How to retry network request that has failed

Question

I'm somewhat new to Swift/iOS and have been working with URLSession to make a network call to a REST API. Here's the (slightly cleaned up) code that I'm using to make the network request:

enum ApiRequestError: Error {
    case statusCodeOtherThan200(statusCode: Int)
    // other error cases will be added here
}

enum ApiResponse {
    case success(Data)
    case failure(Error)
}

typealias myCompletionHandler = (ApiResponse) -> ()

func sampleRestCall(token: String, completionHandler: @escaping myCompletionHandler) {

    let url = URL(string: "https://www.server.com")
    // removed headers, parameters, etc. for brevity
    let request = URLRequest(url: url!)
    URLSession.shared.dataTask(with: request) { (data, response, error) in
        if let error = error {
            myCompletionHandler(.failure(error))
            return
        } else if let data = data, let response = response as? HTTPURLResponse {
            if response.statusCode == 200 {
                myCompletionHandler(.success(data))
            } else {
                print("Server returned unexpected response: \(response.statusCode) - (\(HTTPURLResponse.localizedString(forStatusCode: response.statusCode)))")
                completionHandler(.failure(ApiRequestError.statusCodeOtherThan200(statusCode: response.statusCode)))
            }
        }
    }.resume()
}

func testSampleRestCall() {
    sampleRestCall(token: "12345678") { apiResponse in
        switch apiResponse {
        case .success(let data):
            print("JSON response:")
            if let jsonResponse = String(data: data, encoding: String.Encoding.utf8) {
                print("\(jsonResponse)")
            }
        case .failure(let error):
            print("Failure! \(error)")
        }
    }
}

The code works well enough but I'm wondering about how to retry a network request if it fails. I understand that a request could fail for lots of different reasons but for the sake of this question, I'd like to focus on a scenario where the failure is only temporary and could be solved simply by retrying the request after a few seconds. Ideally, I'd like to have some kind of "retry" wrapper that will allow me to specify that a call should be retried X times before giving up and notifying the user. As an added feature, I would probably insert a small wait between each retry. I've found a couple of libraries that do something like this but I'd like to understand how to do it myself rather than just relying on a library. If anyone has a suggestion on achieving this kind of functionality, I would certainly appreciate the info!

Answer 1

Try this

case .failure(let error):
        print("Failure! \(error)")
       if(self.counter<3)
        {
           self.testSampleRestCall()                
            counter = counter+1           
         }
         else
         {
              // notify user check if this a thread other than main to wrap code in main queue

          }


    }