config: expose the InvoiceDB interface in DatabaseInstances

By now the only implementation is still the one in channeldb but other
project can use their custom implementations if needed.

config_builder.go

@@ -25,6 +25,7 @@ import (
 	"github.com/lightningnetwork/lnd/blockcache"
 	"github.com/lightningnetwork/lnd/chainreg"
 	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/invoices"
 	"github.com/lightningnetwork/lnd/keychain"
 	"github.com/lightningnetwork/lnd/kvdb"
 	"github.com/lightningnetwork/lnd/lncfg"
@@ -764,6 +765,9 @@ type DatabaseInstances struct {
 	// HeightHintDB is the database that stores height hints for spends.
 	HeightHintDB kvdb.Backend
 
+	// InvoiceDB is the database that stores information about invoices.
+	InvoiceDB invoices.InvoiceDB
+
 	// MacaroonDB is the database that stores macaroon root keys.
 	MacaroonDB kvdb.Backend
 
@@ -915,6 +919,12 @@ func (d *DefaultDatabaseBuilder) BuildDatabase(
 	// using the same struct (and DB backend) instance.
 	dbs.ChanStateDB = dbs.GraphDB
 
+	// For now the only InvoiceDB implementation is the *channeldb.DB.
+	//
+	// TODO(positiveblue): use a sql first implementation for this
+	// interface.
+	dbs.InvoiceDB = dbs.GraphDB
+
 	// Wrap the watchtower client DB and make sure we clean up.
 	if cfg.WtClient.Active {
 		dbs.TowerClientDB, err = wtdb.OpenClientDB(

server.go

@@ -614,7 +614,7 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		uint32(currentHeight), currentHash, cc.ChainNotifier,
 	)
 	s.invoices = invoices.NewRegistry(
-		dbs.ChanStateDB, expiryWatcher, &registryConfig,
+		dbs.InvoiceDB, expiryWatcher, &registryConfig,
 	)
 
 	s.htlcNotifier = htlcswitch.NewHtlcNotifier(time.Now)