Add TrampolineForward variant to HTLCSource enum

Add new HTLCSource::TrampolineForward variant to track trampoline routing
information. Implement hash trait and serialization for the new variant.

Author: a-mpch

lightning/src/chain/channelmonitor.rs

@@ -2726,6 +2726,7 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 				let outbound_payment = match source {
 					None => panic!("Outbound HTLCs should have a source"),
 					Some(&HTLCSource::PreviousHopData(_)) => false,
+					Some(&HTLCSource::TrampolineForward { .. }) => false,
 					Some(&HTLCSource::OutboundRoute { .. }) => true,
 				};
 				return Some(Balance::MaybeTimeoutClaimableHTLC {
@@ -2935,6 +2936,7 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitor<Signer> {
 					let outbound_payment = match source {
 						None => panic!("Outbound HTLCs should have a source"),
 						Some(HTLCSource::PreviousHopData(_)) => false,
+						Some(&HTLCSource::TrampolineForward { .. }) => false,
 						Some(HTLCSource::OutboundRoute { .. }) => true,
 					};
 					if outbound_payment {

lightning/src/ln/channelmanager.rs

@@ -646,6 +646,7 @@ impl SentHTLCId {
 				short_channel_id: hop_data.short_channel_id,
 				htlc_id: hop_data.htlc_id,
 			},
+			HTLCSource::TrampolineForward { .. } => todo!(),
 			HTLCSource::OutboundRoute { session_priv, .. } => {
 				Self::OutboundRoute { session_priv: session_priv.secret_bytes() }
 			},
@@ -669,13 +670,25 @@ type PerSourcePendingForward =
 type FailedHTLCForward = (HTLCSource, PaymentHash, HTLCFailReason, HTLCHandlingFailureType);
 
 mod fuzzy_channelmanager {
+	use crate::routing::router::RouteHop;
+
 	use super::*;
 
 	/// Tracks the inbound corresponding to an outbound HTLC
 	#[allow(clippy::derive_hash_xor_eq)] // Our Hash is faithful to the data, we just don't have SecretKey::hash
 	#[derive(Clone, Debug, PartialEq, Eq)]
 	pub enum HTLCSource {
 		PreviousHopData(HTLCPreviousHopData),
+		TrampolineForward {
+			/// We might be forwarding an incoming payment that was received over MPP, and therefore
+			/// need to store the vector of corresponding `HTLCPreviousHopId` values.
+			previous_hop_data: Vec<HTLCPreviousHopData>,
+			incoming_trampoline_shared_secret: [u8; 32],
+			hops: Vec<RouteHop>,
+			/// In order to decode inter-Trampoline errors, we need to store the session_priv key
+			/// given we're effectively creating new outbound routes.
+			session_priv: SecretKey,
+		},
 		OutboundRoute {
 			path: Path,
 			session_priv: SecretKey,
@@ -738,6 +751,18 @@ impl core::hash::Hash for HTLCSource {
 				first_hop_htlc_msat.hash(hasher);
 				bolt12_invoice.hash(hasher);
 			},
+			HTLCSource::TrampolineForward {
+				previous_hop_data,
+				incoming_trampoline_shared_secret,
+				hops,
+				session_priv,
+			} => {
+				2u8.hash(hasher);
+				previous_hop_data.hash(hasher);
+				incoming_trampoline_shared_secret.hash(hasher);
+				hops.hash(hasher);
+				session_priv[..].hash(hasher);
+			},
 		}
 	}
 }
@@ -8050,6 +8075,7 @@ where
 					None,
 				));
 			},
+			HTLCSource::TrampolineForward { .. } => todo!(),
 		}
 	}
 
@@ -8767,6 +8793,7 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 					},
 				);
 			},
+			HTLCSource::TrampolineForward { .. } => todo!(),
 		}
 	}
 
@@ -15064,6 +15091,24 @@ impl Readable for HTLCSource {
 				})
 			}
 			1 => Ok(HTLCSource::PreviousHopData(Readable::read(reader)?)),
+			2 => {
+				let mut previous_hop_data = Vec::new();
+				let mut incoming_trampoline_shared_secret: crate::util::ser::RequiredWrapper<[u8; 32]> = crate::util::ser::RequiredWrapper(None);
+				let mut session_priv: crate::util::ser::RequiredWrapper<SecretKey> = crate::util::ser::RequiredWrapper(None);
+				let mut hops = Vec::new();
+				read_tlv_fields!(reader, {
+					(0, previous_hop_data, required_vec),
+					(2, incoming_trampoline_shared_secret, required),
+					(4, session_priv, required),
+					(6, hops, required_vec),
+				});
+				Ok(HTLCSource::TrampolineForward {
+					previous_hop_data,
+					incoming_trampoline_shared_secret: incoming_trampoline_shared_secret.0.unwrap(),
+					hops,
+					session_priv: session_priv.0.unwrap(),
+				})
+			},
 			_ => Err(DecodeError::UnknownRequiredFeature),
 		}
 	}
@@ -15096,6 +15141,22 @@ impl Writeable for HTLCSource {
 				1u8.write(writer)?;
 				field.write(writer)?;
 			},
+			HTLCSource::TrampolineForward {
+				previous_hop_data: previous_hop_data_ref,
+				ref incoming_trampoline_shared_secret,
+				ref session_priv,
+				hops: hops_ref,
+			} => {
+				2u8.write(writer)?;
+				let previous_hop_data = previous_hop_data_ref.clone();
+				let hops = hops_ref.clone();
+				write_tlv_fields!(writer, {
+					(0, previous_hop_data, required_vec),
+					(2, incoming_trampoline_shared_secret, required),
+					(4, session_priv, required),
+					(6, hops, required_vec),
+				});
+			},
 		}
 		Ok(())
 	}
@@ -16539,6 +16600,7 @@ where
 									} else { true }
 								});
 							},
+							HTLCSource::TrampolineForward { .. } => todo!(),
 							HTLCSource::OutboundRoute {
 								payment_id,
 								session_priv,

lightning/src/util/ser.rs

@@ -1077,6 +1077,7 @@ impl Readable for Vec<u8> {
 
 impl_for_vec!(ecdsa::Signature);
 impl_for_vec!(crate::chain::channelmonitor::ChannelMonitorUpdate);
+impl_for_vec!(crate::ln::channelmanager::HTLCPreviousHopData);
 impl_for_vec!(crate::ln::channelmanager::MonitorUpdateCompletionAction);
 impl_for_vec!(crate::ln::channelmanager::PaymentClaimDetails);
 impl_for_vec!(crate::ln::msgs::SocketAddress);
@@ -1087,6 +1088,7 @@ impl_for_vec!(InteractiveTxOutput);
 impl_for_vec!(crate::ln::our_peer_storage::PeerStorageMonitorHolder);
 impl_writeable_for_vec!(&crate::routing::router::BlindedTail);
 impl_readable_for_vec!(crate::routing::router::BlindedTail);
+impl_for_vec!(crate::routing::router::RouteHop);
 impl_for_vec!(crate::routing::router::TrampolineHop);
 impl_for_vec_with_element_length_prefix!(crate::ln::msgs::UpdateAddHTLC);
 impl_writeable_for_vec_with_element_length_prefix!(&crate::ln::msgs::UpdateAddHTLC);