PushBlobStep.java

class PushBlobStep implements AsyncStep<BlobDescriptor>, Callable<BlobDescriptor> {
/*(...)*/
  public BlobDescriptor call() throws IOException, RegistryException, ExecutionException {
    /*(...)*/

      RegistryClient registryClient =/*(...)*/
      if (registryClient.checkBlob(blobDescriptor.getDigest()) != null) {
        /*(...)*/
        return blobDescriptor;
      }

      registryClient.pushBlob(blobDescriptor.getDigest(), blob);
      return blobDescriptor;
    }
  }
}