, info)| amount_msats <= info.direction().htlc_maximum_msat)
+					.map(move |(source, scid, info)| (source, scid, info, forward_node.clone()))
+			)
+			// Construct blinded paths where the counterparty's counterparty is the introduction
+			// node:
+			//
+			// source --- info ---> counterparty --- counterparty_forward_node ---> recipient
+			.filter_map(|(introduction_node_id, scid, info, counterparty_forward_node)| {
+				let htlc_minimum_msat = info.direction().htlc_minimum_msat;
+				let htlc_maximum_msat = info.direction().htlc_maximum_msat;
+				let payment_relay: PaymentRelay = match info.try_into() {
+					Ok(payment_relay) => payment_relay,
+					Err(()) => return None,
+				};
+				let payment_constraints = PaymentConstraints {
+					max_cltv_expiry: payment_relay.cltv_expiry_delta as u32
+						+ counterparty_forward_node.tlvs.payment_constraints.max_cltv_expiry,
+					htlc_minimum_msat,
+				};
+				let introduction_forward_node = payment::ForwardNode {
+					tlvs: ForwardTlvs {
+						short_channel_id: scid,
+						payment_relay,
+						payment_constraints,
+						features: BlindedHopFeatures::empty(),
+					},
+					node_id: introduction_node_id.as_pubkey().unwrap(),
+					htlc_maximum_msat,
+				};
+				Some(BlindedPath::new_for_payment(
+					&[introduction_forward_node, counterparty_forward_node], recipient,
+					tlvs.clone(), u64::MAX, MIN_FINAL_CLTV_EXPIRY_DELTA, entropy_source, secp_ctx
+				))
 			})
-			.map(|forward_node| {
+			.take(MAX_PAYMENT_PATHS);
+
+		let two_hop_paths = counterparty_channels
+			.map(|(forward_node, _)| {
 				BlindedPath::new_for_payment(
 					&[forward_node], recipient, tlvs.clone(), u64::MAX, MIN_FINAL_CLTV_EXPIRY_DELTA,
-					&*self.entropy_source, secp_ctx
+					entropy_source, secp_ctx
 				)
 			})
-			.take(MAX_PAYMENT_PATHS)
-			.collect::<Result<Vec<_>, _>>();
-
-		match paths {
-			Ok(paths) if !paths.is_empty() => Ok(paths),
-			_ => {
-				if network_graph.nodes().contains_key(&NodeId::from_pubkey(&recipient)) {
-					BlindedPath::one_hop_for_payment(
-						recipient, tlvs, MIN_FINAL_CLTV_EXPIRY_DELTA, &*self.entropy_source, secp_ctx
-					).map(|path| vec![path])
-				} else {
-					Err(())
-				}
-			},
-		}
+			.take(MAX_PAYMENT_PATHS);
+
+		three_hop_paths
+			.collect::<Result<Vec<_>, _>>().ok()
+			.and_then(|paths| (!paths.is_empty()).then(|| paths))
+			.or_else(|| two_hop_paths.collect::<Result<Vec<_>, _>>().ok())
+			.and_then(|paths| (!paths.is_empty()).then(|| paths))
+			.or_else(|| network_graph
+				.node(&NodeId::from_pubkey(&recipient)).ok_or(())
+				.and_then(|_| BlindedPath::one_hop_for_payment(
+						recipient, tlvs, MIN_FINAL_CLTV_EXPIRY_DELTA, entropy_source, secp_ctx
+					)
+				)
+				.map(|path| vec![path])
+				.ok()
+			)
+			.ok_or(())
 	}
 }