So of course a human can easily check each URL on his/her iPhone and see if the destination is iPhone optimized or not.
But is there a machine driven way to find out?

Is there anyway of programming PHP to find out if a given URL submitted by a user
possesses an iphone optimized version of the site?

I mean a lot of sites use an iPhone dedicated conditional style sheet,
something like this:

<link media="only screen and (max-device-width: 480px)" href="http://www.randomsite.com/iphone.css" type="text/css" rel="stylesheet" />

other sites will use an Apache .htaccess redirect to a dedicated domain or subdomain based on the user agent like this

RewriteCond %{HTTP_USER_AGENT} .*Mobile.*Safari
RewriteRule ^[\./](.*)$ http://beta.mydomain.no/iphone

or even JavaScript like this

<script language=javascript>
<!--
if ((navigator.userAgent.match(/iPhone/i)) || (navigator.userAgent.match(/iPod/i))) {
   location.replace("http://url-to-send-them/iphone.html");
}
-->
</script>

I can't think of any?

If you have cURL installed, the easiest thing to do is set your user-agent to be the same as the iPhone, request the URL, then compare the results against the same page without the user-agent set.

http://php.net/manual/en/book.curl.php

If the redirect is being done with JavaScript this won't work of course.

I can't really think of a solution other than what Abel described, however I think you should take into consideration that this is a relatively expensive operation; the script would have to wait for a response from the remote server twice. This is acceptable if you only need to do a one time, or once in a while, check.

Also, comparing the results to see if they are different is not a trivial problem. The response might be different on every request, regardless of the user-agent. You'd have to know what to look for in order to definitively determine that the site is specifically serving mobile content.

Originally Posted by NullPointer

Also, comparing the results to see if they are different is not a trivial problem. The response might be different on every request, regardless of the user-agent.

This is definitely true, and something I did consider. The best you may be able to do is that if they don't match, you flag the URL in your database as a possible mobile site, and then have a human confirm it.

Originally Posted by wayfarer07

This is definitely true, and something I did consider. The best you may be able to do is that if they don't match, you flag the URL in your database as a possible mobile site, and then have a human confirm it.

Although, with cURL, you can set it not to follow an HTTP 301 or 302 redirect. If I remember right, you can set it to just read the header response and not the body. If you get a Location: header that is different than without sending a mobile user-agent header from your PHP script, it is trying to support mobile, in theory.

Originally Posted by wayfarer07

Although, with cURL, you can set it not to follow an HTTP 301 or 302 redirect. If I remember right, you can set it to just read the header response and not the body. If you get a Location: header that is different than without sending a mobile user-agent header from your PHP script, it is trying to support mobile, in theory.

Is it possible to somehow "read" what CSS characteristics a page is serving up?

Regardless of the root to getting there, if the page contained

some commonly used Mobile Safari CSS properties

that would be a pretty big give away wouldnt it?

So if you could change the user agent using cURL to mimic an iPhone
device and then somehow parse the CSS I think that would be 90% of problem solved. No?

Easier said than done of course.

It would take a little work to scrape out every possible CSS location (link, import, style tags, inline), but if you just eliminate inline it wouldn't be too bad. You'd just have to parse the HTML document to find the correct styles or locations. However, it seems to me detecting iPhone styles may not be very reliable. After all, in the case of a relatively simple site, it may just be a matter of making the whole site smaller or less complex.