Introduce OnchainFeeEstimator

We also decouple fee estimation from the BDK on-chain wallet and BDK's
corresponding `EsploraBlockchain`. Instead we use the esplora client
directly in a dedicated `OnchainFeeEstimator` object.

For one, this change is nice as it allows us
to move more things out of the `Wallet` thread and corresponding locks.
Moreover, it makes things more modular in general, which makes future
upgrades and testing easier.

Author: tnull

bindings/ldk_node.udl

@@ -108,6 +108,7 @@ enum NodeError {
 	"ChannelClosingFailed",
 	"ChannelConfigUpdateFailed",
 	"PersistenceFailed",
+	"FeerateEstimationUpdateFailed",
 	"WalletOperationFailed",
 	"OnchainTxSigningFailed",
 	"MessageSigningFailed",

src/builder.rs

@@ -1,4 +1,5 @@
 use crate::event::EventQueue;
+use crate::fee_estimator::OnchainFeeEstimator;
 use crate::gossip::GossipSource;
 use crate::io;
 use crate::io::sqlite_store::SqliteStore;
@@ -465,7 +466,7 @@ fn build_with_store_internal<K: KVStore + Sync + Send + 'static>(
 		BuildError::WalletSetupFailed
 	})?;
 
-	let (blockchain, tx_sync, tx_broadcaster) = match chain_data_source_config {
+	let (blockchain, tx_sync, tx_broadcaster, fee_estimator) = match chain_data_source_config {
 		Some(ChainDataSourceConfig::Esplora(server_url)) => {
 			let tx_sync = Arc::new(EsploraSyncClient::new(server_url.clone(), Arc::clone(&logger)));
 			let blockchain =
@@ -475,7 +476,9 @@ fn build_with_store_internal<K: KVStore + Sync + Send + 'static>(
 				tx_sync.client().clone(),
 				Arc::clone(&logger),
 			));
-			(blockchain, tx_sync, tx_broadcaster)
+			let fee_estimator =
+				Arc::new(OnchainFeeEstimator::new(tx_sync.client().clone(), Arc::clone(&logger)));
+			(blockchain, tx_sync, tx_broadcaster, fee_estimator)
 		}
 		None => {
 			// Default to Esplora client.
@@ -488,7 +491,9 @@ fn build_with_store_internal<K: KVStore + Sync + Send + 'static>(
 				tx_sync.client().clone(),
 				Arc::clone(&logger),
 			));
-			(blockchain, tx_sync, tx_broadcaster)
+			let fee_estimator =
+				Arc::new(OnchainFeeEstimator::new(tx_sync.client().clone(), Arc::clone(&logger)));
+			(blockchain, tx_sync, tx_broadcaster, fee_estimator)
 		}
 	};
 
@@ -497,6 +502,7 @@ fn build_with_store_internal<K: KVStore + Sync + Send + 'static>(
 		blockchain,
 		bdk_wallet,
 		Arc::clone(&tx_broadcaster),
+		Arc::clone(&fee_estimator),
 		Arc::clone(&logger),
 	));
 
@@ -505,7 +511,7 @@ fn build_with_store_internal<K: KVStore + Sync + Send + 'static>(
 		Some(Arc::clone(&tx_sync)),
 		Arc::clone(&tx_broadcaster),
 		Arc::clone(&logger),
-		Arc::clone(&wallet),
+		Arc::clone(&fee_estimator),
 		Arc::clone(&kv_store),
 	));
 
@@ -605,7 +611,7 @@ fn build_with_store_internal<K: KVStore + Sync + Send + 'static>(
 				Arc::clone(&keys_manager),
 				Arc::clone(&keys_manager),
 				Arc::clone(&keys_manager),
-				Arc::clone(&wallet),
+				Arc::clone(&fee_estimator),
 				Arc::clone(&chain_monitor),
 				Arc::clone(&tx_broadcaster),
 				Arc::clone(&router),
@@ -629,7 +635,7 @@ fn build_with_store_internal<K: KVStore + Sync + Send + 'static>(
 				best_block: BestBlock::new(genesis_block_hash, 0),
 			};
 			channelmanager::ChannelManager::new(
-				Arc::clone(&wallet),
+				Arc::clone(&fee_estimator),
 				Arc::clone(&chain_monitor),
 				Arc::clone(&tx_broadcaster),
 				Arc::clone(&router),
@@ -781,6 +787,7 @@ fn build_with_store_internal<K: KVStore + Sync + Send + 'static>(
 		wallet,
 		tx_sync,
 		tx_broadcaster,
+		fee_estimator,
 		event_queue,
 		channel_manager,
 		chain_monitor,

src/error.rs

@@ -25,6 +25,8 @@ pub enum Error {
 	ChannelConfigUpdateFailed,
 	/// Persistence failed.
 	PersistenceFailed,
+	/// A fee rate estimation update failed.
+	FeerateEstimationUpdateFailed,
 	/// A wallet operation failed.
 	WalletOperationFailed,
 	/// A signing operation for transaction failed.
@@ -79,6 +81,9 @@ impl fmt::Display for Error {
 			Self::ChannelClosingFailed => write!(f, "Failed to close channel."),
 			Self::ChannelConfigUpdateFailed => write!(f, "Failed to update channel config."),
 			Self::PersistenceFailed => write!(f, "Failed to persist data."),
+			Self::FeerateEstimationUpdateFailed => {
+				write!(f, "Failed to update fee rate estimates.")
+			}
 			Self::WalletOperationFailed => write!(f, "Failed to conduct wallet operation."),
 			Self::OnchainTxSigningFailed => write!(f, "Failed to sign given transaction."),
 			Self::MessageSigningFailed => write!(f, "Failed to sign given message."),

src/event.rs

@@ -1,4 +1,4 @@
-use crate::types::{Broadcaster, Wallet};
+use crate::types::{Broadcaster, FeeEstimator, Wallet};
 use crate::{hex_utils, ChannelManager, Config, Error, KeysManager, NetworkGraph, UserChannelId};
 
 use crate::payment_store::{
@@ -11,7 +11,9 @@ use crate::io::{
 };
 use crate::logger::{log_debug, log_error, log_info, Logger};
 
-use lightning::chain::chaininterface::{BroadcasterInterface, ConfirmationTarget, FeeEstimator};
+use lightning::chain::chaininterface::{
+	BroadcasterInterface, ConfirmationTarget, FeeEstimator as LDKFeeEstimator,
+};
 use lightning::events::Event as LdkEvent;
 use lightning::events::PaymentPurpose;
 use lightning::impl_writeable_tlv_based_enum;
@@ -245,6 +247,7 @@ where
 	wallet: Arc<Wallet>,
 	channel_manager: Arc<ChannelManager<K>>,
 	tx_broadcaster: Arc<Broadcaster>,
+	fee_estimator: Arc<FeeEstimator>,
 	network_graph: Arc<NetworkGraph>,
 	keys_manager: Arc<KeysManager>,
 	payment_store: Arc<PaymentStore<K, L>>,
@@ -260,15 +263,16 @@ where
 	pub fn new(
 		event_queue: Arc<EventQueue<K, L>>, wallet: Arc<Wallet>,
 		channel_manager: Arc<ChannelManager<K>>, tx_broadcaster: Arc<Broadcaster>,
-		network_graph: Arc<NetworkGraph>, keys_manager: Arc<KeysManager>,
-		payment_store: Arc<PaymentStore<K, L>>,
+		fee_estimator: Arc<FeeEstimator>, network_graph: Arc<NetworkGraph>,
+		keys_manager: Arc<KeysManager>, payment_store: Arc<PaymentStore<K, L>>,
 		runtime: Arc<RwLock<Option<tokio::runtime::Runtime>>>, logger: L, config: Arc<Config>,
 	) -> Self {
 		Self {
 			event_queue,
 			wallet,
 			channel_manager,
 			tx_broadcaster,
+			fee_estimator,
 			network_graph,
 			keys_manager,
 			payment_store,
@@ -584,7 +588,7 @@ where
 
 				let output_descriptors = &outputs.iter().collect::<Vec<_>>();
 				let tx_feerate = self
-					.wallet
+					.fee_estimator
 					.get_est_sat_per_1000_weight(ConfirmationTarget::NonAnchorChannelFee);
 
 				// We set nLockTime to the current height to discourage fee sniping.

src/fee_estimator.rs

@@ -0,0 +1,131 @@
+use crate::logger::{log_error, log_trace, Logger};
+use crate::Error;
+
+use lightning::chain::chaininterface::{
+	ConfirmationTarget, FeeEstimator, FEERATE_FLOOR_SATS_PER_KW,
+};
+
+use bdk::FeeRate;
+use esplora_client::AsyncClient as EsploraClient;
+
+use std::collections::HashMap;
+use std::ops::Deref;
+use std::sync::RwLock;
+
+pub(crate) struct OnchainFeeEstimator<L: Deref>
+where
+	L::Target: Logger,
+{
+	fee_rate_cache: RwLock<HashMap<ConfirmationTarget, FeeRate>>,
+	esplora_client: EsploraClient,
+	logger: L,
+}
+
+impl<L: Deref> OnchainFeeEstimator<L>
+where
+	L::Target: Logger,
+{
+	pub(crate) fn new(esplora_client: EsploraClient, logger: L) -> Self {
+		let fee_rate_cache = RwLock::new(HashMap::new());
+		Self { fee_rate_cache, esplora_client, logger }
+	}
+
+	pub(crate) async fn update_fee_estimates(&self) -> Result<(), Error> {
+		let confirmation_targets = vec![
+			ConfirmationTarget::OnChainSweep,
+			ConfirmationTarget::MaxAllowedNonAnchorChannelRemoteFee,
+			ConfirmationTarget::MinAllowedAnchorChannelRemoteFee,
+			ConfirmationTarget::MinAllowedNonAnchorChannelRemoteFee,
+			ConfirmationTarget::AnchorChannelFee,
+			ConfirmationTarget::NonAnchorChannelFee,
+			ConfirmationTarget::ChannelCloseMinimum,
+		];
+		for target in confirmation_targets {
+			let num_blocks = match target {
+				ConfirmationTarget::OnChainSweep => 6,
+				ConfirmationTarget::MaxAllowedNonAnchorChannelRemoteFee => 1,
+				ConfirmationTarget::MinAllowedAnchorChannelRemoteFee => 1008,
+				ConfirmationTarget::MinAllowedNonAnchorChannelRemoteFee => 144,
+				ConfirmationTarget::AnchorChannelFee => 1008,
+				ConfirmationTarget::NonAnchorChannelFee => 12,
+				ConfirmationTarget::ChannelCloseMinimum => 144,
+			};
+
+			let estimates = self.esplora_client.get_fee_estimates().await.map_err(|e| {
+				log_error!(
+					self.logger,
+					"Failed to retrieve fee rate estimates for {:?}: {}",
+					target,
+					e
+				);
+				Error::FeerateEstimationUpdateFailed
+			})?;
+
+			let converted_estimates = esplora_client::convert_fee_rate(num_blocks, estimates)
+				.map_err(|e| {
+					log_error!(
+						self.logger,
+						"Failed to convert fee rate estimates for {:?}: {}",
+						target,
+						e
+					);
+					Error::FeerateEstimationUpdateFailed
+				})?;
+
+			let fee_rate = FeeRate::from_sat_per_vb(converted_estimates);
+
+			// LDK 0.0.118 introduced changes to the `ConfirmationTarget` semantics that
+			// require some post-estimation adjustments to the fee rates, which we do here.
+			let adjusted_fee_rate = match target {
+				ConfirmationTarget::MaxAllowedNonAnchorChannelRemoteFee => {
+					let really_high_prio = fee_rate.as_sat_per_vb() * 10.0;
+					FeeRate::from_sat_per_vb(really_high_prio)
+				}
+				ConfirmationTarget::MinAllowedNonAnchorChannelRemoteFee => {
+					let slightly_less_than_background = fee_rate.fee_wu(1000) - 250;
+					FeeRate::from_sat_per_kwu(slightly_less_than_background as f32)
+				}
+				_ => fee_rate,
+			};
+
+			let mut locked_fee_rate_cache = self.fee_rate_cache.write().unwrap();
+			locked_fee_rate_cache.insert(target, adjusted_fee_rate);
+			log_trace!(
+				self.logger,
+				"Fee rate estimation updated for {:?}: {} sats/kwu",
+				target,
+				adjusted_fee_rate.fee_wu(1000)
+			);
+		}
+		Ok(())
+	}
+
+	pub(crate) fn estimate_fee_rate(&self, confirmation_target: ConfirmationTarget) -> FeeRate {
+		let locked_fee_rate_cache = self.fee_rate_cache.read().unwrap();
+
+		let fallback_sats_kwu = match confirmation_target {
+			ConfirmationTarget::OnChainSweep => 5000,
+			ConfirmationTarget::MaxAllowedNonAnchorChannelRemoteFee => 25 * 250,
+			ConfirmationTarget::MinAllowedAnchorChannelRemoteFee => FEERATE_FLOOR_SATS_PER_KW,
+			ConfirmationTarget::MinAllowedNonAnchorChannelRemoteFee => FEERATE_FLOOR_SATS_PER_KW,
+			ConfirmationTarget::AnchorChannelFee => 500,
+			ConfirmationTarget::NonAnchorChannelFee => 1000,
+			ConfirmationTarget::ChannelCloseMinimum => 500,
+		};
+
+		// We'll fall back on this, if we really don't have any other information.
+		let fallback_rate = FeeRate::from_sat_per_kwu(fallback_sats_kwu as f32);
+
+		*locked_fee_rate_cache.get(&confirmation_target).unwrap_or(&fallback_rate)
+	}
+}
+
+impl<L: Deref> FeeEstimator for OnchainFeeEstimator<L>
+where
+	L::Target: Logger,
+{
+	fn get_est_sat_per_1000_weight(&self, confirmation_target: ConfirmationTarget) -> u32 {
+		(self.estimate_fee_rate(confirmation_target).fee_wu(1000) as u32)
+			.max(FEERATE_FLOOR_SATS_PER_KW)
+	}
+}