f - add missing balance check

Author: jkczyz

lightning/src/ln/channel.rs

@@ -11014,6 +11014,22 @@ where
 			)));
 		}
 
+		let their_channel_balance = Amount::from_sat(self.funding.get_value_satoshis())
+			- Amount::from_sat(self.funding.get_value_to_self_msat() / 1000);
+		let post_channel_balance = AddSigned::checked_add_signed(
+			their_channel_balance.to_sat(),
+			their_funding_contribution.to_sat(),
+		);
+
+		if post_channel_balance.is_none() {
+			return Err(ChannelError::WarnAndDisconnect(format!(
+				"Channel {} cannot be spliced out; their {} contribution exhausts their channel balance: {}",
+				self.context.channel_id(),
+				their_funding_contribution,
+				their_channel_balance,
+			)));
+		}
+
 		let splice_funding = FundingScope::for_splice(
 			&self.funding,
 			&self.context,