Cache-Control header default to no-cache on subsequent request when using HttpCacheControlPolicy

[CallMeLaNN]

I am using AttributeBasedCacheControlPolicy with CacheControlHeaderValue that cache privately for a couple of days by default.

When I use HttpCacheControlPolicy(false, 600) in an action, the first request responded as expected "Cache-Control: public, must-revalidate, max-age=600". However the subsequent request (after 600 second or expired) , contain "Cache-Control: no-cache" even though the HTTP status is correct "304 Not Modified". I expect it should always "Cache-Control: public, must-revalidate, max-age=600" to perform 'sliding' expiration.

I inspect using Fiddler

[CallMeLaNN]

Update:

Without using HttpCacheControlPolicy attribute, the default cache config like the code below also only applied on the first request as "Cache-Control: no-transform, must-revalidate, max-age=600". The subsequent request will be "304 Not Modified" with "Cache-Control: no-cache".

        cachingHandler.CacheControlHeaderProvider = (request, cfg) =>
        {
            return new System.Net.Http.Headers.CacheControlHeaderValue()
            {
                Private = false,
                MustRevalidate = true,
                NoTransform = true,
                MaxAge = TimeSpan.FromSeconds(600)
            };
        };

[aliostad]

The behaviour is correct. Cache Header directives are irrelevant for a 304 response since the cache headers must be sent with the original response:

If the status code is 304 (Not Modified), the cache uses the entity- body stored in the cache entry as the entity-body of this outgoing response.

As you can see, there is no mention of headers here. Hope this helps.

In terms of examples outside, sites implement 304 differently. I have seen one that sends cache control and another only ETag. As I said the headers are irrelevant.