Expose counterparty-revoked-outputs in get_claimable_balance

This uses the various new tracking added in the prior commits to
expose a new `Balance` type - `CounterpartyRevokedOutputClaimable`.

Some nontrivial work is required, however, as we now have to track
HTLC outputs as spendable in a transaction that comes *after* an
HTLC-Success/HTLC-Timeout transaction, which we previously didn't
need to do. Thus, we have to check if an
`onchain_events_awaiting_threshold_conf` event spends a commitment
transaction's HTLC output while walking events. Further, because
we now need to track HTLC outputs after the
HTLC-Success/HTLC-Timeout confirms, and because we have to track
the counterparty's `to_self` output as a contentious output which
could be claimed by either party, we have to examine the
`OnchainTxHandler`'s set of outputs to spend when determining if
certain outputs are still spendable.

Two new tests are added which test various different transaction
formats, and hopefully provide good test coverage of the various
revoked output paths.

Author: TheBlueMatt

lightning/src/chain/channelmonitor.rs

@@ -22,6 +22,7 @@
 
 use bitcoin::blockdata::block::BlockHeader;
 use bitcoin::blockdata::transaction::{TxOut,Transaction};
+use bitcoin::blockdata::transaction::OutPoint as BitcoinOutPoint;
 use bitcoin::blockdata::script::{Script, Builder};
 use bitcoin::blockdata::opcodes;
 
@@ -580,6 +581,15 @@ pub enum Balance {
 		/// done so.
 		claimable_height: u32,
 	},
+	/// The channel has been closed, and our counterparty broadcasted a revoked commitment
+	/// transaction.
+	///
+	/// Thus, we're able to claim all outputs in the commitment transaction, one of which has the
+	/// following amount.
+	CounterpartyRevokedOutputClaimable {
+		/// The amount, in satoshis, of the output which we can claim.
+		claimable_amount_satoshis: u64,
+	},
 }
 
 /// An HTLC which has been irrevocably resolved on-chain, and has reached ANTI_REORG_DELAY.
@@ -1402,9 +1412,9 @@ impl<Signer: Sign> ChannelMonitor<Signer> {
 	/// balance, or until our counterparty has claimed the balance and accrued several
 	/// confirmations on the claim transaction.
 	///
-	/// Note that the balances available when you or your counterparty have broadcasted revoked
-	/// state(s) may not be fully captured here.
-	// TODO, fix that ^
+	/// Note that for `ChannelMonitors` which track a channel which went on-chain with versions of
+	/// LDK prior to 0.0.108, balances may not be fully captured if our counterparty broadcasted
+	/// a revoked state.
 	///
 	/// See [`Balance`] for additional details on the types of claimable balances which
 	/// may be returned here and their meanings.
@@ -1413,9 +1423,13 @@ impl<Signer: Sign> ChannelMonitor<Signer> {
 		let us = self.inner.lock().unwrap();
 
 		let mut confirmed_txid = us.funding_spend_confirmed;
+		let mut confirmed_counterparty_output = us.confirmed_commitment_tx_counterparty_output;
 		let mut pending_commitment_tx_conf_thresh = None;
 		let funding_spend_pending = us.onchain_events_awaiting_threshold_conf.iter().find_map(|event| {
-			if let OnchainEvent::FundingSpendConfirmation { .. } = event.event {
+			if let OnchainEvent::FundingSpendConfirmation { commitment_tx_to_counterparty_output, .. } =
+				event.event
+			{
+				confirmed_counterparty_output = commitment_tx_to_counterparty_output;
 				Some((event.txid, event.confirmation_threshold()))
 			} else { None }
 		});
@@ -1427,22 +1441,25 @@ impl<Signer: Sign> ChannelMonitor<Signer> {
 		}
 
 		macro_rules! walk_htlcs {
-			($holder_commitment: expr, $htlc_iter: expr) => {
+			($holder_commitment: expr, $counterparty_revoked_commitment: expr, $htlc_iter: expr) => {
 				for htlc in $htlc_iter {
 					if let Some(htlc_commitment_tx_output_idx) = htlc.transaction_output_index {
+						let mut htlc_spend_txid_opt = None;
 						let mut htlc_update_pending = None;
 						let mut htlc_spend_pending = None;
 						let mut delayed_output_pending = None;
 						for event in us.onchain_events_awaiting_threshold_conf.iter() {
 							match event.event {
 								OnchainEvent::HTLCUpdate { commitment_tx_output_idx, htlc_value_satoshis, .. }
 								if commitment_tx_output_idx == Some(htlc_commitment_tx_output_idx) => {
+									htlc_spend_txid_opt = event.transaction.as_ref().map(|tx| tx.txid());
 									debug_assert!(htlc_update_pending.is_none());
 									debug_assert_eq!(htlc_value_satoshis.unwrap(), htlc.amount_msat / 1000);
 									htlc_update_pending = Some(event.confirmation_threshold());
 								},
 								OnchainEvent::HTLCSpendConfirmation { commitment_tx_output_idx, preimage, .. }
 								if commitment_tx_output_idx == htlc_commitment_tx_output_idx => {
+									htlc_spend_txid_opt = event.transaction.as_ref().map(|tx| tx.txid());
 									debug_assert!(htlc_spend_pending.is_none());
 									htlc_spend_pending = Some((event.confirmation_threshold(), preimage.is_some()));
 								},
@@ -1456,22 +1473,77 @@ impl<Signer: Sign> ChannelMonitor<Signer> {
 							}
 						}
 						let htlc_resolved = us.htlcs_resolved_on_chain.iter()
-							.find(|v| v.commitment_tx_output_idx == htlc_commitment_tx_output_idx);
+							.find(|v| if v.commitment_tx_output_idx == htlc_commitment_tx_output_idx {
+								debug_assert_ne!(v.resolving_txid, confirmed_txid);
+								htlc_spend_txid_opt = v.resolving_txid;
+								true
+							} else { false });
 						debug_assert!(htlc_update_pending.is_some() as u8 + htlc_spend_pending.is_some() as u8 + htlc_resolved.is_some() as u8 <= 1);
 
+						let htlc_output_needs_spending =
+							us.onchain_tx_handler.is_output_spend_pending(&
+								if let Some(txid) = htlc_spend_txid_opt {
+									debug_assert!(
+										us.onchain_tx_handler.channel_transaction_parameters.opt_anchors.is_none(),
+										"This code needs updating for anchors");
+									BitcoinOutPoint::new(txid, 0)
+								} else {
+									BitcoinOutPoint::new(confirmed_txid.unwrap(), htlc_commitment_tx_output_idx)
+								});
+
 						if let Some(conf_thresh) = delayed_output_pending {
 							debug_assert!($holder_commitment);
 							res.push(Balance::ClaimableAwaitingConfirmations {
 								claimable_amount_satoshis: htlc.amount_msat / 1000,
 								confirmation_height: conf_thresh,
 							});
-						} else if htlc_resolved.is_some() {
+						} else if htlc_resolved.is_some() && !htlc_output_needs_spending {
 							// Funding transaction spends should be fully confirmed by the time any
 							// HTLC transactions are resolved, unless we're talking about a holder
 							// commitment tx, whose resolution is delayed until the CSV timeout is
 							// reached, even though HTLCs may be resolved after only
 							// ANTI_REORG_DELAY confirmations.
 							debug_assert!($holder_commitment || us.funding_spend_confirmed.is_some());
+						} else if $counterparty_revoked_commitment {
+							let htlc_output_claim_pending = us.onchain_events_awaiting_threshold_conf.iter().find_map(|event| {
+								if let OnchainEvent::MaturingOutput {
+									descriptor: SpendableOutputDescriptor::StaticOutput { .. }
+								} = &event.event {
+									if event.transaction.as_ref().map(|tx| tx.input.iter().any(|inp| {
+										if let Some(htlc_spend_txid) = htlc_spend_txid_opt {
+											Some(tx.txid()) == htlc_spend_txid_opt ||
+												inp.previous_output.txid == htlc_spend_txid
+										} else {
+											Some(inp.previous_output.txid) == confirmed_txid &&
+												inp.previous_output.vout == htlc_commitment_tx_output_idx
+										}
+									})).unwrap_or(false) {
+										Some(())
+									} else { None }
+								} else { None }
+							});
+							if htlc_output_claim_pending.is_some() {
+								// We already push `Balance`s onto the `res` list for every
+								// `StaticOutput` in a `MaturingOutput` in the revoked
+								// counterparty commitment transaction case generally, so don't
+								// need to do so again here.
+							} else if htlc_spend_pending.is_some() {
+								res.push(Balance::CounterpartyRevokedOutputClaimable {
+									claimable_amount_satoshis: htlc.amount_msat / 1000,
+								});
+							} else if htlc_resolved.is_some() {
+								res.push(Balance::CounterpartyRevokedOutputClaimable {
+									claimable_amount_satoshis: htlc.amount_msat / 1000,
+								});
+							} else {
+								debug_assert!(htlc_update_pending.is_none(),
+									"HTLCUpdate OnchainEvents should never appear for preimage claims");
+								debug_assert!(htlc_spend_pending.is_none() || !htlc_spend_pending.unwrap().1,
+									"We don't (currently) generate preimage claims against revoked outputs, where did you get one?!");
+								res.push(Balance::CounterpartyRevokedOutputClaimable {
+									claimable_amount_satoshis: htlc.amount_msat / 1000,
+								});
+							}
 						} else {
 							if htlc.offered == $holder_commitment {
 								// If the payment was outbound, check if there's an HTLCUpdate
@@ -1515,8 +1587,8 @@ impl<Signer: Sign> ChannelMonitor<Signer> {
 
 		if let Some(txid) = confirmed_txid {
 			let mut found_commitment_tx = false;
-			if Some(txid) == us.current_counterparty_commitment_txid || Some(txid) == us.prev_counterparty_commitment_txid {
-				walk_htlcs!(false, us.counterparty_claimable_outpoints.get(&txid).unwrap().iter().map(|(a, _)| a));
+			if let Some(counterparty_tx_htlcs) = us.counterparty_claimable_outpoints.get(&txid) {
+				// First look for the to_remote output back to us.
 				if let Some(conf_thresh) = pending_commitment_tx_conf_thresh {
 					if let Some(value) = us.onchain_events_awaiting_threshold_conf.iter().find_map(|event| {
 						if let OnchainEvent::MaturingOutput {
@@ -1535,9 +1607,50 @@ impl<Signer: Sign> ChannelMonitor<Signer> {
 						// confirmation with the same height or have never met our dust amount.
 					}
 				}
+				if Some(txid) == us.current_counterparty_commitment_txid || Some(txid) == us.prev_counterparty_commitment_txid {
+					walk_htlcs!(false, false, counterparty_tx_htlcs.iter().map(|(a, _)| a));
+				} else {
+					walk_htlcs!(false, true, counterparty_tx_htlcs.iter().map(|(a, _)| a));
+					// The counterparty broadcasted a revoked state!
+					// Look for a StaticOutput spend first, as it should be spending the full set
+					// of commitment transaction outputs, if we see one, assume that it did and
+					// just return that.
+					let mut spent_counterparty_output = false;
+					for event in us.onchain_events_awaiting_threshold_conf.iter() {
+						if let OnchainEvent::MaturingOutput {
+							descriptor: SpendableOutputDescriptor::StaticOutput { output, .. }
+						} = &event.event {
+							res.push(Balance::ClaimableAwaitingConfirmations {
+								claimable_amount_satoshis: output.value,
+								confirmation_height: event.confirmation_threshold(),
+							});
+							if let Some(confirmed_to_self_idx) = confirmed_counterparty_output.map(|(idx, _)| idx) {
+								if event.transaction.as_ref().map(|tx|
+									tx.input.iter().any(|inp| inp.previous_output.vout == confirmed_to_self_idx)
+								).unwrap_or(false) {
+									spent_counterparty_output = true;
+								}
+							}
+						}
+					}
+
+					if spent_counterparty_output {
+					} else if let Some((confirmed_to_self_idx, amt)) = confirmed_counterparty_output {
+						let output_spendable = us.onchain_tx_handler
+							.is_output_spend_pending(&BitcoinOutPoint::new(txid, confirmed_to_self_idx));
+						if output_spendable {
+							res.push(Balance::CounterpartyRevokedOutputClaimable {
+								claimable_amount_satoshis: amt,
+							});
+						}
+					} else {
+						// Counterparty output is missing, either it was broadcasted on a
+						// previous version of LDK or the counterparty hadn't met dust.
+					}
+				}
 				found_commitment_tx = true;
 			} else if txid == us.current_holder_commitment_tx.txid {
-				walk_htlcs!(true, us.current_holder_commitment_tx.htlc_outputs.iter().map(|(a, _, _)| a));
+				walk_htlcs!(true, false, us.current_holder_commitment_tx.htlc_outputs.iter().map(|(a, _, _)| a));
 				if let Some(conf_thresh) = pending_commitment_tx_conf_thresh {
 					res.push(Balance::ClaimableAwaitingConfirmations {
 						claimable_amount_satoshis: us.current_holder_commitment_tx.to_self_value_sat,
@@ -1547,7 +1660,7 @@ impl<Signer: Sign> ChannelMonitor<Signer> {
 				found_commitment_tx = true;
 			} else if let Some(prev_commitment) = &us.prev_holder_signed_commitment_tx {
 				if txid == prev_commitment.txid {
-					walk_htlcs!(true, prev_commitment.htlc_outputs.iter().map(|(a, _, _)| a));
+					walk_htlcs!(true, false, prev_commitment.htlc_outputs.iter().map(|(a, _, _)| a));
 					if let Some(conf_thresh) = pending_commitment_tx_conf_thresh {
 						res.push(Balance::ClaimableAwaitingConfirmations {
 							claimable_amount_satoshis: prev_commitment.to_self_value_sat,
@@ -1568,8 +1681,6 @@ impl<Signer: Sign> ChannelMonitor<Signer> {
 					});
 				}
 			}
-			// TODO: Add logic to provide claimable balances for counterparty broadcasting revoked
-			// outputs.
 		} else {
 			let mut claimable_inbound_htlc_value_sat = 0;
 			for (htlc, _, _) in us.current_holder_commitment_tx.htlc_outputs.iter() {

lightning/src/chain/onchaintx.rs

@@ -690,6 +690,10 @@ impl<ChannelSigner: Sign> OnchainTxHandler<ChannelSigner> {
 		}
 	}
 
+	pub(crate) fn is_output_spend_pending(&self, outpoint: &BitcoinOutPoint) -> bool {
+		self.claimable_outpoints.get(outpoint).is_some()
+	}
+
 	pub(crate) fn get_relevant_txids(&self) -> Vec<Txid> {
 		let mut txids: Vec<Txid> = self.onchain_events_awaiting_threshold_conf
 			.iter()