vfs

type File interface {
	io.Reader
	io.Writer
	io.Seeker
	io.Closer

	ReadAt(p []byte, off int64) (n int, err error)
	WriteAt(p []byte, off int64) (n int, err error)

	// Sync commits the file's contents to stable storage. A driver that
	// simulates a power cut discards everything not yet passed to Sync.
	Sync() error

	// Truncate changes the file's size.
	Truncate(size int64) error

	// Name returns the name the file was opened with.
	Name() string
}

type FileSystem interface {
	// Open opens a file with the semantics of os.OpenFile.
	Open(name string, flag int, perm os.FileMode) (File, error)

	// Remove deletes a file, with the semantics of os.Remove.
	Remove(name string) error

	// Rename moves a file, with the semantics of os.Rename. graphdb relies on
	// this being atomic on POSIX for snapshot and WAL rotation, so an
	// implementation that cannot offer atomicity must say so in its docs.
	Rename(oldpath, newpath string) error

	// Stat returns file metadata, with the semantics of os.Stat.
	Stat(name string) (os.FileInfo, error)

	// MkdirAll creates a directory tree, with the semantics of os.MkdirAll.
	MkdirAll(path string, perm os.FileMode) error

	// ReadDir lists a directory, with the semantics of os.ReadDir.
	//
	// Added when pkg/lsm became the second caller: it enumerates its SSTables,
	// and a driver that cannot fail a directory listing cannot test what
	// happens when that listing fails. The method set is the intersection of
	// what callers actually use, so the intersection grew.
	ReadDir(name string) ([]os.DirEntry, error)

	// Name identifies the driver, for diagnostics and for tests that assert
	// which driver is installed. "os" is the default.
	Name() string
}

type Mapper interface {
	// Map returns the file's entire contents and a function that releases them.
	//
	// The bytes stay valid until release is called, and the caller must not
	// retain them afterwards. Callers must call release exactly once, even
	// when they only read part of the data.
	//
	// A driver that cannot map returns ErrMapUnsupported, and the caller falls
	// back to reading the file through Open.
	Map(name string) (data []byte, release func() error, err error)
}