content: change Writer/ReaderAt to take OCI

This change allows implementations to resolve the location of the actual data
using OCI descriptor fields such as MediaType.

No OCI descriptor field is written to the store.

No change on gRPC API.

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

images/oci/exporter.go

@@ -93,7 +93,7 @@ func blobRecord(cs content.Provider, desc ocispec.Descriptor) tarRecord {
 			Typeflag: tar.TypeReg,
 		},
 		CopyTo: func(ctx context.Context, w io.Writer) (int64, error) {
-			r, err := cs.ReaderAt(ctx, desc.Digest)
+			r, err := cs.ReaderAt(ctx, desc)
 			if err != nil {
 				return 0, err
 			}

images/oci/importer.go

@@ -140,7 +140,7 @@ func onUntarBlob(ctx context.Context, r io.Reader, store content.Ingester, name
 		return errors.Errorf("unsupported algorithm: %s", algo)
 	}
 	dgst := digest.NewDigestFromHex(algo.String(), split[2])
-	return content.WriteBlob(ctx, store, "unknown-"+dgst.String(), r, size, dgst)
+	return content.WriteBlob(ctx, store, "unknown-"+dgst.String(), r, ocispec.Descriptor{Size: size, Digest: dgst})
 }
 
 // GetChildrenDescriptors returns children blob descriptors for the following supported types:
@@ -175,7 +175,7 @@ func setGCRefContentLabels(ctx context.Context, store content.Store, desc ocispe
 		}
 		return err
 	}
-	ra, err := store.ReaderAt(ctx, desc.Digest)
+	ra, err := store.ReaderAt(ctx, desc)
 	if err != nil {
 		return err
 	}