Track the txid that resolves HTLCs even after resolution completes

We need this information when we look up if we still need to spend
a revoked output from an HTLC-Success/HTLC-Timeout transaction for
balance calculation.

Author: TheBlueMatt

lightning/src/chain/channelmonitor.rs

@@ -596,13 +596,20 @@ pub enum Balance {
 #[derive(PartialEq)]
 struct IrrevocablyResolvedHTLC {
 	commitment_tx_output_idx: u32,
+	/// The txid of the transaction which resolved the HTLC, this may be a commitment,
+	/// HTLC-Success, or HTLC-Timeout transaction.
+	resolving_txid: Option<Txid>,
+	/// The amount of the output for this HTLC in `resolving_txid`.
+	onchain_value_satoshis: Option<u64>,
 	/// Only set if the HTLC claim was ours using a payment preimage
 	payment_preimage: Option<PaymentPreimage>,
 }
 
 impl_writeable_tlv_based!(IrrevocablyResolvedHTLC, {
 	(0, commitment_tx_output_idx, required),
+	(1, resolving_txid, option),
 	(2, payment_preimage, option),
+	(3, onchain_value_satoshis, option),
 });
 
 /// A ChannelMonitor handles chain events (blocks connected and disconnected) and generates
@@ -2675,7 +2682,7 @@ impl<Signer: Sign> ChannelMonitorImpl<Signer> {
 		// Produce actionable events from on-chain events having reached their threshold.
 		for entry in onchain_events_reaching_threshold_conf.drain(..) {
 			match entry.event {
-				OnchainEvent::HTLCUpdate { ref source, payment_hash, htlc_value_satoshis, commitment_tx_output_idx, .. } => {
+				OnchainEvent::HTLCUpdate { ref source, payment_hash, htlc_value_satoshis, commitment_tx_output_idx, onchain_value_satoshis } => {
 					// Check for duplicate HTLC resolutions.
 					#[cfg(debug_assertions)]
 					{
@@ -2701,7 +2708,10 @@ impl<Signer: Sign> ChannelMonitorImpl<Signer> {
 						htlc_value_satoshis,
 					}));
 					if let Some(idx) = commitment_tx_output_idx {
-						self.htlcs_resolved_on_chain.push(IrrevocablyResolvedHTLC { commitment_tx_output_idx: idx, payment_preimage: None });
+						self.htlcs_resolved_on_chain.push(IrrevocablyResolvedHTLC {
+							commitment_tx_output_idx: idx, resolving_txid: Some(entry.txid),
+							payment_preimage: None, onchain_value_satoshis,
+						});
 					}
 				},
 				OnchainEvent::MaturingOutput { descriptor } => {
@@ -2710,8 +2720,10 @@ impl<Signer: Sign> ChannelMonitorImpl<Signer> {
 						outputs: vec![descriptor]
 					});
 				},
-				OnchainEvent::HTLCSpendConfirmation { commitment_tx_output_idx, preimage, .. } => {
-					self.htlcs_resolved_on_chain.push(IrrevocablyResolvedHTLC { commitment_tx_output_idx, payment_preimage: preimage });
+				OnchainEvent::HTLCSpendConfirmation { commitment_tx_output_idx, preimage, onchain_value_satoshis, .. } => {
+					self.htlcs_resolved_on_chain.push(IrrevocablyResolvedHTLC {
+						commitment_tx_output_idx, resolving_txid: Some(entry.txid),
+						payment_preimage: preimage, onchain_value_satoshis });
 				},
 				OnchainEvent::FundingSpendConfirmation { commitment_tx_to_counterparty_output, .. } => {
 					self.funding_spend_confirmed = Some(entry.txid);