Refactor: Introduce ForwardInfo

NextPacketDetails currently bundles four fields used to define the
forwarding details for the packet. With the introduction of dummy
hops, not all of these fields apply in those paths.

To avoid overloading NextPacketDetails with conditional semantics, this
refactor extracts the forwarding-specific pieces into a dedicated
ForwardInfo struct. This keeps the data model clean, reusable, and
makes the logic around dummy hops easier to follow.

Author: shaavan

lightning/src/ln/blinded_payment_tests.rs

@@ -1675,8 +1675,9 @@ fn route_blinding_spec_test_vector() {
 		hop_data: carol_packet_bytes,
 		hmac: carol_hmac,
 	};
+	let carol_forward_info = carol_packet_details.next_hop_forward_info.unwrap();
 	let carol_update_add = update_add_msg(
-		carol_packet_details.outgoing_amt_msat, carol_packet_details.outgoing_cltv_value,
+		carol_forward_info.outgoing_amt_msat, carol_forward_info.outgoing_cltv_value,
 		Some(pubkey_from_hex("034e09f450a80c3d252b258aba0a61215bf60dda3b0dc78ffb0736ea1259dfd8a0")),
 		carol_onion
 	);
@@ -1709,8 +1710,9 @@ fn route_blinding_spec_test_vector() {
 		hop_data: dave_packet_bytes,
 		hmac: dave_hmac,
 	};
+	let dave_forward_info = dave_packet_details.next_hop_forward_info.unwrap();
 	let dave_update_add = update_add_msg(
-		dave_packet_details.outgoing_amt_msat, dave_packet_details.outgoing_cltv_value,
+		dave_forward_info.outgoing_amt_msat, dave_forward_info.outgoing_cltv_value,
 		Some(pubkey_from_hex("031b84c5567b126440995d3ed5aaba0565d71e1834604819ff9c17f5e9d5dd078f")),
 		dave_onion
 	);
@@ -1743,8 +1745,9 @@ fn route_blinding_spec_test_vector() {
 		hop_data: eve_packet_bytes,
 		hmac: eve_hmac,
 	};
+	let eve_forward_info = eve_packet_details.next_hop_forward_info.unwrap();
 	let eve_update_add = update_add_msg(
-		eve_packet_details.outgoing_amt_msat, eve_packet_details.outgoing_cltv_value,
+		eve_forward_info.outgoing_amt_msat, eve_forward_info.outgoing_cltv_value,
 		Some(pubkey_from_hex("03e09038ee76e50f444b19abf0a555e8697e035f62937168b80adf0931b31ce52a")),
 		eve_onion
 	);
@@ -1977,7 +1980,8 @@ fn test_trampoline_inbound_payment_decoding() {
 		hop_data: carol_packet_bytes,
 		hmac: carol_hmac,
 	};
-	let carol_update_add = update_add_msg(carol_packet_details.outgoing_amt_msat, carol_packet_details.outgoing_cltv_value, None, carol_onion);
+	let carol_forward_info = carol_packet_details.next_hop_forward_info.unwrap();
+	let carol_update_add = update_add_msg(carol_forward_info.outgoing_amt_msat, carol_forward_info.outgoing_cltv_value, None, carol_onion);
 
 	let carol_node_signer = TestEcdhSigner { node_secret: carol_secret };
 	let (carol_peeled_onion, _) = onion_payment::decode_incoming_update_add_htlc_onion(

lightning/src/ln/channelmanager.rs

@@ -74,7 +74,7 @@ use crate::ln::msgs::{
 use crate::ln::onion_payment::{
 	check_incoming_htlc_cltv, create_fwd_pending_htlc_info, create_recv_pending_htlc_info,
 	decode_incoming_update_add_htlc_onion, invalid_payment_err_data, HopConnector, InboundHTLCErr,
-	NextPacketDetails,
+	NextHopForwardInfo, NextPacketDetails,
 };
 use crate::ln::onion_utils::{self};
 use crate::ln::onion_utils::{
@@ -4904,7 +4904,7 @@ where
 
 	#[rustfmt::skip]
 	fn can_forward_htlc_to_outgoing_channel(
-		&self, chan: &mut FundedChannel<SP>, msg: &msgs::UpdateAddHTLC, next_packet: &NextPacketDetails
+		&self, chan: &mut FundedChannel<SP>, msg: &msgs::UpdateAddHTLC, forward_info: &NextHopForwardInfo
 	) -> Result<(), LocalHTLCFailureReason> {
 		if !chan.context.should_announce()
 			&& !self.config.read().unwrap().accept_forwards_to_priv_channels
@@ -4914,7 +4914,7 @@ where
 			// we don't allow forwards outbound over them.
 			return Err(LocalHTLCFailureReason::PrivateChannelForward);
 		}
-		if let HopConnector::ShortChannelId(outgoing_scid) = next_packet.outgoing_connector {
+		if let HopConnector::ShortChannelId(outgoing_scid) = forward_info.outgoing_connector {
 			if chan.funding.get_channel_type().supports_scid_privacy() && outgoing_scid != chan.context.outbound_scid_alias() {
 				// `option_scid_alias` (referred to in LDK as `scid_privacy`) means
 				// "refuse to forward unless the SCID alias was used", so we pretend
@@ -4937,10 +4937,10 @@ where
 				return Err(LocalHTLCFailureReason::ChannelNotReady);
 			}
 		}
-		if next_packet.outgoing_amt_msat < chan.context.get_counterparty_htlc_minimum_msat() {
+		if forward_info.outgoing_amt_msat < chan.context.get_counterparty_htlc_minimum_msat() {
 			return Err(LocalHTLCFailureReason::AmountBelowMinimum);
 		}
-		chan.htlc_satisfies_config(msg, next_packet.outgoing_amt_msat, next_packet.outgoing_cltv_value)?;
+		chan.htlc_satisfies_config(msg, forward_info.outgoing_amt_msat, forward_info.outgoing_cltv_value)?;
 
 		Ok(())
 	}
@@ -4972,14 +4972,20 @@ where
 	fn can_forward_htlc(
 		&self, msg: &msgs::UpdateAddHTLC, next_packet_details: &NextPacketDetails
 	) -> Result<(), LocalHTLCFailureReason> {
-		let outgoing_scid = match next_packet_details.outgoing_connector {
+		let next_hop_forward_info = next_packet_details
+			.next_hop_forward_info
+			.as_ref()
+			.ok_or(LocalHTLCFailureReason::InvalidOnionPayload)?;
+
+		let outgoing_scid = match next_hop_forward_info.outgoing_connector {
 			HopConnector::ShortChannelId(scid) => scid,
 			HopConnector::Trampoline(_) => {
 				return Err(LocalHTLCFailureReason::InvalidTrampolineForward);
 			}
 		};
+
 		match self.do_funded_channel_callback(outgoing_scid, |chan: &mut FundedChannel<SP>| {
-			self.can_forward_htlc_to_outgoing_channel(chan, msg, next_packet_details)
+			self.can_forward_htlc_to_outgoing_channel(chan, msg, next_hop_forward_info)
 		}) {
 			Some(Ok(())) => {},
 			Some(Err(e)) => return Err(e),
@@ -4996,7 +5002,7 @@ where
 		}
 
 		let cur_height = self.best_block.read().unwrap().height + 1;
-		check_incoming_htlc_cltv(cur_height, next_packet_details.outgoing_cltv_value, msg.cltv_expiry)?;
+		check_incoming_htlc_cltv(cur_height, next_hop_forward_info.outgoing_cltv_value, msg.cltv_expiry)?;
 
 		Ok(())
 	}
@@ -6951,11 +6957,12 @@ where
 					};
 
 				let is_intro_node_blinded_forward = next_hop.is_intro_node_blinded_forward();
-				let outgoing_scid_opt =
-					next_packet_details_opt.as_ref().and_then(|d| match d.outgoing_connector {
+				let outgoing_scid_opt = next_packet_details_opt.as_ref().and_then(|d| {
+					d.next_hop_forward_info.as_ref().and_then(|f| match f.outgoing_connector {
 						HopConnector::ShortChannelId(scid) => Some(scid),
 						HopConnector::Trampoline(_) => None,
-					});
+					})
+				});
 				let shared_secret = next_hop.shared_secret().secret_bytes();
 
 				// Nodes shouldn't expect us to hold HTLCs for them if we don't advertise htlc_hold feature

lightning/src/ln/onion_payment.rs

@@ -506,16 +506,19 @@ where
 	Ok(match hop {
 		onion_utils::Hop::Forward { shared_secret, .. } |
 		onion_utils::Hop::BlindedForward { shared_secret, .. } => {
-			let NextPacketDetails {
-				next_packet_pubkey, outgoing_amt_msat: _, outgoing_connector: _, outgoing_cltv_value
-			} = match next_packet_details_opt {
-				Some(next_packet_details) => next_packet_details,
+			let (next_packet_pubkey, outgoing_cltv_value) = match next_packet_details_opt {
+				Some(NextPacketDetails {
+					next_packet_pubkey,
+					next_hop_forward_info: Some(NextHopForwardInfo { outgoing_cltv_value, .. }),
+				}) => (next_packet_pubkey, outgoing_cltv_value),
 				// Forward should always include the next hop details
-				None => return Err(InboundHTLCErr {
-					msg: "Failed to decode update add htlc onion",
-					reason: LocalHTLCFailureReason::InvalidOnionPayload,
-					err_data: Vec::new(),
-				}),
+				_ => {
+					return Err(InboundHTLCErr {
+						msg: "Failed to decode update add htlc onion",
+						reason: LocalHTLCFailureReason::InvalidOnionPayload,
+						err_data: Vec::new(),
+					});
+				}
 			};
 
 			if let Err(reason) = check_incoming_htlc_cltv(
@@ -552,6 +555,10 @@ pub(super) enum HopConnector {
 
 pub(super) struct NextPacketDetails {
 	pub(super) next_packet_pubkey: Result<PublicKey, secp256k1::Error>,
+	pub(super) next_hop_forward_info: Option<NextHopForwardInfo>,
+}
+
+pub(super) struct NextHopForwardInfo {
 	pub(super) outgoing_connector: HopConnector,
 	pub(super) outgoing_amt_msat: u64,
 	pub(super) outgoing_cltv_value: u32,
@@ -628,8 +635,12 @@ where
 			let next_packet_pubkey = onion_utils::next_hop_pubkey(secp_ctx,
 				msg.onion_routing_packet.public_key.unwrap(), &shared_secret.secret_bytes());
 			Some(NextPacketDetails {
-				next_packet_pubkey, outgoing_connector: HopConnector::ShortChannelId(short_channel_id),
-				outgoing_amt_msat: amt_to_forward, outgoing_cltv_value
+				next_packet_pubkey,
+				next_hop_forward_info: Some(NextHopForwardInfo {
+					outgoing_connector: HopConnector::ShortChannelId(short_channel_id),
+					outgoing_amt_msat: amt_to_forward,
+					outgoing_cltv_value,
+				}),
 			})
 		}
 		onion_utils::Hop::BlindedForward { next_hop_data: msgs::InboundOnionBlindedForwardPayload { short_channel_id, ref payment_relay, ref payment_constraints, ref features, .. }, shared_secret, .. } => {
@@ -645,19 +656,31 @@ where
 			let next_packet_pubkey = onion_utils::next_hop_pubkey(&secp_ctx,
 				msg.onion_routing_packet.public_key.unwrap(), &shared_secret.secret_bytes());
 			Some(NextPacketDetails {
-				next_packet_pubkey, outgoing_connector: HopConnector::ShortChannelId(short_channel_id), outgoing_amt_msat: amt_to_forward,
-				outgoing_cltv_value
+				next_packet_pubkey,
+				next_hop_forward_info: Some(NextHopForwardInfo {
+					outgoing_connector: HopConnector::ShortChannelId(short_channel_id),
+					outgoing_amt_msat: amt_to_forward,
+					outgoing_cltv_value,
+				}),
 			})
 		}
 		onion_utils::Hop::TrampolineForward { next_trampoline_hop_data: msgs::InboundTrampolineForwardPayload { amt_to_forward, outgoing_cltv_value, next_trampoline }, trampoline_shared_secret, incoming_trampoline_public_key, .. } => {
 			let next_trampoline_packet_pubkey = onion_utils::next_hop_pubkey(secp_ctx,
 				incoming_trampoline_public_key, &trampoline_shared_secret.secret_bytes());
 			Some(NextPacketDetails {
 				next_packet_pubkey: next_trampoline_packet_pubkey,
-				outgoing_connector: HopConnector::Trampoline(next_trampoline),
-				outgoing_amt_msat: amt_to_forward,
-				outgoing_cltv_value,
+				next_hop_forward_info: Some(NextHopForwardInfo {
+					outgoing_connector: HopConnector::Trampoline(next_trampoline),
+					outgoing_amt_msat: amt_to_forward,
+					outgoing_cltv_value,
+				}),
 			})
+		},
+		onion_utils::Hop::Dummy { shared_secret, .. } => {
+			let next_packet_pubkey = onion_utils::next_hop_pubkey(secp_ctx,
+				msg.onion_routing_packet.public_key.unwrap(), &shared_secret.secret_bytes());
+
+			Some(NextPacketDetails { next_packet_pubkey, next_hop_forward_info: None })
 		}
 		onion_utils::Hop::TrampolineBlindedForward { next_trampoline_hop_data: msgs::InboundTrampolineBlindedForwardPayload { next_trampoline, ref payment_relay, ref payment_constraints, ref features, .. }, outer_shared_secret, trampoline_shared_secret, incoming_trampoline_public_key, .. } => {
 			let (amt_to_forward, outgoing_cltv_value) = match check_blinded_forward(
@@ -673,9 +696,11 @@ where
 				incoming_trampoline_public_key, &trampoline_shared_secret.secret_bytes());
 			Some(NextPacketDetails {
 				next_packet_pubkey: next_trampoline_packet_pubkey,
-				outgoing_connector: HopConnector::Trampoline(next_trampoline),
-				outgoing_amt_msat: amt_to_forward,
-				outgoing_cltv_value,
+				next_hop_forward_info: Some(NextHopForwardInfo {
+					outgoing_connector: HopConnector::Trampoline(next_trampoline),
+					outgoing_amt_msat: amt_to_forward,
+					outgoing_cltv_value
+				}),
 			})
 		}
 		_ => None