Is it possible to prevent an NSURLRequest from caching data or remove cached data following a request?

user_1221378 0
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On iPhone, I perform a HTTP request using NSURLRequest for a chunk of data. Object allocation spikes and I assign the data accordingly. When I finish with the data, I free it up accordingly - however instruments doesn't show any data to have been freed!

My theory is that by default HTTP requests are cached, however - I don't want my iPhone app to cache this data.

Is there a way to clear this cache after a request or prevent any data from being cached in the first place?

I've tried using all the cache policies documented a little like below:

NSMutableURLRequest *theRequest = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:url]];
theRequest.cachePolicy = NSURLRequestReloadIgnoringLocalCacheData;

but nothing seems to free up the memory!

caching cocoa-touch
6 Answers

Usually it's easier to create the request like this

NSURLRequest *request = [NSURLRequest requestWithURL:url
      cachePolicy:NSURLRequestReloadIgnoringCacheData
      timeoutInterval:60.0];

Then create the connection

NSURLConnection *conn = [NSURLConnection connectionWithRequest:request
       delegate:self];

and implement the connection:willCacheResponse: method on the delegate. Just returning nil should do it.

- (NSCachedURLResponse *)connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse {
  return nil;
}
user_331650

If you use NSURLConnection take a look at the delegate:

- (NSCachedURLResponse *)connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse

Return Value

The actual cached response to store in the cache. The delegate may return cachedResponse unmodified, return a modified cached response, or return nil if no cached response should be stored for the connection.

catlan_230280

If you're using NSURLSession, another solution to prevent request and parameters being written to the Cache.db iOS creates within the app's Caches directory, is to set the NSURLCache for the session's configuration to a 0 size memory and 0 size disk cache e.g.

let configuration = URLSessionConfiguration.default    
configuration.urlCache = URLCache(memoryCapacity: 0, diskCapacity: 0, diskPath: nil)
let session = URLSession(configuration: configuration)

or as mentioned above set at a global cache level 

URLCache.shared = URLCache(memoryCapacity: 0, diskCapacity: 0, diskPath: nil)

Presumably it's the 0 for disk size that stops iOS writing to disk but if you have a policy to reloadIgnoringLocalCacheData then you probably aren't interested in memory caching either.

Note This will prevent any Caches/Cache.db (requests & responses) or Caches/fsCachedData/ folder (response data) being created at all. We've decided to take this approach in an app for security purposes as we don't want our requests to be stored on disk cache ever.

If anyone knows is there's a way to stop only request caching but keep response data caching from the iOS URL Loading mechanism, I'd be interested to know. (there's no API or official documentation about this from what I can tell)

user_69445680
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