title: Can gmail's random-signatures-from-an-RSS-feed be used for truly dynamic signatures?
body: <p>This is a new gmail labs feature that lets you specify an RSS feed to grab random quotes from to append to your email signature.  I'd like to use that to generate signatures programmatically based on parameters I pass in, the current time, etc.  (For example, I have a script in pine that appends the current probabilities of McCain and Obama winning, fetched from intrade's API.  See below.)  But it seems gmail caches the contents of the URL you specify.  Any way to control that or anyone know how often gmail looks at the URL?</p>
  
  <p>ADDED: Here's the program I'm using to test this.  This file lives at <a href="http://kibotzer.com/sigs.php" rel="nofollow noreferrer">http://kibotzer.com/sigs.php</a>. The no-cache header idea, taken from here -- <a href="http://mapki.com/wiki/Dynamic_XML" rel="nofollow noreferrer">http://mapki.com/wiki/Dynamic_XML</a> -- seems to not help.</p>
  
  <pre><code>&lt;?php
  
  header("Expires: Mon, 26 Jul 1997 05:00:00 GMT"); // Date in the past
  header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
  // HTTP/1.1
  header("Cache-Control: no-store, no-cache, must-revalidate");
  header("Cache-Control: post-check=0, pre-check=0", false);
  // HTTP/1.0
  header("Pragma: no-cache");
  //XML Header
  header("content-type:text/xml");
  ?&gt;
  
  &lt;!DOCTYPE rss PUBLIC "-//Netscape Communications//DTD RSS 0.91//EN" "http://my.netscape.com/publish/formats/rss-0.91.dtd"&gt;
  &lt;rss version="0.91"&gt;
  &lt;channel&gt;
  &lt;title&gt;Dynamic Signatures&lt;/title&gt;
  &lt;link&gt;http://kibotzer.com&lt;/link&gt;
  &lt;description&gt;Blah blah&lt;/description&gt;
  &lt;language&gt;en-us&lt;/language&gt;
  &lt;pubDate&gt;26 Sep 2008 02:15:01 -0000&lt;/pubDate&gt;
  &lt;webMaster&gt;dreeves@kibotzer.com&lt;/webMaster&gt;
  &lt;managingEditor&gt;dreeves@kibotzer.com (Daniel Reeves)&lt;/managingEditor&gt;
  &lt;lastBuildDate&gt;26 Sep 2008 02:15:01 -0000&lt;/lastBuildDate&gt;
  
  &lt;image&gt;
  &lt;title&gt;Kibotzer Logo&lt;/title&gt;
  &lt;url&gt;http://kibotzer.com/logos/kibo-logo-1.gif&lt;/url&gt;
  &lt;link&gt;http://kibotzer.com/&lt;/link&gt;
  &lt;width&gt;120&lt;/width&gt;
  &lt;height&gt;60&lt;/height&gt;
  &lt;description&gt;Kibotzer&lt;/description&gt;
  &lt;/image&gt;
  
  &lt;item&gt;
  &lt;title&gt;
  Dynamic Signature 1 (&lt;?php echo gmdate("H:i:s"); ?&gt;) 
  &lt;/title&gt;
  &lt;link&gt;http://kibotzer.com&lt;/link&gt;
  &lt;description&gt;This is the description for Signature 1 (&lt;?php echo gmdate("H:i:s"); ?&gt;) &lt;/description&gt;
  &lt;/item&gt;
  
  &lt;item&gt;
  &lt;title&gt;
  Dynamic Signature 2 (&lt;?php echo gmdate("H:i:s"); ?&gt;) 
  &lt;/title&gt;
  &lt;link&gt;http://kibotzer.com&lt;/link&gt;
  &lt;description&gt;This is the description for Signature 2 (&lt;?php echo gmdate("H:i:s"); ?&gt;) &lt;/description&gt;
  &lt;/item&gt;
  
  &lt;/channel&gt;
  &lt;/rss&gt;
  </code></pre>
  
  <pre>
  --
  http://ai.eecs.umich.edu/people/dreeves  - -  search://"Daniel Reeves"
  
  Latest probabilities from intrade...
    42.1%  McCain becomes president (last trade 18:07 FRI)
    57.0%  Obama becomes president (last trade 18:34 FRI)
    17.6%  US recession in 2008 (last trade 16:24 FRI)
    16.1%  Overt air strike against Iran in '08 (last trade 17:39 FRI)
  </pre>