storage

type ErrCorrupted struct {
	Fd  FileDesc
	Err error
}

type FileDesc struct {
	Type FileType
	Num  int64
}

type FileType int

type Lock interface {
	util.Releaser
}

type Reader interface {
	io.ReadSeeker
	io.ReaderAt
	io.Closer
}

type Storage interface {
	// Lock locks the storage. Any subsequent attempt to call Lock will fail
	// until the last lock released.
	// After use the caller should call the Release method.
	Lock() (Lock, 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 sets to point to the given fd, which then can be acquired using
	// GetMeta method.
	// SetMeta should be implemented in such way that changes should happened
	// atomically.
	SetMeta(fd FileDesc) error

	// GetManifest returns a manifest file.
	// Returns os.ErrNotExist if meta doesn't point to any fd, or point to fd
	// that doesn't exist.
	GetMeta() (FileDesc, error)

	// List returns fds 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 fd 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 fd, 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 fd.
	// 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
}

type Syncer interface {
	// Sync commits the current contents of the file to stable storage.
	Sync() error
}

type Writer interface {
	io.WriteCloser
	Syncer
}