1 files changed, 161 insertions, 0 deletions
diff --git a/pkg/v1/layout/index.go b/pkg/v1/layout/index.go
new file mode 100644
index 0000000..7404f18
--- /dev/null
+++ b/pkg/v1/layout/index.go
@@ -0,0 +1,161 @@
+// Copyright 2018 Google LLC All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package layout
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+
+	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/partial"
+	"github.com/google/go-containerregistry/pkg/v1/types"
+)
+
+var _ v1.ImageIndex = (*layoutIndex)(nil)
+
+type layoutIndex struct {
+	mediaType types.MediaType
+	path      Path
+	rawIndex  []byte
+}
+
+// ImageIndexFromPath is a convenience function which constructs a Path and returns its v1.ImageIndex.
+func ImageIndexFromPath(path string) (v1.ImageIndex, error) {
+	lp, err := FromPath(path)
+	if err != nil {
+		return nil, err
+	}
+	return lp.ImageIndex()
+}
+
+// ImageIndex returns a v1.ImageIndex for the Path.
+func (l Path) ImageIndex() (v1.ImageIndex, error) {
+	rawIndex, err := os.ReadFile(l.path("index.json"))
+	if err != nil {
+		return nil, err
+	}
+
+	idx := &layoutIndex{
+		mediaType: types.OCIImageIndex,
+		path:      l,
+		rawIndex:  rawIndex,
+	}
+
+	return idx, nil
+}
+
+func (i *layoutIndex) MediaType() (types.MediaType, error) {
+	return i.mediaType, nil
+}
+
+func (i *layoutIndex) Digest() (v1.Hash, error) {
+	return partial.Digest(i)
+}
+
+func (i *layoutIndex) Size() (int64, error) {
+	return partial.Size(i)
+}
+
+func (i *layoutIndex) IndexManifest() (*v1.IndexManifest, error) {
+	var index v1.IndexManifest
+	err := json.Unmarshal(i.rawIndex, &index)
+	return &index, err
+}
+
+func (i *layoutIndex) RawManifest() ([]byte, error) {
+	return i.rawIndex, nil
+}
+
+func (i *layoutIndex) Image(h v1.Hash) (v1.Image, error) {
+	// Look up the digest in our manifest first to return a better error.
+	desc, err := i.findDescriptor(h)
+	if err != nil {
+		return nil, err
+	}
+
+	if !isExpectedMediaType(desc.MediaType, types.OCIManifestSchema1, types.DockerManifestSchema2) {
+		return nil, fmt.Errorf("unexpected media type for %v: %s", h, desc.MediaType)
+	}
+
+	img := &layoutImage{
+		path: i.path,
+		desc: *desc,
+	}
+	return partial.CompressedToImage(img)
+}
+
+func (i *layoutIndex) ImageIndex(h v1.Hash) (v1.ImageIndex, error) {
+	// Look up the digest in our manifest first to return a better error.
+	desc, err := i.findDescriptor(h)
+	if err != nil {
+		return nil, err
+	}
+
+	if !isExpectedMediaType(desc.MediaType, types.OCIImageIndex, types.DockerManifestList) {
+		return nil, fmt.Errorf("unexpected media type for %v: %s", h, desc.MediaType)
+	}
+
+	rawIndex, err := i.path.Bytes(h)
+	if err != nil {
+		return nil, err
+	}
+
+	return &layoutIndex{
+		mediaType: desc.MediaType,
+		path:      i.path,
+		rawIndex:  rawIndex,
+	}, nil
+}
+
+func (i *layoutIndex) Blob(h v1.Hash) (io.ReadCloser, error) {
+	return i.path.Blob(h)
+}
+
+func (i *layoutIndex) findDescriptor(h v1.Hash) (*v1.Descriptor, error) {
+	im, err := i.IndexManifest()
+	if err != nil {
+		return nil, err
+	}
+
+	if h == (v1.Hash{}) {
+		if len(im.Manifests) != 1 {
+			return nil, errors.New("oci layout must contain only a single image to be used with layout.Image")
+		}
+		return &(im.Manifests)[0], nil
+	}
+
+	for _, desc := range im.Manifests {
+		if desc.Digest == h {
+			return &desc, nil
+		}
+	}
+
+	return nil, fmt.Errorf("could not find descriptor in index: %s", h)
+}
+
+// TODO: Pull this out into methods on types.MediaType? e.g. instead, have:
+// * mt.IsIndex()
+// * mt.IsImage()
+func isExpectedMediaType(mt types.MediaType, expected ...types.MediaType) bool {
+	for _, allowed := range expected {
+		if mt == allowed {
+			return true
+		}
+	}
+	return false
+}