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[Custom Transactions] Define the TxBuilder trait #3606

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[Custom Transactions] Define the TxBuilder trait #3606

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ca8c728
Provide built commitment transactions to `ChannelMonitor`
tankyleo Feb 25, 2025
3dcf40a
Relax the requirements of building a `CommitmentTransaction`
tankyleo Feb 27, 2025
2a82a1f
Remove redundant parameters from the `CommitmentTransaction` constructor
tankyleo Feb 26, 2025
a50d32d
Let `CommitmentTransaction` build the `TxCreationKeys` it will cache
tankyleo Feb 26, 2025
d60cfda
Begin removing per-commitment key derivations from channel objects
tankyleo Feb 26, 2025
df9a561
Remove `i64` casts in `ChannelContext::build_commitment_transaction`
tankyleo Feb 26, 2025
ca3fa4e
Clean up tautologies in `ChannelContext::build_commitment_transaction`
tankyleo Feb 26, 2025
570ca77
Reorder the operations in `ChannelContext::build_commitment_transaction`
tankyleo Feb 27, 2025
82b40fc
Remove redundant fields in `CommitmentStats`
tankyleo Feb 26, 2025
5c97de0
Tweak return values of `ChannelContext::build_commitment_transaction`
tankyleo Feb 27, 2025
42d5a79
[Custom Transactions] Define the `TxBuilder` trait
tankyleo Feb 26, 2025
300b396
f: Just handle new updates for now, but don't set them
tankyleo Mar 2, 2025
3318e4a
f: Remove parameter from `provide_initial_counterparty_commitment_tx`
tankyleo Mar 1, 2025
7c2d605
f: Remove all explicit `TxCreationKeys` in channel
tankyleo Mar 1, 2025
ad05a2c
f: Break up a long line
tankyleo Mar 1, 2025
338532f
f: Correct comments describing commitment structs
tankyleo Mar 2, 2025
87a35dd
f: Delete a big branch in non-dust htlc scan
tankyleo Mar 2, 2025
dcfb0f9
Remove unnecessary allocation in `send_commitment_no_state_update`
tankyleo Mar 2, 2025
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72 changes: 19 additions & 53 deletions lightning/src/ln/channel.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1968,8 +1968,7 @@ trait InitialRemoteCommitmentReceiver<SP: Deref> where SP::Target: SignerProvide
) -> Result<CommitmentTransaction, ChannelError> where L::Target: Logger {
let funding_script = self.context().get_funding_redeemscript();

let keys = self.context().build_holder_transaction_keys(holder_commitment_point.current_point());
let initial_commitment_tx = self.context().build_commitment_transaction(self.funding(), holder_commitment_point.transaction_number(), &keys, true, false, logger).tx;
let initial_commitment_tx = self.context().build_commitment_transaction(self.funding(), holder_commitment_point.transaction_number(), &holder_commitment_point.current_point(), true, false, logger).tx;
let trusted_tx = initial_commitment_tx.trust();
let initial_commitment_bitcoin_tx = trusted_tx.built_transaction();
let sighash = initial_commitment_bitcoin_tx.get_sighash_all(&funding_script, self.funding().channel_value_satoshis);
Expand Down Expand Up @@ -2006,8 +2005,7 @@ trait InitialRemoteCommitmentReceiver<SP: Deref> where SP::Target: SignerProvide
}
};
let context = self.context();
let counterparty_keys = context.build_remote_transaction_keys();
let counterparty_initial_commitment_tx = context.build_commitment_transaction(self.funding(), context.cur_counterparty_commitment_transaction_number, &counterparty_keys, false, false, logger).tx;
let counterparty_initial_commitment_tx = context.build_commitment_transaction(self.funding(), context.cur_counterparty_commitment_transaction_number, &context.counterparty_cur_commitment_point.unwrap(), false, false, logger).tx;
let counterparty_trusted_tx = counterparty_initial_commitment_tx.trust();
let counterparty_initial_bitcoin_tx = counterparty_trusted_tx.built_transaction();

Expand Down Expand Up @@ -3412,7 +3410,7 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
/// generated by the peer which proposed adding the HTLCs, and thus we need to understand both
/// which peer generated this transaction and "to whom" this transaction flows.
#[inline]
fn build_commitment_transaction<L: Deref>(&self, funding: &FundingScope, commitment_number: u64, keys: &TxCreationKeys, local: bool, generated_by_local: bool, logger: &L) -> CommitmentStats
fn build_commitment_transaction<L: Deref>(&self, funding: &FundingScope, commitment_number: u64, per_commitment_point: &PublicKey, local: bool, generated_by_local: bool, logger: &L) -> CommitmentStats
where L::Target: Logger
{
let mut included_dust_htlcs: Vec<(HTLCOutputInCommitment, Option<&HTLCSource>)> = Vec::new();
Expand Down Expand Up @@ -3614,7 +3612,7 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
if local { self.channel_transaction_parameters.as_holder_broadcastable() }
else { self.channel_transaction_parameters.as_counterparty_broadcastable() };
let tx = CommitmentTransaction::new(commitment_number,
&keys.per_commitment_point,
&per_commitment_point,
value_to_a as u64,
value_to_b as u64,
feerate_per_kw,
Expand All @@ -3640,32 +3638,6 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
}
}

#[inline]
/// Creates a set of keys for build_commitment_transaction to generate a transaction which our
/// counterparty will sign (ie DO NOT send signatures over a transaction created by this to
/// our counterparty!)
/// The result is a transaction which we can revoke broadcastership of (ie a "local" transaction)
/// TODO Some magic rust shit to compile-time check this?
fn build_holder_transaction_keys(&self, per_commitment_point: PublicKey) -> TxCreationKeys {
let delayed_payment_base = &self.get_holder_pubkeys().delayed_payment_basepoint;
let htlc_basepoint = &self.get_holder_pubkeys().htlc_basepoint;
let counterparty_pubkeys = self.get_counterparty_pubkeys();

TxCreationKeys::derive_new(&self.secp_ctx, &per_commitment_point, delayed_payment_base, htlc_basepoint, &counterparty_pubkeys.revocation_basepoint, &counterparty_pubkeys.htlc_basepoint)
}

#[inline]
/// Creates a set of keys for build_commitment_transaction to generate a transaction which we
/// will sign and send to our counterparty.
/// If an Err is returned, it is a ChannelError::Close (for get_funding_created)
fn build_remote_transaction_keys(&self) -> TxCreationKeys {
let revocation_basepoint = &self.get_holder_pubkeys().revocation_basepoint;
let htlc_basepoint = &self.get_holder_pubkeys().htlc_basepoint;
let counterparty_pubkeys = self.get_counterparty_pubkeys();

TxCreationKeys::derive_new(&self.secp_ctx, &self.counterparty_cur_commitment_point.unwrap(), &counterparty_pubkeys.delayed_payment_basepoint, &counterparty_pubkeys.htlc_basepoint, revocation_basepoint, htlc_basepoint)
}

/// Gets the redeemscript for the funding transaction output (ie the funding transaction output
/// pays to get_funding_redeemscript().to_p2wsh()).
/// Panics if called before accept_channel/InboundV1Channel::new
Expand Down Expand Up @@ -4459,9 +4431,8 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
SP::Target: SignerProvider,
L::Target: Logger
{
let counterparty_keys = self.build_remote_transaction_keys();
let counterparty_initial_commitment_tx = self.build_commitment_transaction(
funding, self.cur_counterparty_commitment_transaction_number, &counterparty_keys, false, false, logger).tx;
funding, self.cur_counterparty_commitment_transaction_number, &self.counterparty_cur_commitment_point.unwrap(), false, false, logger).tx;
match self.holder_signer {
// TODO (taproot|arik): move match into calling method for Taproot
ChannelSignerType::Ecdsa(ref ecdsa) => {
Expand Down Expand Up @@ -5454,9 +5425,7 @@ impl<SP: Deref> FundedChannel<SP> where

let funding_script = self.context.get_funding_redeemscript();

let keys = self.context.build_holder_transaction_keys(self.holder_commitment_point.current_point());

let commitment_stats = self.context.build_commitment_transaction(&self.funding, self.holder_commitment_point.transaction_number(), &keys, true, false, logger);
let commitment_stats = self.context.build_commitment_transaction(&self.funding, self.holder_commitment_point.transaction_number(), &self.holder_commitment_point.current_point(), true, false, logger);
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If we're already touching some of these long lines, let's try to break them up as we go to reduce the changes when we rustfmt this file.

let commitment_txid = {
let trusted_tx = commitment_stats.tx.trust();
let bitcoin_tx = trusted_tx.built_transaction();
Expand Down Expand Up @@ -5524,19 +5493,20 @@ impl<SP: Deref> FundedChannel<SP> where

let mut nondust_htlc_sources = Vec::with_capacity(htlcs_cloned.len());
let mut htlcs_and_sigs = Vec::with_capacity(htlcs_cloned.len());
let holder_keys = TxCreationKeys::from_channel_static_keys(&self.holder_commitment_point.current_point(), self.context.get_holder_pubkeys(), self.context.get_counterparty_pubkeys(), &self.context.secp_ctx);
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We should be able to get these from the built commitment transaction above?

for (idx, (htlc, mut source_opt)) in htlcs_cloned.drain(..).enumerate() {
if let Some(_) = htlc.transaction_output_index {
let htlc_tx = chan_utils::build_htlc_transaction(&commitment_txid, commitment_stats.feerate_per_kw,
self.context.get_counterparty_selected_contest_delay().unwrap(), &htlc, &self.context.channel_type,
&keys.broadcaster_delayed_payment_key, &keys.revocation_key);
&holder_keys.broadcaster_delayed_payment_key, &holder_keys.revocation_key);

let htlc_redeemscript = chan_utils::get_htlc_redeemscript(&htlc, &self.context.channel_type, &keys);
let htlc_redeemscript = chan_utils::get_htlc_redeemscript(&htlc, &self.context.channel_type, &holder_keys);
let htlc_sighashtype = if self.context.channel_type.supports_anchors_zero_fee_htlc_tx() { EcdsaSighashType::SinglePlusAnyoneCanPay } else { EcdsaSighashType::All };
let htlc_sighash = hash_to_message!(&sighash::SighashCache::new(&htlc_tx).p2wsh_signature_hash(0, &htlc_redeemscript, htlc.to_bitcoin_amount(), htlc_sighashtype).unwrap()[..]);
log_trace!(logger, "Checking HTLC tx signature {} by key {} against tx {} (sighash {}) with redeemscript {} in channel {}.",
log_bytes!(msg.htlc_signatures[idx].serialize_compact()[..]), log_bytes!(keys.countersignatory_htlc_key.to_public_key().serialize()),
log_bytes!(msg.htlc_signatures[idx].serialize_compact()[..]), log_bytes!(holder_keys.countersignatory_htlc_key.to_public_key().serialize()),
encode::serialize_hex(&htlc_tx), log_bytes!(htlc_sighash[..]), encode::serialize_hex(&htlc_redeemscript), &self.context.channel_id());
if let Err(_) = self.context.secp_ctx.verify_ecdsa(&htlc_sighash, &msg.htlc_signatures[idx], &keys.countersignatory_htlc_key.to_public_key()) {
if let Err(_) = self.context.secp_ctx.verify_ecdsa(&htlc_sighash, &msg.htlc_signatures[idx], &holder_keys.countersignatory_htlc_key.to_public_key()) {
return Err(ChannelError::close("Invalid HTLC tx signature from peer".to_owned()));
}
if !separate_nondust_htlc_sources {
Expand Down Expand Up @@ -6218,8 +6188,7 @@ impl<SP: Deref> FundedChannel<SP> where
// Before proposing a feerate update, check that we can actually afford the new fee.
let dust_exposure_limiting_feerate = self.context.get_dust_exposure_limiting_feerate(&fee_estimator);
let htlc_stats = self.context.get_pending_htlc_stats(Some(feerate_per_kw), dust_exposure_limiting_feerate);
let keys = self.context.build_holder_transaction_keys(self.holder_commitment_point.current_point());
let commitment_stats = self.context.build_commitment_transaction(&self.funding, self.holder_commitment_point.transaction_number(), &keys, true, true, logger);
let commitment_stats = self.context.build_commitment_transaction(&self.funding, self.holder_commitment_point.transaction_number(), &self.holder_commitment_point.current_point(), true, true, logger);
let buffer_fee_msat = commit_tx_fee_sat(feerate_per_kw, commitment_stats.num_nondust_htlcs + htlc_stats.on_holder_tx_outbound_holding_cell_htlcs_count as usize + CONCURRENT_INBOUND_HTLC_FEE_BUFFER as usize, self.context.get_channel_type()) * 1000;
let holder_balance_msat = commitment_stats.local_balance_msat - htlc_stats.outbound_holding_cell_msat;
if holder_balance_msat < buffer_fee_msat + self.funding.counterparty_selected_channel_reserve_satoshis.unwrap() * 1000 {
Expand Down Expand Up @@ -6532,8 +6501,7 @@ impl<SP: Deref> FundedChannel<SP> where
self.holder_commitment_point.try_resolve_pending(&self.context.holder_signer, &self.context.secp_ctx, logger);
}
let funding_signed = if self.context.signer_pending_funding && !self.context.is_outbound() {
let counterparty_keys = self.context.build_remote_transaction_keys();
let counterparty_initial_commitment_tx = self.context.build_commitment_transaction(&self.funding, self.context.cur_counterparty_commitment_transaction_number + 1, &counterparty_keys, false, false, logger).tx;
let counterparty_initial_commitment_tx = self.context.build_commitment_transaction(&self.funding, self.context.cur_counterparty_commitment_transaction_number + 1, &self.context.counterparty_cur_commitment_point.unwrap(), false, false, logger).tx;
self.context.get_funding_signed_msg(logger, counterparty_initial_commitment_tx)
} else { None };
// Provide a `channel_ready` message if we need to, but only if we're _not_ still pending
Expand Down Expand Up @@ -8469,8 +8437,7 @@ impl<SP: Deref> FundedChannel<SP> where
-> (Vec<(HTLCOutputInCommitment, Option<&HTLCSource>)>, CommitmentTransaction)
where L::Target: Logger
{
let counterparty_keys = self.context.build_remote_transaction_keys();
let commitment_stats = self.context.build_commitment_transaction(&self.funding, self.context.cur_counterparty_commitment_transaction_number, &counterparty_keys, false, true, logger);
let commitment_stats = self.context.build_commitment_transaction(&self.funding, self.context.cur_counterparty_commitment_transaction_number, &self.context.counterparty_cur_commitment_point.unwrap(), false, true, logger);
let counterparty_commitment_tx = commitment_stats.tx;

#[cfg(any(test, fuzzing))]
Expand Down Expand Up @@ -8501,8 +8468,7 @@ impl<SP: Deref> FundedChannel<SP> where
#[cfg(any(test, fuzzing))]
self.build_commitment_no_state_update(logger);

let counterparty_keys = self.context.build_remote_transaction_keys();
let commitment_stats = self.context.build_commitment_transaction(&self.funding, self.context.cur_counterparty_commitment_transaction_number, &counterparty_keys, false, true, logger);
let commitment_stats = self.context.build_commitment_transaction(&self.funding, self.context.cur_counterparty_commitment_transaction_number, &self.context.counterparty_cur_commitment_point.unwrap(), false, true, logger);
let counterparty_commitment_txid = commitment_stats.tx.trust().txid();

match &self.context.holder_signer {
Expand All @@ -8528,7 +8494,8 @@ impl<SP: Deref> FundedChannel<SP> where
encode::serialize_hex(&commitment_stats.tx.trust().built_transaction().transaction),
&counterparty_commitment_txid, encode::serialize_hex(&self.context.get_funding_redeemscript()),
log_bytes!(signature.serialize_compact()[..]), &self.context.channel_id());


let counterparty_keys = TxCreationKeys::from_channel_static_keys(&self.context.counterparty_cur_commitment_point.unwrap(), self.context.get_counterparty_pubkeys(), self.context.get_holder_pubkeys(), &self.context.secp_ctx);
for (ref htlc_sig, ref htlc) in htlc_signatures.iter().zip(htlcs) {
log_trace!(logger, "Signed remote HTLC tx {} with redeemscript {} with pubkey {} -> {} in channel {}",
encode::serialize_hex(&chan_utils::build_htlc_transaction(&counterparty_commitment_txid, commitment_stats.feerate_per_kw, self.context.get_holder_selected_contest_delay(), htlc, &self.context.channel_type, &counterparty_keys.broadcaster_delayed_payment_key, &counterparty_keys.revocation_key)),
Expand Down Expand Up @@ -8980,8 +8947,7 @@ impl<SP: Deref> OutboundV1Channel<SP> where SP::Target: SignerProvider {

/// Only allowed after [`ChannelContext::channel_transaction_parameters`] is set.
fn get_funding_created_msg<L: Deref>(&mut self, logger: &L) -> Option<msgs::FundingCreated> where L::Target: Logger {
let counterparty_keys = self.context.build_remote_transaction_keys();
let counterparty_initial_commitment_tx = self.context.build_commitment_transaction(&self.funding, self.context.cur_counterparty_commitment_transaction_number, &counterparty_keys, false, false, logger).tx;
let counterparty_initial_commitment_tx = self.context.build_commitment_transaction(&self.funding, self.context.cur_counterparty_commitment_transaction_number, &self.context.counterparty_cur_commitment_point.unwrap(), false, false, logger).tx;
let signature = match &self.context.holder_signer {
// TODO (taproot|arik): move match into calling method for Taproot
ChannelSignerType::Ecdsa(ecdsa) => {
Expand Down Expand Up @@ -11633,7 +11599,7 @@ mod tests {
$( { $htlc_idx: expr, $counterparty_htlc_sig_hex: expr, $htlc_sig_hex: expr, $htlc_tx_hex: expr } ), *
} ) => { {
let (commitment_tx, htlcs): (_, Vec<HTLCOutputInCommitment>) = {
let mut commitment_stats = chan.context.build_commitment_transaction(&chan.funding, 0xffffffffffff - 42, &keys, true, false, &logger);
let mut commitment_stats = chan.context.build_commitment_transaction(&chan.funding, 0xffffffffffff - 42, &per_commitment_point, true, false, &logger);

let htlcs = commitment_stats.htlcs_included.drain(..)
.filter_map(|(htlc, _)| if htlc.transaction_output_index.is_some() { Some(htlc) } else { None })
Expand Down