Apple Push Notifications on Google Appengine

Last year, I worked on a Nine Men's Morris (Mühle) implementation for Android, called Doublemill. Since I'm an iPhone user, I decided to port the game to iPhone/iPod touch and the iPad. There are 3 versions: Doublemill Premium, Doublemill Lite and Doublemill for iPad.

I've written about the Google Appengine (GAE) a couple of times before and the same goes for Apple Push Notifications (APN). For Doublemill I had to bring those two technologies together and it was a pain and pleasure at the same time.

Let me start with the pain! Apples Push Notifications in a restricted environment like the Google Appengine is no fun to implement! My first approach was to use notnoop's java-apn, which I've used before and works quite well. Unfortunately, there is currently no way of using a client certificate, which you'll need in order to talk to Apple's server on the Google Appengine. There are some javax.security classes missing on GAE.

That's where the pleasure part begins! Thanks to Urban Airship, it's easy to hook up your application running on Google Appengine to Apple's Push Notifications! And the best part - it's free (although not unlimited)! Urban Airshipe provides an easy to use REST interface, which you can call from your Java code on GAE with a good old HttpURLConnection. It uses Basic Auth over Https to ensure that only your application can send Push Notifications to your iPhone App.

I won't provide any code for you here, because it's the basic concept that's the most interesting part when bringing APN to GAE. The first thing you need to do, is store your user's deviceToken. You should do that each time the App launches, to ensure it's the correct token. That token, along with the information you want to present to your user, needs to be passed to Urban Airship's REST interface, everytime you want to send a notification. A Cron Job or Task on Google Appengine could handle that for you.

If your application is designed with notifications in mind, then it's quite easy to bring Apple Push Notifications to the Google Appengine, thanks to Urban Airship!

Push Notifications in Production

Last year, I worked on a Nine Men's Morris (Mühle) implementation for Android, called Doublemill. Since I'm an iPhone user, I decided to port the game to iPhone/iPod touch and the iPad. There are 3 versions: Doublemill Premium, Doublemill Lite and Doublemill for iPad.

In a previous blog post I highlighted a couple of gotchas you need to be aware of when implementing Apple Push Notifications. Unfortunately, I didn't really pay attention to one of them myself:

The first problem I ran into, had to do with my provisioning profile for development. I enabled APN in my Provisioning Portal, installed the certificate and implemented all the delegate methods according to the documentation, but somehow the method

- (void)application:(UIApplication *)application didFailToRegisterForRemoteNotificationsWithError:(NSError *)error

was called with error code 3000 - "no valid 'aps-environment' entitlement string found for application". I was pretty sure, I setup everything correctly. However, I missed one little thing:

After you have generated your Client SSL certificate, create a new provisioning profile containing the App ID you wish to use for notifications.

This bit me after submitting Doublemill Premium to the App Store and being rejected for promoting Push Notifications in my App description, but according to Apple, not implementing it. During beta testing, everything worked fine. I had a correct implementation and the App was asking me for permission to use Push Notifications.

However, I did forget to create a new distribution provisioning profile for the App Store, after enabling Push Notifications for production. So, it didn't work for the reviewer at Apple. Forgetting about something like this is very painful, especially since I'm waiting for the 3rd round of review for the next release of Doublemill. That makes it 3 weeks since the initial submission.

When asking about this on the Apple Developer Forums, Mike was so kind to point out a neat trick on the command line, which helps you identify, whether APN for production is enabled:

codesign -dvvvv --entitlements - /path/to/App

<key>aps-environment</key>
<string>production</string>

If you see aps-environment=production, you should be save. Push notifications should work. If the key is missing, then you should create a new provisioning profile and rebuild you App with that.

It would be nice if Apple built this kind of checks into XCode or at least invalidate the provisioning profiles as soon as you enable Push Notifications in your App ID.