Add basic fee estimation to on-chain wallet

src/payment/onchain.rs

@@ -122,4 +122,63 @@ impl OnchainPayment {
 		let fee_rate_opt = maybe_map_fee_rate_opt!(fee_rate);
 		self.wallet.send_to_address(address, send_amount, fee_rate_opt)
 	}
+
+	/// Estimates the fee for sending an on-chain payment to the given address.
+	///
+	/// 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 for estimating 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 estimate_send_to_address(
+		&self, address: &Address, amount_sats: u64, fee_rate: Option<FeeRate>,
+	) -> Result<bitcoin::Amount, Error> {
+		let rt_lock = self.runtime.read().unwrap();
+		if rt_lock.is_none() {
+			return Err(Error::NotRunning);
+		}
+
+		let cur_anchor_reserve_sats =
+			crate::total_anchor_channels_reserve_sats(&self.channel_manager, &self.config);
+		let send_amount =
+			OnchainSendAmount::ExactRetainingReserve { amount_sats, cur_anchor_reserve_sats };
+		let fee_rate_opt = maybe_map_fee_rate_opt!(fee_rate);
+		self.wallet.estimate_fee(address, send_amount, fee_rate_opt)
+	}
+
+	/// Estimates the fee for sending an on-chain payment to the given address, draining the available funds.
+	///
+	/// This is useful if you have closed all channels and want to migrate funds to another
+	/// on-chain wallet.
+	///
+	/// Please note that if `retain_reserves` is set to `false` this will **not** retain any on-chain reserves, which might be potentially
+	/// dangerous if you have open Anchor channels for which you can't trust the counterparty to
+	/// spend the Anchor output after channel closure. If `retain_reserves` is set to `true`, this
+	/// 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 estimate_send_all_to_address(
+		&self, address: &Address, retain_reserves: bool, fee_rate: Option<FeeRate>,
+	) -> Result<bitcoin::Amount, Error> {
+		let rt_lock = self.runtime.read().unwrap();
+		if rt_lock.is_none() {
+			return Err(Error::NotRunning);
+		}
+
+		let send_amount = if retain_reserves {
+			let cur_anchor_reserve_sats =
+				crate::total_anchor_channels_reserve_sats(&self.channel_manager, &self.config);
+			OnchainSendAmount::AllRetainingReserve { cur_anchor_reserve_sats }
+		} else {
+			OnchainSendAmount::AllDrainingReserve
+		};
+		let fee_rate_opt = maybe_map_fee_rate_opt!(fee_rate);
+		self.wallet.estimate_fee(address, send_amount, fee_rate_opt)
+	}
 }