mtags/utils/stringutils.js

Media file tag parser

/**
 * Copyright (c) 2010, António Afonso <antonio.afonso gmail.com>. All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without modification, are
 * permitted provided that the following conditions are met:
 * 
 *    1. Redistributions of source code must retain the above copyright notice, this list of
 *       conditions and the following disclaimer.
 * 
 *    2. Redistributions in binary form must reproduce the above copyright notice, this list
 *       of conditions and the following disclaimer in the documentation and/or other materials
 *       provided with the distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY António Afonso ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
var StringUtils = exports;

/**
 *
 */
StringUtils.readUTF16String = function (bytes, bigEndian, maxBytes) {
  var ix = 0;
  var offset1 = 1, offset2 = 0;
  maxBytes = Math.min(maxBytes||bytes.length, bytes.length);

  if( bytes[0] == 0xFE && bytes[1] == 0xFF ) {
    bigEndian = true;
    ix = 2;
  } else if( bytes[0] == 0xFF && bytes[1] == 0xFE ) {
    bigEndian = false;
    ix = 2;
  }
  if( bigEndian ) {
    offset1 = 0;
    offset2 = 1;
  }

  var arr = [];
  for( var j = 0; ix < maxBytes; j++ ) {
    var byte1 = bytes[ix+offset1];
    var byte2 = bytes[ix+offset2];
    var word1 = (byte1<<8)+byte2;
    ix += 2;
    if( word1 == 0x0000 ) {
      break;
    } else if( byte1 < 0xD8 || byte1 >= 0xE0 ) {
      arr[j] = String.fromCharCode(word1);
    } else {
      var byte3 = bytes[ix+offset1];
      var byte4 = bytes[ix+offset2];
      var word2 = (byte3<<8)+byte4;
      ix += 2;
      arr[j] = String.fromCharCode(word1, word2);
    }
  }
  var string = new String(arr.join(""));
  string.bytesReadCount = ix;
  return string;
};

/**
 *
 */
StringUtils.readUTF8String = function (bytes, maxBytes) {
  var ix = 0;
  maxBytes = Math.min(maxBytes||bytes.length, bytes.length);

  if( bytes[0] == 0xEF && bytes[1] == 0xBB && bytes[2] == 0xBF ) {
    ix = 3;
  }

  var arr = [];
  for( var j = 0; ix < maxBytes; j++ ) {
    var byte1 = bytes[ix++];
    if( byte1 == 0x00 ) {
      break;
    } else if( byte1 < 0x80 ) {
      arr[j] = String.fromCharCode(byte1);
    } else if( byte1 >= 0xC2 && byte1 < 0xE0 ) {
      var byte2 = bytes[ix++];
      arr[j] = String.fromCharCode(((byte1&0x1F)<<6) + (byte2&0x3F));
    } else if( byte1 >= 0xE0 && byte1 < 0xF0 ) {
      var byte2 = bytes[ix++];
      var byte3 = bytes[ix++];
      arr[j] = String.fromCharCode(((byte1&0xFF)<<12) + ((byte2&0x3F)<<6) + (byte3&0x3F));
    } else if( byte1 >= 0xF0 && byte1 < 0xF5) {
      var byte2 = bytes[ix++];
      var byte3 = bytes[ix++];
      var byte4 = bytes[ix++];
      var codepoint = ((byte1&0x07)<<18) + ((byte2&0x3F)<<12)+ ((byte3&0x3F)<<6) + (byte4&0x3F) - 0x10000;
      arr[j] = String.fromCharCode(
          (codepoint>>10) + 0xD800,
          (codepoint&0x3FF) + 0xDC00
          );
    }
  }
  var string = new String(arr.join(""));
  string.bytesReadCount = ix;
  return string;
};

/**
 *
 */
StringUtils.readNullTerminatedString = function (bytes, maxBytes) {
  var arr = [];
  maxBytes = maxBytes || bytes.length;
  for ( var i = 0; i < maxBytes; ) {
    var byte1 = bytes[i++];
    if( byte1 == 0x00 ) break;
    arr[i-1] = String.fromCharCode(byte1);
  }	    
  var string = new String(arr.join(""));
  string.bytesReadCount = i;
  return string;
};