fixup: Use the weight of the single input-output pair, not the full tx

Author: tankyleo

lightning/src/events/bump_transaction/mod.rs

@@ -970,10 +970,10 @@ where
 			let expected_signed_tx_weight = unsigned_tx_weight + total_satisfaction_weight;
 			if expected_signed_tx_weight >= max_weight {
 				let extra_weight = expected_signed_tx_weight - max_weight;
-				let htlcs_to_remove = (extra_weight / chan_utils::htlc_timeout_tx_weight(channel_type)
-					// If we remove extra_weight / timeout_weight + 1 we sometimes still land above max_weight
-					+ 2) as usize;
-				batch_size = batch_size.checked_sub(htlcs_to_remove).ok_or(())?;
+				let htlcs_to_remove = extra_weight
+					/ chan_utils::htlc_timeout_input_output_pair_weight(channel_type)
+					+ 1;
+				batch_size = batch_size.checked_sub(htlcs_to_remove as usize).ok_or(())?;
 				continue;
 			}
 			broadcasted_htlcs += batch_size;

lightning/src/ln/chan_utils.rs

@@ -11,6 +11,7 @@
 //! largely of interest for those implementing the traits on [`crate::sign`] by hand.
 
 use bitcoin::amount::Amount;
+use bitcoin::constants::WITNESS_SCALE_FACTOR;
 use bitcoin::opcodes;
 use bitcoin::script::{Builder, Script, ScriptBuf};
 use bitcoin::sighash;
@@ -96,7 +97,7 @@ pub const P2A_ANCHOR_INPUT_WITNESS_WEIGHT: u64 = 1;
 pub const P2A_MAX_VALUE: u64 = 240;
 
 /// The maximum weight of a TRUC transaction.
-pub const TRUC_MAX_WEIGHT: u64 = 10_000 * bitcoin::constants::WITNESS_SCALE_FACTOR as u64;
+pub const TRUC_MAX_WEIGHT: u64 = 10_000 * WITNESS_SCALE_FACTOR as u64;
 
 /// The upper bound weight of an HTLC timeout input from a commitment transaction with keyed anchor outputs.
 pub const HTLC_TIMEOUT_INPUT_KEYED_ANCHOR_WITNESS_WEIGHT: u64 = 288;
@@ -137,6 +138,15 @@ pub fn htlc_success_tx_weight(channel_type_features: &ChannelTypeFeatures) -> u6
 	if channel_type_features.supports_anchors_zero_fee_htlc_tx() { HTLC_SUCCESS_ANCHOR_TX_WEIGHT } else { HTLC_SUCCESS_TX_WEIGHT }
 }
 
+/// Gets the weight of a single input-output pair in HTLC-success transactions
+pub fn htlc_success_input_output_pair_weight(channel_type_features: &ChannelTypeFeatures) -> u64 {
+	const TXIN_WEIGHT: u64 = 41 * WITNESS_SCALE_FACTOR as u64;
+	const TXOUT_WEIGHT: u64 = 43 * WITNESS_SCALE_FACTOR as u64;
+	let witness_weight =
+		if channel_type_features.supports_anchors_zero_fee_htlc_tx() { 327 } else { 324 };
+	TXIN_WEIGHT + TXOUT_WEIGHT + witness_weight
+}
+
 /// Gets the weight for an HTLC-Timeout transaction.
 #[inline]
 #[rustfmt::skip]
@@ -146,6 +156,15 @@ pub fn htlc_timeout_tx_weight(channel_type_features: &ChannelTypeFeatures) -> u6
 	if channel_type_features.supports_anchors_zero_fee_htlc_tx() { HTLC_TIMEOUT_ANCHOR_TX_WEIGHT } else { HTLC_TIMEOUT_TX_WEIGHT }
 }
 
+/// Gets the weight of a single input-output pair in HTLC-timeout transactions
+pub fn htlc_timeout_input_output_pair_weight(channel_type_features: &ChannelTypeFeatures) -> u64 {
+	const TXIN_WEIGHT: u64 = 41 * WITNESS_SCALE_FACTOR as u64;
+	const TXOUT_WEIGHT: u64 = 43 * WITNESS_SCALE_FACTOR as u64;
+	let witness_weight =
+		if channel_type_features.supports_anchors_zero_fee_htlc_tx() { 288 } else { 285 };
+	TXIN_WEIGHT + TXOUT_WEIGHT + witness_weight
+}
+
 /// Describes the type of HTLC claim as determined by analyzing the witness.
 #[derive(PartialEq, Eq)]
 pub enum HTLCClaim {

lightning/src/ln/zero_fee_commitment_tests.rs

@@ -163,10 +163,10 @@ fn test_htlc_claim_chunking() {
 	check_spends!(htlc_claims[0], node_1_commit_tx[0], coinbase_tx);
 	check_spends!(htlc_claims[1], node_1_commit_tx[0], coinbase_tx);
 
-	assert_eq!(htlc_claims[0].input.len(), 60);
-	assert_eq!(htlc_claims[0].output.len(), 60);
-	assert_eq!(htlc_claims[1].input.len(), 17);
-	assert_eq!(htlc_claims[1].output.len(), 17);
+	assert_eq!(htlc_claims[0].input.len(), 59);
+	assert_eq!(htlc_claims[0].output.len(), 59);
+	assert_eq!(htlc_claims[1].input.len(), 18);
+	assert_eq!(htlc_claims[1].output.len(), 18);
 
 	check_closed_broadcast!(nodes[0], true);
 	check_added_monitors!(nodes[0], 1);
@@ -205,8 +205,8 @@ fn test_htlc_claim_chunking() {
 	let fresh_htlc_claims = nodes[1].tx_broadcaster.txn_broadcast();
 	assert_eq!(fresh_htlc_claims.len(), 1);
 	check_spends!(fresh_htlc_claims[0], node_1_commit_tx[0], htlc_claims[0]);
-	assert_eq!(fresh_htlc_claims[0].input.len(), 17);
-	assert_eq!(fresh_htlc_claims[0].output.len(), 17);
+	assert_eq!(fresh_htlc_claims[0].input.len(), 18);
+	assert_eq!(fresh_htlc_claims[0].output.len(), 18);
 
 	// Assert when we handled the second `BumpTransaction::HTLCResolution` event, we
 	// assigned the same UTXO id to that set of HTLCs