go/src/io/fs/sub.go

type SubFS …

// Sub returns an [FS] corresponding to the subtree rooted at fsys's dir.
//
// If dir is ".", Sub returns fsys unchanged.
// Otherwise, if fs implements [SubFS], Sub returns fsys.Sub(dir).
// Otherwise, Sub returns a new [FS] implementation sub that,
// in effect, implements sub.Open(name) as fsys.Open(path.Join(dir, name)).
// The implementation also translates calls to ReadDir, ReadFile, and Glob appropriately.
//
// Note that Sub(os.DirFS("/"), "prefix") is equivalent to os.DirFS("/prefix")
// and that neither of them guarantees to avoid operating system
// accesses outside "/prefix", because the implementation of [os.DirFS]
// does not check for symbolic links inside "/prefix" that point to
// other directories. That is, [os.DirFS] is not a general substitute for a
// chroot-style security mechanism, and Sub does not change that fact.
func Sub(fsys FS, dir string) (FS, error) { … }

type subFS …

// fullName maps name to the fully-qualified name dir/name.
func (f *subFS) fullName(op string, name string) (string, error) { … }

// shorten maps name, which should start with f.dir, back to the suffix after f.dir.
func (f *subFS) shorten(name string) (rel string, ok bool) { … }

// fixErr shortens any reported names in PathErrors by stripping f.dir.
func (f *subFS) fixErr(err error) error { … }

func (f *subFS) Open(name string) (File, error) { … }

func (f *subFS) ReadDir(name string) ([]DirEntry, error) { … }

func (f *subFS) ReadFile(name string) ([]byte, error) { … }

func (f *subFS) Glob(pattern string) ([]string, error) { … }

func (f *subFS) Sub(dir string) (FS, error) { … }