**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,@"");
         }

     }];
}