BanAdmin::validateForm

public BanAdmin::validateForm(array &$form, FormStateInterface $form_state)

public function validateForm(array &$form, FormStateInterface $form_state) {
  $ip = trim($form_state->getValue('ip'));
  if ($this->ipManager->isBanned($ip)) {
    $form_state->setErrorByName('ip', $this->t('This IP address is already banned.'));
  }
  elseif ($ip == $this->getRequest()->getClientIP()) {
    $form_state->setErrorByName('ip', $this->t('You may not ban your own IP address.'));
  }
  elseif (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_RES_RANGE) == FALSE) {
    $form_state->setErrorByName('ip', $this->t('Enter a valid IP address.'));
  }
}