Function subFS

echo.go:896–911

(currentFs fs.FS, root string)

}

func subFS(currentFs fs.FS, root string) (fs.FS, error) {
	root = filepath.ToSlash(filepath.Clean(root)) // note: fs.FS operates only with slashes. `ToSlash` is necessary for Windows
	if dFS, ok := currentFs.(*defaultFS); ok {
		// we need to make exception for `defaultFS` instances as it interprets root prefix differently from fs.FS.
		// fs.Fs.Open does not like relative paths ("./", "../") and absolute paths at all but prior echo.Filesystem we
		// were able to use paths like `./myfile.log`, `/etc/hosts` and these would work fine with `os.Open` but not with fs.Fs
		if !filepath.IsAbs(root) {
			root = filepath.Join(dFS.prefix, root)
		}
		return &defaultFS{
			prefix: root,
			fs:     os.DirFS(root),
		}, nil
	}
	return fs.Sub(currentFs, root)
}

// MustSubFS creates sub FS from current filesystem or panic on failure.
// Panic happens when `fsRoot` contains invalid path according to `fs.ValidPath` rules.