Minor preparation, post_value computation

Author: optout21

lightning/src/ln/channel.rs

@@ -1738,6 +1738,23 @@ struct PendingSplice {
 	pub our_funding_contribution: i64,
 }
 
+#[cfg(splicing)]
+impl PendingSplice {
+	#[inline]
+	fn add_checked(base: u64, delta: i64) -> u64 {
+		if delta >= 0 {
+			base.saturating_add(delta as u64)
+		} else {
+			base.saturating_sub(delta.abs() as u64)
+		}
+	}
+
+	/// Compute the post-splice channel value from the pre-splice values and the peer contributions
+	pub fn compute_post_value(pre_channel_value: u64, our_funding_contribution: i64, their_funding_contribution: i64) -> u64 {
+		Self::add_checked(pre_channel_value, our_funding_contribution.saturating_add(their_funding_contribution))
+	}
+}
+
 /// Contains everything about the channel including state, and various flags.
 pub(super) struct ChannelContext<SP: Deref> where SP::Target: SignerProvider {
 	config: LegacyChannelConfig,
@@ -8592,7 +8609,11 @@ impl<SP: Deref> FundedChannel<SP> where
 
 		// Note on channel reserve requirement pre-check: as the splice acceptor does not contribute,
 		// it can't go below reserve, therefore no pre-check is done here.
-		// TODO(splicing): Once splice acceptor can contribute, add reserve pre-check, similar to the one in `splice_ack`.
+
+		let pre_channel_value = self.funding.value_to_self_msat;
+		let _post_channel_value = PendingSplice::compute_post_value(pre_channel_value, their_funding_contribution_satoshis, our_funding_contribution_satoshis);
+		let _post_balance = PendingSplice::add_checked(self.funding.value_to_self_msat, our_funding_contribution_satoshis);
+		// TODO: Early check for reserve requirement
 
 		// TODO(splicing): Store msg.funding_pubkey
 		// TODO(splicing): Apply start of splice (splice_start)
@@ -8611,14 +8632,24 @@ impl<SP: Deref> FundedChannel<SP> where
 
 	/// Handle splice_ack
 	#[cfg(splicing)]
-	pub fn splice_ack(&mut self, _msg: &msgs::SpliceAck) -> Result<(), ChannelError> {
+	pub fn splice_ack(&mut self, msg: &msgs::SpliceAck) -> Result<(), ChannelError> {
 		// check if splice is pending
-		if self.pending_splice.is_none() {
+		let pending_splice = if let Some(pending_splice) = &self.pending_splice {
+			pending_splice
+		} else {
 			return Err(ChannelError::Warn(format!("Channel is not in pending splice")));
 		};
 
 		// TODO(splicing): Pre-check for reserve requirement
 		// (Note: It should also be checked later at tx_complete)
+
+		let our_funding_contribution = pending_splice.our_funding_contribution;
+		let their_funding_contribution_satoshis = msg.funding_contribution_satoshis;
+
+		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);
+		// TODO: Early check for reserve requirement
 		Ok(())
 	}
 
@@ -13206,4 +13237,69 @@ mod tests {
 			);
 		}
 	}
+
+	#[cfg(all(test, splicing))]
+	fn get_pre_and_post(pre_channel_value: u64, our_funding_contribution: i64, their_funding_contribution: i64) -> (u64, u64) {
+		use crate::ln::channel::PendingSplice;
+
+		let post_channel_value = PendingSplice::compute_post_value(pre_channel_value, our_funding_contribution, their_funding_contribution);
+		(pre_channel_value, post_channel_value)
+	}
+
+	#[cfg(all(test, splicing))]
+	#[test]
+	fn test_splice_compute_post_value() {
+		{
+			// increase, small amounts
+			let (pre_channel_value, post_channel_value) = get_pre_and_post(9_000, 6_000, 0);
+			assert_eq!(pre_channel_value, 9_000);
+			assert_eq!(post_channel_value, 15_000);
+		}
+		{
+			// increase, small amounts
+			let (pre_channel_value, post_channel_value) = get_pre_and_post(9_000, 4_000, 2_000);
+			assert_eq!(pre_channel_value, 9_000);
+			assert_eq!(post_channel_value, 15_000);
+		}
+		{
+			// increase, small amounts
+			let (pre_channel_value, post_channel_value) = get_pre_and_post(9_000, 0, 6_000);
+			assert_eq!(pre_channel_value, 9_000);
+			assert_eq!(post_channel_value, 15_000);
+		}
+		{
+			// decrease, small amounts
+			let (pre_channel_value, post_channel_value) = get_pre_and_post(15_000, -6_000, 0);
+			assert_eq!(pre_channel_value, 15_000);
+			assert_eq!(post_channel_value, 9_000);
+		}
+		{
+			// decrease, small amounts
+			let (pre_channel_value, post_channel_value) = get_pre_and_post(15_000, -4_000, -2_000);
+			assert_eq!(pre_channel_value, 15_000);
+			assert_eq!(post_channel_value, 9_000);
+		}
+		{
+			// increase and decrease
+			let (pre_channel_value, post_channel_value) = get_pre_and_post(15_000, 4_000, -2_000);
+			assert_eq!(pre_channel_value, 15_000);
+			assert_eq!(post_channel_value, 17_000);
+		}
+		let base2: u64 = 2;
+		let huge63i3 = (base2.pow(63) - 3) as i64;
+		assert_eq!(huge63i3, 9223372036854775805);
+		assert_eq!(-huge63i3, -9223372036854775805);
+		{
+			// increase, large amount
+			let (pre_channel_value, post_channel_value) = get_pre_and_post(9_000, huge63i3, 3);
+			assert_eq!(pre_channel_value, 9_000);
+			assert_eq!(post_channel_value, 9223372036854784807);
+		}
+		{
+			// increase, large amounts
+			let (pre_channel_value, post_channel_value) = get_pre_and_post(9_000, huge63i3, huge63i3);
+			assert_eq!(pre_channel_value, 9_000);
+			assert_eq!(post_channel_value, 9223372036854784807);
+		}
+	}
 }