Perform interactive tx negotiation during splicing

Author: optout21

lightning/src/ln/channel.rs

@@ -32,7 +32,7 @@ use crate::ln::types::ChannelId;
 use crate::types::payment::{PaymentPreimage, PaymentHash};
 use crate::types::features::{ChannelTypeFeatures, InitFeatures};
 use crate::ln::interactivetxs::{
-	get_output_weight, calculate_change_output_value, HandleTxCompleteValue, HandleTxCompleteResult, InteractiveTxConstructor,
+	estimate_input_weight, get_output_weight, calculate_change_output_value, HandleTxCompleteValue, HandleTxCompleteResult, InteractiveTxConstructor,
 	InteractiveTxConstructorArgs, InteractiveTxMessageSend, InteractiveTxSigningSession, InteractiveTxMessageSendResult,
 	OutputOwned, SharedOwnedOutput, TX_COMMON_FIELDS_WEIGHT,
 };
@@ -1142,7 +1142,7 @@ pub(super) enum Channel<SP: Deref> where SP::Target: SignerProvider {
 	Funded(FundedChannel<SP>),
 	#[cfg(splicing)]
 	/// Used during splicing, channel is funded but a new funding is being renegotiated.
-	RefundingV2(FundedChannel<SP>),
+	RefundingV2(SplicingChannel<SP>),
 }
 
 impl<SP: Deref> Channel<SP> where
@@ -1156,7 +1156,7 @@ impl<SP: Deref> Channel<SP> where
 			Channel::UnfundedInboundV1(chan) => &chan.context,
 			Channel::UnfundedV2(chan) => &chan.context,
 			#[cfg(splicing)]
-			Channel::RefundingV2(chan) => &chan.context,
+			Channel::RefundingV2(chan) => &chan.pre_funded.context,
 		}
 	}
 
@@ -1167,7 +1167,7 @@ impl<SP: Deref> Channel<SP> where
 			Channel::UnfundedInboundV1(ref mut chan) => &mut chan.context,
 			Channel::UnfundedV2(ref mut chan) => &mut chan.context,
 			#[cfg(splicing)]
-			Channel::RefundingV2(ref mut chan) => &mut chan.context,
+			Channel::RefundingV2(ref mut chan) => &mut chan.pre_funded.context,
 		}
 	}
 
@@ -1183,22 +1183,29 @@ impl<SP: Deref> Channel<SP> where
 	}
 
 	pub fn is_funded(&self) -> bool {
-		matches!(self, Channel::Funded(_))
+		match self {
+			Channel::Funded(_) => true,
+			#[cfg(splicing)]
+			Channel::RefundingV2(_) => true,
+			_ => false,
+		}
 	}
 
 	pub fn as_funded(&self) -> Option<&FundedChannel<SP>> {
-		if let Channel::Funded(channel) = self {
-			Some(channel)
-		} else {
-			None
+		match self {
+			Channel::Funded(channel) => Some(channel),
+			#[cfg(splicing)]
+			Channel::RefundingV2(channel) => Some(&channel.pre_funded),
+			_ => None,
 		}
 	}
 
 	pub fn as_funded_mut(&mut self) -> Option<&mut FundedChannel<SP>> {
-		if let Channel::Funded(channel) = self {
-			Some(channel)
-		} else {
-			None
+		match self {
+			Channel::Funded(channel) => Some(channel),
+			#[cfg(splicing)]
+			Channel::RefundingV2(channel) => Some(&mut channel.pre_funded),
+			_ => None,
 		}
 	}
 
@@ -1239,10 +1246,11 @@ impl<SP: Deref> Channel<SP> where
 	}
 
 	pub fn as_unfunded_v2_mut(&mut self) -> Option<&mut PendingV2Channel<SP>> {
-		if let Channel::UnfundedV2(channel) = self {
-			Some(channel)
-		} else {
-			None
+		match self {
+			Channel::UnfundedV2(channel) => Some(channel),
+			#[cfg(splicing)]
+			Channel::RefundingV2(channel) => Some(&mut channel.post_pending),
+			_ => None,
 		}
 	}
 
@@ -1294,7 +1302,7 @@ impl<SP: Deref> Channel<SP> where
 			},
 			Channel::UnfundedV2(_) => None,
 			#[cfg(splicing)]
-			Channel::RefundingV2(chan) => Some(chan.signer_maybe_unblocked(logger)),
+			Channel::RefundingV2(chan) => Some(chan.pre_funded.signer_maybe_unblocked(logger)),
 		}
 	}
 
@@ -1423,6 +1431,55 @@ where
 	}
 }
 
+/// Struct holding together various state dureing splicing negotiation
+#[cfg(splicing)]
+pub(super) struct SplicingChannel<SP: Deref> where SP::Target: SignerProvider {
+	pub pre_funded: FundedChannel<SP>,
+	pub post_pending: PendingV2Channel<SP>,
+	pub post_funded: Option<FundedChannel<SP>>,
+}
+
+#[cfg(splicing)]
+impl<SP: Deref> SplicingChannel<SP> where SP::Target: SignerProvider {
+	pub(super) fn new(pre_funded: FundedChannel<SP>, post_pending: PendingV2Channel<SP>) -> Self {
+		Self {
+			pre_funded,
+			post_pending,
+			post_funded: None,
+		}
+	}
+
+	pub fn splice_init<ES: Deref, L: Deref>(
+		&mut self, msg: &msgs::SpliceInit, signer_provider: &SP, entropy_source: &ES, holder_node_id: PublicKey, logger: &L,
+	) -> Result<msgs::SpliceAck,ChannelError> where ES::Target: EntropySource, L::Target: Logger {
+		self.post_pending.splice_init(msg, signer_provider, entropy_source, holder_node_id, logger)
+	}
+
+	pub fn splice_ack<ES: Deref, L: Deref>(
+		&mut self, msg: &msgs::SpliceAck, our_funding_contribution: i64, signer_provider: &SP, entropy_source: &ES, holder_node_id: PublicKey, logger: &L,
+	) -> Result<Option<InteractiveTxMessageSend>, ChannelError> where ES::Target: EntropySource, L::Target: Logger {
+		self.post_pending.splice_ack(msg, our_funding_contribution, signer_provider, entropy_source, holder_node_id, logger)
+	}
+
+	pub fn tx_add_input(&mut self, msg: &msgs::TxAddInput) -> InteractiveTxMessageSendResult {
+		self.post_pending.tx_add_input(msg)
+	}
+
+	pub fn tx_add_output(&mut self, msg: &msgs::TxAddOutput)-> InteractiveTxMessageSendResult {
+		self.post_pending.tx_add_output(msg)
+	}
+
+	pub fn tx_complete(&mut self, msg: &msgs::TxComplete) -> HandleTxCompleteResult {
+		self.post_pending.tx_complete(msg)
+	}
+
+	pub fn funding_tx_constructed<L: Deref>(
+		&mut self, signing_session: &mut InteractiveTxSigningSession, logger: &L
+	) -> Result<(msgs::CommitmentSigned, Option<Event>), ChannelError> where L::Target: Logger {
+		self.post_pending.funding_tx_constructed(signing_session, logger)
+	}
+}
+
 /// Contains all state common to unfunded inbound/outbound channels.
 pub(super) struct UnfundedChannelContext {
 	/// A counter tracking how many ticks have elapsed since this unfunded channel was
@@ -1455,7 +1512,7 @@ impl UnfundedChannelContext {
 /// Info about a pending splice, used in the pre-splice channel
 #[cfg(splicing)]
 #[derive(Clone)]
-struct PendingSplicePre {
+pub(super) struct PendingSplicePre {
 	pub our_funding_contribution: i64,
 	pub funding_feerate_perkw: u32,
 	pub locktime: u32,
@@ -4869,6 +4926,54 @@ fn get_v2_channel_reserve_satoshis(channel_value_satoshis: u64, dust_limit_satos
 	cmp::min(channel_value_satoshis, cmp::max(q, dust_limit_satoshis))
 }
 
+pub(super) fn maybe_add_funding_change_output<SP: Deref>(signer_provider: &SP, is_initiator: bool,
+	our_funding_satoshis: u64, funding_inputs_prev_outputs: &Vec<TxOut>,
+	funding_outputs: &mut Vec<OutputOwned>, funding_feerate_sat_per_1000_weight: u32,
+	total_input_satoshis: u64, holder_dust_limit_satoshis: u64, channel_keys_id: [u8; 32],
+) -> Result<Option<TxOut>, ChannelError> where
+	SP::Target: SignerProvider,
+{
+	let our_funding_inputs_weight = funding_inputs_prev_outputs.iter().fold(0u64, |weight, prev_output| {
+		weight.saturating_add(estimate_input_weight(prev_output).to_wu())
+	});
+	let our_funding_outputs_weight = funding_outputs.iter().fold(0u64, |weight, out| {
+		weight.saturating_add(get_output_weight(&out.tx_out().script_pubkey).to_wu())
+	});
+	let our_contributed_weight = our_funding_outputs_weight.saturating_add(our_funding_inputs_weight);
+	let mut fees_sats = fee_for_weight(funding_feerate_sat_per_1000_weight, our_contributed_weight);
+
+	// If we are the initiator, we must pay for weight of all common fields in the funding transaction.
+	if is_initiator {
+		let common_fees = fee_for_weight(funding_feerate_sat_per_1000_weight, TX_COMMON_FIELDS_WEIGHT);
+		fees_sats = fees_sats.saturating_add(common_fees);
+	}
+
+	let remaining_value = total_input_satoshis
+		.saturating_sub(our_funding_satoshis)
+		.saturating_sub(fees_sats);
+
+	if remaining_value < holder_dust_limit_satoshis {
+		Ok(None)
+	} else {
+		let change_script = signer_provider.get_destination_script(channel_keys_id).map_err(
+			|_| ChannelError::Close((
+				"Failed to get change script as new destination script".to_owned(),
+				ClosureReason::ProcessingError { err: "Failed to get change script as new destination script".to_owned() }
+			))
+		)?;
+		let mut change_output = TxOut {
+			value: Amount::from_sat(remaining_value),
+			script_pubkey: change_script,
+		};
+		let change_output_weight = get_output_weight(&change_output.script_pubkey).to_wu();
+
+		let change_output_fee = fee_for_weight(funding_feerate_sat_per_1000_weight, change_output_weight);
+		change_output.value = Amount::from_sat(remaining_value.saturating_sub(change_output_fee));
+		funding_outputs.push(OutputOwned::Single(change_output.clone()));
+		Ok(Some(change_output))
+	}
+}
+
 pub(super) fn calculate_our_funding_satoshis(
 	is_initiator: bool, funding_inputs: &[(TxIn, TransactionU16LenLimited)],
 	total_witness_weight: Weight, funding_feerate_sat_per_1000_weight: u32,
@@ -4941,7 +5046,7 @@ pub(super) struct FundedChannel<SP: Deref> where SP::Target: SignerProvider {
 	holder_commitment_point: HolderCommitmentPoint,
 	/// Info about an in-progress, pending splice (if any), on the pre-splice channel
 	#[cfg(splicing)]
-	pending_splice_pre: Option<PendingSplicePre>,
+	pub pending_splice_pre: Option<PendingSplicePre>,
 	/// Info about an in-progress, pending splice (if any), on the post-splice channel
 	#[cfg(splicing)]
 	pending_splice_post: Option<PendingSplicePost>,
@@ -8632,11 +8737,11 @@ impl<SP: Deref> FundedChannel<SP> where
 		Ok(msg)
 	}
 
-	/// Handle splice_init
+	/// Checks during handling splice_init
 	#[cfg(splicing)]
-	pub fn splice_init<ES: Deref, L: Deref>(
-		&mut self, msg: &msgs::SpliceInit, _signer_provider: &SP, _entropy_source: &ES, _holder_node_id: PublicKey, logger: &L,
-	) -> Result<msgs::SpliceAck, ChannelError> where ES::Target: EntropySource, L::Target: Logger {
+	pub fn splice_init_checks<ES: Deref>(
+		&mut self, msg: &msgs::SpliceInit, _signer_provider: &SP, _entropy_source: &ES, _holder_node_id: PublicKey,
+	) -> Result<(), ChannelError> where ES::Target: EntropySource {
 		let their_funding_contribution_satoshis = msg.funding_contribution_satoshis;
 		// TODO(splicing): Currently not possible to contribute on the splicing-acceptor side
 		let our_funding_contribution_satoshis = 0i64;
@@ -8677,52 +8782,7 @@ impl<SP: Deref> FundedChannel<SP> where
 		// Early check for reserve requirement, assuming maximum balance of full channel value
 		// This will also be checked later at tx_complete
 		let _res = self.context.check_balance_meets_reserve_requirements(post_balance, post_channel_value)?;
-
-		// TODO(splicing): Store msg.funding_pubkey
-
-		// Apply start of splice change in the state
-		self.context.splice_start(false, logger);
-
-		let splice_ack_msg = self.context.get_splice_ack(our_funding_contribution_satoshis);
-
-		// TODO(splicing): start interactive funding negotiation
-		// let _msg = self.begin_interactive_funding_tx_construction(signer_provider, entropy_source, holder_node_id)
-		// 	.map_err(|err| ChannelError::Warn(format!("Failed to start interactive transaction construction, {:?}", err)))?;
-
-		Ok(splice_ack_msg)
-	}
-
-	/// Handle splice_ack
-	#[cfg(splicing)]
-	pub fn splice_ack<ES: Deref, L: Deref>(
-		&mut self, msg: &msgs::SpliceAck, _signer_provider: &SP, _entropy_source: &ES, _holder_node_id: PublicKey, logger: &L,
-	) -> Result<Option<InteractiveTxMessageSend>, ChannelError> where ES::Target: EntropySource, L::Target: Logger {
-		let their_funding_contribution_satoshis = msg.funding_contribution_satoshis;
-
-		// check if splice is pending
-		let pending_splice = if let Some(pending_splice) = &self.pending_splice_pre {
-			pending_splice
-		} else {
-			return Err(ChannelError::Warn(format!("Channel is not in pending splice")));
-		};
-
-		let our_funding_contribution = pending_splice.our_funding_contribution;
-
-		let pre_channel_value = self.context.get_value_satoshis();
-		let post_channel_value = PendingSplicePre::compute_post_value(pre_channel_value, our_funding_contribution, their_funding_contribution_satoshis);
-		let post_balance = PendingSplicePre::add_checked(self.context.value_to_self_msat, our_funding_contribution);
-		// Early check for reserve requirement, assuming maximum balance of full channel value
-		// This will also be checked later at tx_complete
-		let _res = self.context.check_balance_meets_reserve_requirements(post_balance, post_channel_value)?;
-
-		// Apply start of splice change in the state
-		self.context.splice_start(true, logger);
-
-		// TODO(splicing): start interactive funding negotiation
-		// let tx_msg_opt = self.begin_interactive_funding_tx_construction(signer_provider, entropy_source, holder_node_id)
-		// 	.map_err(|err| ChannelError::Warn(format!("V2 channel rejected due to sender error, {:?}", err)))?;
-		// Ok(tx_msg_opt)
-		Ok(None)
+		Ok(())
 	}
 
 	// Send stuff to our remote peers:
@@ -9965,6 +10025,56 @@ impl<SP: Deref> PendingV2Channel<SP> where SP::Target: SignerProvider {
 		}
 	}
 
+	pub fn into_channel(self, signing_session: InteractiveTxSigningSession) -> Result<FundedChannel<SP>, ChannelError>{
+		let holder_commitment_point = self.unfunded_context.holder_commitment_point.ok_or(ChannelError::close(
+			format!("Expected to have holder commitment points available upon finishing interactive tx construction for channel {}",
+			self.context.channel_id())))?;
+		let channel = FundedChannel {
+			context: self.context,
+			interactive_tx_signing_session: Some(signing_session),
+			holder_commitment_point,
+			#[cfg(splicing)]
+			pending_splice_pre: None,
+			#[cfg(splicing)]
+			pending_splice_post: self.pending_splice_post,
+		};
+
+		Ok(channel)
+	}
+
+	/// Handle splice_ack
+	#[cfg(splicing)]
+	pub fn splice_ack<ES: Deref, L: Deref>(
+		&mut self, msg: &msgs::SpliceAck, our_funding_contribution: i64, signer_provider: &SP, entropy_source: &ES, holder_node_id: PublicKey, logger: &L,
+	) -> Result<Option<InteractiveTxMessageSend>, ChannelError> where ES::Target: EntropySource, L::Target: Logger {
+		let their_funding_contribution_satoshis = msg.funding_contribution_satoshis;
+
+		// check if splice is pending
+		let pending_splice = if let Some(pending_splice) = &self.pending_splice_post {
+			pending_splice
+		} else {
+			return Err(ChannelError::Warn(format!("Channel is not in pending splice")));
+		};
+
+		let pre_channel_value = self.context.get_value_satoshis();
+		let post_channel_value = PendingSplicePre::compute_post_value(pre_channel_value, our_funding_contribution, their_funding_contribution_satoshis);
+		let post_balance = PendingSplicePre::add_checked(self.context.value_to_self_msat, our_funding_contribution);
+		// Early check for reserve requirement, assuming maximum balance of full channel value
+		// This will also be checked later at tx_complete
+		let _res = self.context.check_balance_meets_reserve_requirements(post_balance, post_channel_value)?;
+
+		// We need the current funding tx as an extra input
+		let prev_funding_input = pending_splice.get_input_of_previous_funding()?;
+
+		// Apply start of splice change in the state
+		self.context.splice_start(true, logger);
+
+		// Start interactive funding negotiation, with the previous funding transaction as an extra shared input
+		let tx_msg_opt = self.begin_interactive_funding_tx_construction(signer_provider, entropy_source, holder_node_id, Some(prev_funding_input))
+			.map_err(|err| ChannelError::Warn(format!("V2 channel rejected due to sender error, {:?}", err)))?;
+		Ok(tx_msg_opt)
+	}
+
 	/// Creates a new dual-funded channel from a remote side's request for one.
 	/// Assumes chain_hash has already been checked and corresponds with what we expect!
 	#[allow(dead_code)] // TODO(dual_funding): Remove once V2 channels is enabled.
@@ -10149,21 +10259,27 @@ impl<SP: Deref> PendingV2Channel<SP> where SP::Target: SignerProvider {
 		self.generate_accept_channel_v2_message()
 	}
 
-	pub fn into_channel(self, signing_session: InteractiveTxSigningSession) -> Result<FundedChannel<SP>, ChannelError>{
-		let holder_commitment_point = self.unfunded_context.holder_commitment_point.ok_or(ChannelError::close(
-			format!("Expected to have holder commitment points available upon finishing interactive tx construction for channel {}",
-			self.context.channel_id())))?;
-		let channel = FundedChannel {
-			context: self.context,
-			interactive_tx_signing_session: Some(signing_session),
-			holder_commitment_point,
-			#[cfg(splicing)]
-			pending_splice_pre: None,
-			#[cfg(splicing)]
-			pending_splice_post: self.pending_splice_post,
-		};
+	/// Handle splice_init
+	/// See also [`splice_init_checks`]
+	#[cfg(splicing)]
+	pub fn splice_init<ES: Deref, L: Deref>(
+		&mut self, _msg: &msgs::SpliceInit, signer_provider: &SP, entropy_source: &ES, holder_node_id: PublicKey, logger: &L,
+	) -> Result<msgs::SpliceAck,ChannelError> where ES::Target: EntropySource, L::Target: Logger {
+		// TODO(splicing): Currently not possible to contribute on the splicing-acceptor side
+		let our_funding_contribution_satoshis = 0i64;
 
-		Ok(channel)
+		// TODO(splicing): Store msg.funding_pubkey
+
+		// Apply start of splice change in the state
+		self.context.splice_start(false, logger);
+
+		let splice_ack_msg = self.context.get_splice_ack(our_funding_contribution_satoshis);
+
+		// Start interactive funding negotiation. No extra input, as we are not the splice initiator
+		let _msg = self.begin_interactive_funding_tx_construction(signer_provider, entropy_source, holder_node_id, None)
+			.map_err(|err| ChannelError::Warn(format!("Failed to start interactive transaction construction, {:?}", err)))?;
+
+		Ok(splice_ack_msg)
 	}
 }