Refined balance reserve check; add locking (review)

Author: optout21

lightning/src/ln/channel.rs

@@ -4095,29 +4095,30 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 		}
 	}
 
-	/// Check that a balance value meets the channel reserve requirements or violates them (below reserve).
+	/// Check that balances meet the channel reserve requirements or violates them (below reserve).
 	/// The channel value is an input as opposed to using from self, so that this can be used in case of splicing
 	/// to checks with new channel value (before being comitted to it).
 	#[cfg(splicing)]
-	pub fn check_balance_meets_v2_reserve_requirements(&self, balance: u64, channel_value: u64) -> Result<(), ChannelError> {
-		if balance == 0 {
-			return Ok(());
-		}
-		let holder_selected_channel_reserve_satoshis = get_v2_channel_reserve_satoshis(
-			channel_value, self.holder_dust_limit_satoshis);
-		if balance < holder_selected_channel_reserve_satoshis {
-			return Err(ChannelError::Warn(format!(
-				"Balance below reserve mandated by holder, {} vs {}",
-				balance, holder_selected_channel_reserve_satoshis,
-			)));
+	pub fn check_balance_meets_v2_reserve_requirements(&self, self_balance: u64, counterparty_balance: u64, channel_value: u64) -> Result<(), ChannelError> {
+		if self_balance > 0 {
+			let holder_selected_channel_reserve_satoshis = get_v2_channel_reserve_satoshis(
+				channel_value, self.holder_dust_limit_satoshis);
+			if self_balance < holder_selected_channel_reserve_satoshis {
+				return Err(ChannelError::Warn(format!(
+					"Balance below reserve mandated by holder, {} vs {}",
+					self_balance, holder_selected_channel_reserve_satoshis,
+				)));
+			}
 		}
-		let counterparty_selected_channel_reserve_satoshis = get_v2_channel_reserve_satoshis(
-			channel_value, self.counterparty_dust_limit_satoshis);
-		if balance < counterparty_selected_channel_reserve_satoshis {
-			return Err(ChannelError::Warn(format!(
-				"Balance below reserve mandated by counterparty, {} vs {}",
-				balance, counterparty_selected_channel_reserve_satoshis,
-			)));
+		if counterparty_balance > 0 {
+			let counterparty_selected_channel_reserve_satoshis = get_v2_channel_reserve_satoshis(
+				channel_value, self.counterparty_dust_limit_satoshis);
+			if counterparty_balance < counterparty_selected_channel_reserve_satoshis {
+				return Err(ChannelError::Warn(format!(
+					"Balance below reserve mandated by counterparty, {} vs {}",
+					counterparty_balance, counterparty_selected_channel_reserve_satoshis,
+				)));
+			}
 		}
 		Ok(())
 	}
@@ -8554,10 +8555,11 @@ impl<SP: Deref> FundedChannel<SP> where
 
 		let pre_channel_value = self.funding.get_value_satoshis();
 		let post_channel_value = PendingSplice::compute_post_value(pre_channel_value, our_funding_contribution, their_funding_contribution_satoshis);
-		let post_balance = PendingSplice::add_checked(self.funding.value_to_self_msat, our_funding_contribution);
-		// Pre-check for reserve requirement, assuming maximum balance of full channel value
+		let post_balance_self = PendingSplice::add_checked(self.funding.value_to_self_msat, our_funding_contribution);
+		let post_balance_counterparty = post_channel_value.saturating_sub(post_balance_self);
+		// Pre-check for reserve requirement
 		// This will also be checked later at tx_complete
-		let _res = self.context.check_balance_meets_v2_reserve_requirements(post_balance, post_channel_value)?;
+		let _res = self.context.check_balance_meets_v2_reserve_requirements(post_balance_self, post_balance_counterparty, post_channel_value)?;
 		Ok(())
 	}
 

lightning/src/ln/channelmanager.rs

@@ -4292,6 +4292,7 @@ where
 		our_funding_inputs: Vec<(TxIn, Transaction, Weight)>,
 		funding_feerate_per_kw: u32, locktime: u32,
 	) -> Result<(), APIError> {
+		let _persistence_guard = PersistenceNotifierGuard::notify_on_drop(self);
 		let per_peer_state = self.per_peer_state.read().unwrap();
 
 		let peer_state_mutex = per_peer_state.get(counterparty_node_id)