How to fetch images, css, js from cache (with http status 200 (cache) not 304)

Question

I have web page which refers large number of JS, Images files. when teh page is loaded second time, 304 requests goes to the server. I would like to get http 200 (cache) status for cached object rather than 304.

I am using asp.net 4, iis 7.

Setting the Expiry header is not working, it still sends 304 requests. I want http status 200 (cache).

Please let me know if there is any technique for this.

Answer 1

You've said that setting the expiry doesn't help, but it does if you set the right headers.

Here's a good example: Google's library hosting. Here are the (relevant) headers Google sends back if you ask for a fully-qualified version of a library (e.g., jQuery 1.7.2, not jQuery 1., or jQuery 1.7.):

Date:Thu, 07 Jun 2012 14:43:04 GMT
Cache-Control:public, max-age=31536000
Expires:Fri, 07 Jun 2013 14:43:04 GMT

(Date isn't really relevant, I just include it so you know when the headers above were generated.) There, as you can see, Cache-Control has been set explicitly with a max-age of a year, and the Expires header also specifies an expiration date a year from now. Subsequent access (within a year) to the same fully-qualified library doesn't even result in an If-Modified-Since request to the server, because the browser knows the cached copy is fresh.

This description of caching in HTTP 1.1 in RFC 2616 should help.