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POStrange NSURLConnection caching behaviour
 

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  1. POStrange NSURLConnection caching behaviour
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    <p>I have a simple method that takes a url and loads it from the server:</p> <pre><code>- (void)loadURL:(NSString*)url { NSMutableURLRequest* request = [[NSMutableURLRequest alloc] init]; request.HTTPMethod = @"GET"; request.URL = [NSURL URLWithString:url]; NSHTTPURLResponse* response; [NSURLConnection sendSynchronousRequest:request returningResponse:&amp;response error:nil]; } </code></pre> <p>The server returns a response with max-age of 1 day.</p> <p>Problem is that when I run these 3 lines repeatedly, 2 of them randomly miss the cache and reload the response:</p> <pre><code>[self loadURL:@"http://192.168.0.105:8080/users/51bdbc73808897302f000001/avatar?size=200x200&amp;access_token=abcdefghijklmnopqrstuvwxyzzp77eDLqub3EWfXGe4c09RoyipmXgcENwfE6EV9yzvgp5VTSZww"]; [self loadURL:@"http://192.168.0.105:8080/users/51ee9d4e263d08fe04000003/avatar?size=200x200&amp;access_token=abcdefghijklmnopqrstuvwxyzzp77eDLqub3EWfXGe4c09RoyipmXgcENwfE6EV9yzvgp5VTSZww"]; [self loadURL:@"http://192.168.0.105:8080/users/51d17b81de38c60b20000006/avatar?size=200x200&amp;access_token=abcdefghijklmnopqrstuvwxyzzp77eDLqub3EWfXGe4c09RoyipmXgcENwfE6EV9yzvgp5VTSZww"]; </code></pre> <p>If I add some random unique data (&amp;x, &amp;y, &amp;z) to each request's query string it fixes the problem:</p> <pre><code>[self loadURL:@"http://192.168.0.105:8080/users/51bdbc73808897302f000001/avatar?size=200x200&amp;access_token=abcdefghijklmnopqrstuvwxyzzp77eDLqub3EWfXGe4c09RoyipmXgcENwfE6EV9yzvgp5VTSZww&amp;x"]; [self loadURL:@"http://192.168.0.105:8080/users/51ee9d4e263d08fe04000003/avatar?size=200x200&amp;access_token=abcdefghijklmnopqrstuvwxyzzp77eDLqub3EWfXGe4c09RoyipmXgcENwfE6EV9yzvgp5VTSZww&amp;y"]; [self loadURL:@"http://192.168.0.105:8080/users/51d17b81de38c60b20000006/avatar?size=200x200&amp;access_token=abcdefghijklmnopqrstuvwxyzzp77eDLqub3EWfXGe4c09RoyipmXgcENwfE6EV9yzvgp5VTSZww&amp;z"]; </code></pre> <p>Also, if I reduce the length of query strings to 80 chars it fixes the problem as well:</p> <pre><code>[self loadURL:@"http://192.168.0.105:8080/users/51bdbc73808897302f000001/avatar?size=200x200&amp;access_token=abcdefghijklmnopqrstuvwxyzzp77eDLqub3EWfXGe4c09Royipm"]; [self loadURL:@"http://192.168.0.105:8080/users/51ee9d4e263d08fe04000003/avatar?size=200x200&amp;access_token=abcdefghijklmnopqrstuvwxyzzp77eDLqub3EWfXGe4c09Royipm"]; [self loadURL:@"http://192.168.0.105:8080/users/51d17b81de38c60b20000006/avatar?size=200x200&amp;access_token=abcdefghijklmnopqrstuvwxyzzp77eDLqub3EWfXGe4c09Royipm"]; </code></pre> <p>What's going on? Is this a bug in iOS? How can I fix it?</p> <p>P.S: I've tested this in an empty application with no extra stuff both on iOS 5 and 6.</p>
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    1. COHow do you verify whether the URL loading system reads from the cache or accesses the remote server? What cache-control headers are set in the request? Does the client use a cache at all? Note that a cache may ignore a server's specified expiration time.
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    2. CO@CouchDeveloper I run 'tail -f server.log | grep avatar' to see requests in realtime as they come in. Server sets the Cache-Control header with a value of 'max-age=86400'. And the client has NSURLCache set.
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    3. COYou need to check the cache-control headers from the request. As mentioned, a client can ignore the expiration date set from a server or proxy. Caching is quite complex: [13 Caching in HTTP](http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html)
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