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nsurlconnectionnsurlrequestnsurlcachensurlconnectiondelegate

How to know if a NSURLResponse comes from cache?

I set NSURLCache on a specific folder (../../Application Support/Offline so it won't be deleted randomly by the OS), then I send a NSURLRequest with NSURLRequestReturnCacheDataElseLoad policy.

How can I tell that the response, handled by a class conforming to NSURLConnectionDelegate, comes from the cache or from the net?

Solution

  • Good article here about the problem:

    http://andrewmarinov.com/ioss-corenetwork-lying/

    Basically, from the NSHTTPURLResponse the status code is always 200

    So if you really need to know, you can check the item is in the cache before you make the request

    NSCachedURLResponse *cachedResponse = [[NSURLCache sharedURLCache] cachedResponseForRequest:request];
NSHTTPURLResponse *httpCacheResponse = (NSHTTPURLResponse *)cachedResponse.response;

    If so save the modified 'etag' or 'modified-date' header

    NSString* etag = httpCacheResponse.allHeaderFields[@"etag"];

    Then, in the response handler check the etag or modified-date is the same. If so, the response was from the cache!