Include HTLC amts in ClaimableOnChannelClose.transaction_fee_satoshis

In addition to the amount set by `commit_tx_fee_sat`, the transaction
fee of a commitment transaction may also increase due to HTLC amounts
that get burned to fees, and any elided anchors. We now include these
amounts in the `transaction_fee_satoshis` field of
`Balance::ClaimableOnChannelClose` too.

This commit also makes the `transaction_fee_satoshis` field correct for
custom transactions not encompassed in `chan_utils::commit_tx_fee_sat`.

Author: tankyleo

lightning/src/chain/channelmonitor.rs

@@ -2736,15 +2736,11 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitor<Signer> {
 			}
 		} else {
 			let mut claimable_inbound_htlc_value_sat = 0;
-			let mut nondust_htlc_count = 0;
 			let mut outbound_payment_htlc_rounded_msat = 0;
 			let mut outbound_forwarded_htlc_rounded_msat = 0;
 			let mut inbound_claiming_htlc_rounded_msat = 0;
 			let mut inbound_htlc_rounded_msat = 0;
 			for (htlc, source) in holder_commitment_htlcs!(us, CURRENT_WITH_SOURCES) {
-				if htlc.transaction_output_index.is_some() {
-					nondust_htlc_count += 1;
-				}
 				let rounded_value_msat = if htlc.transaction_output_index.is_none() {
 					htlc.amount_msat
 				} else { htlc.amount_msat % 1000 };
@@ -2788,11 +2784,12 @@ 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
 				transaction_fee_satoshis: if us.holder_pays_commitment_tx_fee.unwrap_or(true) {
-					chan_utils::commit_tx_fee_sat(
-						us.funding.current_holder_commitment_tx.feerate_per_kw(), nondust_htlc_count,
-						us.channel_type_features(),
-					)
+					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();
+					us.funding.channel_parameters.channel_value_satoshis - output_value_sat
 				} else { 0 },
 				outbound_payment_htlc_rounded_msat,
 				outbound_forwarded_htlc_rounded_msat,

lightning/src/ln/monitor_tests.rs

@@ -544,9 +544,11 @@ fn do_test_claim_value_force_close(anchors: bool, prev_commitment_tx: bool) {
 	let commitment_tx_fee = chan_feerate as u64 *
 		(chan_utils::commitment_tx_base_weight(&channel_type_features) + 2 * chan_utils::COMMITMENT_TX_WEIGHT_PER_HTLC) / 1000;
 	let anchor_outputs_value = if anchors { 2 * channel::ANCHOR_OUTPUT_VALUE_SATOSHI } else { 0 };
+	let amount_satoshis = 1_000_000 - 3_000 - 4_000 - 1_000 - 3 - commitment_tx_fee - anchor_outputs_value - 1; /* msat amount that is burned to fees */
 	assert_eq!(sorted_vec(vec![Balance::ClaimableOnChannelClose {
-			amount_satoshis: 1_000_000 - 3_000 - 4_000 - 1_000 - 3 - commitment_tx_fee - anchor_outputs_value - 1 /* msat amount that is burned to fees */,
-			transaction_fee_satoshis: commitment_tx_fee,
+			amount_satoshis,
+			// In addition to `commitment_tx_fee`, this also includes the dust HTLC, and the total msat amount rounded down from non-dust HTLCs
+			transaction_fee_satoshis: 1_000_000 - 4_000 - 3_000 - 1_000 - amount_satoshis - anchor_outputs_value,
 			outbound_payment_htlc_rounded_msat: 3300,
 			outbound_forwarded_htlc_rounded_msat: 0,
 			inbound_claiming_htlc_rounded_msat: 0,
@@ -598,16 +600,18 @@ fn do_test_claim_value_force_close(anchors: bool, prev_commitment_tx: bool) {
 	let commitment_tx_fee = chan_feerate as u64 *
 		(chan_utils::commitment_tx_base_weight(&channel_type_features) +
 		if prev_commitment_tx { 1 } else { 2 } * chan_utils::COMMITMENT_TX_WEIGHT_PER_HTLC) / 1000;
-	let mut a_expected_balances = vec![Balance::ClaimableOnChannelClose {
-			amount_satoshis: 1_000_000 - // Channel funding value in satoshis
+	let amount_satoshis = 1_000_000 - // Channel funding value in satoshis
 				4_000 - // The to-be-failed HTLC value in satoshis
 				3_000 - // The claimed HTLC value in satoshis
 				1_000 - // The push_msat value in satoshis
 				3 - // The dust HTLC value in satoshis
 				commitment_tx_fee - // The commitment transaction fee with two HTLC outputs
 				anchor_outputs_value - // The anchor outputs value in satoshis
-				1, // The rounded up msat part of the one HTLC
-			transaction_fee_satoshis: commitment_tx_fee,
+				1; // The rounded up msat part of the one HTLC
+	let mut a_expected_balances = vec![Balance::ClaimableOnChannelClose {
+			amount_satoshis, // Channel funding value in satoshis
+			// In addition to `commitment_tx_fee`, this also includes the dust HTLC, and the total msat amount rounded down from non-dust HTLCs
+			transaction_fee_satoshis: 1_000_000 - 4_000 - 3_000 - 1_000 - amount_satoshis - anchor_outputs_value,
 			outbound_payment_htlc_rounded_msat: 3000 + if prev_commitment_tx {
 			    200 /* 1 to-be-failed HTLC */ } else { 300 /* 2 HTLCs */ },
 			outbound_forwarded_htlc_rounded_msat: 0,