Track ChannelTransactionParameters in ChannelMonitor

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.

This commit tracks the `ChannelTransactionParameters` for the current
`FundingScope` of a `ChannelMonitor` and deprecates the one found in
`OnchainTxHandler`.

Author: wpaulino

lightning/src/chain/channelmonitor.rs

@@ -1398,6 +1398,7 @@ impl<Signer: EcdsaChannelSigner> Writeable for ChannelMonitorImpl<Signer> {
 			(25, self.payment_preimages, required),
 			(27, self.first_confirmed_funding_txo, required),
 			(29, self.initial_counterparty_commitment_tx, option),
+			(31, self.funding.channel_parameters, required),
 		});
 
 		Ok(())
@@ -5278,6 +5279,7 @@ impl<'a, 'b, ES: EntropySource, SP: SignerProvider> ReadableArgs<(&'a ES, &'b SP
 		let mut holder_pays_commitment_tx_fee = None;
 		let mut payment_preimages_with_info: Option<HashMap<_, _>> = None;
 		let mut first_confirmed_funding_txo = RequiredWrapper(None);
+		let mut channel_parameters = None;
 		read_tlv_fields!(reader, {
 			(1, funding_spend_confirmed, option),
 			(3, htlcs_resolved_on_chain, optional_vec),
@@ -5294,6 +5296,7 @@ impl<'a, 'b, ES: EntropySource, SP: SignerProvider> ReadableArgs<(&'a ES, &'b SP
 			(25, payment_preimages_with_info, option),
 			(27, first_confirmed_funding_txo, (default_value, outpoint)),
 			(29, initial_counterparty_commitment_tx, option),
+			(31, channel_parameters, (option: ReadableArgs, None)),
 		});
 		if let Some(payment_preimages_with_info) = payment_preimages_with_info {
 			if payment_preimages_with_info.len() != payment_preimages.len() {
@@ -5322,7 +5325,9 @@ impl<'a, 'b, ES: EntropySource, SP: SignerProvider> ReadableArgs<(&'a ES, &'b SP
 			}
 		}
 
-		let channel_parameters = onchain_tx_handler.channel_transaction_parameters.clone();
+		let channel_parameters = channel_parameters.unwrap_or_else(|| {
+			onchain_tx_handler.channel_parameters().clone()
+		});
 
 		// Monitors for anchor outputs channels opened in v0.0.116 suffered from a bug in which the
 		// wrong `counterparty_payment_script` was being tracked. Fix it now on deserialization to

lightning/src/chain/onchaintx.rs

@@ -42,7 +42,6 @@ use core::cmp;
 use core::ops::Deref;
 use core::mem::replace;
 use core::mem::swap;
-use crate::types::features::ChannelTypeFeatures;
 
 const MAX_ALLOC_SIZE: usize = 64*1024;
 
@@ -220,14 +219,14 @@ pub(crate) enum FeerateStrategy {
 /// do RBF bumping if possible.
 #[derive(Clone)]
 pub struct OnchainTxHandler<ChannelSigner: EcdsaChannelSigner> {
-	channel_value_satoshis: u64,
+	channel_value_satoshis: u64, // Deprecated as of 0.2.
 	channel_keys_id: [u8; 32], // Deprecated as of 0.2.
 	destination_script: ScriptBuf, // Deprecated as of 0.2.
 	holder_commitment: HolderCommitmentTransaction,
 	prev_holder_commitment: Option<HolderCommitmentTransaction>,
 
 	pub(super) signer: ChannelSigner,
-	pub(crate) channel_transaction_parameters: ChannelTransactionParameters,
+	channel_transaction_parameters: ChannelTransactionParameters, // Deprecated as of 0.2.
 
 	// Used to track claiming requests. If claim tx doesn't confirm before height timer expiration we need to bump
 	// it (RBF or CPFP). If an input has been part of an aggregate tx at first claim try, we need to keep it within
@@ -676,7 +675,7 @@ impl<ChannelSigner: EcdsaChannelSigner> OnchainTxHandler<ChannelSigner> {
 
 					// We'll locate an anchor output we can spend within the commitment transaction.
 					let channel_parameters = output.channel_parameters.as_ref()
-						.unwrap_or(&self.channel_transaction_parameters);
+						.unwrap_or(self.channel_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.
@@ -1203,8 +1202,9 @@ impl<ChannelSigner: EcdsaChannelSigner> OnchainTxHandler<ChannelSigner> {
 		self.prev_holder_commitment = Some(replace(&mut self.holder_commitment, tx));
 	}
 
-	pub(crate) fn channel_type_features(&self) -> &ChannelTypeFeatures {
-		&self.channel_transaction_parameters.channel_type_features
+	// Deprecated as of 0.2, only use in cases where it was not previously available.
+	pub(crate) fn channel_parameters(&self) -> &ChannelTransactionParameters {
+		&self.channel_transaction_parameters
 	}
 
 	// Deprecated as of 0.2, only use in cases where it was not previously available.

lightning/src/chain/package.rs

@@ -465,7 +465,7 @@ impl HolderHTLCOutput {
 
 		let channel_parameters = self.htlc_descriptor.as_ref()
 			.map(|d| &d.channel_derivation_parameters.transaction_parameters)
-			.unwrap_or(&onchain_tx_handler.channel_transaction_parameters);
+			.unwrap_or(onchain_tx_handler.channel_parameters());
 
 		let get_htlc_descriptor = |holder_commitment: &HolderCommitmentTransaction| {
 			let trusted_tx = holder_commitment.trust();
@@ -616,7 +616,7 @@ impl HolderFundingOutput {
 		&self, onchain_tx_handler: &mut OnchainTxHandler<Signer>,
 	) -> MaybeSignedTransaction {
 		let channel_parameters = self.channel_parameters.as_ref().
-			unwrap_or(&onchain_tx_handler.channel_transaction_parameters);
+			unwrap_or(onchain_tx_handler.channel_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
@@ -788,7 +788,7 @@ impl PackageSolvingData {
 		}
 	}
 	fn finalize_input<Signer: EcdsaChannelSigner>(&self, bumped_tx: &mut Transaction, i: usize, onchain_handler: &mut OnchainTxHandler<Signer>) -> bool {
-		let channel_parameters = &onchain_handler.channel_transaction_parameters;
+		let channel_parameters = onchain_handler.channel_parameters();
 		match self {
 			PackageSolvingData::RevokedOutput(ref outp) => {
 				let channel_parameters = outp.channel_parameters.as_ref().unwrap_or(channel_parameters);