PHP is_rss（$ url）？

Question

Is there a way through PHP where I can either with the URL, or $string=file_get_contents($url) where I could find out if a given URL is an RSS feed?

I would also like to be able to handle FeedBurner feeds as a potential issue feed type...

I'm looking to try to automate the discovery of these feeds - (I don't know if this type of thing exists - an example to a reference would be extremely helpful :) based on WordPress and Blogger standards.

Answer 1

A barebones unreliable test:

$string = file_get_contents($url);
if (strpos($string, '<rss') !== FALSE)) {
   ... yes, it's probably rss
}

A more complicated version would be to load the XML string (assuming it does look like xml) into an XML validator and see if it conforms to the RSS DTD. More work, but also far more reliable.