title: How to skip known entries when syncing with Google Reader?
body: <p>for writing an offline client to the Google Reader service I would like to know how to best sync with the service. </p>
  
  <p>There doesn't seem to be official documentation yet and the best source I found so far is this: <a href="http://code.google.com/p/pyrfeed/wiki/GoogleReaderAPI" rel="noreferrer">http://code.google.com/p/pyrfeed/wiki/GoogleReaderAPI</a></p>
  
  <p>Now consider this: With the information from above I can download all unread items, I can specify how many items to download and using the atom-id I can detect duplicate entries that I already downloaded.</p>
  
  <p>What's missing for me is a way to specify that I just want the updates since my last sync.
  I can say give me the 10 (parameter <em>n</em>=10) latest (parameter <em>r</em>=d) entries. If I specify the parameter <em>r</em>=o (date ascending) then I can also specify parameter <em>ot</em>=[last time of sync], but only then and the ascending order doesn't make any sense when I just want to read some items versus all items.</p>
  
  <p>Any idea how to solve that without downloading all items again and just rejecting duplicates? Not a very economic way of polling.</p>
  
  <p>Someone proposed that I can specify that I only want the unread entries. But to make that solution work in the way that Google Reader will not offer this entries again, I would need to mark them as read. In turn that would mean that I need to keep my own read/unread state on the client <em>and</em> that the entries are already marked as read when the user logs on to the online version of Google Reader. That doesn't work for me.</p>
  
  <p>Cheers,
  Mariano </p>