Add ability to retrieve latest commitment transactions from ChannelMa…

…nager

lightning/src/chain/chainmonitor.rs

@@ -669,6 +669,12 @@ where C::Target: chain::Filter,
 		}
 	}
 
+	fn get_latest_holder_commitment_txn(&self, funding_txo: OutPoint) -> Vec<bitcoin::Transaction> {
+		let monitors = self.monitors.read().unwrap();
+		let monitor = monitors.get(&funding_txo).expect("To have a monitor for the requested channel");
+		monitor.monitor.get_latest_holder_commitment_txn_internal(&self.logger)
+	}
+
 	/// Note that we persist the given `ChannelMonitor` update while holding the
 	/// `ChainMonitor` monitors lock.
 	fn update_channel(&self, funding_txo: OutPoint, update: &ChannelMonitorUpdate) -> ChannelMonitorUpdateStatus {

lightning/src/chain/channelmonitor.rs

@@ -1357,6 +1357,11 @@ impl<Signer: WriteableEcdsaChannelSigner> ChannelMonitor<Signer> {
 		self.inner.lock().unwrap().get_latest_holder_commitment_txn(logger)
 	}
 
+	pub(crate) fn get_latest_holder_commitment_txn_internal<L: Deref>(&self, logger: &L) -> Vec<Transaction>
+	where L::Target: Logger {
+		self.inner.lock().unwrap().get_latest_holder_commitment_txn_internal(logger)
+	}
+
 	/// Unsafe test-only version of get_latest_holder_commitment_txn used by our test framework
 	/// to bypass HolderCommitmentTransaction state update lockdown after signature and generate
 	/// revoked commitment transaction.
@@ -2848,8 +2853,12 @@ impl<Signer: WriteableEcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 	}
 
 	pub fn get_latest_holder_commitment_txn<L: Deref>(&mut self, logger: &L) -> Vec<Transaction> where L::Target: Logger {
-		log_debug!(logger, "Getting signed latest holder commitment transaction!");
 		self.holder_tx_signed = true;
+		self.get_latest_holder_commitment_txn_internal(logger)
+	}
+
+	pub(crate) fn get_latest_holder_commitment_txn_internal<L: Deref>(&mut self, logger: &L) -> Vec<Transaction> where L::Target: Logger {
+		log_debug!(logger, "Getting signed latest holder commitment transaction!");
 		let commitment_tx = self.onchain_tx_handler.get_fully_signed_holder_tx(&self.funding_redeemscript);
 		let txid = commitment_tx.txid();
 		let mut holder_transactions = vec![commitment_tx];

lightning/src/chain/mod.rs

@@ -299,6 +299,9 @@ pub trait Watch<ChannelSigner: WriteableEcdsaChannelSigner> {
 	/// Update the outpoint funding the channel.
 	fn update_channel_funding_txo(&self, old_funding_txo: OutPoint, new_funding_txo: OutPoint, channel_value_satoshis: u64) -> ChannelMonitorUpdateStatus;
 
+	/// Get the latest commitment transaction to broadcast
+	fn get_latest_holder_commitment_txn(&self, funding_txo: OutPoint) -> Vec<bitcoin::Transaction>;
+
 	/// Returns any monitor events since the last call. Subsequent calls must only return new
 	/// events.
 	///

lightning/src/ln/chan_utils.rs

@@ -823,7 +823,14 @@ pub struct ChannelTransactionParameters {
 	/// The late-bound counterparty channel transaction parameters.
 	/// These parameters are populated at the point in the protocol where the counterparty provides them.
 	pub counterparty_parameters: Option<CounterpartyChannelTransactionParameters>,
-	/// The late-bound funding outpoint
+	/// The late-bound funding outpoint.
+	///
+	/// If it's a vanilla LN channel, this value corresponds to the actual funding outpoint that
+	/// goes on-chain when the channel is created.
+	///
+	/// If instead we're dealing with a split channel, this value corresponds to the output of a
+	/// glue transaction which sits in between the funding transaction and the commitment
+	/// transaction.
 	pub funding_outpoint: Option<chain::transaction::OutPoint>,
 	/// Are anchors (zero fee HTLC transaction variant) used for this channel. Boolean is
 	/// serialization backwards-compatible.
@@ -832,7 +839,9 @@ pub struct ChannelTransactionParameters {
 	/// It is intended merely for backwards compatibility with signers that need it.
 	/// There is no support for this feature in LDK channel negotiation.
 	pub opt_non_zero_fee_anchors: Option<()>,
-	///
+	/// This value always corresponds to the actual funding outpoint. This is different to
+	/// [`ChannelTransactionParameters::funding_outpoint`], which varies depending on the type
+	/// of Lightning channel we have.
 	pub original_funding_outpoint: Option<chain::transaction::OutPoint>,
 }
 

lightning/src/ln/channel.rs

@@ -5119,8 +5119,54 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
 						return Ok((Some(channel_ready), announcement_sigs));
 					}
 				}
+
+				// If we have a vanilla LN channel, this checks if the transaction
+				// spends from the actual funding output. That could be either a
+				// commitment transaction or a mutual close transaction.
+				//
+				// If we have a split channel, this checks if the transaction spends
+				// from the glue output. That could only be a commitment
+				// transaction.
+				let is_funding_or_glue_txo = |prev_outpoint: &bitcoin::OutPoint| -> bool {
+					prev_outpoint == &funding_txo.into_bitcoin_outpoint()
+				};
+
+				// This check only runs if the check above returns `false`. We know
+				// that a vanilla LN channel can only be closed by spending from the
+				// original funding output, so in this check we are only considering
+				// split channels.
+				//
+				// The other ways in which a split channel could be closed are:
+				//
+				// - Through a mutual close of the _LN_ channel, which would spend
+				// directly from the original funding output.
+				//
+				// - Through the publication of a revoked commitment transaction
+				// spending from the original funding output!
+				//
+				// And that's exactly what we check here: whether the transaction
+				// spends from the original funding output and, if it does, whether
+				// the transaction is NOT the split transaction (the only other
+				// possible option).
+				//
+				// We do not announce the closing of the LN channel with the split
+				// transaction, because that is reserved to either mutual close or
+				// commitment transactions. LDK will only react to this announcement
+				// once, so we should not waste it on the split transaction, as this
+				// can lead to loss of funds.
+				let is_final_tx_spending_from_original_funding_txo = |prev_outpoint: &bitcoin::OutPoint, outputs: &[bitcoin::TxOut]| -> bool {
+					match self.get_original_funding_txo().map(|x| x.into_bitcoin_outpoint()) {
+						Some(original_funding_outpoint) => {
+						        // Transaction spends from actual funding output.
+						        prev_outpoint == &original_funding_outpoint &&
+							// Transaction is _not_ a split transaction.
+						        !(outputs.len() == 2 && outputs[0].script_pubkey == outputs[1].script_pubkey)
+					        }
+						None => false,
+					}
+				};
 				for inp in tx.input.iter() {
-					if inp.previous_output == funding_txo.into_bitcoin_outpoint() {
+					if is_funding_or_glue_txo(&inp.previous_output) || is_final_tx_spending_from_original_funding_txo(&inp.previous_output, &tx.output) {
 						log_info!(logger, "Detected channel-closing tx {} spending {}:{}, closing channel {}", tx.txid(), inp.previous_output.txid, inp.previous_output.vout, log_bytes!(self.channel_id()));
 						return Err(ClosureReason::CommitmentTxConfirmed);
 					}

lightning/src/ln/channelmanager.rs

@@ -2015,6 +2015,15 @@ where
 		let chan = &mut channel_lock.channel;
 
 		chan.set_funding_outpoint(funding_outpoint, channel_value, own_balance, false, &self.logger);
+		if ChannelMonitorUpdateStatus::Completed != self.chain_monitor.update_channel_funding_txo(chan.get_original_funding_txo().unwrap(), *funding_outpoint, channel_value) {
+			log_error!(self.logger, "Error setting funding txo on chain monitor");
+		}
+	}
+
+	fn get_latest_holder_commitment_txn_internal(&self, channel_lock: &ChannelLock<<SP::Target as SignerProvider>::Signer>) -> Vec<Transaction> {
+		let chan = &channel_lock.channel;
+
+		self.chain_monitor.get_latest_holder_commitment_txn(chan.get_original_funding_txo().expect("To have a funding txo"))
 	}
 
 	fn close_channel_internal(&self, channel_id: &[u8; 32], counterparty_node_id: &PublicKey, target_feerate_sats_per_1000_weight: Option<u32>) -> Result<(), APIError> {
@@ -2146,6 +2155,11 @@ where
 		self.set_funding_outpoint_internal(channel_lock, funding_output, channel_value_satoshis, value_to_self_msat);
 	}
 
+	///
+	pub fn get_latest_holder_commitment_txn(&self, channel_lock: &ChannelLock<<SP::Target as SignerProvider>::Signer>) -> Vec<Transaction> {
+		self.get_latest_holder_commitment_txn_internal(channel_lock)
+	}
+
 	#[inline]
 	fn finish_force_close_channel(&self, shutdown_res: ShutdownResult) {
 		let (monitor_update_option, mut failed_htlcs) = shutdown_res;