multi: use kvdb.Backend for height hint DB

In order to separate our databases more clearly, we refactor the height
hint cache DB to use a kvdb backend instead of the channel DB instance
directly.

chainntnfs/height_hint_cache.go

@@ -84,7 +84,7 @@ type ConfirmHintCache interface {
 // will be stored.
 type HeightHintCache struct {
 	cfg CacheConfig
-	db  *channeldb.DB
+	db  kvdb.Backend
 }
 
 // Compile-time checks to ensure HeightHintCache satisfies the SpendHintCache
@@ -93,7 +93,9 @@ var _ SpendHintCache = (*HeightHintCache)(nil)
 var _ ConfirmHintCache = (*HeightHintCache)(nil)
 
 // NewHeightHintCache returns a new height hint cache backed by a database.
-func NewHeightHintCache(cfg CacheConfig, db *channeldb.DB) (*HeightHintCache, error) {
+func NewHeightHintCache(cfg CacheConfig, db kvdb.Backend) (*HeightHintCache,
+	error) {
+
 	cache := &HeightHintCache{cfg, db}
 	if err := cache.initBuckets(); err != nil {
 		return nil, err
@@ -105,7 +107,7 @@ func NewHeightHintCache(cfg CacheConfig, db *channeldb.DB) (*HeightHintCache, er
 // initBuckets ensures that the primary buckets used by the circuit are
 // initialized so that we can assume their existence after startup.
 func (c *HeightHintCache) initBuckets() error {
-	return kvdb.Batch(c.db.Backend, func(tx kvdb.RwTx) error {
+	return kvdb.Batch(c.db, func(tx kvdb.RwTx) error {
 		_, err := tx.CreateTopLevelBucket(spendHintBucket)
 		if err != nil {
 			return err
@@ -127,7 +129,7 @@ func (c *HeightHintCache) CommitSpendHint(height uint32,
 	Log.Tracef("Updating spend hint to height %d for %v", height,
 		spendRequests)
 
-	return kvdb.Batch(c.db.Backend, func(tx kvdb.RwTx) error {
+	return kvdb.Batch(c.db, func(tx kvdb.RwTx) error {
 		spendHints := tx.ReadWriteBucket(spendHintBucket)
 		if spendHints == nil {
 			return ErrCorruptedHeightHintCache
@@ -197,7 +199,7 @@ func (c *HeightHintCache) PurgeSpendHint(spendRequests ...SpendRequest) error {
 
 	Log.Tracef("Removing spend hints for %v", spendRequests)
 
-	return kvdb.Batch(c.db.Backend, func(tx kvdb.RwTx) error {
+	return kvdb.Batch(c.db, func(tx kvdb.RwTx) error {
 		spendHints := tx.ReadWriteBucket(spendHintBucket)
 		if spendHints == nil {
 			return ErrCorruptedHeightHintCache
@@ -228,7 +230,7 @@ func (c *HeightHintCache) CommitConfirmHint(height uint32,
 	Log.Tracef("Updating confirm hints to height %d for %v", height,
 		confRequests)
 
-	return kvdb.Batch(c.db.Backend, func(tx kvdb.RwTx) error {
+	return kvdb.Batch(c.db, func(tx kvdb.RwTx) error {
 		confirmHints := tx.ReadWriteBucket(confirmHintBucket)
 		if confirmHints == nil {
 			return ErrCorruptedHeightHintCache
@@ -299,7 +301,7 @@ func (c *HeightHintCache) PurgeConfirmHint(confRequests ...ConfRequest) error {
 
 	Log.Tracef("Removing confirm hints for %v", confRequests)
 
-	return kvdb.Batch(c.db.Backend, func(tx kvdb.RwTx) error {
+	return kvdb.Batch(c.db, func(tx kvdb.RwTx) error {
 		confirmHints := tx.ReadWriteBucket(confirmHintBucket)
 		if confirmHints == nil {
 			return ErrCorruptedHeightHintCache

chainreg/chainregistry.go

@@ -28,6 +28,7 @@ import (
 	"github.com/lightningnetwork/lnd/htlcswitch"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/keychain"
+	"github.com/lightningnetwork/lnd/kvdb"
 	"github.com/lightningnetwork/lnd/lncfg"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwallet/btcwallet"
@@ -70,7 +71,7 @@ type Config struct {
 
 	// HeightHintDB is a pointer to the database that stores the height
 	// hints.
-	HeightHintDB *channeldb.DB
+	HeightHintDB kvdb.Backend
 
 	// ChanStateDB is a pointer to the database that stores the channel
 	// state.

lncfg/db.go

@@ -91,6 +91,10 @@ type DatabaseBackends struct {
 	// ChanStateDB points to a possibly networked replicated backend that
 	// contains the critical channel state related data.
 	ChanStateDB kvdb.Backend
+
+	// HeightHintDB points to a possibly networked replicated backend that
+	// contains the chain height hint related data.
+	HeightHintDB kvdb.Backend
 }
 
 // GetBackends returns a set of kvdb.Backends as set in the DB config.
@@ -124,8 +128,9 @@ func (db *DB) GetBackends(ctx context.Context, dbPath string) (
 	}
 
 	return &DatabaseBackends{
-		GraphDB:     localDB,
-		ChanStateDB: remoteDB,
+		GraphDB:      localDB,
+		ChanStateDB:  remoteDB,
+		HeightHintDB: localDB,
 	}, nil
 }
 

lnd.go

@@ -43,6 +43,7 @@ import (
 	"github.com/lightningnetwork/lnd/chanacceptor"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/keychain"
+	"github.com/lightningnetwork/lnd/kvdb"
 	"github.com/lightningnetwork/lnd/lncfg"
 	"github.com/lightningnetwork/lnd/lnrpc"
 	"github.com/lightningnetwork/lnd/lnwallet"
@@ -706,7 +707,7 @@ func Main(cfg *Config, lisCfg ListenerCfg, interceptor signal.Interceptor) error
 		LitecoindMode:               cfg.LitecoindMode,
 		BtcdMode:                    cfg.BtcdMode,
 		LtcdMode:                    cfg.LtcdMode,
-		HeightHintDB:                dbs.graphDB,
+		HeightHintDB:                dbs.heightHintDB,
 		ChanStateDB:                 dbs.chanStateDB,
 		PrivateWalletPw:             privateWalletPw,
 		PublicWalletPw:              publicWalletPw,
@@ -1624,8 +1625,9 @@ func waitForWalletPassword(cfg *Config,
 // databaseInstances is a struct that holds all instances to the actual
 // databases that are used in lnd.
 type databaseInstances struct {
-	graphDB     *channeldb.DB
-	chanStateDB *channeldb.DB
+	graphDB      *channeldb.DB
+	chanStateDB  *channeldb.DB
+	heightHintDB kvdb.Backend
 }
 
 // initializeDatabases extracts the current databases that we'll use for normal
@@ -1655,7 +1657,9 @@ func initializeDatabases(ctx context.Context,
 	// If the remoteDB is nil, then we'll just open a local DB as normal,
 	// having the remote and local pointer be the exact same instance.
 	var (
-		dbs        = &databaseInstances{}
+		dbs = &databaseInstances{
+			heightHintDB: databaseBackends.HeightHintDB,
+		}
 		closeFuncs []func()
 	)
 	if databaseBackends.ChanStateDB == nil {