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phrase_captcha.module in CAPTCHA Pack 8

Implementation of a phrase based CAPTCHA, for use with the CAPTCHA module.

@todo: add character picking of current word, which is harder for spam bots than plain word guessing.

File

text_captcha/modules/phrase_captcha/phrase_captcha.module
View source 
<?php

/**
 * @file
 * Implementation of a phrase based CAPTCHA, for use with the CAPTCHA module.
 *
 * @todo: add character picking of current word, which is harder for spam bots
 * than plain word guessing.
 */
define('PHRASE_CAPTCHA_GENERATE_NONSENSE_WORDS', 0);
define('PHRASE_CAPTCHA_USER_DEFINED_WORDS', 1);

/**
 * Implements hook_help().
 */
function phrase_captcha_help($path, $arg) {
  switch ($path) {
    case 'admin/config/people/captcha/phrase_captcha':
      return '<p>' . t('This phrase based CAPTCHA presents a CAPTCHA phrase of a given number of words and asks to pick the right word (based on counting, alphabetical order, etc).') . '</p>';
  }
}

/**
 * Implements hook_captcha().
 */
function phrase_captcha_captcha($op, $captcha_type = '') {
  $config = \Drupal::config('phrase_captcha.settings');
  switch ($op) {
    case 'list':
      return [
        'Phrase CAPTCHA',
      ];
    case 'generate':
      if ($captcha_type == 'Phrase CAPTCHA') {

        // Generate words.
        $words = _phrase_captcha_generate_words($config
          ->get('phrase_captcha_word_quantity'));

        // Pick a random word selection challenge.
        $word_challenges = _phrase_captcha_enabled_word_challenges();
        $key = array_rand($word_challenges);
        $function = $word_challenges[$key];
        list($phrase_words, $question, $solution) = call_user_func($function, $words);

        // Build options list.
        $all_words = array_merge($words, _phrase_captcha_generate_words($config
          ->get('phrase_captcha_additional_word_quantity')));
        shuffle($all_words);
        $options = [];
        foreach ($all_words as $word) {
          $options[$word] = $word;
        }

        // Store the answer and build the form elements.
        $captcha = [];
        $captcha['solution'] = $solution;
        $captcha['form']['captcha_phrase'] = [
          '#type' => 'markup',
          '#value' => '"' . implode(' ', $phrase_words) . '"',
          '#weight' => -2,
        ];
        $captcha['form']['captcha_response'] = [
          '#type' => 'radios',
          '#title' => $question,
          '#options' => $options,
          // Extra class needed for additional CSS'ing of the options.
          '#attributes' => [
            'class' => [
              'text-captcha-word-list-radios',
            ],
          ],
          // The following entry '#DANGEROUS_SKIP_CHECK' is needed to prevent
          // that Drupal checks during validation phase if a submitted option
          // is in the list of possible options. (see includes/form.inc)
          // The options are randomly generated on each call and consequently
          // almost never the same during the generate phase and the validation
          // phase.
          //
          '#DANGEROUS_SKIP_CHECK' => TRUE,
          '#required' => TRUE,
          '#cache' => [
            'max-age' => 0,
          ],
        ];
        \Drupal::service('page_cache_kill_switch')
          ->trigger();

        // Add css to form.
        $captcha['form']['captcha_response']['#attached']['library'][] = 'text_captcha/base';
        return $captcha;
      }
  }
}

/**
 * Function for generating a random nonsense word of a given number of chars.
 */
function _phrase_captcha_generate_nonsense_word($characters) {
  $vowels = 'bcdfghjklmnpqrstvwxyz';
  $consonants = 'aeiou';
  $vowel_max = strlen($vowels) - 1;
  $consonant_max = strlen($consonants) - 1;
  $word = '';

  // Randomly start with vowel or consonant.
  $o = mt_rand(0, 1);
  for ($i = 0; $i < $characters; ++$i) {
    if (($i + $o) % 2) {
      $word .= $consonants[mt_rand(0, $consonant_max)];
    }
    else {
      $word .= $vowels[mt_rand(0, $vowel_max)];
    }
  }
  return $word;
}

/**
 * Function for generating an array of words.
 */
function _phrase_captcha_generate_words($num) {
  $words = [];
  if (\Drupal::config('phrase_captcha.settings')
    ->get('phrase_captcha_words') == PHRASE_CAPTCHA_USER_DEFINED_WORDS) {

    // Use user defined words.
    $uwords = _text_captcha_word_pool_get_content('phrase_captcha_userdefined_word_pool', NULL, '', TRUE);
    switch ($num) {
      case 0:
        break;
      case 1:
        $words[] = $uwords[array_rand($uwords, $num)];
        break;
      default:
        $keys = array_rand($uwords, $num);
        foreach ($keys as $key) {
          $words[] = $uwords[$key];
        }
        break;
    }
  }
  else {

    // Generate nonsense words.
    for ($w = 0; $w < $num; ++$w) {
      $words[] = _phrase_captcha_generate_nonsense_word(mt_rand(3, 7));
    }
  }
  return $words;
}

/**
 * Function that returns a textual representation of an ordinal.
 */
function _phrase_captcha_ordinal($n) {
  $ordinalmap = [
    1 => t('first'),
    2 => t('second'),
    3 => t('third'),
    4 => t('fourth'),
    5 => t('fifth'),
    6 => t('sixth'),
    7 => t('seventh'),
    8 => t('eighth'),
    9 => t('ninth'),
    10 => t('tenth'),
  ];
  if (array_key_exists($n, $ordinalmap)) {
    return $ordinalmap[$n];
  }
  else {
    return "{$n}th";
  }
}

/**
 * Return array with available word challenges.
 */
function _phrase_captcha_available_word_challenges() {
  return [
    '_phrase_captcha_word_question_word_index' => 'Word index',
    '_phrase_captcha_word_question_alphabetical_misplaced' => 'Alphabetical misplacement',
    '_phrase_captcha_word_question_double_occurence' => 'Double occurence',
  ];
}

/**
 * Return enabled challenges.
 */
function _phrase_captcha_enabled_word_challenges() {
  $word_challenges = \Drupal::config('phrase_captcha.settings')
    ->get('phrase_captcha_word_selection_challenges');
  if ($word_challenges) {
    return array_keys(array_filter($word_challenges));
  }
  else {
    return array_keys(_phrase_captcha_available_word_challenges());
  }
}

/**
 * Return details of 'word index' challenge.
 */
function _phrase_captcha_word_question_word_index($words) {
  $key = array_rand($words, 1);
  $answer = $words[$key];
  if (mt_rand(0, 1)) {
    $description = t('What is the @nth word in the CAPTCHA phrase above?', [
      '@nth' => _phrase_captcha_ordinal($key + 1),
    ]);
  }
  else {
    $n = count($words) - $key;
    if ($n == 1) {
      $description = t('What is the last word in the CAPTCHA phrase above?');
    }
    else {
      $description = t('What is the @nth last word in the CAPTCHA phrase above?', [
        '@nth' => _phrase_captcha_ordinal($n),
      ]);
    }
  }
  return [
    $words,
    $description,
    $answer,
  ];
}

/**
 * Return details of 'alphabetical misplaced' challenge.
 */
function _phrase_captcha_word_question_alphabetical_misplaced($words) {

  // Sort the words.
  mt_rand(0, 1) ? sort($words) : rsort($words);

  // Pick a word and its new destination
  // New destination has to be at least 2 places from the original place,
  // otherwise it could lead to something like swapping two neighbours,
  // in which case there is no unique answer.
  $from = 0;
  $to = 0;
  while (abs($from - $to) < 2) {
    $from = array_rand($words, 1);
    $to = array_rand($words, 1);
  }

  // Get the word.
  $answer = $words[$from];

  // Move the word from $from to $to.
  unset($words[$from]);
  array_splice($words, $to, 0, $answer);

  // bBuild the description.
  $description = t('Which word does not follow the alphabetical order in the CAPTCHA phrase above?');
  return [
    $words,
    $description,
    $answer,
  ];
}

/**
 * Return details of 'double occurrence' challenge.
 */
function _phrase_captcha_word_question_double_occurence($words) {

  // Assure single occurence of each word.
  $words = array_unique($words);

  // Pick a word.
  $key = array_rand($words, 1);
  $answer = $words[$key];

  // Replace another word with it.
  while (($pos = array_rand($words, 1)) == $key) {

    // NOP aka NOOP aka pass.
  }
  array_splice($words, $pos, 1, $answer);
  $description = t('Which word occurs two times in the CAPTCHA phrase above?');
  return [
    $words,
    $description,
    $answer,
  ];
}

Functions

Namesort descending Description
phrase_captcha_captcha Implements hook_captcha().
phrase_captcha_help Implements hook_help().
_phrase_captcha_available_word_challenges Return array with available word challenges.
_phrase_captcha_enabled_word_challenges Return enabled challenges.
_phrase_captcha_generate_nonsense_word Function for generating a random nonsense word of a given number of chars.
_phrase_captcha_generate_words Function for generating an array of words.
_phrase_captcha_ordinal Function that returns a textual representation of an ordinal.
_phrase_captcha_word_question_alphabetical_misplaced Return details of 'alphabetical misplaced' challenge.
_phrase_captcha_word_question_double_occurence Return details of 'double occurrence' challenge.
_phrase_captcha_word_question_word_index Return details of 'word index' challenge.

Constants

Namesort descending Description
PHRASE_CAPTCHA_GENERATE_NONSENSE_WORDS @file Implementation of a phrase based CAPTCHA, for use with the CAPTCHA module.
PHRASE_CAPTCHA_USER_DEFINED_WORDS