antispam.module

<?php

/**
 * @file
 * Additions to contact form handling.
 */

use Drupal\Core\Render\Element;
use Symfony\Cmf\Component\Routing\RouteObjectInterface;

/**
 * Implements hook_form_alter().
 */
function antispam_contact_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
  if (isset($form['#entity_type']) && $form['#entity_type'] == 'contact_message' && !in_array($form['#form_id'], ['entity_form_display_edit_form', 'entity_view_display_edit_form'])) {
    // Add our validators.
    $form['#validate'][] = 'antispam_contact_validate';
  }
}

/**
 * Validate contact form submissions.
 */
function antispam_contact_validate(&$form, \Drupal\Core\Form\FormStateInterface $form_state) {
  $values = $form_state->getValues();

  // Really simple spam checks.
  $submission = array();
  // @TODO: Make this automated or configurable.
  $fields = array('field_comments', 'field_email', 'field_name', 'field_organization', 'field_title');
  // Look for these strings in the input.
  // @TODO: Make this configurable.
  $checks = array(
    'Xrumer',
    'michael kors',
    'hotmail.com',
    'yourmail@gmail.com',
    'air jordans',
    'air max',
    'louis vuitton',
    'thin32.info',
    'Cheap goods',
    'Faster and Easier than the SBA',
    'fundingteam+',
    'Elsner Technologies',
  );
  $errors = array();
  foreach ($fields as $field) {
    if (isset($values[$field][0]['value'])) {
      $submission[$field] = trim($values[$field][0]['value']);
      foreach ($checks as $check) {
        if (stristr($submission[$field], $check)) {
          $errors[] = $check;
        }
      }
    }
  }
  // Some spam is just same name / organization.
  if (isset($values['field_name'][0]['value']) && isset($values['field_organization'][0]['value'])) {
    if (trim($values['field_name'][0]['value']) == trim($values['field_organization'][0]['value'])) {
      $errors[] = 'replication';
    }
  }
  // Make sure the form isn't all duplicate values.
  if (count(array_unique($submission)) < 2) {
    $errors[] = 'duplication';
  }
  if (!empty($errors)) {
    $form_state->setErrorByName('form_token', 'An illegal form request has been detected. If the problem persists, please give us a call at the number below.');
  }
}