Track ChannelTransactionParameters in RevokedOutput

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 `RevokedOutput` 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

Diff for: lightning/src/chain/channelmonitor.rs

@@ -3734,12 +3734,9 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 			for (idx, outp) in tx.output.iter().enumerate() {
 				if outp.script_pubkey == revokeable_p2wsh {
 					let revk_outp = RevokedOutput::build(
-						per_commitment_point,
-						self.counterparty_commitment_params.counterparty_delayed_payment_base_key,
-						self.counterparty_commitment_params.counterparty_htlc_base_key,
-						per_commitment_key, outp.value,
-						self.counterparty_commitment_params.on_counterparty_tx_csv,
-						self.channel_type_features().supports_anchors_zero_fee_htlc_tx(),
+						per_commitment_point, per_commitment_key, outp.value,
+						self.funding.channel_parameters.channel_type_features.supports_anchors_zero_fee_htlc_tx(),
+						self.funding.channel_parameters.clone(),
 					);
 					let justice_package = PackageTemplate::build_package(
 						commitment_txid, idx as u32,
@@ -3936,10 +3933,8 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 			if input.previous_output.txid == *commitment_txid && input.witness.len() == 5 && tx.output.get(idx).is_some() {
 				log_error!(logger, "Got broadcast of revoked counterparty HTLC transaction, spending {}:{}", htlc_txid, idx);
 				let revk_outp = RevokedOutput::build(
-					per_commitment_point, self.counterparty_commitment_params.counterparty_delayed_payment_base_key,
-					self.counterparty_commitment_params.counterparty_htlc_base_key, per_commitment_key,
-					tx.output[idx].value, self.counterparty_commitment_params.on_counterparty_tx_csv,
-					false
+					per_commitment_point, per_commitment_key, tx.output[idx].value, false,
+					self.funding.channel_parameters.clone(),
 				);
 				let justice_package = PackageTemplate::build_package(
 					htlc_txid, idx as u32, PackageSolvingData::RevokedOutput(revk_outp),

Diff for: lightning/src/chain/package.rs

@@ -136,10 +136,19 @@ pub(crate) struct RevokedOutput {
 	amount: Amount,
 	on_counterparty_tx_csv: u16,
 	is_counterparty_balance_on_anchors: Option<()>,
+	channel_parameters: Option<ChannelTransactionParameters>,
 }
 
 impl RevokedOutput {
-	pub(crate) fn build(per_commitment_point: PublicKey, counterparty_delayed_payment_base_key: DelayedPaymentBasepoint, counterparty_htlc_base_key: HtlcBasepoint, per_commitment_key: SecretKey, amount: Amount, on_counterparty_tx_csv: u16, is_counterparty_balance_on_anchors: bool) -> Self {
+	pub(crate) fn build(
+		per_commitment_point: PublicKey, per_commitment_key: SecretKey, amount: Amount,
+		is_counterparty_balance_on_anchors: bool, channel_parameters: ChannelTransactionParameters,
+	) -> Self {
+		let directed_params = channel_parameters.as_counterparty_broadcastable();
+		let counterparty_keys = directed_params.broadcaster_pubkeys();
+		let counterparty_delayed_payment_base_key = counterparty_keys.delayed_payment_basepoint;
+		let counterparty_htlc_base_key = counterparty_keys.htlc_basepoint;
+		let on_counterparty_tx_csv = directed_params.contest_delay();
 		RevokedOutput {
 			per_commitment_point,
 			counterparty_delayed_payment_base_key,
@@ -148,7 +157,8 @@ impl RevokedOutput {
 			weight: WEIGHT_REVOKED_OUTPUT,
 			amount,
 			on_counterparty_tx_csv,
-			is_counterparty_balance_on_anchors: if is_counterparty_balance_on_anchors { Some(()) } else { None }
+			is_counterparty_balance_on_anchors: if is_counterparty_balance_on_anchors { Some(()) } else { None },
+			channel_parameters: Some(channel_parameters),
 		}
 	}
 }
@@ -161,7 +171,8 @@ impl_writeable_tlv_based!(RevokedOutput, {
 	(8, weight, required),
 	(10, amount, required),
 	(12, on_counterparty_tx_csv, required),
-	(14, is_counterparty_balance_on_anchors, option)
+	(14, is_counterparty_balance_on_anchors, option),
+	(15, channel_parameters, (option: ReadableArgs, None)), // Added in 0.2.
 });
 
 /// A struct to describe a revoked offered output and corresponding information to generate a
@@ -778,8 +789,8 @@ impl PackageSolvingData {
 		let channel_parameters = &onchain_handler.channel_transaction_parameters;
 		match self {
 			PackageSolvingData::RevokedOutput(ref outp) => {
-				let directed_parameters =
-					&onchain_handler.channel_transaction_parameters.as_counterparty_broadcastable();
+				let channel_parameters = outp.channel_parameters.as_ref().unwrap_or(channel_parameters);
+				let directed_parameters = channel_parameters.as_counterparty_broadcastable();
 				debug_assert_eq!(
 					directed_parameters.broadcaster_pubkeys().delayed_payment_basepoint,
 					outp.counterparty_delayed_payment_base_key,
@@ -1589,7 +1600,6 @@ mod tests {
 		ChannelTransactionParameters, HolderCommitmentTransaction, HTLCOutputInCommitment,
 	};
 	use crate::types::payment::{PaymentPreimage, PaymentHash};
-	use crate::ln::channel_keys::{DelayedPaymentBasepoint, HtlcBasepoint};
 	use crate::sign::{ChannelDerivationParameters, HTLCDescriptor};
 
 	use bitcoin::absolute::LockTime;
@@ -1627,7 +1637,11 @@ mod tests {
 				let secp_ctx = Secp256k1::new();
 				let dumb_scalar = SecretKey::from_slice(&<Vec<u8>>::from_hex("0101010101010101010101010101010101010101010101010101010101010101").unwrap()[..]).unwrap();
 				let dumb_point = PublicKey::from_secret_key(&secp_ctx, &dumb_scalar);
-				PackageSolvingData::RevokedOutput(RevokedOutput::build(dumb_point, DelayedPaymentBasepoint::from(dumb_point), HtlcBasepoint::from(dumb_point), dumb_scalar, Amount::ZERO, 0, $is_counterparty_balance_on_anchors))
+				let channel_parameters = ChannelTransactionParameters::test_dummy(0);
+				PackageSolvingData::RevokedOutput(RevokedOutput::build(
+					dumb_point, dumb_scalar, Amount::ZERO, $is_counterparty_balance_on_anchors,
+					channel_parameters,
+				))
 			}
 		}
 	}