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interface.go
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interface.go
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// Copyright 2015, Google Inc. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package backupstorage contains the interface and file system implementation
// of the backup system.
package backupstorage
import (
"flag"
"fmt"
"io"
"golang.org/x/net/context"
)
var (
// BackupStorageImplementation is the implementation to use
// for BackupStorage. Exported for test purposes.
BackupStorageImplementation = flag.String("backup_storage_implementation", "", "which implementation to use for the backup storage feature")
)
// BackupHandle describes an individual backup.
type BackupHandle interface {
// Directory is the location of the backup. Will contain keyspace/shard.
Directory() string
// Name is the individual name of the backup. Will contain
// tabletAlias-timestamp.
Name() string
// AddFile opens a new file to be added to the backup.
// Only works for read-write backups (created by StartBackup).
// filename is guaranteed to only contain alphanumerical
// characters and hyphens.
// It should be thread safe, it is possible to call AddFile in
// multiple go routines once a backup has been started.
// The context is valid for the duration of the writes, until the
// WriteCloser is closed.
AddFile(ctx context.Context, filename string) (io.WriteCloser, error)
// EndBackup stops and closes a backup. The contents should be kept.
// Only works for read-write backups (created by StartBackup).
EndBackup(ctx context.Context) error
// AbortBackup stops a backup, and removes the contents that
// have been copied already. It is called if an error occurs
// while the backup is being taken, and the backup cannot be finished.
// Only works for read-write backups (created by StartBackup).
AbortBackup(ctx context.Context) error
// ReadFile starts reading a file from a backup.
// Only works for read-only backups (created by ListBackups).
// The context is valid for the duration of the reads, until the
// ReadCloser is closed.
ReadFile(ctx context.Context, filename string) (io.ReadCloser, error)
}
// BackupStorage is the interface to the storage system
type BackupStorage interface {
// ListBackups returns all the backups in a directory. The
// returned backups are read-only (ReadFile can be called, but
// AddFile/EndBackup/AbortBackup cannot).
// The backups are string-sorted by Name(), ascending (ends up
// being the oldest backup first).
ListBackups(ctx context.Context, dir string) ([]BackupHandle, error)
// StartBackup creates a new backup with the given name. If a
// backup with the same name already exists, it's an error.
// The returned backup is read-write
// (AddFile/EndBackup/AbortBackup can all be called, not
// ReadFile). The provided context is only valid for that
// function, and should not be remembered by the implementation.
StartBackup(ctx context.Context, dir, name string) (BackupHandle, error)
// RemoveBackup removes all the data associated with a backup.
// It will not appear in ListBackups after RemoveBackup succeeds.
RemoveBackup(ctx context.Context, dir, name string) error
// Close frees resources associated with an active backup
// session, such as closing connections. Implementations of
// BackupStorage must support being reused after Close() is called.
Close() error
}
// BackupStorageMap contains the registered implementations for BackupStorage
var BackupStorageMap = make(map[string]BackupStorage)
// GetBackupStorage returns the current BackupStorage implementation.
// Should be called after flags have been initialized.
// When all operations are done, call BackupStorage.Close() to free resources.
func GetBackupStorage() (BackupStorage, error) {
bs, ok := BackupStorageMap[*BackupStorageImplementation]
if !ok {
return nil, fmt.Errorf("no registered implementation of BackupStorage")
}
return bs, nil
}