R – Why doesn’t the expires headers make the files stay in cache

cachingfirefox

I'm using valid expires and no-cache headers for my static files and they stay cached for as long as I keep browsing, but when I close my browser and use it back after a while I see the static files loading again, even when not refreshing with ctrl (+ shift) + r

I'm using Firefox, cache size set to 250MB and I don't let it remove any private or cached data.

Headers:
Accept-Ranges: bytes
Cache-Control: max-age=29030400, public
Content-Length: 142061
Content-Type: image/png
Date: Tue, 08 Dec 2009 19:18:43 GMT
Expires: Tue, 09 Nov 2010 19:18:43 GMT
Last-Modified: Sun, 18 Jan 2009 18:33:48 GMT
Server: Apache/2.2.14 (EL)

Best Answer

Which version of Firefox? Is the server sending Etags for the static files? You can view details about Firefox cache by going to the address about:cache and poking around. That will give you an idea of what Firefox is caching.

Update: After looking at your header tags, it seems as if the max-age value is set to a date that is way in the past and that is overriding the the value being set in the Expires header. See the HTTP 1.1 protocol definition at: http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9.3.

If a response includes both an Expires header and a max-age directive, the max-age directive overrides the Expires header, even if the Expires header is more restrictive. This rule allows an origin server to provide, for a given response, a longer expiration time to an HTTP/1.1 (or later) cache than to an HTTP/1.0 cache. This might be useful if certain HTTP/1.0 caches improperly calculate ages or expiration times, perhaps due to desynchronized clocks.

You will have to modify your Cache-Control header being sent by the server.

Related Solutions

Asp.net-mvc – ASP.NET MVC: Make browser cache images from action

First thing to note is that when you hit F5 (refresh) in Chrome, Safari or IE the images will be requested again, even if they've been cached in the browser.

To tell the browser that it doesn't need to download the image again you'll need to return a 304 response with no content, as per below.

Response.StatusCode = 304;
Response.StatusDescription = "Not Modified";
Response.AddHeader("Content-Length", "0");

You'll want to check the If-Modified-Since request header before returning the 304 response though. So you'll need to check the If-Modified-Since date against the modified date of your image resource (whether this be from the file or stored in the database, etc). If the file hasn't changed then return the 304, otherwise return with the image (resource).

Here are some good examples of implementing this functionality (these are for a HttpHandler but the same principles can be applied to the MVC action method)

Tomcat – IE 11 ignoring Cache Control header in response

There is Microsoft's own documentation on cache-control.

Short answer: you have to use Pragma: no-cache, Cache-Control: no-cache and Expires all together.

Update 2019-01-24

The above instructions are for disabling caching, while the answer to being able to force caching can be found in this fine SO answer: Make IE to cache resources but always revalidate

Best Answer

Related Solutions

Asp.net-mvc – ASP.NET MVC: Make browser cache images from action

Tomcat – IE 11 ignoring Cache Control header in response

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