Add min mempool estimate for feerate updates on anchor channels

fuzz/src/chanmon_consistency.rs

@@ -78,7 +78,7 @@ impl FeeEstimator for FuzzEstimator {
 		// Background feerate which is <= the minimum Normal feerate.
 		match conf_target {
 			ConfirmationTarget::HighPriority => MAX_FEE,
-			ConfirmationTarget::Background => 253,
+			ConfirmationTarget::Background|ConfirmationTarget::MempoolMinimum => 253,
 			ConfirmationTarget::Normal => cmp::min(self.ret_val.load(atomic::Ordering::Acquire), MAX_FEE),
 		}
 	}

lightning/src/chain/chaininterface.rs

@@ -35,15 +35,24 @@ pub trait BroadcasterInterface {
 	fn broadcast_transactions(&self, txs: &[&Transaction]);
 }
 
-/// An enum that represents the speed at which we want a transaction to confirm used for feerate
+/// An enum that represents the priority at which we want a transaction to confirm used for feerate
 /// estimation.
 #[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
 pub enum ConfirmationTarget {
-	/// We are happy with this transaction confirming slowly when feerate drops some.
+	/// We'd like a transaction to confirm in the future, but don't want to commit most of the fees
+	/// required to do so yet. The remaining fees will come via a Child-Pays-For-Parent (CPFP) fee
+	/// bump of the transaction.
+	///
+	/// The feerate returned should be the absolute minimum feerate required to enter most node
+	/// mempools across the network. Note that if you are not able to obtain this feerate estimate,
+	/// you should likely use the furthest-out estimate allowed by your fee estimator.
+	MempoolMinimum,
+	/// We are happy with a transaction confirming slowly, at least within a day or so worth of
+	/// blocks.
 	Background,
-	/// We'd like this transaction to confirm without major delay, but 12-18 blocks is fine.
+	/// We'd like a transaction to confirm without major delayed, i.e., within the next 12-24 blocks.
 	Normal,
-	/// We'd like this transaction to confirm in the next few blocks.
+	/// We'd like a transaction to confirm in the next few blocks.
 	HighPriority,
 }
 

lightning/src/ln/channel.rs

@@ -2045,20 +2045,35 @@ struct CommitmentTxInfoCached {
 }
 
 impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
-	fn check_remote_fee<F: Deref, L: Deref>(fee_estimator: &LowerBoundedFeeEstimator<F>,
-		feerate_per_kw: u32, cur_feerate_per_kw: Option<u32>, logger: &L)
-		-> Result<(), ChannelError> where F::Target: FeeEstimator, L::Target: Logger,
+	fn check_remote_fee<F: Deref, L: Deref>(
+		channel_type: &ChannelTypeFeatures, fee_estimator: &LowerBoundedFeeEstimator<F>,
+		feerate_per_kw: u32, cur_feerate_per_kw: Option<u32>, logger: &L
+	) -> Result<(), ChannelError> where F::Target: FeeEstimator, L::Target: Logger,
 	{
 		// We only bound the fee updates on the upper side to prevent completely absurd feerates,
 		// always accepting up to 25 sat/vByte or 10x our fee estimator's "High Priority" fee.
 		// We generally don't care too much if they set the feerate to something very high, but it
-		// could result in the channel being useless due to everything being dust.
-		let upper_limit = cmp::max(250 * 25,
-			fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::HighPriority) as u64 * 10);
-		if feerate_per_kw as u64 > upper_limit {
-			return Err(ChannelError::Close(format!("Peer's feerate much too high. Actual: {}. Our expected upper limit: {}", feerate_per_kw, upper_limit)));
-		}
-		let lower_limit = fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::Background);
+		// could result in the channel being useless due to everything being dust. This doesn't
+		// apply to channels supporting anchor outputs since HTLC transactions are pre-signed with a
+		// zero fee, so their fee is no longer considered to determine dust limits.
+		if !channel_type.supports_anchors_zero_fee_htlc_tx() {
+			let upper_limit = cmp::max(250 * 25,
+				fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::HighPriority) as u64 * 10);
+			if feerate_per_kw as u64 > upper_limit {
+				return Err(ChannelError::Close(format!("Peer's feerate much too high. Actual: {}. Our expected upper limit: {}", feerate_per_kw, upper_limit)));
+			}
+		}
+
+		// We can afford to use a lower bound with anchors than previously since we can now bump
+		// fees when broadcasting our commitment. However, we must still make sure we meet the
+		// minimum mempool feerate, until package relay is deployed, such that we can ensure the
+		// commitment transaction propagates throughout node mempools on its own.
+		let lower_limit_conf_target = if channel_type.supports_anchors_zero_fee_htlc_tx() {
+			ConfirmationTarget::MempoolMinimum
+		} else {
+			ConfirmationTarget::Background
+		};
+		let lower_limit = fee_estimator.bounded_sat_per_1000_weight(lower_limit_conf_target);
 		// Some fee estimators round up to the next full sat/vbyte (ie 250 sats per kw), causing
 		// occasional issues with feerate disagreements between an initiator that wants a feerate
 		// of 1.1 sat/vbyte and a receiver that wants 1.1 rounded up to 2. Thus, we always add 250
@@ -3688,7 +3703,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
 		if self.context.channel_state & (ChannelState::PeerDisconnected as u32) == ChannelState::PeerDisconnected as u32 {
 			return Err(ChannelError::Close("Peer sent update_fee when we needed a channel_reestablish".to_owned()));
 		}
-		Channel::<Signer>::check_remote_fee(fee_estimator, msg.feerate_per_kw, Some(self.context.feerate_per_kw), logger)?;
+		Channel::<Signer>::check_remote_fee(&self.context.channel_type, fee_estimator, msg.feerate_per_kw, Some(self.context.feerate_per_kw), logger)?;
 		let feerate_over_dust_buffer = msg.feerate_per_kw > self.context.get_dust_buffer_feerate(None);
 
 		self.context.pending_update_fee = Some((msg.feerate_per_kw, FeeUpdateState::RemoteAnnounced));
@@ -5502,10 +5517,15 @@ impl<Signer: WriteableEcdsaChannelSigner> OutboundV1Channel<Signer> {
 		let channel_type = Self::get_initial_channel_type(&config, their_features);
 		debug_assert!(channel_type.is_subset(&channelmanager::provided_channel_type_features(&config)));
 
-		let feerate = fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::Normal);
+		let commitment_conf_target = if channel_type.supports_anchors_zero_fee_htlc_tx() {
+			ConfirmationTarget::MempoolMinimum
+		} else {
+			ConfirmationTarget::Normal
+		};
+		let commitment_feerate = fee_estimator.bounded_sat_per_1000_weight(commitment_conf_target);
 
 		let value_to_self_msat = channel_value_satoshis * 1000 - push_msat;
-		let commitment_tx_fee = commit_tx_fee_msat(feerate, MIN_AFFORDABLE_HTLC_COUNT, &channel_type);
+		let commitment_tx_fee = commit_tx_fee_msat(commitment_feerate, MIN_AFFORDABLE_HTLC_COUNT, &channel_type);
 		if value_to_self_msat < commitment_tx_fee {
 			return Err(APIError::APIMisuseError{ err: format!("Funding amount ({}) can't even pay fee for initial commitment transaction fee of {}.", value_to_self_msat / 1000, commitment_tx_fee / 1000) });
 		}
@@ -5599,7 +5619,7 @@ impl<Signer: WriteableEcdsaChannelSigner> OutboundV1Channel<Signer> {
 				short_channel_id: None,
 				channel_creation_height: current_chain_height,
 
-				feerate_per_kw: feerate,
+				feerate_per_kw: commitment_feerate,
 				counterparty_dust_limit_satoshis: 0,
 				holder_dust_limit_satoshis: MIN_CHAN_DUST_LIMIT_SATOSHIS,
 				counterparty_max_htlc_value_in_flight_msat: 0,
@@ -5753,7 +5773,12 @@ impl<Signer: WriteableEcdsaChannelSigner> OutboundV1Channel<Signer> {
 	/// If we receive an error message, it may only be a rejection of the channel type we tried,
 	/// not of our ability to open any channel at all. Thus, on error, we should first call this
 	/// and see if we get a new `OpenChannel` message, otherwise the channel is failed.
-	pub(crate) fn maybe_handle_error_without_close(&mut self, chain_hash: BlockHash) -> Result<msgs::OpenChannel, ()> {
+	pub(crate) fn maybe_handle_error_without_close<F: Deref>(
+		&mut self, chain_hash: BlockHash, fee_estimator: &LowerBoundedFeeEstimator<F>
+	) -> Result<msgs::OpenChannel, ()>
+	where
+		F::Target: FeeEstimator
+	{
 		if !self.context.is_outbound() || self.context.channel_state != ChannelState::OurInitSent as u32 { return Err(()); }
 		if self.context.channel_type == ChannelTypeFeatures::only_static_remote_key() {
 			// We've exhausted our options
@@ -5770,6 +5795,7 @@ impl<Signer: WriteableEcdsaChannelSigner> OutboundV1Channel<Signer> {
 		// whatever reason.
 		if self.context.channel_type.supports_anchors_zero_fee_htlc_tx() {
 			self.context.channel_type.clear_anchors_zero_fee_htlc_tx();
+			self.context.feerate_per_kw = fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::Normal);
 			assert!(!self.context.channel_transaction_parameters.channel_type_features.supports_anchors_nonzero_fee_htlc_tx());
 		} else if self.context.channel_type.supports_scid_privacy() {
 			self.context.channel_type.clear_scid_privacy();
@@ -6039,7 +6065,7 @@ impl<Signer: WriteableEcdsaChannelSigner> InboundV1Channel<Signer> {
 		if msg.htlc_minimum_msat >= full_channel_value_msat {
 			return Err(ChannelError::Close(format!("Minimum htlc value ({}) was larger than full channel value ({})", msg.htlc_minimum_msat, full_channel_value_msat)));
 		}
-		Channel::<Signer>::check_remote_fee(fee_estimator, msg.feerate_per_kw, None, logger)?;
+		Channel::<Signer>::check_remote_fee(&channel_type, fee_estimator, msg.feerate_per_kw, None, logger)?;
 
 		let max_counterparty_selected_contest_delay = u16::min(config.channel_handshake_limits.their_to_self_delay, MAX_LOCAL_BREAKDOWN_TIMEOUT);
 		if msg.to_self_delay > max_counterparty_selected_contest_delay {
@@ -7441,7 +7467,8 @@ mod tests {
 		// arithmetic, causing a panic with debug assertions enabled.
 		let fee_est = TestFeeEstimator { fee_est: 42 };
 		let bounded_fee_estimator = LowerBoundedFeeEstimator::new(&fee_est);
-		assert!(Channel::<InMemorySigner>::check_remote_fee(&bounded_fee_estimator,
+		assert!(Channel::<InMemorySigner>::check_remote_fee(
+			&ChannelTypeFeatures::only_static_remote_key(), &bounded_fee_estimator,
 			u32::max_value(), None, &&test_utils::TestLogger::new()).is_err());
 	}
 

lightning/src/ln/channelmanager.rs

@@ -4235,13 +4235,19 @@ where
 		PersistenceNotifierGuard::optionally_notify(&self.total_consistency_lock, &self.persistence_notifier, || {
 			let mut should_persist = self.process_background_events();
 
-			let new_feerate = self.fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::Normal);
+			let normal_feerate = self.fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::Normal);
+			let min_mempool_feerate = self.fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::MempoolMinimum);
 
 			let per_peer_state = self.per_peer_state.read().unwrap();
 			for (_cp_id, peer_state_mutex) in per_peer_state.iter() {
 				let mut peer_state_lock = peer_state_mutex.lock().unwrap();
 				let peer_state = &mut *peer_state_lock;
 				for (chan_id, chan) in peer_state.channel_by_id.iter_mut() {
+					let new_feerate = if chan.context.get_channel_type().supports_anchors_zero_fee_htlc_tx() {
+						min_mempool_feerate
+					} else {
+						normal_feerate
+					};
 					let chan_needs_persist = self.update_channel_fee(chan_id, chan, new_feerate);
 					if chan_needs_persist == NotifyOption::DoPersist { should_persist = NotifyOption::DoPersist; }
 				}
@@ -4271,7 +4277,8 @@ where
 		PersistenceNotifierGuard::optionally_notify(&self.total_consistency_lock, &self.persistence_notifier, || {
 			let mut should_persist = self.process_background_events();
 
-			let new_feerate = self.fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::Normal);
+			let normal_feerate = self.fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::Normal);
+			let min_mempool_feerate = self.fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::MempoolMinimum);
 
 			let mut handle_errors: Vec<(Result<(), _>, _)> = Vec::new();
 			let mut timed_out_mpp_htlcs = Vec::new();
@@ -4284,6 +4291,11 @@ where
 					let pending_msg_events = &mut peer_state.pending_msg_events;
 					let counterparty_node_id = *counterparty_node_id;
 					peer_state.channel_by_id.retain(|chan_id, chan| {
+						let new_feerate = if chan.context.get_channel_type().supports_anchors_zero_fee_htlc_tx() {
+							min_mempool_feerate
+						} else {
+							normal_feerate
+						};
 						let chan_needs_persist = self.update_channel_fee(chan_id, chan, new_feerate);
 						if chan_needs_persist == NotifyOption::DoPersist { should_persist = NotifyOption::DoPersist; }
 
@@ -7250,7 +7262,7 @@ where
 				let mut peer_state_lock = peer_state_mutex_opt.unwrap().lock().unwrap();
 				let peer_state = &mut *peer_state_lock;
 				if let Some(chan) = peer_state.outbound_v1_channel_by_id.get_mut(&msg.channel_id) {
-					if let Ok(msg) = chan.maybe_handle_error_without_close(self.genesis_hash) {
+					if let Ok(msg) = chan.maybe_handle_error_without_close(self.genesis_hash, &self.fee_estimator) {
 						peer_state.pending_msg_events.push(events::MessageSendEvent::SendOpenChannel {
 							node_id: *counterparty_node_id,
 							msg,