Force cache refresh after deployment - php

Question

Is there a way to force a client's cache to reload an HTML file if you can't change the URI referencing that file (e.g., can't add a timestamp param)?
Here's my situation:
A plugin deployed to a 1000 users
That plugin loads example.com/page.html which calls on script.js
The resource URI example.com/page.html cannot be changed (w/o plugin updates)
page.html has been changed. I need to clear the old page.html from users' cache so the new page.html can load.
Any ideas? Htaccess? The PHP API that the old & new page.html call on?
Thanks!

Answer 1

Well, if the page is already cached by a browser it's difficult to tell it not to use its cached version because it probably won't bother to check again before it determines its cached version is stale. You'll just have to send a snail-mail letter to all of your users informing them to press ctrl+f5 :)
There is a chance that the browser might at least try a HEAD request to check the modified timestamp before it serves up its cached version, though. In this case the following will help you out.
Browsers negotiate their content from your web server using HTTP standard headers. Going forward if you want to tell a browser not to cache a file, you have to send the appropriate HTTP headers. If you want to do this in PHP you can use the header function to send the appropriate HTTP headers to the browser:
header('Cache-Control: no-cache');
header('Pragma: no-cache');
If it has to be done via HTML you can do the following in your page header:
<meta http-equiv="Expires" content="Tue, 01 Jan 1995 12:12:12 GMT">
<meta http-equiv="Pragma" content="no-cache">
There is no way for you to be sure if the browser will honor your request that it not cache a page, however. There are some other things like eTags and whatnot but frankly I don't think that's going to help you out if the page is already cached.
UPDATE
From the HTTP/1.1 specification on Response Cacheability:
If there is neither a cache validator nor an explicit expiration time
associated with a response, we do not expect it to be cached, but
certain caches MAY violate this expectation (for example, when little
or no network connectivity is available).

Answer 2

Perhaps PHP could be used to add a timestamp to the javascript call. You could then run this for the duration...........For example:
check_if_cache_should_be_disabled.php
<?php
$deployment_flag = true; // Uncomment this if you want to disable normal cache.
//$deployment_flag = false // Uncomment this if you want to enable normal cache.
?>
page.php
<script src="/js/script.js<?php
require('check_if_cache_should_be_disabled.php');
// File Get Contents can be used for a remote server
//file_get_contents('http://yourserver.com/check_if_cache_should_be_disabled.php');
if ($deployment_flag == true) {
print ( '?ts='.date() );
}
?>"></script>

Answer 3

You can change the file name, for example page_v2.html which will make the browser load the page as a new page.

Answer 4

This answer may be oversimplified, but you could always append a GET value to the end of the file that contains a file version. Modern browsers usually take that as a new version and will ignore previous caches and fetch the newest one. So all you'd have to do is update the version when you want the most up-to-date code to be cached instead.
For example:
<script type="javascript" src="example.js?version=2.0.8"></script>
You could even go as far as writing a PHP script that automatically does this for you when a file changes based on some specific parameter like "last updated."