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Refactor ConstructedTransaction to contain Transaction #4097

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Merged
merged 10 commits into from
Sep 24, 2025
+282 −348
Merged

Refactor ConstructedTransaction to contain Transaction #4097

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91845e4
Use FundingTxInput in InteractiveTxConstructorArgs
jkczyz Sep 19, 2025
1e510cc
Track satisfaction_weight in InteractiveTxInput
jkczyz Sep 19, 2025
0a1d445
Remove NegotiatedTxInput::weight
jkczyz Sep 19, 2025
e262326
Compute ConstructedTransaction weight from Transaction
jkczyz Sep 19, 2025
d01df5a
Rename NegotiatedTxInput to TxInMetadata
jkczyz Sep 22, 2025
0cab3c3
Remove duplicate TxOut persistence
jkczyz Sep 19, 2025
a8d7646
Remove unused fields from ConstructedTransaction
jkczyz Sep 22, 2025
105c686
Remove input value fields from ConstructedTransaction
jkczyz Sep 23, 2025
f20a477
Persist witnesses in InteractiveTxSigningSession
jkczyz Sep 22, 2025
86ed012
Reduce visibility of ConstructedTransaction methods
jkczyz Sep 23, 2025
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142 changes: 71 additions & 71 deletions lightning/src/ln/interactivetxs.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,6 @@ use bitcoin::constants::WITNESS_SCALE_FACTOR;
use bitcoin::ecdsa::Signature as BitcoinSignature;
use bitcoin::key::Secp256k1;
use bitcoin::policy::MAX_STANDARD_TX_WEIGHT;
use bitcoin::secp256k1::ecdsa::Signature;
use bitcoin::secp256k1::{Message, PublicKey};
use bitcoin::sighash::SighashCache;
use bitcoin::transaction::Version;
Expand Down Expand Up @@ -339,11 +338,54 @@ impl ConstructedTransaction {
.sum()
}

fn finalize(
&self, holder_tx_signatures: &TxSignatures, counterparty_tx_signatures: &TxSignatures,
shared_input_sig: Option<&SharedInputSignature>,
) -> Option<Transaction> {
let mut tx = self.tx.clone();
self.add_local_witnesses(&mut tx, holder_tx_signatures.witnesses.clone());
self.add_remote_witnesses(&mut tx, counterparty_tx_signatures.witnesses.clone());

if let Some(shared_input_index) = self.shared_input_index {
let holder_shared_input_sig =
holder_tx_signatures.shared_input_signature.or_else(|| {
debug_assert!(false);
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I think it'd be better to debug_assert_eq!(shared_input_index.is_some(), holder_tx_signatures.shared_input_signature.is_some()) to catch the other possible cases as well

None
})?;
let counterparty_shared_input_sig =
counterparty_tx_signatures.shared_input_signature.or_else(|| {
debug_assert!(false);
None
})?;

let shared_input_sig = shared_input_sig.or_else(|| {
debug_assert!(false);
None
})?;

let mut witness = Witness::new();
witness.push(Vec::new());
let holder_sig = BitcoinSignature::sighash_all(holder_shared_input_sig);
let counterparty_sig = BitcoinSignature::sighash_all(counterparty_shared_input_sig);
if shared_input_sig.holder_signature_first {
witness.push_ecdsa_signature(&holder_sig);
witness.push_ecdsa_signature(&counterparty_sig);
} else {
witness.push_ecdsa_signature(&counterparty_sig);
witness.push_ecdsa_signature(&holder_sig);
}
witness.push(&shared_input_sig.witness_script);
tx.input[shared_input_index as usize].witness = witness;
}

Some(tx)
}

/// Adds provided holder witnesses to holder inputs of unsigned transaction.
///
/// Note that it is assumed that the witness count equals the holder input count.
fn add_local_witnesses(&mut self, witnesses: Vec<Witness>) {
self.tx
fn add_local_witnesses(&self, transaction: &mut Transaction, witnesses: Vec<Witness>) {
transaction
.input
.iter_mut()
.zip(self.input_metadata.iter())
Expand All @@ -362,8 +404,8 @@ impl ConstructedTransaction {
/// Adds counterparty witnesses to counterparty inputs of unsigned transaction.
///
/// Note that it is assumed that the witness count equals the counterparty input count.
fn add_remote_witnesses(&mut self, witnesses: Vec<Witness>) {
self.tx
fn add_remote_witnesses(&self, transaction: &mut Transaction, witnesses: Vec<Witness>) {
transaction
.input
.iter_mut()
.zip(self.input_metadata.iter())
Expand Down Expand Up @@ -392,13 +434,11 @@ impl ConstructedTransaction {
pub(crate) struct SharedInputSignature {
holder_signature_first: bool,
witness_script: ScriptBuf,
counterparty_signature: Option<Signature>,
}

impl_writeable_tlv_based!(SharedInputSignature, {
(1, holder_signature_first, required),
(3, witness_script, required),
(5, counterparty_signature, required),
});

/// The InteractiveTxSigningSession coordinates the signing flow of interactively constructed
Expand All @@ -413,9 +453,9 @@ pub(crate) struct InteractiveTxSigningSession {
unsigned_tx: ConstructedTransaction,
holder_sends_tx_signatures_first: bool,
has_received_commitment_signed: bool,
has_received_tx_signatures: bool,
shared_input_signature: Option<SharedInputSignature>,
holder_tx_signatures: Option<TxSignatures>,
counterparty_tx_signatures: Option<TxSignatures>,
}

impl InteractiveTxSigningSession {
Expand All @@ -432,7 +472,7 @@ impl InteractiveTxSigningSession {
}

pub fn has_received_tx_signatures(&self) -> bool {
self.has_received_tx_signatures
self.counterparty_tx_signatures.is_some()
}

pub fn holder_tx_signatures(&self) -> &Option<TxSignatures> {
Expand All @@ -457,7 +497,7 @@ impl InteractiveTxSigningSession {
pub fn received_tx_signatures(
&mut self, tx_signatures: &TxSignatures,
) -> Result<(Option<TxSignatures>, Option<Transaction>), String> {
if self.has_received_tx_signatures {
if self.has_received_tx_signatures() {
return Err("Already received a tx_signatures message".to_string());
}
if self.remote_inputs_count() != tx_signatures.witnesses.len() {
Expand All @@ -470,26 +510,15 @@ impl InteractiveTxSigningSession {
return Err("Unexpected shared input signature".to_string());
}

self.unsigned_tx.add_remote_witnesses(tx_signatures.witnesses.clone());
if let Some(ref mut shared_input_sig) = self.shared_input_signature {
shared_input_sig.counterparty_signature = tx_signatures.shared_input_signature.clone();
}
self.has_received_tx_signatures = true;
self.counterparty_tx_signatures = Some(tx_signatures.clone());

let holder_tx_signatures = if !self.holder_sends_tx_signatures_first {
self.holder_tx_signatures.clone()
} else {
None
};

// Check if the holder has provided its signatures and if so,
// return the finalized funding transaction.
let funding_tx_opt = if self.holder_tx_signatures.is_some() {
Some(self.finalize_funding_tx())
} else {
// This means we're still waiting for the holder to provide their signatures.
None
};
let funding_tx_opt = self.maybe_finalize_funding_tx();

Ok((holder_tx_signatures, funding_tx_opt))
}
Expand All @@ -516,15 +545,15 @@ impl InteractiveTxSigningSession {

self.verify_interactive_tx_signatures(secp_ctx, &tx_signatures.witnesses)?;

self.unsigned_tx.add_local_witnesses(tx_signatures.witnesses.clone());
self.holder_tx_signatures = Some(tx_signatures);

let funding_tx_opt = self.has_received_tx_signatures.then(|| self.finalize_funding_tx());
let holder_tx_signatures =
(self.holder_sends_tx_signatures_first || self.has_received_tx_signatures).then(|| {
debug_assert!(self.has_received_commitment_signed);
self.holder_tx_signatures.clone().expect("Holder tx_signatures were just provided")
});
let funding_tx_opt = self.maybe_finalize_funding_tx();
let holder_tx_signatures = (self.holder_sends_tx_signatures_first
|| self.has_received_tx_signatures())
.then(|| {
debug_assert!(self.has_received_commitment_signed);
self.holder_tx_signatures.clone().expect("Holder tx_signatures were just provided")
});

Ok((holder_tx_signatures, funding_tx_opt))
}
Expand Down Expand Up @@ -576,43 +605,15 @@ impl InteractiveTxSigningSession {
})
}

fn finalize_funding_tx(&mut self) -> Transaction {
if let Some(shared_input_index) = self.unsigned_tx.shared_input_index {
if let Some(holder_shared_input_sig) = self
.holder_tx_signatures
.as_ref()
.and_then(|holder_tx_sigs| holder_tx_sigs.shared_input_signature)
{
if let Some(ref shared_input_sig) = self.shared_input_signature {
if let Some(counterparty_shared_input_sig) =
shared_input_sig.counterparty_signature
{
let mut witness = Witness::new();
witness.push(Vec::new());
let holder_sig = BitcoinSignature::sighash_all(holder_shared_input_sig);
let counterparty_sig =
BitcoinSignature::sighash_all(counterparty_shared_input_sig);
if shared_input_sig.holder_signature_first {
witness.push_ecdsa_signature(&holder_sig);
witness.push_ecdsa_signature(&counterparty_sig);
} else {
witness.push_ecdsa_signature(&counterparty_sig);
witness.push_ecdsa_signature(&holder_sig);
}
witness.push(&shared_input_sig.witness_script);
self.unsigned_tx.tx.input[shared_input_index as usize].witness = witness;
} else {
debug_assert!(false);
}
} else {
debug_assert!(false);
}
} else {
debug_assert!(false);
}
}

self.unsigned_tx.tx.clone()
fn maybe_finalize_funding_tx(&mut self) -> Option<Transaction> {
let holder_tx_signatures = self.holder_tx_signatures.as_ref()?;
let counterparty_tx_signatures = self.counterparty_tx_signatures.as_ref()?;
let shared_input_signature = self.shared_input_signature.as_ref();
self.unsigned_tx.finalize(
holder_tx_signatures,
counterparty_tx_signatures,
shared_input_signature,
)
}

fn verify_interactive_tx_signatures<C: bitcoin::secp256k1::Verification>(
Expand Down Expand Up @@ -781,7 +782,7 @@ impl_writeable_tlv_based!(InteractiveTxSigningSession, {
(1, unsigned_tx, required),
(3, has_received_commitment_signed, required),
(5, holder_tx_signatures, required),
(7, has_received_tx_signatures, required),
(7, counterparty_tx_signatures, required),
(9, holder_sends_tx_signatures_first, required),
(11, shared_input_signature, required),
});
Expand Down Expand Up @@ -1372,7 +1373,6 @@ macro_rules! define_state_transitions {
.as_ref()
.map(|shared_input| SharedInputSignature {
holder_signature_first: shared_input.holder_sig_first,
counterparty_signature: None,
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Should probably rename SharedInputSignature since it doesn't contain a signature anymore

witness_script: shared_input.witness_script.clone(),
});
let holder_node_id = context.holder_node_id;
Expand All @@ -1394,9 +1394,9 @@ macro_rules! define_state_transitions {
unsigned_tx: tx,
holder_sends_tx_signatures_first,
has_received_commitment_signed: false,
has_received_tx_signatures: false,
shared_input_signature,
holder_tx_signatures: None,
counterparty_tx_signatures: None,
};
Ok(NegotiationComplete(signing_session))
}
Expand Down Expand Up @@ -3319,9 +3319,9 @@ mod tests {
unsigned_tx,
holder_sends_tx_signatures_first: false, // N/A for test
has_received_commitment_signed: false, // N/A for test
has_received_tx_signatures: false, // N/A for test
shared_input_signature: None,
holder_tx_signatures: None,
counterparty_tx_signatures: None,
}
.verify_interactive_tx_signatures(
&secp_ctx,
Expand Down