feat(cache): cacheable v1.ImageIndex (#1380)

Co-authored-by: Eric Stroczynski <estroz@slim.ai>

pkg/v1/cache/cache.go

@@ -156,3 +156,39 @@ func (i *image) LayerByDiffID(h v1.Hash) (v1.Layer, error) {
 	}
 	return l, err
 }
+
+// ImageIndex returns a new ImageIndex which wraps the given ImageIndex's
+// children with either Image(child, c) or ImageIndex(child, c) depending on type.
+func ImageIndex(ii v1.ImageIndex, c Cache) v1.ImageIndex {
+	return &imageIndex{
+		inner: ii,
+		c:     c,
+	}
+}
+
+type imageIndex struct {
+	inner v1.ImageIndex
+	c     Cache
+}
+
+func (ii *imageIndex) MediaType() (types.MediaType, error)       { return ii.inner.MediaType() }
+func (ii *imageIndex) Digest() (v1.Hash, error)                  { return ii.inner.Digest() }
+func (ii *imageIndex) Size() (int64, error)                      { return ii.inner.Size() }
+func (ii *imageIndex) IndexManifest() (*v1.IndexManifest, error) { return ii.inner.IndexManifest() }
+func (ii *imageIndex) RawManifest() ([]byte, error)              { return ii.inner.RawManifest() }
+
+func (ii *imageIndex) Image(h v1.Hash) (v1.Image, error) {
+	i, err := ii.inner.Image(h)
+	if err != nil {
+		return nil, err
+	}
+	return Image(i, ii.c), nil
+}
+
+func (ii *imageIndex) ImageIndex(h v1.Hash) (v1.ImageIndex, error) {
+	idx, err := ii.inner.ImageIndex(h)
+	if err != nil {
+		return nil, err
+	}
+	return ImageIndex(idx, ii.c), nil
+}

pkg/v1/cache/cache_test.go

@@ -21,6 +21,7 @@ import (
 	"testing"
 
 	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/mutate"
 	"github.com/google/go-containerregistry/pkg/v1/random"
 	"github.com/google/go-containerregistry/pkg/v1/validate"
 )
@@ -42,6 +43,30 @@ func TestImage(t *testing.T) {
 	}
 }
 
+func TestImageIndex(t *testing.T) {
+	// ImageIndex with child Image and ImageIndex manifests.
+	ii, err := random.Index(1024, 5, 2)
+	if err != nil {
+		t.Fatalf("random.Index: %v", err)
+	}
+	iiChild, err := random.Index(1024, 5, 2)
+	if err != nil {
+		t.Fatalf("random.Index: %v", err)
+	}
+	ii = mutate.AppendManifests(ii, mutate.IndexAddendum{Add: iiChild})
+
+	m := &memcache{map[v1.Hash]v1.Layer{}}
+	ii = ImageIndex(ii, m)
+
+	// Validate twice to hit the cache.
+	if err := validate.Index(ii); err != nil {
+		t.Errorf("Validate: %v", err)
+	}
+	if err := validate.Index(ii); err != nil {
+		t.Errorf("Validate: %v", err)
+	}
+}
+
 func TestLayersLazy(t *testing.T) {
 	img, err := random.Image(1024, 5)
 	if err != nil {