XMLHTTPRequest returning stale file from the cache

waveking · June 1st, 2006, 12:59 AM

I have made a small stock ticker style extension for firefox, which uses XMLHTTPRequest to download a csv file from my server. This csv has the latest market value, which I display on the user interface.

My problem is that fierfox is caching it! My script is fetching the url based csv file every hour, and the server indeed has updated file, but eh browser is returning the stale copy from its cache every time.

Please help.

Thanks.

richard.york · June 1st, 2006, 06:59 AM

Insert cache control HTTP response headers.

Here's what a PHP version would look like:

Code:

<?php

    header('Pragma: public');
    header('Expires: Mon, 26 Jul 1997 05:00:00 GMT');
    header('Last-Modified: '.gmdate('D, d M Y H:i:s').' GMT');
    header('Cache-Control: must-revalidate');

    // etc
?>

Regards,
Rich

--
Author,
Beginning CSS: Cascading Style Sheets For Web Design
CSS Instant Results

http://www.catb.org/~esr/faqs/smart-questions.html

woodyz · June 5th, 2006, 03:50 PM

One way to deal with this is to make sure each request has a unique member. For example, if you are using a GET, you can add a p
parameter to hold a randomly generated value:
(Assuming we have a method named statChanged to handle the Ajax callback)

Code:

var xmlHttp
var url="MyAjaxHandler.php?r=" + Math.random() + "&search=" + document.getElementById("txtSearch").value
xmlHttp=GetXmlHttpObject(stateChanged)
xmlHttp.open("GET", url, true)

The url variable now includes a parameter named "r" that will hold a random value. This makes each request unique, thereby averting the caching problem. The "r" parameter isn't used in the code handling this call - its only purpose is to make the request unique.

Make sense?

Woody Z http://www.learntoprogramnow.com