Allow holder commitment and HTLC signature requests to fail

As part of the ongoing async signer work, our holder signatures must
also be capable of being obtained asynchronously. We expose a new
`ChannelMonitor::signer_unblocked` method to retry pending onchain
claims by re-signing and rebroadcasting transactions. Unfortunately, we
cannot retry said claims without them being registered first, so if
we're not able to obtain the signature synchronously, we must return the
transaction as unsigned and ensure it is not broadcast.

Author: wpaulino

lightning/src/chain/channelmonitor.rs

@@ -1749,6 +1749,25 @@ impl<Signer: WriteableEcdsaChannelSigner> ChannelMonitor<Signer> {
 		);
 	}
 
+	/// Triggers rebroadcasts of pending claims from a force-closed channel after a transaction
+	/// signature generation failure.
+	pub fn signer_unblocked<B: Deref, F: Deref, L: Deref>(
+		&self, broadcaster: B, fee_estimator: F, logger: &L,
+	)
+	where
+		B::Target: BroadcasterInterface,
+		F::Target: FeeEstimator,
+		L::Target: Logger,
+	{
+		let fee_estimator = LowerBoundedFeeEstimator::new(fee_estimator);
+		let mut inner = self.inner.lock().unwrap();
+		let logger = WithChannelMonitor::from_impl(logger, &*inner);
+		let current_height = inner.best_block.height;
+		inner.onchain_tx_handler.rebroadcast_pending_claims(
+			current_height, FeerateStrategy::RetryPrevious, &broadcaster, &fee_estimator, &logger,
+		);
+	}
+
 	/// Returns the descriptors for relevant outputs (i.e., those that we can spend) within the
 	/// transaction if they exist and the transaction has at least [`ANTI_REORG_DELAY`]
 	/// confirmations. For [`SpendableOutputDescriptor::DelayedPaymentOutput`] descriptors to be
@@ -1791,6 +1810,12 @@ impl<Signer: WriteableEcdsaChannelSigner> ChannelMonitor<Signer> {
 	pub fn set_counterparty_payment_script(&self, script: ScriptBuf) {
 		self.inner.lock().unwrap().counterparty_payment_script = script;
 	}
+
+	#[cfg(test)]
+	pub fn do_signer_call<F: FnMut(&Signer) -> ()>(&self, mut f: F) {
+		let inner = self.inner.lock().unwrap();
+		f(&inner.onchain_tx_handler.signer);
+	}
 }
 
 impl<Signer: WriteableEcdsaChannelSigner> ChannelMonitorImpl<Signer> {
@@ -3484,9 +3509,12 @@ impl<Signer: WriteableEcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 						continue;
 					}
 				} else { None };
-				if let Some(htlc_tx) = self.onchain_tx_handler.get_fully_signed_htlc_tx(
-					&::bitcoin::OutPoint { txid, vout }, &preimage) {
-					holder_transactions.push(htlc_tx);
+				if let Some(htlc_tx) = self.onchain_tx_handler.get_maybe_signed_htlc_tx(
+					&::bitcoin::OutPoint { txid, vout }, &preimage
+				) {
+					if !htlc_tx.input.iter().any(|input| input.witness.is_empty()) {
+						holder_transactions.push(htlc_tx);
+					}
 				}
 			}
 		}

lightning/src/chain/onchaintx.rs

@@ -212,6 +212,8 @@ pub(crate) enum OnchainClaim {
 
 /// Represents the different feerates a pending request can use when generating a claim.
 pub(crate) enum FeerateStrategy {
+	/// We must reuse the most recently used feerate, if any.
+	RetryPrevious,
 	/// We must pick the highest between the most recently used and the current feerate estimate.
 	HighestOfPreviousOrNew,
 	/// We must force a bump of the most recently used feerate, either by using the current feerate
@@ -506,9 +508,13 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>
 					}
 					match claim {
 						OnchainClaim::Tx(tx) => {
-							let log_start = if bumped_feerate { "Broadcasting RBF-bumped" } else { "Rebroadcasting" };
-							log_info!(logger, "{} onchain {}", log_start, log_tx!(tx));
-							broadcaster.broadcast_transactions(&[&tx]);
+							if tx.input.iter().any(|input| input.witness.is_empty()) {
+								log_info!(logger, "Waiting for signature of unsigned onchain transaction {}", tx.txid());
+							} else {
+								let log_start = if bumped_feerate { "Broadcasting RBF-bumped" } else { "Rebroadcasting" };
+								log_info!(logger, "{} onchain {}", log_start, log_tx!(tx));
+								broadcaster.broadcast_transactions(&[&tx]);
+							}
 						},
 						OnchainClaim::Event(event) => {
 							let log_start = if bumped_feerate { "Yielding fee-bumped" } else { "Replaying" };
@@ -645,8 +651,8 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>
 						let commitment_tx_feerate_sat_per_1000_weight =
 							compute_feerate_sat_per_1000_weight(fee_sat, tx.weight().to_wu());
 						if commitment_tx_feerate_sat_per_1000_weight >= package_target_feerate_sat_per_1000_weight {
-							log_debug!(logger, "Pre-signed {} already has feerate {} sat/kW above required {} sat/kW",
-								log_tx!(tx), commitment_tx_feerate_sat_per_1000_weight,
+							log_debug!(logger, "Pre-signed commitment {} already has feerate {} sat/kW above required {} sat/kW",
+								tx.txid(), commitment_tx_feerate_sat_per_1000_weight,
 								package_target_feerate_sat_per_1000_weight);
 							return Some((new_timer, 0, OnchainClaim::Tx(tx.clone())));
 						}
@@ -785,8 +791,12 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>
 				// `OnchainClaim`.
 				let claim_id = match claim {
 					OnchainClaim::Tx(tx) => {
-						log_info!(logger, "Broadcasting onchain {}", log_tx!(tx));
-						broadcaster.broadcast_transactions(&[&tx]);
+						if tx.input.iter().any(|input| input.witness.is_empty()) {
+							log_info!(logger, "Waiting for signature of unsigned onchain transaction {}", tx.txid());
+						} else {
+							log_info!(logger, "Broadcasting onchain {}", log_tx!(tx));
+							broadcaster.broadcast_transactions(&[&tx]);
+						}
 						ClaimId(tx.txid().to_byte_array())
 					},
 					OnchainClaim::Event(claim_event) => {
@@ -978,8 +988,13 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>
 			) {
 				match bump_claim {
 					OnchainClaim::Tx(bump_tx) => {
-						log_info!(logger, "Broadcasting RBF-bumped onchain {}", log_tx!(bump_tx));
-						broadcaster.broadcast_transactions(&[&bump_tx]);
+						if bump_tx.input.iter().any(|input| input.witness.is_empty()) {
+							log_info!(logger, "Waiting for signature of RBF-bumped unsigned onchain transaction {}",
+								bump_tx.txid());
+						} else {
+							log_info!(logger, "Broadcasting RBF-bumped onchain {}", log_tx!(bump_tx));
+							broadcaster.broadcast_transactions(&[&bump_tx]);
+						}
 					},
 					OnchainClaim::Event(claim_event) => {
 						log_info!(logger, "Yielding RBF-bumped onchain event to spend inputs {:?}", request.outpoints());
@@ -1061,8 +1076,12 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>
 				request.set_feerate(new_feerate);
 				match bump_claim {
 					OnchainClaim::Tx(bump_tx) => {
-						log_info!(logger, "Broadcasting onchain {}", log_tx!(bump_tx));
-						broadcaster.broadcast_transactions(&[&bump_tx]);
+						if bump_tx.input.iter().any(|input| input.witness.is_empty()) {
+							log_info!(logger, "Waiting for signature of unsigned onchain transaction {}", bump_tx.txid());
+						} else {
+							log_info!(logger, "Broadcasting onchain {}", log_tx!(bump_tx));
+							broadcaster.broadcast_transactions(&[&bump_tx]);
+						}
 					},
 					OnchainClaim::Event(claim_event) => {
 						log_info!(logger, "Yielding onchain event after reorg to spend inputs {:?}", request.outpoints());
@@ -1115,13 +1134,10 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>
 		&self.holder_commitment.trust().built_transaction().transaction
 	}
 
-	//TODO: getting lastest holder transactions should be infallible and result in us "force-closing the channel", but we may
-	// have empty holder commitment transaction if a ChannelMonitor is asked to force-close just after OutboundV1Channel::get_funding_created,
-	// before providing a initial commitment transaction. For outbound channel, init ChannelMonitor at Channel::funding_signed, there is nothing
-	// to monitor before.
-	pub(crate) fn get_fully_signed_holder_tx(&mut self, funding_redeemscript: &Script) -> Transaction {
-		let sig = self.signer.sign_holder_commitment(&self.holder_commitment, &self.secp_ctx).expect("signing holder commitment");
-		self.holder_commitment.add_holder_sig(funding_redeemscript, sig)
+	pub(crate) fn get_maybe_signed_holder_tx(&mut self, funding_redeemscript: &Script) -> Transaction {
+		self.signer.sign_holder_commitment(&self.holder_commitment, &self.secp_ctx)
+			.map(|sig| self.holder_commitment.add_holder_sig(funding_redeemscript, sig))
+			.unwrap_or_else(|_| self.get_unsigned_holder_commitment_tx().clone())
 	}
 
 	#[cfg(any(test, feature="unsafe_revoked_tx_signing"))]
@@ -1130,7 +1146,7 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>
 		self.holder_commitment.add_holder_sig(funding_redeemscript, sig)
 	}
 
-	pub(crate) fn get_fully_signed_htlc_tx(&mut self, outp: &::bitcoin::OutPoint, preimage: &Option<PaymentPreimage>) -> Option<Transaction> {
+	pub(crate) fn get_maybe_signed_htlc_tx(&mut self, outp: &::bitcoin::OutPoint, preimage: &Option<PaymentPreimage>) -> Option<Transaction> {
 		let get_signed_htlc_tx = |holder_commitment: &HolderCommitmentTransaction| {
 			let trusted_tx = holder_commitment.trust();
 			if trusted_tx.txid() != outp.txid {
@@ -1158,10 +1174,11 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner> OnchainTxHandler<ChannelSigner>
 				preimage: preimage.clone(),
 				counterparty_sig: counterparty_htlc_sig.clone(),
 			};
-			let htlc_sig = self.signer.sign_holder_htlc_transaction(&htlc_tx, 0, &htlc_descriptor, &self.secp_ctx).unwrap();
-			htlc_tx.input[0].witness = trusted_tx.build_htlc_input_witness(
-				htlc_idx, &counterparty_htlc_sig, &htlc_sig, preimage,
-			);
+			if let Ok(htlc_sig) = self.signer.sign_holder_htlc_transaction(&htlc_tx, 0, &htlc_descriptor, &self.secp_ctx) {
+				htlc_tx.input[0].witness = trusted_tx.build_htlc_input_witness(
+					htlc_idx, &counterparty_htlc_sig, &htlc_sig, preimage,
+				);
+			}
 			Some(htlc_tx)
 		};
 

lightning/src/chain/package.rs

@@ -637,10 +637,10 @@ impl PackageSolvingData {
 		match self {
 			PackageSolvingData::HolderHTLCOutput(ref outp) => {
 				debug_assert!(!outp.channel_type_features.supports_anchors_zero_fee_htlc_tx());
-				return onchain_handler.get_fully_signed_htlc_tx(outpoint, &outp.preimage);
+				onchain_handler.get_maybe_signed_htlc_tx(outpoint, &outp.preimage)
 			}
 			PackageSolvingData::HolderFundingOutput(ref outp) => {
-				return Some(onchain_handler.get_fully_signed_holder_tx(&outp.funding_redeemscript));
+				Some(onchain_handler.get_maybe_signed_holder_tx(&outp.funding_redeemscript))
 			}
 			_ => { panic!("API Error!"); }
 		}
@@ -996,6 +996,7 @@ impl PackageTemplate {
 		if self.feerate_previous != 0 {
 			let previous_feerate = self.feerate_previous.try_into().unwrap_or(u32::max_value());
 			match feerate_strategy {
+				FeerateStrategy::RetryPrevious => previous_feerate,
 				FeerateStrategy::HighestOfPreviousOrNew => cmp::max(previous_feerate, feerate_estimate),
 				FeerateStrategy::ForceBump => if feerate_estimate > previous_feerate {
 					feerate_estimate
@@ -1141,6 +1142,10 @@ where
 	// If old feerate inferior to actual one given back by Fee Estimator, use it to compute new fee...
 	let (new_fee, new_feerate) = if let Some((new_fee, new_feerate)) = compute_fee_from_spent_amounts(input_amounts, predicted_weight, fee_estimator, logger) {
 		match feerate_strategy {
+			FeerateStrategy::RetryPrevious => {
+				let previous_fee = previous_feerate * predicted_weight / 1000;
+				(previous_fee, previous_feerate)
+			},
 			FeerateStrategy::HighestOfPreviousOrNew => if new_feerate > previous_feerate {
 				(new_fee, new_feerate)
 			} else {