title: How to detect additional mime type in Golang
body: <p>There are <code>http.DetectContentType([]byte)</code> function in <code>net/http</code> package. But only limited number of types are supported. How to add support of <code>docx</code>, <code>doc</code>, <code>xls</code>, <code>xlsx</code>, <code>ppt</code>, <code>pps</code>, <code>odt</code>, <code>ods</code>, <code>odp</code> files not by extension, but by the content.
  As far as I know, there are some problems, because <code>docx</code>/<code>xlsx</code>/<code>pptx</code>/<code>odp</code>/<code>odt</code> files has the same signature as the <code>zip</code> file (50 4B 03 04).</p>