Implement support for accepting V2 channels

Author: dunxen

lightning/src/events/mod.rs

@@ -591,6 +591,20 @@ impl_writeable_tlv_based_enum_upgradable!(PaymentFailureReason,
 	(10, UnexpectedError) => {},
 );
 
+/// Used to indicate the kind of funding for this channel by the channel acceptor (us).
+///
+/// Allows the differentiation between a request for a dual-funded and non-dual-funded channel.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum InboundChannelFunds {
+	/// For a non-dual-funded channel, the `push_msat` value from the channel initiator to us.
+	PushMsat(u64),
+	/// Indicates the open request is for a dual funded channel.
+	///
+	/// Note that these channels do not support starting with initial funds pushed from the counterparty,
+	/// who is the channel opener in this case.
+	DualFunded,
+}
+
 /// An Event which you should probably take some action in response to.
 ///
 /// Note that while Writeable and Readable are implemented for Event, you probably shouldn't use
@@ -1322,9 +1336,14 @@ pub enum Event {
 	},
 	/// Indicates a request to open a new channel by a peer.
 	///
-	/// To accept the request, call [`ChannelManager::accept_inbound_channel`]. To reject the request,
-	/// call [`ChannelManager::force_close_without_broadcasting_txn`]. Note that a ['ChannelClosed`]
-	/// event will _not_ be triggered if the channel is rejected.
+	/// If `channel_negotiation_type` is `InboundChannelFunds::DualFunded`, this indicates that the peer wishes to
+	/// open a dual-funded channel. Otherwise, this field will be `InboundChannelFunds::PushMsats`,
+	/// indicating the `push_msats` value our peer is pushing to us for a non-dual-funded channel.
+	///
+	/// To accept the request (and in the case of a dual-funded channel, not contribute funds),
+	/// call [`ChannelManager::accept_inbound_channel`].
+	/// To reject the request, call [`ChannelManager::force_close_without_broadcasting_txn`].
+	/// Note that a ['ChannelClosed`] event will _not_ be triggered if the channel is rejected.
 	///
 	/// The event is only triggered when a new open channel request is received and the
 	/// [`UserConfig::manually_accept_inbound_channels`] config flag is set to true.
@@ -1358,8 +1377,10 @@ pub enum Event {
 		counterparty_node_id: PublicKey,
 		/// The channel value of the requested channel.
 		funding_satoshis: u64,
-		/// Our starting balance in the channel if the request is accepted, in milli-satoshi.
-		push_msat: u64,
+		/// If `channel_negotiation_type` is `InboundChannelFunds::DualFunded`, this indicates that the peer wishes to
+		/// open a dual-funded channel. Otherwise, this field will be `InboundChannelFunds::PushMsats`,
+		/// indicating the `push_msats` value our peer is pushing to us for a non-dual-funded channel.
+		channel_negotiation_type: InboundChannelFunds,
 		/// The features that this channel will operate with. If you reject the channel, a
 		/// well-behaved counterparty may automatically re-attempt the channel with a new set of
 		/// feature flags.

lightning/src/ln/channel.rs

@@ -10,10 +10,11 @@
 use bitcoin::amount::Amount;
 use bitcoin::constants::ChainHash;
 use bitcoin::script::{Script, ScriptBuf, Builder};
-use bitcoin::transaction::Transaction;
+use bitcoin::transaction::{Transaction, TxIn, TxOut};
 use bitcoin::sighash;
 use bitcoin::sighash::EcdsaSighashType;
 use bitcoin::consensus::encode;
+use bitcoin::absolute::LockTime;
 
 use bitcoin::hashes::Hash;
 use bitcoin::hashes::sha256::Hash as Sha256;
@@ -28,7 +29,11 @@ use bitcoin::secp256k1;
 use crate::ln::types::ChannelId;
 use crate::types::payment::{PaymentPreimage, PaymentHash};
 use crate::types::features::{ChannelTypeFeatures, InitFeatures};
-use crate::ln::interactivetxs::InteractiveTxConstructor;
+use crate::ln::interactivetxs::{
+	estimate_input_weight, get_output_weight, HandleTxCompleteResult,
+	InteractiveTxConstructor, InteractiveTxConstructorArgs, InteractiveTxMessageSend,
+	InteractiveTxMessageSendResult, TX_COMMON_FIELDS_WEIGHT,
+};
 use crate::ln::msgs;
 use crate::ln::msgs::{ClosingSigned, ClosingSignedFeeRange, DecodeError};
 use crate::ln::script::{self, ShutdownScript};
@@ -45,14 +50,14 @@ use crate::ln::chan_utils::{
 use crate::ln::chan_utils;
 use crate::ln::onion_utils::HTLCFailReason;
 use crate::chain::BestBlock;
-use crate::chain::chaininterface::{FeeEstimator, ConfirmationTarget, LowerBoundedFeeEstimator};
+use crate::chain::chaininterface::{FeeEstimator, ConfirmationTarget, LowerBoundedFeeEstimator, fee_for_weight};
 use crate::chain::channelmonitor::{ChannelMonitor, ChannelMonitorUpdate, ChannelMonitorUpdateStep, LATENCY_GRACE_PERIOD_BLOCKS, CLOSED_CHANNEL_UPDATE_ID};
 use crate::chain::transaction::{OutPoint, TransactionData};
 use crate::sign::ecdsa::EcdsaChannelSigner;
 use crate::sign::{EntropySource, ChannelSigner, SignerProvider, NodeSigner, Recipient};
 use crate::events::ClosureReason;
 use crate::routing::gossip::NodeId;
-use crate::util::ser::{Readable, ReadableArgs, Writeable, Writer};
+use crate::util::ser::{Readable, ReadableArgs, TransactionU16LenLimited, Writeable, Writer};
 use crate::util::logger::{Logger, Record, WithContext};
 use crate::util::errors::APIError;
 use crate::util::config::{UserConfig, ChannelConfig, LegacyChannelConfig, ChannelHandshakeConfig, ChannelHandshakeLimits, MaxDustHTLCExposure};
@@ -1637,6 +1642,109 @@ impl<SP: Deref> InitialRemoteCommitmentReceiver<SP> for InboundV1Channel<SP> whe
 	}
 }
 
+pub(super) trait InteractivelyFunded<SP: Deref> where SP::Target: SignerProvider {
+	fn context(&self) -> &ChannelContext<SP>;
+
+	fn context_mut(&mut self) -> &mut ChannelContext<SP>;
+
+	fn interactive_tx_constructor_mut(&mut self) -> &mut Option<InteractiveTxConstructor>;
+
+	fn dual_funding_context(&self) -> &DualFundingChannelContext;
+
+	fn set_interactive_tx_constructor(&mut self, interactive_tx_constructor: InteractiveTxConstructor);
+
+	fn tx_add_input(&mut self, msg: &msgs::TxAddInput) -> InteractiveTxMessageSendResult {
+		InteractiveTxMessageSendResult(match self.interactive_tx_constructor_mut() {
+			Some(ref mut tx_constructor) => tx_constructor.handle_tx_add_input(msg).map_err(
+				|reason| reason.into_tx_abort_msg(self.context().channel_id())),
+			None => Err(msgs::TxAbort {
+				channel_id: self.context().channel_id(),
+				data: b"No interactive transaction negotiation in progress".to_vec()
+			}),
+		})
+	}
+
+	fn tx_add_output(&mut self, msg: &msgs::TxAddOutput)-> InteractiveTxMessageSendResult {
+		InteractiveTxMessageSendResult(match self.interactive_tx_constructor_mut() {
+			Some(ref mut tx_constructor) => tx_constructor.handle_tx_add_output(msg).map_err(
+				|reason| reason.into_tx_abort_msg(self.context().channel_id())),
+			None => Err(msgs::TxAbort {
+				channel_id: self.context().channel_id(),
+				data: b"No interactive transaction negotiation in progress".to_vec()
+			}),
+		})
+	}
+
+	fn tx_remove_input(&mut self, msg: &msgs::TxRemoveInput)-> InteractiveTxMessageSendResult {
+		InteractiveTxMessageSendResult(match self.interactive_tx_constructor_mut() {
+			Some(ref mut tx_constructor) => tx_constructor.handle_tx_remove_input(msg).map_err(
+				|reason| reason.into_tx_abort_msg(self.context().channel_id())),
+			None => Err(msgs::TxAbort {
+				channel_id: self.context().channel_id(),
+				data: b"No interactive transaction negotiation in progress".to_vec()
+			}),
+		})
+	}
+
+	fn tx_remove_output(&mut self, msg: &msgs::TxRemoveOutput)-> InteractiveTxMessageSendResult {
+		InteractiveTxMessageSendResult(match self.interactive_tx_constructor_mut() {
+			Some(ref mut tx_constructor) => tx_constructor.handle_tx_remove_output(msg).map_err(
+				|reason| reason.into_tx_abort_msg(self.context().channel_id())),
+			None => Err(msgs::TxAbort {
+				channel_id: self.context().channel_id(),
+				data: b"No interactive transaction negotiation in progress".to_vec()
+			}),
+		})
+	}
+
+	fn tx_complete(&mut self, msg: &msgs::TxComplete) -> HandleTxCompleteResult {
+		HandleTxCompleteResult(match self.interactive_tx_constructor_mut() {
+			Some(ref mut tx_constructor) => tx_constructor.handle_tx_complete(msg).map_err(
+				|reason| reason.into_tx_abort_msg(self.context().channel_id())),
+			None => Err(msgs::TxAbort {
+				channel_id: self.context().channel_id(),
+				data: b"No interactive transaction negotiation in progress".to_vec()
+			}),
+		})
+	}
+}
+
+impl<SP: Deref> InteractivelyFunded<SP> for OutboundV2Channel<SP> where SP::Target: SignerProvider {
+	fn context(&self) -> &ChannelContext<SP> {
+		&self.context
+	}
+	fn context_mut(&mut self) -> &mut ChannelContext<SP> {
+		&mut self.context
+	}
+	fn dual_funding_context(&self) -> &DualFundingChannelContext {
+		&self.dual_funding_context
+	}
+	fn interactive_tx_constructor_mut(&mut self) -> &mut Option<InteractiveTxConstructor> {
+		&mut self.interactive_tx_constructor
+	}
+	fn set_interactive_tx_constructor(&mut self, interactive_tx_constructor: InteractiveTxConstructor) {
+		self.interactive_tx_constructor = Some(interactive_tx_constructor);
+	}
+}
+
+impl<SP: Deref> InteractivelyFunded<SP> for InboundV2Channel<SP> where SP::Target: SignerProvider {
+	fn context(&self) -> &ChannelContext<SP> {
+		&self.context
+	}
+	fn context_mut(&mut self) -> &mut ChannelContext<SP> {
+		&mut self.context
+	}
+	fn dual_funding_context(&self) -> &DualFundingChannelContext {
+		&self.dual_funding_context
+	}
+	fn interactive_tx_constructor_mut(&mut self) -> &mut Option<InteractiveTxConstructor> {
+		&mut self.interactive_tx_constructor
+	}
+	fn set_interactive_tx_constructor(&mut self, interactive_tx_constructor: InteractiveTxConstructor) {
+		self.interactive_tx_constructor = Some(interactive_tx_constructor);
+	}
+}
+
 impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 	fn new_for_inbound_channel<'a, ES: Deref, F: Deref, L: Deref>(
 		fee_estimator: &'a LowerBoundedFeeEstimator<F>,
@@ -3766,6 +3874,16 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 		self.channel_transaction_parameters.channel_type_features = self.channel_type.clone();
 		Ok(())
 	}
+
+	// Interactive transaction construction
+
+	pub fn tx_signatures(&self, msg: &msgs::TxSignatures) -> Result<InteractiveTxMessageSend, ChannelError> {
+		todo!();
+	}
+
+	pub fn tx_abort(&self, msg: &msgs::TxAbort) -> Result<InteractiveTxMessageSend, ChannelError> {
+		todo!();
+	}
 }
 
 // Internal utility functions for channels
@@ -3823,6 +3941,42 @@ 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 calculate_our_funding_satoshis(
+	is_initiator: bool, funding_inputs: &[(TxIn, TransactionU16LenLimited)],
+	funding_outputs: &[TxOut], funding_feerate_sat_per_1000_weight: u32,
+	holder_dust_limit_satoshis: u64,
+) -> Result<u64, APIError> {
+	let mut total_input_satoshis = 0u64;
+	let mut our_contributed_weight = 0u64;
+
+	for (idx, input) in funding_inputs.iter().enumerate() {
+		if let Some(output) = input.1.as_transaction().output.get(input.0.previous_output.vout as usize) {
+			total_input_satoshis = total_input_satoshis.saturating_add(output.value.to_sat());
+			our_contributed_weight = our_contributed_weight.saturating_add(estimate_input_weight(output).to_wu());
+		} else {
+			return Err(APIError::APIMisuseError {
+				err: format!("Transaction with txid {} does not have an output with vout of {} corresponding to TxIn at funding_inputs[{}]",
+					input.1.as_transaction().compute_txid(), input.0.previous_output.vout, idx) });
+		}
+	}
+	our_contributed_weight = our_contributed_weight.saturating_add(funding_outputs.iter().fold(0u64, |weight, txout| {
+		weight.saturating_add(get_output_weight(&txout.script_pubkey).to_wu())
+	}));
+
+	// If we are the initiator, we must pay for weight of all common fields in the funding transaction.
+	if is_initiator {
+		our_contributed_weight = our_contributed_weight.saturating_add(TX_COMMON_FIELDS_WEIGHT);
+	}
+
+	let funding_satoshis = total_input_satoshis
+		.saturating_sub(fee_for_weight(funding_feerate_sat_per_1000_weight, our_contributed_weight));
+	if funding_satoshis < holder_dust_limit_satoshis {
+		Ok(0)
+	} else {
+		Ok(funding_satoshis)
+	}
+}
+
 /// Context for dual-funded channels.
 pub(super) struct DualFundingChannelContext {
 	/// The amount in satoshis we will be contributing to the channel.
@@ -3831,9 +3985,15 @@ pub(super) struct DualFundingChannelContext {
 	pub their_funding_satoshis: u64,
 	/// The funding transaction locktime suggested by the initiator. If set by us, it is always set
 	/// to the current block height to align incentives against fee-sniping.
-	pub funding_tx_locktime: u32,
+	pub funding_tx_locktime: LockTime,
 	/// The feerate set by the initiator to be used for the funding transaction.
 	pub funding_feerate_sat_per_1000_weight: u32,
+	/// The funding inputs we will be contributing to the channel.
+	///
+	/// Note that the `our_funding_satoshis` field is equal to the total value of `our_funding_inputs`
+	/// minus any fees paid for our contributed weight. This means that change will never be generated
+	/// and the maximum value possible will go towards funding the channel.
+	pub our_funding_inputs: Vec<(TxIn, TransactionU16LenLimited)>,
 }
 
 // Holder designates channel data owned for the benefit of the user client.
@@ -8264,8 +8424,9 @@ impl<SP: Deref> OutboundV2Channel<SP> where SP::Target: SignerProvider {
 	pub fn new<ES: Deref, F: Deref, L: Deref>(
 		fee_estimator: &LowerBoundedFeeEstimator<F>, entropy_source: &ES, signer_provider: &SP,
 		counterparty_node_id: PublicKey, their_features: &InitFeatures, funding_satoshis: u64,
-		user_id: u128, config: &UserConfig, current_chain_height: u32, outbound_scid_alias: u64,
-		funding_confirmation_target: ConfirmationTarget, logger: L,
+		funding_inputs: Vec<(TxIn, TransactionU16LenLimited)>, user_id: u128, config: &UserConfig,
+		current_chain_height: u32, outbound_scid_alias: u64, funding_confirmation_target: ConfirmationTarget,
+		logger: L,
 	) -> Result<OutboundV2Channel<SP>, APIError>
 	where ES::Target: EntropySource,
 	      F::Target: FeeEstimator,
@@ -8281,7 +8442,11 @@ impl<SP: Deref> OutboundV2Channel<SP> where SP::Target: SignerProvider {
 			funding_satoshis, MIN_CHAN_DUST_LIMIT_SATOSHIS);
 
 		let funding_feerate_sat_per_1000_weight = fee_estimator.bounded_sat_per_1000_weight(funding_confirmation_target);
-		let funding_tx_locktime = current_chain_height;
+		let funding_tx_locktime = LockTime::from_height(current_chain_height)
+			.map_err(|_| APIError::APIMisuseError {
+				err: format!(
+					"Provided current chain height of {} doesn't make sense for a height-based timelock for the funding transaction",
+					current_chain_height) })?;
 
 		let chan = Self {
 			context: ChannelContext::new_for_outbound_channel(
@@ -8309,6 +8474,7 @@ impl<SP: Deref> OutboundV2Channel<SP> where SP::Target: SignerProvider {
 				their_funding_satoshis: 0,
 				funding_tx_locktime,
 				funding_feerate_sat_per_1000_weight,
+				our_funding_inputs: funding_inputs,
 			},
 			interactive_tx_constructor: None,
 		};
@@ -8373,7 +8539,7 @@ impl<SP: Deref> OutboundV2Channel<SP> where SP::Target: SignerProvider {
 			},
 			funding_feerate_sat_per_1000_weight: self.context.feerate_per_kw,
 			second_per_commitment_point,
-			locktime: self.dual_funding_context.funding_tx_locktime,
+			locktime: self.dual_funding_context.funding_tx_locktime.to_consensus_u32(),
 			require_confirmed_inputs: None,
 		}
 	}
@@ -8394,13 +8560,22 @@ impl<SP: Deref> InboundV2Channel<SP> where SP::Target: SignerProvider {
 	pub fn new<ES: Deref, F: Deref, L: Deref>(
 		fee_estimator: &LowerBoundedFeeEstimator<F>, entropy_source: &ES, signer_provider: &SP,
 		counterparty_node_id: PublicKey, our_supported_features: &ChannelTypeFeatures,
-		their_features: &InitFeatures, msg: &msgs::OpenChannelV2, funding_satoshis: u64, user_id: u128,
-		config: &UserConfig, current_chain_height: u32, logger: &L,
+		their_features: &InitFeatures, msg: &msgs::OpenChannelV2,
+		funding_inputs: Vec<(TxIn, TransactionU16LenLimited)>, user_id: u128, config: &UserConfig,
+		current_chain_height: u32, logger: &L,
 	) -> Result<InboundV2Channel<SP>, ChannelError>
 		where ES::Target: EntropySource,
 			  F::Target: FeeEstimator,
 			  L::Target: Logger,
 	{
+		let funding_satoshis = calculate_our_funding_satoshis(
+			false, &funding_inputs, &[], msg.funding_feerate_sat_per_1000_weight,
+			msg.common_fields.dust_limit_satoshis
+		).map_err(|_| ChannelError::Close(
+			(
+				"Failed to accept channel".to_string(),
+				ClosureReason::HolderForceClosed { broadcasted_latest_txn: Some(false) },
+			)))?;
 		let channel_value_satoshis = funding_satoshis.saturating_add(msg.common_fields.funding_satoshis);
 		let counterparty_selected_channel_reserve_satoshis = get_v2_channel_reserve_satoshis(
 			channel_value_satoshis, msg.common_fields.dust_limit_satoshis);
@@ -8449,19 +8624,43 @@ impl<SP: Deref> InboundV2Channel<SP> where SP::Target: SignerProvider {
 			&context.get_counterparty_pubkeys().revocation_basepoint);
 		context.channel_id = channel_id;
 
-		let chan = Self {
+		let mut channel = Self {
 			context,
 			unfunded_context: UnfundedChannelContext { unfunded_channel_age_ticks: 0 },
 			dual_funding_context: DualFundingChannelContext {
 				our_funding_satoshis: funding_satoshis,
 				their_funding_satoshis: msg.common_fields.funding_satoshis,
-				funding_tx_locktime: msg.locktime,
+				funding_tx_locktime: LockTime::from_consensus(msg.locktime),
 				funding_feerate_sat_per_1000_weight: msg.funding_feerate_sat_per_1000_weight,
+				our_funding_inputs: funding_inputs,
 			},
 			interactive_tx_constructor: None,
 		};
 
-		Ok(chan)
+		match InteractiveTxConstructor::new(
+			InteractiveTxConstructorArgs {
+				entropy_source,
+				channel_id: channel.context.channel_id,
+				feerate_sat_per_kw: channel.dual_funding_context.funding_feerate_sat_per_1000_weight,
+				funding_tx_locktime: channel.dual_funding_context.funding_tx_locktime,
+				is_initiator: false,
+			    inputs_to_contribute: channel.dual_funding_context.our_funding_inputs.clone(),
+			    outputs_to_contribute: Vec::new(),
+			    expected_remote_shared_funding_output: Some((channel.context().get_funding_redeemscript(), channel.context().channel_value_satoshis)),
+			}
+		) {
+			Ok(tx_constructor) => {
+				channel.set_interactive_tx_constructor(tx_constructor);
+			},
+			Err(_) => {
+				return Err(ChannelError::Close((
+					"V2 channel rejected due to sender error".into(),
+					ClosureReason::HolderForceClosed { broadcasted_latest_txn: Some(false) },
+				)))
+			}
+		}
+
+		Ok(channel)
 	}
 
 	/// Marks an inbound channel as accepted and generates a [`msgs::AcceptChannelV2`] message which