Uploaded docx files turning into zip

Question

I am currently using symfony 1.4 and would like to allow users to upload Microsoft Word docx files. Using the sfWidgetFormInputFile widget and sfValidatorFile below users are able to select and successfully upload their docx files using a simple web form.

$this->widgetSchema['file_name'] = new sfWidgetFormInputFile(array('label' => 'File'));

$this->validatorSchema['file_name'] = new sfValidatorFile(array(
  'required'   => true,
  'path'       => sfConfig::get('sf_upload_dir').DIRECTORY_SEPARATOR.sfConfig::get('app_dir_file_sharing').DIRECTORY_SEPARATOR,
  'mime_types' => array('application/msword',
                        'application/vnd.ms-word',
                        'application/msword',
                        'application/msword; charset=binary')
), array(
    'invalid'    => 'Invalid file.',
    'required'   => 'Select a file to upload.',
    'mime_types' => 'The file must be a supported type.'
));

The problem is that after the file is uploaded, the extension is changed to .zip and the file contains a file tree of xml files. My understanding is that this is because Office 2007 are now using Open xml file formats. Is there any way to prevent this from happening using symfony or PHP?

Answer 1

The problem is Content-Sniffing. The new Office formats ARE .zip files, and if on upload, the content is sniffed, the browser will identify this as a ZIP file and set the Content-Type header as such. Similarly, on download unless your server sets the proper Content-Type HTTP response header, the browser will assume that this is a ZIP file.