"      op: '__OP_NAME__'"
      "    }"
      "    ret {"
      "      key: 'out'"
      "      value: 'error_op:out'"
      "    }";
  tensorflow::FunctionDef def;
  CHECK(tensorflow::protobuf::TextFormat::ParseFromString(
      tensorflow::str_util::StringReplace(func_str, "__OP_NAME__", op_name,
                                          /*replace_all=*/true),
      &def));
  return def.SerializeAsString();
}