URLSession.swift

    func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
        if let response = task.response as? HTTPURLResponse, response.statusCode >= 400 {
            return
        }
        
        // Workaround a CFNetwork bug which cause a write posix error.
        // Invalidates session and start tasks again.
        if let error = error as? POSIXError, error.code == .ENOENT {
            session.invalidateAndCancel()
            return
        }
        
        // Manage Errors
        if let error = error as? URLError, let dlItem = dlItem {
            let resumeData = error.userInfo[NSURLSessionDownloadTaskResumeData] as? Data
            let errorReasonNum = error.userInfo[NSURLErrorBackgroundTaskCancelledReasonKey] as? Int ?? Int.min
            let cancelledManually = error.code == .cancelled && errorReasonNum == Int.min
            let forceQuit = error.code == .cancelled && errorReasonNum == NSURLErrorCancelledReasonUserForceQuitApplication
            
            if !cancelledManually, let resumeData = resumeData {
                // Save data
            }
    }

    func urlSession(_ session: URLSession, didBecomeInvalidWithError error: Error?) {
        print("Invalidated session")
        // Reinstall session
    }