How to check resume capability of current URLSessionDownloadTask?

Currently i'm working on downloading a file from server, and this is working good.

class Downloader:NSObject,URLSessionDownloadDelegate {
    /*
     SOME PROPERTIES & DECLARATIONS
     */

    override init() {
        super.init()
        let backgroundSessionConfiguration = URLSessionConfiguration.background(withIdentifier: url.absoluteString)
        backgroundSessionConfiguration.networkServiceType = .default
        self.defaultSession = URLSession(configuration: backgroundSessionConfiguration, delegate: self, delegateQueue: OperationQueue.main)
    }

    func start(_ block:DownloaderCompletionHandler?) {
        guard self.input == nil else { return }
        guard self.output == nil else { return }
        if let data = self.resumableData {
            self.downloadTask = self.defaultSession.downloadTask(withResumeData: data)
        }else {
            let request = URLRequest(url: self.input!, cachePolicy: .useProtocolCachePolicy, timeoutInterval: 0.60)
            self.downloadTask = self.defaultSession.downloadTask(with: request)
        }
        self.downloadTask.resume()
    }
    func pause() {
        self.downloadTask.cancel { (data) in
            self.resumableData = data
        }
    }
}

please , guid me on this situation. THANKS IN ADVANCE