WIP: Add FundingNeeded event for splicing

Rather than requiring the user to pass FundingTxInputs when initiating a
splice, generate a FundingNeeded event once the channel has become
quiescent. This simplifies error handling and UTXO / change address
clean-up by consolidating it in SpliceFailed event handling.

Later, this event will be used for opportunistic contributions (i.e.,
when the counterparty wins quiescence or initiates), dual-funding, and
RBF.

Author: jkczyz

lightning/src/events/bump_transaction/mod.rs

@@ -29,6 +29,7 @@ use crate::ln::chan_utils::{
 	HTLC_TIMEOUT_INPUT_KEYED_ANCHOR_WITNESS_WEIGHT, HTLC_TIMEOUT_INPUT_P2A_ANCHOR_WITNESS_WEIGHT,
 	P2WSH_TXOUT_WEIGHT, SEGWIT_MARKER_FLAG_WEIGHT, TRUC_CHILD_MAX_WEIGHT, TRUC_MAX_WEIGHT,
 };
+use crate::ln::funding::FundingTxInput;
 use crate::ln::types::ChannelId;
 use crate::prelude::*;
 use crate::sign::ecdsa::EcdsaChannelSigner;
@@ -49,7 +50,7 @@ use bitcoin::secp256k1::ecdsa::Signature;
 use bitcoin::secp256k1::{PublicKey, Secp256k1};
 use bitcoin::transaction::Version;
 use bitcoin::{
-	OutPoint, Psbt, PubkeyHash, ScriptBuf, Sequence, Transaction, TxIn, TxOut, WPubkeyHash, Witness,
+	FeeRate, OutPoint, Psbt, PubkeyHash, ScriptBuf, Sequence, Transaction, TxIn, TxOut, WPubkeyHash, Witness,
 };
 
 /// A descriptor used to sign for a commitment transaction's anchor output.
@@ -269,6 +270,12 @@ pub struct Input {
 	pub satisfaction_weight: u64,
 }
 
+impl_writeable_tlv_based!(Input, {
+	(1, outpoint, required),
+	(3, previous_utxo, required),
+	(5, satisfaction_weight, required),
+});
+
 /// An unspent transaction output that is available to spend resulting from a successful
 /// [`CoinSelection`] attempt.
 #[derive(Clone, Debug, Hash, PartialOrd, Ord, PartialEq, Eq)]
@@ -413,9 +420,16 @@ pub trait CoinSelectionSource {
 pub trait WalletSource {
 	/// Returns all UTXOs, with at least 1 confirmation each, that are available to spend.
 	fn list_confirmed_utxos<'a>(&'a self) -> AsyncResult<'a, Vec<Utxo>, ()>;
+
+	///
+	fn select_confirmed_utxos<'a>(
+		&'a self, must_spend: Vec<Input>, must_pay_to: &[TxOut], fee_rate: FeeRate,
+	) -> AsyncResult<'a, Vec<FundingTxInput>, ()>;
+
 	/// Returns a script to use for change above dust resulting from a successful coin selection
 	/// attempt.
 	fn get_change_script<'a>(&'a self) -> AsyncResult<'a, ScriptBuf, ()>;
+
 	/// Signs and provides the full [`TxIn::script_sig`] and [`TxIn::witness`] for all inputs within
 	/// the transaction known to the wallet (i.e., any provided via
 	/// [`WalletSource::list_confirmed_utxos`]).

lightning/src/events/bump_transaction/sync.rs

@@ -15,12 +15,13 @@ use core::task;
 
 use crate::chain::chaininterface::BroadcasterInterface;
 use crate::chain::ClaimId;
+use crate::ln::funding::FundingTxInput;
 use crate::prelude::*;
 use crate::sign::SignerProvider;
 use crate::util::async_poll::{dummy_waker, AsyncResult, MaybeSend, MaybeSync};
 use crate::util::logger::Logger;
 
-use bitcoin::{Psbt, ScriptBuf, Transaction, TxOut};
+use bitcoin::{FeeRate, Psbt, ScriptBuf, Transaction, TxOut};
 
 use super::BumpTransactionEvent;
 use super::{
@@ -36,9 +37,16 @@ use super::{
 pub trait WalletSourceSync {
 	/// Returns all UTXOs, with at least 1 confirmation each, that are available to spend.
 	fn list_confirmed_utxos(&self) -> Result<Vec<Utxo>, ()>;
+
+	///
+	fn select_confirmed_utxos(
+		&self, must_spend: Vec<Input>, must_pay_to: &[TxOut], fee_rate: FeeRate,
+	) -> Result<Vec<FundingTxInput>, ()>;
+
 	/// Returns a script to use for change above dust resulting from a successful coin selection
 	/// attempt.
 	fn get_change_script(&self) -> Result<ScriptBuf, ()>;
+
 	/// Signs and provides the full [`TxIn::script_sig`] and [`TxIn::witness`] for all inputs within
 	/// the transaction known to the wallet (i.e., any provided via
 	/// [`WalletSource::list_confirmed_utxos`]).
@@ -76,6 +84,13 @@ where
 		Box::pin(async move { utxos })
 	}
 
+	fn select_confirmed_utxos<'a>(
+		&'a self, must_spend: Vec<Input>, must_pay_to: &[TxOut], fee_rate: FeeRate,
+	) -> AsyncResult<'a, Vec<FundingTxInput>, ()> {
+		let utxos = self.0.select_confirmed_utxos(must_spend, must_pay_to, fee_rate);
+		Box::pin(async move { utxos })
+	}
+
 	fn get_change_script<'a>(&'a self) -> AsyncResult<'a, ScriptBuf, ()> {
 		let script = self.0.get_change_script();
 		Box::pin(async move { script })

lightning/src/events/mod.rs

@@ -25,6 +25,7 @@ use crate::blinded_path::payment::{
 use crate::chain::transaction;
 use crate::ln::channel::FUNDING_CONF_DEADLINE_BLOCKS;
 use crate::ln::channelmanager::{InterceptId, PaymentId, RecipientOnionFields};
+use crate::ln::funding::FundingTemplate;
 use crate::ln::types::ChannelId;
 use crate::ln::{msgs, LocalHTLCFailureReason};
 use crate::offers::invoice::Bolt12Invoice;
@@ -1816,6 +1817,28 @@ pub enum Event {
 		/// [`ChannelManager::respond_to_static_invoice_request`]: crate::ln::channelmanager::ChannelManager::respond_to_static_invoice_request
 		invoice_request: InvoiceRequest,
 	},
+	///
+	FundingNeeded {
+		/// The `channel_id` of the channel which you'll need to pass back into
+		/// [`ChannelManager::funding_contributed`].
+		///
+		/// [`ChannelManager::funding_contributed`]: crate::ln::channelmanager::ChannelManager::funding_contributed
+		channel_id: ChannelId,
+		/// The counterparty's `node_id`, which you'll need to pass back into
+		/// [`ChannelManager::funding_contributed`].
+		///
+		/// [`ChannelManager::funding_contributed`]: crate::ln::channelmanager::ChannelManager::funding_contributed
+		counterparty_node_id: PublicKey,
+		/// The `user_channel_id` value passed in for outbound channels, or for inbound channels if
+		/// [`UserConfig::manually_accept_inbound_channels`] config flag is set to true. Otherwise
+		/// `user_channel_id` will be randomized for inbound channels.
+		///
+		/// [`UserConfig::manually_accept_inbound_channels`]: crate::util::config::UserConfig::manually_accept_inbound_channels
+		user_channel_id: u128,
+
+		///
+		funding_template: FundingTemplate,
+	},
 	/// Indicates that a channel funding transaction constructed interactively is ready to be
 	/// signed. This event will only be triggered if at least one input was contributed.
 	///
@@ -2347,6 +2370,20 @@ impl Writeable for Event {
 					(13, *contributed_outputs, optional_vec),
 				});
 			},
+			&Event::FundingNeeded {
+				ref channel_id,
+				ref user_channel_id,
+				ref counterparty_node_id,
+				ref funding_template,
+			} => {
+				54u8.write(writer)?;
+				write_tlv_fields!(writer, {
+					(1, channel_id, required),
+					(3, user_channel_id, required),
+					(5, counterparty_node_id, required),
+					(7, funding_template, required),
+				});
+			},
 			// Note that, going forward, all new events must only write data inside of
 			// `write_tlv_fields`. Versions 0.0.101+ will ignore odd-numbered events that write
 			// data via `write_tlv_fields`.
@@ -2978,6 +3015,24 @@ impl MaybeReadable for Event {
 				};
 				f()
 			},
+			54u8 => {
+				let mut f = || {
+					_init_and_read_len_prefixed_tlv_fields!(reader, {
+						(1, channel_id, required),
+						(3, user_channel_id, required),
+						(5, counterparty_node_id, required),
+						(7, funding_template, required),
+					});
+
+					Ok(Some(Event::FundingNeeded {
+						channel_id: channel_id.0.unwrap(),
+						user_channel_id: user_channel_id.0.unwrap(),
+						counterparty_node_id: counterparty_node_id.0.unwrap(),
+						funding_template: funding_template.0.unwrap(),
+					}))
+				};
+				f()
+			},
 			// Versions prior to 0.0.100 did not ignore odd types, instead returning InvalidValue.
 			// Version 0.0.100 failed to properly ignore odd types, possibly resulting in corrupt
 			// reads.