From b11dcf9ba8c75b50c5915402ad8c29b972b0f8a0 Mon Sep 17 00:00:00 2001 From: Elias Rohrer Date: Thu, 24 Mar 2022 09:12:26 -0600 Subject: [PATCH 1/2] Randomize candidate paths during route selection. --- lightning/src/routing/router.rs | 40 +++++++++++++++++++++++---------- 1 file changed, 28 insertions(+), 12 deletions(-) diff --git a/lightning/src/routing/router.rs b/lightning/src/routing/router.rs index 1b52af881..8a2aecb58 100644 --- a/lightning/src/routing/router.rs +++ b/lightning/src/routing/router.rs @@ -495,6 +495,10 @@ impl<'a> PaymentPath<'a> { self.hops.last().unwrap().0.fee_msat } + fn get_path_penalty_msat(&self) -> u64 { + self.hops.first().map(|h| h.0.path_penalty_msat).unwrap_or(u64::max_value()) + } + fn get_total_fee_paid_msat(&self) -> u64 { if self.hops.len() < 1 { return 0; @@ -645,7 +649,7 @@ where L::Target: Logger { pub(crate) fn get_route( our_node_pubkey: &PublicKey, payment_params: &PaymentParameters, network_graph: &ReadOnlyNetworkGraph, first_hops: Option<&[&ChannelDetails]>, final_value_msat: u64, final_cltv_expiry_delta: u32, - logger: L, scorer: &S, _random_seed_bytes: &[u8; 32] + logger: L, scorer: &S, random_seed_bytes: &[u8; 32] ) -> Result where L::Target: Logger { let payee_node_id = NodeId::from_pubkey(&payment_params.payee_pubkey); @@ -1449,17 +1453,24 @@ where L::Target: Logger { // Draw multiple sufficient routes by randomly combining the selected paths. let mut drawn_routes = Vec::new(); - for i in 0..payment_paths.len() { + let mut prng = ChaCha20::new(random_seed_bytes, &[0u8; 12]); + let mut random_index_bytes = [0u8; ::core::mem::size_of::()]; + + let num_permutations = payment_paths.len(); + for _ in 0..num_permutations { let mut cur_route = Vec::::new(); let mut aggregate_route_value_msat = 0; // Step (6). - // TODO: real random shuffle - // Currently just starts with i_th and goes up to i-1_th in a looped way. - let cur_payment_paths = [&payment_paths[i..], &payment_paths[..i]].concat(); + // Do a Fisher-Yates shuffle to create a random permutation of the payment paths + for cur_index in (1..payment_paths.len()).rev() { + prng.process_in_place(&mut random_index_bytes); + let random_index = usize::from_be_bytes(random_index_bytes).wrapping_rem(cur_index+1); + payment_paths.swap(cur_index, random_index); + } // Step (7). - for payment_path in cur_payment_paths { + for payment_path in &payment_paths { cur_route.push(payment_path.clone()); aggregate_route_value_msat += payment_path.get_value_msat(); if aggregate_route_value_msat > final_value_msat { @@ -1469,12 +1480,17 @@ where L::Target: Logger { // also makes routing more reliable. let mut overpaid_value_msat = aggregate_route_value_msat - final_value_msat; - // First, drop some expensive low-value paths entirely if possible. - // Sort by value so that we drop many really-low values first, since - // fewer paths is better: the payment is less likely to fail. - // TODO: this could also be optimized by also sorting by feerate_per_sat_routed, - // so that the sender pays less fees overall. And also htlc_minimum_msat. - 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 we + // 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()))) + }); + // We should make sure that at least 1 path left. let mut paths_left = cur_route.len(); cur_route.retain(|path| { From ff7ec0c645c767bc94b692300b1f7611c79c86dd Mon Sep 17 00:00:00 2001 From: Elias Rohrer Date: Thu, 24 Mar 2022 09:12:44 -0600 Subject: [PATCH 2/2] Minor refactor for sort / add, and some nits. - `sort_by_key` to `sort_unstable_by_key` - `checked_add() .. max_value()` to `saturating_add()` - Some typos and nits --- lightning/src/routing/router.rs | 42 ++++++++++++++------------------- 1 file changed, 18 insertions(+), 24 deletions(-) diff --git a/lightning/src/routing/router.rs b/lightning/src/routing/router.rs index 8a2aecb58..f1eeac90e 100644 --- a/lightning/src/routing/router.rs +++ b/lightning/src/routing/router.rs @@ -332,11 +332,9 @@ struct RouteGraphNode { impl cmp::Ord for RouteGraphNode { fn cmp(&self, other: &RouteGraphNode) -> cmp::Ordering { let other_score = cmp::max(other.lowest_fee_to_peer_through_node, other.path_htlc_minimum_msat) - .checked_add(other.path_penalty_msat) - .unwrap_or_else(|| u64::max_value()); + .saturating_add(other.path_penalty_msat); let self_score = cmp::max(self.lowest_fee_to_peer_through_node, self.path_htlc_minimum_msat) - .checked_add(self.path_penalty_msat) - .unwrap_or_else(|| u64::max_value()); + .saturating_add(self.path_penalty_msat); other_score.cmp(&self_score).then_with(|| other.node_id.cmp(&self.node_id)) } } @@ -837,7 +835,7 @@ where L::Target: Logger { .entry(short_channel_id) .or_insert_with(|| $candidate.effective_capacity().as_msat()); - // It is tricky to substract $next_hops_fee_msat from available liquidity here. + // It is tricky to subtract $next_hops_fee_msat from available liquidity here. // It may be misleading because we might later choose to reduce the value transferred // over these channels, and the channel which was insufficient might become sufficient. // Worst case: we drop a good channel here because it can't cover the high following @@ -877,8 +875,7 @@ where L::Target: Logger { .checked_sub(2*MEDIAN_HOP_CLTV_EXPIRY_DELTA) .unwrap_or(payment_params.max_total_cltv_expiry_delta - final_cltv_expiry_delta); let hop_total_cltv_delta = ($next_hops_cltv_delta as u32) - .checked_add($candidate.cltv_expiry_delta()) - .unwrap_or(u32::max_value()); + .saturating_add($candidate.cltv_expiry_delta()); let doesnt_exceed_cltv_delta_limit = hop_total_cltv_delta <= max_total_cltv_expiry_delta; let value_contribution_msat = cmp::min(available_value_contribution_msat, $next_hops_value_contribution); @@ -985,9 +982,9 @@ where L::Target: Logger { } } - let path_penalty_msat = $next_hops_path_penalty_msat.checked_add( - scorer.channel_penalty_msat(short_channel_id, amount_to_transfer_over_msat, *available_liquidity_msat, - &$src_node_id, &$dest_node_id)).unwrap_or_else(|| u64::max_value()); + let path_penalty_msat = $next_hops_path_penalty_msat.saturating_add( + scorer.channel_penalty_msat(short_channel_id, amount_to_transfer_over_msat, + *available_liquidity_msat, &$src_node_id, &$dest_node_id)); let new_graph_node = RouteGraphNode { node_id: $src_node_id, lowest_fee_to_peer_through_node: total_fee_msat, @@ -1015,11 +1012,9 @@ where L::Target: Logger { // the fees included in $next_hops_path_htlc_minimum_msat, but also // can't use something that may decrease on future hops. let old_cost = cmp::max(old_entry.total_fee_msat, old_entry.path_htlc_minimum_msat) - .checked_add(old_entry.path_penalty_msat) - .unwrap_or_else(|| u64::max_value()); + .saturating_add(old_entry.path_penalty_msat); let new_cost = cmp::max(total_fee_msat, path_htlc_minimum_msat) - .checked_add(path_penalty_msat) - .unwrap_or_else(|| u64::max_value()); + .saturating_add(path_penalty_msat); if !old_entry.was_processed && new_cost < old_cost { targets.push(new_graph_node); @@ -1203,12 +1198,10 @@ where L::Target: Logger { .unwrap_or_else(|| CandidateRouteHop::PrivateHop { hint: hop }); let capacity_msat = candidate.effective_capacity().as_msat(); aggregate_next_hops_path_penalty_msat = aggregate_next_hops_path_penalty_msat - .checked_add(scorer.channel_penalty_msat(hop.short_channel_id, final_value_msat, capacity_msat, &source, &target)) - .unwrap_or_else(|| u64::max_value()); + .saturating_add(scorer.channel_penalty_msat(hop.short_channel_id, final_value_msat, capacity_msat, &source, &target)); aggregate_next_hops_cltv_delta = aggregate_next_hops_cltv_delta - .checked_add(hop.cltv_expiry_delta as u32) - .unwrap_or_else(|| u32::max_value()); + .saturating_add(hop.cltv_expiry_delta as u32); if !add_entry!(candidate, source, target, aggregate_next_hops_fee_msat, path_value_msat, aggregate_next_hops_path_htlc_minimum_msat, aggregate_next_hops_path_penalty_msat, aggregate_next_hops_cltv_delta) { // If this hop was not used then there is no use checking the preceding hops @@ -1446,7 +1439,7 @@ where L::Target: Logger { } // Sort by total fees and take the best paths. - payment_paths.sort_by_key(|path| path.get_total_fee_paid_msat()); + payment_paths.sort_unstable_by_key(|path| path.get_total_fee_paid_msat()); if payment_paths.len() > 50 { payment_paths.truncate(50); } @@ -1514,13 +1507,14 @@ where L::Target: Logger { assert!(cur_route.len() > 0); // Step (8). - // Now, substract the overpaid value from the most-expensive path. + // Now, subtract the overpaid value from the most-expensive path. // TODO: this could also be optimized by also sorting by feerate_per_sat_routed, // so that the sender pays less fees overall. And also htlc_minimum_msat. - cur_route.sort_by_key(|path| { path.hops.iter().map(|hop| hop.0.candidate.fees().proportional_millionths as u64).sum::() }); + cur_route.sort_unstable_by_key(|path| { path.hops.iter().map(|hop| hop.0.candidate.fees().proportional_millionths as u64).sum::() }); let expensive_payment_path = cur_route.first_mut().unwrap(); - // We already dropped all the small channels above, meaning all the - // remaining channels are larger than remaining overpaid_value_msat. + + // We already dropped all the small value paths above, meaning all the + // remaining paths are larger than remaining overpaid_value_msat. // Thus, this can't be negative. let expensive_path_new_value_msat = expensive_payment_path.get_value_msat() - overpaid_value_msat; expensive_payment_path.update_value_and_recompute_fees(expensive_path_new_value_msat); @@ -1532,7 +1526,7 @@ where L::Target: Logger { // Step (9). // Select the best route by lowest total fee. - drawn_routes.sort_by_key(|paths| paths.iter().map(|path| path.get_total_fee_paid_msat()).sum::()); + drawn_routes.sort_unstable_by_key(|paths| paths.iter().map(|path| path.get_total_fee_paid_msat()).sum::()); let mut selected_paths = Vec::>>::new(); for payment_path in drawn_routes.first().unwrap() { let mut path = payment_path.hops.iter().map(|(payment_hop, node_features)| {