export manifest from tar file (#1046)

Signed-off-by: 刘畅 <basefly@outlook.com>

pkg/v1/tarball/image.go

@@ -70,6 +70,22 @@ func ImageFromPath(path string, tag *name.Tag) (v1.Image, error) {
 	return Image(pathOpener(path), tag)
 }
 
+// LoadManifest load manifest
+func LoadManifest(opener Opener) (Manifest, error) {
+	m, err := extractFileFromTar(opener, "manifest.json")
+	if err != nil {
+		return nil, err
+	}
+	defer m.Close()
+
+	var manifest Manifest
+
+	if err := json.NewDecoder(m).Decode(&manifest); err != nil {
+		return nil, err
+	}
+	return manifest, nil
+}
+
 // Image exposes an image from the tarball at the provided path.
 func Image(opener Opener, tag *name.Tag) (v1.Image, error) {
 	img := &image{

pkg/v1/tarball/image_test.go

@@ -127,3 +127,14 @@ func TestLayerLink(t *testing.T) {
 		t.Errorf("layer.Uncompressed() returned a link file")
 	}
 }
+
+func TestLoadManifest(t *testing.T) {
+
+	manifest, err := LoadManifest(pathOpener("testdata/test_load_manifest.tar"))
+	if err != nil {
+		t.Fatalf("Error load manifest: %v", err)
+	}
+	if len(manifest) == 0 {
+		t.Fatalf("get nothing")
+	}
+}