Split ConfirmationTarget::OnChainSweep into urgent and non-urgent

When we force-close a channel, occasionally its due to feerate
disagreements or other non-HTLC-related issues. In those cases,
there's no reason to use a very urgent feerate estimate - we don't
have any timers expiring soon.

Instead, we should give users the information they need to be more
economical on fees in this case, which we do here by splitting
`OnChainSweep` into `UrgentOnChainSweep` and
`NonUrgentOnChainSweep` `ConfirmationTarget`s.

Author: TheBlueMatt

fuzz/src/chanmon_consistency.rs

@@ -97,7 +97,9 @@ impl FeeEstimator for FuzzEstimator {
 		// always return a HighPriority feerate here which is >= the maximum Normal feerate and a
 		// Background feerate which is <= the minimum Normal feerate.
 		match conf_target {
-			ConfirmationTarget::MaximumFeeEstimate | ConfirmationTarget::OnChainSweep => MAX_FEE,
+			ConfirmationTarget::MaximumFeeEstimate | ConfirmationTarget::UrgentOnChainSweep => {
+				MAX_FEE
+			},
 			ConfirmationTarget::ChannelCloseMinimum
 			| ConfirmationTarget::AnchorChannelFee
 			| ConfirmationTarget::MinAllowedAnchorChannelRemoteFee

lightning/src/chain/chaininterface.rs

@@ -56,10 +56,12 @@ pub enum ConfirmationTarget {
 	/// trying to burn channel balance to dust.
 	MaximumFeeEstimate,
 	/// We have some funds available on chain which we need to spend prior to some expiry time at
-	/// which point our counterparty may be able to steal them. Generally we have in the high tens
-	/// to low hundreds of blocks to get our transaction on-chain, but we shouldn't risk too low a
-	/// fee - this should be a relatively high priority feerate.
-	OnChainSweep,
+	/// which point our counterparty may be able to steal them.
+	///
+	/// Generally we have in the high tens to low hundreds of blocks to get our transaction
+	/// on-chain (it doesn't have to happen in the next few blocks!), but we shouldn't risk too low
+	/// a fee - this should be a relatively high priority feerate.
+	UrgentOnChainSweep,
 	/// This is the lowest feerate we will allow our channel counterparty to have in an anchor
 	/// channel in order to close the channel if a channel party goes away.
 	///
@@ -130,14 +132,18 @@ pub enum ConfirmationTarget {
 	///
 	/// [`ChannelManager::close_channel_with_feerate_and_script`]: crate::ln::channelmanager::ChannelManager::close_channel_with_feerate_and_script
 	ChannelCloseMinimum,
-	/// The feerate [`OutputSweeper`] will use on transactions spending
-	/// [`SpendableOutputDescriptor`]s after a channel closure.
+	/// The feerate used to claim on-chain funds when there is no particular urgency to do so.
+	///
+	/// It is used to get commitment transactions without any HTLCs confirmed in [`ChannelMonitor`]
+	/// and by  [`OutputSweeper`] on transactions spending [`SpendableOutputDescriptor`]s after a
+	/// channel closure.
 	///
 	/// Generally spending these outputs is safe as long as they eventually confirm, so a value
 	/// (slightly above) the mempool minimum should suffice. However, as this value will influence
 	/// how long funds will be unavailable after channel closure, [`FeeEstimator`] implementors
 	/// might want to choose a higher feerate to regain control over funds faster.
 	///
+	/// [`ChannelMonitor`]: crate::chain::channelmonitor::ChannelMonitor
 	/// [`OutputSweeper`]: crate::util::sweep::OutputSweeper
 	/// [`SpendableOutputDescriptor`]: crate::sign::SpendableOutputDescriptor
 	OutputSpendingFee,

lightning/src/chain/channelmonitor.rs

@@ -40,7 +40,7 @@ use crate::ln::chan_utils::{self,CommitmentTransaction, CounterpartyCommitmentSe
 use crate::ln::channelmanager::{HTLCSource, SentHTLCId};
 use crate::chain;
 use crate::chain::{BestBlock, WatchedOutput};
-use crate::chain::chaininterface::{BroadcasterInterface, FeeEstimator, LowerBoundedFeeEstimator};
+use crate::chain::chaininterface::{BroadcasterInterface, ConfirmationTarget, FeeEstimator, LowerBoundedFeeEstimator};
 use crate::chain::transaction::{OutPoint, TransactionData};
 use crate::sign::{ChannelDerivationParameters, HTLCDescriptor, SpendableOutputDescriptor, StaticPaymentOutputDescriptor, DelayedPaymentOutputDescriptor, ecdsa::EcdsaChannelSigner, SignerProvider, EntropySource};
 use crate::chain::onchaintx::{ClaimEvent, FeerateStrategy, OnchainTxHandler};
@@ -1902,8 +1902,9 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitor<Signer> {
 		let mut inner = self.inner.lock().unwrap();
 		let logger = WithChannelMonitor::from_impl(logger, &*inner, None);
 		let current_height = inner.best_block.height;
+		let conf_target = inner.closure_conf_target();
 		inner.onchain_tx_handler.rebroadcast_pending_claims(
-			current_height, FeerateStrategy::HighestOfPreviousOrNew, &broadcaster, &fee_estimator, &logger,
+			current_height, FeerateStrategy::HighestOfPreviousOrNew, &broadcaster, conf_target, &fee_estimator, &logger,
 		);
 	}
 
@@ -1927,8 +1928,9 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitor<Signer> {
 		let mut inner = self.inner.lock().unwrap();
 		let logger = WithChannelMonitor::from_impl(logger, &*inner, None);
 		let current_height = inner.best_block.height;
+		let conf_target = inner.closure_conf_target();
 		inner.onchain_tx_handler.rebroadcast_pending_claims(
-			current_height, FeerateStrategy::RetryPrevious, &broadcaster, &fee_estimator, &logger,
+			current_height, FeerateStrategy::RetryPrevious, &broadcaster, conf_target, &fee_estimator, &logger,
 		);
 	}
 
@@ -2684,6 +2686,30 @@ pub fn deliberately_bogus_accepted_htlc_witness() -> Vec<Vec<u8>> {
 }
 
 impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
+	/// Gets the [`ConfirmationTarget`] we should use when selecting feerates for channel closure
+	/// transactions for this channel right now.
+	fn closure_conf_target(&self) -> ConfirmationTarget {
+		// Treat the sweep as urgent as long as there is at least one HTLC which is pending on a
+		// valid commitment transaction.
+		if !self.current_holder_commitment_tx.htlc_outputs.is_empty() {
+			return ConfirmationTarget::UrgentOnChainSweep;
+		}
+		if self.prev_holder_signed_commitment_tx.as_ref().map(|t| !t.htlc_outputs.is_empty()).unwrap_or(false) {
+			return ConfirmationTarget::UrgentOnChainSweep;
+		}
+		if let Some(txid) = self.current_counterparty_commitment_txid {
+			if !self.counterparty_claimable_outpoints.get(&txid).unwrap().is_empty() {
+				return ConfirmationTarget::UrgentOnChainSweep;
+			}
+		}
+		if let Some(txid) = self.prev_counterparty_commitment_txid {
+			if !self.counterparty_claimable_outpoints.get(&txid).unwrap().is_empty() {
+				return ConfirmationTarget::UrgentOnChainSweep;
+			}
+		}
+		ConfirmationTarget::OutputSpendingFee
+	}
+
 	/// Inserts a revocation secret into this channel monitor. Prunes old preimages if neither
 	/// needed by holder commitment transactions HTCLs nor by counterparty ones. Unless we haven't already seen
 	/// counterparty commitment transaction's secret, they are de facto pruned (we can use revocation key).
@@ -2928,7 +2954,8 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 		macro_rules! claim_htlcs {
 			($commitment_number: expr, $txid: expr, $htlcs: expr) => {
 				let (htlc_claim_reqs, _) = self.get_counterparty_output_claim_info($commitment_number, $txid, None, $htlcs);
-				self.onchain_tx_handler.update_claims_view_from_requests(htlc_claim_reqs, self.best_block.height, self.best_block.height, broadcaster, fee_estimator, logger);
+				let conf_target = self.closure_conf_target();
+				self.onchain_tx_handler.update_claims_view_from_requests(htlc_claim_reqs, self.best_block.height, self.best_block.height, broadcaster, conf_target, fee_estimator, logger);
 			}
 		}
 		if let Some(txid) = self.current_counterparty_commitment_txid {
@@ -2976,7 +3003,8 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 				// block. Even if not, its a reasonable metric for the bump criteria on the HTLC
 				// transactions.
 				let (claim_reqs, _) = self.get_broadcasted_holder_claims(&holder_commitment_tx, self.best_block.height);
-				self.onchain_tx_handler.update_claims_view_from_requests(claim_reqs, self.best_block.height, self.best_block.height, broadcaster, fee_estimator, logger);
+				let conf_target = self.closure_conf_target();
+				self.onchain_tx_handler.update_claims_view_from_requests(claim_reqs, self.best_block.height, self.best_block.height, broadcaster, conf_target, fee_estimator, logger);
 			}
 		}
 	}
@@ -3036,9 +3064,10 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 		L::Target: Logger,
 	{
 		let (claimable_outpoints, _) = self.generate_claimable_outpoints_and_watch_outputs(ClosureReason::HolderForceClosed { broadcasted_latest_txn: Some(true) });
+		let conf_target = self.closure_conf_target();
 		self.onchain_tx_handler.update_claims_view_from_requests(
 			claimable_outpoints, self.best_block.height, self.best_block.height, broadcaster,
-			fee_estimator, logger
+			conf_target, fee_estimator, logger,
 		);
 	}
 
@@ -3851,7 +3880,8 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 			self.best_block = BestBlock::new(block_hash, height);
 			log_trace!(logger, "Best block re-orged, replaced with new block {} at height {}", block_hash, height);
 			self.onchain_events_awaiting_threshold_conf.retain(|ref entry| entry.height <= height);
-			self.onchain_tx_handler.block_disconnected(height + 1, broadcaster, fee_estimator, logger);
+			let conf_target = self.closure_conf_target();
+			self.onchain_tx_handler.block_disconnected(height + 1, broadcaster, conf_target, fee_estimator, logger);
 			Vec::new()
 		} else { Vec::new() }
 	}
@@ -4116,8 +4146,9 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 			}
 		}
 
-		self.onchain_tx_handler.update_claims_view_from_requests(claimable_outpoints, conf_height, self.best_block.height, broadcaster, fee_estimator, logger);
-		self.onchain_tx_handler.update_claims_view_from_matched_txn(&txn_matched, conf_height, conf_hash, self.best_block.height, broadcaster, fee_estimator, logger);
+		let conf_target = self.closure_conf_target();
+		self.onchain_tx_handler.update_claims_view_from_requests(claimable_outpoints, conf_height, self.best_block.height, broadcaster, conf_target, fee_estimator, logger);
+		self.onchain_tx_handler.update_claims_view_from_matched_txn(&txn_matched, conf_height, conf_hash, self.best_block.height, broadcaster, conf_target, fee_estimator, logger);
 
 		// Determine new outputs to watch by comparing against previously known outputs to watch,
 		// updating the latter in the process.
@@ -4156,7 +4187,8 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 		self.onchain_events_awaiting_threshold_conf.retain(|ref entry| entry.height < height);
 
 		let bounded_fee_estimator = LowerBoundedFeeEstimator::new(fee_estimator);
-		self.onchain_tx_handler.block_disconnected(height, broadcaster, &bounded_fee_estimator, logger);
+		let conf_target = self.closure_conf_target();
+		self.onchain_tx_handler.block_disconnected(height, broadcaster, conf_target, &bounded_fee_estimator, logger);
 
 		self.best_block = BestBlock::new(header.prev_blockhash, height - 1);
 	}
@@ -4190,7 +4222,8 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 
 		debug_assert!(!self.onchain_events_awaiting_threshold_conf.iter().any(|ref entry| entry.txid == *txid));
 
-		self.onchain_tx_handler.transaction_unconfirmed(txid, broadcaster, fee_estimator, logger);
+		let conf_target = self.closure_conf_target();
+		self.onchain_tx_handler.transaction_unconfirmed(txid, broadcaster, conf_target, fee_estimator, logger);
 	}
 
 	/// Filters a block's `txdata` for transactions spending watched outputs or for any child

lightning/src/chain/onchaintx.rs

@@ -24,13 +24,13 @@ use bitcoin::secp256k1::PublicKey;
 use bitcoin::secp256k1::{Secp256k1, ecdsa::Signature};
 use bitcoin::secp256k1;
 
-use crate::chain::chaininterface::compute_feerate_sat_per_1000_weight;
+use crate::chain::chaininterface::{ConfirmationTarget, compute_feerate_sat_per_1000_weight};
 use crate::sign::{ChannelDerivationParameters, HTLCDescriptor, ChannelSigner, EntropySource, SignerProvider, ecdsa::EcdsaChannelSigner};
 use crate::ln::msgs::DecodeError;
 use crate::ln::types::PaymentPreimage;
 use crate::ln::chan_utils::{self, ChannelTransactionParameters, HTLCOutputInCommitment, HolderCommitmentTransaction};
 use crate::chain::ClaimId;
-use crate::chain::chaininterface::{ConfirmationTarget, FeeEstimator, BroadcasterInterface, LowerBoundedFeeEstimator};
+use crate::chain::chaininterface::{FeeEstimator, BroadcasterInterface, LowerBoundedFeeEstimator};
 use crate::chain::channelmonitor::{ANTI_REORG_DELAY, CLTV_SHARED_CLAIM_BUFFER};
 use crate::chain::package::{PackageSolvingData, PackageTemplate};
 use crate::chain::transaction::MaybeSignedTransaction;
@@ -487,7 +487,7 @@ impl<ChannelSigner: EcdsaChannelSigner> OnchainTxHandler<ChannelSigner> {
 	/// connections, like on mobile.
 	pub(super) fn rebroadcast_pending_claims<B: Deref, F: Deref, L: Logger>(
 		&mut self, current_height: u32, feerate_strategy: FeerateStrategy, broadcaster: &B,
-		fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L,
+		conf_target: ConfirmationTarget, fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L,
 	)
 	where
 		B::Target: BroadcasterInterface,
@@ -500,7 +500,7 @@ impl<ChannelSigner: EcdsaChannelSigner> OnchainTxHandler<ChannelSigner> {
 			bump_requests.push((*claim_id, request.clone()));
 		}
 		for (claim_id, request) in bump_requests {
-			self.generate_claim(current_height, &request, &feerate_strategy, fee_estimator, logger)
+			self.generate_claim(current_height, &request, &feerate_strategy, conf_target, 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) {
@@ -552,7 +552,7 @@ impl<ChannelSigner: EcdsaChannelSigner> OnchainTxHandler<ChannelSigner> {
 	/// 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, feerate_strategy: &FeerateStrategy,
-		fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L,
+		conf_target: ConfirmationTarget, fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L,
 	) -> Option<(u32, u64, OnchainClaim)>
 	where F::Target: FeeEstimator,
 	{
@@ -600,7 +600,7 @@ impl<ChannelSigner: EcdsaChannelSigner> 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, feerate_strategy,
+					fee_estimator, conf_target, feerate_strategy,
 				);
 				if let Some(htlcs) = cached_request.construct_malleable_package_with_external_funding(self) {
 					return Some((
@@ -620,7 +620,7 @@ impl<ChannelSigner: EcdsaChannelSigner> 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.minimal_non_dust().to_sat(),
-				feerate_strategy, fee_estimator, logger,
+				feerate_strategy, conf_target, fee_estimator, logger,
 			) {
 				assert!(new_feerate != 0);
 
@@ -650,7 +650,6 @@ impl<ChannelSigner: EcdsaChannelSigner> OnchainTxHandler<ChannelSigner> {
 					debug_assert_eq!(tx.0.compute_txid(), self.holder_commitment.trust().txid(),
 						"Holder commitment transaction mismatch");
 
-					let conf_target = ConfirmationTarget::OnChainSweep;
 					let package_target_feerate_sat_per_1000_weight = cached_request
 						.compute_package_feerate(fee_estimator, conf_target, feerate_strategy);
 					if let Some(input_amount_sat) = output.funding_amount {
@@ -728,7 +727,8 @@ impl<ChannelSigner: EcdsaChannelSigner> OnchainTxHandler<ChannelSigner> {
 	/// `cur_height`, however it must never be higher than `cur_height`.
 	pub(super) fn update_claims_view_from_requests<B: Deref, F: Deref, L: Logger>(
 		&mut self, requests: Vec<PackageTemplate>, conf_height: u32, cur_height: u32,
-		broadcaster: &B, fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L
+		broadcaster: &B, conf_target: ConfirmationTarget,
+		fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L
 	) where
 		B::Target: BroadcasterInterface,
 		F::Target: FeeEstimator,
@@ -798,7 +798,7 @@ impl<ChannelSigner: EcdsaChannelSigner> 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, &FeerateStrategy::ForceBump, &*fee_estimator, &*logger,
+				cur_height, &req, &FeerateStrategy::ForceBump, conf_target, &*fee_estimator, &*logger,
 			) {
 				req.set_timer(new_timer);
 				req.set_feerate(new_feerate);
@@ -863,7 +863,8 @@ impl<ChannelSigner: EcdsaChannelSigner> OnchainTxHandler<ChannelSigner> {
 	/// provided via `cur_height`, however it must never be higher than `cur_height`.
 	pub(super) fn update_claims_view_from_matched_txn<B: Deref, F: Deref, L: Logger>(
 		&mut self, txn_matched: &[&Transaction], conf_height: u32, conf_hash: BlockHash,
-		cur_height: u32, broadcaster: &B, fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L
+		cur_height: u32, broadcaster: &B, conf_target: ConfirmationTarget,
+		fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L
 	) where
 		B::Target: BroadcasterInterface,
 		F::Target: FeeEstimator,
@@ -1014,7 +1015,7 @@ impl<ChannelSigner: EcdsaChannelSigner> OnchainTxHandler<ChannelSigner> {
 
 		for (claim_id, request) in bump_candidates.iter() {
 			if let Some((new_timer, new_feerate, bump_claim)) = self.generate_claim(
-				cur_height, &request, &FeerateStrategy::ForceBump, &*fee_estimator, &*logger,
+				cur_height, &request, &FeerateStrategy::ForceBump, conf_target, &*fee_estimator, &*logger,
 			) {
 				match bump_claim {
 					OnchainClaim::Tx(bump_tx) => {
@@ -1049,6 +1050,7 @@ impl<ChannelSigner: EcdsaChannelSigner> OnchainTxHandler<ChannelSigner> {
 		&mut self,
 		txid: &Txid,
 		broadcaster: B,
+		conf_target: ConfirmationTarget,
 		fee_estimator: &LowerBoundedFeeEstimator<F>,
 		logger: &L,
 	) where
@@ -1064,11 +1066,14 @@ impl<ChannelSigner: EcdsaChannelSigner> OnchainTxHandler<ChannelSigner> {
 		}
 
 		if let Some(height) = height {
-			self.block_disconnected(height, broadcaster, fee_estimator, logger);
+			self.block_disconnected(height, broadcaster, conf_target, fee_estimator, logger);
 		}
 	}
 
-	pub(super) fn block_disconnected<B: Deref, F: Deref, L: Logger>(&mut self, height: u32, broadcaster: B, fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L)
+	pub(super) fn block_disconnected<B: Deref, F: Deref, L: Logger>(
+		&mut self, height: u32, broadcaster: B, conf_target: ConfirmationTarget,
+		fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L,
+	)
 		where B::Target: BroadcasterInterface,
 			F::Target: FeeEstimator,
 	{
@@ -1100,7 +1105,7 @@ impl<ChannelSigner: EcdsaChannelSigner> 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, &FeerateStrategy::ForceBump, fee_estimator, logger
+				current_height, &request, &FeerateStrategy::ForceBump, conf_target, fee_estimator, logger
 			) {
 				request.set_timer(new_timer);
 				request.set_feerate(new_feerate);