contractcourt: add spend path helpers in timeout/success resolver

This commit adds a few helper methods to decide how the htlc output
should be spent.

contractcourt/htlc_timeout_resolver.go

@@ -634,7 +634,7 @@ func (h *htlcTimeoutResolver) spendHtlcOutput() (
 	// HTLC transaction that is signed using sighash SINGLE|ANYONECANPAY
 	// (the case for anchor type channels). In this case we can re-sign it
 	// and attach fees at will. We let the sweeper handle this job.
-	case h.htlcResolution.SignDetails != nil && !h.outputIncubating:
+	case h.isZeroFeeOutput() && !h.outputIncubating:
 		if err := h.sweepSecondLevelTx(); err != nil {
 			log.Errorf("Sending timeout tx to sweeper: %v", err)
 
@@ -643,7 +643,7 @@ func (h *htlcTimeoutResolver) spendHtlcOutput() (
 
 	// If this is a remote commitment there's no second level timeout txn,
 	// and we can just send this directly to the sweeper.
-	case h.htlcResolution.SignedTimeoutTx == nil && !h.outputIncubating:
+	case h.isRemoteCommitOutput() && !h.outputIncubating:
 		if err := h.sweepDirectHtlcOutput(); err != nil {
 			log.Errorf("Sending direct spend to sweeper: %v", err)
 
@@ -653,7 +653,7 @@ func (h *htlcTimeoutResolver) spendHtlcOutput() (
 	// If we have a SignedTimeoutTx but no SignDetails, this is a local
 	// commitment for a non-anchor channel, so we'll send it to the utxo
 	// nursery.
-	case h.htlcResolution.SignDetails == nil && !h.outputIncubating:
+	case h.isLegacyOutput() && !h.outputIncubating:
 		if err := h.sendSecondLevelTxLegacy(); err != nil {
 			log.Errorf("Sending timeout tx to nursery: %v", err)
 
@@ -769,7 +769,7 @@ func (h *htlcTimeoutResolver) handleCommitSpend(
 	// If the sweeper is handling the second level transaction, wait for
 	// the CSV and possible CLTV lock to expire, before sweeping the output
 	// on the second-level.
-	case h.htlcResolution.SignDetails != nil:
+	case h.isZeroFeeOutput():
 		waitHeight := h.deriveWaitHeight(
 			h.htlcResolution.CsvDelay, commitSpend,
 		)
@@ -851,7 +851,7 @@ func (h *htlcTimeoutResolver) handleCommitSpend(
 	// Finally, if this was an output on our commitment transaction, we'll
 	// wait for the second-level HTLC output to be spent, and for that
 	// transaction itself to confirm.
-	case h.htlcResolution.SignedTimeoutTx != nil:
+	case !h.isRemoteCommitOutput():
 		log.Infof("%T(%v): waiting for nursery/sweeper to spend CSV "+
 			"delayed output", h, claimOutpoint)
 
@@ -1232,7 +1232,7 @@ func (h *htlcTimeoutResolver) consumeSpendEvents(resultChan chan *spendResult,
 			// continue the loop.
 			hasPreimage := isPreimageSpend(
 				h.isTaproot(), spendDetail,
-				h.htlcResolution.SignedTimeoutTx != nil,
+				!h.isRemoteCommitOutput(),
 			)
 			if !hasPreimage {
 				log.Debugf("HTLC output %s spent doesn't "+
@@ -1260,3 +1260,31 @@ func (h *htlcTimeoutResolver) consumeSpendEvents(resultChan chan *spendResult,
 		}
 	}
 }
+
+// isRemoteCommitOutput returns a bool to indicate whether the htlc output is
+// on the remote commitment.
+func (h *htlcTimeoutResolver) isRemoteCommitOutput() bool {
+	// If we don't have a timeout transaction, then this means that this is
+	// an output on the remote party's commitment transaction.
+	return h.htlcResolution.SignedTimeoutTx == nil
+}
+
+// isZeroFeeOutput returns a boolean indicating whether the htlc output is from
+// a anchor-enabled channel, which uses the sighash SINGLE|ANYONECANPAY.
+func (h *htlcTimeoutResolver) isZeroFeeOutput() bool {
+	// If we have non-nil SignDetails, this means it has a 2nd level HTLC
+	// transaction that is signed using sighash SINGLE|ANYONECANPAY (the
+	// case for anchor type channels). In this case we can re-sign it and
+	// attach fees at will.
+	return h.htlcResolution.SignedTimeoutTx != nil &&
+		h.htlcResolution.SignDetails != nil
+}
+
+// isLegacyOutput returns a boolean indicating whether the htlc output is from
+// a non-anchor-enabled channel.
+func (h *htlcTimeoutResolver) isLegacyOutput() bool {
+	// If we have a SignedTimeoutTx but no SignDetails, this is a local
+	// commitment for a non-anchor channel.
+	return h.htlcResolution.SignedTimeoutTx != nil &&
+		h.htlcResolution.SignDetails == nil
+}