Add failure mode info to BlindedForward struct.

See added docs.

Author: valentinewallace

lightning/src/ln/channelmanager.rs

@@ -202,7 +202,9 @@ pub struct BlindedForward {
 	/// onion payload if we're the introduction node. Useful for calculating the next hop's
 	/// [`msgs::UpdateAddHTLC::blinding_point`].
 	pub inbound_blinding_point: PublicKey,
-	// Another field will be added here when we support forwarding as a non-intro node.
+	/// If needed, this determines how this HTLC should be failed backwards, based on whether we are
+	/// the introduction node.
+	pub failure: BlindedFailure,
 }
 
 impl PendingHTLCRouting {
@@ -9500,6 +9502,7 @@ impl_writeable_tlv_based!(PhantomRouteHints, {
 
 impl_writeable_tlv_based!(BlindedForward, {
 	(0, inbound_blinding_point, required),
+	(1, failure, (default_value, BlindedFailure::FromIntroductionNode)),
 });
 
 impl_writeable_tlv_based_enum!(PendingHTLCRouting,

lightning/src/ln/onion_payment.rs

@@ -12,7 +12,7 @@ use crate::blinded_path;
 use crate::blinded_path::payment::{PaymentConstraints, PaymentRelay};
 use crate::chain::channelmonitor::{HTLC_FAIL_BACK_BUFFER, LATENCY_GRACE_PERIOD_BLOCKS};
 use crate::ln::PaymentHash;
-use crate::ln::channelmanager::{BlindedForward, CLTV_FAR_FAR_AWAY, HTLCFailureMsg, MIN_CLTV_EXPIRY_DELTA, PendingHTLCInfo, PendingHTLCRouting};
+use crate::ln::channelmanager::{BlindedFailure, BlindedForward, CLTV_FAR_FAR_AWAY, HTLCFailureMsg, MIN_CLTV_EXPIRY_DELTA, PendingHTLCInfo, PendingHTLCRouting};
 use crate::ln::features::BlindedHopFeatures;
 use crate::ln::msgs;
 use crate::ln::onion_utils;
@@ -106,7 +106,12 @@ pub(super) fn create_fwd_pending_htlc_info(
 			onion_packet: outgoing_packet,
 			short_channel_id,
 			blinded: intro_node_blinding_point.or(msg.blinding_point)
-				.map(|bp| BlindedForward { inbound_blinding_point: bp }),
+				.map(|bp| BlindedForward {
+					inbound_blinding_point: bp,
+					failure: intro_node_blinding_point
+						.map(|_| BlindedFailure::FromIntroductionNode)
+						.unwrap_or(BlindedFailure::FromBlindedNode),
+				}),
 		},
 		payment_hash: msg.payment_hash,
 		incoming_shared_secret: shared_secret,