title: What's the meaning of QNetworkReply::ProtocolUnknownError?
body: <p>I use a object of <code>QNetworkAccessManager</code> to post json data to a website. </p>
  
  <p>when handle the reply which is a pointer of <code>QNetworkReply</code> class in the slot function, the value of <code>reply-&gt;error()</code> is <code>301</code> and the value of <code>reply-&gt;errorString()</code> is <code>Error downloading http://www.example.com/query - server replied: Service Unavailable</code>. </p>
  
  <p>I check the documentation of <code>QNetworkReply</code>, the description of this error is:</p>
  
  <blockquote>
    <p>QNetworkReply::ProtocolUnknownError|301|the Network Access API cannot honor the request because the protocol is not known</p>
  </blockquote>
  
  <p>and I also known this error is different form the http status 301.</p>
  
  <p>and I have add <code>http://</code> before the url.</p>
  
  <p>Can someone give some info about this?</p>