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>

client_test.go

@@ -214,7 +214,7 @@ func TestImagePullAllPlatforms(t *testing.T) {
 		}
 		// check if childless data type has blob in content store
 		for _, desc := range children {
-			ra, err := cs.ReaderAt(ctx, desc.Digest)
+			ra, err := cs.ReaderAt(ctx, desc)
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -275,7 +275,7 @@ func TestImagePullSomePlatforms(t *testing.T) {
 
 			// check if childless data type has blob in content store
 			for _, desc := range children {
-				ra, err := cs.ReaderAt(ctx, desc.Digest)
+				ra, err := cs.ReaderAt(ctx, desc)
 				if err != nil {
 					t.Fatal(err)
 				}