how can I receive data from Api by parts?

Question

I have to read the file from API, but its size is about 1.6 MB, and it takes a long time. How can I read it by parts of 21 bytes?
Received data: ScreenShot
I have this code, which read all file:

func getLogBinData() {
    if let url = URL(string: httpString + "log.bin") {
        var request = URLRequest(url: url)
        request.httpMethod = "GET"
        let task = URLSession.shared.dataTask(with: request, completionHandler: { (data, response, error) in
            if let data = data {
                print()
            }
        })
        task.resume()
    }
} 

I tried next code, but delegate method don't work. Why?
I adding button, which print in console task.countOfBytesReceived, and it works well
code:

class ViewController: UIViewController, URLSessionTaskDelegate, URLSessionDelegate, URLSessionDataDelegate {

    var task = URLSessionDataTask()

    var httpString = "here ip dress of my API"

    override func viewDidLoad() {
        super.viewDidLoad()
        getLogBinData()
    }


    func getLogBinData() {
        if let url = URL(string: httpString + "log.bin") {
            var request = URLRequest(url: url)
            request.httpMethod = "GET"
            task = URLSession.shared.dataTask(with: request)
            task.resume()
        }
    }

    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
        if dataTask.countOfBytesReceived >= 20 {
            print(dataTask.countOfBytesReceived)
        }
    }

}

Answer 1

You would need to use the URLSession delegate methods to monitor the receive progress of the download/request.

• URLSessionDataDelegate
• URLSessionDownloadDelegate

These protocols contain methods like func urlSession(URLSession, dataTask: URLSessionDataTask, didReceive: Data) which will pass you the received data chunks as they come in.

You will need to keep track of how much data you have received and parsed, once you have a new amount of data >= 21 bytes you can append it to your data and read the next packet.