IOS: Check existence of remote file - ios

Question

Is there any resource efficient way (something that does not tie up the main thread) in IOS to check the existence of a remote file?
I have user images stored on a server. While there is a consistent url scheme, some images are .jpg, others are .gif, etc. so to get the correct image name, I need to check does user/file.gif exist, user/file.jpg exist etc. in order to download the file to the IOS app.
I found this code in another answer in IOS
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:[NSURL URLWithString:urlString]];
[request setHTTPMethod:#"HEAD"];
NSURLConnection *conn = [[NSURLConnection alloc] initWithRequest:request delegate:self];
But I am not sure how to use it. Ideally, I would like to get a boolean yes or no as to whether the .gif file exists, the .jpg file exists etc for the users profile pic so I can fill in the correct name to download the user pic.
The alternative would be to write a service on the back end to return the file but wondering if it can all be done in IOS.
Thanks for any suggestions.

Answer 1

**Use this function below to check whether file exists at specified url**
+(void)checkWhetherFileExistsIn:(NSURL *)fileUrl Completion:(void (^)(BOOL success, NSString *fileSize ))completion
{
//MAKING A HEAD REQUEST
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:fileUrl];
request.HTTPMethod = #"HEAD";
request.timeoutInterval = 3;
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue currentQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError)
{
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *) response;
if (connectionError == nil) {
if ((long)[httpResponse statusCode] == 200)
{
//FILE EXISTS
NSDictionary *dic = httpResponse.allHeaderFields;
NSLog(#"Response 1 %#",[dic valueForKey:#"Content-Length"]);
completion(TRUE,[dic valueForKey:#"Content-Length"]);
}
else
{
//FILE DOESNT EXIST
NSLog(#"Response 2");
completion(FALSE,#"");
}
}
else
{
NSLog(#"Response 3");
completion(FALSE,#"");
}
}];
}