JAVASCRIPT 22
String_decoder.js Guest on 2nd May 2021 01:50:35 PM
  1. // Copyright Joyent, Inc. and other Node contributors.
  2. //
  3. // Permission is hereby granted, free of charge, to any person obtaining a
  4. // copy of this software and associated documentation files (the
  5. // "Software"), to deal in the Software without restriction, including
  6. // without limitation the rights to use, copy, modify, merge, publish,
  7. // distribute, sublicense, and/or sell copies of the Software, and to permit
  8. // persons to whom the Software is furnished to do so, subject to the
  9. // following conditions:
  10. //
  11. // The above copyright notice and this permission notice shall be included
  12. // in all copies or substantial portions of the Software.
  13. //
  14. // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  15. // OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  16. // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
  17. // NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
  18. // DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
  19. // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
  20. // USE OR OTHER DEALINGS IN THE SOFTWARE.
  21.  
  22. 'use strict';
  23.  
  24. /*<replacement>*/
  25.  
  26. var Buffer = require('safe-buffer').Buffer;
  27. /*</replacement>*/
  28.  
  29. var isEncoding = Buffer.isEncoding || function (encoding) {
  30.   encoding = '' + encoding;
  31.   switch (encoding && encoding.toLowerCase()) {
  32.     case 'hex':case 'utf8':case 'utf-8':case 'ascii':case 'binary':case 'base64':case 'ucs2':case 'ucs-2':case 'utf16le':case 'utf-16le':case 'raw':
  33.       return true;
  34.     default:
  35.       return false;
  36.   }
  37. };
  38.  
  39. function _normalizeEncoding(enc) {
  40.   if (!enc) return 'utf8';
  41.   var retried;
  42.   while (true) {
  43.     switch (enc) {
  44.       case 'utf8':
  45.       case 'utf-8':
  46.         return 'utf8';
  47.       case 'ucs2':
  48.       case 'ucs-2':
  49.       case 'utf16le':
  50.       case 'utf-16le':
  51.         return 'utf16le';
  52.       case 'latin1':
  53.       case 'binary':
  54.         return 'latin1';
  55.       case 'base64':
  56.       case 'ascii':
  57.       case 'hex':
  58.         return enc;
  59.       default:
  60.         if (retried) return; // undefined
  61.         enc = ('' + enc).toLowerCase();
  62.         retried = true;
  63.     }
  64.   }
  65. };
  66.  
  67. // Do not cache `Buffer.isEncoding` when checking encoding names as some
  68. // modules monkey-patch it to support additional encodings
  69. function normalizeEncoding(enc) {
  70.   var nenc = _normalizeEncoding(enc);
  71.   if (typeof nenc !== 'string' && (Buffer.isEncoding === isEncoding || !isEncoding(enc))) throw new Error('Unknown encoding: ' + enc);
  72.   return nenc || enc;
  73. }
  74.  
  75. // StringDecoder provides an interface for efficiently splitting a series of
  76. // buffers into a series of JS strings without breaking apart multi-byte
  77. // characters.
  78. exports.StringDecoder = StringDecoder;
  79. function StringDecoder(encoding) {
  80.   this.encoding = normalizeEncoding(encoding);
  81.   var nb;
  82.   switch (this.encoding) {
  83.     case 'utf16le':
  84.       this.text = utf16Text;
  85.       this.end = utf16End;
  86.       nb = 4;
  87.       break;
  88.     case 'utf8':
  89.       this.fillLast = utf8FillLast;
  90.       nb = 4;
  91.       break;
  92.     case 'base64':
  93.       this.text = base64Text;
  94.       this.end = base64End;
  95.       nb = 3;
  96.       break;
  97.     default:
  98.       this.write = simpleWrite;
  99.       this.end = simpleEnd;
  100.       return;
  101.   }
  102.   this.lastNeed = 0;
  103.   this.lastTotal = 0;
  104.   this.lastChar = Buffer.allocUnsafe(nb);
  105. }
  106.  
  107. StringDecoder.prototype.write = function (buf) {
  108.   if (buf.length === 0) return '';
  109.   var r;
  110.   var i;
  111.   if (this.lastNeed) {
  112.     r = this.fillLast(buf);
  113.     if (r === undefined) return '';
  114.     i = this.lastNeed;
  115.     this.lastNeed = 0;
  116.   } else {
  117.     i = 0;
  118.   }
  119.   if (i < buf.length) return r ? r + this.text(buf, i) : this.text(buf, i);
  120.   return r || '';
  121. };
  122.  
  123. StringDecoder.prototype.end = utf8End;
  124.  
  125. // Returns only complete characters in a Buffer
  126. StringDecoder.prototype.text = utf8Text;
  127.  
  128. // Attempts to complete a partial non-UTF-8 character using bytes from a Buffer
  129. StringDecoder.prototype.fillLast = function (buf) {
  130.   if (this.lastNeed <= buf.length) {
  131.     buf.copy(this.lastChar, this.lastTotal - this.lastNeed, 0, this.lastNeed);
  132.     return this.lastChar.toString(this.encoding, 0, this.lastTotal);
  133.   }
  134.   buf.copy(this.lastChar, this.lastTotal - this.lastNeed, 0, buf.length);
  135.   this.lastNeed -= buf.length;
  136. };
  137.  
  138. // Checks the type of a UTF-8 byte, whether it's ASCII, a leading byte, or a
  139. // continuation byte. If an invalid byte is detected, -2 is returned.
  140. function utf8CheckByte(byte) {
  141.   if (byte <= 0x7F) return 0;else if (byte >> 5 === 0x06) return 2;else if (byte >> 4 === 0x0E) return 3;else if (byte >> 3 === 0x1E) return 4;
  142.   return byte >> 6 === 0x02 ? -1 : -2;
  143. }
  144.  
  145. // Checks at most 3 bytes at the end of a Buffer in order to detect an
  146. // incomplete multi-byte UTF-8 character. The total number of bytes (2, 3, or 4)
  147. // needed to complete the UTF-8 character (if applicable) are returned.
  148. function utf8CheckIncomplete(self, buf, i) {
  149.   var j = buf.length - 1;
  150.   if (j < i) return 0;
  151.   var nb = utf8CheckByte(buf[j]);
  152.   if (nb >= 0) {
  153.     if (nb > 0) self.lastNeed = nb - 1;
  154.     return nb;
  155.   }
  156.   if (--j < i || nb === -2) return 0;
  157.   nb = utf8CheckByte(buf[j]);
  158.   if (nb >= 0) {
  159.     if (nb > 0) self.lastNeed = nb - 2;
  160.     return nb;
  161.   }
  162.   if (--j < i || nb === -2) return 0;
  163.   nb = utf8CheckByte(buf[j]);
  164.   if (nb >= 0) {
  165.     if (nb > 0) {
  166.       if (nb === 2) nb = 0;else self.lastNeed = nb - 3;
  167.     }
  168.     return nb;
  169.   }
  170.   return 0;
  171. }
  172.  
  173. // Validates as many continuation bytes for a multi-byte UTF-8 character as
  174. // needed or are available. If we see a non-continuation byte where we expect
  175. // one, we "replace" the validated continuation bytes we've seen so far with
  176. // a single UTF-8 replacement character ('\ufffd'), to match v8's UTF-8 decoding
  177. // behavior. The continuation byte check is included three times in the case
  178. // where all of the continuation bytes for a character exist in the same buffer.
  179. // It is also done this way as a slight performance increase instead of using a
  180. // loop.
  181. function utf8CheckExtraBytes(self, buf, p) {
  182.   if ((buf[0] & 0xC0) !== 0x80) {
  183.     self.lastNeed = 0;
  184.     return '\ufffd';
  185.   }
  186.   if (self.lastNeed > 1 && buf.length > 1) {
  187.     if ((buf[1] & 0xC0) !== 0x80) {
  188.       self.lastNeed = 1;
  189.       return '\ufffd';
  190.     }
  191.     if (self.lastNeed > 2 && buf.length > 2) {
  192.       if ((buf[2] & 0xC0) !== 0x80) {
  193.         self.lastNeed = 2;
  194.         return '\ufffd';
  195.       }
  196.     }
  197.   }
  198. }
  199.  
  200. // Attempts to complete a multi-byte UTF-8 character using bytes from a Buffer.
  201. function utf8FillLast(buf) {
  202.   var p = this.lastTotal - this.lastNeed;
  203.   var r = utf8CheckExtraBytes(this, buf, p);
  204.   if (r !== undefined) return r;
  205.   if (this.lastNeed <= buf.length) {
  206.     buf.copy(this.lastChar, p, 0, this.lastNeed);
  207.     return this.lastChar.toString(this.encoding, 0, this.lastTotal);
  208.   }
  209.   buf.copy(this.lastChar, p, 0, buf.length);
  210.   this.lastNeed -= buf.length;
  211. }
  212.  
  213. // Returns all complete UTF-8 characters in a Buffer. If the Buffer ended on a
  214. // partial character, the character's bytes are buffered until the required
  215. // number of bytes are available.
  216. function utf8Text(buf, i) {
  217.   var total = utf8CheckIncomplete(this, buf, i);
  218.   if (!this.lastNeed) return buf.toString('utf8', i);
  219.   this.lastTotal = total;
  220.   var end = buf.length - (total - this.lastNeed);
  221.   buf.copy(this.lastChar, 0, end);
  222.   return buf.toString('utf8', i, end);
  223. }
  224.  
  225. // For UTF-8, a replacement character is added when ending on a partial
  226. // character.
  227. function utf8End(buf) {
  228.   var r = buf && buf.length ? this.write(buf) : '';
  229.   if (this.lastNeed) return r + '\ufffd';
  230.   return r;
  231. }
  232.  
  233. // UTF-16LE typically needs two bytes per character, but even if we have an even
  234. // number of bytes available, we need to check if we end on a leading/high
  235. // surrogate. In that case, we need to wait for the next two bytes in order to
  236. // decode the last character properly.
  237. function utf16Text(buf, i) {
  238.   if ((buf.length - i) % 2 === 0) {
  239.     var r = buf.toString('utf16le', i);
  240.     if (r) {
  241.       var c = r.charCodeAt(r.length - 1);
  242.       if (c >= 0xD800 && c <= 0xDBFF) {
  243.         this.lastNeed = 2;
  244.         this.lastTotal = 4;
  245.         this.lastChar[0] = buf[buf.length - 2];
  246.         this.lastChar[1] = buf[buf.length - 1];
  247.         return r.slice(0, -1);
  248.       }
  249.     }
  250.     return r;
  251.   }
  252.   this.lastNeed = 1;
  253.   this.lastTotal = 2;
  254.   this.lastChar[0] = buf[buf.length - 1];
  255.   return buf.toString('utf16le', i, buf.length - 1);
  256. }
  257.  
  258. // For UTF-16LE we do not explicitly append special replacement characters if we
  259. // end on a partial character, we simply let v8 handle that.
  260. function utf16End(buf) {
  261.   var r = buf && buf.length ? this.write(buf) : '';
  262.   if (this.lastNeed) {
  263.     var end = this.lastTotal - this.lastNeed;
  264.     return r + this.lastChar.toString('utf16le', 0, end);
  265.   }
  266.   return r;
  267. }
  268.  
  269. function base64Text(buf, i) {
  270.   var n = (buf.length - i) % 3;
  271.   if (n === 0) return buf.toString('base64', i);
  272.   this.lastNeed = 3 - n;
  273.   this.lastTotal = 3;
  274.   if (n === 1) {
  275.     this.lastChar[0] = buf[buf.length - 1];
  276.   } else {
  277.     this.lastChar[0] = buf[buf.length - 2];
  278.     this.lastChar[1] = buf[buf.length - 1];
  279.   }
  280.   return buf.toString('base64', i, buf.length - n);
  281. }
  282.  
  283. function base64End(buf) {
  284.   var r = buf && buf.length ? this.write(buf) : '';
  285.   if (this.lastNeed) return r + this.lastChar.toString('base64', 0, 3 - this.lastNeed);
  286.   return r;
  287. }
  288.  
  289. // Pass bytes on through for single-byte encodings (e.g. ascii, latin1, hex)
  290. function simpleWrite(buf) {
  291.   return buf.toString(this.encoding);
  292. }
  293.  
  294. function simpleEnd(buf) {
  295.   return buf && buf.length ? this.write(buf) : '';
  296. }

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