Push splice initiation through the quiescent pipeline

diff --git a/lightning/src/events/bump_transaction/mod.rs b/lightning/src/events/bump_transaction/mod.rs
index 6f12769..fb872d6 100644
--- a/lightning/src/events/bump_transaction/mod.rs
+++ b/lightning/src/events/bump_transaction/mod.rs
@@ -264,6 +264,12 @@ pub struct Utxo {
 	pub satisfaction_weight: u64,
 }
 
+impl_writeable_tlv_based!(Utxo, {
+	(1, outpoint, required),
+	(3, output, required),
+	(5, satisfaction_weight, required),
+});
+
 impl Utxo {
 	/// Returns a `Utxo` with the `satisfaction_weight` estimate for a legacy P2PKH output.
 	pub fn new_p2pkh(outpoint: OutPoint, value: Amount, pubkey_hash: &PubkeyHash) -> Self {
diff --git a/lightning/src/ln/channel.rs b/lightning/src/ln/channel.rs
index 6cff41b..47eea77 100644
--- a/lightning/src/ln/channel.rs
+++ b/lightning/src/ln/channel.rs
@@ -2448,13 +2448,46 @@ impl PendingSplice {
 	}
 }
 
+pub(crate) struct SpliceInstructions {
+	adjusted_funding_contribution: SignedAmount,
+	our_funding_inputs: Vec<FundingTxInput>,
+	our_funding_outputs: Vec<TxOut>,
+	change_script: Option<ScriptBuf>,
+	funding_feerate_per_kw: u32,
+	locktime: u32,
+	original_funding_txo: OutPoint,
+}
+
+impl_writeable_tlv_based!(SpliceInstructions, {
+	(1, adjusted_funding_contribution, required),
+	(3, our_funding_inputs, required_vec),
+	(5, our_funding_outputs, required_vec),
+	(7, change_script, option),
+	(9, funding_feerate_per_kw, required),
+	(11, locktime, required),
+	(13, original_funding_txo, required),
+});
+
 pub(crate) enum QuiescentAction {
-	// TODO: Make this test-only once we have another variant (as some code requires *a* variant).
+	Splice(SpliceInstructions),
+	#[cfg(any(test, fuzzing))]
 	DoNothing,
 }
 
+pub(crate) enum StfuResponse {
+	Stfu(msgs::Stfu),
+	#[cfg_attr(not(splicing), allow(unused))]
+	SpliceInit(msgs::SpliceInit),
+}
+
+#[cfg(any(test, fuzzing))]
 impl_writeable_tlv_based_enum_upgradable!(QuiescentAction,
-	(99, DoNothing) => {},
+	(0, DoNothing) => {},
+	{1, Splice} => (),
+);
+#[cfg(not(any(test, fuzzing)))]
+impl_writeable_tlv_based_enum_upgradable!(QuiescentAction,,
+	{1, Splice} => (),
 );
 
 /// Wrapper around a [`Transaction`] useful for caching the result of [`Transaction::compute_txid`].
@@ -10748,9 +10781,13 @@ where
 	/// - `change_script`: an option change output script. If `None` and needed, one will be
 	///   generated by `SignerProvider::get_destination_script`.
 	#[cfg(splicing)]
-	pub fn splice_channel(
+	pub fn splice_channel<L: Deref>(
 		&mut self, contribution: SpliceContribution, funding_feerate_per_kw: u32, locktime: u32,
-	) -> Result<msgs::SpliceInit, APIError> {
+		logger: &L,
+	) -> Result<Option<msgs::Stfu>, APIError>
+	where
+		L::Target: Logger,
+	{
 		if self.holder_commitment_point.current_point().is_none() {
 			return Err(APIError::APIMisuseError {
 				err: format!(
@@ -10762,7 +10799,7 @@ where
 
 		// Check if a splice has been initiated already.
 		// Note: only a single outstanding splice is supported (per spec)
-		if self.pending_splice.is_some() {
+		if self.pending_splice.is_some() || self.quiescent_action.is_some() {
 			return Err(APIError::APIMisuseError {
 				err: format!(
 					"Channel {} cannot be spliced, as it has already a splice pending",
@@ -10780,8 +10817,6 @@ where
 			});
 		}
 
-		// TODO(splicing): check for quiescence
-
 		let our_funding_contribution = contribution.value();
 		if our_funding_contribution == SignedAmount::ZERO {
 			return Err(APIError::APIMisuseError {
@@ -10876,8 +10911,50 @@ where
 			}
 		}
 
-		let prev_funding_input = self.funding.to_splice_funding_input();
+		let original_funding_txo = self.funding.get_funding_txo().ok_or_else(|| {
+			debug_assert!(false);
+			APIError::APIMisuseError { err: "Channel isn't yet fully funded".to_owned() }
+		})?;
+
 		let (our_funding_inputs, our_funding_outputs, change_script) = contribution.into_tx_parts();
+
+		let action = QuiescentAction::Splice(SpliceInstructions {
+			adjusted_funding_contribution,
+			our_funding_inputs,
+			our_funding_outputs,
+			change_script,
+			funding_feerate_per_kw,
+			locktime,
+			original_funding_txo,
+		});
+		self.propose_quiescence(logger, action)
+			.map_err(|e| APIError::APIMisuseError { err: e.to_owned() })
+	}
+
+	#[cfg(splicing)]
+	fn send_splice_init(
+		&mut self, instructions: SpliceInstructions,
+	) -> Result<msgs::SpliceInit, String> {
+		let SpliceInstructions {
+			adjusted_funding_contribution,
+			our_funding_inputs,
+			our_funding_outputs,
+			change_script,
+			funding_feerate_per_kw,
+			locktime,
+			original_funding_txo,
+		} = instructions;
+
+		// Check if a splice has been initiated already.
+		// Note: only a single outstanding splice is supported (per spec)
+		if self.pending_splice.is_some() {
+			return Err(format!(
+				"Channel {} cannot be spliced, as it has already a splice pending",
+				self.context.channel_id(),
+			));
+		}
+
+		let prev_funding_input = self.funding.to_splice_funding_input();
 		let funding_negotiation_context = FundingNegotiationContext {
 			is_initiator: true,
 			our_funding_contribution: adjusted_funding_contribution,
@@ -11820,23 +11897,21 @@ where
 		);
 	}
 
-	#[cfg(any(test, fuzzing))]
+	#[cfg(any(splicing, test, fuzzing))]
 	#[rustfmt::skip]
 	pub fn propose_quiescence<L: Deref>(
 		&mut self, logger: &L, action: QuiescentAction,
-	) -> Result<Option<msgs::Stfu>, ChannelError>
+	) -> Result<Option<msgs::Stfu>, &'static str>
 	where
 		L::Target: Logger,
 	{
 		log_debug!(logger, "Attempting to initiate quiescence");
 
 		if !self.context.is_usable() {
-			return Err(ChannelError::Ignore(
-				"Channel is not in a usable state to propose quiescence".to_owned()
-			));
+			return Err("Channel is not in a usable state to propose quiescence");
 		}
 		if self.quiescent_action.is_some() {
-			return Err(ChannelError::Ignore("Channel is already quiescing".to_owned()));
+			return Err("Channel already has a pending quiescent action and cannot start another");
 		}
 
 		self.quiescent_action = Some(action);
@@ -11857,7 +11932,7 @@ where
 
 	// Assumes we are either awaiting quiescence or our counterparty has requested quiescence.
 	#[rustfmt::skip]
-	pub fn send_stfu<L: Deref>(&mut self, logger: &L) -> Result<msgs::Stfu, ChannelError>
+	pub fn send_stfu<L: Deref>(&mut self, logger: &L) -> Result<msgs::Stfu, &'static str>
 	where
 		L::Target: Logger,
 	{
@@ -11871,9 +11946,7 @@ where
 		if self.context.is_waiting_on_peer_pending_channel_update()
 			|| self.context.is_monitor_or_signer_pending_channel_update()
 		{
-			return Err(ChannelError::Ignore(
-				"We cannot send `stfu` while state machine is pending".to_owned()
-			));
+			return Err("We cannot send `stfu` while state machine is pending")
 		}
 
 		let initiator = if self.context.channel_state.is_remote_stfu_sent() {
@@ -11899,7 +11972,7 @@ where
 	#[rustfmt::skip]
 	pub fn stfu<L: Deref>(
 		&mut self, msg: &msgs::Stfu, logger: &L
-	) -> Result<Option<msgs::Stfu>, ChannelError> where L::Target: Logger {
+	) -> Result<Option<StfuResponse>, ChannelError> where L::Target: Logger {
 		if self.context.channel_state.is_quiescent() {
 			return Err(ChannelError::Warn("Channel is already quiescent".to_owned()));
 		}
@@ -11930,7 +12003,10 @@ where
 			self.context.channel_state.set_remote_stfu_sent();
 
 			log_debug!(logger, "Received counterparty stfu proposing quiescence");
-			return self.send_stfu(logger).map(|stfu| Some(stfu));
+			return self
+				.send_stfu(logger)
+				.map(|stfu| Some(StfuResponse::Stfu(stfu)))
+				.map_err(|e| ChannelError::Ignore(e.to_owned()));
 		}
 
 		// We already sent `stfu` and are now processing theirs. It may be in response to ours, or
@@ -11971,6 +12047,13 @@ where
 						"Internal Error: Didn't have anything to do after reaching quiescence".to_owned()
 					));
 				},
+				Some(QuiescentAction::Splice(_instructions)) => {
+					#[cfg(splicing)]
+					return self.send_splice_init(_instructions)
+						.map(|splice_init| Some(StfuResponse::SpliceInit(splice_init)))
+						.map_err(|e| ChannelError::WarnAndDisconnect(e.to_owned()));
+				},
+				#[cfg(any(test, fuzzing))]
 				Some(QuiescentAction::DoNothing) => {
 					// In quiescence test we want to just hang out here, letting the test manually
 					// leave quiescence.
@@ -12003,7 +12086,10 @@ where
 			|| (self.context.channel_state.is_remote_stfu_sent()
 				&& !self.context.channel_state.is_local_stfu_sent())
 		{
-			return self.send_stfu(logger).map(|stfu| Some(stfu));
+			return self
+				.send_stfu(logger)
+				.map(|stfu| Some(stfu))
+				.map_err(|e| ChannelError::Ignore(e.to_owned()));
 		}
 
 		// We're either:
diff --git a/lightning/src/ln/channelmanager.rs b/lightning/src/ln/channelmanager.rs
index c953e39..89992dd 100644
--- a/lightning/src/ln/channelmanager.rs
+++ b/lightning/src/ln/channelmanager.rs
@@ -61,7 +61,7 @@ use crate::ln::channel::QuiescentAction;
 use crate::ln::channel::{
 	self, hold_time_since, Channel, ChannelError, ChannelUpdateStatus, FundedChannel,
 	InboundV1Channel, OutboundV1Channel, PendingV2Channel, ReconnectionMsg, ShutdownResult,
-	UpdateFulfillCommitFetch, WithChannelContext,
+	StfuResponse, UpdateFulfillCommitFetch, WithChannelContext,
 };
 use crate::ln::channel_state::ChannelDetails;
 #[cfg(splicing)]
@@ -4494,12 +4494,19 @@ where
 			hash_map::Entry::Occupied(mut chan_phase_entry) => {
 				let locktime = locktime.unwrap_or_else(|| self.current_best_block().height);
 				if let Some(chan) = chan_phase_entry.get_mut().as_funded_mut() {
-					let msg =
-						chan.splice_channel(contribution, funding_feerate_per_kw, locktime)?;
-					peer_state.pending_msg_events.push(MessageSendEvent::SendSpliceInit {
-						node_id: *counterparty_node_id,
-						msg,
-					});
+					let logger = WithChannelContext::from(&self.logger, &chan.context, None);
+					let msg_opt = chan.splice_channel(
+						contribution,
+						funding_feerate_per_kw,
+						locktime,
+						&&logger,
+					)?;
+					if let Some(msg) = msg_opt {
+						peer_state.pending_msg_events.push(MessageSendEvent::SendStfu {
+							node_id: *counterparty_node_id,
+							msg,
+						});
+					}
 					Ok(())
 				} else {
 					Err(APIError::ChannelUnavailable {
@@ -10875,7 +10882,6 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 			));
 		}
 
-		let mut sent_stfu = false;
 		match peer_state.channel_by_id.entry(msg.channel_id) {
 			hash_map::Entry::Occupied(mut chan_entry) => {
 				if let Some(chan) = chan_entry.get_mut().as_funded_mut() {
@@ -10883,14 +10889,24 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 						&self.logger, Some(*counterparty_node_id), Some(msg.channel_id), None
 					);
 
-					if let Some(stfu) = try_channel_entry!(
-						self, peer_state, chan.stfu(&msg, &&logger), chan_entry
-					) {
-						sent_stfu = true;
-						peer_state.pending_msg_events.push(MessageSendEvent::SendStfu {
-							node_id: *counterparty_node_id,
-							msg: stfu,
-						});
+					let res = chan.stfu(&msg, &&logger);
+					let resp = try_channel_entry!(self, peer_state, res, chan_entry);
+					match resp {
+						None => Ok(false),
+						Some(StfuResponse::Stfu(msg)) => {
+							peer_state.pending_msg_events.push(MessageSendEvent::SendStfu {
+								node_id: *counterparty_node_id,
+								msg,
+							});
+							Ok(true)
+						},
+						Some(StfuResponse::SpliceInit(msg)) => {
+							peer_state.pending_msg_events.push(MessageSendEvent::SendSpliceInit {
+								node_id: *counterparty_node_id,
+								msg,
+							});
+							Ok(true)
+						},
 					}
 				} else {
 					let msg = "Peer sent `stfu` for an unfunded channel";
@@ -10905,8 +10921,6 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 				msg.channel_id
 			))
 		}
-
-		Ok(sent_stfu)
 	}
 
 	#[rustfmt::skip]
@@ -13873,8 +13887,8 @@ where
 			let persist = match &res {
 				Err(e) if e.closes_channel() => NotifyOption::DoPersist,
 				Err(_) => NotifyOption::SkipPersistHandleEvents,
-				Ok(sent_stfu) => {
-					if *sent_stfu {
+				Ok(responded) => {
+					if *responded {
 						NotifyOption::SkipPersistHandleEvents
 					} else {
 						NotifyOption::SkipPersistNoEvents
diff --git a/lightning/src/ln/funding.rs b/lightning/src/ln/funding.rs
index e42c338..a87a3cb 100644
--- a/lightning/src/ln/funding.rs
+++ b/lightning/src/ln/funding.rs
@@ -104,6 +104,12 @@ pub struct FundingTxInput {
 	pub(super) prevtx: Transaction,
 }
 
+impl_writeable_tlv_based!(FundingTxInput, {
+	(1, utxo, required),
+	(3, sequence, required),
+	(5, prevtx, required),
+});
+
 impl FundingTxInput {
 	fn new<F: FnOnce(&bitcoin::Script) -> bool>(
 		prevtx: Transaction, vout: u32, witness_weight: Weight, script_filter: F,
diff --git a/lightning/src/ln/splicing_tests.rs b/lightning/src/ln/splicing_tests.rs
index 2445a2d..b60903d 100644
--- a/lightning/src/ln/splicing_tests.rs
+++ b/lightning/src/ln/splicing_tests.rs
@@ -28,6 +28,8 @@ fn test_v1_splice_in() {
 	let acceptor_node_index = 1;
 	let initiator_node = &nodes[initiator_node_index];
 	let acceptor_node = &nodes[acceptor_node_index];
+	let initiator_node_id = initiator_node.node.get_our_node_id();
+	let acceptor_node_id = acceptor_node.node.get_our_node_id();
 
 	let channel_value_sat = 100_000;
 	let channel_reserve_amnt_sat = 1_000;
@@ -87,12 +89,16 @@ fn test_v1_splice_in() {
 			None, // locktime
 		)
 		.unwrap();
+
+	let init_stfu = get_event_msg!(initiator_node, MessageSendEvent::SendStfu, acceptor_node_id);
+	acceptor_node.node.handle_stfu(initiator_node_id, &init_stfu);
+
+	let ack_stfu = get_event_msg!(acceptor_node, MessageSendEvent::SendStfu, initiator_node_id);
+	initiator_node.node.handle_stfu(acceptor_node_id, &ack_stfu);
+
 	// Extract the splice_init message
-	let splice_init_msg = get_event_msg!(
-		initiator_node,
-		MessageSendEvent::SendSpliceInit,
-		acceptor_node.node.get_our_node_id()
-	);
+	let splice_init_msg =
+		get_event_msg!(initiator_node, MessageSendEvent::SendSpliceInit, acceptor_node_id);
 	assert_eq!(splice_init_msg.funding_contribution_satoshis, splice_in_sats as i64);
 	assert_eq!(splice_init_msg.funding_feerate_per_kw, funding_feerate_per_kw);
 	assert_eq!(splice_init_msg.funding_pubkey.to_string(), expected_initiator_funding_key);
diff --git a/lightning/src/util/ser.rs b/lightning/src/util/ser.rs
index b2521d9..15fd7fe 100644
--- a/lightning/src/util/ser.rs
+++ b/lightning/src/util/ser.rs
@@ -26,7 +26,7 @@ use core::ops::Deref;
 use alloc::collections::BTreeMap;
 
 use bitcoin::absolute::LockTime as AbsoluteLockTime;
-use bitcoin::amount::Amount;
+use bitcoin::amount::{Amount, SignedAmount};
 use bitcoin::consensus::Encodable;
 use bitcoin::constants::ChainHash;
 use bitcoin::hash_types::{BlockHash, Txid};
@@ -41,7 +41,7 @@ use bitcoin::secp256k1::ecdsa;
 use bitcoin::secp256k1::schnorr;
 use bitcoin::secp256k1::{PublicKey, SecretKey};
 use bitcoin::transaction::{OutPoint, Transaction, TxOut};
-use bitcoin::{consensus, TxIn, Weight, Witness};
+use bitcoin::{consensus, Sequence, TxIn, Weight, Witness};
 
 use dnssec_prover::rr::Name;
 
@@ -1383,6 +1383,19 @@ impl Readable for Amount {
 	}
 }
 
+impl Writeable for SignedAmount {
+	fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
+		self.to_sat().write(w)
+	}
+}
+
+impl Readable for SignedAmount {
+	fn read<R: Read>(r: &mut R) -> Result<Self, DecodeError> {
+		let amount: i64 = Readable::read(r)?;
+		Ok(SignedAmount::from_sat(amount))
+	}
+}
+
 impl Writeable for Weight {
 	fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 		self.to_wu().write(w)
@@ -1487,6 +1500,7 @@ impl_consensus_ser!(Transaction);
 impl_consensus_ser!(TxIn);
 impl_consensus_ser!(TxOut);
 impl_consensus_ser!(Witness);
+impl_consensus_ser!(Sequence);
 
 impl<T: Readable> Readable for Mutex<T> {
 	fn read<R: Read>(r: &mut R) -> Result<Self, DecodeError> {