def gcs_url_for_backup_directory(backup_bucket_name, fuzzer_name,
                                 project_qualified_target_name):
  """Build GCS URL for corpus backup directory.

  Returns:
    A string giving the GCS URL.
  """
  return 'gs://%s/corpus/%s/%s/' % (backup_bucket_name, fuzzer_name,
                                    project_qualified_target_name)