Pathfind Trampoline forward [rephrase]

Don't immediately reject Trampoline forwards…

Author: arik-so

lightning/src/ln/channelmanager.rs

@@ -56,7 +56,7 @@ use crate::ln::channel_state::ChannelDetails;
 use crate::types::features::{Bolt12InvoiceFeatures, ChannelFeatures, ChannelTypeFeatures, InitFeatures, NodeFeatures};
 #[cfg(any(feature = "_test_utils", test))]
 use crate::types::features::Bolt11InvoiceFeatures;
-use crate::routing::router::{BlindedTail, InFlightHtlcs, Path, Payee, PaymentParameters, RouteParameters, RouteParametersConfig, Router, FixedRouter, Route};
+use crate::routing::router::{BlindedTail, FixedRouter, InFlightHtlcs, Path, Payee, PaymentParameters, RouteParameters, RouteParametersConfig, Route, RouteHop, Router, MAX_PATH_LENGTH_ESTIMATE};
 use crate::ln::onion_payment::{check_incoming_htlc_cltv, create_recv_pending_htlc_info, create_fwd_pending_htlc_info, decode_incoming_update_add_htlc_onion, HopConnector, InboundHTLCErr, NextPacketDetails};
 use crate::ln::msgs;
 use crate::ln::onion_utils::{self};
@@ -186,6 +186,8 @@ pub enum PendingHTLCRouting {
 		blinded: Option<BlindedForward>,
 		/// The absolute CLTV of the inbound HTLC
 		incoming_cltv_expiry: u32,
+		/// Path to send the packet to the next hop
+		hops: Vec<RouteHop>
 	},
 	/// The onion indicates that this is a payment for an invoice (supposedly) generated by us.
 	///
@@ -4353,8 +4355,6 @@ where
 				// we don't have the channel here.
 				return Err(("Refusing to forward over real channel SCID as our counterparty requested.", 0x4000 | 10));
 			}
-		} else {
-			return Err(("Cannot forward by Node ID without SCID.", 0x4000 | 10));
 		}
 
 		// Note that we could technically not return an error yet here and just hope
@@ -4404,12 +4404,17 @@ where
 	}
 
 	fn can_forward_htlc(
-		&self, msg: &msgs::UpdateAddHTLC, next_packet_details: &NextPacketDetails
+		&self, msg: &msgs::UpdateAddHTLC, next_packet_details: &NextPacketDetails, trampoline_outgoing_scid: Option<u64>
 	) -> Result<(), (&'static str, u16)> {
 		let outgoing_scid = match next_packet_details.outgoing_connector {
 			HopConnector::ShortChannelId(scid) => scid,
 			HopConnector::Trampoline(_) => {
-				return Err(("Cannot forward by Node ID without SCID.", 0x4000 | 10));
+				match trampoline_outgoing_scid {
+					Some(scid) => scid,
+					None => {
+						return Err(("Cannot forward by Node ID without SCID.", 0x4000 | 10));
+					}
+				}
 			}
 		};
 		match self.do_funded_channel_callback(outgoing_scid, |chan: &mut FundedChannel<SP>| {
@@ -4494,6 +4499,7 @@ where
 		&self, msg: &msgs::UpdateAddHTLC, counterparty_node_id: &PublicKey, shared_secret: [u8; 32],
 		decoded_hop: onion_utils::Hop, allow_underpay: bool,
 		next_packet_pubkey_opt: Option<Result<PublicKey, secp256k1::Error>>,
+		inter_trampoline_path_option: Option<Vec<RouteHop>>
 	) -> PendingHTLCStatus {
 		macro_rules! return_err {
 			($msg: expr, $err_code: expr, $data: expr) => {
@@ -4541,13 +4547,13 @@ where
 				}
 			},
 			onion_utils::Hop::Forward { .. } | onion_utils::Hop::BlindedForward { .. } => {
-				match create_fwd_pending_htlc_info(msg, decoded_hop, shared_secret, next_packet_pubkey_opt) {
+				match create_fwd_pending_htlc_info(msg, decoded_hop, shared_secret, next_packet_pubkey_opt, None) {
 					Ok(info) => PendingHTLCStatus::Forward(info),
 					Err(InboundHTLCErr { err_code, err_data, msg }) => return_err!(msg, err_code, &err_data)
 				}
 			},
 			onion_utils::Hop::TrampolineForward { .. } | onion_utils::Hop::TrampolineBlindedForward { .. } => {
-				match create_fwd_pending_htlc_info(msg, decoded_hop, shared_secret, next_packet_pubkey_opt) {
+				match create_fwd_pending_htlc_info(msg, decoded_hop, shared_secret, next_packet_pubkey_opt, inter_trampoline_path_option) {
 					Ok(info) => PendingHTLCStatus::Forward(info),
 					Err(InboundHTLCErr { err_code, err_data, msg }) => return_err!(msg, err_code, &err_data)
 				}
@@ -5828,10 +5834,50 @@ where
 					None => continue 'outer_loop,
 				}
 
+				let mut inter_trampoline_path = None;
+
 				// Now process the HTLC on the outgoing channel if it's a forward.
 				if let Some(next_packet_details) = next_packet_details_opt.as_ref() {
+					let first_hop_scid_override = match (&next_packet_details.outgoing_connector, &next_hop) {
+						(HopConnector::Trampoline(next_node_id), onion_utils::Hop::TrampolineForward { ref outer_hop_data, .. } | onion_utils::Hop::TrampolineBlindedForward { ref outer_hop_data, .. }) => {
+							let incoming_amount = outer_hop_data.amt_to_forward;
+							let incoming_cltv = outer_hop_data.outgoing_cltv_value;
+							let outgoing_amount = next_packet_details.outgoing_amt_msat;
+							let outgoing_cltv = next_packet_details.outgoing_cltv_value;
+
+							let routes = self.router.find_route(
+								&self.node_signer.get_node_id(Recipient::Node).unwrap(),
+								&RouteParameters {
+									payment_params: PaymentParameters {
+										payee: Payee::Clear {
+											node_id: next_node_id.clone(),
+											route_hints: vec![],
+											features: None,
+											final_cltv_expiry_delta: 0,
+										},
+										expiry_time: None,
+										max_total_cltv_expiry_delta: incoming_cltv - outgoing_cltv,
+										max_path_count: 1,
+										max_path_length: MAX_PATH_LENGTH_ESTIMATE.div_ceil(2),
+										max_channel_saturation_power_of_half: 2,
+										previously_failed_channels: vec![],
+										previously_failed_blinded_path_idxs: vec![],
+									},
+									final_value_msat: outgoing_amount,
+									max_total_routing_fee_msat: Some(incoming_amount - outgoing_amount),
+								},
+								None,
+								InFlightHtlcs::new()
+							).unwrap();
+
+							inter_trampoline_path = routes.paths.first().map(|path| path.hops.clone());
+							inter_trampoline_path.as_ref().and_then(|hops| hops.first().map(|hop| hop.short_channel_id))
+						},
+						_ => None
+					};
+
 					if let Err((err, code)) = self.can_forward_htlc(
-						&update_add_htlc, next_packet_details
+						&update_add_htlc, next_packet_details, first_hop_scid_override
 					) {
 						let htlc_fail = self.htlc_failure_from_update_add_err(
 							&update_add_htlc, &incoming_counterparty_node_id, err, code,
@@ -5845,7 +5891,7 @@ where
 
 				match self.construct_pending_htlc_status(
 					&update_add_htlc, &incoming_counterparty_node_id, shared_secret, next_hop,
-					incoming_accept_underpaying_htlcs, next_packet_details_opt.map(|d| d.next_packet_pubkey),
+					incoming_accept_underpaying_htlcs, next_packet_details_opt.map(|d| d.next_packet_pubkey), inter_trampoline_path
 				) {
 					PendingHTLCStatus::Forward(htlc_forward) => {
 						htlc_forwards.push((htlc_forward, update_add_htlc.htlc_id));
@@ -9086,7 +9132,7 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 				for (forward_info, prev_htlc_id) in pending_forwards.drain(..) {
 					let scid = match forward_info.routing {
 						PendingHTLCRouting::Forward { short_channel_id, .. } => short_channel_id,
-						PendingHTLCRouting::TrampolineForward { .. } => 0,
+						PendingHTLCRouting::TrampolineForward { ref hops, .. } => hops.first().map_or(0, |hop| hop.short_channel_id),
 						PendingHTLCRouting::Receive { .. } => 0,
 						PendingHTLCRouting::ReceiveKeysend { .. } => 0,
 					};
@@ -12950,6 +12996,7 @@ impl_writeable_tlv_based_enum!(PendingHTLCRouting,
 		(4, blinded, option),
 		(6, node_id, required),
 		(8, incoming_cltv_expiry, required),
+		(10, hops, required),
 	}
 );
 

lightning/src/ln/onion_payment.rs

@@ -17,6 +17,7 @@ use crate::types::features::BlindedHopFeatures;
 use crate::ln::msgs;
 use crate::ln::onion_utils;
 use crate::ln::onion_utils::{HTLCFailReason, INVALID_ONION_BLINDING, ONION_DATA_LEN};
+use crate::routing::router::RouteHop;
 use crate::sign::{NodeSigner, Recipient};
 use crate::util::logger::Logger;
 
@@ -89,7 +90,8 @@ enum RoutingInfo {
 
 pub(super) fn create_fwd_pending_htlc_info(
 	msg: &msgs::UpdateAddHTLC, hop_data: onion_utils::Hop, shared_secret: [u8; 32],
-	next_packet_pubkey_opt: Option<Result<PublicKey, secp256k1::Error>>
+	next_packet_pubkey_opt: Option<Result<PublicKey, secp256k1::Error>>,
+	inter_trampoline_path_option: Option<Vec<RouteHop>>,
 ) -> Result<PendingHTLCInfo, InboundHTLCErr> {
 	debug_assert!(next_packet_pubkey_opt.is_some());
 
@@ -240,7 +242,8 @@ pub(super) fn create_fwd_pending_htlc_info(
 						failure: intro_node_blinding_point
 							.map(|_| BlindedFailure::FromIntroductionNode)
 							.unwrap_or(BlindedFailure::FromBlindedNode),
-					})
+					}),
+				hops: inter_trampoline_path_option.unwrap_or(vec![])
 			}
 		}
 	};
@@ -506,7 +509,7 @@ where
 
 			// TODO: If this is potentially a phantom payment we should decode the phantom payment
 			// onion here and check it.
-			create_fwd_pending_htlc_info(msg, hop, shared_secret.secret_bytes(), Some(next_packet_pubkey))?
+			create_fwd_pending_htlc_info(msg, hop, shared_secret.secret_bytes(), Some(next_packet_pubkey), None)?
 		},
 		_ => {
 			let shared_secret = hop.shared_secret().secret_bytes();