multi: make watchtower client/server DBs remote compatible

The final database that needs to be made remote compatible is the
watchtower server and client database.
They are handled a bit differently because both of them are not always
active, only when specifically turned on in the config.

watchtower/wtdb/db_common.go

@@ -3,18 +3,10 @@ package wtdb
 import (
 	"encoding/binary"
 	"errors"
-	"os"
-	"path/filepath"
-	"time"
 
 	"github.com/lightningnetwork/lnd/kvdb"
 )
 
-const (
-	// dbFilePermission requests read+write access to the db file.
-	dbFilePermission = 0600
-)
-
 var (
 	// metadataBkt stores all the meta information concerning the state of
 	// the database.
@@ -35,67 +27,19 @@ var (
 	byteOrder = binary.BigEndian
 )
 
-// fileExists returns true if the file exists, and false otherwise.
-func fileExists(path string) bool {
-	if _, err := os.Stat(path); err != nil {
-		if os.IsNotExist(err) {
-			return false
-		}
-	}
-
-	return true
-}
-
-// createDBIfNotExist opens the boltdb database at dbPath/name, creating one if
-// one doesn't exist. The boolean returned indicates if the database did not
-// exist before, or if it has been created but no version metadata exists within
-// it.
-func createDBIfNotExist(dbPath, name string,
-	dbTimeout time.Duration) (kvdb.Backend, bool, error) {
-
-	path := filepath.Join(dbPath, name)
-
-	// If the database file doesn't exist, this indicates we much initialize
-	// a fresh database with the latest version.
-	firstInit := !fileExists(path)
-	if firstInit {
-		// Ensure all parent directories are initialized.
-		err := os.MkdirAll(dbPath, 0700)
-		if err != nil {
-			return nil, false, err
-		}
-	}
-
-	// Specify bbolt freelist options to reduce heap pressure in case the
-	// freelist grows to be very large.
-	bdb, err := kvdb.Create(
-		kvdb.BoltBackendName, path, true, dbTimeout,
-	)
+// isFirstInit returns true if the given database has not yet been initialized,
+// e.g. no metadata bucket is present yet.
+func isFirstInit(db kvdb.Backend) (bool, error) {
+	var metadataExists bool
+	err := kvdb.View(db, func(tx kvdb.RTx) error {
+		metadataExists = tx.ReadBucket(metadataBkt) != nil
+		return nil
+	}, func() {
+		metadataExists = false
+	})
 	if err != nil {
-		return nil, false, err
+		return false, err
 	}
 
-	// If the file existed previously, we'll now check to see that the
-	// metadata bucket is properly initialized. It could be the case that
-	// the database was created, but we failed to actually populate any
-	// metadata. If the metadata bucket does not actually exist, we'll
-	// set firstInit to true so that we can treat is initialize the bucket.
-	if !firstInit {
-		var metadataExists bool
-		err = kvdb.View(bdb, func(tx kvdb.RTx) error {
-			metadataExists = tx.ReadBucket(metadataBkt) != nil
-			return nil
-		}, func() {
-			metadataExists = false
-		})
-		if err != nil {
-			return nil, false, err
-		}
-
-		if !metadataExists {
-			firstInit = true
-		}
-	}
-
-	return bdb, firstInit, nil
+	return !metadataExists, nil
 }