package loopdb import ( "errors" "fmt" "github.com/coreos/bbolt" ) var ( // metaBucket stores all the meta information concerning the state of // the database. metaBucketKey = []byte("metadata") // dbVersionKey is a boltdb key and it's used for storing/retrieving // current database version. dbVersionKey = []byte("dbp") // ErrDBReversion is returned when detecting an attempt to revert to a // prior database version. ErrDBReversion = fmt.Errorf("channel db cannot revert to prior version") ) // migration is a function which takes a prior outdated version of the database // instances and mutates the key/bucket structure to arrive at a more // up-to-date version of the database. type migration func(tx *bbolt.Tx) error var ( // dbVersions is storing all versions of database. If current version // of database don't match with latest version this list will be used // for retrieving all migration function that are need to apply to the // current db. migrations = []migration{migrateCosts} latestDBVersion = uint32(len(migrations)) ) // getDBVersion retrieves the current db version. func getDBVersion(db *bbolt.DB) (uint32, error) { var version uint32 err := db.View(func(tx *bbolt.Tx) error { metaBucket := tx.Bucket(metaBucketKey) if metaBucket == nil { return errors.New("bucket does not exist") } data := metaBucket.Get(dbVersionKey) // If no version key found, assume version is 0. if data != nil { version = byteOrder.Uint32(data) } return nil }) if err != nil { return 0, err } return version, nil } // setDBVersion updates the current db version. func setDBVersion(tx *bbolt.Tx, version uint32) error { metaBucket, err := tx.CreateBucketIfNotExists(metaBucketKey) if err != nil { return fmt.Errorf("set db version: %v", err) } scratch := make([]byte, 4) byteOrder.PutUint32(scratch, version) return metaBucket.Put(dbVersionKey, scratch) } // syncVersions function is used for safe db version synchronization. It // applies migration functions to the current database and recovers the // previous state of db if at least one error/panic appeared during migration. func syncVersions(db *bbolt.DB) error { currentVersion, err := getDBVersion(db) if err != nil { return err } log.Infof("Checking for schema update: latest_version=%v, "+ "db_version=%v", latestDBVersion, currentVersion) switch { // If the database reports a higher version that we are aware of, the // user is probably trying to revert to a prior version of lnd. We fail // here to prevent reversions and unintended corruption. case currentVersion > latestDBVersion: log.Errorf("Refusing to revert from db_version=%d to "+ "lower version=%d", currentVersion, latestDBVersion) return ErrDBReversion // If the current database version matches the latest version number, // then we don't need to perform any migrations. case currentVersion == latestDBVersion: return nil } log.Infof("Performing database schema migration") // Otherwise we execute the migrations serially within a single // database transaction to ensure the migration is atomic. return db.Update(func(tx *bbolt.Tx) error { for v := currentVersion; v < latestDBVersion; v++ { log.Infof("Applying migration #%v", v+1) migration := migrations[v] if err := migration(tx); err != nil { log.Infof("Unable to apply migration #%v", v+1) return err } } return setDBVersion(tx, latestDBVersion) }) }