Nadav Samet’s Blog

Internet Explorer is known to cache the responses of GET calls. The problem occurs if your javascript functions request the same url over and over again. Internet Explorer will cache the response of the first call, and subsequent calls will automatically return the same response, without actually contacting the server. There are two approaches to solve this problem.

One approach could be to add a random part to the url (i.e.: /poll?random=f2dee87716f). So, the browser will think of it as a different URL everytime. An alternative approach could be to set the response headers correctly. The HTTP headers that need to be set are as follows:

Expires: Sun, 19 Nov 1978 05:00:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache

Here’s how I do it in TurboGears. To each method that I don’t want IE to cache, I add the strongly_expire decorator, like this:

    @expose()
    @strongly_expire
    def cant_cache_me(self, position):
        ...

The code of the decorator, which is responsible to set the headers propertly:

def strongly_expire(func):
    """Decorator that sends headers that instruct browsers and proxies not to cache.
    """
    def newfunc(*args, **kwargs):
        cherrypy.response.headers['Expires'] = ‘Sun, 19 Nov 1978 05:00:00 GMT’
        cherrypy.response.headers['Cache-Control'] = ‘no-store, no-cache, must-revalidate, post-check=0, pre-check=0′
        cherrypy.response.headers['Pragma'] = ‘no-cache’
        return func(*args, **kwargs)
    return newfunc