SubmitOnce server-side test/POC

serverside.php

/**
 * Implements hook_civicrm_validateForm().
 *
 * @param string $formName
 * @param array $fields
 * @param array $files
 * @param CRM_Core_Form $form
 * @param array $errors
 */
function serverside_civicrm_validateForm($formName, &$fields, &$files, &$form, &$errors) {
  if (!empty($fields['submit_once_unid'])) {
    // I wouldn't do this here for real, just for POC.
    CRM_Core_DAO::executeQuery("CREATE TABLE IF NOT EXISTS submitted_forms (unid varchar(64) PRIMARY KEY)");

    $sqlParams = array( 1 => array( $fields['submit_once_unid'], 'String' ) );
    $dao = CRM_Core_DAO::executeQuery("SELECT unid FROM submitted_forms WHERE unid = %1", $sqlParams);
    if ($dao->fetch()) {
      if (!empty($dao->unid)) {
        $errors['submit_once_unid'] = ts('Duplicate submitted.');
      }
    }
  }
}

/**
 * Implements hook_civicrm_postProcess().
 *
 * @param string $formName
 * @param CRM_Core_Form $form
 */
function serverside_civicrm_postProcess($formName, &$form) {
  if (!empty($form->_submitValues['submit_once_unid'])) {



    $sqlParams = array( 1 => array( $form->_submitValues['submit_once_unid'], 'String' ) );
    $dao = CRM_Core_DAO::executeQuery("INSERT INTO submitted_forms (unid) VALUES (%1)", $sqlParams);
  }
}

/**
 * Implements hook_civicrm_buildForm().
 *
 * @param string $formName
 * @param CRM_Core_Form $form
 */
function serverside_civicrm_buildForm($formName, &$form) {
  // I wouldn't use uniqid for real. Something better, and ideally compatible with clustering.
  $form->add('hidden', 'submit_once_unid', uniqid());
}

/**
 * TODO: Some cron function to clean up old unids
 */