server+tapchannel: make aux signer partially stateless

We allow any stateless methods of the aux leaf signer to be called
without the server needing to be fully started, so reduce the number of
potential startup wait dependencies there could be.

Author: guggero

server.go

@@ -863,11 +863,9 @@ func (s *Server) PackSigs(
 
 	srvrLog.Debugf("PackSigs called")
 
-	if err := s.waitForReady(); err != nil {
-		return lfn.None[tlv.Blob](), err
-	}
-
-	return s.cfg.AuxLeafSigner.PackSigs(blob)
+	// We don't need to wait for the server to be ready here, as the
+	// PackSigs method is fully stateless.
+	return tapchannel.PackSigs(blob)
 }
 
 // UnpackSigs takes a packed blob of signatures and returns the original
@@ -879,11 +877,9 @@ func (s *Server) UnpackSigs(blob lfn.Option[tlv.Blob]) ([]lfn.Option[tlv.Blob],
 
 	srvrLog.Debugf("UnpackSigs called")
 
-	if err := s.waitForReady(); err != nil {
-		return nil, err
-	}
-
-	return s.cfg.AuxLeafSigner.UnpackSigs(blob)
+	// We don't need to wait for the server to be ready here, as the
+	// UnpackSigs method is fully stateless.
+	return tapchannel.UnpackSigs(blob)
 }
 
 // VerifySecondLevelSigs attempts to synchronously verify a batch of aux sig
@@ -895,12 +891,10 @@ func (s *Server) VerifySecondLevelSigs(chanState *channeldb.OpenChannel,
 
 	srvrLog.Debugf("VerifySecondLevelSigs called")
 
-	if err := s.waitForReady(); err != nil {
-		return err
-	}
-
-	return s.cfg.AuxLeafSigner.VerifySecondLevelSigs(
-		chanState, commitTx, verifyJob,
+	// We don't need to wait for the server to be ready here, as the
+	// VerifySecondLevelSigs method is fully stateless.
+	return tapchannel.VerifySecondLevelSigs(
+		s.chainParams, chanState, commitTx, verifyJob,
 	)
 }
 
@@ -1089,8 +1083,8 @@ func (s *Server) FinalizeClose(desc chancloser.AuxCloseDesc,
 
 // ResolveContract attempts to obtain a resolution blob for the specified
 // contract.
-func (s *Server) ResolveContract(req lnwallet.ResolutionReq,
-) lfn.Result[tlv.Blob] {
+func (s *Server) ResolveContract(
+	req lnwallet.ResolutionReq) lfn.Result[tlv.Blob] {
 
 	srvrLog.Infof("ResolveContract called, req=%v", spew.Sdump(req))
 

tapchannel/aux_leaf_signer.go

@@ -94,10 +94,6 @@ func (s *AuxLeafSigner) Stop() error {
 	return stopErr
 }
 
-// A compile-time check to ensure that AuxLeafSigner fully implements the
-// lnwallet.AuxSigner interface.
-var _ lnwallet.AuxSigner = (*AuxLeafSigner)(nil)
-
 // SubmitSecondLevelSigBatch takes a batch of aux sign jobs and processes them
 // asynchronously.
 func (s *AuxLeafSigner) SubmitSecondLevelSigBatch(
@@ -112,9 +108,7 @@ func (s *AuxLeafSigner) SubmitSecondLevelSigBatch(
 
 // PackSigs takes a series of aux signatures and packs them into a single blob
 // that can be sent alongside the CommitSig messages.
-func (s *AuxLeafSigner) PackSigs(
-	sigBlob []lfn.Option[tlv.Blob]) (lfn.Option[tlv.Blob], error) {
-
+func PackSigs(sigBlob []lfn.Option[tlv.Blob]) (lfn.Option[tlv.Blob], error) {
 	htlcSigs := make([][]*cmsg.AssetSig, len(sigBlob))
 	for idx := range sigBlob {
 		err := lfn.MapOptionZ(
@@ -150,9 +144,7 @@ func (s *AuxLeafSigner) PackSigs(
 
 // UnpackSigs takes a packed blob of signatures and returns the original
 // signatures for each HTLC, keyed by HTLC index.
-func (s *AuxLeafSigner) UnpackSigs(
-	blob lfn.Option[tlv.Blob]) ([]lfn.Option[tlv.Blob], error) {
-
+func UnpackSigs(blob lfn.Option[tlv.Blob]) ([]lfn.Option[tlv.Blob], error) {
 	if blob.IsNone() {
 		return nil, nil
 	}
@@ -173,8 +165,9 @@ func (s *AuxLeafSigner) UnpackSigs(
 
 // VerifySecondLevelSigs attempts to synchronously verify a batch of aux sig
 // jobs.
-func (s *AuxLeafSigner) VerifySecondLevelSigs(chanState *channeldb.OpenChannel,
-	commitTx *wire.MsgTx, verifyJobs []lnwallet.AuxVerifyJob) error {
+func VerifySecondLevelSigs(chainParams *address.ChainParams,
+	chanState *channeldb.OpenChannel, commitTx *wire.MsgTx,
+	verifyJobs []lnwallet.AuxVerifyJob) error {
 
 	for idx := range verifyJobs {
 		verifyJob := verifyJobs[idx]
@@ -225,9 +218,10 @@ func (s *AuxLeafSigner) VerifySecondLevelSigs(chanState *channeldb.OpenChannel,
 			continue
 		}
 
-		err = s.verifyHtlcSignature(
-			chanState, commitTx, verifyJobs[idx].KeyRing,
-			assetSigs.Sigs, htlcOutputs, verifyJobs[idx].BaseAuxJob,
+		err = verifyHtlcSignature(
+			chainParams, chanState, commitTx,
+			verifyJobs[idx].KeyRing, assetSigs.Sigs, htlcOutputs,
+			verifyJobs[idx].BaseAuxJob,
 		)
 		if err != nil {
 			return fmt.Errorf("error verifying second level sig: "+
@@ -330,13 +324,14 @@ func (s *AuxLeafSigner) processAuxSigBatch(chanState *channeldb.OpenChannel,
 
 // verifyHtlcSignature verifies the HTLC signature in the commitment transaction
 // described by the sign job.
-func (s *AuxLeafSigner) verifyHtlcSignature(chanState *channeldb.OpenChannel,
-	commitTx *wire.MsgTx, keyRing lnwallet.CommitmentKeyRing,
-	sigs []*cmsg.AssetSig, htlcOutputs []*cmsg.AssetOutput,
-	baseJob lnwallet.BaseAuxJob) error {
+func verifyHtlcSignature(chainParams *address.ChainParams,
+	chanState *channeldb.OpenChannel, commitTx *wire.MsgTx,
+	keyRing lnwallet.CommitmentKeyRing, sigs []*cmsg.AssetSig,
+	htlcOutputs []*cmsg.AssetOutput, baseJob lnwallet.BaseAuxJob) error {
 
-	vPackets, err := s.htlcSecondLevelPacketsFromCommit(
-		chanState, commitTx, baseJob.KeyRing, htlcOutputs, baseJob,
+	vPackets, err := htlcSecondLevelPacketsFromCommit(
+		chainParams, chanState, commitTx, baseJob.KeyRing, htlcOutputs,
+		baseJob,
 	)
 	if err != nil {
 		return fmt.Errorf("error generating second level packets: %w",
@@ -470,8 +465,9 @@ func (s *AuxLeafSigner) generateHtlcSignature(chanState *channeldb.OpenChannel,
 	signDesc input.SignDescriptor,
 	baseJob lnwallet.BaseAuxJob) (lnwallet.AuxSigJobResp, error) {
 
-	vPackets, err := s.htlcSecondLevelPacketsFromCommit(
-		chanState, commitTx, baseJob.KeyRing, htlcOutputs, baseJob,
+	vPackets, err := htlcSecondLevelPacketsFromCommit(
+		s.cfg.ChainParams, chanState, commitTx, baseJob.KeyRing,
+		htlcOutputs, baseJob,
 	)
 	if err != nil {
 		return lnwallet.AuxSigJobResp{}, fmt.Errorf("error generating "+
@@ -556,14 +552,14 @@ func (s *AuxLeafSigner) generateHtlcSignature(chanState *channeldb.OpenChannel,
 // htlcSecondLevelPacketsFromCommit generates the HTLC second level packets from
 // the commitment transaction. A bool is returned indicating if the HTLC was
 // incoming or outgoing.
-func (s *AuxLeafSigner) htlcSecondLevelPacketsFromCommit(
+func htlcSecondLevelPacketsFromCommit(chainParams *address.ChainParams,
 	chanState *channeldb.OpenChannel, commitTx *wire.MsgTx,
 	keyRing lnwallet.CommitmentKeyRing, htlcOutputs []*cmsg.AssetOutput,
 	baseJob lnwallet.BaseAuxJob) ([]*tappsbt.VPacket, error) {
 
 	packets, _, err := CreateSecondLevelHtlcPackets(
 		chanState, commitTx, baseJob.HTLC.Amount.ToSatoshis(),
-		keyRing, s.cfg.ChainParams, htlcOutputs,
+		keyRing, chainParams, htlcOutputs,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("error creating second level HTLC "+