ios - Objective-c Check file size from URL without downloading

Question

I need to check the size of file from a URL. I get the file size perfectly when downloading file with AFNetworking.

AFHTTPRequestOperation *operation = [client HTTPRequestOperationWithRequest:request
                                                                        success:^(AFHTTPRequestOperation *operation, id responseObject) {
                                                                            // Success Callback

                                                                        } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
                                                                            // Failure Callback

                                                                        }];

and get file size in another block

[operation setDownloadProgressBlock:^(NSUInteger bytesRead, long long totalBytesRead, long long totalBytesExpectedToRead) {

    }];

But i need to check file size before initiating download request, so that i can prompt to user. I have also tried another method

NSURL *url = [NSURL URLWithString:@"http://lasp.colorado.edu/home/wp-content/uploads/2011/03/suncombo1.jpg"];
NSData *data = [NSData dataWithContentsOfURL:url];
NSLog(@"original = %d", [data length]);

But it blocks the UI, coz it download all data to calculate its size. Is there any way to check file size before downloading? Any help is appreciated.

Answer 1

If the server supports it you can make a request to just get the headers (HEAD, as opposed to GET) without the actual data payload and this should include the Content-Length.

If you can't do that then you need to start the download and use expectedContentLength of the NSURLResponse.

---

Basically, create an instance of NSMutableURLRequest and call setHTTPMethod: with the method parameter set to @"HEAD" (to replace the default which is GET). Then send that to the server as you currently request for the full set of data (same URL).