TF_Status* status) {
  const tensorflow::OpDef* op_def = nullptr;
  status->status =
      tensorflow::OpRegistry::Global()->LookUpOpDef(op_name, &op_def);
  if (!status->status.ok()) return nullptr;

  if (input_index >= op_def->input_arg_size() || input_index < 0) {
    status->status = tensorflow::errors::InvalidArgument(

                      TF_Buffer* output_op_def, TF_Status* status) {
  const OpDef* op_def;
  {
    mutex_lock l(graph->mu);
    status->status = graph->graph.op_registry()->LookUpOpDef(op_name, &op_def);
    if (!status->status.ok()) return;
  }
  status->status = MessageToBuffer(*op_def, output_op_def);
}

void TF_GraphVersions(TF_Graph* graph, TF_Buffer* output_version_def,

  TF_Buffer* buffer = TF_NewBuffer();

  TF_GraphGetOpDef(graph, "Add", buffer, status);
  ASSERT_EQ(TF_OK, TF_GetCode(status));
  const OpDef* expected_op_def;
  TF_ASSERT_OK(OpRegistry::Global()->LookUpOpDef("Add", &expected_op_def));
  string expected_serialized;
  expected_op_def->SerializeToString(&expected_serialized);
  string actual_string(reinterpret_cast<const char*>(buffer->data),