From e43cfbd5f16c0c1d0a62a499dd356335e6eef4b9 Mon Sep 17 00:00:00 2001 From: Gleb Naumenko Date: Tue, 7 Mar 2023 10:01:05 +0200 Subject: [PATCH] Consider commitment tx fee while assembling a route When calculating the amount available to send for the next HTLC, if we over-count we may create routes which are not actually usable. Historically this has been an issue, which we resolve over a few commits. Here we include the cost of the commitment transaction fee in our calculation, subtracting the commitment tx fee cost from the available as we do in `send_payment`. We also add some testing when sending to ensure that send failures are accounted for in our balance calculations. This commit is based on original work by Gleb Naumenko and modified by Matt Corallo . --- lightning/src/ln/channel.rs | 48 +++++++++++++++++++++++++--- lightning/src/ln/functional_tests.rs | 26 +++++++++++---- 2 files changed, 62 insertions(+), 12 deletions(-) diff --git a/lightning/src/ln/channel.rs b/lightning/src/ln/channel.rs index 829ce3a99..bda0bfa50 100644 --- a/lightning/src/ln/channel.rs +++ b/lightning/src/ln/channel.rs @@ -2686,10 +2686,45 @@ impl Channel { } balance_msat -= outbound_stats.pending_htlcs_value_msat; - let outbound_capacity_msat = cmp::max(self.value_to_self_msat as i64 - - outbound_stats.pending_htlcs_value_msat as i64 - - self.counterparty_selected_channel_reserve_satoshis.unwrap_or(0) as i64 * 1000, - 0) as u64; + let outbound_capacity_msat = self.value_to_self_msat + .saturating_sub(outbound_stats.pending_htlcs_value_msat) + .saturating_sub( + self.counterparty_selected_channel_reserve_satoshis.unwrap_or(0) * 1000); + + let mut available_capacity_msat = outbound_capacity_msat; + + if self.is_outbound() { + // We should mind channel commit tx fee when computing how much of the available capacity + // can be used in the next htlc. Mirrors the logic in send_htlc. + // + // The fee depends on whether the amount we will be sending is above dust or not, + // and the answer will in turn change the amount itself — making it a circular + // dependency. + // This complicates the computation around dust-values, up to the one-htlc-value. + let mut real_dust_limit_timeout_sat = self.holder_dust_limit_satoshis; + if !self.opt_anchors() { + real_dust_limit_timeout_sat += self.feerate_per_kw as u64 * htlc_timeout_tx_weight(false) / 1000; + } + + let htlc_above_dust = HTLCCandidate::new(real_dust_limit_timeout_sat * 1000, HTLCInitiator::LocalOffered); + let max_reserved_commit_tx_fee_msat = FEE_SPIKE_BUFFER_FEE_INCREASE_MULTIPLE * self.next_local_commit_tx_fee_msat(htlc_above_dust, Some(())); + let htlc_dust = HTLCCandidate::new(real_dust_limit_timeout_sat * 1000 - 1, HTLCInitiator::LocalOffered); + let min_reserved_commit_tx_fee_msat = FEE_SPIKE_BUFFER_FEE_INCREASE_MULTIPLE * self.next_local_commit_tx_fee_msat(htlc_dust, Some(())); + + // We will first subtract the fee as if we were above-dust. Then, if the resulting + // value ends up being below dust, we have this fee available again. In that case, + // match the value to right-below-dust. + let mut capacity_minus_commitment_fee_msat: i64 = (available_capacity_msat as i64) - (max_reserved_commit_tx_fee_msat as i64); + if capacity_minus_commitment_fee_msat < (real_dust_limit_timeout_sat as i64) * 1000 { + let one_htlc_difference_msat = max_reserved_commit_tx_fee_msat - min_reserved_commit_tx_fee_msat; + debug_assert!(one_htlc_difference_msat != 0); + capacity_minus_commitment_fee_msat += one_htlc_difference_msat as i64; + capacity_minus_commitment_fee_msat = cmp::min(real_dust_limit_timeout_sat as i64 * 1000 - 1, capacity_minus_commitment_fee_msat); + available_capacity_msat = cmp::max(0, cmp::min(capacity_minus_commitment_fee_msat, available_capacity_msat as i64)) as u64; + } else { + available_capacity_msat = capacity_minus_commitment_fee_msat as u64; + } + } AvailableBalances { inbound_capacity_msat: cmp::max(self.channel_value_satoshis as i64 * 1000 - self.value_to_self_msat as i64 @@ -2697,7 +2732,7 @@ impl Channel { - self.holder_selected_channel_reserve_satoshis as i64 * 1000, 0) as u64, outbound_capacity_msat, - next_outbound_htlc_limit_msat: cmp::max(cmp::min(outbound_capacity_msat as i64, + next_outbound_htlc_limit_msat: cmp::max(cmp::min(available_capacity_msat as i64, self.counterparty_max_htlc_value_in_flight_msat as i64 - outbound_stats.pending_htlcs_value_msat as i64), 0) as u64, @@ -5896,6 +5931,7 @@ impl Channel { let holder_balance_msat = self.value_to_self_msat .saturating_sub(outbound_stats.pending_htlcs_value_msat); if holder_balance_msat < amount_msat { + debug_assert!(amount_msat > self.get_available_balances().next_outbound_htlc_limit_msat); return Err(ChannelError::Ignore(format!("Cannot send value that would overdraw remaining funds. Amount: {}, pending value to self {}", amount_msat, holder_balance_msat))); } @@ -5905,6 +5941,7 @@ impl Channel { FEE_SPIKE_BUFFER_FEE_INCREASE_MULTIPLE * self.next_local_commit_tx_fee_msat(htlc_candidate, Some(())) } else { 0 }; if holder_balance_msat - amount_msat < commit_tx_fee_msat { + debug_assert!(amount_msat > self.get_available_balances().next_outbound_htlc_limit_msat); return Err(ChannelError::Ignore(format!("Cannot send value that would not leave enough to pay for fees. Pending value to self: {}. local_commit_tx_fee {}", holder_balance_msat, commit_tx_fee_msat))); } @@ -5912,6 +5949,7 @@ impl Channel { // reserve for the remote to have something to claim if we misbehave) let chan_reserve_msat = self.counterparty_selected_channel_reserve_satoshis.unwrap() * 1000; if holder_balance_msat - amount_msat - commit_tx_fee_msat < chan_reserve_msat { + debug_assert!(amount_msat > self.get_available_balances().next_outbound_htlc_limit_msat); return Err(ChannelError::Ignore(format!("Cannot send value that would put our balance under counterparty-announced channel reserve value ({})", chan_reserve_msat))); } diff --git a/lightning/src/ln/functional_tests.rs b/lightning/src/ln/functional_tests.rs index 92a6e2695..81c42861a 100644 --- a/lightning/src/ln/functional_tests.rs +++ b/lightning/src/ln/functional_tests.rs @@ -1342,7 +1342,9 @@ fn test_basic_channel_reserve() { // The 2* and +1 are for the fee spike reserve. let commit_tx_fee = 2 * commit_tx_fee_msat(get_feerate!(nodes[0], nodes[1], chan.2), 1 + 1, get_opt_anchors!(nodes[0], nodes[1], chan.2)); let max_can_send = 5000000 - channel_reserve - commit_tx_fee; - let (route, our_payment_hash, _, our_payment_secret) = get_route_and_payment_hash!(nodes[0], nodes[1], max_can_send + 1); + let (mut route, our_payment_hash, _, our_payment_secret) = + get_route_and_payment_hash!(nodes[0], nodes[1], max_can_send); + route.paths[0].hops.last_mut().unwrap().fee_msat += 1; let err = nodes[0].node.send_payment_with_route(&route, our_payment_hash, RecipientOnionFields::secret_only(our_payment_secret), PaymentId(our_payment_hash.0)).err().unwrap(); match err { @@ -1369,7 +1371,9 @@ fn test_fee_spike_violation_fails_htlc() { let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs); let chan = create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 100000, 95000000); - let (route, payment_hash, _, payment_secret) = get_route_and_payment_hash!(nodes[0], nodes[1], 3460001); + let (mut route, payment_hash, _, payment_secret) = + get_route_and_payment_hash!(nodes[0], nodes[1], 3460000); + route.paths[0].hops[0].fee_msat += 1; // Need to manually create the update_add_htlc message to go around the channel reserve check in send_htlc() let secp_ctx = Secp256k1::new(); let session_priv = SecretKey::from_slice(&[42; 32]).expect("RNG is bad!"); @@ -1732,7 +1736,8 @@ fn test_chan_reserve_violation_inbound_htlc_inbound_chan() { let commit_tx_fee_2_htlcs = commit_tx_fee_msat(feerate, 2, opt_anchors); let recv_value_2 = chan_stat.value_to_self_msat - amt_msat_1 - chan_stat.channel_reserve_msat - total_routing_fee_msat - commit_tx_fee_2_htlcs + 1; let amt_msat_2 = recv_value_2 + total_routing_fee_msat; - let (route_2, _, _, _) = get_route_and_payment_hash!(nodes[0], nodes[2], amt_msat_2); + let mut route_2 = route_1.clone(); + route_2.paths[0].hops.last_mut().unwrap().fee_msat = amt_msat_2; // Need to manually create the update_add_htlc message to go around the channel reserve check in send_htlc() let secp_ctx = Secp256k1::new(); @@ -1901,7 +1906,9 @@ fn test_channel_reserve_holding_cell_htlcs() { // channel reserve test with htlc pending output > 0 let recv_value_2 = stat01.value_to_self_msat - amt_msat_1 - stat01.channel_reserve_msat - total_fee_msat - commit_tx_fee_2_htlcs; { - let (route, our_payment_hash, _, our_payment_secret) = get_route_and_payment_hash!(nodes[0], nodes[2], recv_value_2 + 1); + let mut route = route_1.clone(); + route.paths[0].hops.last_mut().unwrap().fee_msat = recv_value_2 + 1; + let (_, our_payment_hash, our_payment_secret) = get_payment_preimage_hash!(nodes[2]); unwrap_send_err!(nodes[0].node.send_payment_with_route(&route, our_payment_hash, RecipientOnionFields::secret_only(our_payment_secret), PaymentId(our_payment_hash.0) ), true, APIError::ChannelUnavailable { ref err }, @@ -1930,7 +1937,9 @@ fn test_channel_reserve_holding_cell_htlcs() { // test with outbound holding cell amount > 0 { - let (route, our_payment_hash, _, our_payment_secret) = get_route_and_payment_hash!(nodes[0], nodes[2], recv_value_22+1); + let (mut route, our_payment_hash, _, our_payment_secret) = + get_route_and_payment_hash!(nodes[0], nodes[2], recv_value_22); + route.paths[0].hops.last_mut().unwrap().fee_msat += 1; unwrap_send_err!(nodes[0].node.send_payment_with_route(&route, our_payment_hash, RecipientOnionFields::secret_only(our_payment_secret), PaymentId(our_payment_hash.0) ), true, APIError::ChannelUnavailable { ref err }, @@ -6241,12 +6250,15 @@ fn test_update_add_htlc_bolt2_receiver_check_max_htlc_limit() { let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs); let chan = create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 100000, 95000000); - let (route, our_payment_hash, _, our_payment_secret) = get_route_and_payment_hash!(nodes[0], nodes[1], 3999999); + let send_amt = 3999999; + let (mut route, our_payment_hash, _, our_payment_secret) = + get_route_and_payment_hash!(nodes[0], nodes[1], 1000); + route.paths[0].hops[0].fee_msat = send_amt; let session_priv = SecretKey::from_slice(&[42; 32]).unwrap(); let cur_height = nodes[0].node.best_block.read().unwrap().height() + 1; let onion_keys = onion_utils::construct_onion_keys(&Secp256k1::signing_only(), &route.paths[0], &session_priv).unwrap(); let (onion_payloads, _htlc_msat, htlc_cltv) = onion_utils::build_onion_payloads( - &route.paths[0], 3999999, RecipientOnionFields::secret_only(our_payment_secret), cur_height, &None).unwrap(); + &route.paths[0], send_amt, RecipientOnionFields::secret_only(our_payment_secret), cur_height, &None).unwrap(); let onion_packet = onion_utils::construct_onion_packet(onion_payloads, onion_keys, [0; 32], &our_payment_hash).unwrap(); let mut msg = msgs::UpdateAddHTLC { -- 2.39.5