Sort candidate route once with custom comparator.

Author: tnull

lightning/src/routing/router.rs

@@ -1485,16 +1485,22 @@ where L::Target: Logger {
 				// also makes routing more reliable.
 				let mut overpaid_value_msat = aggregate_route_value_msat - final_value_msat;
 
-				// First, we drop some expensive low-value paths entirely if possible.
-				// In order to do so, we pre-sort by total fees paid, so that in case of equal
-				// values we prefer lower cost paths.
-				// (Descending order, so we drop higher-fee paths first)
-				cur_route.sort_by_key(|path| path.get_total_fee_paid_msat());
-				cur_route.reverse();
-
-				// Then sort by value so that we drop many really-low values first, since
-				// fewer paths is better: the payment is less likely to fail.
-				cur_route.sort_by_key(|path| path.get_value_msat());
+				// First, we drop some expensive low-value paths entirely if possible, since fewer
+				// paths is better: the payment is less likely to fail. In order to do so, we sort
+				// by value and fall back to total fees paid, i.e., in case of equal values values
+				// we prefer lower cost paths.
+				cur_route.sort_unstable_by(|a, b| {
+					let a_value = a.get_value_msat();
+					let b_value = b.get_value_msat();
+					if a_value.cmp(&b_value).is_eq() {
+						let a_fees = a.get_total_fee_paid_msat();
+						let b_fees = b.get_total_fee_paid_msat();
+						// Reverse ordering here, so we drop higher-fee paths first
+						b_fees.cmp(&a_fees)
+					} else {
+						a_value.cmp(&b_value)
+					}
+				});
 
 				// We should make sure that at least 1 path left.
 				let mut paths_left = cur_route.len();