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   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          trigger_error('Cannot instantiate encoder, call methods statically', E_USER_ERROR);
  15      }
  16  
  17      /**
  18       * Error-handler that mutes errors, alternative to shut-up operator.
  19       */
  20      private static function muteErrorHandler() {}
  21  
  22      /**
  23       * Cleans a UTF-8 string for well-formedness and SGML validity
  24       *
  25       * It will parse according to UTF-8 and return a valid UTF8 string, with
  26       * non-SGML codepoints excluded.
  27       *
  28       * @note Just for reference, the non-SGML code points are 0 to 31 and
  29       *       127 to 159, inclusive.  However, we allow code points 9, 10
  30       *       and 13, which are the tab, line feed and carriage return
  31       *       respectively. 128 and above the code points map to multibyte
  32       *       UTF-8 representations.
  33       *
  34       * @note Fallback code adapted from utf8ToUnicode by Henri Sivonen and
  35       *       [email protected] at <http://iki.fi/hsivonen/php-utf8/> under the
  36       *       LGPL license.  Notes on what changed are inside, but in general,
  37       *       the original code transformed UTF-8 text into an array of integer
  38       *       Unicode codepoints. Understandably, transforming that back to
  39       *       a string would be somewhat expensive, so the function was modded to
  40       *       directly operate on the string.  However, this discourages code
  41       *       reuse, and the logic enumerated here would be useful for any
  42       *       function that needs to be able to understand UTF-8 characters.
  43       *       As of right now, only smart lossless character encoding converters
  44       *       would need that, and I'm probably not going to implement them.
  45       *       Once again, PHP 6 should solve all our problems.
  46       */
  47      public static function cleanUTF8($str, $force_php = false) {
  48  
  49          // UTF-8 validity is checked since PHP 4.3.5
  50          // This is an optimization: if the string is already valid UTF-8, no
  51          // need to do PHP stuff. 99% of the time, this will be the case.
  52          // The regexp matches the XML char production, as well as well as excluding
  53          // non-SGML codepoints U+007F to U+009F
  54          if (preg_match('/^[\x{9}\x{A}\x{D}\x{20}-\x{7E}\x{A0}-\x{D7FF}\x{E000}-\x{FFFD}\x{10000}-\x{10FFFF}]*$/Du', $str)) {
  55              return $str;
  56          }
  57  
  58          $mState = 0; // cached expected number of octets after the current octet
  59                       // until the beginning of the next UTF8 character sequence
  60          $mUcs4  = 0; // cached Unicode character
  61          $mBytes = 1; // cached expected number of octets in the current sequence
  62  
  63          // original code involved an $out that was an array of Unicode
  64          // codepoints.  Instead of having to convert back into UTF-8, we've
  65          // decided to directly append valid UTF-8 characters onto a string
  66          // $out once they're done.  $char accumulates raw bytes, while $mUcs4
  67          // turns into the Unicode code point, so there's some redundancy.
  68  
  69          $out = '';
  70          $char = '';
  71  
  72          $len = strlen($str);
  73          for($i = 0; $i < $len; $i++) {
  74              $in = ord($str{$i});
  75              $char .= $str[$i]; // append byte to char
  76              if (0 == $mState) {
  77                  // When mState is zero we expect either a US-ASCII character
  78                  // or a multi-octet sequence.
  79                  if (0 == (0x80 & ($in))) {
  80                      // US-ASCII, pass straight through.
  81                      if (($in <= 31 || $in == 127) &&
  82                          !($in == 9 || $in == 13 || $in == 10) // save \r\t\n
  83                      ) {
  84                          // control characters, remove
  85                      } else {
  86                          $out .= $char;
  87                      }
  88                      // reset
  89                      $char = '';
  90                      $mBytes = 1;
  91                  } elseif (0xC0 == (0xE0 & ($in))) {
  92                      // First octet of 2 octet sequence
  93                      $mUcs4 = ($in);
  94                      $mUcs4 = ($mUcs4 & 0x1F) << 6;
  95                      $mState = 1;
  96                      $mBytes = 2;
  97                  } elseif (0xE0 == (0xF0 & ($in))) {
  98                      // First octet of 3 octet sequence
  99                      $mUcs4 = ($in);
 100                      $mUcs4 = ($mUcs4 & 0x0F) << 12;
 101                      $mState = 2;
 102                      $mBytes = 3;
 103                  } elseif (0xF0 == (0xF8 & ($in))) {
 104                      // First octet of 4 octet sequence
 105                      $mUcs4 = ($in);
 106                      $mUcs4 = ($mUcs4 & 0x07) << 18;
 107                      $mState = 3;
 108                      $mBytes = 4;
 109                  } elseif (0xF8 == (0xFC & ($in))) {
 110                      // First octet of 5 octet sequence.
 111                      //
 112                      // This is illegal because the encoded codepoint must be
 113                      // either:
 114                      // (a) not the shortest form or
 115                      // (b) outside the Unicode range of 0-0x10FFFF.
 116                      // Rather than trying to resynchronize, we will carry on
 117                      // until the end of the sequence and let the later error
 118                      // handling code catch it.
 119                      $mUcs4 = ($in);
 120                      $mUcs4 = ($mUcs4 & 0x03) << 24;
 121                      $mState = 4;
 122                      $mBytes = 5;
 123                  } elseif (0xFC == (0xFE & ($in))) {
 124                      // First octet of 6 octet sequence, see comments for 5
 125                      // octet sequence.
 126                      $mUcs4 = ($in);
 127                      $mUcs4 = ($mUcs4 & 1) << 30;
 128                      $mState = 5;
 129                      $mBytes = 6;
 130                  } else {
 131                      // Current octet is neither in the US-ASCII range nor a
 132                      // legal first octet of a multi-octet sequence.
 133                      $mState = 0;
 134                      $mUcs4  = 0;
 135                      $mBytes = 1;
 136                      $char = '';
 137                  }
 138              } else {
 139                  // When mState is non-zero, we expect a continuation of the
 140                  // multi-octet sequence
 141                  if (0x80 == (0xC0 & ($in))) {
 142                      // Legal continuation.
 143                      $shift = ($mState - 1) * 6;
 144                      $tmp = $in;
 145                      $tmp = ($tmp & 0x0000003F) << $shift;
 146                      $mUcs4 |= $tmp;
 147  
 148                      if (0 == --$mState) {
 149                          // End of the multi-octet sequence. mUcs4 now contains
 150                          // the final Unicode codepoint to be output
 151  
 152                          // Check for illegal sequences and codepoints.
 153  
 154                          // From Unicode 3.1, non-shortest form is illegal
 155                          if (((2 == $mBytes) && ($mUcs4 < 0x0080)) ||
 156                              ((3 == $mBytes) && ($mUcs4 < 0x0800)) ||
 157                              ((4 == $mBytes) && ($mUcs4 < 0x10000)) ||
 158                              (4 < $mBytes) ||
 159                              // From Unicode 3.2, surrogate characters = illegal
 160                              (($mUcs4 & 0xFFFFF800) == 0xD800) ||
 161                              // Codepoints outside the Unicode range are illegal
 162                              ($mUcs4 > 0x10FFFF)
 163                          ) {
 164  
 165                          } elseif (0xFEFF != $mUcs4 && // omit BOM
 166                              // check for valid Char unicode codepoints
 167                              (
 168                                  0x9 == $mUcs4 ||
 169                                  0xA == $mUcs4 ||
 170                                  0xD == $mUcs4 ||
 171                                  (0x20 <= $mUcs4 && 0x7E >= $mUcs4) ||
 172                                  // 7F-9F is not strictly prohibited by XML,
 173                                  // but it is non-SGML, and thus we don't allow it
 174                                  (0xA0 <= $mUcs4 && 0xD7FF >= $mUcs4) ||
 175                                  (0x10000 <= $mUcs4 && 0x10FFFF >= $mUcs4)
 176                              )
 177                          ) {
 178                              $out .= $char;
 179                          }
 180                          // initialize UTF8 cache (reset)
 181                          $mState = 0;
 182                          $mUcs4  = 0;
 183                          $mBytes = 1;
 184                          $char = '';
 185                      }
 186                  } else {
 187                      // ((0xC0 & (*in) != 0x80) && (mState != 0))
 188                      // Incomplete multi-octet sequence.
 189                      // used to result in complete fail, but we'll reset
 190                      $mState = 0;
 191                      $mUcs4  = 0;
 192                      $mBytes = 1;
 193                      $char ='';
 194                  }
 195              }
 196          }
 197          return $out;
 198      }
 199  
 200      /**
 201       * Translates a Unicode codepoint into its corresponding UTF-8 character.
 202       * @note Based on Feyd's function at
 203       *       <http://forums.devnetwork.net/viewtopic.php?p=191404#191404>,
 204       *       which is in public domain.
 205       * @note While we're going to do code point parsing anyway, a good
 206       *       optimization would be to refuse to translate code points that
 207       *       are non-SGML characters.  However, this could lead to duplication.
 208       * @note This is very similar to the unichr function in
 209       *       maintenance/generate-entity-file.php (although this is superior,
 210       *       due to its sanity checks).
 211       */
 212  
 213      // +----------+----------+----------+----------+
 214      // | 33222222 | 22221111 | 111111   |          |
 215      // | 10987654 | 32109876 | 54321098 | 76543210 | bit
 216      // +----------+----------+----------+----------+
 217      // |          |          |          | 0xxxxxxx | 1 byte 0x00000000..0x0000007F
 218      // |          |          | 110yyyyy | 10xxxxxx | 2 byte 0x00000080..0x000007FF
 219      // |          | 1110zzzz | 10yyyyyy | 10xxxxxx | 3 byte 0x00000800..0x0000FFFF
 220      // | 11110www | 10wwzzzz | 10yyyyyy | 10xxxxxx | 4 byte 0x00010000..0x0010FFFF
 221      // +----------+----------+----------+----------+
 222      // | 00000000 | 00011111 | 11111111 | 11111111 | Theoretical upper limit of legal scalars: 2097151 (0x001FFFFF)
 223      // | 00000000 | 00010000 | 11111111 | 11111111 | Defined upper limit of legal scalar codes
 224      // +----------+----------+----------+----------+
 225  
 226      public static function unichr($code) {
 227          if($code > 1114111 or $code < 0 or
 228            ($code >= 55296 and $code <= 57343) ) {
 229              // bits are set outside the "valid" range as defined
 230              // by UNICODE 4.1.0
 231              return '';
 232          }
 233  
 234          $x = $y = $z = $w = 0;
 235          if ($code < 128) {
 236              // regular ASCII character
 237              $x = $code;
 238          } else {
 239              // set up bits for UTF-8
 240              $x = ($code & 63) | 128;
 241              if ($code < 2048) {
 242                  $y = (($code & 2047) >> 6) | 192;
 243              } else {
 244                  $y = (($code & 4032) >> 6) | 128;
 245                  if($code < 65536) {
 246                      $z = (($code >> 12) & 15) | 224;
 247                  } else {
 248                      $z = (($code >> 12) & 63) | 128;
 249                      $w = (($code >> 18) & 7)  | 240;
 250                  }
 251              }
 252          }
 253          // set up the actual character
 254          $ret = '';
 255          if($w) $ret .= chr($w);
 256          if($z) $ret .= chr($z);
 257          if($y) $ret .= chr($y);
 258          $ret .= chr($x);
 259  
 260          return $ret;
 261      }
 262  
 263      /**
 264       * Converts a string to UTF-8 based on configuration.
 265       */
 266      public static function convertToUTF8($str, $config, $context) {
 267          $encoding = $config->get('Core', 'Encoding');
 268          if ($encoding === 'utf-8') return $str;
 269          static $iconv = null;
 270          if ($iconv === null) $iconv = function_exists('iconv');
 271          set_error_handler(array('HTMLPurifier_Encoder', 'muteErrorHandler'));
 272          if ($iconv && !$config->get('Test', 'ForceNoIconv')) {
 273              $str = iconv($encoding, 'utf-8//IGNORE', $str);
 274              if ($str === false) {
 275                  // $encoding is not a valid encoding
 276                  restore_error_handler();
 277                  trigger_error('Invalid encoding ' . $encoding, E_USER_ERROR);
 278                  return '';
 279              }
 280              // If the string is bjorked by Shift_JIS or a similar encoding
 281              // that doesn't support all of ASCII, convert the naughty
 282              // characters to their true byte-wise ASCII/UTF-8 equivalents.
 283              $str = strtr($str, HTMLPurifier_Encoder::testEncodingSupportsASCII($encoding));
 284              restore_error_handler();
 285              return $str;
 286          } elseif ($encoding === 'iso-8859-1') {
 287              $str = utf8_encode($str);
 288              restore_error_handler();
 289              return $str;
 290          }
 291          trigger_error('Encoding not supported, please install iconv', E_USER_ERROR);
 292      }
 293  
 294      /**
 295       * Converts a string from UTF-8 based on configuration.
 296       * @note Currently, this is a lossy conversion, with unexpressable
 297       *       characters being omitted.
 298       */
 299      public static function convertFromUTF8($str, $config, $context) {
 300          $encoding = $config->get('Core', 'Encoding');
 301          if ($encoding === 'utf-8') return $str;
 302          static $iconv = null;
 303          if ($iconv === null) $iconv = function_exists('iconv');
 304          if ($escape = $config->get('Core', 'EscapeNonASCIICharacters')) {
 305              $str = HTMLPurifier_Encoder::convertToASCIIDumbLossless($str);
 306          }
 307          set_error_handler(array('HTMLPurifier_Encoder', 'muteErrorHandler'));
 308          if ($iconv && !$config->get('Test', 'ForceNoIconv')) {
 309              // Undo our previous fix in convertToUTF8, otherwise iconv will barf
 310              $ascii_fix = HTMLPurifier_Encoder::testEncodingSupportsASCII($encoding);
 311              if (!$escape && !empty($ascii_fix)) {
 312                  $clear_fix = array();
 313                  foreach ($ascii_fix as $utf8 => $native) $clear_fix[$utf8] = '';
 314                  $str = strtr($str, $clear_fix);
 315              }
 316              $str = strtr($str, array_flip($ascii_fix));
 317              // Normal stuff
 318              $str = iconv('utf-8', $encoding . '//IGNORE', $str);
 319              restore_error_handler();
 320              return $str;
 321          } elseif ($encoding === 'iso-8859-1') {
 322              $str = utf8_decode($str);
 323              restore_error_handler();
 324              return $str;
 325          }
 326          trigger_error('Encoding not supported', E_USER_ERROR);
 327      }
 328  
 329      /**
 330       * Lossless (character-wise) conversion of HTML to ASCII
 331       * @param $str UTF-8 string to be converted to ASCII
 332       * @returns ASCII encoded string with non-ASCII character entity-ized
 333       * @warning Adapted from MediaWiki, claiming fair use: this is a common
 334       *       algorithm. If you disagree with this license fudgery,
 335       *       implement it yourself.
 336       * @note Uses decimal numeric entities since they are best supported.
 337       * @note This is a DUMB function: it has no concept of keeping
 338       *       character entities that the projected character encoding
 339       *       can allow. We could possibly implement a smart version
 340       *       but that would require it to also know which Unicode
 341       *       codepoints the charset supported (not an easy task).
 342       * @note Sort of with cleanUTF8() but it assumes that $str is
 343       *       well-formed UTF-8
 344       */
 345      public static function convertToASCIIDumbLossless($str) {
 346          $bytesleft = 0;
 347          $result = '';
 348          $working = 0;
 349          $len = strlen($str);
 350          for( $i = 0; $i < $len; $i++ ) {
 351              $bytevalue = ord( $str[$i] );
 352              if( $bytevalue <= 0x7F ) { //0xxx xxxx
 353                  $result .= chr( $bytevalue );
 354                  $bytesleft = 0;
 355              } elseif( $bytevalue <= 0xBF ) { //10xx xxxx
 356                  $working = $working << 6;
 357                  $working += ($bytevalue & 0x3F);
 358                  $bytesleft--;
 359                  if( $bytesleft <= 0 ) {
 360                      $result .= "&#" . $working . ";";
 361                  }
 362              } elseif( $bytevalue <= 0xDF ) { //110x xxxx
 363                  $working = $bytevalue & 0x1F;
 364                  $bytesleft = 1;
 365              } elseif( $bytevalue <= 0xEF ) { //1110 xxxx
 366                  $working = $bytevalue & 0x0F;
 367                  $bytesleft = 2;
 368              } else { //1111 0xxx
 369                  $working = $bytevalue & 0x07;
 370                  $bytesleft = 3;
 371              }
 372          }
 373          return $result;
 374      }
 375  
 376      /**
 377       * This expensive function tests whether or not a given character
 378       * encoding supports ASCII. 7/8-bit encodings like Shift_JIS will
 379       * fail this test, and require special processing. Variable width
 380       * encodings shouldn't ever fail.
 381       *
 382       * @param string $encoding Encoding name to test, as per iconv format
 383       * @param bool $bypass Whether or not to bypass the precompiled arrays.
 384       * @return Array of UTF-8 characters to their corresponding ASCII,
 385       *      which can be used to "undo" any overzealous iconv action.
 386       */
 387      public static function testEncodingSupportsASCII($encoding, $bypass = false) {
 388          static $encodings = array();
 389          if (!$bypass) {
 390              if (isset($encodings[$encoding])) return $encodings[$encoding];
 391              $lenc = strtolower($encoding);
 392              switch ($lenc) {
 393                  case 'shift_jis':
 394                      return array("\xC2\xA5" => '\\', "\xE2\x80\xBE" => '~');
 395                  case 'johab':
 396                      return array("\xE2\x82\xA9" => '\\');
 397              }
 398              if (strpos($lenc, 'iso-8859-') === 0) return array();
 399          }
 400          $ret = array();
 401          set_error_handler(array('HTMLPurifier_Encoder', 'muteErrorHandler'));
 402          if (iconv('UTF-8', $encoding, 'a') === false) return false;
 403          for ($i = 0x20; $i <= 0x7E; $i++) { // all printable ASCII chars
 404              $c = chr($i); // UTF-8 char
 405              $r = iconv('UTF-8', "$encoding//IGNORE", $c); // initial conversion
 406              if (
 407                  $r === '' ||
 408                  // This line is needed for iconv implementations that do not
 409                  // omit characters that do not exist in the target character set
 410                  ($r === $c && iconv($encoding, 'UTF-8//IGNORE', $r) !== $c)
 411              ) {
 412                  // Reverse engineer: what's the UTF-8 equiv of this byte
 413                  // sequence? This assumes that there's no variable width
 414                  // encoding that doesn't support ASCII.
 415                  $ret[iconv($encoding, 'UTF-8//IGNORE', $c)] = $c;
 416              }
 417          }
 418          restore_error_handler();
 419          $encodings[$encoding] = $ret;
 420          return $ret;
 421      }
 422  
 423  
 424  }
 425  
 426  // vim: et sw=4 sts=4