尝试取消任务并再次重新启动 Swift 时获取零数据

Question

我想做的事情：
有时我的 URLSession 调用请求需要很长时间才能得到响应。这就是为什么如果它在 60 秒内没有给出响应，我会尝试再次调用该呼叫请求。 60 秒后，它将取消呼叫请求，然后提醒用户重试。当用户点击重试警报按钮时，它将从头开始再次调用呼叫请求。

我如何尝试：
我为会话任务声明一个全局变量，如下所示：

private weak var IAPTask: URLSessionTask?

这是我的调用请求函数：

代码 1

func receiptValidation(completion: @escaping(_ isPurchaseSchemeActive: Bool, _ error: Error?) -> ()) {
    let receiptFileURL = Bundle.main.appStoreReceiptURL
    guard let receiptData = try? Data(contentsOf: receiptFileURL!) else {
        //This is the First launch app VC pointer call
        completion(false, nil)
        return
    }
    let recieptString = receiptData.base64EncodedString(options: NSData.Base64EncodingOptions(rawValue: 0))
    let jsonDict: [String: AnyObject] = ["receipt-data" : recieptString as AnyObject, "password" : AppSpecificSharedSecret as AnyObject]

    do {
        let requestData = try JSONSerialization.data(withJSONObject: jsonDict, options: JSONSerialization.WritingOptions.prettyPrinted)
        let storeURL = URL(string: self.verifyReceiptURL)!
        var storeRequest = URLRequest(url: storeURL)
        storeRequest.httpMethod = "POST"
        storeRequest.httpBody = requestData
        let session = URLSession(configuration: URLSessionConfiguration.default)
        let task = session.dataTask(with: storeRequest, completionHandler: { [weak self] (data, response, error) in
            do {
                if let jsonResponse = try JSONSerialization.jsonObject(with: data!, options: JSONSerialization.ReadingOptions.mutableContainers) as? NSDictionary {
                    if let latestInfoReceiptObjects = self?.getLatestInfoReceiptObjects(jsonResponse: jsonResponse) {
                        self?.getCurrentTimeFromServer(completionHandler: { currentDateFromServer in
                            let purchaseStatus = self?.isPurchaseActive(currentDateFromServer: currentDateFromServer, latestReceiptInfoArray: latestInfoReceiptObjects)
                            completion(purchaseStatus!, nil)
                        })
                    }
                }
            } catch let parseError {
                completion(false, parseError)
            }
        })
        task.resume()
        self.IAPTask = task
    } catch let parseError {
        completion(false, parseError)
    }
}

我使用计时器每 60 秒调用一次此请求。但每当我尝试第二次调用它时，我都会得到 data 的 nil 值。

let task = session.dataTask(with: storeRequest, completionHandler: { [weak self] (data, response, error) in
    //Getting data = nil here for second time 
})

让我展示如何逐步取消全局变量。

首先在我设置计时器并调用呼叫请求的地方调用它。如果我在 10 秒内收到响应（出于测试目的，我将其设置为 10），我将取消计时器和呼叫请求任务并执行进一步的程序。 ：

代码2

func IAPResponseCheck(iapReceiptValidationFrom: IAPReceiptValidationFrom) {
    let infoDic: [String : String] = ["IAPReceiptValidationFrom" : iapReceiptValidationFrom.rawValue]
    self.IAPTimer = Timer.scheduledTimer(timeInterval: 10.0, target: self, selector: #selector(self.IAPTimerAction), userInfo: infoDic, repeats: false)
    IAPStatusCheck(iapReceiptValidationFrom: iapReceiptValidationFrom) { isSuccessful in
        if isSuccessful == true {
            self.IAPTimer.invalidate()
            self.IAPTask?.cancel()
            self.getTopVisibleViewController { topViewController in
                if let viewController = topViewController {
                    viewController.dismiss(animated: true, completion: nil)
                    self.hideActivityIndicator()
                }
            }
        }
    }
}  

这是我调用调用请求的完成。如果它只是给我响应，我会为完成设置一个真实值。

代码 3

func IAPStatusCheck(iapReceiptValidationFrom: IAPReceiptValidationFrom, complition: @escaping (_ isSuccessful: Bool)->()) {
    receiptValidation() { isPurchaseSchemeActive, error in
        if let err = error {
            self.onBuyProductHandler?(.failure(err))
        } else {
            self.onBuyProductHandler?(.success(isPurchaseSchemeActive))
        }
        complition(true)
    }
}

这是计时器操作，我从这里使计时器无效并取消任务调用请求，然后向用户显示弹出警报：

代码 4

@objc func IAPTimerAction(sender: Timer) {
    if let dic = (sender.userInfo)! as? Dictionary<String, String> {
        let val = dic["IAPReceiptValidationFrom"]!
        let possibleType = IAPReceiptValidationFrom(rawValue: val)
        self.IAPTimer.invalidate()
        self.IAPTask?.cancel()
        self.showAlertForRetryIAP(iapReceiptValidationFrom: possibleType!)
    }
}

最后，在警报“重试”操作中调用相同的初始响应检查函数。

代码 5

func showAlertForRetryIAP(iapReceiptValidationFrom: IAPReceiptValidationFrom) {
    DispatchQueue.main.async {
        let alertVC = UIAlertController(title: "Time Out!" , message: "Apple server seems busy. Please wait or try again.", preferredStyle: UIAlertController.Style.alert)
        alertVC.view.tintColor = UIColor.black
        let okAction = UIAlertAction(title: "Try again", style: UIAlertAction.Style.cancel) { (alert) in
            self.showActivityIndicator()
            self.IAPResponseCheck(iapReceiptValidationFrom: iapReceiptValidationFrom)
        }
        alertVC.addAction(okAction)
        DispatchQueue.main.async {
            self.getTopVisibleViewController { topViewController in
                if let viewController = topViewController {
                    var presentVC = viewController
                    while let next = presentVC.presentedViewController {
                        presentVC = next
                    }
                    presentVC.present(alertVC, animated: true, completion: nil)
                }
            }
        }
    }
}

这是我得到的响应：

▿ Optional<NSURLResponse>
  - some : <NSHTTPURLResponse: 0x281d07680> { URL: https://sandbox.itunes.apple.com/verifyReceipt } { Status Code: 200, Headers {
    Connection =     (
        "keep-alive"
    );
    "Content-Type" =     (
        "application/json"
    );
    Date =     (
        "Sun, 27 Feb 2022 17:28:17 GMT"
    );
    Server =     (
        "daiquiri/3.0.0"
    );
    "Strict-Transport-Security" =     (
        "max-age=31536000; includeSubDomains"
    );
    "Transfer-Encoding" =     (
        Identity
    );
    "apple-originating-system" =     (
        CommerceGateway
    );
    "apple-seq" =     (
        "0.0"
    );
    "apple-timing-app" =     (
        "154 ms"
    );
    "apple-tk" =     (
        false
    );
    b3 =     (
        "48d6c45fe76eb9d8445d83e518f01866-c8bfb32d2a7305e2"
    );
    "x-apple-jingle-correlation-key" =     (
        JDLMIX7HN245QRC5QPSRR4AYMY
    );
    "x-apple-request-uuid" =     (
        "48d6c45f-e76e-b9d8-445d-83e518f01866"
    );
    "x-b3-spanid" =     (
        c8bfb32d2a7305e2
    );
    "x-b3-traceid" =     (
        48d6c45fe76eb9d8445d83e518f01866
    );
    "x-daiquiri-instance" =     (
        "daiquiri:45824002:st44p00it-hyhk15104701:7987:22RELEASE11:daiquiri-amp-commerce-clients-ext-001-st"
    );
    "x-responding-instance" =     (
        "CommerceGateway:020115:::"
    );
} }

这是错误：

▿ Optional<Error>
  - some : Error Domain=NSURLErrorDomain Code=-999 "cancelled" UserInfo={NSErrorFailingURLStringKey=https://sandbox.itunes.apple.com/verifyReceipt, NSErrorFailingURLKey=https://sandbox.itunes.apple.com/verifyReceipt, _NSURLErrorRelatedURLSessionTaskErrorKey=(
    "LocalDataTask <17863FCF-EC4C-43CC-B408-81EC19B04ED7>.<1>"
), _NSURLErrorFailingURLSessionTaskErrorKey=LocalDataTask <17863FCF-EC4C-43CC-B408-81EC19B04ED7>.<1>, NSLocalizedDescription=cancelled}

Answer 1

似乎您重新初始化 URLSessionTask 的方式对我来说看起来不错，但我认为取消任务并使计时器无效时似乎会发生两次，正如您在 code 2 和 code 4 所以调试起来有点棘手。

从错误来看，它似乎是一种竞争条件（我可能是错的）类型的情况，当您初始化新的 URLSession 时，url 会话会被取消。

如果您想尝试，我可以提供一个更简单的替代方案：

在创建 URLRequest 时，不要使用计时器，而是使用 timeoutInterval

storeRequest.httpMethod = "POST" 
storeRequest.httpBody = requestData

// add this
storeRequest.timeoutInterval = timeOutInterval

然后在您的数据任务中，处理程序您可以检查是否由于超时而遇到错误：

let task = session.dataTask(with: storeRequest) { [weak self] (data, response, error) in
    
    do {
        
        if let error = error
        {
            // This checks if the request timed out based on your interval
            if (error as? URLError)?.code == .timedOut
            {
                // retry your request
                self?.receiptValidation(completion: completion)
            }
        }

在我看来，重试的完整机制似乎变得更加简单，您不需要管理 URLSessionTask 对象

这是完整的代码：

private func receiptValidation(completion: @escaping(_ isPurchaseSchemeActive: Bool,
                                                     _ error: Error?) -> ())
{
    // all your initial work to prepare your data and jsonDict data
    // goes here
    
    do {
        let requestData = try JSONSerialization.data(withJSONObject: jsonDict!,
                                                     options: .prettyPrinted)
        
        let storeURL = URL(string: self.verifyReceiptURL)!
        var storeRequest = URLRequest(url: storeURL)
        storeRequest.httpMethod = "POST"
        storeRequest.httpBody = requestData
        storeRequest.timeoutInterval = timeOutInterval
        
        let session = URLSession(configuration: .default)
        
        let task = session.dataTask(with: storeRequest)
        { [weak self] (data, response, error) in
            
            do {
                
                if let error = error
                {
                    // Error due to a timeout
                    if (error as? URLError)?.code == .timedOut
                    {
                        // retry your request
                        self?.receiptValidation(completion: completion)
                    }
                    
                    // some other error
                }
                
                if let data = data,
                   let jsonResponse
                    = try JSONSerialization.jsonObject(with: data,
                                                       options: .mutableContainers) as? NSDictionary
                {
                    // do your work or call completion handler
                    print("JSON: \(jsonResponse)")
                }
            }
            catch
            {
                print("Response error: \(error)")
            }
        }
        
        task.resume()
    }
    catch
    {
        print("Request creation error: \(error)")
    }
}

我正在重试请求当我弄清楚请求后立即超时，但是您会显示警报，而不是要求用户重试。

一旦他们点击重试，您所需要做的就是再次调用您的函数 receiptValidation(completion:completion) 因此，完成闭包可能就是需要存储的内容，以便 receiptValidation 可以再次重新启动。

我知道这并不能准确地找到您代码中的错误，但看看这是否可以帮助您的用例并简化事情？