Location: PHPKode > scripts > Prioritexter > Html.php
<?php
class Html {
  
  // safe_html by Chris Snyder (hide@address.com) for http://pcoms.net
  //   - Huge thanks to James Wetterau for testing and feedback!
  
  /*
Copyright 2003 Chris Snyder. All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

   1. Redistributions of source code must retain the above copyright notice, this list of conditions and the 
following disclaimer.
   2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the 
following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;  LOSS OF USE, DATA, OR PROFITS;
OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.  
  */
  
  /* 
set of functions for sanitizing user input:
    keeps "friendly" tags but strips javascript events and style attributes
    closes any open comment tags
    closes any open HTML tags - results may not be valid HTML, but
        at least they will keep the rest of the page from breaking

treats the following as malicious conditions and returns text stripped
of all html tags:
    any instances of ='javascript: 
    event or style attributes remaining after initial replacement
  */
  
  function strip_attributes ($html, $attrs) {
    if (!is_array($attrs)) {
      $array= array( "$attrs" );
      unset($attrs);
      $attrs= $array;
    }
    
    foreach ($attrs AS $attribute) {
      // once for ", once for ', s makes the dot match linebreaks, too.
      $search[]= "/".$attribute.'\s*=\s*".+"/Uis';
      $search[]= "/".$attribute."\s*=\s*'.+'/Uis";
      // and once more for unquoted attributes
      $search[]= "/".$attribute."\s*=\s*\S+/i";
    }
    $html= preg_replace($search, "", $html);
    
    // check for additional matches and strip all tags if found
    foreach ($search AS $pattern) {
      if (preg_match($pattern, $html)) {
	$html= strip_tags($html);
	break;
      }
    }
    
    return $html;
  }
  
  function safe_html ($html, $allowedtags="") {
    $version= "safe_html.php/0.4";
    
    // anything with ="javascript: is right out -- strip all tags and return if found
    $pattern= "/=\s*\S+script:\S+/Ui";
    if (preg_match($pattern, $html)) {
      $html= strip_tags($html);
      return $html;
    }
    
    // setup -- $allowedtags is an array of $tag=>$closeit pairs, where $tag is an HTML tag to allow and $closeit is 1 if the tag requires a matching, closing tag
    if ($allowedtags=="") {
      $allowedtags= array ( "p"=>1, "br"=>0, "a"=>1, "img"=>0, "li"=>1, "ol"=>1, "ul"=>1, "b"=>1, "i"=>1, "em"=>1, "strong"=>1, "del"=>1, "ins"=>1, "u"=>1, "blockquote"=>1, "pre"=>1, "hr"=>0);
    }
    elseif (!is_array($allowedtags)) {
      $array= array( "$allowedtags" );
      unset($allowedtags);
      $allowedtags= $array;
    }
    
    // there's some debate about this.. is strip_tags() better than rolling your own regex?
    // note: a bug in PHP 4.3.1 caused improper handling of ! in tag attributes when using strip_tags()
    $stripallowed= "";
    foreach ($allowedtags AS $tag=>$closeit) {
      $stripallowed.= "<$tag>";
    }
    
    //print "Stripallowed: $stripallowed -- ".print_r($allowedtags,1);
    $html= strip_tags($html, $stripallowed);
    
    // also, lets get rid of some pesky attributes that may be set on the remaining tags...
    $badattrs= array("on\w+", "style");
    $html= Html::strip_attributes($html, $badattrs);
    
    // close html tags if necessary -- note that this WON'T be graceful formatting-wise, it just has to fix any maliciousness
    foreach ($allowedtags AS $tag=>$closeit) {
      if (!$closeit) continue;
      $patternopen= "/<$tag\b[^>]*>/Ui";
      $patternclose= "/<\/$tag\b[^>]*>/Ui";
      $totalopen= preg_match_all ( $patternopen, $html, $matches );
      $totalclose= preg_match_all ( $patternclose, $html, $matches2 );
      if ($totalopen>$totalclose) {
	$html.= str_repeat("</$tag>", ($totalopen - $totalclose));
      }
    }
    
    // close any open <!--'s and identify version just in case
    // ACTUALLY--don't. I don't want to insert anything unnescessary.
    // ONLY if there was an open tag somewhere.
    $pattern= "/<!--/";
    if (preg_match($pattern, $html)) 
      $html.= "<!-- -->";
    
    return $html;
  }
  
}
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