Merge pull request #3945 from tankyleo/txbuilder-fixups

#3775 follow-ups

Author: TheBlueMatt

lightning/src/chain/channelmonitor.rs

@@ -774,6 +774,8 @@ pub enum Balance {
 		amount_satoshis: u64,
 		/// The transaction fee we pay for the closing commitment transaction. This amount is not
 		/// included in the [`Balance::ClaimableOnChannelClose::amount_satoshis`] value.
+		/// This amount includes the sum of dust HTLCs on the commitment transaction, any elided anchors,
+		/// as well as the sum of msat amounts rounded down from non-dust HTLCs.
 		///
 		/// Note that if this channel is inbound (and thus our counterparty pays the commitment
 		/// transaction fee) this value will be zero. For [`ChannelMonitor`]s created prior to LDK
@@ -2860,11 +2862,11 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitor<Signer> {
 			let to_self_value_sat = us.funding.current_holder_commitment_tx.to_broadcaster_value_sat();
 			res.push(Balance::ClaimableOnChannelClose {
 				amount_satoshis: to_self_value_sat + claimable_inbound_htlc_value_sat,
-				// In addition to `commit_tx_fee_sat`, this can also include dust HTLCs, and the total msat amount rounded down from non-dust HTLCs
+				// In addition to `commit_tx_fee_sat`, this can also include dust HTLCs, any elided anchors,
+				// and the total msat amount rounded down from non-dust HTLCs
 				transaction_fee_satoshis: if us.holder_pays_commitment_tx_fee.unwrap_or(true) {
 					let transaction = &us.funding.current_holder_commitment_tx.trust().built_transaction().transaction;
-					// Unwrap here; commitment transactions always have at least one output
-					let output_value_sat = transaction.output.iter().map(|txout| txout.value).reduce(|sum, value| sum + value).unwrap().to_sat();
+					let output_value_sat: u64 = transaction.output.iter().map(|txout| txout.value.to_sat()).sum();
 					us.funding.channel_parameters.channel_value_satoshis - output_value_sat
 				} else { 0 },
 				outbound_payment_htlc_rounded_msat,

lightning/src/ln/channel.rs

@@ -4140,12 +4140,17 @@ where
 		// Channel state once they will not be present in the next received commitment
 		// transaction).
 		let (local_balance_before_fee_msat, remote_balance_before_fee_msat) = {
-			let mut removed_outbound_total_msat = 0;
-			for htlc in self.pending_outbound_htlcs.iter() {
-				if let OutboundHTLCState::AwaitingRemoteRevokeToRemove(OutboundHTLCOutcome::Success(_, _)) | OutboundHTLCState::AwaitingRemovedRemoteRevoke(OutboundHTLCOutcome::Success(_, _)) = htlc.state {
-					removed_outbound_total_msat += htlc.amount_msat;
-				}
-			}
+			let removed_outbound_total_msat: u64 = self.pending_outbound_htlcs
+				.iter()
+				.filter_map(|htlc| {
+					matches!(
+						htlc.state,
+						OutboundHTLCState::AwaitingRemoteRevokeToRemove(OutboundHTLCOutcome::Success(_, _))
+						| OutboundHTLCState::AwaitingRemovedRemoteRevoke(OutboundHTLCOutcome::Success(_, _))
+					)
+					.then_some(htlc.amount_msat)
+				})
+				.sum();
 			let pending_value_to_self_msat =
 				funding.value_to_self_msat + htlc_stats.pending_inbound_htlcs_value_msat - removed_outbound_total_msat;
 			let pending_remote_value_msat =
@@ -4372,13 +4377,17 @@ where
 		}
 
 		if !funding.is_outbound() {
-			let mut removed_outbound_total_msat = 0;
-			for htlc in self.pending_outbound_htlcs.iter() {
-				if let OutboundHTLCState::AwaitingRemoteRevokeToRemove(OutboundHTLCOutcome::Success(_, _)) | OutboundHTLCState::AwaitingRemovedRemoteRevoke(OutboundHTLCOutcome::Success(_, _)) = htlc.state {
-					removed_outbound_total_msat += htlc.amount_msat;
-				}
-			}
-
+			let removed_outbound_total_msat: u64 = self.pending_outbound_htlcs
+				.iter()
+				.filter_map(|htlc| {
+					matches!(
+						htlc.state,
+						OutboundHTLCState::AwaitingRemoteRevokeToRemove(OutboundHTLCOutcome::Success(_, _))
+						| OutboundHTLCState::AwaitingRemovedRemoteRevoke(OutboundHTLCOutcome::Success(_, _))
+					)
+					.then_some(htlc.amount_msat)
+				})
+				.sum();
 			let pending_value_to_self_msat =
 				funding.value_to_self_msat + htlc_stats.pending_inbound_htlcs_value_msat - removed_outbound_total_msat;
 			let pending_remote_value_msat =
@@ -4615,7 +4624,7 @@ where
 			broadcaster_dust_limit_sat,
 			logger,
 		);
-		debug_assert_eq!(stats, self.build_commitment_stats(funding, local, generated_by_local, None, None));
+		debug_assert_eq!(stats, self.build_commitment_stats(funding, local, generated_by_local, None, None), "Caught an inconsistency between `TxBuilder::build_commitment_transaction` and the rest of the `TxBuilder` methods");
 
 		// This populates the HTLC-source table with the indices from the HTLCs in the commitment
 		// transaction.