Add support for manifest list ("fat manifest")

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

docs/storage/manifestlisthandler.go

@@ -0,0 +1,96 @@
+package storage
+
+import (
+	"fmt"
+
+	"encoding/json"
+	"github.com/docker/distribution"
+	"github.com/docker/distribution/context"
+	"github.com/docker/distribution/digest"
+	"github.com/docker/distribution/manifest/manifestlist"
+)
+
+// manifestListHandler is a ManifestHandler that covers schema2 manifest lists.
+type manifestListHandler struct {
+	repository *repository
+	blobStore  *linkedBlobStore
+	ctx        context.Context
+}
+
+var _ ManifestHandler = &manifestListHandler{}
+
+func (ms *manifestListHandler) Unmarshal(ctx context.Context, dgst digest.Digest, content []byte) (distribution.Manifest, error) {
+	context.GetLogger(ms.ctx).Debug("(*manifestListHandler).Unmarshal")
+
+	var m manifestlist.DeserializedManifestList
+	if err := json.Unmarshal(content, &m); err != nil {
+		return nil, err
+	}
+
+	return &m, nil
+}
+
+func (ms *manifestListHandler) Put(ctx context.Context, manifestList distribution.Manifest, skipDependencyVerification bool) (digest.Digest, error) {
+	context.GetLogger(ms.ctx).Debug("(*manifestListHandler).Put")
+
+	m, ok := manifestList.(*manifestlist.DeserializedManifestList)
+	if !ok {
+		return "", fmt.Errorf("wrong type put to manifestListHandler: %T", manifestList)
+	}
+
+	if err := ms.verifyManifest(ms.ctx, *m, skipDependencyVerification); err != nil {
+		return "", err
+	}
+
+	mt, payload, err := m.Payload()
+	if err != nil {
+		return "", err
+	}
+
+	revision, err := ms.blobStore.Put(ctx, mt, payload)
+	if err != nil {
+		context.GetLogger(ctx).Errorf("error putting payload into blobstore: %v", err)
+		return "", err
+	}
+
+	// Link the revision into the repository.
+	if err := ms.blobStore.linkBlob(ctx, revision); err != nil {
+		return "", err
+	}
+
+	return revision.Digest, nil
+}
+
+// verifyManifest ensures that the manifest content is valid from the
+// perspective of the registry. As a policy, the registry only tries to
+// store valid content, leaving trust policies of that content up to
+// consumers.
+func (ms *manifestListHandler) verifyManifest(ctx context.Context, mnfst manifestlist.DeserializedManifestList, skipDependencyVerification bool) error {
+	var errs distribution.ErrManifestVerification
+
+	if !skipDependencyVerification {
+		// This manifest service is different from the blob service
+		// returned by Blob. It uses a linked blob store to ensure that
+		// only manifests are accessible.
+		manifestService, err := ms.repository.Manifests(ctx)
+		if err != nil {
+			return err
+		}
+
+		for _, manifestDescriptor := range mnfst.References() {
+			exists, err := manifestService.Exists(ctx, manifestDescriptor.Digest)
+			if err != nil && err != distribution.ErrBlobUnknown {
+				errs = append(errs, err)
+			}
+			if err != nil || !exists {
+				// On error here, we always append unknown blob errors.
+				errs = append(errs, distribution.ErrManifestBlobUnknown{Digest: manifestDescriptor.Digest})
+			}
+		}
+	}
+	if len(errs) != 0 {
+		return errs
+	}
+
+	return nil
+}