server+tapchannel: make aux leaf creator stateless

This fixes a startup dependency issue between lnd and tapd where both
wait for each other to become ready.
Because the aux leaf creator doesn't depend on any other components that
need to be started first, and also doesn't carry any state by itself, we
can declare it to be fully stateless and not block on server startup
before being able to use it.

Author: guggero

config.go

@@ -197,8 +197,6 @@ type Config struct {
 
 	UniverseStats universe.Telemetry
 
-	AuxLeafCreator *tapchannel.AuxLeafCreator
-
 	AuxLeafSigner *tapchannel.AuxLeafSigner
 
 	AuxFundingController *tapchannel.FundingController

server.go

@@ -196,10 +196,7 @@ func (s *Server) initialize(interceptorChain *rpcperms.InterceptorChain) error {
 		return fmt.Errorf("unable to start RFQ manager: %w", err)
 	}
 
-	// Start the auxiliary leaf creator and signer.
-	if err := s.cfg.AuxLeafCreator.Start(); err != nil {
-		return fmt.Errorf("unable to start aux leaf creator: %w", err)
-	}
+	// Start the auxiliary components.
 	if err := s.cfg.AuxLeafSigner.Start(); err != nil {
 		return fmt.Errorf("unable to start aux leaf signer: %w", err)
 	}
@@ -657,9 +654,6 @@ func (s *Server) Stop() error {
 		return err
 	}
 
-	if err := s.cfg.AuxLeafCreator.Stop(); err != nil {
-		return err
-	}
 	if err := s.cfg.AuxLeafSigner.Stop(); err != nil {
 		return err
 	}
@@ -733,13 +727,11 @@ func (s *Server) FetchLeavesFromView(chanState *channeldb.OpenChannel,
 		"numTheirUpdates=%d", isOurCommit, ourBalance, theirBalance,
 		len(view.OurUpdates), len(view.TheirUpdates))
 
-	if err := s.waitForReady(); err != nil {
-		return lfn.None[lnwallet.CommitAuxLeaves](), nil, err
-	}
-
-	return s.cfg.AuxLeafCreator.FetchLeavesFromView(
-		chanState, prevBlob, view, isOurCommit, ourBalance,
-		theirBalance, keys,
+	// The aux leaf creator is fully stateless, and we don't need to wait
+	// for the server to be started before being able to use it.
+	return tapchannel.FetchLeavesFromView(
+		s.chainParams, chanState, prevBlob, view, isOurCommit,
+		ourBalance, theirBalance, keys,
 	)
 }
 
@@ -757,11 +749,11 @@ func (s *Server) FetchLeavesFromCommit(chanState *channeldb.OpenChannel,
 		"theirBalance=%v, numHtlcs=%d", com.LocalBalance,
 		com.RemoteBalance, len(com.Htlcs))
 
-	if err := s.waitForReady(); err != nil {
-		return lfn.None[lnwallet.CommitAuxLeaves](), err
-	}
-
-	return s.cfg.AuxLeafCreator.FetchLeavesFromCommit(chanState, com, keys)
+	// The aux leaf creator is fully stateless, and we don't need to wait
+	// for the server to be started before being able to use it.
+	return tapchannel.FetchLeavesFromCommit(
+		s.chainParams, chanState, com, keys,
+	)
 }
 
 // FetchLeavesFromRevocation attempts to fetch the auxiliary leaves
@@ -776,11 +768,9 @@ func (s *Server) FetchLeavesFromRevocation(
 		"teirBalance=%v, numHtlcs=%d", rev.OurBalance, rev.TheirBalance,
 		len(rev.HTLCEntries))
 
-	if err := s.waitForReady(); err != nil {
-		return lfn.None[lnwallet.CommitAuxLeaves](), err
-	}
-
-	return s.cfg.AuxLeafCreator.FetchLeavesFromRevocation(rev)
+	// The aux leaf creator is fully stateless, and we don't need to wait
+	// for the server to be started before being able to use it.
+	return tapchannel.FetchLeavesFromRevocation(rev)
 }
 
 // ApplyHtlcView serves as the state transition function for the custom
@@ -798,13 +788,11 @@ func (s *Server) ApplyHtlcView(chanState *channeldb.OpenChannel,
 		"numTheirUpdates=%d", isOurCommit, ourBalance, theirBalance,
 		len(originalView.OurUpdates), len(originalView.TheirUpdates))
 
-	if err := s.waitForReady(); err != nil {
-		return lfn.None[tlv.Blob](), err
-	}
-
-	return s.cfg.AuxLeafCreator.ApplyHtlcView(
-		chanState, prevBlob, originalView, isOurCommit, ourBalance,
-		theirBalance, keys,
+	// The aux leaf creator is fully stateless, and we don't need to wait
+	// for the server to be started before being able to use it.
+	return tapchannel.ApplyHtlcView(
+		s.chainParams, chanState, prevBlob, originalView, isOurCommit,
+		ourBalance, theirBalance, keys,
 	)
 }
 

tapcfg/server.go

@@ -406,11 +406,6 @@ func genServerConfig(cfg *Config, cfgLogger btclog.Logger,
 		},
 	)
 
-	auxLeafCreator := tapchannel.NewAuxLeafCreator(
-		&tapchannel.LeafCreatorConfig{
-			ChainParams: &tapChainParams,
-		},
-	)
 	auxLeafSigner := tapchannel.NewAuxLeafSigner(
 		&tapchannel.LeafSignerConfig{
 			ChainParams: &tapChainParams,
@@ -554,7 +549,6 @@ func genServerConfig(cfg *Config, cfgLogger btclog.Logger,
 		UniverseQueriesPerSecond: cfg.Universe.UniverseQueriesPerSecond,
 		UniverseQueriesBurst:     cfg.Universe.UniverseQueriesBurst,
 		RfqManager:               rfqManager,
-		AuxLeafCreator:           auxLeafCreator,
 		AuxLeafSigner:            auxLeafSigner,
 		AuxFundingController:     auxFundingController,
 		AuxChanCloser:            auxChanCloser,

tapchannel/aux_leaf_creator.go

@@ -3,13 +3,11 @@ package tapchannel
 import (
 	"bytes"
 	"fmt"
-	"sync"
 	"time"
 
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/lightninglabs/taproot-assets/address"
-	"github.com/lightninglabs/taproot-assets/fn"
 	cmsg "github.com/lightninglabs/taproot-assets/tapchannelmsg"
 	"github.com/lightningnetwork/lnd/channeldb"
 	lfn "github.com/lightningnetwork/lnd/fn"
@@ -25,67 +23,12 @@ const (
 	DefaultTimeout = 30 * time.Second
 )
 
-// LeafCreatorConfig defines the configuration for the auxiliary leaf creator.
-type LeafCreatorConfig struct {
-	ChainParams *address.ChainParams
-}
-
-// AuxLeafCreator is a Taproot Asset auxiliary leaf creator that can be used to
-// create auxiliary leaves for Taproot Asset channels.
-type AuxLeafCreator struct {
-	startOnce sync.Once
-	stopOnce  sync.Once
-
-	cfg *LeafCreatorConfig
-
-	// ContextGuard provides a wait group and main quit channel that can be
-	// used to create guarded contexts.
-	*fn.ContextGuard
-}
-
-// NewAuxLeafCreator creates a new Taproot Asset auxiliary leaf creator based on
-// the passed config.
-func NewAuxLeafCreator(cfg *LeafCreatorConfig) *AuxLeafCreator {
-	return &AuxLeafCreator{
-		cfg: cfg,
-		ContextGuard: &fn.ContextGuard{
-			DefaultTimeout: DefaultTimeout,
-			Quit:           make(chan struct{}),
-		},
-	}
-}
-
-// Start attempts to start a new aux leaf creator.
-func (c *AuxLeafCreator) Start() error {
-	var startErr error
-	c.startOnce.Do(func() {
-		log.Info("Starting aux leaf creator")
-	})
-	return startErr
-}
-
-// Stop signals for a custodian to gracefully exit.
-func (c *AuxLeafCreator) Stop() error {
-	var stopErr error
-	c.stopOnce.Do(func() {
-		log.Info("Stopping aux leaf creator")
-
-		close(c.Quit)
-		c.Wg.Wait()
-	})
-
-	return stopErr
-}
-
-// A compile-time check to ensure that AuxLeafCreator fully implements the
-// lnwallet.AuxLeafStore interface.
-var _ lnwallet.AuxLeafStore = (*AuxLeafCreator)(nil)
-
 // FetchLeavesFromView attempts to fetch the auxiliary leaves that correspond to
 // the passed aux blob, and pending fully evaluated HTLC view.
-func (c *AuxLeafCreator) FetchLeavesFromView(chanState *channeldb.OpenChannel,
-	prevBlob tlv.Blob, originalView *lnwallet.HtlcView, isOurCommit bool,
-	ourBalance, theirBalance lnwire.MilliSatoshi,
+func FetchLeavesFromView(chainParams *address.ChainParams,
+	chanState *channeldb.OpenChannel, prevBlob tlv.Blob,
+	originalView *lnwallet.HtlcView, isOurCommit bool, ourBalance,
+	theirBalance lnwire.MilliSatoshi,
 	keys lnwallet.CommitmentKeyRing) (lfn.Option[lnwallet.CommitAuxLeaves],
 	lnwallet.CommitSortFunc, error) {
 
@@ -112,7 +55,7 @@ func (c *AuxLeafCreator) FetchLeavesFromView(chanState *channeldb.OpenChannel,
 
 	allocations, newCommitment, err := GenerateCommitmentAllocations(
 		prevState, chanState, chanAssetState, isOurCommit, ourBalance,
-		theirBalance, originalView, c.cfg.ChainParams, keys,
+		theirBalance, originalView, chainParams, keys,
 	)
 	if err != nil {
 		return none, nil, fmt.Errorf("unable to generate allocations: "+
@@ -132,8 +75,8 @@ func (c *AuxLeafCreator) FetchLeavesFromView(chanState *channeldb.OpenChannel,
 
 // FetchLeavesFromCommit attempts to fetch the auxiliary leaves that correspond
 // to the passed aux blob, and an existing channel commitment.
-func (c *AuxLeafCreator) FetchLeavesFromCommit(chanState *channeldb.OpenChannel,
-	com channeldb.ChannelCommitment,
+func FetchLeavesFromCommit(chainParams *address.ChainParams,
+	chanState *channeldb.OpenChannel, com channeldb.ChannelCommitment,
 	keys lnwallet.CommitmentKeyRing) (lfn.Option[lnwallet.CommitAuxLeaves],
 	error) {
 
@@ -173,7 +116,7 @@ func (c *AuxLeafCreator) FetchLeavesFromCommit(chanState *channeldb.OpenChannel,
 
 			leaf, err := CreateSecondLevelHtlcTx(
 				chanState, com.CommitTx, htlc.Amt.ToSatoshis(),
-				keys, c.cfg.ChainParams, htlcOutputs,
+				keys, chainParams, htlcOutputs,
 			)
 			if err != nil {
 				return none, fmt.Errorf("unable to create "+
@@ -204,7 +147,7 @@ func (c *AuxLeafCreator) FetchLeavesFromCommit(chanState *channeldb.OpenChannel,
 
 			leaf, err := CreateSecondLevelHtlcTx(
 				chanState, com.CommitTx, htlc.Amt.ToSatoshis(),
-				keys, c.cfg.ChainParams, htlcOutputs,
+				keys, chainParams, htlcOutputs,
 			)
 			if err != nil {
 				return none, fmt.Errorf("unable to create "+
@@ -231,7 +174,7 @@ func (c *AuxLeafCreator) FetchLeavesFromCommit(chanState *channeldb.OpenChannel,
 
 // FetchLeavesFromRevocation attempts to fetch the auxiliary leaves
 // from a channel revocation that stores balance + blob information.
-func (c *AuxLeafCreator) FetchLeavesFromRevocation(
+func FetchLeavesFromRevocation(
 	rev *channeldb.RevocationLog) (lfn.Option[lnwallet.CommitAuxLeaves],
 	error) {
 
@@ -255,8 +198,9 @@ func (c *AuxLeafCreator) FetchLeavesFromRevocation(
 // ApplyHtlcView serves as the state transition function for the custom
 // channel's blob. Given the old blob, and an HTLC view, then a new
 // blob should be returned that reflects the pending updates.
-func (c *AuxLeafCreator) ApplyHtlcView(chanState *channeldb.OpenChannel,
-	prevBlob tlv.Blob, originalView *lnwallet.HtlcView, isOurCommit bool,
+func ApplyHtlcView(chainParams *address.ChainParams,
+	chanState *channeldb.OpenChannel, prevBlob tlv.Blob,
+	originalView *lnwallet.HtlcView, isOurCommit bool,
 	ourBalance, theirBalance lnwire.MilliSatoshi,
 	keys lnwallet.CommitmentKeyRing) (lfn.Option[tlv.Blob], error) {
 
@@ -283,7 +227,7 @@ func (c *AuxLeafCreator) ApplyHtlcView(chanState *channeldb.OpenChannel,
 
 	_, newCommitment, err := GenerateCommitmentAllocations(
 		prevState, chanState, chanAssetState, isOurCommit, ourBalance,
-		theirBalance, originalView, c.cfg.ChainParams, keys,
+		theirBalance, originalView, chainParams, keys,
 	)
 	if err != nil {
 		return none, fmt.Errorf("unable to generate allocations: %w",