Replace funding input tuple with struct

The funding inputs used for splicing and v2 channel establishment are
passed as a tuple of txin, prevtx, and witness weight. Add a struct so
that the items included can be better documented.

Author: jkczyz

lightning/src/ln/channel.rs

@@ -13,7 +13,7 @@ use bitcoin::consensus::encode;
 use bitcoin::constants::ChainHash;
 use bitcoin::script::{Builder, Script, ScriptBuf, WScriptHash};
 use bitcoin::sighash::EcdsaSighashType;
-use bitcoin::transaction::{Transaction, TxIn, TxOut};
+use bitcoin::transaction::{Transaction, TxOut};
 use bitcoin::{Weight, Witness};
 
 use bitcoin::hash_types::{BlockHash, Txid};
@@ -24,9 +24,9 @@ use bitcoin::hashes::Hash;
 use bitcoin::secp256k1::constants::PUBLIC_KEY_SIZE;
 use bitcoin::secp256k1::{ecdsa::Signature, Secp256k1};
 use bitcoin::secp256k1::{PublicKey, SecretKey};
-#[cfg(splicing)]
-use bitcoin::Sequence;
 use bitcoin::{secp256k1, sighash};
+#[cfg(splicing)]
+use bitcoin::{Sequence, TxIn};
 
 use crate::chain::chaininterface::{
 	fee_for_weight, ConfirmationTarget, FeeEstimator, LowerBoundedFeeEstimator,
@@ -53,7 +53,7 @@ use crate::ln::channel_state::{
 	OutboundHTLCDetails, OutboundHTLCStateDetails,
 };
 use crate::ln::channelmanager::{
-	self, FundingConfirmedMessage, HTLCFailureMsg, HTLCSource, OpenChannelMessage,
+	self, FundingConfirmedMessage, FundingTxInput, HTLCFailureMsg, HTLCSource, OpenChannelMessage,
 	PaymentClaimDetails, PendingHTLCInfo, PendingHTLCStatus, RAACommitmentOrder, SentHTLCId,
 	BREAKDOWN_TIMEOUT, MAX_LOCAL_BREAKDOWN_TIMEOUT, MIN_CLTV_EXPIRY_DELTA,
 };
@@ -5915,10 +5915,11 @@ fn estimate_v2_funding_transaction_fee(
 #[cfg(splicing)]
 #[rustfmt::skip]
 fn check_v2_funding_inputs_sufficient(
-	contribution_amount: i64, funding_inputs: &[(TxIn, Transaction, Weight)], is_initiator: bool,
+	contribution_amount: i64, funding_inputs: &[FundingTxInput], is_initiator: bool,
 	is_splice: bool, funding_feerate_sat_per_1000_weight: u32,
 ) -> Result<u64, ChannelError> {
-	let mut total_input_witness_weight = Weight::from_wu(funding_inputs.iter().map(|(_, _, w)| w.to_wu()).sum());
+	let mut total_input_witness_weight =
+		funding_inputs.iter().map(|FundingTxInput { witness_weight, .. }| witness_weight).sum();
 	let mut funding_inputs_len = funding_inputs.len();
 	if is_initiator && is_splice {
 		// consider the weight of the input and witness needed for spending the old funding transaction
@@ -5928,13 +5929,13 @@ fn check_v2_funding_inputs_sufficient(
 	let estimated_fee = estimate_v2_funding_transaction_fee(is_initiator, funding_inputs_len, total_input_witness_weight, funding_feerate_sat_per_1000_weight);
 
 	let mut total_input_sats = 0u64;
-	for (idx, input) in funding_inputs.iter().enumerate() {
-		if let Some(output) = input.1.output.get(input.0.previous_output.vout as usize) {
+	for (idx, FundingTxInput { txin, prevtx, .. }) in funding_inputs.iter().enumerate() {
+		if let Some(output) = prevtx.output.get(txin.previous_output.vout as usize) {
 			total_input_sats = total_input_sats.saturating_add(output.value.to_sat());
 		} else {
 			return Err(ChannelError::Warn(format!(
 				"Transaction with txid {} does not have an output with vout of {} corresponding to TxIn at funding_inputs[{}]",
-				input.1.compute_txid(), input.0.previous_output.vout, idx
+				prevtx.compute_txid(), txin.previous_output.vout, idx
 			)));
 		}
 	}
@@ -5978,7 +5979,7 @@ pub(super) struct FundingNegotiationContext {
 	pub shared_funding_input: Option<SharedOwnedInput>,
 	/// The funding inputs we will be contributing to the channel.
 	#[allow(dead_code)] // TODO(dual_funding): Remove once contribution to V2 channels is enabled.
-	pub our_funding_inputs: Vec<(TxIn, Transaction, Weight)>,
+	pub our_funding_inputs: Vec<FundingTxInput>,
 	/// The change output script. This will be used if needed or -- if not set -- generated using
 	/// `SignerProvider::get_destination_script`.
 	#[allow(dead_code)] // TODO(splicing): Remove once splicing is enabled.
@@ -6050,8 +6051,11 @@ impl FundingNegotiationContext {
 			}
 		}
 
-		let funding_inputs =
-			self.our_funding_inputs.into_iter().map(|(txin, tx, _)| (txin, tx)).collect();
+		let funding_inputs = self
+			.our_funding_inputs
+			.into_iter()
+			.map(|FundingTxInput { txin, prevtx, .. }| (txin, prevtx))
+			.collect();
 
 		let constructor_args = InteractiveTxConstructorArgs {
 			entropy_source,
@@ -10604,9 +10608,8 @@ where
 	///   generated by `SignerProvider::get_destination_script`.
 	#[cfg(splicing)]
 	pub fn splice_channel(
-		&mut self, our_funding_contribution_satoshis: i64,
-		our_funding_inputs: Vec<(TxIn, Transaction, Weight)>, change_script: Option<ScriptBuf>,
-		funding_feerate_per_kw: u32, locktime: u32,
+		&mut self, our_funding_contribution_satoshis: i64, our_funding_inputs: Vec<FundingTxInput>,
+		change_script: Option<ScriptBuf>, funding_feerate_per_kw: u32, locktime: u32,
 	) -> Result<msgs::SpliceInit, APIError> {
 		// Check if a splice has been initiated already.
 		// Note: only a single outstanding splice is supported (per spec)
@@ -10672,7 +10675,7 @@ where
 			),
 		})?;
 
-		for (txin, tx, _) in our_funding_inputs.iter() {
+		for FundingTxInput { txin, prevtx, .. } in our_funding_inputs.iter() {
 			const MESSAGE_TEMPLATE: msgs::TxAddInput = msgs::TxAddInput {
 				channel_id: ChannelId([0; 32]),
 				serial_id: 0,
@@ -10681,7 +10684,7 @@ where
 				sequence: 0,
 				shared_input_txid: None,
 			};
-			let message_len = MESSAGE_TEMPLATE.serialized_length() + tx.serialized_length();
+			let message_len = MESSAGE_TEMPLATE.serialized_length() + prevtx.serialized_length();
 			if message_len > LN_MAX_MSG_LEN {
 				return Err(APIError::APIMisuseError {
 					err: format!(
@@ -12468,7 +12471,7 @@ where
 	pub fn new_outbound<ES: Deref, F: Deref, L: Deref>(
 		fee_estimator: &LowerBoundedFeeEstimator<F>, entropy_source: &ES, signer_provider: &SP,
 		counterparty_node_id: PublicKey, their_features: &InitFeatures, funding_satoshis: u64,
-		funding_inputs: Vec<(TxIn, Transaction, Weight)>, user_id: u128, config: &UserConfig,
+		funding_inputs: Vec<FundingTxInput>, user_id: u128, config: &UserConfig,
 		current_chain_height: u32, outbound_scid_alias: u64, funding_confirmation_target: ConfirmationTarget,
 		logger: L,
 	) -> Result<Self, APIError>
@@ -12682,8 +12685,10 @@ where
 			value: Amount::from_sat(funding.get_value_satoshis()),
 			script_pubkey: funding.get_funding_redeemscript().to_p2wsh(),
 		};
-		let inputs_to_contribute =
-			our_funding_inputs.into_iter().map(|(txin, tx, _)| (txin, tx)).collect();
+		let inputs_to_contribute = our_funding_inputs
+			.into_iter()
+			.map(|FundingTxInput { txin, prevtx, .. }| (txin, prevtx))
+			.collect();
 
 		let interactive_tx_constructor = Some(InteractiveTxConstructor::new(
 			InteractiveTxConstructorArgs {
@@ -14119,6 +14124,8 @@ mod tests {
 		TOTAL_BITCOIN_SUPPLY_SATOSHIS,
 	};
 	use crate::ln::channel_keys::{RevocationBasepoint, RevocationKey};
+	#[cfg(splicing)]
+	use crate::ln::channelmanager::FundingTxInput;
 	use crate::ln::channelmanager::{self, HTLCSource, PaymentId};
 	use crate::ln::msgs;
 	use crate::ln::msgs::{ChannelUpdate, UnsignedChannelUpdate, MAX_VALUE_MSAT};
@@ -14155,7 +14162,7 @@ mod tests {
 	use bitcoin::transaction::TxIn;
 	use bitcoin::transaction::{Transaction, TxOut, Version};
 	#[cfg(splicing)]
-	use bitcoin::Weight;
+	use bitcoin::{ScriptBuf, Weight};
 	use bitcoin::{WitnessProgram, WitnessVersion};
 	use std::cmp;
 
@@ -15897,19 +15904,21 @@ mod tests {
 
 	#[cfg(splicing)]
 	#[rustfmt::skip]
-	fn funding_input_sats(input_value_sats: u64) -> (TxIn, Transaction, Weight) {
+	fn funding_input_sats(input_value_sats: u64) -> FundingTxInput {
 		use crate::sign::P2WPKH_WITNESS_WEIGHT;
 
-		let input_1_prev_out = TxOut { value: Amount::from_sat(input_value_sats), script_pubkey: bitcoin::ScriptBuf::default() };
-		let input_1_prev_tx = Transaction {
-			input: vec![], output: vec![input_1_prev_out],
+		let prevout = TxOut { value: Amount::from_sat(input_value_sats), script_pubkey: ScriptBuf::default() };
+		let prevtx = Transaction {
+			input: vec![], output: vec![prevout],
 			version: Version::TWO, lock_time: bitcoin::absolute::LockTime::ZERO,
 		};
-		let input_1_txin = TxIn {
-			previous_output: bitcoin::OutPoint { txid: input_1_prev_tx.compute_txid(), vout: 0 },
+		let txin = TxIn {
+			previous_output: bitcoin::OutPoint { txid: prevtx.compute_txid(), vout: 0 },
 			..Default::default()
 		};
-		(input_1_txin, input_1_prev_tx, Weight::from_wu(P2WPKH_WITNESS_WEIGHT))
+		let witness_weight = Weight::from_wu(P2WPKH_WITNESS_WEIGHT);
+
+		FundingTxInput { txin, prevtx, witness_weight }
 	}
 
 	#[cfg(splicing)]

lightning/src/ln/channelmanager.rs

@@ -30,9 +30,9 @@ use bitcoin::hashes::{Hash, HashEngine, HmacEngine};
 
 use bitcoin::secp256k1::Secp256k1;
 use bitcoin::secp256k1::{PublicKey, SecretKey};
-use bitcoin::{secp256k1, Sequence, SignedAmount};
 #[cfg(splicing)]
-use bitcoin::{ScriptBuf, TxIn, Weight};
+use bitcoin::ScriptBuf;
+use bitcoin::{secp256k1, Sequence, SignedAmount, TxIn, Weight};
 
 use crate::blinded_path::message::MessageForwardNode;
 use crate::blinded_path::message::{AsyncPaymentsContext, OffersContext};
@@ -200,6 +200,26 @@ pub use crate::ln::outbound_payment::{
 };
 use crate::ln::script::ShutdownScript;
 
+/// An input to contribute to a channel's funding transaction either when using the v2 channel
+/// establishment protocol or when splicing.
+#[derive(Clone)]
+pub struct FundingTxInput {
+	/// An input for the funding transaction used to cover the channel contributions.
+	pub txin: TxIn,
+
+	/// The transaction containing the unspent [`TxOut`] referenced by [`txin`].
+	///
+	/// [`TxOut`]: bitcoin::TxOut
+	/// [`txin`]: Self::txin
+	pub prevtx: Transaction,
+
+	/// The weight of the witness that is needed to spend the [`TxOut`] referenced by [`txin`].
+	///
+	/// [`TxOut`]: bitcoin::TxOut
+	/// [`txin`]: Self::txin
+	pub witness_weight: Weight,
+}
+
 // We hold various information about HTLC relay in the HTLC objects in Channel itself:
 //
 // Upon receipt of an HTLC from a peer, we'll give it a PendingHTLCStatus indicating if it should
@@ -4459,7 +4479,7 @@ where
 	#[rustfmt::skip]
 	pub fn splice_channel(
 		&self, channel_id: &ChannelId, counterparty_node_id: &PublicKey, our_funding_contribution_satoshis: i64,
-		our_funding_inputs: Vec<(TxIn, Transaction, Weight)>, change_script: Option<ScriptBuf>,
+		our_funding_inputs: Vec<FundingTxInput>, change_script: Option<ScriptBuf>,
 		funding_feerate_per_kw: u32, locktime: Option<u32>,
 	) -> Result<(), APIError> {
 		let mut res = Ok(());
@@ -4480,9 +4500,8 @@ where
 	#[cfg(splicing)]
 	fn internal_splice_channel(
 		&self, channel_id: &ChannelId, counterparty_node_id: &PublicKey,
-		our_funding_contribution_satoshis: i64,
-		our_funding_inputs: Vec<(TxIn, Transaction, Weight)>, change_script: Option<ScriptBuf>,
-		funding_feerate_per_kw: u32, locktime: Option<u32>,
+		our_funding_contribution_satoshis: i64, our_funding_inputs: Vec<FundingTxInput>,
+		change_script: Option<ScriptBuf>, funding_feerate_per_kw: u32, locktime: Option<u32>,
 	) -> Result<(), APIError> {
 		let per_peer_state = self.per_peer_state.read().unwrap();
 

lightning/src/ln/dual_funding_tests.rs

@@ -18,6 +18,7 @@ use {
 	},
 	crate::ln::channel::PendingV2Channel,
 	crate::ln::channel_keys::{DelayedPaymentBasepoint, HtlcBasepoint, RevocationBasepoint},
+	crate::ln::channelmanager::FundingTxInput,
 	crate::ln::functional_test_utils::*,
 	crate::ln::msgs::{BaseMessageHandler, ChannelMessageHandler, MessageSendEvent},
 	crate::ln::msgs::{CommitmentSigned, TxAddInput, TxAddOutput, TxComplete, TxSignatures},
@@ -82,12 +83,13 @@ fn do_test_v2_channel_establishment(session: V2ChannelEstablishmentTestSession)
 		&RevocationBasepoint::from(open_channel_v2_msg.common_fields.revocation_basepoint),
 	);
 
+	let FundingTxInput { txin, prevtx, .. } = &initiator_funding_inputs[0];
 	let tx_add_input_msg = TxAddInput {
 		channel_id,
 		serial_id: 2, // Even serial_id from initiator.
-		prevtx: Some(initiator_funding_inputs[0].1.clone()),
+		prevtx: Some(prevtx.clone()),
 		prevtx_out: 0,
-		sequence: initiator_funding_inputs[0].0.sequence.0,
+		sequence: txin.sequence.0,
 		shared_input_txid: None,
 	};
 	let input_value = tx_add_input_msg.prevtx.as_ref().unwrap().output

lightning/src/ln/functional_test_utils.rs

@@ -23,8 +23,8 @@ use crate::events::{
 };
 use crate::ln::chan_utils::{commitment_tx_base_weight, COMMITMENT_TX_WEIGHT_PER_HTLC};
 use crate::ln::channelmanager::{
-	AChannelManager, ChainParameters, ChannelManager, ChannelManagerReadArgs, PaymentId,
-	RAACommitmentOrder, RecipientOnionFields, MIN_CLTV_EXPIRY_DELTA,
+	AChannelManager, ChainParameters, ChannelManager, ChannelManagerReadArgs, FundingTxInput,
+	PaymentId, RAACommitmentOrder, RecipientOnionFields, MIN_CLTV_EXPIRY_DELTA,
 };
 use crate::ln::msgs;
 use crate::ln::msgs::{
@@ -1440,7 +1440,7 @@ fn internal_create_funding_transaction<'a, 'b, 'c>(
 /// Return the inputs (with prev tx), and the total witness weight for these inputs
 pub fn create_dual_funding_utxos_with_prev_txs(
 	node: &Node<'_, '_, '_>, utxo_values_in_satoshis: &[u64],
-) -> Vec<(TxIn, Transaction, Weight)> {
+) -> Vec<FundingTxInput> {
 	// Ensure we have unique transactions per node by using the locktime.
 	let tx = Transaction {
 		version: TxVersion::TWO,
@@ -1462,17 +1462,17 @@ pub fn create_dual_funding_utxos_with_prev_txs(
 
 	let mut inputs = vec![];
 	for i in 0..utxo_values_in_satoshis.len() {
-		inputs.push((
-			TxIn {
+		inputs.push(FundingTxInput {
+			txin: TxIn {
 				previous_output: OutPoint { txid: tx.compute_txid(), index: i as u16 }
 					.into_bitcoin_outpoint(),
 				script_sig: ScriptBuf::new(),
 				sequence: Sequence::ZERO,
 				witness: Witness::new(),
 			},
-			tx.clone(),
-			Weight::from_wu(P2WPKH_WITNESS_WEIGHT),
-		));
+			prevtx: tx.clone(),
+			witness_weight: Weight::from_wu(P2WPKH_WITNESS_WEIGHT),
+		});
 	}
 
 	inputs

lightning/src/ln/interactivetxs.rs

@@ -28,6 +28,7 @@ use crate::chain::chaininterface::fee_for_weight;
 use crate::events::bump_transaction::{BASE_INPUT_WEIGHT, EMPTY_SCRIPT_SIG_WEIGHT};
 use crate::ln::chan_utils::FUNDING_TRANSACTION_WITNESS_WEIGHT;
 use crate::ln::channel::{FundingNegotiationContext, TOTAL_BITCOIN_SUPPLY_SATOSHIS};
+use crate::ln::channelmanager::FundingTxInput;
 use crate::ln::msgs;
 use crate::ln::msgs::{MessageSendEvent, SerialId, TxSignatures};
 use crate::ln::types::ChannelId;
@@ -2075,17 +2076,18 @@ pub(super) fn calculate_change_output_value(
 
 	let mut total_input_satoshis = 0u64;
 	let mut our_funding_inputs_weight = 0u64;
-	for (txin, tx, _) in context.our_funding_inputs.iter() {
-		let txid = tx.compute_txid();
+	for FundingTxInput { txin, prevtx, witness_weight } in context.our_funding_inputs.iter() {
+		let txid = prevtx.compute_txid();
 		if txin.previous_output.txid != txid {
 			return Err(AbortReason::PrevTxOutInvalid);
 		}
-		let output = tx
+		let output = prevtx
 			.output
 			.get(txin.previous_output.vout as usize)
 			.ok_or(AbortReason::PrevTxOutInvalid)?;
 		total_input_satoshis = total_input_satoshis.saturating_add(output.value.to_sat());
-		let weight = estimate_input_weight(output).to_wu();
+
+		let weight = BASE_INPUT_WEIGHT + EMPTY_SCRIPT_SIG_WEIGHT + witness_weight.to_wu();
 		our_funding_inputs_weight = our_funding_inputs_weight.saturating_add(weight);
 	}
 
@@ -2128,6 +2130,7 @@ pub(super) fn calculate_change_output_value(
 mod tests {
 	use crate::chain::chaininterface::{fee_for_weight, FEERATE_FLOOR_SATS_PER_KW};
 	use crate::ln::channel::{FundingNegotiationContext, TOTAL_BITCOIN_SUPPLY_SATOSHIS};
+	use crate::ln::channelmanager::FundingTxInput;
 	use crate::ln::interactivetxs::{
 		calculate_change_output_value, generate_holder_serial_id, AbortReason,
 		HandleTxCompleteValue, InteractiveTxConstructor, InteractiveTxConstructorArgs,
@@ -2155,7 +2158,8 @@ mod tests {
 	use super::{
 		get_output_weight, AddingRole, ConstructedTransaction, InteractiveTxOutput,
 		InteractiveTxSigningSession, NegotiatedTxInput, OutputOwned, P2TR_INPUT_WEIGHT_LOWER_BOUND,
-		P2WPKH_INPUT_WEIGHT_LOWER_BOUND, P2WSH_INPUT_WEIGHT_LOWER_BOUND, TX_COMMON_FIELDS_WEIGHT,
+		P2WPKH_INPUT_WEIGHT_LOWER_BOUND, P2WPKH_WITNESS_WEIGHT, P2WSH_INPUT_WEIGHT_LOWER_BOUND,
+		TX_COMMON_FIELDS_WEIGHT,
 	};
 
 	const TEST_FEERATE_SATS_PER_KW: u32 = FEERATE_FLOOR_SATS_PER_KW * 10;
@@ -3147,23 +3151,23 @@ mod tests {
 		let inputs = input_prevouts
 			.iter()
 			.map(|txout| {
-				let tx = Transaction {
+				let prevtx = Transaction {
 					input: Vec::new(),
 					output: vec![(*txout).clone()],
 					lock_time: AbsoluteLockTime::ZERO,
 					version: Version::TWO,
 				};
-				let txid = tx.compute_txid();
+				let txid = prevtx.compute_txid();
 				let txin = TxIn {
 					previous_output: OutPoint { txid, vout: 0 },
 					script_sig: ScriptBuf::new(),
 					sequence: Sequence::ZERO,
 					witness: Witness::new(),
 				};
-				let weight = Weight::ZERO;
-				(txin, tx, weight)
+				let witness_weight = Weight::from_wu(P2WPKH_WITNESS_WEIGHT);
+				FundingTxInput { txin, prevtx, witness_weight }
 			})
-			.collect::<Vec<(TxIn, Transaction, Weight)>>();
+			.collect();
 		let our_contributed = 110_000;
 		let txout = TxOut { value: Amount::from_sat(10_000), script_pubkey: ScriptBuf::new() };
 		let outputs = vec![txout];