includes/Sanitizer.php

   1 <?php
   2 /**
   3  * HTML sanitizer for %MediaWiki.
   4  *
   5  * Copyright © 2002-2005 Brion Vibber <brion@pobox.com> et al
   6  * https://www.mediawiki.org/
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License as published by
  10  * the Free Software Foundation; either version 2 of the License, or
  11  * (at your option) any later version.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License along
  19  * with this program; if not, write to the Free Software Foundation, Inc.,
  20  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  21  * http://www.gnu.org/copyleft/gpl.html
  22  *
  23  * @file
  24  * @ingroup Parser
  25  */
  26
  27 /**
  28  * HTML sanitizer for MediaWiki
  29  * @ingroup Parser
  30  */
  31 class Sanitizer {
  32         /**
  33          * Regular expression to match various types of character references in
  34          * Sanitizer::normalizeCharReferences and Sanitizer::decodeCharReferences
  35          */
  36         const CHAR_REFS_REGEX =
  37                 '/&([A-Za-z0-9\x80-\xff]+);
  38                  |&\#([0-9]+);
  39                  |&\#[xX]([0-9A-Fa-f]+);
  40                  |(&)/x';
  41
  42         /**
  43          * Acceptable tag name charset from HTML5 parsing spec
  44          * https://www.w3.org/TR/html5/syntax.html#tag-open-state
  45          */
  46         const ELEMENT_BITS_REGEX = '!^(/?)([A-Za-z][^\t\n\v />\0]*+)([^>]*?)(/?>)([^<]*)$!';
  47
  48         /**
  49          * Blacklist for evil uris like javascript:
  50          * WARNING: DO NOT use this in any place that actually requires blacklisting
  51          * for security reasons. There are NUMEROUS[1] ways to bypass blacklisting, the
  52          * only way to be secure from javascript: uri based xss vectors is to whitelist
  53          * things that you know are safe and deny everything else.
  54          * [1]: http://ha.ckers.org/xss.html
  55          */
  56         const EVIL_URI_PATTERN = '!(^|\s|\*/\s*)(javascript|vbscript)([^\w]|$)!i';
  57         const XMLNS_ATTRIBUTE_PATTERN = "/^xmlns:[:A-Z_a-z-.0-9]+$/";
  58
  59         /**
  60          * List of all named character entities defined in HTML 4.01
  61          * https://www.w3.org/TR/html4/sgml/entities.html
  62          * As well as &apos; which is only defined starting in XHTML1.
  63          */
  64         private static $htmlEntities = [
  65                 'Aacute'   => 193,
  66                 'aacute'   => 225,
  67                 'Acirc'    => 194,
  68                 'acirc'    => 226,
  69                 'acute'    => 180,
  70                 'AElig'    => 198,
  71                 'aelig'    => 230,
  72                 'Agrave'   => 192,
  73                 'agrave'   => 224,
  74                 'alefsym'  => 8501,
  75                 'Alpha'    => 913,
  76                 'alpha'    => 945,
  77                 'amp'      => 38,
  78                 'and'      => 8743,
  79                 'ang'      => 8736,
  80                 'apos'     => 39, // New in XHTML & HTML 5; avoid in output for compatibility with IE.
  81                 'Aring'    => 197,
  82                 'aring'    => 229,
  83                 'asymp'    => 8776,
  84                 'Atilde'   => 195,
  85                 'atilde'   => 227,
  86                 'Auml'     => 196,
  87                 'auml'     => 228,
  88                 'bdquo'    => 8222,
  89                 'Beta'     => 914,
  90                 'beta'     => 946,
  91                 'brvbar'   => 166,
  92                 'bull'     => 8226,
  93                 'cap'      => 8745,
  94                 'Ccedil'   => 199,
  95                 'ccedil'   => 231,
  96                 'cedil'    => 184,
  97                 'cent'     => 162,
  98                 'Chi'      => 935,
  99                 'chi'      => 967,
 100                 'circ'     => 710,
 101                 'clubs'    => 9827,
 102                 'cong'     => 8773,
 103                 'copy'     => 169,
 104                 'crarr'    => 8629,
 105                 'cup'      => 8746,
 106                 'curren'   => 164,
 107                 'dagger'   => 8224,
 108                 'Dagger'   => 8225,
 109                 'darr'     => 8595,
 110                 'dArr'     => 8659,
 111                 'deg'      => 176,
 112                 'Delta'    => 916,
 113                 'delta'    => 948,
 114                 'diams'    => 9830,
 115                 'divide'   => 247,
 116                 'Eacute'   => 201,
 117                 'eacute'   => 233,
 118                 'Ecirc'    => 202,
 119                 'ecirc'    => 234,
 120                 'Egrave'   => 200,
 121                 'egrave'   => 232,
 122                 'empty'    => 8709,
 123                 'emsp'     => 8195,
 124                 'ensp'     => 8194,
 125                 'Epsilon'  => 917,
 126                 'epsilon'  => 949,
 127                 'equiv'    => 8801,
 128                 'Eta'      => 919,
 129                 'eta'      => 951,
 130                 'ETH'      => 208,
 131                 'eth'      => 240,
 132                 'Euml'     => 203,
 133                 'euml'     => 235,
 134                 'euro'     => 8364,
 135                 'exist'    => 8707,
 136                 'fnof'     => 402,
 137                 'forall'   => 8704,
 138                 'frac12'   => 189,
 139                 'frac14'   => 188,
 140                 'frac34'   => 190,
 141                 'frasl'    => 8260,
 142                 'Gamma'    => 915,
 143                 'gamma'    => 947,
 144                 'ge'       => 8805,
 145                 'gt'       => 62,
 146                 'harr'     => 8596,
 147                 'hArr'     => 8660,
 148                 'hearts'   => 9829,
 149                 'hellip'   => 8230,
 150                 'Iacute'   => 205,
 151                 'iacute'   => 237,
 152                 'Icirc'    => 206,
 153                 'icirc'    => 238,
 154                 'iexcl'    => 161,
 155                 'Igrave'   => 204,
 156                 'igrave'   => 236,
 157                 'image'    => 8465,
 158                 'infin'    => 8734,
 159                 'int'      => 8747,
 160                 'Iota'     => 921,
 161                 'iota'     => 953,
 162                 'iquest'   => 191,
 163                 'isin'     => 8712,
 164                 'Iuml'     => 207,
 165                 'iuml'     => 239,
 166                 'Kappa'    => 922,
 167                 'kappa'    => 954,
 168                 'Lambda'   => 923,
 169                 'lambda'   => 955,
 170                 'lang'     => 9001,
 171                 'laquo'    => 171,
 172                 'larr'     => 8592,
 173                 'lArr'     => 8656,
 174                 'lceil'    => 8968,
 175                 'ldquo'    => 8220,
 176                 'le'       => 8804,
 177                 'lfloor'   => 8970,
 178                 'lowast'   => 8727,
 179                 'loz'      => 9674,
 180                 'lrm'      => 8206,
 181                 'lsaquo'   => 8249,
 182                 'lsquo'    => 8216,
 183                 'lt'       => 60,
 184                 'macr'     => 175,
 185                 'mdash'    => 8212,
 186                 'micro'    => 181,
 187                 'middot'   => 183,
 188                 'minus'    => 8722,
 189                 'Mu'       => 924,
 190                 'mu'       => 956,
 191                 'nabla'    => 8711,
 192                 'nbsp'     => 160,
 193                 'ndash'    => 8211,
 194                 'ne'       => 8800,
 195                 'ni'       => 8715,
 196                 'not'      => 172,
 197                 'notin'    => 8713,
 198                 'nsub'     => 8836,
 199                 'Ntilde'   => 209,
 200                 'ntilde'   => 241,
 201                 'Nu'       => 925,
 202                 'nu'       => 957,
 203                 'Oacute'   => 211,
 204                 'oacute'   => 243,
 205                 'Ocirc'    => 212,
 206                 'ocirc'    => 244,
 207                 'OElig'    => 338,
 208                 'oelig'    => 339,
 209                 'Ograve'   => 210,
 210                 'ograve'   => 242,
 211                 'oline'    => 8254,
 212                 'Omega'    => 937,
 213                 'omega'    => 969,
 214                 'Omicron'  => 927,
 215                 'omicron'  => 959,
 216                 'oplus'    => 8853,
 217                 'or'       => 8744,
 218                 'ordf'     => 170,
 219                 'ordm'     => 186,
 220                 'Oslash'   => 216,
 221                 'oslash'   => 248,
 222                 'Otilde'   => 213,
 223                 'otilde'   => 245,
 224                 'otimes'   => 8855,
 225                 'Ouml'     => 214,
 226                 'ouml'     => 246,
 227                 'para'     => 182,
 228                 'part'     => 8706,
 229                 'permil'   => 8240,
 230                 'perp'     => 8869,
 231                 'Phi'      => 934,
 232                 'phi'      => 966,
 233                 'Pi'       => 928,
 234                 'pi'       => 960,
 235                 'piv'      => 982,
 236                 'plusmn'   => 177,
 237                 'pound'    => 163,
 238                 'prime'    => 8242,
 239                 'Prime'    => 8243,
 240                 'prod'     => 8719,
 241                 'prop'     => 8733,
 242                 'Psi'      => 936,
 243                 'psi'      => 968,
 244                 'quot'     => 34,
 245                 'radic'    => 8730,
 246                 'rang'     => 9002,
 247                 'raquo'    => 187,
 248                 'rarr'     => 8594,
 249                 'rArr'     => 8658,
 250                 'rceil'    => 8969,
 251                 'rdquo'    => 8221,
 252                 'real'     => 8476,
 253                 'reg'      => 174,
 254                 'rfloor'   => 8971,
 255                 'Rho'      => 929,
 256                 'rho'      => 961,
 257                 'rlm'      => 8207,
 258                 'rsaquo'   => 8250,
 259                 'rsquo'    => 8217,
 260                 'sbquo'    => 8218,
 261                 'Scaron'   => 352,
 262                 'scaron'   => 353,
 263                 'sdot'     => 8901,
 264                 'sect'     => 167,
 265                 'shy'      => 173,
 266                 'Sigma'    => 931,
 267                 'sigma'    => 963,
 268                 'sigmaf'   => 962,
 269                 'sim'      => 8764,
 270                 'spades'   => 9824,
 271                 'sub'      => 8834,
 272                 'sube'     => 8838,
 273                 'sum'      => 8721,
 274                 'sup'      => 8835,
 275                 'sup1'     => 185,
 276                 'sup2'     => 178,
 277                 'sup3'     => 179,
 278                 'supe'     => 8839,
 279                 'szlig'    => 223,
 280                 'Tau'      => 932,
 281                 'tau'      => 964,
 282                 'there4'   => 8756,
 283                 'Theta'    => 920,
 284                 'theta'    => 952,
 285                 'thetasym' => 977,
 286                 'thinsp'   => 8201,
 287                 'THORN'    => 222,
 288                 'thorn'    => 254,
 289                 'tilde'    => 732,
 290                 'times'    => 215,
 291                 'trade'    => 8482,
 292                 'Uacute'   => 218,
 293                 'uacute'   => 250,
 294                 'uarr'     => 8593,
 295                 'uArr'     => 8657,
 296                 'Ucirc'    => 219,
 297                 'ucirc'    => 251,
 298                 'Ugrave'   => 217,
 299                 'ugrave'   => 249,
 300                 'uml'      => 168,
 301                 'upsih'    => 978,
 302                 'Upsilon'  => 933,
 303                 'upsilon'  => 965,
 304                 'Uuml'     => 220,
 305                 'uuml'     => 252,
 306                 'weierp'   => 8472,
 307                 'Xi'       => 926,
 308                 'xi'       => 958,
 309                 'Yacute'   => 221,
 310                 'yacute'   => 253,
 311                 'yen'      => 165,
 312                 'Yuml'     => 376,
 313                 'yuml'     => 255,
 314                 'Zeta'     => 918,
 315                 'zeta'     => 950,
 316                 'zwj'      => 8205,
 317                 'zwnj'     => 8204
 318         ];
 319
 320         /**
 321          * Character entity aliases accepted by MediaWiki
 322          */
 323         private static $htmlEntityAliases = [
 324                 'רלמ' => 'rlm',
 325                 'رلم' => 'rlm',
 326         ];
 327
 328         /**
 329          * Lazy-initialised attributes regex, see getAttribsRegex()
 330          */
 331         private static $attribsRegex;
 332
 333         /**
 334          * Regular expression to match HTML/XML attribute pairs within a tag.
 335          * Allows some... latitude. Based on,
 336          * https://www.w3.org/TR/html5/syntax.html#before-attribute-value-state
 337          * Used in Sanitizer::fixTagAttributes and Sanitizer::decodeTagAttributes
 338          * @return string
 339          */
 340         static function getAttribsRegex() {
 341                 if ( self::$attribsRegex === null ) {
 342                         $attribFirst = '[:A-Z_a-z0-9]';
 343                         $attrib = '[:A-Z_a-z-.0-9]';
 344                         $space = '[\x09\x0a\x0c\x0d\x20]';
 345                         self::$attribsRegex =
 346                                 "/(?:^|$space)({$attribFirst}{$attrib}*)
 347                                   ($space*=$space*
 348                                         (?:
 349                                          # The attribute value: quoted or alone
 350                                           \"([^\"]*)(?:\"|\$)
 351                                          | '([^']*)(?:'|\$)
 352                                          |  (((?!$space|>).)*)
 353                                         )
 354                                 )?(?=$space|\$)/sx";
 355                 }
 356                 return self::$attribsRegex;
 357         }
 358
 359         /**
 360          * Return the various lists of recognized tags
 361          * @param array $extratags For any extra tags to include
 362          * @param array $removetags For any tags (default or extra) to exclude
 363          * @return array
 364          */
 365         public static function getRecognizedTagData( $extratags = [], $removetags = [] ) {
 366                 global $wgAllowImageTag;
 367
 368                 static $htmlpairsStatic, $htmlsingle, $htmlsingleonly, $htmlnest, $tabletags,
 369                         $htmllist, $listtags, $htmlsingleallowed, $htmlelementsStatic, $staticInitialised;
 370
 371                 // Base our staticInitialised variable off of the global config state so that if the globals
 372                 // are changed (like in the screwed up test system) we will re-initialise the settings.
 373                 $globalContext = $wgAllowImageTag;
 374                 if ( !$staticInitialised || $staticInitialised != $globalContext ) {
 375                         $htmlpairsStatic = [ # Tags that must be closed
 376                                 'b', 'bdi', 'del', 'i', 'ins', 'u', 'font', 'big', 'small', 'sub', 'sup', 'h1',
 377                                 'h2', 'h3', 'h4', 'h5', 'h6', 'cite', 'code', 'em', 's',
 378                                 'strike', 'strong', 'tt', 'var', 'div', 'center',
 379                                 'blockquote', 'ol', 'ul', 'dl', 'table', 'caption', 'pre',
 380                                 'ruby', 'rb', 'rp', 'rt', 'rtc', 'p', 'span', 'abbr', 'dfn',
 381                                 'kbd', 'samp', 'data', 'time', 'mark'
 382                         ];
 383                         $htmlsingle = [
 384                                 'br', 'wbr', 'hr', 'li', 'dt', 'dd', 'meta', 'link'
 385                         ];
 386
 387                         # Elements that cannot have close tags. This is (not coincidentally)
 388                         # also the list of tags for which the HTML 5 parsing algorithm
 389                         # requires you to "acknowledge the token's self-closing flag", i.e.
 390                         # a self-closing tag like <br/> is not an HTML 5 parse error only
 391                         # for this list.
 392                         $htmlsingleonly = [
 393                                 'br', 'wbr', 'hr', 'meta', 'link'
 394                         ];
 395
 396                         $htmlnest = [ # Tags that can be nested--??
 397                                 'table', 'tr', 'td', 'th', 'div', 'blockquote', 'ol', 'ul',
 398                                 'li', 'dl', 'dt', 'dd', 'font', 'big', 'small', 'sub', 'sup', 'span',
 399                                 'var', 'kbd', 'samp', 'em', 'strong', 'q', 'ruby', 'bdo'
 400                         ];
 401                         $tabletags = [ # Can only appear inside table, we will close them
 402                                 'td', 'th', 'tr',
 403                         ];
 404                         $htmllist = [ # Tags used by list
 405                                 'ul', 'ol',
 406                         ];
 407                         $listtags = [ # Tags that can appear in a list
 408                                 'li',
 409                         ];
 410
 411                         if ( $wgAllowImageTag ) {
 412                                 $htmlsingle[] = 'img';
 413                                 $htmlsingleonly[] = 'img';
 414                         }
 415
 416                         $htmlsingleallowed = array_unique( array_merge( $htmlsingle, $tabletags ) );
 417                         $htmlelementsStatic = array_unique( array_merge( $htmlsingle, $htmlpairsStatic, $htmlnest ) );
 418
 419                         # Convert them all to hashtables for faster lookup
 420                         $vars = [ 'htmlpairsStatic', 'htmlsingle', 'htmlsingleonly', 'htmlnest', 'tabletags',
 421                                 'htmllist', 'listtags', 'htmlsingleallowed', 'htmlelementsStatic' ];
 422                         foreach ( $vars as $var ) {
 423                                 $$var = array_flip( $$var );
 424                         }
 425                         $staticInitialised = $globalContext;
 426                 }
 427
 428                 # Populate $htmlpairs and $htmlelements with the $extratags and $removetags arrays
 429                 $extratags = array_flip( $extratags );
 430                 $removetags = array_flip( $removetags );
 431                 $htmlpairs = array_merge( $extratags, $htmlpairsStatic );
 432                 $htmlelements = array_diff_key( array_merge( $extratags, $htmlelementsStatic ), $removetags );
 433
 434                 return [
 435                         'htmlpairs' => $htmlpairs,
 436                         'htmlsingle' => $htmlsingle,
 437                         'htmlsingleonly' => $htmlsingleonly,
 438                         'htmlnest' => $htmlnest,
 439                         'tabletags' => $tabletags,
 440                         'htmllist' => $htmllist,
 441                         'listtags' => $listtags,
 442                         'htmlsingleallowed' => $htmlsingleallowed,
 443                         'htmlelements' => $htmlelements,
 444                 ];
 445         }
 446
 447         /**
 448          * Cleans up HTML, removes dangerous tags and attributes, and
 449          * removes HTML comments
 450          * @param string $text
 451          * @param callable $processCallback Callback to do any variable or parameter
 452          *   replacements in HTML attribute values
 453          * @param array|bool $args Arguments for the processing callback
 454          * @param array $extratags For any extra tags to include
 455          * @param array $removetags For any tags (default or extra) to exclude
 456          * @param callable $warnCallback (Deprecated) Callback allowing the
 457          *   addition of a tracking category when bad input is encountered.
 458          *   DO NOT ADD NEW PARAMETERS AFTER $warnCallback, since it will be
 459          *   removed shortly.
 460          * @return string
 461          */
 462         public static function removeHTMLtags( $text, $processCallback = null,
 463                 $args = [], $extratags = [], $removetags = [], $warnCallback = null
 464         ) {
 465                 extract( self::getRecognizedTagData( $extratags, $removetags ) );
 466
 467                 # Remove HTML comments
 468                 $text = Sanitizer::removeHTMLcomments( $text );
 469                 $bits = explode( '<', $text );
 470                 $text = str_replace( '>', '&gt;', array_shift( $bits ) );
 471                 if ( !MWTidy::isEnabled() ) {
 472                         $tagstack = $tablestack = [];
 473                         foreach ( $bits as $x ) {
 474                                 $regs = [];
 475                                 # $slash: Does the current element start with a '/'?
 476                                 # $t: Current element name
 477                                 # $params: String between element name and >
 478                                 # $brace: Ending '>' or '/>'
 479                                 # $rest: Everything until the next element of $bits
 480                                 if ( preg_match( self::ELEMENT_BITS_REGEX, $x, $regs ) ) {
 481                                         list( /* $qbar */, $slash, $t, $params, $brace, $rest ) = $regs;
 482                                 } else {
 483                                         $slash = $t = $params = $brace = $rest = null;
 484                                 }
 485
 486                                 $badtag = false;
 487                                 $t = strtolower( $t );
 488                                 if ( isset( $htmlelements[$t] ) ) {
 489                                         # Check our stack
 490                                         if ( $slash && isset( $htmlsingleonly[$t] ) ) {
 491                                                 $badtag = true;
 492                                         } elseif ( $slash ) {
 493                                                 # Closing a tag... is it the one we just opened?
 494                                                 MediaWiki\suppressWarnings();
 495                                                 $ot = array_pop( $tagstack );
 496                                                 MediaWiki\restoreWarnings();
 497
 498                                                 if ( $ot != $t ) {
 499                                                         if ( isset( $htmlsingleallowed[$ot] ) ) {
 500                                                                 # Pop all elements with an optional close tag
 501                                                                 # and see if we find a match below them
 502                                                                 $optstack = [];
 503                                                                 array_push( $optstack, $ot );
 504                                                                 MediaWiki\suppressWarnings();
 505                                                                 $ot = array_pop( $tagstack );
 506                                                                 MediaWiki\restoreWarnings();
 507                                                                 while ( $ot != $t && isset( $htmlsingleallowed[$ot] ) ) {
 508                                                                         array_push( $optstack, $ot );
 509                                                                         MediaWiki\suppressWarnings();
 510                                                                         $ot = array_pop( $tagstack );
 511                                                                         MediaWiki\restoreWarnings();
 512                                                                 }
 513                                                                 if ( $t != $ot ) {
 514                                                                         # No match. Push the optional elements back again
 515                                                                         $badtag = true;
 516                                                                         MediaWiki\suppressWarnings();
 517                                                                         $ot = array_pop( $optstack );
 518                                                                         MediaWiki\restoreWarnings();
 519                                                                         while ( $ot ) {
 520                                                                                 array_push( $tagstack, $ot );
 521                                                                                 MediaWiki\suppressWarnings();
 522                                                                                 $ot = array_pop( $optstack );
 523                                                                                 MediaWiki\restoreWarnings();
 524                                                                         }
 525                                                                 }
 526                                                         } else {
 527                                                                 MediaWiki\suppressWarnings();
 528                                                                 array_push( $tagstack, $ot );
 529                                                                 MediaWiki\restoreWarnings();
 530
 531                                                                 # <li> can be nested in <ul> or <ol>, skip those cases:
 532                                                                 if ( !isset( $htmllist[$ot] ) || !isset( $listtags[$t] ) ) {
 533                                                                         $badtag = true;
 534                                                                 }
 535                                                         }
 536                                                 } else {
 537                                                         if ( $t == 'table' ) {
 538                                                                 $tagstack = array_pop( $tablestack );
 539                                                         }
 540                                                 }
 541                                                 $newparams = '';
 542                                         } else {
 543                                                 # Keep track for later
 544                                                 if ( isset( $tabletags[$t] ) && !in_array( 'table', $tagstack ) ) {
 545                                                         $badtag = true;
 546                                                 } elseif ( in_array( $t, $tagstack ) && !isset( $htmlnest[$t] ) ) {
 547                                                         $badtag = true;
 548                                                 #  Is it a self closed htmlpair ? (bug 5487)
 549                                                 } elseif ( $brace == '/>' && isset( $htmlpairs[$t] ) ) {
 550                                                         // Eventually we'll just remove the self-closing
 551                                                         // slash, in order to be consistent with HTML5
 552                                                         // semantics.
 553                                                         // $brace = '>';
 554                                                         // For now, let's just warn authors to clean up.
 555                                                         if ( is_callable( $warnCallback ) ) {
 556                                                                 call_user_func_array( $warnCallback, [ 'deprecated-self-close-category' ] );
 557                                                         }
 558                                                         $badtag = true;
 559                                                 } elseif ( isset( $htmlsingleonly[$t] ) ) {
 560                                                         # Hack to force empty tag for unclosable elements
 561                                                         $brace = '/>';
 562                                                 } elseif ( isset( $htmlsingle[$t] ) ) {
 563                                                         # Hack to not close $htmlsingle tags
 564                                                         $brace = null;
 565                                                         # Still need to push this optionally-closed tag to
 566                                                         # the tag stack so that we can match end tags
 567                                                         # instead of marking them as bad.
 568                                                         array_push( $tagstack, $t );
 569                                                 } elseif ( isset( $tabletags[$t] ) && in_array( $t, $tagstack ) ) {
 570                                                         // New table tag but forgot to close the previous one
 571                                                         $text .= "</$t>";
 572                                                 } else {
 573                                                         if ( $t == 'table' ) {
 574                                                                 array_push( $tablestack, $tagstack );
 575                                                                 $tagstack = [];
 576                                                         }
 577                                                         array_push( $tagstack, $t );
 578                                                 }
 579
 580                                                 # Replace any variables or template parameters with
 581                                                 # plaintext results.
 582                                                 if ( is_callable( $processCallback ) ) {
 583                                                         call_user_func_array( $processCallback, [ &$params, $args ] );
 584                                                 }
 585
 586                                                 if ( !Sanitizer::validateTag( $params, $t ) ) {
 587                                                         $badtag = true;
 588                                                 }
 589
 590                                                 # Strip non-approved attributes from the tag
 591                                                 $newparams = Sanitizer::fixTagAttributes( $params, $t );
 592                                         }
 593                                         if ( !$badtag ) {
 594                                                 $rest = str_replace( '>', '&gt;', $rest );
 595                                                 $close = ( $brace == '/>' && !$slash ) ? ' /' : '';
 596                                                 $text .= "<$slash$t$newparams$close>$rest";
 597                                                 continue;
 598                                         }
 599                                 }
 600                                 $text .= '&lt;' . str_replace( '>', '&gt;', $x );
 601                         }
 602                         # Close off any remaining tags
 603                         while ( is_array( $tagstack ) && ( $t = array_pop( $tagstack ) ) ) {
 604                                 $text .= "</$t>\n";
 605                                 if ( $t == 'table' ) {
 606                                         $tagstack = array_pop( $tablestack );
 607                                 }
 608                         }
 609                 } else {
 610                         # this might be possible using tidy itself
 611                         foreach ( $bits as $x ) {
 612                                 if ( preg_match( self::ELEMENT_BITS_REGEX, $x, $regs ) ) {
 613                                         list( /* $qbar */, $slash, $t, $params, $brace, $rest ) = $regs;
 614
 615                                         $badtag = false;
 616                                         $t = strtolower( $t );
 617                                         if ( isset( $htmlelements[$t] ) ) {
 618                                                 if ( is_callable( $processCallback ) ) {
 619                                                         call_user_func_array( $processCallback, [ &$params, $args ] );
 620                                                 }
 621
 622                                                 if ( $brace == '/>' && !( isset( $htmlsingle[$t] ) || isset( $htmlsingleonly[$t] ) ) ) {
 623                                                         // Eventually we'll just remove the self-closing
 624                                                         // slash, in order to be consistent with HTML5
 625                                                         // semantics.
 626                                                         // $brace = '>';
 627                                                         // For now, let's just warn authors to clean up.
 628                                                         if ( is_callable( $warnCallback ) ) {
 629                                                                 call_user_func_array( $warnCallback, [ 'deprecated-self-close-category' ] );
 630                                                         }
 631                                                 }
 632                                                 if ( !Sanitizer::validateTag( $params, $t ) ) {
 633                                                         $badtag = true;
 634                                                 }
 635
 636                                                 $newparams = Sanitizer::fixTagAttributes( $params, $t );
 637                                                 if ( !$badtag ) {
 638                                                         if ( $brace === '/>' && !isset( $htmlsingleonly[$t] ) ) {
 639                                                                 # Interpret self-closing tags as empty tags even when
 640                                                                 # HTML 5 would interpret them as start tags. Such input
 641                                                                 # is commonly seen on Wikimedia wikis with this intention.
 642                                                                 $brace = "></$t>";
 643                                                         }
 644
 645                                                         $rest = str_replace( '>', '&gt;', $rest );
 646                                                         $text .= "<$slash$t$newparams$brace$rest";
 647                                                         continue;
 648                                                 }
 649                                         }
 650                                 }
 651                                 $text .= '&lt;' . str_replace( '>', '&gt;', $x );
 652                         }
 653                 }
 654                 return $text;
 655         }
 656
 657         /**
 658          * Remove '<!--', '-->', and everything between.
 659          * To avoid leaving blank lines, when a comment is both preceded
 660          * and followed by a newline (ignoring spaces), trim leading and
 661          * trailing spaces and one of the newlines.
 662          *
 663          * @param string $text
 664          * @return string
 665          */
 666         public static function removeHTMLcomments( $text ) {
 667                 while ( ( $start = strpos( $text, '<!--' ) ) !== false ) {
 668                         $end = strpos( $text, '-->', $start + 4 );
 669                         if ( $end === false ) {
 670                                 # Unterminated comment; bail out
 671                                 break;
 672                         }
 673
 674                         $end += 3;
 675
 676                         # Trim space and newline if the comment is both
 677                         # preceded and followed by a newline
 678                         $spaceStart = max( $start - 1, 0 );
 679                         $spaceLen = $end - $spaceStart;
 680                         while ( substr( $text, $spaceStart, 1 ) === ' ' && $spaceStart > 0 ) {
 681                                 $spaceStart--;
 682                                 $spaceLen++;
 683                         }
 684                         while ( substr( $text, $spaceStart + $spaceLen, 1 ) === ' ' ) {
 685                                 $spaceLen++;
 686                         }
 687                         if ( substr( $text, $spaceStart, 1 ) === "\n"
 688                                 && substr( $text, $spaceStart + $spaceLen, 1 ) === "\n" ) {
 689                                 # Remove the comment, leading and trailing
 690                                 # spaces, and leave only one newline.
 691                                 $text = substr_replace( $text, "\n", $spaceStart, $spaceLen + 1 );
 692                         } else {
 693                                 # Remove just the comment.
 694                                 $text = substr_replace( $text, '', $start, $end - $start );
 695                         }
 696                 }
 697                 return $text;
 698         }
 699
 700         /**
 701          * Takes attribute names and values for a tag and the tag name and
 702          * validates that the tag is allowed to be present.
 703          * This DOES NOT validate the attributes, nor does it validate the
 704          * tags themselves. This method only handles the special circumstances
 705          * where we may want to allow a tag within content but ONLY when it has
 706          * specific attributes set.
 707          *
 708          * @param string $params
 709          * @param string $element
 710          * @return bool
 711          */
 712         static function validateTag( $params, $element ) {
 713                 $params = Sanitizer::decodeTagAttributes( $params );
 714
 715                 if ( $element == 'meta' || $element == 'link' ) {
 716                         if ( !isset( $params['itemprop'] ) ) {
 717                                 // <meta> and <link> must have an itemprop="" otherwise they are not valid or safe in content
 718                                 return false;
 719                         }
 720                         if ( $element == 'meta' && !isset( $params['content'] ) ) {
 721                                 // <meta> must have a content="" for the itemprop
 722                                 return false;
 723                         }
 724                         if ( $element == 'link' && !isset( $params['href'] ) ) {
 725                                 // <link> must have an associated href=""
 726                                 return false;
 727                         }
 728                 }
 729
 730                 return true;
 731         }
 732
 733         /**
 734          * Take an array of attribute names and values and normalize or discard
 735          * illegal values for the given element type.
 736          *
 737          * - Discards attributes not on a whitelist for the given element
 738          * - Unsafe style attributes are discarded
 739          * - Invalid id attributes are re-encoded
 740          *
 741          * @param array $attribs
 742          * @param string $element
 743          * @return array
 744          *
 745          * @todo Check for legal values where the DTD limits things.
 746          * @todo Check for unique id attribute :P
 747          */
 748         static function validateTagAttributes( $attribs, $element ) {
 749                 return Sanitizer::validateAttributes( $attribs,
 750                         Sanitizer::attributeWhitelist( $element ) );
 751         }
 752
 753         /**
 754          * Take an array of attribute names and values and normalize or discard
 755          * illegal values for the given whitelist.
 756          *
 757          * - Discards attributes not on the given whitelist
 758          * - Unsafe style attributes are discarded
 759          * - Invalid id attributes are re-encoded
 760          *
 761          * @param array $attribs
 762          * @param array $whitelist List of allowed attribute names
 763          * @return array
 764          *
 765          * @todo Check for legal values where the DTD limits things.
 766          * @todo Check for unique id attribute :P
 767          */
 768         static function validateAttributes( $attribs, $whitelist ) {
 769                 $whitelist = array_flip( $whitelist );
 770                 $hrefExp = '/^(' . wfUrlProtocols() . ')[^\s]+$/';
 771
 772                 $out = [];
 773                 foreach ( $attribs as $attribute => $value ) {
 774                         # Allow XML namespace declaration to allow RDFa
 775                         if ( preg_match( self::XMLNS_ATTRIBUTE_PATTERN, $attribute ) ) {
 776                                 if ( !preg_match( self::EVIL_URI_PATTERN, $value ) ) {
 777                                         $out[$attribute] = $value;
 778                                 }
 779
 780                                 continue;
 781                         }
 782
 783                         # Allow any attribute beginning with "data-"
 784                         # However:
 785                         # * data-ooui is reserved for ooui
 786                         # * data-mw and data-parsoid are reserved for parsoid
 787                         # * data-mw-<name here> is reserved for extensions (or core) if
 788                         #   they need to communicate some data to the client and want to be
 789                         #   sure that it isn't coming from an untrusted user.
 790                         # * Ensure that the attribute is not namespaced by banning
 791                         #   colons.
 792                         if ( !preg_match( '/^data-(?!ooui|mw|parsoid)[^:]*$/i', $attribute )
 793                                 && !isset( $whitelist[$attribute] )
 794                         ) {
 795                                 continue;
 796                         }
 797
 798                         # Strip javascript "expression" from stylesheets.
 799                         # http://msdn.microsoft.com/workshop/author/dhtml/overview/recalc.asp
 800                         if ( $attribute == 'style' ) {
 801                                 $value = Sanitizer::checkCss( $value );
 802                         }
 803
 804                         # Escape HTML id attributes
 805                         if ( $attribute === 'id' ) {
 806                                 $value = Sanitizer::escapeId( $value, 'noninitial' );
 807                         }
 808
 809                         # Escape HTML id reference lists
 810                         if ( $attribute === 'aria-describedby'
 811                                 || $attribute === 'aria-flowto'
 812                                 || $attribute === 'aria-labelledby'
 813                                 || $attribute === 'aria-owns'
 814                         ) {
 815                                 $value = Sanitizer::escapeIdReferenceList( $value, 'noninitial' );
 816                         }
 817
 818                         // RDFa and microdata properties allow URLs, URIs and/or CURIs.
 819                         // Check them for sanity.
 820                         if ( $attribute === 'rel' || $attribute === 'rev'
 821                                 # RDFa
 822                                 || $attribute === 'about' || $attribute === 'property'
 823                                 || $attribute === 'resource' || $attribute === 'datatype'
 824                                 || $attribute === 'typeof'
 825                                 # HTML5 microdata
 826                                 || $attribute === 'itemid' || $attribute === 'itemprop'
 827                                 || $attribute === 'itemref' || $attribute === 'itemscope'
 828                                 || $attribute === 'itemtype'
 829                         ) {
 830                                 // Paranoia. Allow "simple" values but suppress javascript
 831                                 if ( preg_match( self::EVIL_URI_PATTERN, $value ) ) {
 832                                         continue;
 833                                 }
 834                         }
 835
 836                         # NOTE: even though elements using href/src are not allowed directly, supply
 837                         #       validation code that can be used by tag hook handlers, etc
 838                         if ( $attribute === 'href' || $attribute === 'src' ) {
 839                                 if ( !preg_match( $hrefExp, $value ) ) {
 840                                         continue; // drop any href or src attributes not using an allowed protocol.
 841                                         // NOTE: this also drops all relative URLs
 842                                 }
 843                         }
 844
 845                         // If this attribute was previously set, override it.
 846                         // Output should only have one attribute of each name.
 847                         $out[$attribute] = $value;
 848                 }
 849
 850                 # itemtype, itemid, itemref don't make sense without itemscope
 851                 if ( !array_key_exists( 'itemscope', $out ) ) {
 852                         unset( $out['itemtype'] );
 853                         unset( $out['itemid'] );
 854                         unset( $out['itemref'] );
 855                 }
 856                 # TODO: Strip itemprop if we aren't descendants of an itemscope or pointed to by an itemref.
 857
 858                 return $out;
 859         }
 860
 861         /**
 862          * Merge two sets of HTML attributes.  Conflicting items in the second set
 863          * will override those in the first, except for 'class' attributes which
 864          * will be combined (if they're both strings).
 865          *
 866          * @todo implement merging for other attributes such as style
 867          * @param array $a
 868          * @param array $b
 869          * @return array
 870          */
 871         static function mergeAttributes( $a, $b ) {
 872                 $out = array_merge( $a, $b );
 873                 if ( isset( $a['class'] ) && isset( $b['class'] )
 874                         && is_string( $a['class'] ) && is_string( $b['class'] )
 875                         && $a['class'] !== $b['class']
 876                 ) {
 877                         $classes = preg_split( '/\s+/', "{$a['class']} {$b['class']}",
 878                                 -1, PREG_SPLIT_NO_EMPTY );
 879                         $out['class'] = implode( ' ', array_unique( $classes ) );
 880                 }
 881                 return $out;
 882         }
 883
 884         /**
 885          * Normalize CSS into a format we can easily search for hostile input
 886          *  - decode character references
 887          *  - decode escape sequences
 888          *  - convert characters that IE6 interprets into ascii
 889          *  - remove comments, unless the entire value is one single comment
 890          * @param string $value the css string
 891          * @return string normalized css
 892          */
 893         public static function normalizeCss( $value ) {
 894
 895                 // Decode character references like &#123;
 896                 $value = Sanitizer::decodeCharReferences( $value );
 897
 898                 // Decode escape sequences and line continuation
 899                 // See the grammar in the CSS 2 spec, appendix D.
 900                 // This has to be done AFTER decoding character references.
 901                 // This means it isn't possible for this function to return
 902                 // unsanitized escape sequences. It is possible to manufacture
 903                 // input that contains character references that decode to
 904                 // escape sequences that decode to character references, but
 905                 // it's OK for the return value to contain character references
 906                 // because the caller is supposed to escape those anyway.
 907                 static $decodeRegex;
 908                 if ( !$decodeRegex ) {
 909                         $space = '[\\x20\\t\\r\\n\\f]';
 910                         $nl = '(?:\\n|\\r\\n|\\r|\\f)';
 911                         $backslash = '\\\\';
 912                         $decodeRegex = "/ $backslash
 913                                 (?:
 914                                         ($nl) |  # 1. Line continuation
 915                                         ([0-9A-Fa-f]{1,6})$space? |  # 2. character number
 916                                         (.) | # 3. backslash cancelling special meaning
 917                                         () | # 4. backslash at end of string
 918                                 )/xu";
 919                 }
 920                 $value = preg_replace_callback( $decodeRegex,
 921                         [ __CLASS__, 'cssDecodeCallback' ], $value );
 922
 923                 // Normalize Halfwidth and Fullwidth Unicode block that IE6 might treat as ascii
 924                 $value = preg_replace_callback(
 925                         '/[！-［］-ｚ]/u', // U+FF01 to U+FF5A, excluding U+FF3C (bug 58088)
 926                         function ( $matches ) {
 927                                 $cp = UtfNormal\Utils::utf8ToCodepoint( $matches[0] );
 928                                 if ( $cp === false ) {
 929                                         return '';
 930                                 }
 931                                 return chr( $cp - 65248 ); // ASCII range \x21-\x7A
 932                         },
 933                         $value
 934                 );
 935
 936                 // Convert more characters IE6 might treat as ascii
 937                 // U+0280, U+0274, U+207F, U+029F, U+026A, U+207D, U+208D
 938                 $value = str_replace(
 939                         [ 'ʀ', 'ɴ', 'ⁿ', 'ʟ', 'ɪ', '⁽', '₍' ],
 940                         [ 'r', 'n', 'n', 'l', 'i', '(', '(' ],
 941                         $value
 942                 );
 943
 944                 // Let the value through if it's nothing but a single comment, to
 945                 // allow other functions which may reject it to pass some error
 946                 // message through.
 947                 if ( !preg_match( '! ^ \s* /\* [^*\\/]* \*/ \s* $ !x', $value ) ) {
 948                         // Remove any comments; IE gets token splitting wrong
 949                         // This must be done AFTER decoding character references and
 950                         // escape sequences, because those steps can introduce comments
 951                         // This step cannot introduce character references or escape
 952                         // sequences, because it replaces comments with spaces rather
 953                         // than removing them completely.
 954                         $value = StringUtils::delimiterReplace( '/*', '*/', ' ', $value );
 955
 956                         // Remove anything after a comment-start token, to guard against
 957                         // incorrect client implementations.
 958                         $commentPos = strpos( $value, '/*' );
 959                         if ( $commentPos !== false ) {
 960                                 $value = substr( $value, 0, $commentPos );
 961                         }
 962                 }
 963
 964                 // S followed by repeat, iteration, or prolonged sound marks,
 965                 // which IE will treat as "ss"
 966                 $value = preg_replace(
 967                         '/s(?:
 968                                 \xE3\x80\xB1 | # U+3031
 969                                 \xE3\x82\x9D | # U+309D
 970                                 \xE3\x83\xBC | # U+30FC
 971                                 \xE3\x83\xBD | # U+30FD
 972                                 \xEF\xB9\xBC | # U+FE7C
 973                                 \xEF\xB9\xBD | # U+FE7D
 974                                 \xEF\xBD\xB0   # U+FF70
 975                         )/ix',
 976                         'ss',
 977                         $value
 978                 );
 979
 980                 return $value;
 981         }
 982
 983         /**
 984          * Pick apart some CSS and check it for forbidden or unsafe structures.
 985          * Returns a sanitized string. This sanitized string will have
 986          * character references and escape sequences decoded and comments
 987          * stripped (unless it is itself one valid comment, in which case the value
 988          * will be passed through). If the input is just too evil, only a comment
 989          * complaining about evilness will be returned.
 990          *
 991          * Currently URL references, 'expression', 'tps' are forbidden.
 992          *
 993          * NOTE: Despite the fact that character references are decoded, the
 994          * returned string may contain character references given certain
 995          * clever input strings. These character references must
 996          * be escaped before the return value is embedded in HTML.
 997          *
 998          * @param string $value
 999          * @return string
1000          */
1001         static function checkCss( $value ) {
1002                 $value = self::normalizeCss( $value );
1003
1004                 // Reject problematic keywords and control characters
1005                 if ( preg_match( '/[\000-\010\013\016-\037\177]/', $value ) ||
1006                         strpos( $value, UtfNormal\Constants::UTF8_REPLACEMENT ) !== false ) {
1007                         return '/* invalid control char */';
1008                 } elseif ( preg_match(
1009                         '! expression
1010                                 | filter\s*:
1011                                 | accelerator\s*:
1012                                 | -o-link\s*:
1013                                 | -o-link-source\s*:
1014                                 | -o-replace\s*:
1015                                 | url\s*\(
1016                                 | image\s*\(
1017                                 | image-set\s*\(
1018                                 | attr\s*\([^)]+[\s,]+url
1019                         !ix', $value ) ) {
1020                         return '/* insecure input */';
1021                 }
1022                 return $value;
1023         }
1024
1025         /**
1026          * @param array $matches
1027          * @return string
1028          */
1029         static function cssDecodeCallback( $matches ) {
1030                 if ( $matches[1] !== '' ) {
1031                         // Line continuation
1032                         return '';
1033                 } elseif ( $matches[2] !== '' ) {
1034                         $char = UtfNormal\Utils::codepointToUtf8( hexdec( $matches[2] ) );
1035                 } elseif ( $matches[3] !== '' ) {
1036                         $char = $matches[3];
1037                 } else {
1038                         $char = '\\';
1039                 }
1040                 if ( $char == "\n" || $char == '"' || $char == "'" || $char == '\\' ) {
1041                         // These characters need to be escaped in strings
1042                         // Clean up the escape sequence to avoid parsing errors by clients
1043                         return '\\' . dechex( ord( $char ) ) . ' ';
1044                 } else {
1045                         // Decode unnecessary escape
1046                         return $char;
1047                 }
1048         }
1049
1050         /**
1051          * Take a tag soup fragment listing an HTML element's attributes
1052          * and normalize it to well-formed XML, discarding unwanted attributes.
1053          * Output is safe for further wikitext processing, with escaping of
1054          * values that could trigger problems.
1055          *
1056          * - Normalizes attribute names to lowercase
1057          * - Discards attributes not on a whitelist for the given element
1058          * - Turns broken or invalid entities into plaintext
1059          * - Double-quotes all attribute values
1060          * - Attributes without values are given the name as attribute
1061          * - Double attributes are discarded
1062          * - Unsafe style attributes are discarded
1063          * - Prepends space if there are attributes.
1064          * - (Optionally) Sorts attributes by name.
1065          *
1066          * @param string $text
1067          * @param string $element
1068          * @param bool $sorted Whether to sort the attributes (default: false)
1069          * @return string
1070          */
1071         static function fixTagAttributes( $text, $element, $sorted = false ) {
1072                 if ( trim( $text ) == '' ) {
1073                         return '';
1074                 }
1075
1076                 $decoded = Sanitizer::decodeTagAttributes( $text );
1077                 $stripped = Sanitizer::validateTagAttributes( $decoded, $element );
1078
1079                 if ( $sorted ) {
1080                         ksort( $stripped );
1081                 }
1082
1083                 return Sanitizer::safeEncodeTagAttributes( $stripped );
1084         }
1085
1086         /**
1087          * Encode an attribute value for HTML output.
1088          * @param string $text
1089          * @return string HTML-encoded text fragment
1090          */
1091         static function encodeAttribute( $text ) {
1092                 $encValue = htmlspecialchars( $text, ENT_QUOTES );
1093
1094                 // Whitespace is normalized during attribute decoding,
1095                 // so if we've been passed non-spaces we must encode them
1096                 // ahead of time or they won't be preserved.
1097                 $encValue = strtr( $encValue, [
1098                         "\n" => '&#10;',
1099                         "\r" => '&#13;',
1100                         "\t" => '&#9;',
1101                 ] );
1102
1103                 return $encValue;
1104         }
1105
1106         /**
1107          * Encode an attribute value for HTML tags, with extra armoring
1108          * against further wiki processing.
1109          * @param string $text
1110          * @return string HTML-encoded text fragment
1111          */
1112         static function safeEncodeAttribute( $text ) {
1113                 $encValue = Sanitizer::encodeAttribute( $text );
1114
1115                 # Templates and links may be expanded in later parsing,
1116                 # creating invalid or dangerous output. Suppress this.
1117                 $encValue = strtr( $encValue, [
1118                         '<'    => '&lt;',   // This should never happen,
1119                         '>'    => '&gt;',   // we've received invalid input
1120                         '"'    => '&quot;', // which should have been escaped.
1121                         '{'    => '&#123;',
1122                         '}'    => '&#125;', // prevent unpaired language conversion syntax
1123                         '['    => '&#91;',
1124                         "''"   => '&#39;&#39;',
1125                         'ISBN' => '&#73;SBN',
1126                         'RFC'  => '&#82;FC',
1127                         'PMID' => '&#80;MID',
1128                         '|'    => '&#124;',
1129                         '__'   => '&#95;_',
1130                 ] );
1131
1132                 # Stupid hack
1133                 $encValue = preg_replace_callback(
1134                         '/((?i)' . wfUrlProtocols() . ')/',
1135                         [ 'Sanitizer', 'armorLinksCallback' ],
1136                         $encValue );
1137                 return $encValue;
1138         }
1139
1140         /**
1141          * Given a value, escape it so that it can be used in an id attribute and
1142          * return it.  This will use HTML5 validation if $wgExperimentalHtmlIds is
1143          * true, allowing anything but ASCII whitespace.  Otherwise it will use
1144          * HTML 4 rules, which means a narrow subset of ASCII, with bad characters
1145          * escaped with lots of dots.
1146          *
1147          * To ensure we don't have to bother escaping anything, we also strip ', ",
1148          * & even if $wgExperimentalIds is true.  TODO: Is this the best tactic?
1149          * We also strip # because it upsets IE, and % because it could be
1150          * ambiguous if it's part of something that looks like a percent escape
1151          * (which don't work reliably in fragments cross-browser).
1152          *
1153          * @see https://www.w3.org/TR/html401/types.html#type-name Valid characters
1154          *   in the id and name attributes
1155          * @see https://www.w3.org/TR/html401/struct/links.html#h-12.2.3 Anchors with
1156          *   the id attribute
1157          * @see https://www.w3.org/TR/html5/dom.html#the-id-attribute
1158          *   HTML5 definition of id attribute
1159          *
1160          * @param string $id Id to escape
1161          * @param string|array $options String or array of strings (default is array()):
1162          *   'noninitial': This is a non-initial fragment of an id, not a full id,
1163          *       so don't pay attention if the first character isn't valid at the
1164          *       beginning of an id.  Only matters if $wgExperimentalHtmlIds is
1165          *       false.
1166          *   'legacy': Behave the way the old HTML 4-based ID escaping worked even
1167          *       if $wgExperimentalHtmlIds is used, so we can generate extra
1168          *       anchors and links won't break.
1169          * @return string
1170          */
1171         static function escapeId( $id, $options = [] ) {
1172                 global $wgExperimentalHtmlIds;
1173                 $options = (array)$options;
1174
1175                 $id = Sanitizer::decodeCharReferences( $id );
1176
1177                 if ( $wgExperimentalHtmlIds && !in_array( 'legacy', $options ) ) {
1178                         $id = preg_replace( '/[ \t\n\r\f_\'"&#%]+/', '_', $id );
1179                         $id = trim( $id, '_' );
1180                         if ( $id === '' ) {
1181                                 // Must have been all whitespace to start with.
1182                                 return '_';
1183                         } else {
1184                                 return $id;
1185                         }
1186                 }
1187
1188                 // HTML4-style escaping
1189                 static $replace = [
1190                         '%3A' => ':',
1191                         '%' => '.'
1192                 ];
1193
1194                 $id = urlencode( strtr( $id, ' ', '_' ) );
1195                 $id = str_replace( array_keys( $replace ), array_values( $replace ), $id );
1196
1197                 if ( !preg_match( '/^[a-zA-Z]/', $id ) && !in_array( 'noninitial', $options ) ) {
1198                         // Initial character must be a letter!
1199                         $id = "x$id";
1200                 }
1201                 return $id;
1202         }
1203
1204         /**
1205          * Given a string containing a space delimited list of ids, escape each id
1206          * to match ids escaped by the escapeId() function.
1207          *
1208          * @since 1.27
1209          *
1210          * @param string $referenceString Space delimited list of ids
1211          * @param string|array $options String or array of strings (default is array()):
1212          *   'noninitial': This is a non-initial fragment of an id, not a full id,
1213          *       so don't pay attention if the first character isn't valid at the
1214          *       beginning of an id.  Only matters if $wgExperimentalHtmlIds is
1215          *       false.
1216          *   'legacy': Behave the way the old HTML 4-based ID escaping worked even
1217          *       if $wgExperimentalHtmlIds is used, so we can generate extra
1218          *       anchors and links won't break.
1219          * @return string
1220          */
1221         static function escapeIdReferenceList( $referenceString, $options = [] ) {
1222                 # Explode the space delimited list string into an array of tokens
1223                 $references = preg_split( '/\s+/', "{$referenceString}", -1, PREG_SPLIT_NO_EMPTY );
1224
1225                 # Escape each token as an id
1226                 foreach ( $references as &$ref ) {
1227                         $ref = Sanitizer::escapeId( $ref, $options );
1228                 }
1229
1230                 # Merge the array back to a space delimited list string
1231                 # If the array is empty, the result will be an empty string ('')
1232                 $referenceString = implode( ' ', $references );
1233
1234                 return $referenceString;
1235         }
1236
1237         /**
1238          * Given a value, escape it so that it can be used as a CSS class and
1239          * return it.
1240          *
1241          * @todo For extra validity, input should be validated UTF-8.
1242          *
1243          * @see https://www.w3.org/TR/CSS21/syndata.html Valid characters/format
1244          *
1245          * @param string $class
1246          * @return string
1247          */
1248         static function escapeClass( $class ) {
1249                 // Convert ugly stuff to underscores and kill underscores in ugly places
1250                 return rtrim( preg_replace(
1251                         [ '/(^[0-9\\-])|[\\x00-\\x20!"#$%&\'()*+,.\\/:;<=>?@[\\]^`{|}~]|\\xC2\\xA0/', '/_+/' ],
1252                         '_',
1253                         $class ), '_' );
1254         }
1255
1256         /**
1257          * Given HTML input, escape with htmlspecialchars but un-escape entities.
1258          * This allows (generally harmless) entities like &#160; to survive.
1259          *
1260          * @param string $html HTML to escape
1261          * @return string Escaped input
1262          */
1263         static function escapeHtmlAllowEntities( $html ) {
1264                 $html = Sanitizer::decodeCharReferences( $html );
1265                 # It seems wise to escape ' as well as ", as a matter of course.  Can't
1266                 # hurt. Use ENT_SUBSTITUTE so that incorrectly truncated multibyte characters
1267                 # don't cause the entire string to disappear.
1268                 $html = htmlspecialchars( $html, ENT_QUOTES | ENT_SUBSTITUTE );
1269                 return $html;
1270         }
1271
1272         /**
1273          * Regex replace callback for armoring links against further processing.
1274          * @param array $matches
1275          * @return string
1276          */
1277         private static function armorLinksCallback( $matches ) {
1278                 return str_replace( ':', '&#58;', $matches[1] );
1279         }
1280
1281         /**
1282          * Return an associative array of attribute names and values from
1283          * a partial tag string. Attribute names are forced to lowercase,
1284          * character references are decoded to UTF-8 text.
1285          *
1286          * @param string $text
1287          * @return array
1288          */
1289         public static function decodeTagAttributes( $text ) {
1290                 if ( trim( $text ) == '' ) {
1291                         return [];
1292                 }
1293
1294                 $attribs = [];
1295                 $pairs = [];
1296                 if ( !preg_match_all(
1297                         self::getAttribsRegex(),
1298                         $text,
1299                         $pairs,
1300                         PREG_SET_ORDER ) ) {
1301                         return $attribs;
1302                 }
1303
1304                 foreach ( $pairs as $set ) {
1305                         $attribute = strtolower( $set[1] );
1306                         $value = Sanitizer::getTagAttributeCallback( $set );
1307
1308                         // Normalize whitespace
1309                         $value = preg_replace( '/[\t\r\n ]+/', ' ', $value );
1310                         $value = trim( $value );
1311
1312                         // Decode character references
1313                         $attribs[$attribute] = Sanitizer::decodeCharReferences( $value );
1314                 }
1315                 return $attribs;
1316         }
1317
1318         /**
1319          * Build a partial tag string from an associative array of attribute
1320          * names and values as returned by decodeTagAttributes.
1321          *
1322          * @param array $assoc_array
1323          * @return string
1324          */
1325         public static function safeEncodeTagAttributes( $assoc_array ) {
1326                 $attribs = [];
1327                 foreach ( $assoc_array as $attribute => $value ) {
1328                         $encAttribute = htmlspecialchars( $attribute );
1329                         $encValue = Sanitizer::safeEncodeAttribute( $value );
1330
1331                         $attribs[] = "$encAttribute=\"$encValue\"";
1332                 }
1333                 return count( $attribs ) ? ' ' . implode( ' ', $attribs ) : '';
1334         }
1335
1336         /**
1337          * Pick the appropriate attribute value from a match set from the
1338          * attribs regex matches.
1339          *
1340          * @param array $set
1341          * @throws MWException When tag conditions are not met.
1342          * @return string
1343          */
1344         private static function getTagAttributeCallback( $set ) {
1345                 if ( isset( $set[5] ) ) {
1346                         # No quotes.
1347                         return $set[5];
1348                 } elseif ( isset( $set[4] ) ) {
1349                         # Single-quoted
1350                         return $set[4];
1351                 } elseif ( isset( $set[3] ) ) {
1352                         # Double-quoted
1353                         return $set[3];
1354                 } elseif ( !isset( $set[2] ) ) {
1355                         # In XHTML, attributes must have a value so return an empty string.
1356                         # See "Empty attribute syntax",
1357                         # https://www.w3.org/TR/html5/syntax.html#syntax-attribute-name
1358                         return "";
1359                 } else {
1360                         throw new MWException( "Tag conditions not met. This should never happen and is a bug." );
1361                 }
1362         }
1363
1364         /**
1365          * @param string $text
1366          * @return string
1367          */
1368         private static function normalizeWhitespace( $text ) {
1369                 return preg_replace(
1370                         '/\r\n|[\x20\x0d\x0a\x09]/',
1371                         ' ',
1372                         $text );
1373         }
1374
1375         /**
1376          * Normalizes whitespace in a section name, such as might be returned
1377          * by Parser::stripSectionName(), for use in the id's that are used for
1378          * section links.
1379          *
1380          * @param string $section
1381          * @return string
1382          */
1383         static function normalizeSectionNameWhitespace( $section ) {
1384                 return trim( preg_replace( '/[ _]+/', ' ', $section ) );
1385         }
1386
1387         /**
1388          * Ensure that any entities and character references are legal
1389          * for XML and XHTML specifically. Any stray bits will be
1390          * &amp;-escaped to result in a valid text fragment.
1391          *
1392          * a. named char refs can only be &lt; &gt; &amp; &quot;, others are
1393          *   numericized (this way we're well-formed even without a DTD)
1394          * b. any numeric char refs must be legal chars, not invalid or forbidden
1395          * c. use lower cased "&#x", not "&#X"
1396          * d. fix or reject non-valid attributes
1397          *
1398          * @param string $text
1399          * @return string
1400          * @private
1401          */
1402         static function normalizeCharReferences( $text ) {
1403                 return preg_replace_callback(
1404                         self::CHAR_REFS_REGEX,
1405                         [ 'Sanitizer', 'normalizeCharReferencesCallback' ],
1406                         $text );
1407         }
1408
1409         /**
1410          * @param string $matches
1411          * @return string
1412          */
1413         static function normalizeCharReferencesCallback( $matches ) {
1414                 $ret = null;
1415                 if ( $matches[1] != '' ) {
1416                         $ret = Sanitizer::normalizeEntity( $matches[1] );
1417                 } elseif ( $matches[2] != '' ) {
1418                         $ret = Sanitizer::decCharReference( $matches[2] );
1419                 } elseif ( $matches[3] != '' ) {
1420                         $ret = Sanitizer::hexCharReference( $matches[3] );
1421                 }
1422                 if ( is_null( $ret ) ) {
1423                         return htmlspecialchars( $matches[0] );
1424                 } else {
1425                         return $ret;
1426                 }
1427         }
1428
1429         /**
1430          * If the named entity is defined in the HTML 4.0/XHTML 1.0 DTD,
1431          * return the equivalent numeric entity reference (except for the core &lt;
1432          * &gt; &amp; &quot;). If the entity is a MediaWiki-specific alias, returns
1433          * the HTML equivalent. Otherwise, returns HTML-escaped text of
1434          * pseudo-entity source (eg &amp;foo;)
1435          *
1436          * @param string $name
1437          * @return string
1438          */
1439         static function normalizeEntity( $name ) {
1440                 if ( isset( self::$htmlEntityAliases[$name] ) ) {
1441                         return '&' . self::$htmlEntityAliases[$name] . ';';
1442                 } elseif ( in_array( $name, [ 'lt', 'gt', 'amp', 'quot' ] ) ) {
1443                         return "&$name;";
1444                 } elseif ( isset( self::$htmlEntities[$name] ) ) {
1445                         return '&#' . self::$htmlEntities[$name] . ';';
1446                 } else {
1447                         return "&amp;$name;";
1448                 }
1449         }
1450
1451         /**
1452          * @param int $codepoint
1453          * @return null|string
1454          */
1455         static function decCharReference( $codepoint ) {
1456                 $point = intval( $codepoint );
1457                 if ( Sanitizer::validateCodepoint( $point ) ) {
1458                         return sprintf( '&#%d;', $point );
1459                 } else {
1460                         return null;
1461                 }
1462         }
1463
1464         /**
1465          * @param int $codepoint
1466          * @return null|string
1467          */
1468         static function hexCharReference( $codepoint ) {
1469                 $point = hexdec( $codepoint );
1470                 if ( Sanitizer::validateCodepoint( $point ) ) {
1471                         return sprintf( '&#x%x;', $point );
1472                 } else {
1473                         return null;
1474                 }
1475         }
1476
1477         /**
1478          * Returns true if a given Unicode codepoint is a valid character in
1479          * both HTML5 and XML.
1480          * @param int $codepoint
1481          * @return bool
1482          */
1483         private static function validateCodepoint( $codepoint ) {
1484                 # U+000C is valid in HTML5 but not allowed in XML.
1485                 # U+000D is valid in XML but not allowed in HTML5.
1486                 # U+007F - U+009F are disallowed in HTML5 (control characters).
1487                 return $codepoint == 0x09
1488                         || $codepoint == 0x0a
1489                         || ( $codepoint >= 0x20 && $codepoint <= 0x7e )
1490                         || ( $codepoint >= 0xa0 && $codepoint <= 0xd7ff )
1491                         || ( $codepoint >= 0xe000 && $codepoint <= 0xfffd )
1492                         || ( $codepoint >= 0x10000 && $codepoint <= 0x10ffff );
1493         }
1494
1495         /**
1496          * Decode any character references, numeric or named entities,
1497          * in the text and return a UTF-8 string.
1498          *
1499          * @param string $text
1500          * @return string
1501          */
1502         public static function decodeCharReferences( $text ) {
1503                 return preg_replace_callback(
1504                         self::CHAR_REFS_REGEX,
1505                         [ 'Sanitizer', 'decodeCharReferencesCallback' ],
1506                         $text );
1507         }
1508
1509         /**
1510          * Decode any character references, numeric or named entities,
1511          * in the next and normalize the resulting string. (bug 14952)
1512          *
1513          * This is useful for page titles, not for text to be displayed,
1514          * MediaWiki allows HTML entities to escape normalization as a feature.
1515          *
1516          * @param string $text Already normalized, containing entities
1517          * @return string Still normalized, without entities
1518          */
1519         public static function decodeCharReferencesAndNormalize( $text ) {
1520                 global $wgContLang;
1521                 $text = preg_replace_callback(
1522                         self::CHAR_REFS_REGEX,
1523                         [ 'Sanitizer', 'decodeCharReferencesCallback' ],
1524                         $text, /* limit */ -1, $count );
1525
1526                 if ( $count ) {
1527                         return $wgContLang->normalize( $text );
1528                 } else {
1529                         return $text;
1530                 }
1531         }
1532
1533         /**
1534          * @param string $matches
1535          * @return string
1536          */
1537         static function decodeCharReferencesCallback( $matches ) {
1538                 if ( $matches[1] != '' ) {
1539                         return Sanitizer::decodeEntity( $matches[1] );
1540                 } elseif ( $matches[2] != '' ) {
1541                         return Sanitizer::decodeChar( intval( $matches[2] ) );
1542                 } elseif ( $matches[3] != '' ) {
1543                         return Sanitizer::decodeChar( hexdec( $matches[3] ) );
1544                 }
1545                 # Last case should be an ampersand by itself
1546                 return $matches[0];
1547         }
1548
1549         /**
1550          * Return UTF-8 string for a codepoint if that is a valid
1551          * character reference, otherwise U+FFFD REPLACEMENT CHARACTER.
1552          * @param int $codepoint
1553          * @return string
1554          * @private
1555          */
1556         static function decodeChar( $codepoint ) {
1557                 if ( Sanitizer::validateCodepoint( $codepoint ) ) {
1558                         return UtfNormal\Utils::codepointToUtf8( $codepoint );
1559                 } else {
1560                         return UtfNormal\Constants::UTF8_REPLACEMENT;
1561                 }
1562         }
1563
1564         /**
1565          * If the named entity is defined in the HTML 4.0/XHTML 1.0 DTD,
1566          * return the UTF-8 encoding of that character. Otherwise, returns
1567          * pseudo-entity source (eg "&foo;")
1568          *
1569          * @param string $name
1570          * @return string
1571          */
1572         static function decodeEntity( $name ) {
1573                 if ( isset( self::$htmlEntityAliases[$name] ) ) {
1574                         $name = self::$htmlEntityAliases[$name];
1575                 }
1576                 if ( isset( self::$htmlEntities[$name] ) ) {
1577                         return UtfNormal\Utils::codepointToUtf8( self::$htmlEntities[$name] );
1578                 } else {
1579                         return "&$name;";
1580                 }
1581         }
1582
1583         /**
1584          * Fetch the whitelist of acceptable attributes for a given element name.
1585          *
1586          * @param string $element
1587          * @return array
1588          */
1589         static function attributeWhitelist( $element ) {
1590                 $list = Sanitizer::setupAttributeWhitelist();
1591                 return isset( $list[$element] )
1592                         ? $list[$element]
1593                         : [];
1594         }
1595
1596         /**
1597          * Foreach array key (an allowed HTML element), return an array
1598          * of allowed attributes
1599          * @return array
1600          */
1601         static function setupAttributeWhitelist() {
1602                 static $whitelist;
1603
1604                 if ( $whitelist !== null ) {
1605                         return $whitelist;
1606                 }
1607
1608                 $common = [
1609                         # HTML
1610                         'id',
1611                         'class',
1612                         'style',
1613                         'lang',
1614                         'dir',
1615                         'title',
1616
1617                         # WAI-ARIA
1618                         'aria-describedby',
1619                         'aria-flowto',
1620                         'aria-label',
1621                         'aria-labelledby',
1622                         'aria-owns',
1623                         'role',
1624
1625                         # RDFa
1626                         # These attributes are specified in section 9 of
1627                         # https://www.w3.org/TR/2008/REC-rdfa-syntax-20081014
1628                         'about',
1629                         'property',
1630                         'resource',
1631                         'datatype',
1632                         'typeof',
1633
1634                         # Microdata. These are specified by
1635                         # https://html.spec.whatwg.org/multipage/microdata.html#the-microdata-model
1636                         'itemid',
1637                         'itemprop',
1638                         'itemref',
1639                         'itemscope',
1640                         'itemtype',
1641                 ];
1642
1643                 $block = array_merge( $common, [ 'align' ] );
1644                 $tablealign = [ 'align', 'valign' ];
1645                 $tablecell = [
1646                         'abbr',
1647                         'axis',
1648                         'headers',
1649                         'scope',
1650                         'rowspan',
1651                         'colspan',
1652                         'nowrap', # deprecated
1653                         'width', # deprecated
1654                         'height', # deprecated
1655                         'bgcolor', # deprecated
1656                 ];
1657
1658                 # Numbers refer to sections in HTML 4.01 standard describing the element.
1659                 # See: https://www.w3.org/TR/html4/
1660                 $whitelist = [
1661                         # 7.5.4
1662                         'div'        => $block,
1663                         'center'     => $common, # deprecated
1664                         'span'       => $common,
1665
1666                         # 7.5.5
1667                         'h1'         => $block,
1668                         'h2'         => $block,
1669                         'h3'         => $block,
1670                         'h4'         => $block,
1671                         'h5'         => $block,
1672                         'h6'         => $block,
1673
1674                         # 7.5.6
1675                         # address
1676
1677                         # 8.2.4
1678                         'bdo'        => $common,
1679
1680                         # 9.2.1
1681                         'em'         => $common,
1682                         'strong'     => $common,
1683                         'cite'       => $common,
1684                         'dfn'        => $common,
1685                         'code'       => $common,
1686                         'samp'       => $common,
1687                         'kbd'        => $common,
1688                         'var'        => $common,
1689                         'abbr'       => $common,
1690                         # acronym
1691
1692                         # 9.2.2
1693                         'blockquote' => array_merge( $common, [ 'cite' ] ),
1694                         'q'          => array_merge( $common, [ 'cite' ] ),
1695
1696                         # 9.2.3
1697                         'sub'        => $common,
1698                         'sup'        => $common,
1699
1700                         # 9.3.1
1701                         'p'          => $block,
1702
1703                         # 9.3.2
1704                         'br'         => array_merge( $common, [ 'clear' ] ),
1705
1706                         # https://www.w3.org/TR/html5/text-level-semantics.html#the-wbr-element
1707                         'wbr'        => $common,
1708
1709                         # 9.3.4
1710                         'pre'        => array_merge( $common, [ 'width' ] ),
1711
1712                         # 9.4
1713                         'ins'        => array_merge( $common, [ 'cite', 'datetime' ] ),
1714                         'del'        => array_merge( $common, [ 'cite', 'datetime' ] ),
1715
1716                         # 10.2
1717                         'ul'         => array_merge( $common, [ 'type' ] ),
1718                         'ol'         => array_merge( $common, [ 'type', 'start', 'reversed' ] ),
1719                         'li'         => array_merge( $common, [ 'type', 'value' ] ),
1720
1721                         # 10.3
1722                         'dl'         => $common,
1723                         'dd'         => $common,
1724                         'dt'         => $common,
1725
1726                         # 11.2.1
1727                         'table'      => array_merge( $common,
1728                                                                 [ 'summary', 'width', 'border', 'frame',
1729                                                                                 'rules', 'cellspacing', 'cellpadding',
1730                                                                                 'align', 'bgcolor',
1731                                                                 ] ),
1732
1733                         # 11.2.2
1734                         'caption'    => $block,
1735
1736                         # 11.2.3
1737                         'thead'      => $common,
1738                         'tfoot'      => $common,
1739                         'tbody'      => $common,
1740
1741                         # 11.2.4
1742                         'colgroup'   => array_merge( $common, [ 'span' ] ),
1743                         'col'        => array_merge( $common, [ 'span' ] ),
1744
1745                         # 11.2.5
1746                         'tr'         => array_merge( $common, [ 'bgcolor' ], $tablealign ),
1747
1748                         # 11.2.6
1749                         'td'         => array_merge( $common, $tablecell, $tablealign ),
1750                         'th'         => array_merge( $common, $tablecell, $tablealign ),
1751
1752                         # 12.2
1753                         # NOTE: <a> is not allowed directly, but the attrib
1754                         # whitelist is used from the Parser object
1755                         'a'          => array_merge( $common, [ 'href', 'rel', 'rev' ] ), # rel/rev esp. for RDFa
1756
1757                         # 13.2
1758                         # Not usually allowed, but may be used for extension-style hooks
1759                         # such as <math> when it is rasterized, or if $wgAllowImageTag is
1760                         # true
1761                         'img'        => array_merge( $common, [ 'alt', 'src', 'width', 'height' ] ),
1762
1763                         # 15.2.1
1764                         'tt'         => $common,
1765                         'b'          => $common,
1766                         'i'          => $common,
1767                         'big'        => $common,
1768                         'small'      => $common,
1769                         'strike'     => $common,
1770                         's'          => $common,
1771                         'u'          => $common,
1772
1773                         # 15.2.2
1774                         'font'       => array_merge( $common, [ 'size', 'color', 'face' ] ),
1775                         # basefont
1776
1777                         # 15.3
1778                         'hr'         => array_merge( $common, [ 'width' ] ),
1779
1780                         # HTML Ruby annotation text module, simple ruby only.
1781                         # https://www.w3.org/TR/html5/text-level-semantics.html#the-ruby-element
1782                         'ruby'       => $common,
1783                         # rbc
1784                         'rb'         => $common,
1785                         'rp'         => $common,
1786                         'rt'         => $common, # array_merge( $common, array( 'rbspan' ) ),
1787                         'rtc'         => $common,
1788
1789                         # MathML root element, where used for extensions
1790                         # 'title' may not be 100% valid here; it's XHTML
1791                         # https://www.w3.org/TR/REC-MathML/
1792                         'math'       => [ 'class', 'style', 'id', 'title' ],
1793
1794                         # HTML 5 section 4.6
1795                         'bdi' => $common,
1796
1797                         # HTML5 elements, defined by:
1798                         # https://html.spec.whatwg.org/multipage/semantics.html#the-data-element
1799                         'data' => array_merge( $common, [ 'value' ] ),
1800                         'time' => array_merge( $common, [ 'datetime' ] ),
1801                         'mark' => $common,
1802
1803                         // meta and link are only permitted by removeHTMLtags when Microdata
1804                         // is enabled so we don't bother adding a conditional to hide these
1805                         // Also meta and link are only valid in WikiText as Microdata elements
1806                         // (ie: validateTag rejects tags missing the attributes needed for Microdata)
1807                         // So we don't bother including $common attributes that have no purpose.
1808                         'meta' => [ 'itemprop', 'content' ],
1809                         'link' => [ 'itemprop', 'href' ],
1810                 ];
1811
1812                 return $whitelist;
1813         }
1814
1815         /**
1816          * Take a fragment of (potentially invalid) HTML and return
1817          * a version with any tags removed, encoded as plain text.
1818          *
1819          * Warning: this return value must be further escaped for literal
1820          * inclusion in HTML output as of 1.10!
1821          *
1822          * @param string $text HTML fragment
1823          * @return string
1824          */
1825         static function stripAllTags( $text ) {
1826                 # Actual <tags>
1827                 $text = StringUtils::delimiterReplace( '<', '>', '', $text );
1828
1829                 # Normalize &entities and whitespace
1830                 $text = self::decodeCharReferences( $text );
1831                 $text = self::normalizeWhitespace( $text );
1832
1833                 return $text;
1834         }
1835
1836         /**
1837          * Hack up a private DOCTYPE with HTML's standard entity declarations.
1838          * PHP 4 seemed to know these if you gave it an HTML doctype, but
1839          * PHP 5.1 doesn't.
1840          *
1841          * Use for passing XHTML fragments to PHP's XML parsing functions
1842          *
1843          * @return string
1844          */
1845         static function hackDocType() {
1846                 $out = "<!DOCTYPE html [\n";
1847                 foreach ( self::$htmlEntities as $entity => $codepoint ) {
1848                         $out .= "<!ENTITY $entity \"&#$codepoint;\">";
1849                 }
1850                 $out .= "]>\n";
1851                 return $out;
1852         }
1853
1854         /**
1855          * @param string $url
1856          * @return mixed|string
1857          */
1858         static function cleanUrl( $url ) {
1859                 # Normalize any HTML entities in input. They will be
1860                 # re-escaped by makeExternalLink().
1861                 $url = Sanitizer::decodeCharReferences( $url );
1862
1863                 # Escape any control characters introduced by the above step
1864                 $url = preg_replace_callback( '/[\][<>"\\x00-\\x20\\x7F\|]/',
1865                         [ __CLASS__, 'cleanUrlCallback' ], $url );
1866
1867                 # Validate hostname portion
1868                 $matches = [];
1869                 if ( preg_match( '!^([^:]+:)(//[^/]+)?(.*)$!iD', $url, $matches ) ) {
1870                         list( /* $whole */, $protocol, $host, $rest ) = $matches;
1871
1872                         // Characters that will be ignored in IDNs.
1873                         // https://tools.ietf.org/html/rfc3454#section-3.1
1874                         // Strip them before further processing so blacklists and such work.
1875                         $strip = "/
1876                                 \\s|          # general whitespace
1877                                 \xc2\xad|     # 00ad SOFT HYPHEN
1878                                 \xe1\xa0\x86| # 1806 MONGOLIAN TODO SOFT HYPHEN
1879                                 \xe2\x80\x8b| # 200b ZERO WIDTH SPACE
1880                                 \xe2\x81\xa0| # 2060 WORD JOINER
1881                                 \xef\xbb\xbf| # feff ZERO WIDTH NO-BREAK SPACE
1882                                 \xcd\x8f|     # 034f COMBINING GRAPHEME JOINER
1883                                 \xe1\xa0\x8b| # 180b MONGOLIAN FREE VARIATION SELECTOR ONE
1884                                 \xe1\xa0\x8c| # 180c MONGOLIAN FREE VARIATION SELECTOR TWO
1885                                 \xe1\xa0\x8d| # 180d MONGOLIAN FREE VARIATION SELECTOR THREE
1886                                 \xe2\x80\x8c| # 200c ZERO WIDTH NON-JOINER
1887                                 \xe2\x80\x8d| # 200d ZERO WIDTH JOINER
1888                                 [\xef\xb8\x80-\xef\xb8\x8f] # fe00-fe0f VARIATION SELECTOR-1-16
1889                                 /xuD";
1890
1891                         $host = preg_replace( $strip, '', $host );
1892
1893                         // IPv6 host names are bracketed with [].  Url-decode these.
1894                         if ( substr_compare( "//%5B", $host, 0, 5 ) === 0 &&
1895                                 preg_match( '!^//%5B([0-9A-Fa-f:.]+)%5D((:\d+)?)$!', $host, $matches )
1896                         ) {
1897                                 $host = '//[' . $matches[1] . ']' . $matches[2];
1898                         }
1899
1900                         // @todo FIXME: Validate hostnames here
1901
1902                         return $protocol . $host . $rest;
1903                 } else {
1904                         return $url;
1905                 }
1906         }
1907
1908         /**
1909          * @param array $matches
1910          * @return string
1911          */
1912         static function cleanUrlCallback( $matches ) {
1913                 return urlencode( $matches[0] );
1914         }
1915
1916         /**
1917          * Does a string look like an e-mail address?
1918          *
1919          * This validates an email address using an HTML5 specification found at:
1920          * http://www.whatwg.org/html/states-of-the-type-attribute.html#valid-e-mail-address
1921          * Which as of 2011-01-24 says:
1922          *
1923          *   A valid e-mail address is a string that matches the ABNF production
1924          *   1*( atext / "." ) "@" ldh-str *( "." ldh-str ) where atext is defined
1925          *   in RFC 5322 section 3.2.3, and ldh-str is defined in RFC 1034 section
1926          *   3.5.
1927          *
1928          * This function is an implementation of the specification as requested in
1929          * bug 22449.
1930          *
1931          * Client-side forms will use the same standard validation rules via JS or
1932          * HTML 5 validation; additional restrictions can be enforced server-side
1933          * by extensions via the 'isValidEmailAddr' hook.
1934          *
1935          * Note that this validation doesn't 100% match RFC 2822, but is believed
1936          * to be liberal enough for wide use. Some invalid addresses will still
1937          * pass validation here.
1938          *
1939          * @since 1.18
1940          *
1941          * @param string $addr E-mail address
1942          * @return bool
1943          */
1944         public static function validateEmail( $addr ) {
1945                 $result = null;
1946                 if ( !Hooks::run( 'isValidEmailAddr', [ $addr, &$result ] ) ) {
1947                         return $result;
1948                 }
1949
1950                 // Please note strings below are enclosed in brackets [], this make the
1951                 // hyphen "-" a range indicator. Hence it is double backslashed below.
1952                 // See bug 26948
1953                 $rfc5322_atext = "a-z0-9!#$%&'*+\\-\/=?^_`{|}~";
1954                 $rfc1034_ldh_str = "a-z0-9\\-";
1955
1956                 $html5_email_regexp = "/
1957                 ^                      # start of string
1958                 [$rfc5322_atext\\.]+    # user part which is liberal :p
1959                 @                      # 'apostrophe'
1960                 [$rfc1034_ldh_str]+       # First domain part
1961                 (\\.[$rfc1034_ldh_str]+)*  # Following part prefixed with a dot
1962                 $                      # End of string
1963                 /ix"; // case Insensitive, eXtended
1964
1965                 return (bool)preg_match( $html5_email_regexp, $addr );
1966         }
1967 }