fs: Skip files named . during walk (#384)

This happens from tar files being created in their target directory, apparently.
Avoid infinite walk. Fix #383.

* Cleaning up directories containing dots

* Cleaning up some debug bits

* More descriptive tests

* Update fs.go

Updating per suggestion, looks great!

Co-authored-by: Matt Holt <mholt@users.noreply.github.com>

* Update fs.go

---------

Co-authored-by: Matt Holt <mholt@users.noreply.github.com>

fs.go

@@ -567,6 +567,9 @@ func (f ArchiveFS) ReadDir(name string) ([]fs.DirEntry, error) {
 	)
 	handler := func(_ context.Context, file File) error {
 		file.NameInArchive = strings.Trim(file.NameInArchive, "/")
+		if file.NameInArchive == "." {
+			return nil
+		}
 		files = append(files, file)
 		if file.NameInArchive == name && !file.IsDir() {
 			foundFile = true

fs_test.go

@@ -8,6 +8,7 @@ import (
 	"io/fs"
 	"log"
 	"net/http"
+	"os"
 	"path"
 	"reflect"
 	"sort"
@@ -53,6 +54,34 @@ var (
 	unorderZip []byte
 )
 
+func TestSelfTar(t *testing.T) {
+	fn := "testdata/self-tar.tar"
+	fh, err := os.Open(fn)
+	if err != nil {
+		t.Fatalf("Could not load test tar: %v", fn)
+	}
+	fstat, err := os.Stat(fn)
+	if err != nil {
+		t.Fatalf("Could not stat test tar: %v", fn)
+	}
+	fsys := ArchiveFS{
+		Stream: io.NewSectionReader(fh, 0, fstat.Size()),
+		Format: Tar{},
+	}
+	var count int
+	err = fs.WalkDir(fsys, ".", func(path string, d fs.DirEntry, err error) error {
+		if count > 10 {
+			t.Error("walking test tar appears to be recursing in error")
+			return fmt.Errorf("recursing tar: %v", fn)
+		}
+		count++
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
 func ExampleArchiveFS_Stream() {
 	fsys := ArchiveFS{
 		Stream: io.NewSectionReader(bytes.NewReader(testZIP), 0, int64(len(testZIP))),