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',
);

function codepointToUtf8($codepoint)
{
    if ($codepoint < 0x80) {
        return chr($codepoint);
    }
    if ($codepoint < 0x800) {
        return chr($codepoint >> 6 & 0x3f | 0xc0) .
            chr($codepoint & 0x3f | 0x80);
    }
    if ($codepoint < 0x10000) {
        return chr($codepoint >> 12 & 0x0f | 0xe0) .
            chr($codepoint >> 6 & 0x3f | 0x80) .
            chr($codepoint & 0x3f | 0x80);
    }
    if ($codepoint < 0x110000) {
        return chr($codepoint >> 18 & 0x07 | 0xf0) .
            chr($codepoint >> 12 & 0x3f | 0x80) .
            chr($codepoint >> 6 & 0x3f | 0x80) .
            chr($codepoint & 0x3f | 0x80);
    }
    return "";
}


class Sanitizer
{
    public 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();
                                $optstack[] = $ot;
                                while ((($ot = @array_pop($tagstack)) != $t) &&
                                        isset($htmlsingleallowed[$ot])) {
                                    $optstack[] = $ot;
                                }
                                if ($t != $ot) {
                                    # No match. Push the optinal elements back again
                                    $badtag = 1;
                                    while ($ot = @array_pop($optstack)) {
                                        $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)) {
                            $badtag = 1;
                        } elseif (in_array($t, $tagstack) &&
                        !isset($htmlnest [$t ])) {
                            $badtag = 1 ;
                        # Is it a self closed htmlpair ? (bug 5487)
                        } elseif ($brace == '/>' &&
                        isset($htmlpairs[$t])) {
                            $badtag = 1;
                        } elseif (isset($htmlsingleonly[$t])) {
                            # Hack to force empty tag for uncloseable elements
                            $brace = '/>';
                        } elseif (isset($htmlsingle[$t])) {
                            # Hack to not close $htmlsingle tags
                            $brace = null;
                        } elseif (isset($tabletags[$t])
                        && in_array($t, $tagstack)) {
                            // New table tag but forgot to close the previous one
                            $text .= "</$t>";
                        } else {
                            if ($t == 'table') {
                                $tablestack[] = $tagstack;
                                $tagstack = array();
                            }
                            $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;
    }

    public 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;
    }

    public 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;
    }

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

        return $value;
    }

    public 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) : '';
    }

    public 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;
    }

    public 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;
    }

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

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

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

    public 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]);
    }

    public 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
        );
    }

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

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

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

    public 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
        );
    }

    public 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];
    }

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

    public 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;";
        }
    }

    public static function attributeWhitelist($element)
    {
        static $list;
        if (!isset($list)) {
            $list = Sanitizer::setupAttributeWhitelist();
        }

        return $list[$element] ?? array();
    }

    public 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;
    }

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

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

        return $text;
    }

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

    public 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_callback(
            '/[\][<>"\\x00-\\x20\\x7F]/',
            function ($hit) {
                if ($hit[0] === '"') {
                    return urlencode('\\"');
                } else {
                    return urlencode($hit[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;
        }
    }
}