Check that funder covers the fee spike buffer multiple after a splice

lightning/src/ln/channel.rs

@@ -2834,7 +2834,7 @@ impl FundingScope {
 
 		// New reserve values are based on the new channel value and are v2-specific
 		let counterparty_selected_channel_reserve_satoshis =
-			Some(get_v2_channel_reserve_satoshis(post_channel_value, MIN_CHAN_DUST_LIMIT_SATOSHIS));
+			get_v2_channel_reserve_satoshis(post_channel_value, MIN_CHAN_DUST_LIMIT_SATOSHIS);
 		let holder_selected_channel_reserve_satoshis = get_v2_channel_reserve_satoshis(
 			post_channel_value,
 			context.counterparty_dust_limit_satoshis,
@@ -2844,23 +2844,39 @@ impl FundingScope {
 			channel_transaction_parameters: post_channel_transaction_parameters,
 			value_to_self_msat: post_value_to_self_msat,
 			funding_transaction: None,
-			counterparty_selected_channel_reserve_satoshis,
+			counterparty_selected_channel_reserve_satoshis: Some(
+				counterparty_selected_channel_reserve_satoshis,
+			),
 			holder_selected_channel_reserve_satoshis,
 			#[cfg(debug_assertions)]
 			holder_prev_commitment_tx_balance: {
 				let prev = *prev_funding.holder_prev_commitment_tx_balance.lock().unwrap();
-				Mutex::new((
-					prev.0.saturating_add_signed(our_funding_contribution.to_sat() * 1000),
-					prev.1.saturating_add_signed(their_funding_contribution.to_sat() * 1000),
-				))
+				let new_holder_balance_msat =
+					prev.0.saturating_add_signed(our_funding_contribution.to_sat() * 1000);
+				let new_counterparty_balance_msat =
+					prev.1.saturating_add_signed(their_funding_contribution.to_sat() * 1000);
+				if new_holder_balance_msat < counterparty_selected_channel_reserve_satoshis {
+					assert_eq!(new_holder_balance_msat, prev.0);
+				}
+				if new_counterparty_balance_msat < holder_selected_channel_reserve_satoshis {
+					assert_eq!(new_counterparty_balance_msat, prev.1);
+				}
+				Mutex::new((new_holder_balance_msat, new_counterparty_balance_msat))
 			},
 			#[cfg(debug_assertions)]
 			counterparty_prev_commitment_tx_balance: {
 				let prev = *prev_funding.counterparty_prev_commitment_tx_balance.lock().unwrap();
-				Mutex::new((
-					prev.0.saturating_add_signed(our_funding_contribution.to_sat() * 1000),
-					prev.1.saturating_add_signed(their_funding_contribution.to_sat() * 1000),
-				))
+				let new_holder_balance_msat =
+					prev.0.saturating_add_signed(our_funding_contribution.to_sat() * 1000);
+				let new_counterparty_balance_msat =
+					prev.1.saturating_add_signed(their_funding_contribution.to_sat() * 1000);
+				if new_holder_balance_msat < counterparty_selected_channel_reserve_satoshis {
+					assert_eq!(new_holder_balance_msat, prev.0);
+				}
+				if new_counterparty_balance_msat < holder_selected_channel_reserve_satoshis {
+					assert_eq!(new_counterparty_balance_msat, prev.1);
+				}
+				Mutex::new((new_holder_balance_msat, new_counterparty_balance_msat))
 			},
 			#[cfg(any(test, fuzzing))]
 			next_local_fee: Mutex::new(PredictedNextFee::default()),
@@ -5942,7 +5958,9 @@ impl<SP: SignerProvider> ChannelContext<SP> {
 				max_reserved_commit_tx_fee_msat as i64;
 			if capacity_minus_commitment_fee_msat < (real_dust_limit_timeout_sat as i64) * 1000 {
 				let one_htlc_difference_msat = max_reserved_commit_tx_fee_msat - min_reserved_commit_tx_fee_msat;
-				debug_assert!(one_htlc_difference_msat != 0);
+				if !funding.get_channel_type().supports_anchor_zero_fee_commitments() {
+					debug_assert!(one_htlc_difference_msat != 0);
+				}
 				capacity_minus_commitment_fee_msat += one_htlc_difference_msat as i64;
 				capacity_minus_commitment_fee_msat = cmp::min(real_dust_limit_timeout_sat as i64 * 1000 - 1, capacity_minus_commitment_fee_msat);
 				available_capacity_msat = cmp::max(0, cmp::min(capacity_minus_commitment_fee_msat, available_capacity_msat as i64)) as u64;
@@ -12702,20 +12720,34 @@ where
 		&self, funding: &FundingScope,
 	) -> Result<(Amount, Amount), String> {
 		let include_counterparty_unknown_htlcs = true;
-		// Make sure that that the funder of the channel can pay the transaction fees for an additional
-		// nondust HTLC on the channel.
-		let addl_nondust_htlc_count = 1;
 		// We are not interested in dust exposure
 		let dust_exposure_limiting_feerate = None;
 
+		let addl_nondust_htlc_count =
+			if funding.get_channel_type().supports_anchor_zero_fee_commitments() {
+				0
+			} else {
+				// Require the channel opener to reserve enough funds to pay the fees for an
+				// additional non-dust HTLC in the channel.
+				1
+			};
+
+		let feerate_per_kw = if !funding.get_channel_type().supports_anchors_zero_fee_htlc_tx() {
+			// Similar to HTLC additions, require the funder to have enough funds reserved for
+			// fees such that the feerate can jump without rendering the channel useless.
+			self.context.feerate_per_kw * FEE_SPIKE_BUFFER_FEE_INCREASE_MULTIPLE as u32
+		} else {
+			self.context.feerate_per_kw
+		};
+
 		let local_commitment_stats = self
 			.context
 			.get_next_local_commitment_stats(
 				funding,
 				None, // htlc_candidate
 				include_counterparty_unknown_htlcs,
 				addl_nondust_htlc_count,
-				self.context.feerate_per_kw,
+				feerate_per_kw,
 				dust_exposure_limiting_feerate,
 			)
 			.map_err(|()| "Balance after HTLCs and anchors exhausted on local commitment")?;
@@ -12731,7 +12763,7 @@ where
 				None, // htlc_candidate
 				include_counterparty_unknown_htlcs,
 				addl_nondust_htlc_count,
-				self.context.feerate_per_kw,
+				feerate_per_kw,
 				dust_exposure_limiting_feerate,
 			)
 			.map_err(|()| "Balance after HTLCs and anchors exhausted on remote commitment")?;