<?php
/**
 * htmlfilter.inc
 * ---------------
 * This set of functions allows you to filter html in order to remove
 * any malicious tags from it. Useful in cases when you need to filter
 * user input for any cross-site-scripting attempts.
 *
 * Copyright (c) 2002 by Duke University
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  
 * 02111-1307, USA.
 *
 * @Author  Konstantin Riabitsev <icon@linux.duke.edu>
 * @Version 1.0.5 (Oct-16-2002)
 */

/**
 * This is a debugging function used throughout the code. To enable
 * debugging you have to specify a global variable called "debug" before
 * calling sanitize() and set it to true. 
 *
 * Note: Although insignificantly, debugging does slow you down even
 * when $debug is set to false. If you wish to get rid of all
 * debugging calls, run the following command:
 *
 * fgrep -v 'spew("' htmlfilter.inc > htmlfilter.inc.new
 *
 * htmlfilter.inc.new will contain no debugging calls.
 *
 * @param  $message  A string with the message to output.
 * @return           void.
 */
function spew($message){
  global $debug;
  if ($debug == true){
    echo "$message";
  }
}

/**
 * This function returns the final tag out of the tag name, an array
 * of attributes, and the type of the tag. This function is called by 
 * sanitize internally.
 *
 * @param  $tagname  the name of the tag.
 * @param  $attary   the array of attributes and their values
 * @param  $tagtype  The type of the tag (see in comments).
 * @return           a string with the final tag representation.
 */
function tagprint($tagname, $attary, $tagtype){
  $me = 'tagprint';
  if ($tagtype == 2){
    $fulltag = '</' . $tagname . '>';
  } else {
    $fulltag = '<' . $tagname;
    if (is_array($attary) && sizeof($attary)){
      $atts = Array();
      while (list($attname, $attvalue) = each($attary)){
        array_push($atts, "$attname=$attvalue");
      }
      $fulltag .= ' ' . join(' ', $atts);
    }
    if ($tagtype == 3){
      $fulltag .= ' /';
    }
    $fulltag .= '>';
  }
  spew("$me: $fulltag\n");
  return $fulltag;
}

/**
 * A small helper function to use with array_walk. Modifies a by-ref
 * value and makes it lowercase.
 *
 * @param  $val a value passed by-ref.
 * @return      void since it modifies a by-ref value.
 */
function casenormalize(&$val){
  $val = strtolower($val);
}

/**
 * This function skips any whitespace from the current position within
 * a string and to the next non-whitespace value.
 * 
 * @param  $body   the string
 * @param  $offset the offset within the string where we should start
 *                 looking for the next non-whitespace character.
 * @return         the location within the $body where the next
 *                 non-whitespace char is located.
 */
function skipspace($body, $offset){
  $me = 'skipspace';
  preg_match('/^(\s*)/s', substr($body, $offset), $matches);
  if (sizeof($matches{1})){
    $count = strlen($matches{1});
    spew("$me: skipped $count chars\n");
    $offset += $count;
  }
  return $offset;
}

/**
 * This function looks for the next character within a string.  It's
 * really just a glorified "strpos", except it catches the failures
 * nicely.
 *
 * @param  $body   The string to look for needle in.
 * @param  $offset Start looking from this position.
 * @param  $needle The character/string to look for.
 * @return         location of the next occurance of the needle, or
 *                 strlen($body) if needle wasn't found.
 */
function findnxstr($body, $offset, $needle){
  $me = 'findnxstr';
  $pos = strpos($body, $needle, $offset);
  if ($pos === FALSE){
    $pos = strlen($body);
    spew("$me: end of body reached\n");
  }
  spew("$me: '$needle' found at pos $pos\n");
  return $pos;
}

/**
 * This function takes a PCRE-style regexp and tries to match it
 * within the string.
 *
 * @param  $body   The string to look for needle in.
 * @param  $offset Start looking from here.
 * @param  $reg    A PCRE-style regex to match.
 * @return         Returns a false if no matches found, or an array
 *                 with the following members:
 *                 - integer with the location of the match within $body
 *                 - string with whatever content between offset and the match
 *                 - string with whatever it is we matched
 */
function findnxreg($body, $offset, $reg){
  $me = 'findnxreg';
  $matches = Array();
  $retarr = Array();
  $preg_rule = '%^(.*?)(' . $reg . ')%s';
  preg_match($preg_rule, substr($body, $offset), $matches);
  if (!$matches{0}){
    spew("$me: No matches found.\n");
    $retarr = false;
  } else {
    $retarr{0} = $offset + strlen($matches{1});
    $retarr{1} = $matches{1};
    $retarr{2} = $matches{2};
    spew("$me: '$reg' found at pos $offset matching '".$matches{2}."'\n");
  }
  return $retarr;
}

/**
 * This function looks for the next tag.
 *
 * @param  $body   String where to look for the next tag.
 * @param  $offset Start looking from here.
 * @return         false if no more tags exist in the body, or
 *                 an array with the following members:
 *                 - string with the name of the tag
 *                 - array with attributes and their values
 *                 - integer with tag type (1, 2, or 3)
 *                 - integer where the tag starts (starting "<")
 *                 - integer where the tag ends (ending ">")
 *                 first three members will be false, if the tag is invalid.
 */
function getnxtag($body, $offset){
  $me = 'getnxtag';
  if ($offset > strlen($body)){
    spew("$me: Past the end of body\n");
    return false;
  }
  $lt = findnxstr($body, $offset, '<');
  if ($lt == strlen($body)){
    spew("$me: No more tags found!\n");
    return false;
  }
  /**
   * We are here:
   * blah blah <tag attribute="value">
   * \---------^
   */
  spew("$me: Found '<' at pos $lt\n");
  $pos = skipspace($body, $lt + 1);
  if ($pos >= strlen($body)){
    spew("$me: End of body reached.\n");
    return Array(false, false, false, $lt, strlen($body));
  }
  /**
   * There are 3 kinds of tags:
   * 1. Opening tag, e.g.:
   *    <a href="blah">
   * 2. Closing tag, e.g.:
   *    </a>
   * 3. XHTML-style content-less tag, e.g.:
   *    <img src="blah"/>
   */
  $tagtype = false;
  switch (substr($body, $pos, 1)){
  case '/':
    spew("$me: This is a closing tag (type 2)\n");
    $tagtype = 2;
    $pos++;
    break;
  case '!':
    /**
     * A comment or an SGML declaration.
     */
    if (substr($body, $pos+1, 2) == '--'){
      spew("$me: A comment found. Stripping.\n");
      $gt = strpos($body, '-->', $pos);
      if ($gt === false){
        $gt = strlen($body);
      } else {
        $gt += 2;
      }
      return Array(false, false, false, $lt, $gt);
    } else {
      spew("$me: An SGML declaration found. Stripping.\n");
      $gt = findnxstr($body, $pos, '>');
      return Array(false, false, false, $lt, $gt);
    }
    break;
  default:
    /**
     * Assume tagtype 1 for now. If it's type 3, we'll switch values
     * later.
     */
    $tagtype = 1;
    break;
  }
  
  $tag_start = $pos;
  $tagname = '';
  /**
   * Look for next [\W-_], which will indicate the end of the tag name.
   */
  $regary = findnxreg($body, $pos, '[^\w\-_]');
  if ($regary == false){
    spew("$me: End of body reached while analyzing tag name\n");
    return Array(false, false, false, $lt, strlen($body));
  }
  list($pos, $tagname, $match) = $regary;
  $tagname = strtolower($tagname);
  
  /**
   * $match can be either of these:
   * '>'  indicating the end of the tag entirely.
   * '\s' indicating the end of the tag name.
   * '/'  indicating that this is type-3 xhtml tag.
   * 
   * Whatever else we find there indicates an invalid tag.
   */
  switch ($match){
  case '/':
    /**
     * This is an xhtml-style tag with a closing / at the
     * end, like so: <img src="blah"/>. Check if it's followed
     * by the closing bracket. If not, then this tag is invalid
     */
    if (substr($body, $pos, 2) == '/>'){
      spew("$me: XHTML-style tag found.\n");
      $pos++;
      spew("$me: Setting tagtype to 3\n");
      $tagtype = 3;
    } else {
      spew("$me: Found invalid character '/'.\n");
      $gt = findnxstr($body, $pos, '>');
      spew("$me: Tag is invalid. Returning.\n");
      $retary = Array(false, false, false, $lt, $gt);
      return $retary;
    }
  case '>':
    spew("$me: End of tag found at $pos\n");
    spew("$me: Tagname is '$tagname'\n");
    spew("$me: This tag has no attributes\n");
    return Array($tagname, false, $tagtype, $lt, $pos);
    break;
  default:
    /**
     * Check if it's whitespace
     */
    if (preg_match('/\s/', $match)){
      spew("$me: Tagname is '$tagname'\n");
    } else {
      /**
       * This is an invalid tag! Look for the next closing ">".
       */
      spew("$me: Invalid characters found in tag name: $match\n");
      $gt = findnxstr($body, $offset, '>');
      return Array(false, false, false, $lt, $gt);
    }
  }
  
  /**
   * At this point we're here:
   * <tagname  attribute='blah'>
   * \-------^
   *
   * At this point we loop in order to find all attributes.
   */
  $attname = '';
  $atttype = false;
  $attary = Array();
  
  while ($pos <= strlen($body)){
    $pos = skipspace($body, $pos);
    if ($pos == strlen($body)){
      /**
       * Non-closed tag.
       */
      spew("$me: End of body reached before end of tag. Discarding.\n");
      return Array(false, false, false, $lt, $pos);
    }
    /**
     * See if we arrived at a ">" or "/>", which means that we reached
     * the end of the tag.
     */
    $matches = Array();
    preg_match('%^(\s*)(>|/>)%s', substr($body, $pos), $matches);
    if (isset($matches{0}) && $matches{0}){
      /**
       * Yep. So we did.
       */
      spew("$me: Arrived at the end of the tag.\n");
      $pos += strlen($matches{1});
      if ($matches{2} == '/>'){
        $tagtype = 3;
        $pos++;
      }
      return Array($tagname, $attary, $tagtype, $lt, $pos);
    }
    
    /**
     * There are several types of attributes, with optional
     * [:space:] between members.
     * Type 1:
     *   attrname[:space:]=[:space:]'CDATA'
     * Type 2:
     *   attrname[:space:]=[:space:]"CDATA"
     * Type 3:
     *   attr[:space:]=[:space:]CDATA
     * Type 4:
     *   attrname
     *
     * We leave types 1 and 2 the same, type 3 we check for
     * '"' and convert to "&quot" if needed, then wrap in
     * double quotes. Type 4 we convert into:
     * attrname="yes".
     */
    $regary = findnxreg($body, $pos, '[^\w\-_]');
    if ($regary == false){
      /**
       * Looks like body ended before the end of tag.
       */
      spew("$me: End of body found before end of tag.\n");
      spew("$me: Invalid, returning\n");
      return Array(false, false, false, $lt, strlen($body));
    }
    list($pos, $attname, $match) = $regary;
    $attname = strtolower($attname);
    spew("$me: Attribute '$attname' found\n");
    /**
     * We arrived at the end of attribute name. Several things possible
     * here:
     * '>'  means the end of the tag and this is attribute type 4
     * '/'  if followed by '>' means the same thing as above
     * '\s' means a lot of things -- look what it's followed by.
     *      anything else means the attribute is invalid.
     */
    switch($match){
    case '/':
      /**
       * This is an xhtml-style tag with a closing / at the
       * end, like so: <img src="blah"/>. Check if it's followed
       * by the closing bracket. If not, then this tag is invalid
       */
      if (substr($body, $pos, 2) == '/>'){
        spew("$me: This is an xhtml-style tag.\n");
        $pos++;
        spew("$me: Setting tagtype to 3\n");
        $tagtype = 3;
      } else {
        spew("$me: Found invalid character '/'.\n");
        $gt = findnxstr($body, $pos, '>');
        spew("$me: Tag is invalid. Returning.\n");
        $retary = Array(false, false, false, $lt, $gt);
        return $retary;
      }
    case '>':
      spew("$me: found type 4 attribute.\n");
      spew("$me: Additionally, end of tag found at $pos\n");
      spew("$me: Attname is '$attname'\n");
      spew("$me: Setting attvalue to 'yes'\n");
      $attary{$attname} = '"yes"';
      return Array($tagname, $attary, $tagtype, $lt, $pos);
      break;
    default:
      /**
       * Skip whitespace and see what we arrive at.
       */
      $pos = skipspace($body, $pos);
      $char = substr($body, $pos, 1);
      /**
       * Two things are valid here:
       * '=' means this is attribute type 1 2 or 3.
       * \w means this was attribute type 4.
       * anything else we ignore and re-loop. End of tag and
       * invalid stuff will be caught by our checks at the beginning
       * of the loop.
       */
      if ($char == '='){
        spew("$me: Attribute type 1, 2, or 3 found.\n");
        $pos++;
        $pos = skipspace($body, $pos);
        /**
         * Here are 3 possibilities:
         * "'"  attribute type 1
         * '"'  attribute type 2
         * everything else is the content of tag type 3
         */
        $quot = substr($body, $pos, 1);
        if ($quot == '\''){
          spew("$me: In fact, this is attribute type 1\n");
          spew("$me: looking for closing quote\n");
          $regary = findnxreg($body, $pos+1, '\'');
          if ($regary == false){
            spew("$me: end of body reached before end of val\n");
            spew("$me: Returning\n");
            return Array(false, false, false, $lt, strlen($body));
          }
          list($pos, $attval, $match) = $regary;
          spew("$me: Attvalue is '$attval'\n");
          $pos++;
          $attary{$attname} = '\'' . $attval . '\'';
        } else if ($quot == '"'){
          spew("$me: In fact, this is attribute type 2\n");
          spew("$me: looking for closing quote\n");
          $regary = findnxreg($body, $pos+1, '\"');
          if ($regary == false){
            spew("$me: end of body reached before end of val\n");
            spew("$me: Returning\n");
            return Array(false, false, false, $lt, strlen($body));
          }
          list($pos, $attval, $match) = $regary;
          spew("$me: Attvalue is \"$attval\"\n");
          $pos++;
          $attary{$attname} = '"' . $attval . '"';
        } else {
          spew("$me: This looks like attribute type 3\n");
          /**
           * These are hateful. Look for \s, or >.
           */
          spew("$me: Looking for end of attval\n");
          $regary = findnxreg($body, $pos, '[\s>]');
          if ($regary == false){
            spew("$me: end of body reached before end of val\n");
            spew("$me: Returning\n");
            return Array(false, false, false, $lt, strlen($body));
          }
          list($pos, $attval, $match) = $regary;
          /**
           * If it's ">" it will be caught at the top.
           */
          spew("$me: translating '\"' into &quot;\n");
          $attval = preg_replace('/\"/s', '&quot;', $attval);
          spew("$me: wrapping in quotes\n");
          $attary{$attname} = '"' . $attval . '"';
        }
      } else if (preg_match('|[\w/>]|', $char)) {
        /**
         * That was attribute type 4.
         */
        spew("$me: attribute type 4 found.\n");
        spew("$me: Setting value to 'yes'\n");
        $attary{$attname} = '"yes"';
      } else {
        /**
         * An illegal character. Find next '>' and return.
         */
        spew("$me: illegal character '$char' found.\n");
        spew("$me: returning\n");
        $gt = findnxstr($body, $pos, '>');
        return Array(false, false, false, $lt, $gt);
      }
    }
  }
  /**
   * The fact that we got here indicates that the tag end was never
   * found. Return invalid tag indication so it gets stripped.
   */
  spew("$me: No tag end found\n");
  return Array(false, false, false, $lt, strlen($body));
}

/**
 * This function checks attribute values for entity-encoded values
 * and returns them translated into 8-bit strings so we can run
 * checks on them.
 *
 * @param  $attvalue A string to run entity check against.
 * @return           Translated value.
 */
function deent($attvalue){
  $me = 'deent';
  /**
   * See if we have to run the checks first. All entities must start
   * with "&".
   */
  if (strpos($attvalue, '&') === false){
    return $attvalue;
  }
  /**
   * Check named entities first.
   */
  spew("$me: translating named entities\n");
  $trans = get_html_translation_table(HTML_ENTITIES);
  /**
   * Leave &quot; in, as it can mess us up.
   */
  $trans = array_flip($trans);
  unset($trans{'&quot;'});
  while (list($ent, $val) = each($trans)){
    $attvalue = preg_replace('/' . $ent . '*/si', $val, $attvalue);
  }
  /**
   * Now translate numbered entities from 1 to 255 if needed.
   */
  if (strpos($attvalue, '#') !== false){
    spew("$me: translating numbered entities\n");
    $omit = Array(34, 39);
    for ($asc = 256; $asc >= 0; $asc--){
      if (!in_array($asc, $omit)){
        $chr = chr($asc);
        $octrule = '/\&#0*' . $asc . ';*/si';
        $hexrule = '/\&#x0*' . dechex($asc) . ';*/si';
        $attvalue = preg_replace($octrule, $chr, $attvalue);
        $attvalue = preg_replace($hexrule, $chr, $attvalue);
      }
    }
  }
  spew("$me: translated into: $attvalue\n");
  return $attvalue;
}

/**
 * This function runs various checks against the attributes.
 *
 * @param  $tagname         String with the name of the tag.
 * @param  $attary          Array with all tag attributes.
 * @param  $rm_attnames     See description for sanitize
 * @param  $bad_attvals     See description for sanitize
 * @param  $add_attr_to_tag See description for sanitize
 * @return                  Array with modified attributes.
 */
function fixatts($tagname, 
                 $attary, 
                 $rm_attnames,
                 $bad_attvals,
                 $add_attr_to_tag
                 ){
  $me = 'fixatts';
  spew("$me: Fixing attributes\n");
  while (list($attname, $attvalue) = each($attary)){
    /**
     * See if this attribute should be removed.
     */
    foreach ($rm_attnames as $matchtag=>$matchattrs){
      if (preg_match($matchtag, $tagname)){
        foreach ($matchattrs as $matchattr){
          if (preg_match($matchattr, $attname)){
            spew("$me: Attribute '$attname' defined as bad.\n");
            spew("$me: Removing.\n");
            unset($attary{$attname});
            continue;
          }
        }
      }
    }
    /**
     * Remove any entities.
     */
    $attvalue = deent($attvalue);
    
    /**
     * Now let's run checks on the attvalues.
     * I don't expect anyone to comprehend this. If you do,
     * get in touch with me so I can drive to where you live and
     * shake your hand personally. :)
     */
    foreach ($bad_attvals as $matchtag=>$matchattrs){
      if (preg_match($matchtag, $tagname)){
        foreach ($matchattrs as $matchattr=>$valary){
          if (preg_match($matchattr, $attname)){
            /**
             * There are two arrays in valary.
             * First is matches.
             * Second one is replacements
             */
            list($valmatch, $valrepl) = $valary;
            $newvalue = preg_replace($valmatch, $valrepl, $attvalue);
            if ($newvalue != $attvalue){
              spew("$me: attvalue is now $newvalue\n");
              $attary{$attname} = $newvalue;
            }
          }
        }
      }
    }
  }
  /**
   * See if we need to append any attributes to this tag.
   */
  foreach ($add_attr_to_tag as $matchtag=>$addattary){
    if (preg_match($matchtag, $tagname)){
      $attary = array_merge($attary, $addattary);
      spew("$me: Added attributes to this tag\n");
    }
  }
  return $attary;
}

/**
 * This is the main function and the one you should actually be calling.
 * There are several variables you should be aware of an which need
 * special description.
 *
 * $tag_list
 * ----------
 * This is a simple one-dimentional array of strings, except for the
 * very first one. The first member should be einter false or true.
 * In case it's FALSE, the following list will be considered a list of
 * tags that should be explicitly REMOVED from the body, and all
 * others that did not match the list will be allowed.  If the first
 * member is TRUE, then the list is the list of tags that should be
 * explicitly ALLOWED -- any tag not matching this list will be
 * discarded.
 *
 * Examples:
 * $tag_list = Array(
 *                   false,   
 *                   "blink", 
 *                   "link",
 *		     "object",
 *		     "meta",
 *                   "marquee",
 *                   "html"
 *		            );
 *
 * This will allow all tags except for blink, link, object, meta, marquee, 
 * and html.
 *
 * $tag_list = Array(
 *                   true, 
 *                   "b", 
 *                   "a", 
 *                   "i", 
 *                   "img", 
 *                   "strong", 
 *                   "em", 
 *                   "p"
 *                  );
 *
 * This will remove all tags from the body except b, a, i, img, strong, em and
 * p.
 *
 * $rm_tags_with_content
 * ---------------------
 * This is a simple one-dimentional array of strings, which specifies the
 * tags to be removed with any and all content between the beginning and
 * the end of the tag.
 * Example:
 * $rm_tags_with_content = Array(
 *                               "script",
 *                               "style", 
 *                               "applet",
 *                               "embed"
 *                              );
 *
 * This will remove the following structure:
 * <script>
 *  window.alert("Isn't cross-site-scripting fun?!");
 * </script>
 * 
 * $self_closing_tags
 * ------------------
 * This is a simple one-dimentional array of strings, which specifies which
 * tags contain no content and should not be forcefully closed if this option
 * is turned on (see further).
 * Example:
 * $self_closing_tags =  Array(
 *                             "img",
 *                             "br", 
 *                             "hr",
 *                             "input"
 *                            );    
 *
 * $force_tag_closing
 * ------------------
 * Set it to true to forcefully close any tags opened within the document.
 * This is good if you want to take care of people who like to screw up
 * the pages by leaving unclosed tags like <a>, <b>, <i>, etc.
 *
 * $rm_attnames
 * -------------
 * Now we come to parameters that are more obscure. This parameter is
 * a nested array which is used to specify which attributes should be
 * removed. It goes like so:
 * 
 * $rm_attnames = Array(
 *   "PCRE regex to match tag name" =>
 *     Array(
 *           "PCRE regex to match attribute name"
 *           )
 *   );
 *
 * Example:
 * $rm_attnames = Array(
 *   "|.*|" =>
 *     Array(
 *           "|target|i",
 *           "|^on.*|i"  
 *          )
 *   );
 *
 * This will match all attributes (.*), and specify that all attributes
 * named "target" and starting with "on" should be removed. This will take
 * care of the following problem:
 * <em onmouseover="window.alert('muahahahaha')">
 * The "onmouseover" will be removed.
 *
 * $bad_attvals
 * ------------
 * This is where it gets ugly. This is a nested array with many levels.
 * It goes like so:
 *
 * $bad_attvals = Array(
 *   "pcre regex to match tag name" =>
 *     Array(
 *           "pcre regex to match attribute name" =>
 *             Array(
 *                   "pcre regex to match attribute value"
 *                  )
 *             Array(
 *                   "pcre regex replace a match from above with"
 *                  )
 *          )
 *   );
 *
 * An extensive example:
 *
 * $bad_attvals = Array(
 *   "|.*|" =>
 *      Array(
 *            "/^src|background|href|action/i" =>
 *                Array(
 *                      Array(
 *                            "/^([\'\"])\s*\S+script\s*:.*([\'\"])/si"
 *                            ),
 *                      Array(
 *                            "\\1http://veryfunny.com/\\2"
 *                            )
 *                      ),
 *            "/^style/i" =>
 *                Array(
 *                      Array(
 *                            "/expression/si",
 *                            "/url\(([\'\"])\s*https*:.*([\'\"])\)/si",
 *                            "/url\(([\'\"])\s*\S+script:.*([\'\"])\)/si"
 *                           ),
 *                      Array(
 *                            "idiocy",
 *                            "url(\\1http://veryfunny.com/\\2)",
 *                            "url(\\1http://veryfynny.com/\\2)"
 *                           )
 *                      )
 *            )
 *  );
 *
 * This will take care of nearly all known cross-site scripting exploits,
 * plus some (see my filter sample at 
 * http://www.mricon.com/html/phpfilter.html for a working version).
 *
 * $add_attr_to_tag
 * ----------------
 * This is a useful little feature which lets you add attributes to 
 * certain tags. It is a nested array as well, but not at all like
 * the previous one. It goes like so:
 * 
 * $add_attr_to_tag = Array(
 *   "PCRE regex to match tag name" =>
 *     Array(
 *           "attribute name"=>'"attribute value"'
 *          )
 *   );
 * 
 * Note: don't forget quotes around attribute value.
 * 
 * Example:
 * 
 * $add_attr_to_tag = Array(
 *   "/^a$/si" => 
 *     Array(
 *           'target'=>'"_new"'
 *          )
 *   );
 * 
 * This will change all <a> tags and add target="_new" to them so all links
 * open in a new window.
 *
 *
 *
 * @param $body                 the string with HTML you wish to filter
 * @param $tag_list             see description above
 * @param $rm_tags_with_content see description above
 * @param $self_closing_tags    see description above
 * @param $force_tag_closing    see description above
 * @param $rm_attnames          see description above
 * @param $bad_attvals          see description above
 * @param $add_attr_to_tag      see description above
 * @return                      sanitized html safe to show on your pages.
 */
function sanitize($body, 
                  $tag_list, 
                  $rm_tags_with_content,
                  $self_closing_tags,
                  $force_tag_closing,
                  $rm_attnames,
                  $bad_attvals,
                  $add_attr_to_tag
                  ){
  $me = 'sanitize';
  /**
   * Normalize rm_tags and rm_tags_with_content.
   */
  @array_walk($rm_tags, 'casenormalize');
  @array_walk($rm_tags_with_content, 'casenormalize');
  @array_walk($self_closing_tags, 'casenormalize');
  /**
   * See if tag_list is of tags to remove or tags to allow.
   * false  means remove these tags
   * true   means allow these tags
   */
  $rm_tags = array_shift($tag_list);
  $curpos = 0;
  $open_tags = Array();
  $trusted = ""; /* "<!-- begin sanitized html -->\n";*/
  $skip_content = false;
  /**
   * Take care of netscape's stupid javascript entities like
   * &{alert('boo')};
   */
  $body = preg_replace('/&(\{.*?\};)/si', '&amp;\\1', $body);
  spew("$me: invoking the loop\n");
  while (($curtag = getnxtag($body, $curpos)) != FALSE){
    list($tagname, $attary, $tagtype, $lt, $gt) = $curtag;
    spew("$me: grabbing free-standing content\n");
    $free_content = substr($body, $curpos, $lt - $curpos);
    spew("$me: " . strlen($free_content) . " chars grabbed\n");
    if ($skip_content == false){
      spew("$me: appending free content to trusted.\n");
      $trusted .= $free_content;
    } else {
      spew("$me: Skipping free content.\n");
    }
    if ($tagname != FALSE){
      spew("$me: tagname is '$tagname'\n");
      if ($tagtype == 2){
        spew("$me: This is a closing tag\n");
        if ($skip_content == $tagname){
          /**
           * Got to the end of tag we needed to remove.
           */
          spew("$me: Finished removing tag with content\n");
          $tagname = false;
          $skip_content = false;
        } else {
          if ($skip_content == false){
            if (isset($open_tags{$tagname}) && 
                $open_tags{$tagname} > 0){
              spew("$me: popping '$tagname' from open_tags\n");
              $open_tags{$tagname}--;
            } else {
              spew("$me: '$tagname' was never opened\n");
              spew("$me: removing\n");
              $tagname = false;
            }
          } else {
            spew("$me: Skipping this tag\n");
          }
        }
      } else {
        /**
         * $rm_tags_with_content
         */
        if ($skip_content == false){
          /**
           * See if this is a self-closing type and change
           * tagtype appropriately.
           */
          if ($tagtype == 1
              && in_array($tagname, $self_closing_tags)){
            spew("$me: Self-closing tag. Changing tagtype.\n");
            $tagtype = 3;
          }
          /**
           * See if we should skip this tag and any content
           * inside it.
           */
          if ($tagtype == 1 && in_array($tagname, $rm_tags_with_content)){
            spew("$me: removing this tag with content\n");
            $skip_content = $tagname;
          } else {
            if (($rm_tags == false && in_array($tagname, $tag_list)) ||
                ($rm_tags == true && !in_array($tagname, $tag_list))){
              spew("$me: Removing this tag.\n");
              $tagname = false;
            } else {
              if ($tagtype == 1){
                spew("$me: adding '$tagname' to open_tags\n");
                if (isset($open_tags{$tagname})){
                  $open_tags{$tagname}++;
                } else {
                  $open_tags{$tagname} = 1;
                }
              }
              /**
               * This is where we run other checks.
               */
              if (is_array($attary) && sizeof($attary) > 0){
                $attary = fixatts($tagname,
                                  $attary,
                                  $rm_attnames,
                                  $bad_attvals,
                                  $add_attr_to_tag);
              }
            }
          }
        } else {
          spew("$me: Skipping this tag\n");
        }
      }
      if ($tagname != false && $skip_content == false){
        spew("$me: Appending tag to trusted.\n");
        $trusted .= tagprint($tagname, $attary, $tagtype);
      }
    } else {
      spew("$me: Removing invalid tag\n");
    }
    $curpos = $gt + 1;
  }
  spew("$me: Appending any leftover content\n");
  $trusted .= substr($body, $curpos, strlen($body) - $curpos);
  if ($force_tag_closing == true){
    foreach ($open_tags as $tagname=>$opentimes){
      while ($opentimes > 0){
        spew("$me: '$tagname' left open. Closing by force.\n");
        $trusted .= '</' . $tagname . '>';
        $opentimes--;
      }
    }
    $trusted .= "\n";
  }
  /*$trusted .= "<!-- end sanitized html -->\n";*/
  return $trusted;
}
?>