Fix PaymentPathFailed::payment_failed_permanently on blinded path fail

Previously this value would be incorrectly set to true because we wouldn't
account for blinded hops when determining if we were processing the last hop's
failure packet.

diff --git a/lightning/src/ln/onion_utils.rs b/lightning/src/ln/onion_utils.rs
index 4b5ccfe92dd1ce2d768950eee2c1c6df5fa31b3d..f3f8608604d3230ee113996a21f64d36720cd49a 100644 (file)
--- a/lightning/src/ln/onion_utils.rs
+++ b/lightning/src/ln/onion_utils.rs
@@ -481,6 +481,26 @@ pub(super) fn process_onion_failure<T: secp256k1::Signing, L: Deref>(
                        },
                };
 
+               // The failing hop includes either the inbound channel to the recipient or the outbound channel
+               // from the current hop (i.e., the next hop's inbound channel).
+               let num_blinded_hops = path.blinded_tail.as_ref().map_or(0, |bt| bt.hops.len());
+               // For 1-hop blinded paths, the final `path.hops` entry is the recipient.
+               is_from_final_node = route_hop_idx + 1 == path.hops.len() && num_blinded_hops <= 1;
+               let failing_route_hop = if is_from_final_node { route_hop } else {
+                       match path.hops.get(route_hop_idx + 1) {
+                               Some(hop) => hop,
+                               None => {
+                                       // The failing hop is within a multi-hop blinded path.
+                                       error_code_ret = Some(BADONION | PERM | 24); // invalid_onion_blinding
+                                       error_packet_ret = Some(vec![0; 32]);
+                                       res = Some(FailureLearnings {
+                                               network_update: None, short_channel_id: None, payment_failed_permanently: false
+                                       });
+                                       return
+                               }
+                       }
+               };
+
                let amt_to_forward = htlc_msat - route_hop.fee_msat;
                htlc_msat = amt_to_forward;
 
@@ -492,11 +512,6 @@ pub(super) fn process_onion_failure<T: secp256k1::Signing, L: Deref>(
                chacha.process(&packet_decrypted, &mut decryption_tmp[..]);
                packet_decrypted = decryption_tmp;
 
-               // The failing hop includes either the inbound channel to the recipient or the outbound channel
-               // from the current hop (i.e., the next hop's inbound channel).
-               is_from_final_node = route_hop_idx + 1 == path.hops.len();
-               let failing_route_hop = if is_from_final_node { route_hop } else { &path.hops[route_hop_idx + 1] };
-
                let err_packet = match msgs::DecodedOnionErrorPacket::read(&mut Cursor::new(&packet_decrypted)) {
                        Ok(p) => p,
                        Err(_) => return