StoreKit: Receipt validation problems - ios

Question

I am struggling with this for quite some time. First off our problem: In our app we have renewable subscriptions and a one time purchase. I want to read from the receipt if a subscription is still valid or if it is a one time purchase (which is valid lifetime). First off one question:
What does this file contain?
NSData* receiptData = [NSData dataWithContentsOfURL:[[NSBundle mainBundle] appStoreReceiptURL]];
I only have to check if this file is present and if not I request a refresh correct? But if a subscription has been auto renewed do I need to refresh this file as well? Or does the receipt get updated when I verify it with the apple server?
Ok now my process is as follows and starts with the payment queue:
- (void)paymentQueue:(SKPaymentQueue *)queue updatedTransactions:(NSArray *)transactions {
if(SANDBOX_TESTING) NSLog(#"updated transaction");
[self refreshReceipt];
self.transactionCount = [transactions count];
if(SANDBOX_TESTING) NSLog(#"Number of transactions: %ld", (long)self.transactionCount);
for (SKPaymentTransaction * transaction in transactions) {
switch (transaction.transactionState) {
case SKPaymentTransactionStatePurchased:
[self completeTransaction:transaction restore:NO];
[[SKPaymentQueue defaultQueue] finishTransaction:transaction];
break;
case SKPaymentTransactionStateFailed:
[self failedTransaction:transaction];
[[NSNotificationCenter defaultCenter] postNotificationName:IAPProductPurchaseStateChangedNotification object:nil];
[[SKPaymentQueue defaultQueue] finishTransaction:transaction];
break;
case SKPaymentTransactionStateRestored:
NSLog(#"Restore transaction started received");
//Only restore transactions that haven't been restored yet AND if they have a still supported identifier
//IMPORTANT: Original Transaction is only set (transaction.originalTransaction.transactionIdentifier) if it is a restore!
//This first if only helps in a restore case, that not all subscription renewals get looped. If a valid subscription is found for one subscription type, the loop runs only once
if(![self.restoredTransactions containsObject:transaction.payment.productIdentifier] && [[self getAllPurchaseIDsForPlatformType:PURCHASESONPLATFORM_IOS] containsObject:transaction.payment.productIdentifier]){
[self completeTransaction:transaction restore:YES];
} else {
self.transactionCount--;
}
[[SKPaymentQueue defaultQueue] finishTransaction:transaction];
//Moved from paymentQueueRestoreCompletedTransactionsFinished
if(self.transactionCount == 0){
[self.delegate restoredTransactions:[self.restoredTransactions count] withReceipt:self.appleReceipt];
}
break;
default:
break;
}
};
}
So in refreshing the receipt I just do this:
-(void)refreshReceipt{
//TODO: Check if this file exists - if not refresh receipt (and only then...)
NSData* receiptData = [NSData dataWithContentsOfURL:[[NSBundle mainBundle] appStoreReceiptURL]];
NSString *payload = [NSString stringWithFormat:#"{\"receipt-data\" : \"%#\", \"password\" : \"%s\"}",
[receiptData base64EncodedStringWithOptions:0], "xxx"];
NSData *payloadData = [payload dataUsingEncoding:NSUTF8StringEncoding];
//Sending the data to store URL based on the kind of build.
NSURL *storeURL;
if(SANDBOX_TESTING){
storeURL = [[NSURL alloc] initWithString:#"https://sandbox.itunes.apple.com/verifyReceipt"];
} else {
storeURL = [[NSURL alloc] initWithString:#"https://buy.itunes.apple.com/verifyReceipt"];
}
//Sending the POST request.
NSMutableURLRequest *storeRequest = [[NSMutableURLRequest alloc] initWithURL:storeURL];
[storeRequest setHTTPMethod:#"POST"];
[storeRequest setHTTPBody:payloadData];
NSError *error;
NSURLResponse *response;
NSData *data = [[NSURLSession sharedSession] sendSynchronousRequest:storeRequest returningResponse:&response error:&error];
if(error) {
_appleReceipt = [NSArray arrayWithObjects: error, nil];
}
NSError *localError = nil;
//Parsing the response as JSON.
NSDictionary *jsonResponse = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:&localError];
//Getting the latest_receipt_info field value.
_appleReceipt = jsonResponse[#"latest_receipt_info"];
if(SANDBOX_TESTING) NSLog(#"Refresh Apple receipt: %#", _appleReceipt);
}
And after I have the receipt I look through it and look for the correct purchase and extract the expiration date or none if it is a lifetime purchase.
BUT: We have some users getting an error message saying that no apple receipt has been returned (triggered by me, if self.appleReceipt = nil) or that no purchase has been found in this receipt. But very few users and I cannot really see what they share in common and where the error is. In testing I never get an error. I also saw live from one user who made the lifelong purchase that no receipt was returned and I don't know why.
So where is my error? Do I have to refresh the receipt everytime? Or why is sometimes my self.appleReceipt empty? Is my process wrong?

Answer 1

When you verify with the Apple server you do get back the latest updates, including any cancellations or expiration.
Sometimes the receipt may take a while to generate after a purchase, which is why occasionally you will see null receipt data especially if you only check for receipt data immediately after a purchase. Or, it could be even possibly be users attempting to hack your application and not really having receipt data.
What you should also be doing is parsing the receipt data Apple returns, looking at the IAP items for your renewable subscriptions to check on when they might be expiring, or for IAP entries for your one-time purchases - you can find a detailed guide on what data is present in the receipt (along with codes you might encounter) here:
https://www.namiml.com/blog/app-store-verify-receipt-definitive-guide
Note that you should really have a server do this receipt check and processing though, as potentially a hacker could intercept that call to Apple for the receipt verification.