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

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).

Answer 2

here is the code:
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:candidateURL];
[request setHTTPMethod:#"HEAD"];
AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject)
{
NSLog(#"Content-lent: %lld", [operation.response expectedContentLength]);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
NSLog(#"Error: %#", error);
}];