Add last_local_balance_msats field

Introduced to show what your local balance is, when channel is closed, that way you can see how many sats you lost to rounding.
The balance may be increased by outbound pending HTLCs and transaction fees. Check [ChainMonitor::get_claimable_balances] to get more accurate balance which contains fee information.

lightning/src/events/mod.rs

@@ -1276,6 +1276,11 @@ pub enum Event {
 		/// status of the closing tx.
 		/// Note that for instances serialized in v0.0.119 or prior this will be missing (None).
 		channel_funding_txo: Option<transaction::OutPoint>,
+		/// Local balance in msats when a channel is closed.
+		///
+		/// May overstate balance by pending outbound HTLCs and transaction fees.
+		/// For more accurate balances including fee information see [ChainMonitor::get_claimable_balances]
+		last_local_balance_msats: Option<u64>,
 	},
 	/// Used to indicate to the user that they can abandon the funding transaction and recycle the
 	/// inputs for another purpose.
@@ -1555,7 +1560,8 @@ impl Writeable for Event {
 				});
 			},
 			&Event::ChannelClosed { ref channel_id, ref user_channel_id, ref reason,
-				ref counterparty_node_id, ref channel_capacity_sats, ref channel_funding_txo
+				ref counterparty_node_id, ref channel_capacity_sats, ref channel_funding_txo,
+				ref last_local_balance_msats
 			} => {
 				9u8.write(writer)?;
 				// `user_channel_id` used to be a single u64 value. In order to remain backwards
@@ -1571,6 +1577,7 @@ impl Writeable for Event {
 					(5, counterparty_node_id, option),
 					(7, channel_capacity_sats, option),
 					(9, channel_funding_txo, option),
+					(11, last_local_balance_msats, option)
 				});
 			},
 			&Event::DiscardFunding { ref channel_id, ref funding_info } => {
@@ -1939,6 +1946,7 @@ impl MaybeReadable for Event {
 					let mut counterparty_node_id = None;
 					let mut channel_capacity_sats = None;
 					let mut channel_funding_txo = None;
+					let mut last_local_balance_msats = None;
 					read_tlv_fields!(reader, {
 						(0, channel_id, required),
 						(1, user_channel_id_low_opt, option),
@@ -1947,6 +1955,7 @@ impl MaybeReadable for Event {
 						(5, counterparty_node_id, option),
 						(7, channel_capacity_sats, option),
 						(9, channel_funding_txo, option),
+						(11, last_local_balance_msats, option)
 					});
 
 					// `user_channel_id` used to be a single u64 value. In order to remain
@@ -1956,7 +1965,7 @@ impl MaybeReadable for Event {
 						((user_channel_id_high_opt.unwrap_or(0) as u128) << 64);
 
 					Ok(Some(Event::ChannelClosed { channel_id, user_channel_id, reason: _init_tlv_based_struct_field!(reason, upgradable_required),
-						counterparty_node_id, channel_capacity_sats, channel_funding_txo }))
+						counterparty_node_id, channel_capacity_sats, channel_funding_txo, last_local_balance_msats}))
 				};
 				f()
 			},

lightning/src/ln/channel.rs

@@ -937,6 +937,7 @@ pub(crate) struct ShutdownResult {
 	pub(crate) is_manual_broadcast: bool,
 	pub(crate) unbroadcasted_funding_tx: Option<Transaction>,
 	pub(crate) channel_funding_txo: Option<OutPoint>,
+	pub(crate) last_local_balance_msats: u64,
 }
 
 /// Tracks the transaction number, along with current and next commitment points.
@@ -2066,6 +2067,8 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider  {
 		})
 	}
 
+	pub(crate) fn get_value_to_self_msat(&self) -> u64 {self.value_to_self_msat}
+
 	/// Allowed in any state (including after shutdown)
 	pub fn get_update_time_counter(&self) -> u32 {
 		self.update_time_counter
@@ -3532,6 +3535,7 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider  {
 			unbroadcasted_funding_tx,
 			is_manual_broadcast: self.is_manual_broadcast,
 			channel_funding_txo: self.get_funding_txo(),
+			last_local_balance_msats: self.value_to_self_msat,
 		}
 	}
 
@@ -6180,6 +6184,7 @@ impl<SP: Deref> Channel<SP> where
 			unbroadcasted_funding_tx: self.context.unbroadcasted_funding(),
 			is_manual_broadcast: self.context.is_manual_broadcast,
 			channel_funding_txo: self.context.get_funding_txo(),
+			last_local_balance_msats: self.context.value_to_self_msat,
 		}
 	}
 

lightning/src/ln/channelmanager.rs

@@ -3574,6 +3574,7 @@ where
 				counterparty_node_id: Some(shutdown_res.counterparty_node_id),
 				channel_capacity_sats: Some(shutdown_res.channel_capacity_satoshis),
 				channel_funding_txo: shutdown_res.channel_funding_txo,
+				last_local_balance_msats: Some(shutdown_res.last_local_balance_msats),
 			}, None));
 
 			if let Some(transaction) = shutdown_res.unbroadcasted_funding_tx {
@@ -12039,6 +12040,7 @@ where
 						counterparty_node_id: Some(channel.context.get_counterparty_node_id()),
 						channel_capacity_sats: Some(channel.context.get_value_satoshis()),
 						channel_funding_txo: channel.context.get_funding_txo(),
+						last_local_balance_msats: Some(channel.context.get_value_to_self_msat()),
 					}, None));
 					for (channel_htlc_source, payment_hash) in channel.inflight_htlc_sources() {
 						let mut found_htlc = false;
@@ -12095,6 +12097,7 @@ where
 					counterparty_node_id: Some(channel.context.get_counterparty_node_id()),
 					channel_capacity_sats: Some(channel.context.get_value_satoshis()),
 					channel_funding_txo: channel.context.get_funding_txo(),
+					last_local_balance_msats: Some(channel.context.get_value_to_self_msat()),
 				}, None));
 			} else {
 				log_error!(logger, "Missing ChannelMonitor for channel {} needed by ChannelManager.", &channel.context.channel_id());