Allow to override fee rates for onchain payments

We allow to override our fee estimator in the `send_to_address` and
`send_all_to_address` API methods. To this end, we implement a
bindings-compatible wrapper around `bitcoin::FeeRate`.

bindings/ldk_node.udl

@@ -161,9 +161,19 @@ interface OnchainPayment {
 	[Throws=NodeError]
 	Address new_address();
 	[Throws=NodeError]
-	Txid send_to_address([ByRef]Address address, u64 amount_sats);
+	Txid send_to_address([ByRef]Address address, u64 amount_sats, FeeRate? fee_rate);
 	[Throws=NodeError]
-	Txid send_all_to_address([ByRef]Address address, boolean retain_reserve);
+	Txid send_all_to_address([ByRef]Address address, boolean retain_reserve, FeeRate? fee_rate);
+};
+
+interface FeeRate {
+	[Name=from_sat_per_kwu]
+	constructor(u64 sat_kwu);
+	[Name=from_sat_per_vb_unchecked]
+	constructor(u64 sat_vb);
+	u64 to_sat_per_kwu();
+	u64 to_sat_per_vb_floor();
+	u64 to_sat_per_vb_ceil();
 };
 
 interface UnifiedQrPayment {

src/payment/onchain.rs

@@ -17,6 +17,24 @@ use bitcoin::{Address, Txid};
 
 use std::sync::{Arc, RwLock};
 
+#[cfg(not(feature = "uniffi"))]
+type FeeRate = bitcoin::FeeRate;
+#[cfg(feature = "uniffi")]
+type FeeRate = Arc<bitcoin::FeeRate>;
+
+macro_rules! maybe_map_fee_rate_opt {
+	($fee_rate_opt: expr) => {{
+		#[cfg(not(feature = "uniffi"))]
+		{
+			$fee_rate_opt
+		}
+		#[cfg(feature = "uniffi")]
+		{
+			$fee_rate_opt.map(|f| *f)
+		}
+	}};
+}
+
 /// A payment handler allowing to send and receive on-chain payments.
 ///
 /// Should be retrieved by calling [`Node::onchain_payment`].
@@ -50,9 +68,12 @@ impl OnchainPayment {
 	/// This will respect any on-chain reserve we need to keep, i.e., won't allow to cut into
 	/// [`BalanceDetails::total_anchor_channels_reserve_sats`].
 	///
+	/// If `fee_rate` is set it will be used on the resulting transaction. Otherwise we'll retrieve
+	/// a reasonable estimate from the configured chain source.
+	///
 	/// [`BalanceDetails::total_anchor_channels_reserve_sats`]: crate::BalanceDetails::total_anchor_channels_reserve_sats
 	pub fn send_to_address(
-		&self, address: &bitcoin::Address, amount_sats: u64,
+		&self, address: &bitcoin::Address, amount_sats: u64, fee_rate: Option<FeeRate>,
 	) -> Result<Txid, Error> {
 		let rt_lock = self.runtime.read().unwrap();
 		if rt_lock.is_none() {
@@ -63,7 +84,8 @@ impl OnchainPayment {
 			crate::total_anchor_channels_reserve_sats(&self.channel_manager, &self.config);
 		let send_amount =
 			OnchainSendAmount::ExactRetainingReserve { amount_sats, cur_anchor_reserve_sats };
-		self.wallet.send_to_address(address, send_amount)
+		let fee_rate_opt = maybe_map_fee_rate_opt!(fee_rate);
+		self.wallet.send_to_address(address, send_amount, fee_rate_opt)
 	}
 
 	/// Send an on-chain payment to the given address, draining the available funds.
@@ -77,9 +99,12 @@ impl OnchainPayment {
 	/// will try to send all spendable onchain funds, i.e.,
 	/// [`BalanceDetails::spendable_onchain_balance_sats`].
 	///
+	/// If `fee_rate` is set it will be used on the resulting transaction. Otherwise a reasonable
+	/// we'll retrieve an estimate from the configured chain source.
+	///
 	/// [`BalanceDetails::spendable_onchain_balance_sats`]: crate::balance::BalanceDetails::spendable_onchain_balance_sats
 	pub fn send_all_to_address(
-		&self, address: &bitcoin::Address, retain_reserves: bool,
+		&self, address: &bitcoin::Address, retain_reserves: bool, fee_rate: Option<FeeRate>,
 	) -> Result<Txid, Error> {
 		let rt_lock = self.runtime.read().unwrap();
 		if rt_lock.is_none() {
@@ -94,6 +119,7 @@ impl OnchainPayment {
 			OnchainSendAmount::AllDrainingReserve
 		};
 
-		self.wallet.send_to_address(address, send_amount)
+		let fee_rate_opt = maybe_map_fee_rate_opt!(fee_rate);
+		self.wallet.send_to_address(address, send_amount, fee_rate_opt)
 	}
 }

src/payment/unified_qr.rs

@@ -156,8 +156,11 @@ impl UnifiedQrPayment {
 			},
 		};
 
-		let txid =
-			self.onchain_payment.send_to_address(&uri_network_checked.address, amount.to_sat())?;
+		let txid = self.onchain_payment.send_to_address(
+			&uri_network_checked.address,
+			amount.to_sat(),
+			None,
+		)?;
 
 		Ok(QrPaymentResult::Onchain { txid })
 	}

src/uniffi_types.rs

@@ -30,7 +30,7 @@ pub use lightning_types::payment::{PaymentHash, PaymentPreimage, PaymentSecret};
 
 pub use lightning_invoice::Bolt11Invoice;
 
-pub use bitcoin::{Address, BlockHash, Network, OutPoint, Txid};
+pub use bitcoin::{Address, BlockHash, FeeRate, Network, OutPoint, Txid};
 
 pub use bip39::Mnemonic;
 

src/wallet/mod.rs

@@ -39,7 +39,8 @@ use bitcoin::secp256k1::ecdh::SharedSecret;
 use bitcoin::secp256k1::ecdsa::{RecoverableSignature, Signature};
 use bitcoin::secp256k1::{PublicKey, Scalar, Secp256k1, SecretKey, Signing};
 use bitcoin::{
-	Amount, ScriptBuf, Transaction, TxOut, Txid, WPubkeyHash, WitnessProgram, WitnessVersion,
+	Amount, FeeRate, ScriptBuf, Transaction, TxOut, Txid, WPubkeyHash, WitnessProgram,
+	WitnessVersion,
 };
 
 use std::ops::Deref;
@@ -239,9 +240,12 @@ where
 
 	pub(crate) fn send_to_address(
 		&self, address: &bitcoin::Address, send_amount: OnchainSendAmount,
+		fee_rate: Option<FeeRate>,
 	) -> Result<Txid, Error> {
+		// Use the set fee_rate or default to fee estimation.
 		let confirmation_target = ConfirmationTarget::OnchainPayment;
-		let fee_rate = self.fee_estimator.estimate_fee_rate(confirmation_target);
+		let fee_rate =
+			fee_rate.unwrap_or_else(|| self.fee_estimator.estimate_fee_rate(confirmation_target));
 
 		let tx = {
 			let mut locked_wallet = self.inner.lock().unwrap();

tests/integration_tests_rust.rs

@@ -315,11 +315,12 @@ fn onchain_spend_receive() {
 
 	assert_eq!(
 		Err(NodeError::InsufficientFunds),
-		node_a.onchain_payment().send_to_address(&addr_b, expected_node_a_balance + 1)
+		node_a.onchain_payment().send_to_address(&addr_b, expected_node_a_balance + 1, None)
 	);
 
 	let amount_to_send_sats = 1000;
-	let txid = node_b.onchain_payment().send_to_address(&addr_a, amount_to_send_sats).unwrap();
+	let txid =
+		node_b.onchain_payment().send_to_address(&addr_a, amount_to_send_sats, None).unwrap();
 	generate_blocks_and_wait(&bitcoind.client, &electrsd.client, 6);
 	wait_for_tx(&electrsd.client, txid);
 
@@ -334,7 +335,7 @@ fn onchain_spend_receive() {
 	assert!(node_b.list_balances().spendable_onchain_balance_sats < expected_node_b_balance_upper);
 
 	let addr_b = node_b.onchain_payment().new_address().unwrap();
-	let txid = node_a.onchain_payment().send_all_to_address(&addr_b, true).unwrap();
+	let txid = node_a.onchain_payment().send_all_to_address(&addr_b, true, None).unwrap();
 	generate_blocks_and_wait(&bitcoind.client, &electrsd.client, 6);
 	wait_for_tx(&electrsd.client, txid);
 
@@ -350,7 +351,7 @@ fn onchain_spend_receive() {
 	assert!(node_b.list_balances().spendable_onchain_balance_sats < expected_node_b_balance_upper);
 
 	let addr_b = node_b.onchain_payment().new_address().unwrap();
-	let txid = node_a.onchain_payment().send_all_to_address(&addr_b, false).unwrap();
+	let txid = node_a.onchain_payment().send_all_to_address(&addr_b, false, None).unwrap();
 	generate_blocks_and_wait(&bitcoind.client, &electrsd.client, 6);
 	wait_for_tx(&electrsd.client, txid);