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Differences Between: [Versions 310 and 403] [Versions 311 and 403] [Versions 39 and 403] [Versions 400 and 403]

   1  <?php
   2  
   3  /**
   4   * A UTF-8 specific character encoder that handles cleaning and transforming.
   5   * @note All functions in this class should be static.
   6   */
   7  class HTMLPurifier_Encoder
   8  {
   9  
  10      /**
  11       * Constructor throws fatal error if you attempt to instantiate class
  12       */
  13      private function __construct()
  14      {
  15          trigger_error('Cannot instantiate encoder, call methods statically', E_USER_ERROR);
  16      }
  17  
  18      /**
  19       * Error-handler that mutes errors, alternative to shut-up operator.
  20       */
  21      public static function muteErrorHandler()
  22      {
  23      }
  24  
  25      /**
  26       * iconv wrapper which mutes errors, but doesn't work around bugs.
  27       * @param string $in Input encoding
  28       * @param string $out Output encoding
  29       * @param string $text The text to convert
  30       * @return string
  31       */
  32      public static function unsafeIconv($in, $out, $text)
  33      {
  34          set_error_handler(array('HTMLPurifier_Encoder', 'muteErrorHandler'));
  35          $r = iconv($in, $out, $text);
  36          restore_error_handler();
  37          return $r;
  38      }
  39  
  40      /**
  41       * iconv wrapper which mutes errors and works around bugs.
  42       * @param string $in Input encoding
  43       * @param string $out Output encoding
  44       * @param string $text The text to convert
  45       * @param int $max_chunk_size
  46       * @return string
  47       */
  48      public static function iconv($in, $out, $text, $max_chunk_size = 8000)
  49      {
  50          $code = self::testIconvTruncateBug();
  51          if ($code == self::ICONV_OK) {
  52              return self::unsafeIconv($in, $out, $text);
  53          } elseif ($code == self::ICONV_TRUNCATES) {
  54              // we can only work around this if the input character set
  55              // is utf-8
  56              if ($in == 'utf-8') {
  57                  if ($max_chunk_size < 4) {
  58                      trigger_error('max_chunk_size is too small', E_USER_WARNING);
  59                      return false;
  60                  }
  61                  // split into 8000 byte chunks, but be careful to handle
  62                  // multibyte boundaries properly
  63                  if (($c = strlen($text)) <= $max_chunk_size) {
  64                      return self::unsafeIconv($in, $out, $text);
  65                  }
  66                  $r = '';
  67                  $i = 0;
  68                  while (true) {
  69                      if ($i + $max_chunk_size >= $c) {
  70                          $r .= self::unsafeIconv($in, $out, substr($text, $i));
  71                          break;
  72                      }
  73                      // wibble the boundary
  74                      if (0x80 != (0xC0 & ord($text[$i + $max_chunk_size]))) {
  75                          $chunk_size = $max_chunk_size;
  76                      } elseif (0x80 != (0xC0 & ord($text[$i + $max_chunk_size - 1]))) {
  77                          $chunk_size = $max_chunk_size - 1;
  78                      } elseif (0x80 != (0xC0 & ord($text[$i + $max_chunk_size - 2]))) {
  79                          $chunk_size = $max_chunk_size - 2;
  80                      } elseif (0x80 != (0xC0 & ord($text[$i + $max_chunk_size - 3]))) {
  81                          $chunk_size = $max_chunk_size - 3;
  82                      } else {
  83                          return false; // rather confusing UTF-8...
  84                      }
  85                      $chunk = substr($text, $i, $chunk_size); // substr doesn't mind overlong lengths
  86                      $r .= self::unsafeIconv($in, $out, $chunk);
  87                      $i += $chunk_size;
  88                  }
  89                  return $r;
  90              } else {
  91                  return false;
  92              }
  93          } else {
  94              return false;
  95          }
  96      }
  97  
  98      /**
  99       * Cleans a UTF-8 string for well-formedness and SGML validity
 100       *
 101       * It will parse according to UTF-8 and return a valid UTF8 string, with
 102       * non-SGML codepoints excluded.
 103       *
 104       * Specifically, it will permit:
 105       * \x{9}\x{A}\x{D}\x{20}-\x{7E}\x{A0}-\x{D7FF}\x{E000}-\x{FFFD}\x{10000}-\x{10FFFF}
 106       * Source: https://www.w3.org/TR/REC-xml/#NT-Char
 107       * Arguably this function should be modernized to the HTML5 set
 108       * of allowed characters:
 109       * https://www.w3.org/TR/html5/syntax.html#preprocessing-the-input-stream
 110       * which simultaneously expand and restrict the set of allowed characters.
 111       *
 112       * @param string $str The string to clean
 113       * @param bool $force_php
 114       * @return string
 115       *
 116       * @note Just for reference, the non-SGML code points are 0 to 31 and
 117       *       127 to 159, inclusive.  However, we allow code points 9, 10
 118       *       and 13, which are the tab, line feed and carriage return
 119       *       respectively. 128 and above the code points map to multibyte
 120       *       UTF-8 representations.
 121       *
 122       * @note Fallback code adapted from utf8ToUnicode by Henri Sivonen and
 123       *       hsivonen@iki.fi at <http://iki.fi/hsivonen/php-utf8/> under the
 124       *       LGPL license.  Notes on what changed are inside, but in general,
 125       *       the original code transformed UTF-8 text into an array of integer
 126       *       Unicode codepoints. Understandably, transforming that back to
 127       *       a string would be somewhat expensive, so the function was modded to
 128       *       directly operate on the string.  However, this discourages code
 129       *       reuse, and the logic enumerated here would be useful for any
 130       *       function that needs to be able to understand UTF-8 characters.
 131       *       As of right now, only smart lossless character encoding converters
 132       *       would need that, and I'm probably not going to implement them.
 133       */
 134      public static function cleanUTF8($str, $force_php = false)
 135      {
 136          // UTF-8 validity is checked since PHP 4.3.5
 137          // This is an optimization: if the string is already valid UTF-8, no
 138          // need to do PHP stuff. 99% of the time, this will be the case.
 139          if (preg_match(
 140              '/^[\x{9}\x{A}\x{D}\x{20}-\x{7E}\x{A0}-\x{D7FF}\x{E000}-\x{FFFD}\x{10000}-\x{10FFFF}]*$/Du',
 141              $str
 142          )) {
 143              return $str;
 144          }
 145  
 146          $mState = 0; // cached expected number of octets after the current octet
 147                       // until the beginning of the next UTF8 character sequence
 148          $mUcs4  = 0; // cached Unicode character
 149          $mBytes = 1; // cached expected number of octets in the current sequence
 150  
 151          // original code involved an $out that was an array of Unicode
 152          // codepoints.  Instead of having to convert back into UTF-8, we've
 153          // decided to directly append valid UTF-8 characters onto a string
 154          // $out once they're done.  $char accumulates raw bytes, while $mUcs4
 155          // turns into the Unicode code point, so there's some redundancy.
 156  
 157          $out = '';
 158          $char = '';
 159  
 160          $len = strlen($str);
 161          for ($i = 0; $i < $len; $i++) {
 162              $in = ord($str[$i]);
 163              $char .= $str[$i]; // append byte to char
 164              if (0 == $mState) {
 165                  // When mState is zero we expect either a US-ASCII character
 166                  // or a multi-octet sequence.
 167                  if (0 == (0x80 & ($in))) {
 168                      // US-ASCII, pass straight through.
 169                      if (($in <= 31 || $in == 127) &&
 170                          !($in == 9 || $in == 13 || $in == 10) // save \r\t\n
 171                      ) {
 172                          // control characters, remove
 173                      } else {
 174                          $out .= $char;
 175                      }
 176                      // reset
 177                      $char = '';
 178                      $mBytes = 1;
 179                  } elseif (0xC0 == (0xE0 & ($in))) {
 180                      // First octet of 2 octet sequence
 181                      $mUcs4 = ($in);
 182                      $mUcs4 = ($mUcs4 & 0x1F) << 6;
 183                      $mState = 1;
 184                      $mBytes = 2;
 185                  } elseif (0xE0 == (0xF0 & ($in))) {
 186                      // First octet of 3 octet sequence
 187                      $mUcs4 = ($in);
 188                      $mUcs4 = ($mUcs4 & 0x0F) << 12;
 189                      $mState = 2;
 190                      $mBytes = 3;
 191                  } elseif (0xF0 == (0xF8 & ($in))) {
 192                      // First octet of 4 octet sequence
 193                      $mUcs4 = ($in);
 194                      $mUcs4 = ($mUcs4 & 0x07) << 18;
 195                      $mState = 3;
 196                      $mBytes = 4;
 197                  } elseif (0xF8 == (0xFC & ($in))) {
 198                      // First octet of 5 octet sequence.
 199                      //
 200                      // This is illegal because the encoded codepoint must be
 201                      // either:
 202                      // (a) not the shortest form or
 203                      // (b) outside the Unicode range of 0-0x10FFFF.
 204                      // Rather than trying to resynchronize, we will carry on
 205                      // until the end of the sequence and let the later error
 206                      // handling code catch it.
 207                      $mUcs4 = ($in);
 208                      $mUcs4 = ($mUcs4 & 0x03) << 24;
 209                      $mState = 4;
 210                      $mBytes = 5;
 211                  } elseif (0xFC == (0xFE & ($in))) {
 212                      // First octet of 6 octet sequence, see comments for 5
 213                      // octet sequence.
 214                      $mUcs4 = ($in);
 215                      $mUcs4 = ($mUcs4 & 1) << 30;
 216                      $mState = 5;
 217                      $mBytes = 6;
 218                  } else {
 219                      // Current octet is neither in the US-ASCII range nor a
 220                      // legal first octet of a multi-octet sequence.
 221                      $mState = 0;
 222                      $mUcs4  = 0;
 223                      $mBytes = 1;
 224                      $char = '';
 225                  }
 226              } else {
 227                  // When mState is non-zero, we expect a continuation of the
 228                  // multi-octet sequence
 229                  if (0x80 == (0xC0 & ($in))) {
 230                      // Legal continuation.
 231                      $shift = ($mState - 1) * 6;
 232                      $tmp = $in;
 233                      $tmp = ($tmp & 0x0000003F) << $shift;
 234                      $mUcs4 |= $tmp;
 235  
 236                      if (0 == --$mState) {
 237                          // End of the multi-octet sequence. mUcs4 now contains
 238                          // the final Unicode codepoint to be output
 239  
 240                          // Check for illegal sequences and codepoints.
 241  
 242                          // From Unicode 3.1, non-shortest form is illegal
 243                          if (((2 == $mBytes) && ($mUcs4 < 0x0080)) ||
 244                              ((3 == $mBytes) && ($mUcs4 < 0x0800)) ||
 245                              ((4 == $mBytes) && ($mUcs4 < 0x10000)) ||
 246                              (4 < $mBytes) ||
 247                              // From Unicode 3.2, surrogate characters = illegal
 248                              (($mUcs4 & 0xFFFFF800) == 0xD800) ||
 249                              // Codepoints outside the Unicode range are illegal
 250                              ($mUcs4 > 0x10FFFF)
 251                          ) {
 252  
 253                          } elseif (0xFEFF != $mUcs4 && // omit BOM
 254                              // check for valid Char unicode codepoints
 255                              (
 256                                  0x9 == $mUcs4 ||
 257                                  0xA == $mUcs4 ||
 258                                  0xD == $mUcs4 ||
 259                                  (0x20 <= $mUcs4 && 0x7E >= $mUcs4) ||
 260                                  // 7F-9F is not strictly prohibited by XML,
 261                                  // but it is non-SGML, and thus we don't allow it
 262                                  (0xA0 <= $mUcs4 && 0xD7FF >= $mUcs4) ||
 263                                  (0xE000 <= $mUcs4 && 0xFFFD >= $mUcs4) ||
 264                                  (0x10000 <= $mUcs4 && 0x10FFFF >= $mUcs4)
 265                              )
 266                          ) {
 267                              $out .= $char;
 268                          }
 269                          // initialize UTF8 cache (reset)
 270                          $mState = 0;
 271                          $mUcs4  = 0;
 272                          $mBytes = 1;
 273                          $char = '';
 274                      }
 275                  } else {
 276                      // ((0xC0 & (*in) != 0x80) && (mState != 0))
 277                      // Incomplete multi-octet sequence.
 278                      // used to result in complete fail, but we'll reset
 279                      $mState = 0;
 280                      $mUcs4  = 0;
 281                      $mBytes = 1;
 282                      $char ='';
 283                  }
 284              }
 285          }
 286          return $out;
 287      }
 288  
 289      /**
 290       * Translates a Unicode codepoint into its corresponding UTF-8 character.
 291       * @note Based on Feyd's function at
 292       *       <http://forums.devnetwork.net/viewtopic.php?p=191404#191404>,
 293       *       which is in public domain.
 294       * @note While we're going to do code point parsing anyway, a good
 295       *       optimization would be to refuse to translate code points that
 296       *       are non-SGML characters.  However, this could lead to duplication.
 297       * @note This is very similar to the unichr function in
 298       *       maintenance/generate-entity-file.php (although this is superior,
 299       *       due to its sanity checks).
 300       */
 301  
 302      // +----------+----------+----------+----------+
 303      // | 33222222 | 22221111 | 111111   |          |
 304      // | 10987654 | 32109876 | 54321098 | 76543210 | bit
 305      // +----------+----------+----------+----------+
 306      // |          |          |          | 0xxxxxxx | 1 byte 0x00000000..0x0000007F
 307      // |          |          | 110yyyyy | 10xxxxxx | 2 byte 0x00000080..0x000007FF
 308      // |          | 1110zzzz | 10yyyyyy | 10xxxxxx | 3 byte 0x00000800..0x0000FFFF
 309      // | 11110www | 10wwzzzz | 10yyyyyy | 10xxxxxx | 4 byte 0x00010000..0x0010FFFF
 310      // +----------+----------+----------+----------+
 311      // | 00000000 | 00011111 | 11111111 | 11111111 | Theoretical upper limit of legal scalars: 2097151 (0x001FFFFF)
 312      // | 00000000 | 00010000 | 11111111 | 11111111 | Defined upper limit of legal scalar codes
 313      // +----------+----------+----------+----------+
 314  
 315      public static function unichr($code)
 316      {
 317          if ($code > 1114111 or $code < 0 or
 318            ($code >= 55296 and $code <= 57343) ) {
 319              // bits are set outside the "valid" range as defined
 320              // by UNICODE 4.1.0
 321              return '';
 322          }
 323  
 324          $x = $y = $z = $w = 0;
 325          if ($code < 128) {
 326              // regular ASCII character
 327              $x = $code;
 328          } else {
 329              // set up bits for UTF-8
 330              $x = ($code & 63) | 128;
 331              if ($code < 2048) {
 332                  $y = (($code & 2047) >> 6) | 192;
 333              } else {
 334                  $y = (($code & 4032) >> 6) | 128;
 335                  if ($code < 65536) {
 336                      $z = (($code >> 12) & 15) | 224;
 337                  } else {
 338                      $z = (($code >> 12) & 63) | 128;
 339                      $w = (($code >> 18) & 7)  | 240;
 340                  }
 341              }
 342          }
 343          // set up the actual character
 344          $ret = '';
 345          if ($w) {
 346              $ret .= chr($w);
 347          }
 348          if ($z) {
 349              $ret .= chr($z);
 350          }
 351          if ($y) {
 352              $ret .= chr($y);
 353          }
 354          $ret .= chr($x);
 355  
 356          return $ret;
 357      }
 358  
 359      /**
 360       * @return bool
 361       */
 362      public static function iconvAvailable()
 363      {
 364          static $iconv = null;
 365          if ($iconv === null) {
 366              $iconv = function_exists('iconv') && self::testIconvTruncateBug() != self::ICONV_UNUSABLE;
 367          }
 368          return $iconv;
 369      }
 370  
 371      /**
 372       * Convert a string to UTF-8 based on configuration.
 373       * @param string $str The string to convert
 374       * @param HTMLPurifier_Config $config
 375       * @param HTMLPurifier_Context $context
 376       * @return string
 377       */
 378      public static function convertToUTF8($str, $config, $context)
 379      {
 380          $encoding = $config->get('Core.Encoding');
 381          if ($encoding === 'utf-8') {
 382              return $str;
 383          }
 384          static $iconv = null;
 385          if ($iconv === null) {
 386              $iconv = self::iconvAvailable();
 387          }
 388          if ($iconv && !$config->get('Test.ForceNoIconv')) {
 389              // unaffected by bugs, since UTF-8 support all characters
 390              $str = self::unsafeIconv($encoding, 'utf-8//IGNORE', $str);
 391              if ($str === false) {
 392                  // $encoding is not a valid encoding
 393                  trigger_error('Invalid encoding ' . $encoding, E_USER_ERROR);
 394                  return '';
 395              }
 396              // If the string is bjorked by Shift_JIS or a similar encoding
 397              // that doesn't support all of ASCII, convert the naughty
 398              // characters to their true byte-wise ASCII/UTF-8 equivalents.
 399              $str = strtr($str, self::testEncodingSupportsASCII($encoding));
 400              return $str;
 401          } elseif ($encoding === 'iso-8859-1' && function_exists('mb_convert_encoding')) {
 402              $str = mb_convert_encoding($str, 'UTF-8', 'ISO-8859-1');
 403              return $str;
 404          }
 405          $bug = HTMLPurifier_Encoder::testIconvTruncateBug();
 406          if ($bug == self::ICONV_OK) {
 407              trigger_error('Encoding not supported, please install iconv', E_USER_ERROR);
 408          } else {
 409              trigger_error(
 410                  'You have a buggy version of iconv, see https://bugs.php.net/bug.php?id=48147 ' .
 411                  'and http://sourceware.org/bugzilla/show_bug.cgi?id=13541',
 412                  E_USER_ERROR
 413              );
 414          }
 415      }
 416  
 417      /**
 418       * Converts a string from UTF-8 based on configuration.
 419       * @param string $str The string to convert
 420       * @param HTMLPurifier_Config $config
 421       * @param HTMLPurifier_Context $context
 422       * @return string
 423       * @note Currently, this is a lossy conversion, with unexpressable
 424       *       characters being omitted.
 425       */
 426      public static function convertFromUTF8($str, $config, $context)
 427      {
 428          $encoding = $config->get('Core.Encoding');
 429          if ($escape = $config->get('Core.EscapeNonASCIICharacters')) {
 430              $str = self::convertToASCIIDumbLossless($str);
 431          }
 432          if ($encoding === 'utf-8') {
 433              return $str;
 434          }
 435          static $iconv = null;
 436          if ($iconv === null) {
 437              $iconv = self::iconvAvailable();
 438          }
 439          if ($iconv && !$config->get('Test.ForceNoIconv')) {
 440              // Undo our previous fix in convertToUTF8, otherwise iconv will barf
 441              $ascii_fix = self::testEncodingSupportsASCII($encoding);
 442              if (!$escape && !empty($ascii_fix)) {
 443                  $clear_fix = array();
 444                  foreach ($ascii_fix as $utf8 => $native) {
 445                      $clear_fix[$utf8] = '';
 446                  }
 447                  $str = strtr($str, $clear_fix);
 448              }
 449              $str = strtr($str, array_flip($ascii_fix));
 450              // Normal stuff
 451              $str = self::iconv('utf-8', $encoding . '//IGNORE', $str);
 452              return $str;
 453          } elseif ($encoding === 'iso-8859-1' && function_exists('mb_convert_encoding')) {
 454              $str = mb_convert_encoding($str, 'ISO-8859-1', 'UTF-8');
 455              return $str;
 456          }
 457          trigger_error('Encoding not supported', E_USER_ERROR);
 458          // You might be tempted to assume that the ASCII representation
 459          // might be OK, however, this is *not* universally true over all
 460          // encodings.  So we take the conservative route here, rather
 461          // than forcibly turn on %Core.EscapeNonASCIICharacters
 462      }
 463  
 464      /**
 465       * Lossless (character-wise) conversion of HTML to ASCII
 466       * @param string $str UTF-8 string to be converted to ASCII
 467       * @return string ASCII encoded string with non-ASCII character entity-ized
 468       * @warning Adapted from MediaWiki, claiming fair use: this is a common
 469       *       algorithm. If you disagree with this license fudgery,
 470       *       implement it yourself.
 471       * @note Uses decimal numeric entities since they are best supported.
 472       * @note This is a DUMB function: it has no concept of keeping
 473       *       character entities that the projected character encoding
 474       *       can allow. We could possibly implement a smart version
 475       *       but that would require it to also know which Unicode
 476       *       codepoints the charset supported (not an easy task).
 477       * @note Sort of with cleanUTF8() but it assumes that $str is
 478       *       well-formed UTF-8
 479       */
 480      public static function convertToASCIIDumbLossless($str)
 481      {
 482          $bytesleft = 0;
 483          $result = '';
 484          $working = 0;
 485          $len = strlen($str);
 486          for ($i = 0; $i < $len; $i++) {
 487              $bytevalue = ord($str[$i]);
 488              if ($bytevalue <= 0x7F) { //0xxx xxxx
 489                  $result .= chr($bytevalue);
 490                  $bytesleft = 0;
 491              } elseif ($bytevalue <= 0xBF) { //10xx xxxx
 492                  $working = $working << 6;
 493                  $working += ($bytevalue & 0x3F);
 494                  $bytesleft--;
 495                  if ($bytesleft <= 0) {
 496                      $result .= "&#" . $working . ";";
 497                  }
 498              } elseif ($bytevalue <= 0xDF) { //110x xxxx
 499                  $working = $bytevalue & 0x1F;
 500                  $bytesleft = 1;
 501              } elseif ($bytevalue <= 0xEF) { //1110 xxxx
 502                  $working = $bytevalue & 0x0F;
 503                  $bytesleft = 2;
 504              } else { //1111 0xxx
 505                  $working = $bytevalue & 0x07;
 506                  $bytesleft = 3;
 507              }
 508          }
 509          return $result;
 510      }
 511  
 512      /** No bugs detected in iconv. */
 513      const ICONV_OK = 0;
 514  
 515      /** Iconv truncates output if converting from UTF-8 to another
 516       *  character set with //IGNORE, and a non-encodable character is found */
 517      const ICONV_TRUNCATES = 1;
 518  
 519      /** Iconv does not support //IGNORE, making it unusable for
 520       *  transcoding purposes */
 521      const ICONV_UNUSABLE = 2;
 522  
 523      /**
 524       * glibc iconv has a known bug where it doesn't handle the magic
 525       * //IGNORE stanza correctly.  In particular, rather than ignore
 526       * characters, it will return an EILSEQ after consuming some number
 527       * of characters, and expect you to restart iconv as if it were
 528       * an E2BIG.  Old versions of PHP did not respect the errno, and
 529       * returned the fragment, so as a result you would see iconv
 530       * mysteriously truncating output. We can work around this by
 531       * manually chopping our input into segments of about 8000
 532       * characters, as long as PHP ignores the error code.  If PHP starts
 533       * paying attention to the error code, iconv becomes unusable.
 534       *
 535       * @return int Error code indicating severity of bug.
 536       */
 537      public static function testIconvTruncateBug()
 538      {
 539          static $code = null;
 540          if ($code === null) {
 541              // better not use iconv, otherwise infinite loop!
 542              $r = self::unsafeIconv('utf-8', 'ascii//IGNORE', "\xCE\xB1" . str_repeat('a', 9000));
 543              if ($r === false) {
 544                  $code = self::ICONV_UNUSABLE;
 545              } elseif (($c = strlen($r)) < 9000) {
 546                  $code = self::ICONV_TRUNCATES;
 547              } elseif ($c > 9000) {
 548                  trigger_error(
 549                      'Your copy of iconv is extremely buggy. Please notify HTML Purifier maintainers: ' .
 550                      'include your iconv version as per phpversion()',
 551                      E_USER_ERROR
 552                  );
 553              } else {
 554                  $code = self::ICONV_OK;
 555              }
 556          }
 557          return $code;
 558      }
 559  
 560      /**
 561       * This expensive function tests whether or not a given character
 562       * encoding supports ASCII. 7/8-bit encodings like Shift_JIS will
 563       * fail this test, and require special processing. Variable width
 564       * encodings shouldn't ever fail.
 565       *
 566       * @param string $encoding Encoding name to test, as per iconv format
 567       * @param bool $bypass Whether or not to bypass the precompiled arrays.
 568       * @return Array of UTF-8 characters to their corresponding ASCII,
 569       *      which can be used to "undo" any overzealous iconv action.
 570       */
 571      public static function testEncodingSupportsASCII($encoding, $bypass = false)
 572      {
 573          // All calls to iconv here are unsafe, proof by case analysis:
 574          // If ICONV_OK, no difference.
 575          // If ICONV_TRUNCATE, all calls involve one character inputs,
 576          // so bug is not triggered.
 577          // If ICONV_UNUSABLE, this call is irrelevant
 578          static $encodings = array();
 579          if (!$bypass) {
 580              if (isset($encodings[$encoding])) {
 581                  return $encodings[$encoding];
 582              }
 583              $lenc = strtolower($encoding);
 584              switch ($lenc) {
 585                  case 'shift_jis':
 586                      return array("\xC2\xA5" => '\\', "\xE2\x80\xBE" => '~');
 587                  case 'johab':
 588                      return array("\xE2\x82\xA9" => '\\');
 589              }
 590              if (strpos($lenc, 'iso-8859-') === 0) {
 591                  return array();
 592              }
 593          }
 594          $ret = array();
 595          if (self::unsafeIconv('UTF-8', $encoding, 'a') === false) {
 596              return false;
 597          }
 598          for ($i = 0x20; $i <= 0x7E; $i++) { // all printable ASCII chars
 599              $c = chr($i); // UTF-8 char
 600              $r = self::unsafeIconv('UTF-8', "$encoding//IGNORE", $c); // initial conversion
 601              if ($r === '' ||
 602                  // This line is needed for iconv implementations that do not
 603                  // omit characters that do not exist in the target character set
 604                  ($r === $c && self::unsafeIconv($encoding, 'UTF-8//IGNORE', $r) !== $c)
 605              ) {
 606                  // Reverse engineer: what's the UTF-8 equiv of this byte
 607                  // sequence? This assumes that there's no variable width
 608                  // encoding that doesn't support ASCII.
 609                  $ret[self::unsafeIconv($encoding, 'UTF-8//IGNORE', $c)] = $c;
 610              }
 611          }
 612          $encodings[$encoding] = $ret;
 613          return $ret;
 614      }
 615  }
 616  
 617  // vim: et sw=4 sts=4