iOS Swift - URLSessionDataTask doesn't get updated JSON data on refresh

Question

I have a simple app where I get data from a JSON file stored in my own server in this way - I'm using SwiftyJSON:

func queryData(_ fileName:String) {
        guard let url = URL(string: JSON_PATH + fileName + ".json") else {return} // JSON_PATH + fileName + ".json" is the complete path to my db.json file (see below)
        let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
            guard let dataResponse = data, error == nil else {
                self.simpleAlert(error!.localizedDescription)
                return
            }
            let jsonData = try! JSON(data: dataResponse)
            print("ARRAY: \(jsonData)")
        }
        task.resume()
    }

Here's my db.json file:

[
    {
        "objID":"GNoW3vszYz",
        "string":"First (1) string",
        "pointer":["pointer","yN76TF43i8"],
        "boolean":true,
        "number":123,
        "fileURL":"https://example.com/uploads/01.jpg",
        "array":["aaa","bbb","ccc"]
    },
    {
        "objID":"yN76TF43lD",
        "string":"Second (2) string",
        "pointer":["pointer","GNoN3vsz2I"],
        "boolean":false,
        "number":12.55,
        "fileURL":"https://example.com/uploads/02.jpg",
        "array":["aaa","eee","fff"]
    }
]

The problem is that if I manually edit my db.json file, let's say I change "number":123, into "number":5555, save and upload it again in my server and run my app again, the console log shows me the same JSON data as above, like if I had changed nothing.

I've tried to kill the app and run it again 2-3 times with Xcode, no success, the only way I can get the updated JSON file data is to delete the app and install it again via Xcode.

Is there a way to always get updated JSON data with URLSessionDataTask?
Thanks.

If your server has "Cache-Control" enabled URLSession will cache data.Create URLSessionConfiguration and set its requestCachePolicy to reloadIgnoringLocalCacheData.To check this print response and check the value of "Cache-Control" — Vikky, Jul 31 '19 at 08:11

score 6 · Accepted Answer · answered Jul 31 '19 at 08:15

This is due to URLSession caching the data from the server, this is usually sent in the header of the json file coming from the server.

If you can't change anything on the server side then on you can just use the .ephemeral which apple documents here

use this code

let configuration = URLSessionConfiguration.ephemeral
let session = URLSession(configuration: configuration)

.ephemeral is used for data that will only be stored in ram and nothing will be stored on disk

Thanks, this works like a charm, and it's short and easy! – Frank Eno Jul 31 '19 at 08:18 — Frank Eno, Jul 31 '19 at 08:18

score 4 · Answer 2 · answered Jul 31 '19 at 08:08

4

I can think of two ways.

1) add current date time at the end of your url

2) Disable Local Cache.

For 1)

extension Date {
    func currentTimeMillis() -> Int64 {
        return Int64(self.timeIntervalSince1970 * 1000)
    }
}

let url = URL(string: JSON_PATH + fileName + ".json?q=\(Date().currentTimeMillis())")

For 2)

let config = URLSessionConfiguration.default
config.requestCachePolicy = .reloadIgnoringLocalCacheData
config.urlCache = nil

let session = URLSession.init(configuration: config)

Taken From this SO

answered Jul 31 '19 at 08:08

Sahil Manchanda

9,812
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Thanks for your answer, I'd rather using .ephemeral though. – Frank Eno Jul 31 '19 at 08:19
@xscoder np .ephemeral is the right approach. I didn't know about that option. – Sahil Manchanda Jul 31 '19 at 08:23

score 1 · Answer 3 · answered Jan 19 '22 at 00:27

This behavior also can happen with text files (and other non-JSON files) stored on a web server and by using URLSession to fetch data from that text file. .ephemeral also works in this case.

if let url = URL(string: "http://www.somerandomsite.com/mydata.txt") {
     let configuration = URLSessionConfiguration.ephemeral
     var urlSession = URLSession(configuration: configuration).dataTask(with: url) {(data, response, error) in
           if let error = error {
                print(error)
           }
      if var textFile = String(data: data!, encoding: .utf8){
           print(textFile)
      }
}
urlSession.resume()

iOS Swift - URLSessionDataTask doesn't get updated JSON data on refresh

3 Answers3