Question

My app has to download profile pictures from facebook. The code that I wrote to download images works well with image url that has direct links (e.g.: http://www.mydomain.com/profile_picture.png)

But it produces an error for facebook urls (e.g.: http://graph.facebook.com/100000741043402/picture)

Following is the code:

NSURLRequest *imageRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:imageUrl] cachePolicy:NSURLRequestReturnCacheDataDontLoad timeoutInterval:30.0];
    AFImageRequestOperation *operation = [AFImageRequestOperation imageRequestOperationWithRequest:imageRequest
                                                                              imageProcessingBlock:nil
                                                                                         cacheName:@"nscache"
                                                                                           success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image){                                                                                                                                                                                                   profilePicture.image = image;

                                                                                               [profilePicture.layer setBorderColor: [[UIColor colorWithRed:137.0/255.0 green:137.0/255.0 blue:137.0/255.0 alpha:1.0] CGColor]];
                                                                                               [profilePicture.layer setBorderWidth: 2.0];
                                                                                           }
                                                                                           failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error){ NSLog(@"%@",[error description]); }
                                          ];
    [operation start];

And following is the response:

Error Domain=NSURLErrorDomain Code=-1008 "resource unavailable" UserInfo=0x97e0ae0 {NSErrorFailingURLStringKey=http://graph.facebook.com/100000741043402/picture, NSErrorFailingURLKey=http://graph.facebook.com/100000741043402/picture, NSLocalizedDescription=resource unavailable, NSUnderlyingError=0xa3559b0 "resource unavailable"}

Any tips/suggestions would be highly appreciated.

Answer 1

If you use curl to dump the headers of the entire HTTP conversation, you’ll see:

$curl -IL http://graph.facebook.com/100000741043402/picture
HTTP/1.1 302 Found
Access-Control-Allow-Origin: *
Cache-Control: private, no-cache, no-store, must-revalidate
Content-Type: image/jpeg
Expires: Sat, 01 Jan 2000 00:00:00 GMT
Location: http://profile.ak.fbcdn.net/hprofile-ak-snc6/186199_100000741043402_1626005174_q.jpg
Pragma: no-cache
X-FB-Rev: 693801
X-FB-Debug: dB4yzLkbQuq46xPMq51wruVSccPCm94U4tePFC/VKoc=
Date: Thu, 13 Dec 2012 07:00:39 GMT
Connection: keep-alive
Content-Length: 0

HTTP/1.1 200 OK
Content-Type: image/jpeg
Content-Length: 3055
Last-Modified: Fri, 01 Jan 2010 00:00:00 GMT
X-Backend: hs478.snc6
X-BlockId: 186199
X-Object-Type: PHOTO_PROFILE
Access-Control-Allow-Origin: *
Cache-Control: max-age=1209600
Expires: Thu, 27 Dec 2012 07:00:40 GMT
Date: Thu, 13 Dec 2012 07:00:40 GMT
Connection: keep-alive

So FB is redirecting you to the profile picture, but NSURLRequest doesn’t follow redirects by itself. This post (Handling redirects correctly with NSURLConnection) shows how you can handle this, with the main lesson being that you have to follow the redirects until you end up with the 200 response that will indicate the terminal URL.