Merge pull request #1924 from benthecarman/handle-coinbase-funding-channel

Handle if funding output is in a coinbase transaction

Author: TheBlueMatt

lightning/src/ln/channel.rs

@@ -594,6 +594,9 @@ pub(crate) const DISCONNECT_PEER_AWAITING_RESPONSE_TICKS: usize = 2;
 /// exceeding this age limit will be force-closed and purged from memory.
 pub(crate) const UNFUNDED_CHANNEL_AGE_LIMIT_TICKS: usize = 60;
 
+/// Number of blocks needed for an output from a coinbase transaction to be spendable.
+pub(crate) const COINBASE_MATURITY: u32 = 100;
+
 struct PendingChannelMonitorUpdate {
 	update: ChannelMonitorUpdate,
 }
@@ -4734,12 +4737,14 @@ impl<SP: Deref> Channel<SP> where
 							return Err(ClosureReason::ProcessingError { err: err_reason.to_owned() });
 						} else {
 							if self.context.is_outbound() {
-								for input in tx.input.iter() {
-									if input.witness.is_empty() {
-										// We generated a malleable funding transaction, implying we've
-										// just exposed ourselves to funds loss to our counterparty.
-										#[cfg(not(fuzzing))]
-										panic!("Client called ChannelManager::funding_transaction_generated with bogus transaction!");
+								if !tx.is_coin_base() {
+									for input in tx.input.iter() {
+										if input.witness.is_empty() {
+											// We generated a malleable funding transaction, implying we've
+											// just exposed ourselves to funds loss to our counterparty.
+											#[cfg(not(fuzzing))]
+											panic!("Client called ChannelManager::funding_transaction_generated with bogus transaction!");
+										}
 									}
 								}
 							}
@@ -4750,6 +4755,13 @@ impl<SP: Deref> Channel<SP> where
 								Err(_) => panic!("Block was bogus - either height was > 16 million, had > 16 million transactions, or had > 65k outputs"),
 							}
 						}
+						// If this is a coinbase transaction and not a 0-conf channel
+						// we should update our min_depth to 100 to handle coinbase maturity
+						if tx.is_coin_base() &&
+							self.context.minimum_depth.unwrap_or(0) > 0 &&
+							self.context.minimum_depth.unwrap_or(0) < COINBASE_MATURITY {
+							self.context.minimum_depth = Some(COINBASE_MATURITY);
+						}
 					}
 					// If we allow 1-conf funding, we may need to check for channel_ready here and
 					// send it immediately instead of waiting for a best_block_updated call (which
@@ -5821,6 +5833,15 @@ impl<SP: Deref> OutboundV1Channel<SP> where SP::Target: SignerProvider {
 
 		self.context.channel_state = ChannelState::FundingCreated as u32;
 		self.context.channel_id = funding_txo.to_channel_id();
+
+		// If the funding transaction is a coinbase transaction, we need to set the minimum depth to 100.
+		// We can skip this if it is a zero-conf channel.
+		if funding_transaction.is_coin_base() &&
+			self.context.minimum_depth.unwrap_or(0) > 0 &&
+			self.context.minimum_depth.unwrap_or(0) < COINBASE_MATURITY {
+			self.context.minimum_depth = Some(COINBASE_MATURITY);
+		}
+
 		self.context.funding_transaction = Some(funding_transaction);
 
 		let channel = Channel {

lightning/src/ln/channelmanager.rs

@@ -3561,11 +3561,13 @@ where
 	pub fn funding_transaction_generated(&self, temporary_channel_id: &ChannelId, counterparty_node_id: &PublicKey, funding_transaction: Transaction) -> Result<(), APIError> {
 		let _persistence_guard = PersistenceNotifierGuard::notify_on_drop(self);
 
-		for inp in funding_transaction.input.iter() {
-			if inp.witness.is_empty() {
-				return Err(APIError::APIMisuseError {
-					err: "Funding transaction must be fully signed and spend Segwit outputs".to_owned()
-				});
+		if !funding_transaction.is_coin_base() {
+			for inp in funding_transaction.input.iter() {
+				if inp.witness.is_empty() {
+					return Err(APIError::APIMisuseError {
+						err: "Funding transaction must be fully signed and spend Segwit outputs".to_owned()
+					});
+				}
 			}
 		}
 		{

lightning/src/ln/functional_test_utils.rs

@@ -46,7 +46,7 @@ use alloc::rc::Rc;
 use crate::sync::{Arc, Mutex, LockTestExt, RwLock};
 use core::mem;
 use core::iter::repeat;
-use bitcoin::{PackedLockTime, TxMerkleNode};
+use bitcoin::{PackedLockTime, TxIn, TxMerkleNode};
 
 pub const CHAN_CONFIRM_DEPTH: u32 = 10;
 
@@ -1005,7 +1005,23 @@ macro_rules! reload_node {
 	};
 }
 
-pub fn create_funding_transaction<'a, 'b, 'c>(node: &Node<'a, 'b, 'c>, expected_counterparty_node_id: &PublicKey, expected_chan_value: u64, expected_user_chan_id: u128) -> (ChannelId, Transaction, OutPoint) {
+pub fn create_funding_transaction<'a, 'b, 'c>(node: &Node<'a, 'b, 'c>,
+	expected_counterparty_node_id: &PublicKey, expected_chan_value: u64, expected_user_chan_id: u128)
+ -> (ChannelId, Transaction, OutPoint)
+{
+	internal_create_funding_transaction(node, expected_counterparty_node_id, expected_chan_value, expected_user_chan_id, false)
+}
+
+pub fn create_coinbase_funding_transaction<'a, 'b, 'c>(node: &Node<'a, 'b, 'c>,
+	expected_counterparty_node_id: &PublicKey, expected_chan_value: u64, expected_user_chan_id: u128)
+ -> (ChannelId, Transaction, OutPoint)
+{
+	internal_create_funding_transaction(node, expected_counterparty_node_id, expected_chan_value, expected_user_chan_id, true)
+}
+
+fn internal_create_funding_transaction<'a, 'b, 'c>(node: &Node<'a, 'b, 'c>,
+	expected_counterparty_node_id: &PublicKey, expected_chan_value: u64, expected_user_chan_id: u128,
+	coinbase: bool) -> (ChannelId, Transaction, OutPoint) {
 	let chan_id = *node.network_chan_count.borrow();
 
 	let events = node.node.get_and_clear_pending_events();
@@ -1016,7 +1032,16 @@ pub fn create_funding_transaction<'a, 'b, 'c>(node: &Node<'a, 'b, 'c>, expected_
 			assert_eq!(*channel_value_satoshis, expected_chan_value);
 			assert_eq!(user_channel_id, expected_user_chan_id);
 
-			let tx = Transaction { version: chan_id as i32, lock_time: PackedLockTime::ZERO, input: Vec::new(), output: vec![TxOut {
+			let input = if coinbase {
+				vec![TxIn {
+					previous_output: bitcoin::OutPoint::null(),
+					..Default::default()
+				}]
+			} else {
+				Vec::new()
+			};
+
+			let tx = Transaction { version: chan_id as i32, lock_time: PackedLockTime::ZERO, input, output: vec![TxOut {
 				value: *channel_value_satoshis, script_pubkey: output_script.clone(),
 			}]};
 			let funding_outpoint = OutPoint { txid: tx.txid(), index: 0 };
@@ -1025,6 +1050,7 @@ pub fn create_funding_transaction<'a, 'b, 'c>(node: &Node<'a, 'b, 'c>, expected_
 		_ => panic!("Unexpected event"),
 	}
 }
+
 pub fn sign_funding_transaction<'a, 'b, 'c>(node_a: &Node<'a, 'b, 'c>, node_b: &Node<'a, 'b, 'c>, channel_value: u64, expected_temporary_channel_id: ChannelId) -> Transaction {
 	let (temporary_channel_id, tx, funding_output) = create_funding_transaction(node_a, &node_b.node.get_our_node_id(), channel_value, 42);
 	assert_eq!(temporary_channel_id, expected_temporary_channel_id);

lightning/src/ln/functional_tests.rs

@@ -20,7 +20,7 @@ use crate::chain::transaction::OutPoint;
 use crate::sign::{ChannelSigner, EcdsaChannelSigner, EntropySource, SignerProvider};
 use crate::events::{Event, MessageSendEvent, MessageSendEventsProvider, PathFailure, PaymentPurpose, ClosureReason, HTLCDestination, PaymentFailureReason};
 use crate::ln::{ChannelId, PaymentPreimage, PaymentSecret, PaymentHash};
-use crate::ln::channel::{commitment_tx_base_weight, COMMITMENT_TX_WEIGHT_PER_HTLC, CONCURRENT_INBOUND_HTLC_FEE_BUFFER, FEE_SPIKE_BUFFER_FEE_INCREASE_MULTIPLE, MIN_AFFORDABLE_HTLC_COUNT, get_holder_selected_channel_reserve_satoshis, OutboundV1Channel, InboundV1Channel};
+use crate::ln::channel::{commitment_tx_base_weight, COMMITMENT_TX_WEIGHT_PER_HTLC, CONCURRENT_INBOUND_HTLC_FEE_BUFFER, FEE_SPIKE_BUFFER_FEE_INCREASE_MULTIPLE, MIN_AFFORDABLE_HTLC_COUNT, get_holder_selected_channel_reserve_satoshis, OutboundV1Channel, InboundV1Channel, COINBASE_MATURITY};
 use crate::ln::channelmanager::{self, PaymentId, RAACommitmentOrder, PaymentSendFailure, RecipientOnionFields, BREAKDOWN_TIMEOUT, ENABLE_GOSSIP_TICKS, DISABLE_GOSSIP_TICKS, MIN_CLTV_EXPIRY_DELTA};
 use crate::ln::channel::{DISCONNECT_PEER_AWAITING_RESPONSE_TICKS, ChannelError};
 use crate::ln::{chan_utils, onion_utils};
@@ -9133,6 +9133,66 @@ fn test_invalid_funding_tx() {
 	mine_transaction(&nodes[1], &spend_tx);
 }
 
+#[test]
+fn test_coinbase_funding_tx() {
+	// Miners are able to fund channels directly from coinbase transactions, however
+	// by consensus rules, outputs of a coinbase transaction are encumbered by a 100
+	// block maturity timelock. To ensure that a (non-0conf) channel like this is enforceable
+	// on-chain, the minimum depth is updated to 100 blocks for coinbase funding transactions.
+	//
+	// Note that 0conf channels with coinbase funding transactions are unaffected and are
+	// immediately operational after opening.
+	let chanmon_cfgs = create_chanmon_cfgs(2);
+	let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
+	let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None]);
+	let nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+
+	nodes[0].node.create_channel(nodes[1].node.get_our_node_id(), 100000, 10001, 42, None).unwrap();
+	let open_channel = get_event_msg!(nodes[0], MessageSendEvent::SendOpenChannel, nodes[1].node.get_our_node_id());
+
+	nodes[1].node.handle_open_channel(&nodes[0].node.get_our_node_id(), &open_channel);
+	let accept_channel = get_event_msg!(nodes[1], MessageSendEvent::SendAcceptChannel, nodes[0].node.get_our_node_id());
+
+	nodes[0].node.handle_accept_channel(&nodes[1].node.get_our_node_id(), &accept_channel);
+
+	// Create the coinbase funding transaction.
+	let (temporary_channel_id, tx, _) = create_coinbase_funding_transaction(&nodes[0], &nodes[1].node.get_our_node_id(), 100000, 42);
+
+	nodes[0].node.funding_transaction_generated(&temporary_channel_id, &nodes[1].node.get_our_node_id(), tx.clone()).unwrap();
+	check_added_monitors!(nodes[0], 0);
+	let funding_created = get_event_msg!(nodes[0], MessageSendEvent::SendFundingCreated, nodes[1].node.get_our_node_id());
+
+	nodes[1].node.handle_funding_created(&nodes[0].node.get_our_node_id(), &funding_created);
+	check_added_monitors!(nodes[1], 1);
+	expect_channel_pending_event(&nodes[1], &nodes[0].node.get_our_node_id());
+
+	let funding_signed = get_event_msg!(nodes[1], MessageSendEvent::SendFundingSigned, nodes[0].node.get_our_node_id());
+
+	nodes[0].node.handle_funding_signed(&nodes[1].node.get_our_node_id(), &funding_signed);
+	check_added_monitors!(nodes[0], 1);
+
+	expect_channel_pending_event(&nodes[0], &nodes[1].node.get_our_node_id());
+	assert!(nodes[0].node.get_and_clear_pending_events().is_empty());
+
+	// Starting at height 0, we "confirm" the coinbase at height 1.
+	confirm_transaction_at(&nodes[0], &tx, 1);
+	// We connect 98 more blocks to have 99 confirmations for the coinbase transaction.
+	connect_blocks(&nodes[0], COINBASE_MATURITY - 2);
+	// Check that we have no pending message events (we have not queued a `channel_ready` yet).
+	assert!(nodes[0].node.get_and_clear_pending_msg_events().is_empty());
+	// Now connect one more block which results in 100 confirmations of the coinbase transaction.
+	connect_blocks(&nodes[0], 1);
+	// There should now be a `channel_ready` which can be handled.
+	let _ = &nodes[1].node.handle_channel_ready(&nodes[0].node.get_our_node_id(), &get_event_msg!(&nodes[0], MessageSendEvent::SendChannelReady, nodes[1].node.get_our_node_id()));
+
+	confirm_transaction_at(&nodes[1], &tx, 1);
+	connect_blocks(&nodes[1], COINBASE_MATURITY - 2);
+	assert!(nodes[1].node.get_and_clear_pending_msg_events().is_empty());
+	connect_blocks(&nodes[1], 1);
+	expect_channel_ready_event(&nodes[1], &nodes[0].node.get_our_node_id());
+	create_chan_between_nodes_with_value_confirm_second(&nodes[0], &nodes[1]);
+}
+
 fn do_test_tx_confirmed_skipping_blocks_immediate_broadcast(test_height_before_timelock: bool) {
 	// In the first version of the chain::Confirm interface, after a refactor was made to not
 	// broadcast CSV-locked transactions until their CSV lock is up, we wouldn't reliably broadcast