background-save-data.swift

class ViewController: UIViewController, URLSessionTaskDelegate {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let url = URL(string: "http://0.0.0.0")!
        let data = "Secret Message".data(using: .utf8)!
        
        let tempDir = FileManager.default.temporaryDirectory
        let localURL = tempDir.appendingPathComponent("throwaway")
        try? data.write(to: localURL)
        
        let request = URLRequest(url: url)
        let config = URLSessionConfiguration.background(withIdentifier: "uniqueId")
        let session = URLSession(configuration: config, delegate: self, delegateQueue: nil)
        let task = session.uploadTask(with: request, fromFile: localURL)
        task.resume()
    }
    
    func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
        print("We're done here")
    }
}