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Introduce FeerateStrategy enum for onchain claims
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This refactors the existing `force_feerate_bump` flag into an enum as we
plan to introduce a new flag/enum variant in a future commit.
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@wpaulino
wpaulino committed Feb 7, 2024
1 parent 9873209 commit 9b8e1fb
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Showing 3 changed files with 68 additions and 55 deletions.
4 changes: 2 additions & 2 deletions lightning/src/chain/channelmonitor.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -44,7 +44,7 @@ use crate::chain::{BestBlock, WatchedOutput};
use crate::chain::chaininterface::{BroadcasterInterface, FeeEstimator, LowerBoundedFeeEstimator};
use crate::chain::transaction::{OutPoint, TransactionData};
use crate::sign::{ChannelDerivationParameters, HTLCDescriptor, SpendableOutputDescriptor, StaticPaymentOutputDescriptor, DelayedPaymentOutputDescriptor, ecdsa::WriteableEcdsaChannelSigner, SignerProvider, EntropySource};
use crate::chain::onchaintx::{ClaimEvent, OnchainTxHandler};
use crate::chain::onchaintx::{ClaimEvent, FeerateStrategy, OnchainTxHandler};
use crate::chain::package::{CounterpartyOfferedHTLCOutput, CounterpartyReceivedHTLCOutput, HolderFundingOutput, HolderHTLCOutput, PackageSolvingData, PackageTemplate, RevokedOutput, RevokedHTLCOutput};
use crate::chain::Filter;
use crate::util::logger::{Logger, Record};
Expand Down Expand Up @@ -1765,7 +1765,7 @@ impl<Signer: WriteableEcdsaChannelSigner> ChannelMonitor<Signer> {
let logger = WithChannelMonitor::from_impl(logger, &*inner);
let current_height = inner.best_block.height;
inner.onchain_tx_handler.rebroadcast_pending_claims(
current_height, &broadcaster, &fee_estimator, &logger,
current_height, FeerateStrategy::HighestOfPreviousOrNew, &broadcaster, &fee_estimator, &logger,
);
}

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29 changes: 19 additions & 10 deletions lightning/src/chain/onchaintx.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -210,6 +210,15 @@ pub(crate) enum OnchainClaim {
Event(ClaimEvent),
}

/// Represents the different feerates a pending request can use when generating a claim.
pub(crate) enum FeerateStrategy {
/// We must pick the highest between the most recently used and the current feerate estimate.
HighestOfPreviousOrNew,
/// We must force a bump of the most recently used feerate, either by using the current feerate
/// estimate if it's higher, or manually bumping.
ForceBump,
}

/// OnchainTxHandler receives claiming requests, aggregates them if it's sound, broadcast and
/// do RBF bumping if possible.
#[derive(Clone)]
Expand Down Expand Up @@ -474,8 +483,8 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>
/// invoking this every 30 seconds, or lower if running in an environment with spotty
/// connections, like on mobile.
pub(super) fn rebroadcast_pending_claims<B: Deref, F: Deref, L: Logger>(
&mut self, current_height: u32, broadcaster: &B, fee_estimator: &LowerBoundedFeeEstimator<F>,
logger: &L,
&mut self, current_height: u32, feerate_strategy: FeerateStrategy, broadcaster: &B,
fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L,
)
where
B::Target: BroadcasterInterface,
Expand All @@ -488,7 +497,7 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>
bump_requests.push((*claim_id, request.clone()));
}
for (claim_id, request) in bump_requests {
self.generate_claim(current_height, &request, false /* force_feerate_bump */, fee_estimator, logger)
self.generate_claim(current_height, &request, &feerate_strategy, fee_estimator, logger)
.map(|(_, new_feerate, claim)| {
let mut bumped_feerate = false;
if let Some(mut_request) = self.pending_claim_requests.get_mut(&claim_id) {
Expand Down Expand Up @@ -528,7 +537,7 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>
/// Panics if there are signing errors, because signing operations in reaction to on-chain
/// events are not expected to fail, and if they do, we may lose funds.
fn generate_claim<F: Deref, L: Logger>(
&mut self, cur_height: u32, cached_request: &PackageTemplate, force_feerate_bump: bool,
&mut self, cur_height: u32, cached_request: &PackageTemplate, feerate_strategy: &FeerateStrategy,
fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L,
) -> Option<(u32, u64, OnchainClaim)>
where F::Target: FeeEstimator,
Expand Down Expand Up @@ -577,7 +586,7 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>
if cached_request.is_malleable() {
if cached_request.requires_external_funding() {
let target_feerate_sat_per_1000_weight = cached_request.compute_package_feerate(
fee_estimator, ConfirmationTarget::OnChainSweep, force_feerate_bump
fee_estimator, ConfirmationTarget::OnChainSweep, feerate_strategy,
);
if let Some(htlcs) = cached_request.construct_malleable_package_with_external_funding(self) {
return Some((
Expand All @@ -597,7 +606,7 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>
let predicted_weight = cached_request.package_weight(&self.destination_script);
if let Some((output_value, new_feerate)) = cached_request.compute_package_output(
predicted_weight, self.destination_script.dust_value().to_sat(),
force_feerate_bump, fee_estimator, logger,
feerate_strategy, fee_estimator, logger,
) {
assert!(new_feerate != 0);

Expand Down Expand Up @@ -630,7 +639,7 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>

let conf_target = ConfirmationTarget::OnChainSweep;
let package_target_feerate_sat_per_1000_weight = cached_request
.compute_package_feerate(fee_estimator, conf_target, force_feerate_bump);
.compute_package_feerate(fee_estimator, conf_target, feerate_strategy);
if let Some(input_amount_sat) = output.funding_amount {
let fee_sat = input_amount_sat - tx.output.iter().map(|output| output.value).sum::<u64>();
let commitment_tx_feerate_sat_per_1000_weight =
Expand Down Expand Up @@ -767,7 +776,7 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>
// height timer expiration (i.e in how many blocks we're going to take action).
for mut req in preprocessed_requests {
if let Some((new_timer, new_feerate, claim)) = self.generate_claim(
cur_height, &req, true /* force_feerate_bump */, &*fee_estimator, &*logger,
cur_height, &req, &FeerateStrategy::ForceBump, &*fee_estimator, &*logger,
) {
req.set_timer(new_timer);
req.set_feerate(new_feerate);
Expand Down Expand Up @@ -967,7 +976,7 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>
log_trace!(logger, "Bumping {} candidates", bump_candidates.len());
for (claim_id, request) in bump_candidates.iter() {
if let Some((new_timer, new_feerate, bump_claim)) = self.generate_claim(
cur_height, &request, true /* force_feerate_bump */, &*fee_estimator, &*logger,
cur_height, &request, &FeerateStrategy::ForceBump, &*fee_estimator, &*logger,
) {
match bump_claim {
OnchainClaim::Tx(bump_tx) => {
Expand Down Expand Up @@ -1048,7 +1057,7 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>
// `height` is the height being disconnected, so our `current_height` is 1 lower.
let current_height = height - 1;
if let Some((new_timer, new_feerate, bump_claim)) = self.generate_claim(
current_height, &request, true /* force_feerate_bump */, fee_estimator, logger
current_height, &request, &FeerateStrategy::ForceBump, fee_estimator, logger
) {
request.set_timer(new_timer);
request.set_feerate(new_feerate);
Expand Down
90 changes: 47 additions & 43 deletions lightning/src/chain/package.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,7 @@ use crate::ln::channel_keys::{DelayedPaymentBasepoint, HtlcBasepoint};
use crate::ln::msgs::DecodeError;
use crate::chain::chaininterface::{FeeEstimator, ConfirmationTarget, MIN_RELAY_FEE_SAT_PER_1000_WEIGHT, compute_feerate_sat_per_1000_weight, FEERATE_FLOOR_SATS_PER_KW};
use crate::sign::ecdsa::WriteableEcdsaChannelSigner;
use crate::chain::onchaintx::{ExternalHTLCClaim, OnchainTxHandler};
use crate::chain::onchaintx::{FeerateStrategy, ExternalHTLCClaim, OnchainTxHandler};
use crate::util::logger::Logger;
use crate::util::ser::{Readable, Writer, Writeable, RequiredWrapper};

Expand Down Expand Up @@ -963,7 +963,7 @@ impl PackageTemplate {
/// which was used to generate the value. Will not return less than `dust_limit_sats` for the
/// value.
pub(crate) fn compute_package_output<F: Deref, L: Logger>(
&self, predicted_weight: u64, dust_limit_sats: u64, force_feerate_bump: bool,
&self, predicted_weight: u64, dust_limit_sats: u64, feerate_strategy: &FeerateStrategy,
fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L,
) -> Option<(u64, u64)>
where F::Target: FeeEstimator,
Expand All @@ -974,7 +974,7 @@ impl PackageTemplate {
// If old feerate is 0, first iteration of this claim, use normal fee calculation
if self.feerate_previous != 0 {
if let Some((new_fee, feerate)) = feerate_bump(
predicted_weight, input_amounts, self.feerate_previous, force_feerate_bump,
predicted_weight, input_amounts, self.feerate_previous, feerate_strategy,
fee_estimator, logger,
) {
return Some((cmp::max(input_amounts as i64 - new_fee as i64, dust_limit_sats as i64) as u64, feerate));
Expand All @@ -987,32 +987,31 @@ impl PackageTemplate {
None
}

/// Computes a feerate based on the given confirmation target. If a previous feerate was used,
/// the new feerate is below it, and `force_feerate_bump` is set, we'll use a 25% increase of
/// the previous feerate instead of the new feerate.
/// Computes a feerate based on the given confirmation target and feerate strategy.
pub(crate) fn compute_package_feerate<F: Deref>(
&self, fee_estimator: &LowerBoundedFeeEstimator<F>, conf_target: ConfirmationTarget,
force_feerate_bump: bool,
feerate_strategy: &FeerateStrategy,
) -> u32 where F::Target: FeeEstimator {
let feerate_estimate = fee_estimator.bounded_sat_per_1000_weight(conf_target);
if self.feerate_previous != 0 {
// Use the new fee estimate if it's higher than the one previously used.
if feerate_estimate as u64 > self.feerate_previous {
feerate_estimate
} else if !force_feerate_bump {
self.feerate_previous.try_into().unwrap_or(u32::max_value())
} else {
// Our fee estimate has decreased, but our transaction remains unconfirmed after
// using our previous fee estimate. This may point to an unreliable fee estimator,
// so we choose to bump our previous feerate by 25%, making sure we don't use a
// lower feerate or overpay by a large margin by limiting it to 5x the new fee
// estimate.
let previous_feerate = self.feerate_previous.try_into().unwrap_or(u32::max_value());
let mut new_feerate = previous_feerate.saturating_add(previous_feerate / 4);
if new_feerate > feerate_estimate * 5 {
new_feerate = cmp::max(feerate_estimate * 5, previous_feerate);
}
new_feerate
let previous_feerate = self.feerate_previous.try_into().unwrap_or(u32::max_value());
match feerate_strategy {
FeerateStrategy::HighestOfPreviousOrNew => cmp::max(previous_feerate, feerate_estimate),
FeerateStrategy::ForceBump => if feerate_estimate > previous_feerate {
feerate_estimate
} else {
// Our fee estimate has decreased, but our transaction remains unconfirmed after
// using our previous fee estimate. This may point to an unreliable fee estimator,
// so we choose to bump our previous feerate by 25%, making sure we don't use a
// lower feerate or overpay by a large margin by limiting it to 5x the new fee
// estimate.
let previous_feerate = self.feerate_previous.try_into().unwrap_or(u32::max_value());
let mut new_feerate = previous_feerate.saturating_add(previous_feerate / 4);
if new_feerate > feerate_estimate * 5 {
new_feerate = cmp::max(feerate_estimate * 5, previous_feerate);
}
new_feerate
},
}
} else {
feerate_estimate
Expand Down Expand Up @@ -1128,33 +1127,38 @@ fn compute_fee_from_spent_amounts<F: Deref, L: Logger>(input_amounts: u64, predi

/// Attempt to propose a bumping fee for a transaction from its spent output's values and predicted
/// weight. If feerates proposed by the fee-estimator have been increasing since last fee-bumping
/// attempt, use them. If `force_feerate_bump` is set, we bump the feerate by 25% of the previous
/// feerate, or just use the previous feerate otherwise. If a feerate bump did happen, we also
/// verify that those bumping heuristics respect BIP125 rules 3) and 4) and if required adjust the
/// new fee to meet the RBF policy requirement.
/// attempt, use them. If we need to force a feerate bump, we manually bump the feerate by 25% of
/// the previous feerate. If a feerate bump did happen, we also verify that those bumping heuristics
/// respect BIP125 rules 3) and 4) and if required adjust the new fee to meet the RBF policy
/// requirement.
fn feerate_bump<F: Deref, L: Logger>(
predicted_weight: u64, input_amounts: u64, previous_feerate: u64, force_feerate_bump: bool,
predicted_weight: u64, input_amounts: u64, previous_feerate: u64, feerate_strategy: &FeerateStrategy,
fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L,
) -> Option<(u64, u64)>
where
F::Target: FeeEstimator,
{
// If old feerate inferior to actual one given back by Fee Estimator, use it to compute new fee...
let (new_fee, new_feerate) = if let Some((new_fee, new_feerate)) = compute_fee_from_spent_amounts(input_amounts, predicted_weight, fee_estimator, logger) {
if new_feerate > previous_feerate {
(new_fee, new_feerate)
} else if !force_feerate_bump {
let previous_fee = previous_feerate * predicted_weight / 1000;
(previous_fee, previous_feerate)
} else {
// ...else just increase the previous feerate by 25% (because that's a nice number)
let bumped_feerate = previous_feerate + (previous_feerate / 4);
let bumped_fee = bumped_feerate * predicted_weight / 1000;
if input_amounts <= bumped_fee {
log_warn!(logger, "Can't 25% bump new claiming tx, amount {} is too small", input_amounts);
return None;
}
(bumped_fee, bumped_feerate)
match feerate_strategy {
FeerateStrategy::HighestOfPreviousOrNew => if new_feerate > previous_feerate {
(new_fee, new_feerate)
} else {
let previous_fee = previous_feerate * predicted_weight / 1000;
(previous_fee, previous_feerate)
},
FeerateStrategy::ForceBump => if new_feerate > previous_feerate {
(new_fee, new_feerate)
} else {
// ...else just increase the previous feerate by 25% (because that's a nice number)
let bumped_feerate = previous_feerate + (previous_feerate / 4);
let bumped_fee = bumped_feerate * predicted_weight / 1000;
if input_amounts <= bumped_fee {
log_warn!(logger, "Can't 25% bump new claiming tx, amount {} is too small", input_amounts);
return None;
}
(bumped_fee, bumped_feerate)
},
}
} else {
log_warn!(logger, "Can't new-estimation bump new claiming tx, amount {} is too small", input_amounts);
Expand Down

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