Retry with callback in Swift

Question

I wrote the following function:

    func getStringFromRequest(jsonString:NSDictionary, callback: (NSDictionary, String!) -> Void) {
    let request = NSMutableURLRequest(URL: NSURL(string: "https://***.*.*.**:****" )!)
    var result = NSDictionary()

    do {
        request.HTTPBody = try NSJSONSerialization.dataWithJSONObject(jsonString, options: [])
    } catch{
        //error = error1
        request.HTTPBody = nil
    }
    request.timeoutInterval = (number as! NSTimeInterval)
    request.HTTPMethod = "POST"
    request.setValue("application/json", forHTTPHeaderField: "Content-Type")
    request.setValue("gzip", forHTTPHeaderField: "Accept-encoding")

    let configuration = NSURLSessionConfiguration.defaultSessionConfiguration()

    let session = NSURLSession(configuration: configuration, delegate: self, delegateQueue:NSOperationQueue.mainQueue())
    print("--------------------------------NSURLSession Request-------------------------------------------------->:\n \(jsonString)")
    print(NSDate())


    let task = session.dataTaskWithRequest(request){
        (data: NSData?, response: NSURLResponse?, error: NSError?) -> Void in

        if let httpResponse = response as? NSHTTPURLResponse {
            if httpResponse.statusCode != 200 {
                print("response was not 200: \(response)")
                return
            }
            else
            {
                print("response was 200: \(response)")
                print("Data for 200: \(data)")

                result = ((try? NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions())) as? NSDictionary)!
                print("--------------------------------NSURLSession Response-------------------------------------------------->:\n \(result)")
                callback(result, nil)
                return
            }
        }
        if (error != nil) {
            print("error request:\n \(error)")
            print("=======================================================")
            return
        }
    }
    task.resume()
}

The above function is working fine. But I want to implement retry means when this function gets an error in the response it should retry a particular number of time.