Claim HTLC output on-chain if preimage is recv'd after force-close

If we receive a preimage for an outgoing HTLC on a force-closed channel,
we need to claim the HTLC output on-chain.

Note that if no counterparty commitment transaction has been broadcasted,
we currently default to broadcasting two preimage-output-claiming txs
whenever we receive a preimage. This will be fixed in the next commit.

Co-authored-by: Antoine Riard <[email protected]>
Co-authored-by: Valentine Wallace <[email protected]>

Author: valentinewallace

lightning/src/chain/channelmonitor.rs

@@ -64,14 +64,32 @@ pub struct ChannelMonitorUpdate {
 	pub(crate) updates: Vec<ChannelMonitorUpdateStep>,
 	/// The sequence number of this update. Updates *must* be replayed in-order according to this
 	/// sequence number (and updates may panic if they are not). The update_id values are strictly
-	/// increasing and increase by one for each new update.
+	/// increasing and increase by one for each new update, with one exception specified below.
 	///
 	/// This sequence number is also used to track up to which points updates which returned
 	/// ChannelMonitorUpdateErr::TemporaryFailure have been applied to all copies of a given
 	/// ChannelMonitor when ChannelManager::channel_monitor_updated is called.
+	///
+	/// The only instance where update_id values are not strictly increasing is the case where: (1)
+	/// the channel has been force closed and (2) we receive a preimage from a forward link that
+	/// allows us to spend an HTLC output on this channel's (the backward link's) broadcasted
+	/// commitment transaction. In this case, we allow the `ChannelManager` to send a
+	/// `ChannelMonitorUpdate` with an update_id of [`CLOSED_CHANNEL_UPDATE_ID`], with the update
+	/// providing said payment preimage. No other update types are allowed after force-close.
+	///
+	/// [`CLOSED_CHANNEL_UPDATE_ID`]: constant.CLOSED_CHANNEL_UPDATE_ID.html
 	pub update_id: u64,
 }
 
+/// If:
+///    (1) a channel has been force closed and
+///    (2) we receive a preimage from a forward link that allows us to spend an HTLC output on
+///        this channel's (the backward link's) broadcasted commitment transaction
+/// then we allow the `ChannelManager` to send a `ChannelMonitorUpdate` with this update ID,
+/// with the update providing said payment preimage. No other update types are allowed after
+/// force-close.
+pub const CLOSED_CHANNEL_UPDATE_ID: u64 = std::u64::MAX;
+
 impl Writeable for ChannelMonitorUpdate {
 	fn write<W: Writer>(&self, w: &mut W) -> Result<(), ::std::io::Error> {
 		self.update_id.write(w)?;
@@ -1150,6 +1168,46 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 		    L::Target: Logger,
 	{
 		self.payment_preimages.insert(payment_hash.clone(), payment_preimage.clone());
+
+		// If the channel is force closed, try to claim the output from this preimage.
+		// First check if a counterparty commitment transaction has been broadcasted:
+		macro_rules! claim_htlcs {
+			($commitment_number: expr, $txid: expr) => {
+				let (htlc_claim_reqs, set_script) = self.get_counterparty_htlc_output_claim_reqs($commitment_number, $txid, None);
+				if set_script {
+					self.counterparty_payment_script = {
+						// Note that the Network here is ignored as we immediately drop the address for the
+						// script_pubkey version
+						let payment_hash160 = WPubkeyHash::hash(&self.keys.pubkeys().payment_point.serialize());
+						Builder::new().push_opcode(opcodes::all::OP_PUSHBYTES_0).push_slice(&payment_hash160[..]).into_script()
+					};
+				}
+				self.onchain_tx_handler.update_claims_view(&Vec::new(), htlc_claim_reqs, None, broadcaster, fee_estimator, logger);
+			}
+		}
+		if let Some(txid) = self.current_counterparty_commitment_txid {
+			if let Some(commitment_number) = self.counterparty_commitment_txn_on_chain.get(&txid) {
+				claim_htlcs!(*commitment_number, txid);
+				return;
+			}
+		}
+		if let Some(txid) = self.prev_counterparty_commitment_txid {
+			if let Some(commitment_number) = self.counterparty_commitment_txn_on_chain.get(&txid) {
+				claim_htlcs!(*commitment_number, txid);
+				return;
+			}
+		}
+
+		// Then if a holder commitment transaction has been signed, broadcast transactions claiming
+		// the HTLC output from each of the holder commitment transactions.
+		if self.broadcasted_holder_revokable_script.is_some() {
+			let (claim_reqs, _, _) = self.broadcast_by_holder_state(None, &self.current_holder_commitment_tx);
+			self.onchain_tx_handler.update_claims_view(&Vec::new(), claim_reqs, None, broadcaster, fee_estimator, logger);
+			if let Some(ref tx) = self.prev_holder_signed_commitment_tx {
+				let (claim_reqs, _, _) = self.broadcast_by_holder_state(None, &tx);
+				self.onchain_tx_handler.update_claims_view(&Vec::new(), claim_reqs, None, broadcaster, fee_estimator, logger);
+			}
+		}
 	}
 
 	pub(crate) fn broadcast_latest_holder_commitment_txn<B: Deref, L: Deref>(&mut self, broadcaster: &B, logger: &L)
@@ -1171,7 +1229,18 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 		    F::Target: FeeEstimator,
 		    L::Target: Logger,
 	{
-		if self.latest_update_id + 1 != updates.update_id {
+		// ChannelMonitor updates may be applied after force close if we receive a
+		// preimage for a broadcasted commitment transaction HTLC output that we'd
+		// like to claim on-chain. If this is the case, we no longer have guaranteed
+		// access to the monitor's update ID, so we use a sentinel value instead.
+		if updates.update_id == CLOSED_CHANNEL_UPDATE_ID {
+			match updates.updates[0] {
+				ChannelMonitorUpdateStep::PaymentPreimage { .. } => {},
+				_ => panic!("Attempted to apply post-force-close ChannelMonitorUpdate that wasn't providing a payment preimage"),
+			}
+			assert_eq!(updates.updates.len(), 1);
+		}
+		if updates.update_id != CLOSED_CHANNEL_UPDATE_ID && self.latest_update_id + 1 != updates.update_id {
 			panic!("Attempted to apply ChannelMonitorUpdates out of order, check the update_id before passing an update to update_monitor!");
 		}
 		for update in updates.updates.iter() {
@@ -1438,39 +1507,61 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 				check_htlc_fails!(txid, "previous", 'prev_loop);
 			}
 
+			let (htlc_claim_reqs, set_script) = self.get_counterparty_htlc_output_claim_reqs(commitment_number, commitment_txid, Some(tx));
+			if set_script {
+				self.counterparty_payment_script = {
+					// Note that the Network here is ignored as we immediately drop the address for the
+					// script_pubkey version
+					let payment_hash160 = WPubkeyHash::hash(&self.keys.pubkeys().payment_point.serialize());
+					Builder::new().push_opcode(opcodes::all::OP_PUSHBYTES_0).push_slice(&payment_hash160[..]).into_script()
+				};
+			}
+			for req in htlc_claim_reqs {
+				claimable_outpoints.push(req);
+			}
+
+		}
+		(claimable_outpoints, (commitment_txid, watch_outputs))
+	}
+
+	fn get_counterparty_htlc_output_claim_reqs(&self, commitment_number: u64, commitment_txid: Txid, tx: Option<&Transaction>) -> (Vec<ClaimRequest>, bool) {
+		let mut claims = Vec::new();
+		let mut set_counterparty_payment_script = false;
+		if let Some(htlc_outputs) = self.counterparty_claimable_outpoints.get(&commitment_txid) {
 			if let Some(revocation_points) = self.their_cur_revocation_points {
 				let revocation_point_option =
 					if revocation_points.0 == commitment_number { Some(&revocation_points.1) }
-					else if let Some(point) = revocation_points.2.as_ref() {
-						if revocation_points.0 == commitment_number + 1 { Some(point) } else { None }
-					} else { None };
+				else if let Some(point) = revocation_points.2.as_ref() {
+					if revocation_points.0 == commitment_number + 1 { Some(point) } else { None }
+				} else { None };
 				if let Some(revocation_point) = revocation_point_option {
-					self.counterparty_payment_script = {
-						// Note that the Network here is ignored as we immediately drop the address for the
-						// script_pubkey version
-						let payment_hash160 = WPubkeyHash::hash(&self.keys.pubkeys().payment_point.serialize());
-						Builder::new().push_opcode(opcodes::all::OP_PUSHBYTES_0).push_slice(&payment_hash160[..]).into_script()
-					};
+					set_counterparty_payment_script = true;
 
 					// Then, try to find htlc outputs
-					for (_, &(ref htlc, _)) in per_commitment_data.iter().enumerate() {
+					for (_, &(ref htlc, _)) in htlc_outputs.iter().enumerate() {
 						if let Some(transaction_output_index) = htlc.transaction_output_index {
-							if transaction_output_index as usize >= tx.output.len() ||
-									tx.output[transaction_output_index as usize].value != htlc.amount_msat / 1000 {
-								return (claimable_outpoints, (commitment_txid, watch_outputs)); // Corrupted per_commitment_data, fuck this user
+							if let Some(transaction) = tx {
+								if transaction_output_index as usize >= transaction.output.len() ||
+									transaction.output[transaction_output_index as usize].value != htlc.amount_msat / 1000 {
+										return (claims, set_counterparty_payment_script) // Corrupted per_commitment_data, fuck this user
+									}
 							}
-							let preimage = if htlc.offered { if let Some(p) = self.payment_preimages.get(&htlc.payment_hash) { Some(*p) } else { None } } else { None };
+							let preimage = if htlc.offered {
+								if let Some(p) = self.payment_preimages.get(&htlc.payment_hash) {
+									Some(*p)
+								} else { None }
+							} else { None };
 							let aggregable = if !htlc.offered { false } else { true };
 							if preimage.is_some() || !htlc.offered {
 								let witness_data = InputMaterial::CounterpartyHTLC { per_commitment_point: *revocation_point, counterparty_delayed_payment_base_key: self.counterparty_tx_cache.counterparty_delayed_payment_base_key, counterparty_htlc_base_key: self.counterparty_tx_cache.counterparty_htlc_base_key, preimage, htlc: htlc.clone() };
-								claimable_outpoints.push(ClaimRequest { absolute_timelock: htlc.cltv_expiry, aggregable, outpoint: BitcoinOutPoint { txid: commitment_txid, vout: transaction_output_index }, witness_data });
+								claims.push(ClaimRequest { absolute_timelock: htlc.cltv_expiry, aggregable, outpoint: BitcoinOutPoint { txid: commitment_txid, vout: transaction_output_index }, witness_data });
 							}
 						}
 					}
 				}
 			}
 		}
-		(claimable_outpoints, (commitment_txid, watch_outputs))
+		(claims, set_counterparty_payment_script)
 	}
 
 	/// Attempts to claim a counterparty HTLC-Success/HTLC-Timeout's outputs using the revocation key
@@ -1500,7 +1591,7 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 		(claimable_outpoints, Some((htlc_txid, outputs)))
 	}
 
-	fn broadcast_by_holder_state(&self, commitment_tx: &Transaction, holder_tx: &HolderSignedTx) -> (Vec<ClaimRequest>, Vec<(u32, TxOut)>, Option<(Script, PublicKey, PublicKey)>) {
+	fn broadcast_by_holder_state(&self, commitment_tx: Option<&Transaction>, holder_tx: &HolderSignedTx) -> (Vec<ClaimRequest>, Vec<(u32, TxOut)>, Option<(Script, PublicKey, PublicKey)>) {
 		let mut claim_requests = Vec::with_capacity(holder_tx.htlc_outputs.len());
 		let mut watch_outputs = Vec::with_capacity(holder_tx.htlc_outputs.len());
 
@@ -1521,7 +1612,9 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 							} else { None },
 						amount: htlc.amount_msat,
 				}});
-				watch_outputs.push((transaction_output_index, commitment_tx.output[transaction_output_index as usize].clone()));
+				if let Some(commitment_tx) = commitment_tx {
+					watch_outputs.push((transaction_output_index, commitment_tx.output[transaction_output_index as usize].clone()));
+				}
 			}
 		}
 
@@ -1573,13 +1666,13 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 		if self.current_holder_commitment_tx.txid == commitment_txid {
 			is_holder_tx = true;
 			log_trace!(logger, "Got latest holder commitment tx broadcast, searching for available HTLCs to claim");
-			let mut res = self.broadcast_by_holder_state(tx, &self.current_holder_commitment_tx);
+			let mut res = self.broadcast_by_holder_state(Some(tx), &self.current_holder_commitment_tx);
 			append_onchain_update!(res);
 		} else if let &Some(ref holder_tx) = &self.prev_holder_signed_commitment_tx {
 			if holder_tx.txid == commitment_txid {
 				is_holder_tx = true;
 				log_trace!(logger, "Got previous holder commitment tx broadcast, searching for available HTLCs to claim");
-				let mut res = self.broadcast_by_holder_state(tx, holder_tx);
+				let mut res = self.broadcast_by_holder_state(Some(tx), holder_tx);
 				append_onchain_update!(res);
 			}
 		}
@@ -1748,7 +1841,7 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 			self.pending_monitor_events.push(MonitorEvent::CommitmentTxBroadcasted(self.funding_info.0));
 			if let Some(commitment_tx) = self.onchain_tx_handler.get_fully_signed_holder_tx(&self.funding_redeemscript) {
 				self.holder_tx_signed = true;
-				let (mut new_outpoints, new_outputs, _) = self.broadcast_by_holder_state(&commitment_tx, &self.current_holder_commitment_tx);
+				let (mut new_outpoints, new_outputs, _) = self.broadcast_by_holder_state(Some(&commitment_tx), &self.current_holder_commitment_tx);
 				if !new_outputs.is_empty() {
 					watch_outputs.push((self.current_holder_commitment_tx.txid.clone(), new_outputs));
 				}
@@ -1776,7 +1869,7 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 			}
 		}
 
-		self.onchain_tx_handler.block_connected(&txn_matched, claimable_outpoints, height, &*broadcaster, &*fee_estimator, &*logger);
+		self.onchain_tx_handler.update_claims_view(&txn_matched, claimable_outpoints, Some(height), &&*broadcaster, &&*fee_estimator, &&*logger);
 		self.last_block_hash = block_hash;
 
 		// Determine new outputs to watch by comparing against previously known outputs to watch,

lightning/src/ln/channelmanager.rs

@@ -37,7 +37,7 @@ use bitcoin::secp256k1;
 use chain;
 use chain::Watch;
 use chain::chaininterface::{BroadcasterInterface, FeeEstimator};
-use chain::channelmonitor::{ChannelMonitor, ChannelMonitorUpdate, ChannelMonitorUpdateStep, ChannelMonitorUpdateErr, HTLC_FAIL_BACK_BUFFER, CLTV_CLAIM_BUFFER, LATENCY_GRACE_PERIOD_BLOCKS, ANTI_REORG_DELAY, MonitorEvent};
+use chain::channelmonitor::{ChannelMonitor, ChannelMonitorUpdate, ChannelMonitorUpdateStep, ChannelMonitorUpdateErr, HTLC_FAIL_BACK_BUFFER, CLTV_CLAIM_BUFFER, LATENCY_GRACE_PERIOD_BLOCKS, ANTI_REORG_DELAY, MonitorEvent, CLOSED_CHANNEL_UPDATE_ID};
 use chain::transaction::{OutPoint, TransactionData};
 use ln::channel::{Channel, ChannelError};
 use ln::features::{InitFeatures, NodeFeatures};
@@ -2165,7 +2165,7 @@ impl<ChanSigner: ChannelKeys, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref>
 					Ok(()) => Ok(()),
 					Err(None) => {
 						let preimage_update = ChannelMonitorUpdate {
-							update_id: std::u64::MAX,
+							update_id: CLOSED_CHANNEL_UPDATE_ID,
 							updates: vec![ChannelMonitorUpdateStep::PaymentPreimage {
 								payment_preimage: payment_preimage.clone(),
 							}],