fix

Author: naumenkogs

lightning/src/routing/router.rs

@@ -200,6 +200,7 @@ struct PathBuildingHop {
 	/// hop_use_fee_msat pays for the following hops, but is deducted on this one.
 	/// Should not be updated manually and generally should not be accessed.
 	effective_htlc_minimum_msat: u64,
+	overpaid_fee_msat: u64,
 }
 
 impl PathBuildingHop {
@@ -518,8 +519,13 @@ pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, paye
 					// If HTLC minimum is larger than the amount we're going to transfer, we shouldn
 					// transfer that value instead, thus overpaying fees.
 					let effective_htlc_minimum_msat = cmp::max($directional_info.htlc_minimum_msat, $incl_fee_next_hops_htlc_minimum_msat);
-					amount_to_transfer_over_msat = cmp::max(amount_to_transfer_over_msat, effective_htlc_minimum_msat);
-					if contributes_sufficient_value {
+					println!("{} transfer over {} {}", $chan_id, amount_to_transfer_over_msat, effective_htlc_minimum_msat);
+					let overpaid_fee_msat = match effective_htlc_minimum_msat.checked_sub(amount_to_transfer_over_msat) {
+						Some(fee_msat) => fee_msat,
+						None => 0,
+					};
+					amount_to_transfer_over_msat += overpaid_fee_msat;
+					if contributes_sufficient_value  {
 						let hm_entry = dist.entry(&$src_node_id);
 						let old_entry = hm_entry.or_insert_with(|| {
 							// If there was previously no known way to access
@@ -552,6 +558,7 @@ pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, paye
 								total_fee_msat: u64::max_value(),
 								htlc_minimum_msat: $directional_info.htlc_minimum_msat,
 								effective_htlc_minimum_msat,
+								overpaid_fee_msat
 							}
 						});
 
@@ -613,14 +620,15 @@ pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, paye
 								node_features: NodeFeatures::empty(),
 								short_channel_id: $chan_id.clone(),
 								channel_features: $chan_features.clone(),
-								fee_msat: 0, // This value will be later filled with hop_use_fee_msat of the following channel
+								fee_msat: 0,
 								cltv_expiry_delta: $directional_info.cltv_expiry_delta as u32,
 							};
 							old_entry.channel_fees = $directional_info.fees;
 							// It's probably fine to replace the old entry, because the new one
 							// passed the htlc_minimum-related checks above.
 							old_entry.htlc_minimum_msat = cmp::max($directional_info.htlc_minimum_msat, old_entry.htlc_minimum_msat);
 							old_entry.effective_htlc_minimum_msat = effective_htlc_minimum_msat;
+							old_entry.overpaid_fee_msat = overpaid_fee_msat;
 						}
 					}
 				}
@@ -806,11 +814,11 @@ pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, paye
 					// We "propagate" the fees one hop backward (topologically) here,
 					// so that fees paid for a HTLC forwarding on the current channel are
 					// associated with the previous channel (where they will be subtracted).
-					ordered_hops.last_mut().unwrap().route_hop.fee_msat = new_entry.hop_use_fee_msat;
+					ordered_hops.last_mut().unwrap().route_hop.fee_msat = new_entry.hop_use_fee_msat + ordered_hops.last_mut().unwrap().overpaid_fee_msat;
 					ordered_hops.last_mut().unwrap().route_hop.cltv_expiry_delta = new_entry.route_hop.cltv_expiry_delta;
 					ordered_hops.push(new_entry.clone());
 				}
-				ordered_hops.last_mut().unwrap().route_hop.fee_msat = value_contribution_msat;
+				ordered_hops.last_mut().unwrap().route_hop.fee_msat = value_contribution_msat + ordered_hops.last_mut().unwrap().overpaid_fee_msat;
 				ordered_hops.last_mut().unwrap().hop_use_fee_msat = 0;
 				ordered_hops.last_mut().unwrap().route_hop.cltv_expiry_delta = final_cltv;