Truncate text containing HTML, ignoring tags

Question

I want to truncate some text (loaded from a database or text file), but it contains HTML so as a result the tags are included and less text will be returned. This can then result in tags not being closed, or being partially closed (so Tidy may not work properly and there is still less content). How can I truncate based on the text (and probably stopping when you get to a table as that could cause more complex issues).

substr("Hello, my <strong>name</strong> is <em>Sam</em>. I&acute;m a web developer.",0,26)."..."

Would result in:

Hello, my <strong>name</st...

What I would want is:

Hello, my <strong>name</strong> is <em>Sam</em>. I&acute;m...

How can I do this?

While my question is for how to do it in PHP, it would be good to know how to do it in C#... either should be OK as I think I would be able to port the method over (unless it is a built in method).

Also note that I have included an HTML entity ´ - which would have to be considered as a single character (rather than 7 characters as in this example).

strip_tags is a fallback, but I would lose formatting and links and it would still have the problem with HTML entities.

Answer 1

Assuming you are using valid XHTML, it's simple to parse the HTML and make sure tags are handled properly. You simply need to track which tags have been opened so far, and make sure to close them again "on your way out".

<?php header('Content-type: text/plain; charset=utf-8');  function printTruncated($maxLength, $html, $isUtf8=true) {     $printedLength = 0;     $position = 0;     $tags = array();      // For UTF-8, we need to count multibyte sequences as one character.     $re = $isUtf8         ? '{</?([a-z]+)[^>]*>|&#?[a-zA-Z0-9]+;|[\x80-\xFF][\x80-\xBF]*}'         : '{</?([a-z]+)[^>]*>|&#?[a-zA-Z0-9]+;}';      while ($printedLength < $maxLength && preg_match($re, $html, $match, PREG_OFFSET_CAPTURE, $position))     {         list($tag, $tagPosition) = $match[0];          // Print text leading up to the tag.         $str = substr($html, $position, $tagPosition - $position);         if ($printedLength + strlen($str) > $maxLength)         {             print(substr($str, 0, $maxLength - $printedLength));             $printedLength = $maxLength;             break;         }          print($str);         $printedLength += strlen($str);         if ($printedLength >= $maxLength) break;          if ($tag[0] == '&' || ord($tag) >= 0x80)         {             // Pass the entity or UTF-8 multibyte sequence through unchanged.             print($tag);             $printedLength++;         }         else         {             // Handle the tag.             $tagName = $match[1][0];             if ($tag[1] == '/')             {                 // This is a closing tag.                  $openingTag = array_pop($tags);                 assert($openingTag == $tagName); // check that tags are properly nested.                  print($tag);             }             else if ($tag[strlen($tag) - 2] == '/')             {                 // Self-closing tag.                 print($tag);             }             else             {                 // Opening tag.                 print($tag);                 $tags[] = $tagName;             }         }          // Continue after the tag.         $position = $tagPosition + strlen($tag);     }      // Print any remaining text.     if ($printedLength < $maxLength && $position < strlen($html))         print(substr($html, $position, $maxLength - $printedLength));      // Close any open tags.     while (!empty($tags))         printf('</%s>', array_pop($tags)); }   printTruncated(10, '<b>&lt;Hello&gt;</b> <img src="world.png" alt="" /> world!'); print("\n");  printTruncated(10, '<table><tr><td>Heck, </td><td>throw</td></tr><tr><td>in a</td><td>table</td></tr></table>'); print("\n");  printTruncated(10, "<em><b>Hello</b>&#20;w\xC3\xB8rld!</em>"); print("\n"); 

Encoding note: The above code assumes the XHTML is UTF-8 encoded. ASCII-compatible single-byte encodings (such as Latin-1) are also supported, just pass false as the third argument. Other multibyte encodings are not supported, though you may hack in support by using mb_convert_encoding to convert to UTF-8 before calling the function, then converting back again in every print statement.

(You should always be using UTF-8, though.)

Edit: Updated to handle character entities and UTF-8. Fixed bug where the function would print one character too many, if that character was a character entity.

Answer 2

I've written a function that truncates HTML just as yous suggest, but instead of printing it out it puts it just keeps it all in a string variable. handles HTML Entities, as well.

 /**      *  function to truncate and then clean up end of the HTML,      *  truncates by counting characters outside of HTML tags      *        *  @author alex lockwood, alex dot lockwood at websightdesign      *        *  @param string $str the string to truncate      *  @param int $len the number of characters      *  @param string $end the end string for truncation      *  @return string $truncated_html      *        *  **/         public static function truncateHTML($str, $len, $end = '&hellip;'){             //find all tags             $tagPattern = '/(<\/?)([\w]*)(\s*[^>]*)>?|&[\w#]+;/i';  //match html tags and entities             preg_match_all($tagPattern, $str, $matches, PREG_OFFSET_CAPTURE | PREG_SET_ORDER );             //WSDDebug::dump($matches); exit;              $i =0;             //loop through each found tag that is within the $len, add those characters to the len,             //also track open and closed tags             // $matches[$i][0] = the whole tag string  --the only applicable field for html enitities               // IF its not matching an &htmlentity; the following apply             // $matches[$i][1] = the start of the tag either '<' or '</'               // $matches[$i][2] = the tag name             // $matches[$i][3] = the end of the tag             //$matces[$i][$j][0] = the string             //$matces[$i][$j][1] = the str offest              while($matches[$i][0][1] < $len && !empty($matches[$i])){                  $len = $len + strlen($matches[$i][0][0]);                 if(substr($matches[$i][0][0],0,1) == '&' )                     $len = $len-1;                   //if $matches[$i][2] is undefined then its an html entity, want to ignore those for tag counting                 //ignore empty/singleton tags for tag counting                 if(!empty($matches[$i][2][0]) && !in_array($matches[$i][2][0],array('br','img','hr', 'input', 'param', 'link'))){                     //double check                      if(substr($matches[$i][3][0],-1) !='/' && substr($matches[$i][1][0],-1) !='/')                         $openTags[] = $matches[$i][2][0];                     elseif(end($openTags) == $matches[$i][2][0]){                         array_pop($openTags);                     }else{                         $warnings[] = "html has some tags mismatched in it:  $str";                     }                 }                   $i++;              }              $closeTags = '';              if (!empty($openTags)){                 $openTags = array_reverse($openTags);                 foreach ($openTags as $t){                     $closeTagString .="</".$t . ">";                  }             }              if(strlen($str)>$len){                 // Finds the last space from the string new length                 $lastWord = strpos($str, ' ', $len);                 if ($lastWord) {                     //truncate with new len last word                     $str = substr($str, 0, $lastWord);                     //finds last character                     $last_character = (substr($str, -1, 1));                     //add the end text                     $truncated_html = ($last_character == '.' ? $str : ($last_character == ',' ? substr($str, 0, -1) : $str) . $end);                 }                 //restore any open tags                 $truncated_html .= $closeTagString;               }else             $truncated_html = $str;               return $truncated_html;          } 

Answer 3

100% accurate, but pretty difficult approach:

1. Iterate charactes using DOM
2. Use DOM methods to remove remaining elements
3. Serialize the DOM

Easy brute-force approach:

1. Split string into tags (not elements) and text fragments using preg_split('/(<tag>)/') with PREG_DELIM_CAPTURE.
2. Measure text length you want (it'll be every second element from split, you might use html_entity_decode() to help measure accurately)
3. Cut the string (trim &[^\s;]+$ at the end to get rid of possibly chopped entity)
4. Fix it with HTML Tidy

Answer 4

I used a nice function found at http://alanwhipple.com/2011/05/25/php-truncate-string-preserving-html-tags-words, apparently taken from CakePHP

Answer 5

The following is a simple state-machine parser which handles you test case successfully. I fails on nested tags though as it doesn't track the tags themselves. I also chokes on entities within HTML tags (e.g. in an href-attribute of an <a>-tag). So it cannot be considered a 100% solution to this problem but because it's easy to understand it could be the basis for a more advanced function.

function substr_html($string, $length)
{
    $count = 0;
    /*
     * $state = 0 - normal text
     * $state = 1 - in HTML tag
     * $state = 2 - in HTML entity
     */
    $state = 0;    
    for ($i = 0; $i < strlen($string); $i++) {
        $char = $string[$i];
        if ($char == '<') {
            $state = 1;
        } else if ($char == '&') {
            $state = 2;
            $count++;
        } else if ($char == ';') {
            $state = 0;
        } else if ($char == '>') {
            $state = 0;
        } else if ($state === 0) {
            $count++;
        }

        if ($count === $length) {
            return substr($string, 0, $i + 1);
        }
    }
    return $string;
}

Answer 6

you can use tidy as well:

function truncate_html($html, $max_length) {   
  return tidy_repair_string(substr($html, 0, $max_length),
     array('wrap' => 0, 'show-body-only' => TRUE), 'utf8'); 
}