function onend(err, sourceBuffer) {
    if (err) {
      callback(err);
      return;
    }

    data.size = sourceBuffer.length || 0;
    data.crc32 = crc32.unsigned(sourceBuffer);

    self.files.push(data);

    callback(null, data);
  }
[append description]

@param  {(Buffer|Stream)}   source
@param  {EntryData}   data
@param  {Function} callback
@return void