Duffer Derek

/**
 * mux.js
 *
 * Copyright (c) Brightcove
 * Licensed Apache-2.0 https://github.com/videojs/mux.js/blob/master/LICENSE
 *
 * Tools for parsing ID3 frame data
 * @see http://id3.org/id3v2.3.0
 */
'use strict';

var
  typedArrayIndexOf = require('../utils/typed-array').typedArrayIndexOf,
  // Frames that allow different types of text encoding contain a text
  // encoding description byte [ID3v2.4.0 section 4.]
  textEncodingDescriptionByte = {
    Iso88591: 0x00, // ISO-8859-1, terminated with \0.
    Utf16:    0x01, // UTF-16 encoded Unicode BOM, terminated with \0\0
    Utf16be:  0x02, // UTF-16BE encoded Unicode, without BOM, terminated with \0\0
    Utf8:     0x03  // UTF-8 encoded Unicode, terminated with \0
  },
  // return a percent-encoded representation of the specified byte range
  // @see http://en.wikipedia.org/wiki/Percent-encoding 
  percentEncode = function(bytes, start, end) {
    var i, result = '';
    for (i = start; i < end; i++) {
      result += '%' + ('00' + bytes[i].toString(16)).slice(-2);
    }
    return result;
  },
  // return the string representation of the specified byte range,
  // interpreted as UTf-8.
  parseUtf8 = function(bytes, start, end) {
    return decodeURIComponent(percentEncode(bytes, start, end));
  },
  // return the string representation of the specified byte range,
  // interpreted as ISO-8859-1.
  parseIso88591 = function(bytes, start, end) {
    return unescape(percentEncode(bytes, start, end)); // jshint ignore:line
  },
  parseSyncSafeInteger = function(data) {
    return (data[0] << 21) |
            (data[1] << 14) |
            (data[2] << 7) |
            (data[3]);
  },
  frameParsers = {
    'APIC': function(frame) {
      var
        i = 1,
        mimeTypeEndIndex,
        descriptionEndIndex,
        LINK_MIME_TYPE = '-->';

      if (frame.data[0] !== textEncodingDescriptionByte.Utf8) {
        // ignore frames with unrecognized character encodings
        return;
      }

      // parsing fields [ID3v2.4.0 section 4.14.]
      mimeTypeEndIndex = typedArrayIndexOf(frame.data, 0, i);
      if (mimeTypeEndIndex < 0) {
        // malformed frame
        return;
      }
      
      // parsing Mime type field (terminated with \0)
      frame.mimeType = parseIso88591(frame.data, i, mimeTypeEndIndex);
      i = mimeTypeEndIndex + 1;

      // parsing 1-byte Picture Type field
      frame.pictureType = frame.data[i];
      i++

      descriptionEndIndex = typedArrayIndexOf(frame.data, 0, i);
      if (descriptionEndIndex < 0) {
        // malformed frame
        return;
      }

      // parsing Description field (terminated with \0)
      frame.description = parseUtf8(frame.data, i, descriptionEndIndex);
      i = descriptionEndIndex + 1;

      if (frame.mimeType === LINK_MIME_TYPE) {
        // parsing Picture Data field as URL (always represented as ISO-8859-1 [ID3v2.4.0 section 4.])
        frame.url = parseIso88591(frame.data, i, frame.data.length)
      } else {
        // parsing Picture Data field as binary data
        frame.pictureData = frame.data.subarray(i, frame.data.length);
      }
    },
    'T*': function(frame) {
      if (frame.data[0] !== textEncodingDescriptionByte.Utf8) {
        // ignore frames with unrecognized character encodings
        return;
      }
      
      // parse text field, do not include null terminator in the frame value
      // frames that allow different types of encoding contain terminated text [ID3v2.4.0 section 4.]
      frame.value = parseUtf8(frame.data, 1, frame.data.length).replace(/\0*$/, '');
      // text information frames supports multiple strings, stored as a terminator separated list [ID3v2.4.0 section 4.2.]
      frame.values = frame.value.split('\0');
    },
    'TXXX': function(frame) {
      var descriptionEndIndex;

      if (frame.data[0] !== textEncodingDescriptionByte.Utf8) {
        // ignore frames with unrecognized character encodings
        return;
      }

      descriptionEndIndex = typedArrayIndexOf(frame.data, 0, 1);

      if (descriptionEndIndex === -1) {
        return;
      }

      // parse the text fields
      frame.description = parseUtf8(frame.data, 1, descriptionEndIndex);
      // do not include the null terminator in the tag value
      // frames that allow different types of encoding contain terminated text
      // [ID3v2.4.0 section 4.]
      frame.value = parseUtf8(
        frame.data,
        descriptionEndIndex + 1,
        frame.data.length
      ).replace(/\0*$/, '');
      frame.data = frame.value;
    },
    'W*': function(frame) {
      // parse URL field; URL fields are always represented as ISO-8859-1 [ID3v2.4.0 section 4.]
      // if the value is followed by a string termination all the following information should be ignored [ID3v2.4.0 section 4.3]
      frame.url = parseIso88591(frame.data, 0, frame.data.length).replace(/\0.*$/, '');
    },
    'WXXX': function(frame) {
      var descriptionEndIndex;

      if (frame.data[0] !== textEncodingDescriptionByte.Utf8) {
        // ignore frames with unrecognized character encodings
        return;
      }

      descriptionEndIndex = typedArrayIndexOf(frame.data, 0, 1);

      if (descriptionEndIndex === -1) {
        return;
      }

      // parse the description and URL fields
      frame.description = parseUtf8(frame.data, 1, descriptionEndIndex);
      // URL fields are always represented as ISO-8859-1 [ID3v2.4.0 section 4.]
      // if the value is followed by a string termination all the following information
      // should be ignored [ID3v2.4.0 section 4.3]
      frame.url = parseIso88591(
        frame.data,
        descriptionEndIndex + 1,
        frame.data.length
      ).replace(/\0.*$/, '');
    },
    'PRIV': function(frame) {
      var i;

      for (i = 0; i < frame.data.length; i++) {
        if (frame.data[i] === 0) {
          // parse the description and URL fields
          frame.owner = parseIso88591(frame.data, 0, i);
          break;
        }
      }
      frame.privateData = frame.data.subarray(i + 1);
      frame.data = frame.privateData;
    }
  };

var parseId3Frames = function(data) {
  var frameSize, frameHeader,
    frameStart = 10,
    tagSize = 0,
    frames = [];

  // If we don't have enough data for a header, 10 bytes, 
  // or 'ID3' in the first 3 bytes this is not a valid ID3 tag.
  if (data.length < 10 ||
    data[0] !== 'I'.charCodeAt(0) ||
    data[1] !== 'D'.charCodeAt(0) ||
    data[2] !== '3'.charCodeAt(0)) {
    return;
  }
  // the frame size is transmitted as a 28-bit integer in the
  // last four bytes of the ID3 header.
  // The most significant bit of each byte is dropped and the
  // results concatenated to recover the actual value.
  tagSize = parseSyncSafeInteger(data.subarray(6, 10));

  // ID3 reports the tag size excluding the header but it's more
  // convenient for our comparisons to include it
  tagSize += 10;
  // check bit 6 of byte 5 for the extended header flag.
  var hasExtendedHeader = data[5] & 0x40;
  if (hasExtendedHeader) {
    // advance the frame start past the extended header
    frameStart += 4; // header size field
    frameStart += parseSyncSafeInteger(data.subarray(10, 14));
    tagSize -= parseSyncSafeInteger(data.subarray(16, 20)); // clip any padding off the end
  }

  // parse one or more ID3 frames
  // http://id3.org/id3v2.3.0#ID3v2_frame_overview
  do {
    // determine the number of bytes in this frame
    frameSize = parseSyncSafeInteger(data.subarray(frameStart + 4, frameStart + 8));
    if (frameSize < 1) {
      break;
    }
    frameHeader = String.fromCharCode(data[frameStart],
                                      data[frameStart + 1],
                                      data[frameStart + 2],
                                      data[frameStart + 3]);

    var frame = {
      id: frameHeader,
      data: data.subarray(frameStart + 10, frameStart + frameSize + 10)
    };
    frame.key = frame.id;

    // parse frame values
    if (frameParsers[frame.id]) {
      // use frame specific parser
      frameParsers[frame.id](frame);
    } else if (frame.id[0] === 'T') {
      // use text frame generic parser
      frameParsers['T*'](frame);
    } else if (frame.id[0] === 'W') {
      // use URL link frame generic parser
      frameParsers['W*'](frame);
    }

    frames.push(frame);

    frameStart += 10; // advance past the frame header
    frameStart += frameSize; // advance past the frame body
  } while (frameStart < tagSize);

  return frames;
}

module.exports = { 
  parseId3Frames: parseId3Frames,
  parseSyncSafeInteger: parseSyncSafeInteger,
  frameParsers: frameParsers,
};