code: def _op_msg_compressed(flags, command, identifier, docs, check_keys, opts,
                         ctx):
      
      msg, total_size, max_bson_size = _op_msg_no_header(
          flags, command, identifier, docs, check_keys, opts)
      rid, msg = _compress(2013, msg, ctx)
      return rid, msg, total_size, max_bson_size
docs: Internal OP_MSG message helper.