Right way of determining internet speed in iOS 8

You code snippet was taken from this answer. I’ve updated it to use URLSession. The Swift rendition is below:

class ViewController: UIViewController {
    var startTime: CFAbsoluteTime!
    var bytesReceived: Int = 0
    var speedTestCompletionHandler: ((Result<Double, Error>) -> Void)?

    override func viewDidLoad() {
        super.viewDidLoad()

        testDownloadSpeed(timeout: 5) { result in
            switch result {
            case .failure(let error):              print(error)
            case .success(let megabytesPerSecond): print(megabytesPerSecond)
            }
        }
    }

    /// Test speed of download
    ///
    /// Test the speed of a connection by downloading some predetermined resource. Alternatively, you could add the
    /// URL of what to use for testing the connection as a parameter to this method.
    ///
    /// - parameter timeout:             The maximum amount of time for the request.
    /// - parameter completionHandler:   The block to be called when the request finishes (or times out).
    ///                                  The error parameter to this closure indicates whether there was an error downloading
    ///                                  the resource (other than timeout).
    ///
    /// - note:                          Note, the timeout parameter doesn't have to be enough to download the entire
    ///                                  resource, but rather just sufficiently long enough to measure the speed of the download.

    func testDownloadSpeed(timeout: TimeInterval, completionHandler: @escaping (Result<Double, Error>) -> Void) {
        let url = URL(string: "https://insert.your.site.here/yourfile")!

        startTime = CFAbsoluteTimeGetCurrent()
        bytesReceived = 0
        speedTestCompletionHandler = completionHandler

        let configuration = URLSessionConfiguration.ephemeral
        configuration.timeoutIntervalForResource = timeout
        let session = URLSession(configuration: configuration, delegate: self, delegateQueue: nil)
        session.dataTask(with: url).resume()
        session.finishTasksAndInvalidate()
    }
}

extension ViewController: URLSessionDataDelegate {
    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
        bytesReceived += data.count
    }
}

extension ViewController: URLSessionDelegate {
    func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
        let stopTime = CFAbsoluteTimeGetCurrent()
        let elapsed = stopTime - startTime
        guard elapsed != 0 && (error == nil || (error as? URLError)?.code == .timedOut) else {
            speedTestCompletionHandler?(.failure(error ?? URLError(.unknown)))
            return
        }

        let speed = elapsed != 0 ? Double(bytesReceived) / elapsed / 1024.0 / 1024.0 : -1
        speedTestCompletionHandler?(.success(speed))
    }
}