WIP: three-hop blinded payment paths

Author: jkczyz

lightning/src/routing/router.rs

@@ -90,6 +90,8 @@ impl<G: Deref<Target = NetworkGraph<L>> + Clone, L: Deref, S: Deref, SP: Sized,
 		&self, recipient: PublicKey, first_hops: Vec<ChannelDetails>, tlvs: ReceiveTlvs,
 		amount_msats: u64, entropy_source: &ES, secp_ctx: &Secp256k1<T>
 	) -> Result<Vec<(BlindedPayInfo, BlindedPath)>, ()> {
+		let recipient_node_id = NodeId::from_pubkey(&recipient);
+
 		// Limit the number of blinded paths that are computed.
 		const MAX_PAYMENT_PATHS: usize = 3;
 
@@ -98,37 +100,88 @@ impl<G: Deref<Target = NetworkGraph<L>> + Clone, L: Deref, S: Deref, SP: Sized,
 		const MIN_PEER_CHANNELS: usize = 3;
 
 		let network_graph = self.network_graph.deref().read_only();
-		first_hops.into_iter()
-			.filter(|details| details.is_public)
+		first_hops.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(0))
-			.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(|details| (details, NodeId::from_pubkey(&details.counterparty.node_id)))
+			// Limit to counterparties with announced channels
+			.filter_map(|(details, counterparty_node_id)|
+				network_graph
+					.node(&counterparty_node_id)
+					.map(|info| &info.channels[..])
+					.and_then(|channels| (channels.len() >= MIN_PEER_CHANNELS).then(|| channels))
+					.map(|channels| (details, counterparty_node_id, channels))
+			)
+			// Pair counterparties with their other channels
+			.flat_map(|(details, counterparty_node_id, counterparty_channels)|
+				counterparty_channels
+					.iter()
+					.filter_map(|scid| network_graph.channels().get_key_value(scid))
+					.filter_map(move |(scid, info)| info
+						.as_directed_to(&counterparty_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, details))
 			)
-			.map(|details| {
-				let short_channel_id = details.get_inbound_payment_scid().unwrap();
-				let payment_relay: PaymentRelay = details.counterparty.forwarding_info.unwrap().into();
-				let payment_constraints = PaymentConstraints {
-					max_cltv_expiry: tlvs.payment_constraints.max_cltv_expiry
-						+ payment_relay.cltv_expiry_delta as u32,
-					htlc_minimum_msat: details.inbound_htlc_minimum_msat.unwrap_or(0),
+			// Construct blinded paths where the counterparty's counterparty is the introduction
+			// node:
+			//
+			// source --- info ---> counterparty --- details ---> recipient
+			.map(|(introduction_node_id, scid, info, details)| {
+				let counterparty_forward_node = {
+					let short_channel_id = details.get_inbound_payment_scid().unwrap();
+					let payment_relay: PaymentRelay =
+						details.counterparty.forwarding_info.clone().unwrap().into();
+					let payment_constraints = PaymentConstraints {
+						max_cltv_expiry: payment_relay.cltv_expiry_delta as u32
+							+ tlvs.payment_constraints.max_cltv_expiry,
+						htlc_minimum_msat: details.inbound_htlc_minimum_msat.unwrap_or(0),
+					};
+					ForwardNode {
+						tlvs: ForwardTlvs {
+							short_channel_id,
+							payment_relay,
+							payment_constraints,
+							features: BlindedHopFeatures::empty(),
+						},
+						node_id: details.counterparty.node_id,
+						htlc_maximum_msat: details.inbound_htlc_maximum_msat.unwrap_or(0),
+					}
 				};
-				let forward_node = ForwardNode {
-					tlvs: ForwardTlvs {
-						short_channel_id,
-						payment_relay,
-						payment_constraints,
-						features: BlindedHopFeatures::empty(),
-					},
-					node_id: details.counterparty.node_id,
-					htlc_maximum_msat: details.inbound_htlc_maximum_msat.unwrap_or(0),
+				let introduction_forward_node = {
+					let htlc_minimum_msat = info.direction().htlc_minimum_msat;
+					let htlc_maximum_msat = info.direction().htlc_maximum_msat;
+					let payment_relay: PaymentRelay = info.into();
+					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,
+					};
+					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,
+					}
 				};
 				BlindedPath::new_for_payment(
-					&[forward_node], recipient, tlvs.clone(), u64::MAX, entropy_source, secp_ctx
+					&[introduction_forward_node, counterparty_forward_node], recipient,
+					tlvs.clone(), u64::MAX, entropy_source, secp_ctx
 				)
 			})
 			.take(MAX_PAYMENT_PATHS)