Add funding redeem script to ChannelDetails and ChannelPending event

Original context and motivation comes from here: lightningdevkit/ldk-node#677 (comment)

When splicing-in, the default case is our channel utxo + our wallet utxos
being combined. This works great however, it can give our wallet issues
calculating fees after the fact because our wallet needs to know about
our channel's utxo. We currently have it's outpoint and satoshi value
available, but not its output script so we are unable to construct the
TxOut for the channel. This adds the redeem script to the
`ChannelDetails` and `ChannelPending` event which gives us enough
information to be able to construct it.

Author: benthecarman

lightning/src/events/mod.rs

@@ -1413,6 +1413,10 @@ pub enum Event {
 		///
 		/// Will be `None` for channels created prior to LDK version 0.0.122.
 		channel_type: Option<ChannelTypeFeatures>,
+		/// The witness script which can be used to spend the funding output for this channel.
+		///
+		/// This field will be None for objects serialized with LDK versions prior to 0.2.0.
+		funding_redeem_script: Option<ScriptBuf>,
 	},
 	/// Used to indicate that a channel with the given `channel_id` is ready to be used. This event
 	/// is emitted when
@@ -2234,6 +2238,7 @@ impl Writeable for Event {
 				ref counterparty_node_id,
 				ref funding_txo,
 				ref channel_type,
+				ref funding_redeem_script,
 			} => {
 				31u8.write(writer)?;
 				write_tlv_fields!(writer, {
@@ -2243,6 +2248,7 @@ impl Writeable for Event {
 					(4, former_temporary_channel_id, required),
 					(6, counterparty_node_id, required),
 					(8, funding_txo, required),
+					(9, funding_redeem_script, option),
 				});
 			},
 			&Event::ConnectionNeeded { .. } => {
@@ -2815,13 +2821,15 @@ impl MaybeReadable for Event {
 					let mut counterparty_node_id = RequiredWrapper(None);
 					let mut funding_txo = RequiredWrapper(None);
 					let mut channel_type = None;
+					let mut funding_redeem_script = None;
 					read_tlv_fields!(reader, {
 						(0, channel_id, required),
 						(1, channel_type, option),
 						(2, user_channel_id, required),
 						(4, former_temporary_channel_id, required),
 						(6, counterparty_node_id, required),
 						(8, funding_txo, required),
+						(9, funding_redeem_script, option),
 					});
 
 					Ok(Some(Event::ChannelPending {
@@ -2831,6 +2839,7 @@ impl MaybeReadable for Event {
 						counterparty_node_id: counterparty_node_id.0.unwrap(),
 						funding_txo: funding_txo.0.unwrap(),
 						channel_type,
+						funding_redeem_script,
 					}))
 				};
 				f()

lightning/src/ln/chan_utils.rs

@@ -1121,12 +1121,17 @@ impl ChannelTransactionParameters {
 		}
 	}
 
-	#[rustfmt::skip]
 	pub(crate) fn make_funding_redeemscript(&self) -> ScriptBuf {
-		make_funding_redeemscript(
-			&self.holder_pubkeys.funding_pubkey,
-			&self.counterparty_parameters.as_ref().unwrap().pubkeys.funding_pubkey
-		)
+		self.make_funding_redeemscript_opt().unwrap()
+	}
+
+	pub(crate) fn make_funding_redeemscript_opt(&self) -> Option<ScriptBuf> {
+		self.counterparty_parameters.as_ref().map(|p| {
+			make_funding_redeemscript(
+				&self.holder_pubkeys.funding_pubkey,
+				&p.pubkeys.funding_pubkey,
+			)
+		})
 	}
 
 	/// Returns the counterparty's pubkeys.

lightning/src/ln/channel_state.rs

@@ -450,6 +450,10 @@ pub struct ChannelDetails {
 	///
 	/// This field is empty for objects serialized with LDK versions prior to 0.0.122.
 	pub pending_outbound_htlcs: Vec<OutboundHTLCDetails>,
+	/// The witness script which can be used to spend the funding output for this channel.
+	///
+	/// This field will be None for objects serialized with LDK versions prior to 0.2.0.
+	pub funding_redeem_script: Option<bitcoin::ScriptBuf>,
 }
 
 impl ChannelDetails {
@@ -475,6 +479,17 @@ impl ChannelDetails {
 		self.short_channel_id.or(self.outbound_scid_alias)
 	}
 
+	/// Gets the funding output for this channel, if available.
+	pub fn get_channel_output(&self) -> Option<bitcoin::TxOut> {
+		match self.funding_redeem_script.as_ref() {
+			None => None,
+			Some(redeem_script) => Some(bitcoin::TxOut {
+				value: bitcoin::Amount::from_sat(self.channel_value_satoshis),
+				script_pubkey: redeem_script.to_p2wsh(),
+			}),
+		}
+	}
+
 	pub(super) fn from_channel<SP: Deref, F: Deref>(
 		channel: &Channel<SP>, best_block_height: u32, latest_features: InitFeatures,
 		fee_estimator: &LowerBoundedFeeEstimator<F>,
@@ -509,6 +524,9 @@ impl ChannelDetails {
 				outbound_htlc_maximum_msat: context.get_counterparty_htlc_maximum_msat(funding),
 			},
 			funding_txo: funding.get_funding_txo(),
+			funding_redeem_script: funding
+				.channel_transaction_parameters
+				.make_funding_redeemscript_opt(),
 			// Note that accept_channel (or open_channel) is always the first message, so
 			// `have_received_message` indicates that type negotiation has completed.
 			channel_type: if context.have_received_message() {
@@ -583,6 +601,7 @@ impl_writeable_tlv_based!(ChannelDetails, {
 	(41, channel_shutdown_state, option),
 	(43, pending_inbound_htlcs, optional_vec),
 	(45, pending_outbound_htlcs, optional_vec),
+	(47, funding_redeem_script, option),
 	(_unused, user_channel_id, (static_value,
 		_user_channel_id_low.unwrap_or(0) as u128 | ((_user_channel_id_high.unwrap_or(0) as u128) << 64)
 	)),
@@ -627,6 +646,7 @@ mod tests {
 	use crate::{
 		chain::transaction::OutPoint,
 		ln::{
+			chan_utils::make_funding_redeemscript,
 			channel_state::{
 				InboundHTLCDetails, InboundHTLCStateDetails, OutboundHTLCDetails,
 				OutboundHTLCStateDetails,
@@ -658,6 +678,10 @@ mod tests {
 				txid: bitcoin::Txid::from_slice(&[0; 32]).unwrap(),
 				index: 1,
 			}),
+			funding_redeem_script: Some(make_funding_redeemscript(
+				&PublicKey::from_slice(&[2; 33]).unwrap(),
+				&PublicKey::from_slice(&[2; 33]).unwrap(),
+			)),
 			channel_type: None,
 			short_channel_id: None,
 			outbound_scid_alias: None,

lightning/src/ln/channelmanager.rs

@@ -3303,6 +3303,8 @@ macro_rules! emit_channel_pending_event {
 	($locked_events: expr, $channel: expr) => {
 		if $channel.context.should_emit_channel_pending_event() {
 			let funding_txo = $channel.funding.get_funding_txo().unwrap();
+			let funding_redeem_script =
+				Some($channel.funding.channel_transaction_parameters.make_funding_redeemscript());
 			$locked_events.push_back((
 				events::Event::ChannelPending {
 					channel_id: $channel.context.channel_id(),
@@ -3311,6 +3313,7 @@ macro_rules! emit_channel_pending_event {
 					user_channel_id: $channel.context.get_user_id(),
 					funding_txo: funding_txo.into_bitcoin_outpoint(),
 					channel_type: Some($channel.funding.get_channel_type().clone()),
+					funding_redeem_script,
 				},
 				None,
 			));

lightning/src/routing/router.rs

@@ -3926,6 +3926,7 @@ mod tests {
 	use crate::blinded_path::BlindedHop;
 	use crate::chain::transaction::OutPoint;
 	use crate::crypto::chacha20::ChaCha20;
+	use crate::ln::chan_utils::make_funding_redeemscript;
 	use crate::ln::channel_state::{ChannelCounterparty, ChannelDetails, ChannelShutdownState};
 	use crate::ln::channelmanager;
 	use crate::ln::msgs::{UnsignedChannelUpdate, MAX_VALUE_MSAT};
@@ -3984,6 +3985,10 @@ mod tests {
 				outbound_htlc_maximum_msat: None,
 			},
 			funding_txo: Some(OutPoint { txid: bitcoin::Txid::from_slice(&[0; 32]).unwrap(), index: 0 }),
+			funding_redeem_script: Some(make_funding_redeemscript(
+				&PublicKey::from_slice(&[2; 33]).unwrap(),
+				&PublicKey::from_slice(&[2; 33]).unwrap(),
+			)),
 			channel_type: None,
 			short_channel_id,
 			outbound_scid_alias: None,
@@ -9384,6 +9389,7 @@ pub(crate) mod bench_utils {
 	use std::io::Read;
 
 	use crate::chain::transaction::OutPoint;
+	use crate::ln::chan_utils::make_funding_redeemscript;
 	use crate::ln::channel_state::{ChannelCounterparty, ChannelShutdownState};
 	use crate::ln::channelmanager;
 	use crate::ln::types::ChannelId;
@@ -9479,6 +9485,10 @@ pub(crate) mod bench_utils {
 			funding_txo: Some(OutPoint {
 				txid: bitcoin::Txid::from_slice(&[0; 32]).unwrap(), index: 0
 			}),
+			funding_redeem_script: Some(make_funding_redeemscript(
+				&PublicKey::from_slice(&[2; 33]).unwrap(),
+				&PublicKey::from_slice(&[2; 33]).unwrap(),
+			)),
 			channel_type: None,
 			short_channel_id: Some(1),
 			inbound_scid_alias: None,