Sanitizer.php

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<?php
define( 'MW_CHAR_REFS_REGEX',
        '/&([A-Za-z0-9\x80-\xff]+);
         |&\#([0-9]+);
         |&\#x([0-9A-Za-z]+);
         |&\#X([0-9A-Za-z]+);
         |(&)/x' );

$attrib = '[A-Za-z0-9]';
$space = '[\x09\x0a\x0d\x20]';
define( 'MW_ATTRIBS_REGEX',
        "/(?:^|$space)($attrib+)
          ($space*=$space*
                (?:
                 # The attribute value: quoted or alone
                  \"([^<\"]*)\"
                 | '([^<']*)'
                 |  ([a-zA-Z0-9!#$%&()*,\\-.\\/:;<>?@[\\]^_`{|}~]+)
                 |  (\#[0-9a-fA-F]+) # Technically wrong, but lots of
                                                         # colors are specified like this.
                                                         # We'll be normalizing it.
                )
           )?(?=$space|\$)/sx" );

global $wgHtmlEntities;
$wgHtmlEntities = array(
        'Aacute'   => 193,
        'aacute'   => 225,
        'Acirc'    => 194,
        'acirc'    => 226,
        'acute'    => 180,
        'AElig'    => 198,
        'aelig'    => 230,
        'Agrave'   => 192,
        'agrave'   => 224,
        'alefsym'  => 8501,
        'Alpha'    => 913,
        'alpha'    => 945,
        'amp'      => 38,
        'and'      => 8743,
        'ang'      => 8736,
        'Aring'    => 197,
        'aring'    => 229,
        'asymp'    => 8776,
        'Atilde'   => 195,
        'atilde'   => 227,
        'Auml'     => 196,
        'auml'     => 228,
        'bdquo'    => 8222,
        'Beta'     => 914,
        'beta'     => 946,
        'brvbar'   => 166,
        'bull'     => 8226,
        'cap'      => 8745,
        'Ccedil'   => 199,
        'ccedil'   => 231,
        'cedil'    => 184,
        'cent'     => 162,
        'Chi'      => 935,
        'chi'      => 967,
        'circ'     => 710,
        'clubs'    => 9827,
        'cong'     => 8773,
        'copy'     => 169,
        'crarr'    => 8629,
        'cup'      => 8746,
        'curren'   => 164,
        'dagger'   => 8224,
        'Dagger'   => 8225,
        'darr'     => 8595,
        'dArr'     => 8659,
        'deg'      => 176,
        'Delta'    => 916,
        'delta'    => 948,
        'diams'    => 9830,
        'divide'   => 247,
        'Eacute'   => 201,
        'eacute'   => 233,
        'Ecirc'    => 202,
        'ecirc'    => 234,
        'Egrave'   => 200,
        'egrave'   => 232,
        'empty'    => 8709,
        'emsp'     => 8195,
        'ensp'     => 8194,
        'Epsilon'  => 917,
        'epsilon'  => 949,
        'equiv'    => 8801,
        'Eta'      => 919,
        'eta'      => 951,
        'ETH'      => 208,
        'eth'      => 240,
        'Euml'     => 203,
        'euml'     => 235,
        'euro'     => 8364,
        'exist'    => 8707,
        'fnof'     => 402,
        'forall'   => 8704,
        'frac12'   => 189,
        'frac14'   => 188,
        'frac34'   => 190,
        'frasl'    => 8260,
        'Gamma'    => 915,
        'gamma'    => 947,
        'ge'       => 8805,
        'gt'       => 62,
        'harr'     => 8596,
        'hArr'     => 8660,
        'hearts'   => 9829,
        'hellip'   => 8230,
        'Iacute'   => 205,
        'iacute'   => 237,
        'Icirc'    => 206,
        'icirc'    => 238,
        'iexcl'    => 161,
        'Igrave'   => 204,
        'igrave'   => 236,
        'image'    => 8465,
        'infin'    => 8734,
        'int'      => 8747,
        'Iota'     => 921,
        'iota'     => 953,
        'iquest'   => 191,
        'isin'     => 8712,
        'Iuml'     => 207,
        'iuml'     => 239,
        'Kappa'    => 922,
        'kappa'    => 954,
        'Lambda'   => 923,
        'lambda'   => 955,
        'lang'     => 9001,
        'laquo'    => 171,
        'larr'     => 8592,
        'lArr'     => 8656,
        'lceil'    => 8968,
        'ldquo'    => 8220,
        'le'       => 8804,
        'lfloor'   => 8970,
        'lowast'   => 8727,
        'loz'      => 9674,
        'lrm'      => 8206,
        'lsaquo'   => 8249,
        'lsquo'    => 8216,
        'lt'       => 60,
        'macr'     => 175,
        'mdash'    => 8212,
        'micro'    => 181,
        'middot'   => 183,
        'minus'    => 8722,
        'Mu'       => 924,
        'mu'       => 956,
        'nabla'    => 8711,
        'nbsp'     => 160,
        'ndash'    => 8211,
        'ne'       => 8800,
        'ni'       => 8715,
        'not'      => 172,
        'notin'    => 8713,
        'nsub'     => 8836,
        'Ntilde'   => 209,
        'ntilde'   => 241,
        'Nu'       => 925,
        'nu'       => 957,
        'Oacute'   => 211,
        'oacute'   => 243,
        'Ocirc'    => 212,
        'ocirc'    => 244,
        'OElig'    => 338,
        'oelig'    => 339,
        'Ograve'   => 210,
        'ograve'   => 242,
        'oline'    => 8254,
        'Omega'    => 937,
        'omega'    => 969,
        'Omicron'  => 927,
        'omicron'  => 959,
        'oplus'    => 8853,
        'or'       => 8744,
        'ordf'     => 170,
        'ordm'     => 186,
        'Oslash'   => 216,
        'oslash'   => 248,
        'Otilde'   => 213,
        'otilde'   => 245,
        'otimes'   => 8855,
        'Ouml'     => 214,
        'ouml'     => 246,
        'para'     => 182,
        'part'     => 8706,
        'permil'   => 8240,
        'perp'     => 8869,
        'Phi'      => 934,
        'phi'      => 966,
        'Pi'       => 928,
        'pi'       => 960,
        'piv'      => 982,
        'plusmn'   => 177,
        'pound'    => 163,
        'prime'    => 8242,
        'Prime'    => 8243,
        'prod'     => 8719,
        'prop'     => 8733,
        'Psi'      => 936,
        'psi'      => 968,
        'quot'     => 34,
        'radic'    => 8730,
        'rang'     => 9002,
        'raquo'    => 187,
        'rarr'     => 8594,
        'rArr'     => 8658,
        'rceil'    => 8969,
        'rdquo'    => 8221,
        'real'     => 8476,
        'reg'      => 174,
        'rfloor'   => 8971,
        'Rho'      => 929,
        'rho'      => 961,
        'rlm'      => 8207,
        'rsaquo'   => 8250,
        'rsquo'    => 8217,
        'sbquo'    => 8218,
        'Scaron'   => 352,
        'scaron'   => 353,
        'sdot'     => 8901,
        'sect'     => 167,
        'shy'      => 173,
        'Sigma'    => 931,
        'sigma'    => 963,
        'sigmaf'   => 962,
        'sim'      => 8764,
        'spades'   => 9824,
        'sub'      => 8834,
        'sube'     => 8838,
        'sum'      => 8721,
        'sup'      => 8835,
        'sup1'     => 185,
        'sup2'     => 178,
        'sup3'     => 179,
        'supe'     => 8839,
        'szlig'    => 223,
        'Tau'      => 932,
        'tau'      => 964,
        'there4'   => 8756,
        'Theta'    => 920,
        'theta'    => 952,
        'thetasym' => 977,
        'thinsp'   => 8201,
        'THORN'    => 222,
        'thorn'    => 254,
        'tilde'    => 732,
        'times'    => 215,
        'trade'    => 8482,
        'Uacute'   => 218,
        'uacute'   => 250,
        'uarr'     => 8593,
        'uArr'     => 8657,
        'Ucirc'    => 219,
        'ucirc'    => 251,
        'Ugrave'   => 217,
        'ugrave'   => 249,
        'uml'      => 168,
        'upsih'    => 978,
        'Upsilon'  => 933,
        'upsilon'  => 965,
        'Uuml'     => 220,
        'uuml'     => 252,
        'weierp'   => 8472,
        'Xi'       => 926,
        'xi'       => 958,
        'Yacute'   => 221,
        'yacute'   => 253,
        'yen'      => 165,
        'Yuml'     => 376,
        'yuml'     => 255,
        'Zeta'     => 918,
        'zeta'     => 950,
        'zwj'      => 8205,
        'zwnj'     => 8204 );

global $wgHtmlEntityAliases;
$wgHtmlEntityAliases = array(
        'רלמ' => 'rlm',
        'رلم' => 'rlm',
);


class Sanitizer {
        static function removeHTMLtags( $text, $processCallback = null, $args = array() ) {
                global $wgUseTidy;

                static $htmlpairs, $htmlsingle, $htmlsingleonly, $htmlnest, $tabletags,
                        $htmllist, $listtags, $htmlsingleallowed, $htmlelements, $staticInitialised;

                wfProfileIn( __METHOD__ );

                if ( !$staticInitialised ) {

                        $htmlpairs = array( # Tags that must be closed
                                'b', 'del', 'i', 'ins', 'u', 'font', 'big', 'small', 'sub', 'sup', 'h1',
                                'h2', 'h3', 'h4', 'h5', 'h6', 'cite', 'code', 'em', 's',
                                'strike', 'strong', 'tt', 'var', 'div', 'center',
                                'blockquote', 'ol', 'ul', 'dl', 'table', 'caption', 'pre',
                                'ruby', 'rt' , 'rb' , 'rp', 'p', 'span', 'u'
                        );
                        $htmlsingle = array(
                                'br', 'hr', 'li', 'dt', 'dd'
                        );
                        $htmlsingleonly = array( # Elements that cannot have close tags
                                'br', 'hr'
                        );
                        $htmlnest = array( # Tags that can be nested--??
                                'table', 'tr', 'td', 'th', 'div', 'blockquote', 'ol', 'ul',
                                'dl', 'font', 'big', 'small', 'sub', 'sup', 'span'
                        );
                        $tabletags = array( # Can only appear inside table, we will close them
                                'td', 'th', 'tr',
                        );
                        $htmllist = array( # Tags used by list
                                'ul','ol',
                        );
                        $listtags = array( # Tags that can appear in a list
                                'li',
                        );

                        $htmlsingleallowed = array_merge( $htmlsingle, $tabletags );
                        $htmlelements = array_merge( $htmlsingle, $htmlpairs, $htmlnest );

                        # Convert them all to hashtables for faster lookup
                        $vars = array( 'htmlpairs', 'htmlsingle', 'htmlsingleonly', 'htmlnest', 'tabletags', 
                                'htmllist', 'listtags', 'htmlsingleallowed', 'htmlelements' );
                        foreach ( $vars as $var ) {
                                $$var = array_flip( $$var );
                        }
                        $staticInitialised = true;
                }

                # Remove HTML comments
                $text = Sanitizer::removeHTMLcomments( $text );
                $bits = explode( '<', $text );
                $text = str_replace( '>', '&gt;', array_shift( $bits ) );
                if(!$wgUseTidy) {
                        $tagstack = $tablestack = array();
                        foreach ( $bits as $x ) {
                                $regs = array();
                                if( preg_match( '!^(/?)(\\w+)([^>]*?)(/{0,1}>)([^<]*)$!', $x, $regs ) ) {
                                        list( /* $qbar */, $slash, $t, $params, $brace, $rest ) = $regs;
                                } else {
                                        $slash = $t = $params = $brace = $rest = null;
                                }

                                $badtag = 0 ;
                                if ( isset( $htmlelements[$t = strtolower( $t )] ) ) {
                                        # Check our stack
                                        if ( $slash ) {
                                                # Closing a tag...
                                                if( isset( $htmlsingleonly[$t] ) ) {
                                                        $badtag = 1;
                                                } elseif ( ( $ot = @array_pop( $tagstack ) ) != $t ) {
                                                        if ( isset( $htmlsingleallowed[$ot] ) ) {
                                                                # Pop all elements with an optional close tag
                                                                # and see if we find a match below them
                                                                $optstack = array();
                                                                array_push ($optstack, $ot);
                                                                while ( ( ( $ot = @array_pop( $tagstack ) ) != $t ) &&
                                                                                isset( $htmlsingleallowed[$ot] ) ) 
                                                                {
                                                                        array_push ($optstack, $ot);
                                                                }
                                                                if ( $t != $ot ) {
                                                                        # No match. Push the optinal elements back again
                                                                        $badtag = 1;
                                                                        while ( $ot = @array_pop( $optstack ) ) {
                                                                                array_push( $tagstack, $ot );
                                                                        }
                                                                }
                                                        } else {
                                                                @array_push( $tagstack, $ot );
                                                                # <li> can be nested in <ul> or <ol>, skip those cases:
                                                                if(!(isset( $htmllist[$ot] ) && isset( $listtags[$t] ) )) {
                                                                        $badtag = 1;
                                                                }
                                                        }
                                                } else {
                                                        if ( $t == 'table' ) {
                                                                $tagstack = array_pop( $tablestack );
                                                        }
                                                }
                                                $newparams = '';
                                        } else {
                                                # Keep track for later
                                                if ( isset( $tabletags[$t] ) &&
                                                ! in_array( 'table', $tagstack ) ) {
                                                        $badtag = 1;
                                                } else if ( in_array( $t, $tagstack ) &&
                                                ! isset( $htmlnest [$t ] ) ) {
                                                        $badtag = 1 ;
                                                # Is it a self closed htmlpair ? (bug 5487)
                                                } else if( $brace == '/>' &&
                                                isset( $htmlpairs[$t] ) ) {
                                                        $badtag = 1;
                                                } elseif( isset( $htmlsingleonly[$t] ) ) {
                                                        # Hack to force empty tag for uncloseable elements
                                                        $brace = '/>';
                                                } else if( isset( $htmlsingle[$t] ) ) {
                                                        # Hack to not close $htmlsingle tags
                                                        $brace = NULL;
                                                } else if( isset( $tabletags[$t] )
                                                &&  in_array($t ,$tagstack) ) {
                                                        // New table tag but forgot to close the previous one
                                                        $text .= "</$t>";
                                                } else {
                                                        if ( $t == 'table' ) {
                                                                array_push( $tablestack, $tagstack );
                                                                $tagstack = array();
                                                        }
                                                        array_push( $tagstack, $t );
                                                }

                                                # Replace any variables or template parameters with
                                                # plaintext results.
                                                if( is_callable( $processCallback ) ) {
                                                        call_user_func_array( $processCallback, array( &$params, $args ) );
                                                }

                                                # Strip non-approved attributes from the tag
                                                $newparams = Sanitizer::fixTagAttributes( $params, $t );
                                        }
                                        if ( ! $badtag ) {
                                                $rest = str_replace( '>', '&gt;', $rest );
                                                $close = ( $brace == '/>' && !$slash ) ? ' /' : '';
                                                $text .= "<$slash$t$newparams$close>$rest";
                                                continue;
                                        }
                                }
                                $text .= '&lt;' . str_replace( '>', '&gt;', $x);
                        }
                        # Close off any remaining tags
                        while ( is_array( $tagstack ) && ($t = array_pop( $tagstack )) ) {
                                $text .= "</$t>\n";
                                if ( $t == 'table' ) { $tagstack = array_pop( $tablestack ); }
                        }
                } else {
                        # this might be possible using tidy itself
                        foreach ( $bits as $x ) {
                                preg_match( '/^(\\/?)(\\w+)([^>]*?)(\\/{0,1}>)([^<]*)$/',
                                $x, $regs );
                                @list( /* $qbar */, $slash, $t, $params, $brace, $rest ) = $regs;
                                if ( isset( $htmlelements[$t = strtolower( $t )] ) ) {
                                        if( is_callable( $processCallback ) ) {
                                                call_user_func_array( $processCallback, array( &$params, $args ) );
                                        }
                                        $newparams = Sanitizer::fixTagAttributes( $params, $t );
                                        $rest = str_replace( '>', '&gt;', $rest );
                                        $text .= "<$slash$t$newparams$brace$rest";
                                } else {
                                        $text .= '&lt;' . str_replace( '>', '&gt;', $x);
                                }
                        }
                }
                wfProfileOut( __METHOD__ );
                return $text;
        }

        static function removeHTMLcomments( $text ) {
                wfProfileIn( __METHOD__ );
                while (($start = strpos($text, '<!--')) !== false) {
                        $end = strpos($text, '-->', $start + 4);
                        if ($end === false) {
                                # Unterminated comment; bail out
                                break;
                        }

                        $end += 3;

                        # Trim space and newline if the comment is both
                        # preceded and followed by a newline
                        $spaceStart = max($start - 1, 0);
                        $spaceLen = $end - $spaceStart;
                        while (substr($text, $spaceStart, 1) === ' ' && $spaceStart > 0) {
                                $spaceStart--;
                                $spaceLen++;
                        }
                        while (substr($text, $spaceStart + $spaceLen, 1) === ' ')
                                $spaceLen++;
                        if (substr($text, $spaceStart, 1) === "\n" and substr($text, $spaceStart + $spaceLen, 1) === "\n") {
                                # Remove the comment, leading and trailing
                                # spaces, and leave only one newline.
                                $text = substr_replace($text, "\n", $spaceStart, $spaceLen + 1);
                        }
                        else {
                                # Remove just the comment.
                                $text = substr_replace($text, '', $start, $end - $start);
                        }
                }
                wfProfileOut( __METHOD__ );
                return $text;
        }

        static function validateTagAttributes( $attribs, $element ) {
                $whitelist = array_flip( Sanitizer::attributeWhitelist( $element ) );
                $out = array();
                foreach( $attribs as $attribute => $value ) {
                        if( !isset( $whitelist[$attribute] ) ) {
                                continue;
                        }
                        # Strip javascript "expression" from stylesheets.
                        # http://msdn.microsoft.com/workshop/author/dhtml/overview/recalc.asp
                        if( $attribute == 'style' ) {
                                $value = Sanitizer::checkCss( $value );
                                if( $value === false ) {
                                        # haxx0r
                                        continue;
                                }
                        }

                        if ( $attribute === 'id' )
                                $value = Sanitizer::escapeId( $value );

                        // If this attribute was previously set, override it.
                        // Output should only have one attribute of each name.
                        $out[$attribute] = $value;
                }
                return $out;
        }
        
        static function checkCss( $value ) {
                $stripped = Sanitizer::decodeCharReferences( $value );

                // Remove any comments; IE gets token splitting wrong
                $stripped = StringUtils::delimiterReplace( '/*', '*/', ' ', $stripped );
                
                $value = $stripped;

                // ... and continue checks
                $stripped = preg_replace( '!\\\\([0-9A-Fa-f]{1,6})[ \\n\\r\\t\\f]?!e',
                        'codepointToUtf8(hexdec("$1"))', $stripped );
                $stripped = str_replace( '\\', '', $stripped );
                if( preg_match( '/(?:expression|tps*:\/\/|url\\s*\().*/is',
                                $stripped ) ) {
                        # haxx0r
                        return false;
                }
                
                return $value;
        }

        static function fixTagAttributes( $text, $element ) {
                if( trim( $text ) == '' ) {
                        return '';
                }

                $stripped = Sanitizer::validateTagAttributes(
                        Sanitizer::decodeTagAttributes( $text ), $element );

                $attribs = array();
                foreach( $stripped as $attribute => $value ) {
                        $encAttribute = htmlspecialchars( $attribute );
                        $encValue = Sanitizer::safeEncodeAttribute( $value );

                        $attribs[] = "$encAttribute=\"$encValue\"";
                }
                return count( $attribs ) ? ' ' . implode( ' ', $attribs ) : '';
        }

        static function encodeAttribute( $text ) {
                $encValue = htmlspecialchars( $text );

                // Whitespace is normalized during attribute decoding,
                // so if we've been passed non-spaces we must encode them
                // ahead of time or they won't be preserved.
                $encValue = strtr( $encValue, array(
                        "\n" => '&#10;',
                        "\r" => '&#13;',
                        "\t" => '&#9;',
                ) );

                return $encValue;
        }

        static function safeEncodeAttribute( $text ) {
                $encValue = Sanitizer::encodeAttribute( $text );

                # Templates and links may be expanded in later parsing,
                # creating invalid or dangerous output. Suppress this.
                $encValue = strtr( $encValue, array(
                        '<'    => '&lt;',   // This should never happen,
                        '>'    => '&gt;',   // we've received invalid input
                        '"'    => '&quot;', // which should have been escaped.
                        '{'    => '&#123;',
                        '['    => '&#91;',
                        "''"   => '&#39;&#39;',
                        'ISBN' => '&#73;SBN',
                        'RFC'  => '&#82;FC',
                        'PMID' => '&#80;MID',
                        '|'    => '&#124;',
                        '__'   => '&#95;_',
                ) );

                # Stupid hack
                $encValue = preg_replace_callback(
                        '/(' . wfUrlProtocols() . ')/',
                        array( 'Sanitizer', 'armorLinksCallback' ),
                        $encValue );
                return $encValue;
        }

        static function escapeId( $id ) {
                static $replace = array(
                        '%3A' => ':',
                        '%' => '.'
                );

                $id = urlencode( Sanitizer::decodeCharReferences( strtr( $id, ' ', '_' ) ) );

                return str_replace( array_keys( $replace ), array_values( $replace ), $id );
        }

        static function escapeClass( $class ) {
                // Convert ugly stuff to underscores and kill underscores in ugly places
                return rtrim(preg_replace(
                        array('/(^[0-9\\-])|[\\x00-\\x20!"#$%&\'()*+,.\\/:;<=>?@[\\]^`{|}~]|\\xC2\\xA0/','/_+/'),
                        '_',
                        $class ), '_');
        }

        private static function armorLinksCallback( $matches ) {
                return str_replace( ':', '&#58;', $matches[1] );
        }

        static function decodeTagAttributes( $text ) {
                $attribs = array();

                if( trim( $text ) == '' ) {
                        return $attribs;
                }

                $pairs = array();
                if( !preg_match_all(
                        MW_ATTRIBS_REGEX,
                        $text,
                        $pairs,
                        PREG_SET_ORDER ) ) {
                        return $attribs;
                }

                foreach( $pairs as $set ) {
                        $attribute = strtolower( $set[1] );
                        $value = Sanitizer::getTagAttributeCallback( $set );

                        // Normalize whitespace
                        $value = preg_replace( '/[\t\r\n ]+/', ' ', $value );
                        $value = trim( $value );

                        // Decode character references
                        $attribs[$attribute] = Sanitizer::decodeCharReferences( $value );
                }
                return $attribs;
        }

        private static function getTagAttributeCallback( $set ) {
                if( isset( $set[6] ) ) {
                        # Illegal #XXXXXX color with no quotes.
                        return $set[6];
                } elseif( isset( $set[5] ) ) {
                        # No quotes.
                        return $set[5];
                } elseif( isset( $set[4] ) ) {
                        # Single-quoted
                        return $set[4];
                } elseif( isset( $set[3] ) ) {
                        # Double-quoted
                        return $set[3];
                } elseif( !isset( $set[2] ) ) {
                        # In XHTML, attributes must have a value.
                        # For 'reduced' form, return explicitly the attribute name here.
                        return $set[1];
                } else {
                        throw new MWException( "Tag conditions not met. This should never happen and is a bug." );
                }
        }

        private static function normalizeAttributeValue( $text ) {
                return str_replace( '"', '&quot;',
                        self::normalizeWhitespace(
                                Sanitizer::normalizeCharReferences( $text ) ) );
        }
        
        private static function normalizeWhitespace( $text ) {
                return preg_replace(
                        '/\r\n|[\x20\x0d\x0a\x09]/',
                        ' ',
                        $text );
        }

        static function normalizeCharReferences( $text ) {
                return preg_replace_callback(
                        MW_CHAR_REFS_REGEX,
                        array( 'Sanitizer', 'normalizeCharReferencesCallback' ),
                        $text );
        }
        static function normalizeCharReferencesCallback( $matches ) {
                $ret = null;
                if( $matches[1] != '' ) {
                        $ret = Sanitizer::normalizeEntity( $matches[1] );
                } elseif( $matches[2] != '' ) {
                        $ret = Sanitizer::decCharReference( $matches[2] );
                } elseif( $matches[3] != ''  ) {
                        $ret = Sanitizer::hexCharReference( $matches[3] );
                } elseif( $matches[4] != '' ) {
                        $ret = Sanitizer::hexCharReference( $matches[4] );
                }
                if( is_null( $ret ) ) {
                        return htmlspecialchars( $matches[0] );
                } else {
                        return $ret;
                }
        }

        static function normalizeEntity( $name ) {
                global $wgHtmlEntities, $wgHtmlEntityAliases;
                if ( isset( $wgHtmlEntityAliases[$name] ) ) {
                        return "&{$wgHtmlEntityAliases[$name]};";
                } elseif( isset( $wgHtmlEntities[$name] ) ) {
                        return "&$name;";
                } else {
                        return "&amp;$name;";
                }
        }

        static function decCharReference( $codepoint ) {
                $point = intval( $codepoint );
                if( Sanitizer::validateCodepoint( $point ) ) {
                        return sprintf( '&#%d;', $point );
                } else {
                        return null;
                }
        }

        static function hexCharReference( $codepoint ) {
                $point = hexdec( $codepoint );
                if( Sanitizer::validateCodepoint( $point ) ) {
                        return sprintf( '&#x%x;', $point );
                } else {
                        return null;
                }
        }

        private static function validateCodepoint( $codepoint ) {
                return ($codepoint ==    0x09)
                        || ($codepoint ==    0x0a)
                        || ($codepoint ==    0x0d)
                        || ($codepoint >=    0x20 && $codepoint <=   0xd7ff)
                        || ($codepoint >=  0xe000 && $codepoint <=   0xfffd)
                        || ($codepoint >= 0x10000 && $codepoint <= 0x10ffff);
        }

        public static function decodeCharReferences( $text ) {
                return preg_replace_callback(
                        MW_CHAR_REFS_REGEX,
                        array( 'Sanitizer', 'decodeCharReferencesCallback' ),
                        $text );
        }

        static function decodeCharReferencesCallback( $matches ) {
                if( $matches[1] != '' ) {
                        return Sanitizer::decodeEntity( $matches[1] );
                } elseif( $matches[2] != '' ) {
                        return  Sanitizer::decodeChar( intval( $matches[2] ) );
                } elseif( $matches[3] != ''  ) {
                        return  Sanitizer::decodeChar( hexdec( $matches[3] ) );
                } elseif( $matches[4] != '' ) {
                        return  Sanitizer::decodeChar( hexdec( $matches[4] ) );
                }
                # Last case should be an ampersand by itself
                return $matches[0];
        }

        static function decodeChar( $codepoint ) {
                if( Sanitizer::validateCodepoint( $codepoint ) ) {
                        return codepointToUtf8( $codepoint );
                } else {
                        return UTF8_REPLACEMENT;
                }
        }

        static function decodeEntity( $name ) {
                global $wgHtmlEntities, $wgHtmlEntityAliases;
                
                if ( isset( $wgHtmlEntityAliases[$name] ) ) {
                        $name = $wgHtmlEntityAliases[$name];
                }
                if( isset( $wgHtmlEntities[$name] ) ) {
                        return codepointToUtf8( $wgHtmlEntities[$name] );
                } else {
                        return "&$name;";
                }
        }

        static function attributeWhitelist( $element ) {
                static $list;
                if( !isset( $list ) ) {
                        $list = Sanitizer::setupAttributeWhitelist();
                }
                return isset( $list[$element] )
                        ? $list[$element]
                        : array();
        }

        static function setupAttributeWhitelist() {
                $common = array( 'id', 'class', 'lang', 'dir', 'title', 'style' );
                $block = array_merge( $common, array( 'align' ) );
                $tablealign = array( 'align', 'char', 'charoff', 'valign' );
                $tablecell = array( 'abbr',
                                    'axis',
                                    'headers',
                                    'scope',
                                    'rowspan',
                                    'colspan',
                                    'nowrap', # deprecated
                                    'width',  # deprecated
                                    'height', # deprecated
                                    'bgcolor' # deprecated
                                    );

                # Numbers refer to sections in HTML 4.01 standard describing the element.
                # See: http://www.w3.org/TR/html4/
                $whitelist = array (
                        # 7.5.4
                        'div'        => $block,
                        'center'     => $common, # deprecated
                        'span'       => $block, # ??

                        # 7.5.5
                        'h1'         => $block,
                        'h2'         => $block,
                        'h3'         => $block,
                        'h4'         => $block,
                        'h5'         => $block,
                        'h6'         => $block,

                        # 7.5.6
                        # address

                        # 8.2.4
                        # bdo

                        # 9.2.1
                        'em'         => $common,
                        'strong'     => $common,
                        'cite'       => $common,
                        # dfn
                        'code'       => $common,
                        # samp
                        # kbd
                        'var'        => $common,
                        # abbr
                        # acronym

                        # 9.2.2
                        'blockquote' => array_merge( $common, array( 'cite' ) ),
                        # q

                        # 9.2.3
                        'sub'        => $common,
                        'sup'        => $common,

                        # 9.3.1
                        'p'          => $block,

                        # 9.3.2
                        'br'         => array( 'id', 'class', 'title', 'style', 'clear' ),

                        # 9.3.4
                        'pre'        => array_merge( $common, array( 'width' ) ),

                        # 9.4
                        'ins'        => array_merge( $common, array( 'cite', 'datetime' ) ),
                        'del'        => array_merge( $common, array( 'cite', 'datetime' ) ),

                        # 10.2
                        'ul'         => array_merge( $common, array( 'type' ) ),
                        'ol'         => array_merge( $common, array( 'type', 'start' ) ),
                        'li'         => array_merge( $common, array( 'type', 'value' ) ),

                        # 10.3
                        'dl'         => $common,
                        'dd'         => $common,
                        'dt'         => $common,

                        # 11.2.1
                        'table'      => array_merge( $common,
                                                                array( 'summary', 'width', 'border', 'frame',
                                                                                'rules', 'cellspacing', 'cellpadding',
                                                                                'align', 'bgcolor',
                                                                ) ),

                        # 11.2.2
                        'caption'    => array_merge( $common, array( 'align' ) ),

                        # 11.2.3
                        'thead'      => array_merge( $common, $tablealign ),
                        'tfoot'      => array_merge( $common, $tablealign ),
                        'tbody'      => array_merge( $common, $tablealign ),

                        # 11.2.4
                        'colgroup'   => array_merge( $common, array( 'span', 'width' ), $tablealign ),
                        'col'        => array_merge( $common, array( 'span', 'width' ), $tablealign ),

                        # 11.2.5
                        'tr'         => array_merge( $common, array( 'bgcolor' ), $tablealign ),

                        # 11.2.6
                        'td'         => array_merge( $common, $tablecell, $tablealign ),
                        'th'         => array_merge( $common, $tablecell, $tablealign ),

                        # 15.2.1
                        'tt'         => $common,
                        'b'          => $common,
                        'i'          => $common,
                        'big'        => $common,
                        'small'      => $common,
                        'strike'     => $common,
                        's'          => $common,
                        'u'          => $common,

                        # 15.2.2
                        'font'       => array_merge( $common, array( 'size', 'color', 'face' ) ),
                        # basefont

                        # 15.3
                        'hr'         => array_merge( $common, array( 'noshade', 'size', 'width' ) ),

                        # XHTML Ruby annotation text module, simple ruby only.
                        # http://www.w3c.org/TR/ruby/
                        'ruby'       => $common,
                        # rbc
                        # rtc
                        'rb'         => $common,
                        'rt'         => $common, #array_merge( $common, array( 'rbspan' ) ),
                        'rp'         => $common,
                        );
                return $whitelist;
        }

        static function stripAllTags( $text ) {
                # Actual <tags>
                $text = StringUtils::delimiterReplace( '<', '>', '', $text );

                # Normalize &entities and whitespace
                $text = self::decodeCharReferences( $text );
                $text = self::normalizeWhitespace( $text );

                return $text;
        }

        static function hackDocType() {
                global $wgHtmlEntities;
                $out = "<!DOCTYPE html [\n";
                foreach( $wgHtmlEntities as $entity => $codepoint ) {
                        $out .= "<!ENTITY $entity \"&#$codepoint;\">";
                }
                $out .= "]>\n";
                return $out;
        }

        static function cleanUrl( $url, $hostname=true ) {
                # Normalize any HTML entities in input. They will be
                # re-escaped by makeExternalLink().

                $url = Sanitizer::decodeCharReferences( $url );

                # Escape any control characters introduced by the above step
                $url = preg_replace( '/[\][<>"\\x00-\\x20\\x7F]/e', "urlencode('\\0')", $url );

                # Validate hostname portion
                $matches = array();
                if( preg_match( '!^([^:]+:)(//[^/]+)?(.*)$!iD', $url, $matches ) ) {
                        list( /* $whole */, $protocol, $host, $rest ) = $matches;

                        // Characters that will be ignored in IDNs.
                        // http://tools.ietf.org/html/3454#section-3.1
                        // Strip them before further processing so blacklists and such work.
                        $strip = "/
                                \\s|          # general whitespace
                                \xc2\xad|     # 00ad SOFT HYPHEN
                                \xe1\xa0\x86| # 1806 MONGOLIAN TODO SOFT HYPHEN
                                \xe2\x80\x8b| # 200b ZERO WIDTH SPACE
                                \xe2\x81\xa0| # 2060 WORD JOINER
                                \xef\xbb\xbf| # feff ZERO WIDTH NO-BREAK SPACE
                                \xcd\x8f|     # 034f COMBINING GRAPHEME JOINER
                                \xe1\xa0\x8b| # 180b MONGOLIAN FREE VARIATION SELECTOR ONE
                                \xe1\xa0\x8c| # 180c MONGOLIAN FREE VARIATION SELECTOR TWO
                                \xe1\xa0\x8d| # 180d MONGOLIAN FREE VARIATION SELECTOR THREE
                                \xe2\x80\x8c| # 200c ZERO WIDTH NON-JOINER
                                \xe2\x80\x8d| # 200d ZERO WIDTH JOINER
                                [\xef\xb8\x80-\xef\xb8\x8f] # fe00-fe00f VARIATION SELECTOR-1-16
                                /xuD";

                        $host = preg_replace( $strip, '', $host );

                        // @fixme: validate hostnames here

                        return $protocol . $host . $rest;
                } else {
                        return $url;
                }
        }

}

?>