Automatically expire NSURLCache with max-age=0

Question

I am using NSURLCache with AFNetworking. Caching works fine but there is no way to check if a response was actually retrieved from cache. To check if a cached version is available, I use

[[NSURLCache sharedURLCache] cachedResponseForRequest:_request];

to check for a cached version of my file.

My server is sending the following headers:

Cache-Control:public, must-revalidate, max-age=0
ETag:"317a405bf9f69346c1f0438736a3d02e"

This should basically make sure that the cached response is stale immediately after download. However, cachedResponseForRequest: still loads the previously cached version on disk, even if it actually is expired.

• Does NSURLCache never expire or am I not sending the correct headers, etc?
• Am I missing something else here?

EDIT

I have also tried to send

Expires: "Mon, 27 May 2013 14:34:50 GMT"

header and the response is still returned from the cache, even if it already expired. I get the feeling that NSURLCache is not working correctly...

Answer 1

NSURLCache is used automatically by most of the iOS network APIs (such as NSURLConnection). You just need to instantiate a NSURLCache object and set it using [NSURLCache setSharedURLCache:] somewhere before making any network request.

Even if max-age=0 is set, if ETag is provided, NSURLCache has to store the response so that it can send next request with If-None-Match request header set to the previous ETag value. If server replies with 304, it returns the cached response.

So I think cachedResponseForRequest: is returning the cached response regardless of whether it's actually valid or not.

You won't need to get the cache directly. It's all managed transparently by iOS.