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// Copyright (c) 2012, Suryandaru Triandana <syndtr@gmail.com>
// All rights reserved.
//
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Package storage provides storage abstraction for LevelDB.
package storage
import (
"errors"
"fmt"
"io"
)
// FileType represent a file type.
type FileType int
// File types.
const (
TypeManifest FileType = 1 << iota
TypeJournal
TypeTable
TypeTemp
TypeAll = TypeManifest | TypeJournal | TypeTable | TypeTemp
)
func (t FileType) String() string {
switch t {
case TypeManifest:
return "manifest"
case TypeJournal:
return "journal"
case TypeTable:
return "table"
case TypeTemp:
return "temp"
}
return fmt.Sprintf("<unknown:%d>", t)
}
// Common error.
var (
ErrInvalidFile = errors.New("leveldb/storage: invalid file for argument")
ErrLocked = errors.New("leveldb/storage: already locked")
ErrClosed = errors.New("leveldb/storage: closed")
)
// ErrCorrupted is the type that wraps errors that indicate corruption of
// a file. Package storage has its own type instead of using
// errors.ErrCorrupted to prevent circular import.
type ErrCorrupted struct {
Fd FileDesc
Err error
}
func (e *ErrCorrupted) Error() string {
if !e.Fd.Zero() {
return fmt.Sprintf("%v [file=%v]", e.Err, e.Fd)
}
return e.Err.Error()
}
// Syncer is the interface that wraps basic Sync method.
type Syncer interface {
// Sync commits the current contents of the file to stable storage.
Sync() error
}
// Reader is the interface that groups the basic Read, Seek, ReadAt and Close
// methods.
type Reader interface {
io.ReadSeeker
io.ReaderAt
io.Closer
}
// Writer is the interface that groups the basic Write, Sync and Close
// methods.
type Writer interface {
io.WriteCloser
Syncer
}
// Locker is the interface that wraps Unlock method.
type Locker interface {
Unlock()
}
// FileDesc is a 'file descriptor'.
type FileDesc struct {
Type FileType
Num int64
}
func (fd FileDesc) String() string {
switch fd.Type {
case TypeManifest:
return fmt.Sprintf("MANIFEST-%06d", fd.Num)
case TypeJournal:
return fmt.Sprintf("%06d.log", fd.Num)
case TypeTable:
return fmt.Sprintf("%06d.ldb", fd.Num)
case TypeTemp:
return fmt.Sprintf("%06d.tmp", fd.Num)
default:
return fmt.Sprintf("%#x-%d", fd.Type, fd.Num)
}
}
// Zero returns true if fd == (FileDesc{}).
func (fd FileDesc) Zero() bool {
return fd == (FileDesc{})
}
// FileDescOk returns true if fd is a valid 'file descriptor'.
func FileDescOk(fd FileDesc) bool {
switch fd.Type {
case TypeManifest:
case TypeJournal:
case TypeTable:
case TypeTemp:
default:
return false
}
return fd.Num >= 0
}
// Storage is the storage. A storage instance must be safe for concurrent use.
type Storage interface {
// Lock locks the storage. Any subsequent attempt to call Lock will fail
// until the last lock released.
// Caller should call Unlock method after use.
Lock() (Locker, error)
// Log logs a string. This is used for logging.
// An implementation may write to a file, stdout or simply do nothing.
Log(str string)
// SetMeta store 'file descriptor' that can later be acquired using GetMeta
// method. The 'file descriptor' should point to a valid file.
// SetMeta should be implemented in such way that changes should happen
// atomically.
SetMeta(fd FileDesc) error
// GetMeta returns 'file descriptor' stored in meta. The 'file descriptor'
// can be updated using SetMeta method.
// Returns os.ErrNotExist if meta doesn't store any 'file descriptor', or
// 'file descriptor' point to nonexistent file.
GetMeta() (FileDesc, error)
// List returns file descriptors that match the given file types.
// The file types may be OR'ed together.
List(ft FileType) ([]FileDesc, error)
// Open opens file with the given 'file descriptor' read-only.
// Returns os.ErrNotExist error if the file does not exist.
// Returns ErrClosed if the underlying storage is closed.
Open(fd FileDesc) (Reader, error)
// Create creates file with the given 'file descriptor', truncate if already
// exist and opens write-only.
// Returns ErrClosed if the underlying storage is closed.
Create(fd FileDesc) (Writer, error)
// Remove removes file with the given 'file descriptor'.
// Returns ErrClosed if the underlying storage is closed.
Remove(fd FileDesc) error
// Rename renames file from oldfd to newfd.
// Returns ErrClosed if the underlying storage is closed.
Rename(oldfd, newfd FileDesc) error
// Close closes the storage.
// It is valid to call Close multiple times. Other methods should not be
// called after the storage has been closed.
Close() error
}
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