Select best route by lowest total cost

Selecting only by fees rather than cost (fees plus penalty) may result
in preferring higher cost routes over lower cost ones.

diff --git a/lightning/src/routing/router.rs b/lightning/src/routing/router.rs
index 003dc6006db6adc620637b8069e0fdfdc83d64c1..7f6b3afdebc3fe7edbd097e41ffea8fc9fa4fb58 100644 (file)
--- a/lightning/src/routing/router.rs
+++ b/lightning/src/routing/router.rs
@@ -511,6 +511,10 @@ impl<'a> PaymentPath<'a> {
                return result;
        }
 
+       fn get_cost_msat(&self) -> u64 {
+               self.get_total_fee_paid_msat().saturating_add(self.get_path_penalty_msat())
+       }
+
        // If the amount transferred by the path is updated, the fees should be adjusted. Any other way
        // to change fees may result in an inconsistency.
        //
@@ -1502,9 +1506,8 @@ where L::Target: Logger {
                                // prefer lower cost paths.
                                cur_route.sort_unstable_by(|a, b| {
                                        a.get_value_msat().cmp(&b.get_value_msat())
-                                               // Reverse ordering for fees, so we drop higher-fee paths first
-                                               .then_with(|| b.get_total_fee_paid_msat().saturating_add(b.get_path_penalty_msat())
-                                                       .cmp(&a.get_total_fee_paid_msat().saturating_add(a.get_path_penalty_msat())))
+                                               // Reverse ordering for cost, so we drop higher-cost paths first
+                                               .then_with(|| b.get_cost_msat().cmp(&a.get_cost_msat()))
                                });
 
                                // We should make sure that at least 1 path left.
@@ -1548,8 +1551,8 @@ where L::Target: Logger {
        }
 
        // Step (9).
-       // Select the best route by lowest total fee.
-       drawn_routes.sort_unstable_by_key(|paths| paths.iter().map(|path| path.get_total_fee_paid_msat()).sum::<u64>());
+       // Select the best route by lowest total cost.
+       drawn_routes.sort_unstable_by_key(|paths| paths.iter().map(|path| path.get_cost_msat()).sum::<u64>());
        let mut selected_paths = Vec::<Vec<Result<RouteHop, LightningError>>>::new();
        for payment_path in drawn_routes.first().unwrap() {
                let mut path = payment_path.hops.iter().map(|(payment_hop, node_features)| {