1 filter.module _filter_url($text, $filter)

Implements callback_filter_process().

Converts text into hyperlinks automatically.

This filter identifies and makes clickable three types of "links".

Each type must be processed separately, as there is no one regular expression that could possibly match all of the cases in one pass.

Related topics


core/modules/filter/filter.module, line 2170
Framework for handling the filtering of content.


function _filter_url($text, $filter) {
  // Tags to skip and not recurse into.
  $ignore_tags = 'a|script|style|code|pre';

  // Pass length to regexp callback.
  _filter_url_trim(NULL, $filter->settings['filter_url_length']);

  // Create an array which contains the regexps for each type of link.
  // The key to the regexp is the name of a function that is used as
  // callback function to process matches of the regexp. The callback function
  // is to return the replacement for the match. The array is used and
  // matching/replacement done below inside some loops.
  $tasks = array();

  // Prepare protocols pattern for absolute URLs.
  // check_url() will replace any bad protocols with HTTP, so we need to support
  // the identical list. While '//' is technically optional for MAILTO only,
  // we cannot cleanly differ between protocols here without hard-coding MAILTO,
  // so '//' is optional for all protocols.
  // @see filter_xss_bad_protocol()
  $protocols = settings_get('filter_allowed_protocols', array('ftp', 'http', 'https', 'irc', 'mailto', 'news', 'nntp', 'rtsp', 'sftp', 'ssh', 'tel', 'telnet', 'webcal'));
  $protocols = implode(':(?://)?|', $protocols) . ':(?://)?';

  // Prepare domain name pattern.
  // The ICANN seems to be on track towards accepting more diverse top level
  // domains, so this pattern has been "future-proofed" to allow for TLDs
  // of length 2-64.
  $domain = '(?:[A-Za-z0-9._+-]+\.)?[A-Za-z]{2,64}\b';
  $ip = '(?:[0-9]{1,3}\.){3}[0-9]{1,3}';
  $auth = '[a-zA-Z0-9:%_+*~#?&=.,/;-]+@';
  $trail = '[a-zA-Z0-9:%_+*~#&\[\]=/;?!\.,-]*[a-zA-Z0-9:%_+*~#&\[\]=/;-]';

  // Prepare pattern for optional trailing punctuation.
  // Even these characters could have a valid meaning for the URL, such usage is
  // rare compared to using a URL at the end of or within a sentence, so these
  // trailing characters are optionally excluded.
  $punctuation = '[\.,?!]*?';

  // Match absolute URLs.
  $url_pattern = "(?:$auth)?(?:$domain|$ip)/?(?:$trail)?";
  $pattern = "`((?:$protocols)(?:$url_pattern))($punctuation)`";
  $tasks['_filter_url_parse_full_links'] = $pattern;

  // Match e-mail addresses.
  $url_pattern = "[A-Za-z0-9._+-]{1,254}@(?:$domain)";
  $pattern = "`($url_pattern)`";
  $tasks['_filter_url_parse_email_links'] = $pattern;

  // Match www domains.
  $url_pattern = "www\.(?:$domain)/?(?:$trail)?";
  $pattern = "`($url_pattern)($punctuation)`";
  $tasks['_filter_url_parse_partial_links'] = $pattern;

  // Each type of URL needs to be processed separately. The text is joined and
  // re-split after each task, since all injected HTML tags must be correctly
  // protected before the next task.
  foreach ($tasks as $task => $pattern) {
    // HTML comments need to be handled separately, as they may contain HTML
    // markup, especially a '>'. Therefore, remove all comment contents and add
    // them back later.
    _filter_url_escape_comments('', TRUE);
    $text = preg_replace_callback('`<!--(.*?)-->`s', '_filter_url_escape_comments', $text);

    // Split at all tags; ensures that no tags or attributes are processed.
    $chunks = preg_split('/(<.+?>)/is', $text, -1, PREG_SPLIT_DELIM_CAPTURE);
    // PHP ensures that the array consists of alternating delimiters and
    // literals, and begins and ends with a literal (inserting NULL as
    // required). Therefore, the first chunk is always text:
    $chunk_type = 'text';
    // If a tag of $ignore_tags is found, it is stored in $open_tag and only
    // removed when the closing tag is found. Until the closing tag is found,
    // no replacements are made.
    $open_tag = '';

    for ($i = 0; $i < count($chunks); $i++) {
      if ($chunk_type == 'text') {
        // Only process this text if there are no unclosed $ignore_tags.
        if ($open_tag == '') {
          // If there is a match, inject a link into this chunk via the callback
          // function contained in $task.
          $chunks[$i] = preg_replace_callback($pattern, $task, $chunks[$i]);
        // Text chunk is done, so next chunk must be a tag.
        $chunk_type = 'tag';
      else {
        // Only process this tag if there are no unclosed $ignore_tags.
        if ($open_tag == '') {
          // Check whether this tag is contained in $ignore_tags.
          if (preg_match("`<($ignore_tags)(?:\s|>)`i", $chunks[$i], $matches)) {
            $open_tag = $matches[1];
        // Otherwise, check whether this is the closing tag for $open_tag.
        else {
          if (preg_match("`<\/$open_tag>`i", $chunks[$i], $matches)) {
            $open_tag = '';
        // Tag chunk is done, so next chunk must be text.
        $chunk_type = 'text';

    $text = implode($chunks);
    // Revert back to the original comment contents
    _filter_url_escape_comments('', FALSE);
    $text = preg_replace_callback('`<!--(.*?)-->`', '_filter_url_escape_comments', $text);

  return $text;