Trying to plug a tar.Reader into fs.FS

tarfs.go

package main

import (
	"archive/tar"
	"errors"
	"io"
	"io/fs"
	"log"
	"os"
	"path/filepath"
)

func main() {
	fn := os.Args[1]
	f, err := os.Open(fn)
	if err != nil {
		log.Fatal(err)
	}

	tr := tar.NewReader(f)
	if err := fs.WalkDir(FSFromTar(tr), "cmd/", func(path string, _ fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		log.Println(path)
		return nil
	}); err != nil {
		log.Fatal(err)
	}
}

func FSFromTar(tr *tar.Reader) fs.FS { return &fss{tr} }

type fss struct{ tr *tar.Reader }

func (f *fss) Open(n string) (fs.File, error) {
	n = filepath.Clean(n)
	for {
		h, err := f.tr.Next()
		if err == io.EOF {
			return nil, errors.New("file not found")
		}
		if err != nil {
			return nil, err
		}

		if filepath.Clean(h.Name) == n {
			return file{h, f.tr}, nil
		}
	}
}

type file struct {
	h *tar.Header
	r io.Reader
}

func (f file) Stat() (fs.FileInfo, error) {
	return f.h.FileInfo(), nil
}

func (f file) Read(b []byte) (int, error) {
	return f.r.Read(b)
}

func (f file) Close() error {
	return nil
}