The Moose and Squirrel Files

August 23, 2008

Display RSS in a Browser Window

Filed under: Uncategorized — Tags: , — networknerd @ 12:16 pm

One of the knowledge management people at work were amazed by a server application that rendered RSS news feeds as HTML to the client browser. I opined that that was a trivial exercise and that the same thing could be done client side on the browser.  To prove the point I googled up some javascript from Tim Huffam and pasted it straight into a web page. That should have been the end of the story.  Next day I hear that it doesn’t work for some RSS feeds.  Turns out that they are all from feedburner.

Javascript debugging was a bust, so I moved down the application tree and used a telnet client to connect to feeds.feedburner.com. That returned a 302 code and a new host to check feedproxy.feedburner.com.  Trying the feedproxy.feedburner.com url in IE worked. The answer must be that the MSXML2.DOMDocument.3.0 cant handle redirects. All good in theory except that a nagging doubt, confirmed by google, tells me otherwise.

Next move was to open up word and try it in VBA (The debugging is much better than IE).  Naturally it worked properly first time.  So why did the activex object behave differently in IE?  When in doubt look at packets.  Wireshark was installed and a capture was performed using IE and netcat to perform the HTTP GET. For IE the return from the server was HTML.  For netcat the return was pure XML.  The next conclusion I jumped to was that it was dependent on the useragent header in the get request.  Wrong again. I eventually narrowed it down to the referer header. Oh well, most of my exercise does come from jumping to the wrong conclusion.

Feedburner must use some clever server side stuff (mod_rewrite perhaps) to detect if the requester is using a browser based on the referer header.

I did  prove to myself once again though that most application level problems can be more readily identified at the network level.

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