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          * http://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          * http://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 $attribsRegex;
 332
 333         /**
 334          * Regular expression to match HTML/XML attribute pairs within a tag.
 335          * Allows some... latitude. Based on,
 336          * http://www.w3.org/TR/html5/syntax.html#before-attribute-value-state
 337          * Used in Sanitizer::fixTagAttributes and Sanitizer::decodeTagAttributes
 338          * @return string
 339          */
 340         static function getAttribsRegex() {
 341                 if ( self::$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                         !ix', $value ) ) {
1019                         return '/* insecure input */';
1020                 }
1021                 return $value;
1022         }
1023
1024         /**
1025          * @param array $matches
1026          * @return string
1027          */
1028         static function cssDecodeCallback( $matches ) {
1029                 if ( $matches[1] !== '' ) {
1030                         // Line continuation
1031                         return '';
1032                 } elseif ( $matches[2] !== '' ) {
1033                         $char = UtfNormal\Utils::codepointToUtf8( hexdec( $matches[2] ) );
1034                 } elseif ( $matches[3] !== '' ) {
1035                         $char = $matches[3];
1036                 } else {
1037                         $char = '\\';
1038                 }
1039                 if ( $char == "\n" || $char == '"' || $char == "'" || $char == '\\' ) {
1040                         // These characters need to be escaped in strings
1041                         // Clean up the escape sequence to avoid parsing errors by clients
1042                         return '\\' . dechex( ord( $char ) ) . ' ';
1043                 } else {
1044                         // Decode unnecessary escape
1045                         return $char;
1046                 }
1047         }
1048
1049         /**
1050          * Take a tag soup fragment listing an HTML element's attributes
1051          * and normalize it to well-formed XML, discarding unwanted attributes.
1052          * Output is safe for further wikitext processing, with escaping of
1053          * values that could trigger problems.
1054          *
1055          * - Normalizes attribute names to lowercase
1056          * - Discards attributes not on a whitelist for the given element
1057          * - Turns broken or invalid entities into plaintext
1058          * - Double-quotes all attribute values
1059          * - Attributes without values are given the name as attribute
1060          * - Double attributes are discarded
1061          * - Unsafe style attributes are discarded
1062          * - Prepends space if there are attributes.
1063          * - (Optionally) Sorts attributes by name.
1064          *
1065          * @param string $text
1066          * @param string $element
1067          * @param bool $sorted Whether to sort the attributes (default: false)
1068          * @return string
1069          */
1070         static function fixTagAttributes( $text, $element, $sorted = false ) {
1071                 if ( trim( $text ) == '' ) {
1072                         return '';
1073                 }
1074
1075                 $decoded = Sanitizer::decodeTagAttributes( $text );
1076                 $stripped = Sanitizer::validateTagAttributes( $decoded, $element );
1077
1078                 if ( $sorted ) {
1079                         ksort( $stripped );
1080                 }
1081
1082                 return Sanitizer::safeEncodeTagAttributes( $stripped );
1083         }
1084
1085         /**
1086          * Encode an attribute value for HTML output.
1087          * @param string $text
1088          * @return string HTML-encoded text fragment
1089          */
1090         static function encodeAttribute( $text ) {
1091                 $encValue = htmlspecialchars( $text, ENT_QUOTES );
1092
1093                 // Whitespace is normalized during attribute decoding,
1094                 // so if we've been passed non-spaces we must encode them
1095                 // ahead of time or they won't be preserved.
1096                 $encValue = strtr( $encValue, [
1097                         "\n" => '&#10;',
1098                         "\r" => '&#13;',
1099                         "\t" => '&#9;',
1100                 ] );
1101
1102                 return $encValue;
1103         }
1104
1105         /**
1106          * Encode an attribute value for HTML tags, with extra armoring
1107          * against further wiki processing.
1108          * @param string $text
1109          * @return string HTML-encoded text fragment
1110          */
1111         static function safeEncodeAttribute( $text ) {
1112                 $encValue = Sanitizer::encodeAttribute( $text );
1113
1114                 # Templates and links may be expanded in later parsing,
1115                 # creating invalid or dangerous output. Suppress this.
1116                 $encValue = strtr( $encValue, [
1117                         '<'    => '&lt;',   // This should never happen,
1118                         '>'    => '&gt;',   // we've received invalid input
1119                         '"'    => '&quot;', // which should have been escaped.
1120                         '{'    => '&#123;',
1121                         '['    => '&#91;',
1122                         "''"   => '&#39;&#39;',
1123                         'ISBN' => '&#73;SBN',
1124                         'RFC'  => '&#82;FC',
1125                         'PMID' => '&#80;MID',
1126                         '|'    => '&#124;',
1127                         '__'   => '&#95;_',
1128                 ] );
1129
1130                 # Stupid hack
1131                 $encValue = preg_replace_callback(
1132                         '/((?i)' . wfUrlProtocols() . ')/',
1133                         [ 'Sanitizer', 'armorLinksCallback' ],
1134                         $encValue );
1135                 return $encValue;
1136         }
1137
1138         /**
1139          * Given a value, escape it so that it can be used in an id attribute and
1140          * return it.  This will use HTML5 validation if $wgExperimentalHtmlIds is
1141          * true, allowing anything but ASCII whitespace.  Otherwise it will use
1142          * HTML 4 rules, which means a narrow subset of ASCII, with bad characters
1143          * escaped with lots of dots.
1144          *
1145          * To ensure we don't have to bother escaping anything, we also strip ', ",
1146          * & even if $wgExperimentalIds is true.  TODO: Is this the best tactic?
1147          * We also strip # because it upsets IE, and % because it could be
1148          * ambiguous if it's part of something that looks like a percent escape
1149          * (which don't work reliably in fragments cross-browser).
1150          *
1151          * @see http://www.w3.org/TR/html401/types.html#type-name Valid characters
1152          *   in the id and name attributes
1153          * @see http://www.w3.org/TR/html401/struct/links.html#h-12.2.3 Anchors with
1154          *   the id attribute
1155          * @see http://www.whatwg.org/html/elements.html#the-id-attribute
1156          *   HTML5 definition of id attribute
1157          *
1158          * @param string $id Id to escape
1159          * @param string|array $options String or array of strings (default is array()):
1160          *   'noninitial': This is a non-initial fragment of an id, not a full id,
1161          *       so don't pay attention if the first character isn't valid at the
1162          *       beginning of an id.  Only matters if $wgExperimentalHtmlIds is
1163          *       false.
1164          *   'legacy': Behave the way the old HTML 4-based ID escaping worked even
1165          *       if $wgExperimentalHtmlIds is used, so we can generate extra
1166          *       anchors and links won't break.
1167          * @return string
1168          */
1169         static function escapeId( $id, $options = [] ) {
1170                 global $wgExperimentalHtmlIds;
1171                 $options = (array)$options;
1172
1173                 $id = Sanitizer::decodeCharReferences( $id );
1174
1175                 if ( $wgExperimentalHtmlIds && !in_array( 'legacy', $options ) ) {
1176                         $id = preg_replace( '/[ \t\n\r\f_\'"&#%]+/', '_', $id );
1177                         $id = trim( $id, '_' );
1178                         if ( $id === '' ) {
1179                                 // Must have been all whitespace to start with.
1180                                 return '_';
1181                         } else {
1182                                 return $id;
1183                         }
1184                 }
1185
1186                 // HTML4-style escaping
1187                 static $replace = [
1188                         '%3A' => ':',
1189                         '%' => '.'
1190                 ];
1191
1192                 $id = urlencode( strtr( $id, ' ', '_' ) );
1193                 $id = str_replace( array_keys( $replace ), array_values( $replace ), $id );
1194
1195                 if ( !preg_match( '/^[a-zA-Z]/', $id ) && !in_array( 'noninitial', $options ) ) {
1196                         // Initial character must be a letter!
1197                         $id = "x$id";
1198                 }
1199                 return $id;
1200         }
1201
1202         /**
1203          * Given a string containing a space delimited list of ids, escape each id
1204          * to match ids escaped by the escapeId() function.
1205          *
1206          * @since 1.27
1207          *
1208          * @param string $referenceString Space delimited list of ids
1209          * @param string|array $options String or array of strings (default is array()):
1210          *   'noninitial': This is a non-initial fragment of an id, not a full id,
1211          *       so don't pay attention if the first character isn't valid at the
1212          *       beginning of an id.  Only matters if $wgExperimentalHtmlIds is
1213          *       false.
1214          *   'legacy': Behave the way the old HTML 4-based ID escaping worked even
1215          *       if $wgExperimentalHtmlIds is used, so we can generate extra
1216          *       anchors and links won't break.
1217          * @return string
1218          */
1219         static function escapeIdReferenceList( $referenceString, $options = [] ) {
1220                 # Explode the space delimited list string into an array of tokens
1221                 $references = preg_split( '/\s+/', "{$referenceString}", -1, PREG_SPLIT_NO_EMPTY );
1222
1223                 # Escape each token as an id
1224                 foreach ( $references as &$ref ) {
1225                         $ref = Sanitizer::escapeId( $ref, $options );
1226                 }
1227
1228                 # Merge the array back to a space delimited list string
1229                 # If the array is empty, the result will be an empty string ('')
1230                 $referenceString = implode( ' ', $references );
1231
1232                 return $referenceString;
1233         }
1234
1235         /**
1236          * Given a value, escape it so that it can be used as a CSS class and
1237          * return it.
1238          *
1239          * @todo For extra validity, input should be validated UTF-8.
1240          *
1241          * @see http://www.w3.org/TR/CSS21/syndata.html Valid characters/format
1242          *
1243          * @param string $class
1244          * @return string
1245          */
1246         static function escapeClass( $class ) {
1247                 // Convert ugly stuff to underscores and kill underscores in ugly places
1248                 return rtrim( preg_replace(
1249                         [ '/(^[0-9\\-])|[\\x00-\\x20!"#$%&\'()*+,.\\/:;<=>?@[\\]^`{|}~]|\\xC2\\xA0/', '/_+/' ],
1250                         '_',
1251                         $class ), '_' );
1252         }
1253
1254         /**
1255          * Given HTML input, escape with htmlspecialchars but un-escape entities.
1256          * This allows (generally harmless) entities like &#160; to survive.
1257          *
1258          * @param string $html HTML to escape
1259          * @return string Escaped input
1260          */
1261         static function escapeHtmlAllowEntities( $html ) {
1262                 $html = Sanitizer::decodeCharReferences( $html );
1263                 # It seems wise to escape ' as well as ", as a matter of course.  Can't
1264                 # hurt.
1265                 $html = htmlspecialchars( $html, ENT_QUOTES );
1266                 return $html;
1267         }
1268
1269         /**
1270          * Regex replace callback for armoring links against further processing.
1271          * @param array $matches
1272          * @return string
1273          */
1274         private static function armorLinksCallback( $matches ) {
1275                 return str_replace( ':', '&#58;', $matches[1] );
1276         }
1277
1278         /**
1279          * Return an associative array of attribute names and values from
1280          * a partial tag string. Attribute names are forced to lowercase,
1281          * character references are decoded to UTF-8 text.
1282          *
1283          * @param string $text
1284          * @return array
1285          */
1286         public static function decodeTagAttributes( $text ) {
1287                 if ( trim( $text ) == '' ) {
1288                         return [];
1289                 }
1290
1291                 $attribs = [];
1292                 $pairs = [];
1293                 if ( !preg_match_all(
1294                         self::getAttribsRegex(),
1295                         $text,
1296                         $pairs,
1297                         PREG_SET_ORDER ) ) {
1298                         return $attribs;
1299                 }
1300
1301                 foreach ( $pairs as $set ) {
1302                         $attribute = strtolower( $set[1] );
1303                         $value = Sanitizer::getTagAttributeCallback( $set );
1304
1305                         // Normalize whitespace
1306                         $value = preg_replace( '/[\t\r\n ]+/', ' ', $value );
1307                         $value = trim( $value );
1308
1309                         // Decode character references
1310                         $attribs[$attribute] = Sanitizer::decodeCharReferences( $value );
1311                 }
1312                 return $attribs;
1313         }
1314
1315         /**
1316          * Build a partial tag string from an associative array of attribute
1317          * names and values as returned by decodeTagAttributes.
1318          *
1319          * @param array $assoc_array
1320          * @return string
1321          */
1322         public static function safeEncodeTagAttributes( $assoc_array ) {
1323                 $attribs = [];
1324                 foreach ( $assoc_array as $attribute => $value ) {
1325                         $encAttribute = htmlspecialchars( $attribute );
1326                         $encValue = Sanitizer::safeEncodeAttribute( $value );
1327
1328                         $attribs[] = "$encAttribute=\"$encValue\"";
1329                 }
1330                 return count( $attribs ) ? ' ' . implode( ' ', $attribs ) : '';
1331         }
1332
1333         /**
1334          * Pick the appropriate attribute value from a match set from the
1335          * attribs regex matches.
1336          *
1337          * @param array $set
1338          * @throws MWException When tag conditions are not met.
1339          * @return string
1340          */
1341         private static function getTagAttributeCallback( $set ) {
1342                 if ( isset( $set[5] ) ) {
1343                         # No quotes.
1344                         return $set[5];
1345                 } elseif ( isset( $set[4] ) ) {
1346                         # Single-quoted
1347                         return $set[4];
1348                 } elseif ( isset( $set[3] ) ) {
1349                         # Double-quoted
1350                         return $set[3];
1351                 } elseif ( !isset( $set[2] ) ) {
1352                         # In XHTML, attributes must have a value so return an empty string.
1353                         # See "Empty attribute syntax",
1354                         # http://www.w3.org/TR/html5/syntax.html#syntax-attribute-name
1355                         return "";
1356                 } else {
1357                         throw new MWException( "Tag conditions not met. This should never happen and is a bug." );
1358                 }
1359         }
1360
1361         /**
1362          * @param string $text
1363          * @return string
1364          */
1365         private static function normalizeWhitespace( $text ) {
1366                 return preg_replace(
1367                         '/\r\n|[\x20\x0d\x0a\x09]/',
1368                         ' ',
1369                         $text );
1370         }
1371
1372         /**
1373          * Normalizes whitespace in a section name, such as might be returned
1374          * by Parser::stripSectionName(), for use in the id's that are used for
1375          * section links.
1376          *
1377          * @param string $section
1378          * @return string
1379          */
1380         static function normalizeSectionNameWhitespace( $section ) {
1381                 return trim( preg_replace( '/[ _]+/', ' ', $section ) );
1382         }
1383
1384         /**
1385          * Ensure that any entities and character references are legal
1386          * for XML and XHTML specifically. Any stray bits will be
1387          * &amp;-escaped to result in a valid text fragment.
1388          *
1389          * a. named char refs can only be &lt; &gt; &amp; &quot;, others are
1390          *   numericized (this way we're well-formed even without a DTD)
1391          * b. any numeric char refs must be legal chars, not invalid or forbidden
1392          * c. use lower cased "&#x", not "&#X"
1393          * d. fix or reject non-valid attributes
1394          *
1395          * @param string $text
1396          * @return string
1397          * @private
1398          */
1399         static function normalizeCharReferences( $text ) {
1400                 return preg_replace_callback(
1401                         self::CHAR_REFS_REGEX,
1402                         [ 'Sanitizer', 'normalizeCharReferencesCallback' ],
1403                         $text );
1404         }
1405
1406         /**
1407          * @param string $matches
1408          * @return string
1409          */
1410         static function normalizeCharReferencesCallback( $matches ) {
1411                 $ret = null;
1412                 if ( $matches[1] != '' ) {
1413                         $ret = Sanitizer::normalizeEntity( $matches[1] );
1414                 } elseif ( $matches[2] != '' ) {
1415                         $ret = Sanitizer::decCharReference( $matches[2] );
1416                 } elseif ( $matches[3] != '' ) {
1417                         $ret = Sanitizer::hexCharReference( $matches[3] );
1418                 }
1419                 if ( is_null( $ret ) ) {
1420                         return htmlspecialchars( $matches[0] );
1421                 } else {
1422                         return $ret;
1423                 }
1424         }
1425
1426         /**
1427          * If the named entity is defined in the HTML 4.0/XHTML 1.0 DTD,
1428          * return the equivalent numeric entity reference (except for the core &lt;
1429          * &gt; &amp; &quot;). If the entity is a MediaWiki-specific alias, returns
1430          * the HTML equivalent. Otherwise, returns HTML-escaped text of
1431          * pseudo-entity source (eg &amp;foo;)
1432          *
1433          * @param string $name
1434          * @return string
1435          */
1436         static function normalizeEntity( $name ) {
1437                 if ( isset( self::$htmlEntityAliases[$name] ) ) {
1438                         return '&' . self::$htmlEntityAliases[$name] . ';';
1439                 } elseif ( in_array( $name, [ 'lt', 'gt', 'amp', 'quot' ] ) ) {
1440                         return "&$name;";
1441                 } elseif ( isset( self::$htmlEntities[$name] ) ) {
1442                         return '&#' . self::$htmlEntities[$name] . ';';
1443                 } else {
1444                         return "&amp;$name;";
1445                 }
1446         }
1447
1448         /**
1449          * @param int $codepoint
1450          * @return null|string
1451          */
1452         static function decCharReference( $codepoint ) {
1453                 $point = intval( $codepoint );
1454                 if ( Sanitizer::validateCodepoint( $point ) ) {
1455                         return sprintf( '&#%d;', $point );
1456                 } else {
1457                         return null;
1458                 }
1459         }
1460
1461         /**
1462          * @param int $codepoint
1463          * @return null|string
1464          */
1465         static function hexCharReference( $codepoint ) {
1466                 $point = hexdec( $codepoint );
1467                 if ( Sanitizer::validateCodepoint( $point ) ) {
1468                         return sprintf( '&#x%x;', $point );
1469                 } else {
1470                         return null;
1471                 }
1472         }
1473
1474         /**
1475          * Returns true if a given Unicode codepoint is a valid character in
1476          * both HTML5 and XML.
1477          * @param int $codepoint
1478          * @return bool
1479          */
1480         private static function validateCodepoint( $codepoint ) {
1481                 # U+000C is valid in HTML5 but not allowed in XML.
1482                 # U+000D is valid in XML but not allowed in HTML5.
1483                 # U+007F - U+009F are disallowed in HTML5 (control characters).
1484                 return $codepoint == 0x09
1485                         || $codepoint == 0x0a
1486                         || ( $codepoint >= 0x20 && $codepoint <= 0x7e )
1487                         || ( $codepoint >= 0xa0 && $codepoint <= 0xd7ff )
1488                         || ( $codepoint >= 0xe000 && $codepoint <= 0xfffd )
1489                         || ( $codepoint >= 0x10000 && $codepoint <= 0x10ffff );
1490         }
1491
1492         /**
1493          * Decode any character references, numeric or named entities,
1494          * in the text and return a UTF-8 string.
1495          *
1496          * @param string $text
1497          * @return string
1498          */
1499         public static function decodeCharReferences( $text ) {
1500                 return preg_replace_callback(
1501                         self::CHAR_REFS_REGEX,
1502                         [ 'Sanitizer', 'decodeCharReferencesCallback' ],
1503                         $text );
1504         }
1505
1506         /**
1507          * Decode any character references, numeric or named entities,
1508          * in the next and normalize the resulting string. (bug 14952)
1509          *
1510          * This is useful for page titles, not for text to be displayed,
1511          * MediaWiki allows HTML entities to escape normalization as a feature.
1512          *
1513          * @param string $text Already normalized, containing entities
1514          * @return string Still normalized, without entities
1515          */
1516         public static function decodeCharReferencesAndNormalize( $text ) {
1517                 global $wgContLang;
1518                 $text = preg_replace_callback(
1519                         self::CHAR_REFS_REGEX,
1520                         [ 'Sanitizer', 'decodeCharReferencesCallback' ],
1521                         $text, /* limit */ -1, $count );
1522
1523                 if ( $count ) {
1524                         return $wgContLang->normalize( $text );
1525                 } else {
1526                         return $text;
1527                 }
1528         }
1529
1530         /**
1531          * @param string $matches
1532          * @return string
1533          */
1534         static function decodeCharReferencesCallback( $matches ) {
1535                 if ( $matches[1] != '' ) {
1536                         return Sanitizer::decodeEntity( $matches[1] );
1537                 } elseif ( $matches[2] != '' ) {
1538                         return Sanitizer::decodeChar( intval( $matches[2] ) );
1539                 } elseif ( $matches[3] != '' ) {
1540                         return Sanitizer::decodeChar( hexdec( $matches[3] ) );
1541                 }
1542                 # Last case should be an ampersand by itself
1543                 return $matches[0];
1544         }
1545
1546         /**
1547          * Return UTF-8 string for a codepoint if that is a valid
1548          * character reference, otherwise U+FFFD REPLACEMENT CHARACTER.
1549          * @param int $codepoint
1550          * @return string
1551          * @private
1552          */
1553         static function decodeChar( $codepoint ) {
1554                 if ( Sanitizer::validateCodepoint( $codepoint ) ) {
1555                         return UtfNormal\Utils::codepointToUtf8( $codepoint );
1556                 } else {
1557                         return UtfNormal\Constants::UTF8_REPLACEMENT;
1558                 }
1559         }
1560
1561         /**
1562          * If the named entity is defined in the HTML 4.0/XHTML 1.0 DTD,
1563          * return the UTF-8 encoding of that character. Otherwise, returns
1564          * pseudo-entity source (eg "&foo;")
1565          *
1566          * @param string $name
1567          * @return string
1568          */
1569         static function decodeEntity( $name ) {
1570                 if ( isset( self::$htmlEntityAliases[$name] ) ) {
1571                         $name = self::$htmlEntityAliases[$name];
1572                 }
1573                 if ( isset( self::$htmlEntities[$name] ) ) {
1574                         return UtfNormal\Utils::codepointToUtf8( self::$htmlEntities[$name] );
1575                 } else {
1576                         return "&$name;";
1577                 }
1578         }
1579
1580         /**
1581          * Fetch the whitelist of acceptable attributes for a given element name.
1582          *
1583          * @param string $element
1584          * @return array
1585          */
1586         static function attributeWhitelist( $element ) {
1587                 $list = Sanitizer::setupAttributeWhitelist();
1588                 return isset( $list[$element] )
1589                         ? $list[$element]
1590                         : [];
1591         }
1592
1593         /**
1594          * Foreach array key (an allowed HTML element), return an array
1595          * of allowed attributes
1596          * @return array
1597          */
1598         static function setupAttributeWhitelist() {
1599                 static $whitelist;
1600
1601                 if ( $whitelist !== null ) {
1602                         return $whitelist;
1603                 }
1604
1605                 $common = [
1606                         # HTML
1607                         'id',
1608                         'class',
1609                         'style',
1610                         'lang',
1611                         'dir',
1612                         'title',
1613
1614                         # WAI-ARIA
1615                         'aria-describedby',
1616                         'aria-flowto',
1617                         'aria-label',
1618                         'aria-labelledby',
1619                         'aria-owns',
1620                         'role',
1621
1622                         # RDFa
1623                         # These attributes are specified in section 9 of
1624                         # http://www.w3.org/TR/2008/REC-rdfa-syntax-20081014
1625                         'about',
1626                         'property',
1627                         'resource',
1628                         'datatype',
1629                         'typeof',
1630
1631                         # Microdata. These are specified by
1632                         # http://www.whatwg.org/html/microdata.html#the-microdata-model
1633                         'itemid',
1634                         'itemprop',
1635                         'itemref',
1636                         'itemscope',
1637                         'itemtype',
1638                 ];
1639
1640                 $block = array_merge( $common, [ 'align' ] );
1641                 $tablealign = [ 'align', 'valign' ];
1642                 $tablecell = [
1643                         'abbr',
1644                         'axis',
1645                         'headers',
1646                         'scope',
1647                         'rowspan',
1648                         'colspan',
1649                         'nowrap', # deprecated
1650                         'width', # deprecated
1651                         'height', # deprecated
1652                         'bgcolor', # deprecated
1653                 ];
1654
1655                 # Numbers refer to sections in HTML 4.01 standard describing the element.
1656                 # See: http://www.w3.org/TR/html4/
1657                 $whitelist = [
1658                         # 7.5.4
1659                         'div'        => $block,
1660                         'center'     => $common, # deprecated
1661                         'span'       => $common,
1662
1663                         # 7.5.5
1664                         'h1'         => $block,
1665                         'h2'         => $block,
1666                         'h3'         => $block,
1667                         'h4'         => $block,
1668                         'h5'         => $block,
1669                         'h6'         => $block,
1670
1671                         # 7.5.6
1672                         # address
1673
1674                         # 8.2.4
1675                         'bdo'        => $common,
1676
1677                         # 9.2.1
1678                         'em'         => $common,
1679                         'strong'     => $common,
1680                         'cite'       => $common,
1681                         'dfn'        => $common,
1682                         'code'       => $common,
1683                         'samp'       => $common,
1684                         'kbd'        => $common,
1685                         'var'        => $common,
1686                         'abbr'       => $common,
1687                         # acronym
1688
1689                         # 9.2.2
1690                         'blockquote' => array_merge( $common, [ 'cite' ] ),
1691                         'q'          => array_merge( $common, [ 'cite' ] ),
1692
1693                         # 9.2.3
1694                         'sub'        => $common,
1695                         'sup'        => $common,
1696
1697                         # 9.3.1
1698                         'p'          => $block,
1699
1700                         # 9.3.2
1701                         'br'         => array_merge( $common, [ 'clear' ] ),
1702
1703                         # http://www.whatwg.org/html/text-level-semantics.html#the-wbr-element
1704                         'wbr'        => $common,
1705
1706                         # 9.3.4
1707                         'pre'        => array_merge( $common, [ 'width' ] ),
1708
1709                         # 9.4
1710                         'ins'        => array_merge( $common, [ 'cite', 'datetime' ] ),
1711                         'del'        => array_merge( $common, [ 'cite', 'datetime' ] ),
1712
1713                         # 10.2
1714                         'ul'         => array_merge( $common, [ 'type' ] ),
1715                         'ol'         => array_merge( $common, [ 'type', 'start', 'reversed' ] ),
1716                         'li'         => array_merge( $common, [ 'type', 'value' ] ),
1717
1718                         # 10.3
1719                         'dl'         => $common,
1720                         'dd'         => $common,
1721                         'dt'         => $common,
1722
1723                         # 11.2.1
1724                         'table'      => array_merge( $common,
1725                                                                 [ 'summary', 'width', 'border', 'frame',
1726                                                                                 'rules', 'cellspacing', 'cellpadding',
1727                                                                                 'align', 'bgcolor',
1728                                                                 ] ),
1729
1730                         # 11.2.2
1731                         'caption'    => $block,
1732
1733                         # 11.2.3
1734                         'thead'      => $common,
1735                         'tfoot'      => $common,
1736                         'tbody'      => $common,
1737
1738                         # 11.2.4
1739                         'colgroup'   => array_merge( $common, [ 'span' ] ),
1740                         'col'        => array_merge( $common, [ 'span' ] ),
1741
1742                         # 11.2.5
1743                         'tr'         => array_merge( $common, [ 'bgcolor' ], $tablealign ),
1744
1745                         # 11.2.6
1746                         'td'         => array_merge( $common, $tablecell, $tablealign ),
1747                         'th'         => array_merge( $common, $tablecell, $tablealign ),
1748
1749                         # 12.2
1750                         # NOTE: <a> is not allowed directly, but the attrib
1751                         # whitelist is used from the Parser object
1752                         'a'          => array_merge( $common, [ 'href', 'rel', 'rev' ] ), # rel/rev esp. for RDFa
1753
1754                         # 13.2
1755                         # Not usually allowed, but may be used for extension-style hooks
1756                         # such as <math> when it is rasterized, or if $wgAllowImageTag is
1757                         # true
1758                         'img'        => array_merge( $common, [ 'alt', 'src', 'width', 'height' ] ),
1759
1760                         # 15.2.1
1761                         'tt'         => $common,
1762                         'b'          => $common,
1763                         'i'          => $common,
1764                         'big'        => $common,
1765                         'small'      => $common,
1766                         'strike'     => $common,
1767                         's'          => $common,
1768                         'u'          => $common,
1769
1770                         # 15.2.2
1771                         'font'       => array_merge( $common, [ 'size', 'color', 'face' ] ),
1772                         # basefont
1773
1774                         # 15.3
1775                         'hr'         => array_merge( $common, [ 'width' ] ),
1776
1777                         # HTML Ruby annotation text module, simple ruby only.
1778                         # http://www.whatwg.org/html/text-level-semantics.html#the-ruby-element
1779                         'ruby'       => $common,
1780                         # rbc
1781                         'rb'         => $common,
1782                         'rp'         => $common,
1783                         'rt'         => $common, # array_merge( $common, array( 'rbspan' ) ),
1784                         'rtc'         => $common,
1785
1786                         # MathML root element, where used for extensions
1787                         # 'title' may not be 100% valid here; it's XHTML
1788                         # http://www.w3.org/TR/REC-MathML/
1789                         'math'       => [ 'class', 'style', 'id', 'title' ],
1790
1791                         # HTML 5 section 4.6
1792                         'bdi' => $common,
1793
1794                         # HTML5 elements, defined by:
1795                         # http://www.whatwg.org/html/
1796                         'data' => array_merge( $common, [ 'value' ] ),
1797                         'time' => array_merge( $common, [ 'datetime' ] ),
1798                         'mark' => $common,
1799
1800                         // meta and link are only permitted by removeHTMLtags when Microdata
1801                         // is enabled so we don't bother adding a conditional to hide these
1802                         // Also meta and link are only valid in WikiText as Microdata elements
1803                         // (ie: validateTag rejects tags missing the attributes needed for Microdata)
1804                         // So we don't bother including $common attributes that have no purpose.
1805                         'meta' => [ 'itemprop', 'content' ],
1806                         'link' => [ 'itemprop', 'href' ],
1807                 ];
1808
1809                 return $whitelist;
1810         }
1811
1812         /**
1813          * Take a fragment of (potentially invalid) HTML and return
1814          * a version with any tags removed, encoded as plain text.
1815          *
1816          * Warning: this return value must be further escaped for literal
1817          * inclusion in HTML output as of 1.10!
1818          *
1819          * @param string $text HTML fragment
1820          * @return string
1821          */
1822         static function stripAllTags( $text ) {
1823                 # Actual <tags>
1824                 $text = StringUtils::delimiterReplace( '<', '>', '', $text );
1825
1826                 # Normalize &entities and whitespace
1827                 $text = self::decodeCharReferences( $text );
1828                 $text = self::normalizeWhitespace( $text );
1829
1830                 return $text;
1831         }
1832
1833         /**
1834          * Hack up a private DOCTYPE with HTML's standard entity declarations.
1835          * PHP 4 seemed to know these if you gave it an HTML doctype, but
1836          * PHP 5.1 doesn't.
1837          *
1838          * Use for passing XHTML fragments to PHP's XML parsing functions
1839          *
1840          * @return string
1841          */
1842         static function hackDocType() {
1843                 $out = "<!DOCTYPE html [\n";
1844                 foreach ( self::$htmlEntities as $entity => $codepoint ) {
1845                         $out .= "<!ENTITY $entity \"&#$codepoint;\">";
1846                 }
1847                 $out .= "]>\n";
1848                 return $out;
1849         }
1850
1851         /**
1852          * @param string $url
1853          * @return mixed|string
1854          */
1855         static function cleanUrl( $url ) {
1856                 # Normalize any HTML entities in input. They will be
1857                 # re-escaped by makeExternalLink().
1858                 $url = Sanitizer::decodeCharReferences( $url );
1859
1860                 # Escape any control characters introduced by the above step
1861                 $url = preg_replace_callback( '/[\][<>"\\x00-\\x20\\x7F\|]/',
1862                         [ __CLASS__, 'cleanUrlCallback' ], $url );
1863
1864                 # Validate hostname portion
1865                 $matches = [];
1866                 if ( preg_match( '!^([^:]+:)(//[^/]+)?(.*)$!iD', $url, $matches ) ) {
1867                         list( /* $whole */, $protocol, $host, $rest ) = $matches;
1868
1869                         // Characters that will be ignored in IDNs.
1870                         // http://tools.ietf.org/html/3454#section-3.1
1871                         // Strip them before further processing so blacklists and such work.
1872                         $strip = "/
1873                                 \\s|          # general whitespace
1874                                 \xc2\xad|     # 00ad SOFT HYPHEN
1875                                 \xe1\xa0\x86| # 1806 MONGOLIAN TODO SOFT HYPHEN
1876                                 \xe2\x80\x8b| # 200b ZERO WIDTH SPACE
1877                                 \xe2\x81\xa0| # 2060 WORD JOINER
1878                                 \xef\xbb\xbf| # feff ZERO WIDTH NO-BREAK SPACE
1879                                 \xcd\x8f|     # 034f COMBINING GRAPHEME JOINER
1880                                 \xe1\xa0\x8b| # 180b MONGOLIAN FREE VARIATION SELECTOR ONE
1881                                 \xe1\xa0\x8c| # 180c MONGOLIAN FREE VARIATION SELECTOR TWO
1882                                 \xe1\xa0\x8d| # 180d MONGOLIAN FREE VARIATION SELECTOR THREE
1883                                 \xe2\x80\x8c| # 200c ZERO WIDTH NON-JOINER
1884                                 \xe2\x80\x8d| # 200d ZERO WIDTH JOINER
1885                                 [\xef\xb8\x80-\xef\xb8\x8f] # fe00-fe0f VARIATION SELECTOR-1-16
1886                                 /xuD";
1887
1888                         $host = preg_replace( $strip, '', $host );
1889
1890                         // IPv6 host names are bracketed with [].  Url-decode these.
1891                         if ( substr_compare( "//%5B", $host, 0, 5 ) === 0 &&
1892                                 preg_match( '!^//%5B([0-9A-Fa-f:.]+)%5D((:\d+)?)$!', $host, $matches )
1893                         ) {
1894                                 $host = '//[' . $matches[1] . ']' . $matches[2];
1895                         }
1896
1897                         // @todo FIXME: Validate hostnames here
1898
1899                         return $protocol . $host . $rest;
1900                 } else {
1901                         return $url;
1902                 }
1903         }
1904
1905         /**
1906          * @param array $matches
1907          * @return string
1908          */
1909         static function cleanUrlCallback( $matches ) {
1910                 return urlencode( $matches[0] );
1911         }
1912
1913         /**
1914          * Does a string look like an e-mail address?
1915          *
1916          * This validates an email address using an HTML5 specification found at:
1917          * http://www.whatwg.org/html/states-of-the-type-attribute.html#valid-e-mail-address
1918          * Which as of 2011-01-24 says:
1919          *
1920          *   A valid e-mail address is a string that matches the ABNF production
1921          *   1*( atext / "." ) "@" ldh-str *( "." ldh-str ) where atext is defined
1922          *   in RFC 5322 section 3.2.3, and ldh-str is defined in RFC 1034 section
1923          *   3.5.
1924          *
1925          * This function is an implementation of the specification as requested in
1926          * bug 22449.
1927          *
1928          * Client-side forms will use the same standard validation rules via JS or
1929          * HTML 5 validation; additional restrictions can be enforced server-side
1930          * by extensions via the 'isValidEmailAddr' hook.
1931          *
1932          * Note that this validation doesn't 100% match RFC 2822, but is believed
1933          * to be liberal enough for wide use. Some invalid addresses will still
1934          * pass validation here.
1935          *
1936          * @since 1.18
1937          *
1938          * @param string $addr E-mail address
1939          * @return bool
1940          */
1941         public static function validateEmail( $addr ) {
1942                 $result = null;
1943                 if ( !Hooks::run( 'isValidEmailAddr', [ $addr, &$result ] ) ) {
1944                         return $result;
1945                 }
1946
1947                 // Please note strings below are enclosed in brackets [], this make the
1948                 // hyphen "-" a range indicator. Hence it is double backslashed below.
1949                 // See bug 26948
1950                 $rfc5322_atext = "a-z0-9!#$%&'*+\\-\/=?^_`{|}~";
1951                 $rfc1034_ldh_str = "a-z0-9\\-";
1952
1953                 $html5_email_regexp = "/
1954                 ^                      # start of string
1955                 [$rfc5322_atext\\.]+    # user part which is liberal :p
1956                 @                      # 'apostrophe'
1957                 [$rfc1034_ldh_str]+       # First domain part
1958                 (\\.[$rfc1034_ldh_str]+)*  # Following part prefixed with a dot
1959                 $                      # End of string
1960                 /ix"; // case Insensitive, eXtended
1961
1962                 return (bool)preg_match( $html5_email_regexp, $addr );
1963         }
1964 }