NodeForm::save

public NodeForm::save(array $form, FormStateInterface $form_state)

public function save(array $form, FormStateInterface $form_state) {
  $node = $this->entity;
  $insert = $node->isNew();
  $node->save();
  $node_link = $node->link($this->t('View'));
  $context = array('@type' => $node->getType(), '%title' => $node->label(), 'link' => $node_link);
  $t_args = array('@type' => node_get_type_label($node), '%title' => $node->link($node->label()));

  if ($insert) {
    $this->logger('content')->notice('@type: added %title.', $context);
    drupal_set_message(t('@type %title has been created.', $t_args));
  }
  else {
    $this->logger('content')->notice('@type: updated %title.', $context);
    drupal_set_message(t('@type %title has been updated.', $t_args));
  }

  if ($node->id()) {
    $form_state->setValue('nid', $node->id());
    $form_state->set('nid', $node->id());
    if ($node->access('view')) {
      $form_state->setRedirect(
      'entity.node.canonical', 
      array('node' => $node->id())
      );
    }
    else {
      $form_state->setRedirect('<front>');
    }

    // Remove the preview entry from the temp store, if any.
    $store = $this->tempStoreFactory->get('node_preview');
    $store->delete($node->uuid());
  }
  else {
    // In the unlikely case something went wrong on save, the node will be
    // rebuilt and node form redisplayed the same way as in preview.
    drupal_set_message(t('The post could not be saved.'), 'error');
    $form_state->setRebuild();
  }
}