Cache current local commitment number in ChannelMonitor.

By caching current local commitment number instead of deciphering
it from local commitment tx, we may remove local commitment tx
from ChannelMonitor in next commit.

Author: Antoine Riard

lightning/src/ln/channelmonitor.rs

@@ -780,6 +780,9 @@ pub struct ChannelMonitor<ChanSigner: ChannelKeys> {
 	// Used just for ChannelManager to make sure it has the latest channel data during
 	// deserialization
 	current_remote_commitment_number: u64,
+	// Used just for ChannelManager to make sure it has the latest channel data during
+	// deserialization
+	current_local_commitment_number: u64,
 
 	payment_preimages: HashMap<PaymentHash, PaymentPreimage>,
 
@@ -836,6 +839,7 @@ impl<ChanSigner: ChannelKeys> PartialEq for ChannelMonitor<ChanSigner> {
 			self.remote_hash_commitment_number != other.remote_hash_commitment_number ||
 			self.prev_local_signed_commitment_tx != other.prev_local_signed_commitment_tx ||
 			self.current_remote_commitment_number != other.current_remote_commitment_number ||
+			self.current_local_commitment_number != other.current_local_commitment_number ||
 			self.current_local_signed_commitment_tx != other.current_local_signed_commitment_tx ||
 			self.payment_preimages != other.payment_preimages ||
 			self.pending_htlcs_updated != other.pending_htlcs_updated ||
@@ -1008,6 +1012,12 @@ impl<ChanSigner: ChannelKeys + Writeable> ChannelMonitor<ChanSigner> {
 			writer.write_all(&byte_utils::be48_to_array(0))?;
 		}
 
+		if for_local_storage {
+			writer.write_all(&byte_utils::be48_to_array(self.current_local_commitment_number))?;
+		} else {
+			writer.write_all(&byte_utils::be48_to_array(0))?;
+		}
+
 		writer.write_all(&byte_utils::be64_to_array(self.payment_preimages.len() as u64))?;
 		for payment_preimage in self.payment_preimages.values() {
 			writer.write_all(&payment_preimage.0[..])?;
@@ -1126,6 +1136,7 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 			prev_local_signed_commitment_tx: None,
 			current_local_signed_commitment_tx: None,
 			current_remote_commitment_number: 1 << 48,
+			current_local_commitment_number: 0xffff_ffff_ffff,
 
 			payment_preimages: HashMap::new(),
 			pending_htlcs_updated: Vec::new(),
@@ -1262,6 +1273,7 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 		if let Err(_) = self.onchain_tx_handler.provide_latest_local_tx(commitment_tx.clone()) {
 			return Err(MonitorUpdateError("Local commitment signed has already been signed, no further update of LOCAL commitment transaction is allowed"));
 		}
+		self.current_local_commitment_number = 0xffff_ffff_ffff - ((((commitment_tx.without_valid_witness().input[0].sequence as u64 & 0xffffff) << 3*8) | (commitment_tx.without_valid_witness().lock_time as u64 & 0xffffff)) ^ self.commitment_transaction_number_obscure_factor);
 		self.prev_local_signed_commitment_tx = self.current_local_signed_commitment_tx.take();
 		self.current_local_signed_commitment_tx = Some(LocalSignedTx {
 			txid: commitment_tx.txid(),
@@ -1415,9 +1427,7 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 	}
 
 	pub(super) fn get_cur_local_commitment_number(&self) -> u64 {
-		if let &Some(ref local_tx) = &self.current_local_signed_commitment_tx {
-			0xffff_ffff_ffff - ((((local_tx.tx.without_valid_witness().input[0].sequence as u64 & 0xffffff) << 3*8) | (local_tx.tx.without_valid_witness().lock_time as u64 & 0xffffff)) ^ self.commitment_transaction_number_obscure_factor)
-		} else { 0xffff_ffff_ffff }
+		self.current_local_commitment_number
 	}
 
 	/// Attempts to claim a remote commitment transaction's outputs using the revocation key and
@@ -2415,6 +2425,7 @@ impl<ChanSigner: ChannelKeys + Readable> ReadableArgs<Arc<Logger>> for (Sha256dH
 		};
 
 		let current_remote_commitment_number = <U48 as Readable>::read(reader)?.0;
+		let current_local_commitment_number = <U48 as Readable>::read(reader)?.0;
 
 		let payment_preimages_len: u64 = Readable::read(reader)?;
 		let mut payment_preimages = HashMap::with_capacity(cmp::min(payment_preimages_len as usize, MAX_ALLOC_SIZE / 32));
@@ -2512,6 +2523,7 @@ impl<ChanSigner: ChannelKeys + Readable> ReadableArgs<Arc<Logger>> for (Sha256dH
 			prev_local_signed_commitment_tx,
 			current_local_signed_commitment_tx,
 			current_remote_commitment_number,
+			current_local_commitment_number,
 
 			payment_preimages,
 			pending_htlcs_updated,