如何在iOS中检查是否已订阅

Question

我实现了订阅（自动续购）。我想检查我的应用程序每次启动时用户是否仍在订阅。我尝试使用下面的代码，但是即使用户未订阅，它也总是返回“成功”。 如何查看用户订阅状态？

func receiptValidation() {

    let SUBSCRIPTION_SECRET = "password"
    let receiptPath = Bundle.main.appStoreReceiptURL?.path
    if FileManager.default.fileExists(atPath: receiptPath!){
        var receiptData:NSData?
        do{
            receiptData = try NSData(contentsOf: Bundle.main.appStoreReceiptURL!, options: NSData.ReadingOptions.alwaysMapped)
        }
        catch{
            print("ERROR: " + error.localizedDescription)
        }
         //let receiptString = receiptData?.base64EncodedString(options: NSData.Base64EncodingOptions(rawValue: 0))
        let base64encodedReceipt = receiptData?.base64EncodedString(options: NSData.Base64EncodingOptions.endLineWithCarriageReturn)

        print(base64encodedReceipt!)


        let requestDictionary = ["receipt-data":base64encodedReceipt!,"password":SUBSCRIPTION_SECRET]

        guard JSONSerialization.isValidJSONObject(requestDictionary) else {  print("requestDictionary is not valid JSON");  return }
        do {
            let requestData = try JSONSerialization.data(withJSONObject: requestDictionary)
            let validationURLString = "https://sandbox.itunes.apple.com/verifyReceipt"  // this works but as noted above it's best to use your own trusted server
            guard let validationURL = URL(string: validationURLString) else { print("the validation url could not be created, unlikely error"); return }
            let session = URLSession(configuration: URLSessionConfiguration.default)
            var request = URLRequest(url: validationURL)
            request.httpMethod = "POST"
            request.cachePolicy = URLRequest.CachePolicy.reloadIgnoringCacheData
            let task = session.uploadTask(with: request, from: requestData) { (data, response, error) in
                if let data = data , error == nil {
                    do {
                        let appReceiptJSON = try JSONSerialization.jsonObject(with: data)
                        print("success. here is the json representation of the app receipt: \(appReceiptJSON)")
                       // always through here
                    } catch let error as NSError {
                        print("json serialization failed with error: \(error)")
                    }
                } else {
                    print("the upload task returned an error: \(error)")
                }
            }
            task.resume()
        } catch let error as NSError {
            print("json serialization failed with error: \(error)")
        }

    }
}