Track ChannelTransactionParameters in HolderFundingOutput

The `ChannelMonitor` and `OnchainTxHandler` have historically been tied
together, often tracking some of the same state twice. As we introduce
support for splices in the `ChannelMonitor`, we'd like to avoid leaking
some of those details to the `OnchainTxHandler`. Ultimately, the
`OnchainTxHandler` should stand on its own and support claiming funds
from multiple `ChannelMonitor`s, allowing us to save on fees by batching
aggregatable claims across multiple in-flight closing channels.

Once splices are supported, we may run into cases where we are
attempting to claim an output from a specific `FundingScope`, while also
having an additional pending `FundingScope` for a splice. If the pending
splice confirms over the output claim, we need to cancel the claim and
re-offer it with the set of relevant parameters in the new
`FundingScope`.

This commit tracks the `ChannelTransactionParameters` for the specific
`FundingScope` the `HolderFundingOutput` claim originated from. This
allows us to remove the dependency on `OnchainTxHandler` when obtaining
the current `ChannelTransactionParameters` and ensures any alternative
state due to splicing does not leak into the `OnchainTxHandler`.

Author: wpaulino

lightning/src/chain/channelmonitor.rs

@@ -3279,9 +3279,7 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 	fn generate_claimable_outpoints_and_watch_outputs(&mut self, reason: ClosureReason) -> (Vec<PackageTemplate>, Vec<TransactionOutputs>) {
 		let funding_outp = HolderFundingOutput::build(
 			self.funding.current_holder_commitment.tx.clone(),
-			self.funding.redeem_script.clone(),
-			self.funding.channel_parameters.channel_value_satoshis,
-			self.channel_type_features().clone(),
+			self.funding.channel_parameters.clone(),
 		);
 		let funding_outpoint = self.get_funding_txo();
 		let commitment_package = PackageTemplate::build_package(
@@ -3533,6 +3531,7 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 				ClaimEvent::BumpCommitment {
 					package_target_feerate_sat_per_1000_weight, commitment_tx,
 					commitment_tx_fee_satoshis, pending_nondust_htlcs, anchor_output_idx,
+					channel_parameters,
 				} => {
 					let channel_id = self.channel_id;
 					let counterparty_node_id = self.counterparty_node_id;
@@ -3547,8 +3546,8 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 						anchor_descriptor: AnchorDescriptor {
 							channel_derivation_parameters: ChannelDerivationParameters {
 								keys_id: self.channel_keys_id,
-								value_satoshis: self.funding.channel_parameters.channel_value_satoshis,
-								transaction_parameters: self.funding.channel_parameters.clone(),
+								value_satoshis: channel_parameters.channel_value_satoshis,
+								transaction_parameters: channel_parameters,
 							},
 							outpoint: BitcoinOutPoint {
 								txid: commitment_txid,

lightning/src/chain/onchaintx.rs

@@ -196,6 +196,7 @@ pub(crate) enum ClaimEvent {
 		commitment_tx_fee_satoshis: u64,
 		pending_nondust_htlcs: Vec<HTLCOutputInCommitment>,
 		anchor_output_idx: u32,
+		channel_parameters: ChannelTransactionParameters,
 	},
 	/// Event yielded to signal that the commitment transaction has confirmed and its HTLCs must be
 	/// resolved by broadcasting a transaction with sufficient fee to claim them.
@@ -690,7 +691,9 @@ impl<ChannelSigner: EcdsaChannelSigner> OnchainTxHandler<ChannelSigner> {
 					}
 
 					// We'll locate an anchor output we can spend within the commitment transaction.
-					let funding_pubkey = &self.channel_transaction_parameters.holder_pubkeys.funding_pubkey;
+					let channel_parameters = output.channel_parameters.as_ref()
+						.unwrap_or(&self.channel_transaction_parameters);
+					let funding_pubkey = &channel_parameters.holder_pubkeys.funding_pubkey;
 					match chan_utils::get_keyed_anchor_output(&tx, funding_pubkey) {
 						// An anchor output was found, so we should yield a funding event externally.
 						Some((idx, _)) => {
@@ -705,6 +708,7 @@ impl<ChannelSigner: EcdsaChannelSigner> OnchainTxHandler<ChannelSigner> {
 									pending_nondust_htlcs: holder_commitment.htlcs().to_vec(),
 									commitment_tx_fee_satoshis: fee_sat,
 									anchor_output_idx: idx,
+									channel_parameters: channel_parameters.clone(),
 								}),
 							))
 						},

lightning/src/chain/package.rs

@@ -26,7 +26,8 @@ use bitcoin::transaction::Version;
 
 use crate::types::payment::PaymentPreimage;
 use crate::ln::chan_utils::{
-	self, HolderCommitmentTransaction, TxCreationKeys, HTLCOutputInCommitment,
+	self, ChannelTransactionParameters, HolderCommitmentTransaction, TxCreationKeys,
+	HTLCOutputInCommitment,
 };
 use crate::types::features::ChannelTypeFeatures;
 use crate::ln::channel_keys::{DelayedPaymentBasepoint, HtlcBasepoint};
@@ -38,7 +39,7 @@ use crate::chain::transaction::MaybeSignedTransaction;
 use crate::sign::ecdsa::EcdsaChannelSigner;
 use crate::chain::onchaintx::{FeerateStrategy, ExternalHTLCClaim, OnchainTxHandler};
 use crate::util::logger::Logger;
-use crate::util::ser::{Readable, Writer, Writeable, RequiredWrapper};
+use crate::util::ser::{Readable, ReadableArgs, Writer, Writeable, RequiredWrapper};
 
 use crate::io;
 use core::cmp;
@@ -445,26 +446,31 @@ pub(crate) struct HolderFundingOutput {
 	pub(crate) funding_amount_sats: Option<u64>,
 	channel_type_features: ChannelTypeFeatures,
 	pub(crate) commitment_tx: Option<HolderCommitmentTransaction>,
+	pub(crate) channel_parameters: Option<ChannelTransactionParameters>,
 }
 
 
 impl HolderFundingOutput {
 	pub(crate) fn build(
-		commitment_tx: HolderCommitmentTransaction, funding_redeemscript: ScriptBuf,
-		funding_amount_sats: u64, channel_type_features: ChannelTypeFeatures,
+		commitment_tx: HolderCommitmentTransaction, channel_parameters: ChannelTransactionParameters,
 	) -> Self {
+		let funding_redeemscript = channel_parameters.make_funding_redeemscript();
+		let funding_amount_sats = channel_parameters.channel_value_satoshis;
+		let channel_type_features = channel_parameters.channel_type_features.clone();
 		HolderFundingOutput {
 			funding_redeemscript,
 			funding_amount_sats: Some(funding_amount_sats),
 			channel_type_features,
 			commitment_tx: Some(commitment_tx),
+			channel_parameters: Some(channel_parameters),
 		}
 	}
 
 	pub(crate) fn get_maybe_signed_commitment_tx<Signer: EcdsaChannelSigner>(
 		&self, onchain_tx_handler: &mut OnchainTxHandler<Signer>,
 	) -> MaybeSignedTransaction {
-		let channel_parameters = &onchain_tx_handler.channel_transaction_parameters;
+		let channel_parameters = self.channel_parameters.as_ref()
+			.unwrap_or(&onchain_tx_handler.channel_transaction_parameters);
 		let commitment_tx = self.commitment_tx.as_ref()
 			.unwrap_or(onchain_tx_handler.current_holder_commitment_tx());
 		let maybe_signed_tx = onchain_tx_handler.signer
@@ -488,6 +494,7 @@ impl Writeable for HolderFundingOutput {
 			(2, legacy_deserialization_prevention_marker, option),
 			(3, self.funding_amount_sats, option),
 			(5, self.commitment_tx, option), // Added in 0.2
+			(7, self.channel_parameters, option), // Added in 0.2.
 		});
 		Ok(())
 	}
@@ -500,22 +507,27 @@ impl Readable for HolderFundingOutput {
 		let mut channel_type_features = None;
 		let mut funding_amount_sats = None;
 		let mut commitment_tx = None;
+		let mut channel_parameters = None;
 
 		read_tlv_fields!(reader, {
 			(0, funding_redeemscript, required),
 			(1, channel_type_features, option),
 			(2, _legacy_deserialization_prevention_marker, option),
 			(3, funding_amount_sats, option),
 			(5, commitment_tx, option), // Added in 0.2.
+			(7, channel_parameters, (option: ReadableArgs, None)), // Added in 0.2.
 		});
 
 		verify_channel_type_features(&channel_type_features, None)?;
+		let channel_type_features =
+			channel_type_features.unwrap_or(ChannelTypeFeatures::only_static_remote_key());
 
 		Ok(Self {
 			funding_redeemscript: funding_redeemscript.0.unwrap(),
-			channel_type_features: channel_type_features.unwrap_or(ChannelTypeFeatures::only_static_remote_key()),
 			funding_amount_sats,
+			channel_type_features,
 			commitment_tx,
+			channel_parameters,
 		})
 	}
 }
@@ -1434,7 +1446,9 @@ where
 mod tests {
 	use crate::chain::package::{CounterpartyOfferedHTLCOutput, CounterpartyReceivedHTLCOutput, HolderFundingOutput, HolderHTLCOutput, PackageTemplate, PackageSolvingData, RevokedHTLCOutput, RevokedOutput, WEIGHT_REVOKED_OUTPUT, weight_offered_htlc, weight_received_htlc, feerate_bump};
 	use crate::chain::Txid;
-	use crate::ln::chan_utils::{HolderCommitmentTransaction, HTLCOutputInCommitment};
+	use crate::ln::chan_utils::{
+		ChannelTransactionParameters, HolderCommitmentTransaction, HTLCOutputInCommitment,
+	};
 	use crate::types::payment::{PaymentPreimage, PaymentHash};
 	use crate::ln::channel_keys::{DelayedPaymentBasepoint, HtlcBasepoint};
 
@@ -1538,8 +1552,10 @@ mod tests {
 	macro_rules! dumb_funding_output {
 		() => {{
 			let commitment_tx = HolderCommitmentTransaction::dummy(0, &mut Vec::new());
+			let mut channel_parameters = ChannelTransactionParameters::test_dummy(0);
+			channel_parameters.channel_type_features = ChannelTypeFeatures::only_static_remote_key();
 			PackageSolvingData::HolderFundingOutput(HolderFundingOutput::build(
-				commitment_tx, ScriptBuf::new(), 0, ChannelTypeFeatures::only_static_remote_key()
+				commitment_tx, channel_parameters,
 			))
 		}}
 	}