images: move image package to images

Signed-off-by: Stephen J Day <stephen.day@docker.com>

images/image.go

@@ -0,0 +1,88 @@
+package images
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"io/ioutil"
+
+	"github.com/docker/containerd/content"
+	"github.com/docker/containerd/log"
+	digest "github.com/opencontainers/go-digest"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+)
+
+// Image provides the model for how containerd views container images.
+type Image struct {
+	Name       string
+	Descriptor ocispec.Descriptor
+}
+
+// TODO(stevvooe): Many of these functions make strong platform assumptions,
+// which are untrue in a lot of cases. More refactoring must be done here to
+// make this work in all cases.
+
+// Config resolves the image configuration descriptor.
+//
+// The caller can then use the descriptor to resolve and process the
+// configuration of the image.
+func (image *Image) Config(ctx context.Context, provider content.Provider) (ocispec.Descriptor, error) {
+	var configDesc ocispec.Descriptor
+	return configDesc, Walk(ctx, HandlerFunc(func(ctx context.Context, desc ocispec.Descriptor) ([]ocispec.Descriptor, error) {
+		switch image.Descriptor.MediaType {
+		case MediaTypeDockerSchema2Manifest, ocispec.MediaTypeImageManifest:
+			rc, err := provider.Reader(ctx, image.Descriptor.Digest)
+			if err != nil {
+				return nil, err
+			}
+			defer rc.Close()
+
+			p, err := ioutil.ReadAll(rc)
+			if err != nil {
+				return nil, err
+			}
+
+			var manifest ocispec.Manifest
+			if err := json.Unmarshal(p, &manifest); err != nil {
+				return nil, err
+			}
+
+			configDesc = manifest.Config
+
+			return nil, nil
+		default:
+			return nil, errors.New("could not resolve config")
+		}
+
+	}), image.Descriptor)
+}
+
+// RootFS returns the unpacked diffids that make up and images rootfs.
+//
+// These are used to verify that a set of layers unpacked to the expected
+// values.
+func (image *Image) RootFS(ctx context.Context, provider content.Provider) ([]digest.Digest, error) {
+	desc, err := image.Config(ctx, provider)
+	if err != nil {
+		return nil, err
+	}
+
+	p, err := content.ReadBlob(ctx, provider, desc.Digest)
+	if err != nil {
+		log.G(ctx).Fatal(err)
+	}
+
+	var config ocispec.Image
+	if err := json.Unmarshal(p, &config); err != nil {
+		log.G(ctx).Fatal(err)
+	}
+
+	// TODO(stevvooe): Remove this bit when OCI structure uses correct type for
+	// rootfs.DiffIDs.
+	var diffIDs []digest.Digest
+	for _, diffID := range config.RootFS.DiffIDs {
+		diffIDs = append(diffIDs, digest.Digest(diffID))
+	}
+
+	return diffIDs, nil
+}