fix: update error returned when oci.NewFromTar is used with a non-tar file

content/oci/readonlyoci_test.go

@@ -36,6 +36,7 @@ import (
 	"oras.land/oras-go/v2"
 	"oras.land/oras-go/v2/content"
 	"oras.land/oras-go/v2/content/memory"
+	"oras.land/oras-go/v2/errdef"
 	"oras.land/oras-go/v2/internal/docker"
 	"oras.land/oras-go/v2/internal/spec"
 	"oras.land/oras-go/v2/registry"
@@ -836,3 +837,22 @@ func Test_deleteAnnotationRefName(t *testing.T) {
 		})
 	}
 }
+
+func TestNewFromTar_NonTarFile(t *testing.T) {
+
+	emptyfile := "testdata/emptyfile"
+	nonemptyfile := "testdata/nonempty.tar"
+
+	_, err := NewFromTar(context.Background(), emptyfile)
+
+	if want := errdef.ErrNotTarFile; !errors.Is(err, want) {
+		t.Errorf("OCI.NewFromTar(%s) error = %v, wantErr %v", emptyfile, err, want)
+	}
+
+	_, err = NewFromTar(context.Background(), nonemptyfile)
+
+	if want := errdef.ErrNotTarFile; !errors.Is(err, want) {
+		t.Errorf("OCI.NewFromTar(%s) error = %v, wantErr %v", nonemptyfile, err, want)
+	}
+
+}

content/oci/testdata/nonempty.tar

@@ -0,0 +1 @@
+non-empty file

errdef/errors.go

@@ -28,4 +28,5 @@ var (
 	ErrSizeExceedsLimit   = errors.New("size exceeds limit")
 	ErrUnsupported        = errors.New("unsupported")
 	ErrUnsupportedVersion = errors.New("unsupported version")
+	ErrNotTarFile         = errors.New("non-empty tar file expected")
 )

internal/fs/tarfs/tarfs.go

@@ -48,6 +48,7 @@ func New(path string) (*TarFS, error) {
 	if err != nil {
 		return nil, fmt.Errorf("failed to resolve absolute path for %s: %w", path, err)
 	}
+
 	tarfs := &TarFS{
 		path:    pathAbs,
 		entries: make(map[string]*entry),
@@ -135,8 +136,16 @@ func (tfs *TarFS) indexEntries() error {
 		header, err := tr.Next()
 		if err != nil {
 			if errors.Is(err, io.EOF) {
+				if len(tfs.entries) == 0 {
+					// indicates the given file is empty
+					return errdef.ErrNotTarFile
+				}
 				break
 			}
+			if errors.Is(err, io.ErrUnexpectedEOF) {
+				// indicates that its either not a tarfile or it is a corrupted one
+				return errdef.ErrNotTarFile
+			}
 			return err
 		}
 		pos, err := tarFile.Seek(0, io.SeekCurrent)

internal/fs/tarfs/tarfs_test.go

@@ -268,3 +268,28 @@ func TestTarFS_Stat_Unsupported(t *testing.T) {
 		}
 	}
 }
+
+func TestTarFS_New_NonTarFile(t *testing.T) {
+
+	emptyfile := "testdata/emptyfile.tar"
+	nonemptyfile := "testdata/nonempty.tar"
+	tarwithoutextension := "testdata/tarwithoutextension"
+
+	_, err := New(emptyfile)
+
+	if want := errdef.ErrNotTarFile; !errors.Is(err, want) {
+		t.Errorf("TarFS.New(%s) error = %v, wantErr %v", emptyfile, err, want)
+	}
+
+	_, err = New(nonemptyfile)
+
+	if want := errdef.ErrNotTarFile; !errors.Is(err, want) {
+		t.Errorf("TarFS.New(%s) error = %v, wantErr %v", nonemptyfile, err, want)
+	}
+
+	_, err = New(tarwithoutextension)
+
+	if err != nil {
+		t.Errorf("TarFS.New(%s) error = %v, wantErr %v", tarwithoutextension, err, nil)
+	}
+}

internal/fs/tarfs/testdata/nonempty.tar

@@ -0,0 +1 @@
+non-empty file