fix: excessive memory usage (#2164)

instead of reading entire files before calculating their digests
stream them by using their Reader method.

Signed-off-by: Petu Eusebiu <peusebiu@cisco.com>

pkg/test/mocks/image_store_mock.go

@@ -59,6 +59,7 @@ type MockedImageStore struct {
 	PutIndexContentFn            func(repo string, index ispec.Index) error
 	PopulateStorageMetricsFn     func(interval time.Duration, sch *scheduler.Scheduler)
 	StatIndexFn                  func(repo string) (bool, int64, time.Time, error)
+	VerifyBlobDigestValueFn      func(repo string, digest godigest.Digest) error
 }
 
 func (is MockedImageStore) StatIndex(repo string) (bool, int64, time.Time, error) {
@@ -425,3 +426,11 @@ func (is MockedImageStore) PopulateStorageMetrics(interval time.Duration, sch *s
 		is.PopulateStorageMetricsFn(interval, sch)
 	}
 }
+
+func (is MockedImageStore) VerifyBlobDigestValue(repo string, digest godigest.Digest) error {
+	if is.VerifyBlobDigestValueFn != nil {
+		return is.VerifyBlobDigestValueFn(repo, digest)
+	}
+
+	return nil
+}