How to check if a page is cached with php

Question

...and whether it was cached 30 days ago,,

I am using this code:

 $page=get_headers('http://www.w3schools.com/php/func_date_strtotime.asp');

The output is this:

 0=>HTTP/1.1 200 OK 

1=>Connection: close

2=>Date: Thu, 03 May 2012 10:51:00 GMT

3=>Server: Microsoft-IIS/6.0

4=>MicrosoftOfficeWebServer: 5.0_Pub

5=>X-Powered-By: ASP.NET

6=>Pragma: no-cache

7=>Content-Length: 23643

8=>Content-Type: text/html

9=>Expires: Thu, 03 May 2012 10:50:00 GMT

10=>Set-Cookie: ASPSESSIONIDSAARQQST=AAMAAHBBBHBELMHDCHNNLMFP; path=/

11=>Cache-control: no-cache

I read that pragma cache , doesnt necessary mean that the page is uncacheable.

I want to know 2 things: 1) if the page is cached 2) if it was cached 30 days ago.

Can I do this

 $date1=gmdate("D, d M Y H:i:s", strtotime("30 days ago")) . " GMT";
  $date2=$page['Expires'];
  if($date1>$date2)
  {
    echo 'The page was cached for longer than 30 days';
   }

Answer 1

Since PHP is a server side language you cannot check browser cache(which is a client side) using PHP. So you need some client side scripting like Javascript and not server side programming like PHP.