I'm developing an app using Unity (for Android and iOS). I'm using the SOOMLA plugin to allow users to purchase Gems (virtual currency) with In App Purchase.
Users and Gems and all other game logic go through my server on Azure.
I want the following procedure to take place as a single transaction in some way:
User buys Gems with IAP
App notifies server
Server validates the purchase and updates data
But if the internet connection breaks down between step 1 and step 2 - the user payed for Gems that he did not receive (not good!)
So my current approach is this:
User initiates a purchase
App notifies the server
Server blindly updates data accordingly
User buys Gems with IAP
If the purchase is cancelled, notify server to undo it
That way, the user is guaranteed to get his purchased Gems, but I am not guaranteed to get paid (not great...)
Note: I don't want to manage user Gems in the store itself. I want everything on my own server. So the SOOMLA's balance is meaningless to me. I don't care for it.
I was thinking maybe the app can store the purchase data in persistent storage until it manages to notify the server about it, and then delete it. But I was also thinking that this might be a bad solution. Hence this question.
I imagine the best solution as something that will properly handle this scenario:
User buys Gems with IAP
IAP succeeds
Internet breaks down
My own server isn't notified
User uninstalls app from his device
User may then install the app on other devices:
Either he was charged and he got the gems by some magic
Or he was refunded automatically, since the gems were not received
So far it seems like this is impossible by any means, which makes me disappointed with the technology of IAP's. Hoping for answers that will prove me wrong.
Seems like all I'd ever need is the ability get a user's purchase history from my server, with a secured request to Google Play or Apple Store. But that's just not part of the framework.
So what are others doing? What is the best approach?
In general, you seem to suffer from the Two Generals' Problem which was
the first computer communication problem to be proved to be unsolvable.
Since everywhere in your communication protocol a message can be lost (even the acknowledgement or the acknowledgement`s acknowledgement or the ...) you cannot be 100% sure that both communication parties (the user device and your server) have agreed upon the same state. You can only say that upon a certain probability the state information has been interchanged successfully.
I would send a couple of ACKs back-and-forth and store the purchase if a sufficient number got trough. Quote from Wikipedia:
Also, the first general can send a marking on each message saying it is message 1, 2, 3 ... of n. This method will allow the second general to know how reliable the channel is and send an appropriate number of messages back to ensure a high probability of at least one message being received
For customer satisfaction I would take the odds in their favor - 1% not delivered goods will get you in a lot of trouble but 1% loss on your side is acceptable.
Considering your Gems are a virtual currency, then the natural in-app product type should be consumable, i.e. they are not restorable purchases.
To consume a purchase with a Google Play purchase you will call consumePurchase. On iOS you will call finishTransaction on the SKPaymentQueue. In both marketplaces the consumable purchase will remain in an active state until they have been consumed. If the user deletes the app off their device before the purchase is consumed, they will be able to re-install, and restore their previous unconsumed purchases.
In-between the initial purchase and consumption is where you want to put your server-side validation. When a purchase is made, send the receipt or token to your server, perform the validation and respond accordingly. The app should wait for a valid response from the server before consuming the purchase.
(Note that consumed purchases will not appear in the in_app collection on an iTunes receipt. They are only present if the purchase has not been consumed yet).
If the server is timing-out or network connectivity is lost the purchases will remain in an active state and the app should continue trying to send the details periodically until it receives a response it is expecting.
Purchases for both Google Play and iOS are stored locally so you will just need to run a process that looks for unconsumed purchases once network connectivity is re-established.
You can treat the provisioning of Gems in the same way a bank handles deposits of cheques; the new balance will be immediately updated but the amount spendable will not match until the cheque (or in your case a validation) is cleared.
Some pseudo code to make the process clear:
Purchase product or Restore purchases
While consumable purchases > 0
Send purchase receipt to API
If response is ok
If purchase is valid
Consume product
Allocate gems
Break
Else
Remove retroactive gem allocation
Discipline the naughty user
Break
Else
Retroactively allocate un-spendable gems
Pause process until network is re-established
Re-send receipt to API
I don't have much knowledge about android but after reading your post I was really interested to search keenly and more over how game like clash of clans in app purchase logic work and prevent freedom fake purchase hacks.
After doing some research I would like to share my thoughts over your problem, You can implement it by following approach:
Make your in app purchase verification completely online. For e.g., you can consider the game clash of clans.
How it works:
1)Game loads, synced with server. Network connection required, as network connection breaks game reloads from server.
2)User have 10 gems, server also have 10 gems.
3)User purchased gems, server verify purchase separately for the purchased consumables, gems credited to the users account.
4)If in can case network fails, then also server can verify purchase and later on it update it in account of user, whether it is on any device.
5)This will also help you to bypass many fake in app purchase hacks like freedom (prevention) and lucky patcher.
Google provide api for server side to verify or get purchase detail and when purchase from application side and server side match then only you credit gems or consumable item into users account.
For more information about in app purchases and their hack preventions you can visit these links:
1)Server side verification of in app purchase part 1 and part 2.
2)How would you verify in app purchase billing server side.
3)Verify purchase via PHP.
4)Secure in app purchase scenario on web server.
Hope this might lead you in direction which you want to go, also I would love to hear your thoughts over the same.
You can try restoring the In App purchases made with a particular account.
The feature is given just for this case when either the payment was made and user didn't receive the items he was promised or when he switched device.
Upon restoring the purchase you'll receive the purchased product again from the iTunes server and then you can accordingly notify your server.
Some advice:
User buys Gems with IAP
IAP succeeds
Internet breaks down
My own server isn't notified
User uninstalls app from his device
User may then install the app on other devices:
Either he was charged and he got the gems by some magic, or he was refunded automatically, since the gems were not received.
At step 3, receipt information is stored on the user's device. If the user uninstalls and reinstalls your app, the receipt information will be lost. But you can restore it; Apple talk about that here. You can resend a restored receipt to your server. At your server, you verify that plus Gems for the user so he can receive what he should be.
he was refunded automatically, since the gems were not received
This seem impossible with IAP because Apple does not allow a user to cancel their purchase. (With Google IAB, refund are allowed, more about that here)
Related
I want to store in Android app data a token (a random number, e.g. 128 bit long) unique for each install. I also want to deliver this token to the backend after confirmed purchase. That is, the backend should reject hacker's attempts to store the token, if it is not after an app purchase.
In other words, I need to implement app "activation" so, that the activation is possible only after a genuine Google Play purchase.
An explanation why I need this:
Suppose I resell a $1 product for $2 in a $10 paid app.
The right to use this service by the user appears when he purchases my paid app.
If the user can fake app install, then he may obtain 1000 products for $10 and thus I would have $990 loss.
Thus I need to store on server side a token generated on confirmed (on the backend side) purchase.
Is this possible with Play Market?
In Flutter (and I believe, in plain Android, too) it can be done this way:
Every purchase needs to be "acknowledged".
After verifying the purchase receipt and the delivering the content to the user it is important to call InAppPurchase.completePurchase to tell the underlying store that the purchase has been completed. Calling InAppPurchase.completePurchase will inform the underlying store that the app verified and processed the purchase and the store can proceed to finalize the transaction and bill the end user's payment account.
Warning: Failure to call InAppPurchase.completePurchase and get a successful response within 3 days of the purchase will result a refund.
So, the task can be done this way:
The purchase is created (on the client app side, by contacting Play Store).
The app contacts my server with purchase token (and possibly other info).
During the request from the app the server retrieves the purchase by purchases.products.get to verify that the purchase is not forged by a hacker and increases users in-app funds.
App, after receiving a successful reply from the server, acknowledges the purchase by InAppPurchase.completePurchase.
If the app fails to acknowledge, the purchase is refunded in 3 days.
I would like to know how can I avoid having the user re-pay for an in-app subscription he already purchased.
Example: I purchase an App which offers in-app purchase on google play store for 5$ and now I shift from using an Android phone to an iPhone.
I came across this post which says it's not possible as they are two different competitors and would have to re-purchase the same app on the iOS once again, but is there a way to avoid it so that the end-user does not repay the sum of 5$ again?
I was thinking if it would be a good idea to have the receipt stored on a server and then when the user enters his email just do a lookup if there's a receipt associated with that email along with some validation logic.
In theory, I could avoid the user having to pay the 5$ with this approach but at the same time, I am not sure if doing this could get my app rejected or If this could lead to some different issues OR this is not doable at all and the user will have to end up paying 5$ anyways if he shifts from android to ios and vice versa.
The approach you suggested is correct. You would store the receipt on your server, along with the user identifier. Your server is responsible for refreshing the receipt with Apple/Google to keep the status up-to-date. You can then have an endpoint to your backend to check if a user is subscribed - regardless of the platform.
This is well within the App Store Guidelines, and is how large subscription businesses like Netflix and Spotify operate.
i offer 1 in app purchase (full functionality). I save the result of the purchase in a boolean variable in sharedpreference and also use queryPurchases on app start, so if someone deleted and reinstalled the app, he gets his full functionality back.
That works properly, but i also would like to block full functionality, if it turns out, that someone did NOT purchase the full functionality (and cheated the app with a rooted device). That would also include deleting some data that he is not supposed to have without the in app purchase.
However, i am confused about the description of queryPurchases. It says
"Upon a successful purchase, Google Play's In-app Billing service caches the user's purchase data locally."
How long does it store that information? Does it update it automatically if an internet connection is available? How can i avoid getting no purchase even though the user bought the in app purchase and falsely blocking his full functionality? What is there
Is there a way to get the clear information, that the user in fact did NOT purchase a certain item, rather than just no information about a possible purchase? I really want to avoid blocking features if the user paid.
Anything else wrong with my approach (Saving the purchase in sharedpreferences
to have the information available immediatly and additionaly query purchase)
Edit: I also noticed, that if i refund an in app purchase, de- and reinstall the app, queryPurchases still finds that purchase. There must a way to avoid that?
Don't bother storing purchases in shared preferences. They are already on the device via the billing library. The purchases are stored in the Play store data which the billing library retrieves for you.
You can work by assuming that full functionality is enabled until you receive the result of query purchases which will tell you definitively whether the user has bought it or not. If you prefer, you can do that backwards and assume trial mode until you know a purchase exists.
Either way, the query for purchases will return quickly as no network connection is required because billing library simply connects to play store on the device for the data.
If you refund in the developer console, it may take a while for that to filter to the users device but it will eventually. It isn't a real time system and a purchase will remain cached on the device until the refund is fully processed and sent to the users device.
You can consume a purchase directly on a device which removes it instantly from the user account.
I would like to setup subscription based billing for an app that will be sold through Google Play. Is it possible to sell the same subscription to the same user but on a different devices? So that every device that user tries to use the app on would need an active subscription?
I was thinking I could store the device id and user id on my own server and authenticate it that way, but is it correct that a user can't purchase the same subscription more than once? So would I need a pool of basically the same subscriptions if the user wishes to purchase multiple "licenses"? Can Google Play Billing handle any of this natively?
Thanks
The documentation from Google initially seems to make this impossible to achieve but digging deeper, I uncovered the following...
In the Google Play API version 2.0, you could create what was called an "unmanaged" product type that allowed the user to purchase the same thing multiple times. That seems to have partly disappeared in API 3.0 although the Gooogle Developer Console clearly supports this. I assume it's still supported because apps that used the 2.0 API are still out there and Google just can't drop support for that.
In 3.0 however, the "unmanaged" product type is not listed in the API docs but the docs state the following about making multiple purchases for the same product type (one-time purchase or subscription):
If you are using the Version 3 API, you can also consume managed items
within your application. You would typically implement consumption for
items that can be purchased multiple times (such as in-game currency,
fuel, or magic spells). Once purchased, a managed item cannot be
purchased again until you consume the item, by sending a consumption
request to Google Play. To learn more about in-app product consumption,
see Consuming Items
http://developer.android.com/google/play/billing/api.html#consume
IMPORTANT: Subscriptions CANNOT be consumed which means that if you want the customer to periodically renew their license, you will have to contact them and tell them that they must purchase the license again. That's a downside if your service requires a periodic renewal.
To obtain what you are after, you will need a backend server to handle the registration of devices and store tokens the apps receive from Google Play when purchasing. When a user wants to purchase your license, feature, service (or whatever) from another device, the other device MUST first release its "ownership" of the product with Google Play, through a process known as "consuming". It would work something more or less like this:
The first device makes a purchase and receives a purchaseToken
string from Google Play.
The purchaseToken along with the device ID is sent from the app to your server and stored.
The user goes to the second device and wants to purchase the license as well for that device. The app first needs to go to your server and obtain the purchaseToken (that the first device uploaded) and then call Google Play with consumePurchase which releases the "ownership" of the product from the user.
The app then purchases the new license (or whatever) from Google Play, gets a new purchaseToken and stores it on your server along with its device ID.
In essence, Google Play won't keep track of which device has the product. It only associates the Google Account with the product being purchased. It's up to your app and server to manage the licenses.
There is one potential problem I see that you need to address. If for some reason the app fails to send the purchaseToken back to your server (your server is down, the user dropped their device and broke it, your app crashes before it saves the token on the device, etc.), then you may not know if the user paid for the service. Google does provide a server API that lets your backend server query Google Play on Google's server for information about purchases, but I'm not familiar with it nor its limitations.
You will need to implement in app purchases as you would for any other in app item.
Make sure when you create your item in the Dev Console, it is unmanaged, as managed items can only be purchased once per account.
When you receive a confirmation on purchase of your unmanaged item, send the details like the unique ID to your server and store them there.
Now whenever your app starts, check with your server if it is an authorized device. If it isn't, prompt the user to buy it. If it is, let them continue to the app.
This only works if you need a one time payment. If you need a subscription, you will have to make it up of multiple one time payments, as subscriptions are like managed purchases and can only be paid for once by any account.
How do I implement (Auto-renewable) Subscriptions for an Android App.
I've read the documentation
and as far as I understand, the process is the following:
User subscribes to such a subscriptions on the app. This will generate a Purchase token.
The app sends this token to the server along with something to identify this user
The server will store this Purchase token with this user and will mark the subscription as valid
the server validates this Purchase token via the http-api periodically (typically once per day) with something like a cronjob
if the subscription isn't valid anymore, the subscription will be marked as invalid on the server-side.
If the app makes requests to the server to resources that need the subscription, the client will send this user-identity-string along with the requests. We then check in the database, if the subscription of this user is still marked as valid.
My question is now, how we should identify this users? Do we have a simple user id available that we can share between our app and our server? or should we use something different? What is the best practice here?
We did already similar subscriptions on ios and we used the uuid of the device to identify the users (at least as long as we were able to use the uuid).
From the Answer below we should generate a unique ID. This would be unique per device (or per app-installation). But if a user changes his device or reinstalls the application this id would not be the same anymore. So I'm not sure, how the process is in this use case. I thought of something like this:
The user is logged in with the same google play account on his second device.
As the app starts (or becomes active) we would fetch the users subscriptions
We then would receive this purchase token from the subscriptions and send them along with the new unique-ID to our backend-server as if the user had made a new subscription.
Would this be the right process? And stays the purchase token the same as it was on the first device?
Ok, my question about identifiying users is answered, the link provided delivers enough informations. I'll put further questions in new threads on SO, if I have some.
This link maybe helpful to you as you want to identify the users uniquely.Please note that the personal information of a user rests with Google only.And you should avoid getting private information of a user.
http://www.pocketmagic.net/2011/02/android-unique-device-id/#.URIe_B3Wgr7