title: PHP force downloading .xlsx file corrupt
body: <p>I am working on a site that allows teachers to upload documents and students download them. However, there is a problem. Microsoft Word (.docx) files download perfectly, but when downloading an excel (xlsx) file, excel gives a "This file is corrupt and cannot be opened" dialog. Any help with this would be greatly appreciated!</p>
  
  <p>My download code is as follows:</p>
  
  <pre><code>case 'xlsx':
  
      header('Content-type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet');
      header('Content-Disposition: attachment; filename="' . $filename . '"');
      header('Content-Transfer-Encoding: binary');
      header('Expires: 0');
      header('Pragma: no-cache');
      readfile('./uploads/resources/courses/' . $filename);
  
  break;
  </code></pre>