Using C2DM? Time to migrate to Google Cloud Messaging!

OK, here is the indisputable evidence for why Google had to urgently announce “Important: C2DM has been officially deprecated as of June 26, 2012!”

Deadline Google had to meet

The Deadline Google had to meet

Somebody at Google probably remembered just in time that Michael J. Fox‘s car was being “push”ed back to the future using Android and it had better be at its best when it was time! It wouldn’t have looked good if Michael J. Fox had to return to 1985 due to a “Device Quota Exceeded” error, would it?

So, that’s the (undeniable) background – all planned by “Doc” decades back! Now, the rest of the mortal souls have to rise to the occasion, let go of the Google’s “beta” C2DM solution and migrate to the new and shiny one – Google Cloud Messaging (GCM).

But, why should we migrate?

  • For new apps that need events pushed to Android devices, there is no choice now! The Sign-up for C2DM has gone now. New applications have to use GCM.
  • Although the existing C2DM based applications will continue to work, there are not going to be quota requests accepted anymore. That’s not so future-proof, right? We don’t want to be limited to the users we currently have – we want our apps to explode! So, it makes sense for existing apps also to migrate.
  • There are many advantages too:
    • No quotas – no annoying DeviceQuotaExceeded / QuotaExceeded errors anymore. Hopefully it will remain so.
    • Availability of “push” stats – for applications published through Google Play, the GCM stats can be now be monitored – how many messages were sent each day, how many new devices registered, etc. More details on ‘how to setup your app for stats’ available here.
    • Richer API / Better Efficiency – Unlike the plain-text body that could be POSTed to the C2DM endpoint, GCM allows both plain-text / JSON formats in the POST body. The JSON format opens up new implementation opportunities like multicasting a particular message to several devices at a time, or allowing multiple senders to push to one particular device at the same time.
    • Helper libraries for client and server development. No need to deal with request/response with GCM end-point at low-level plain-text or JSON level. There are additional goodies built-in like ‘retry logic with exponential back-off.’
    • Payload size limit is 4096 bytes in GCM, compared to 1024 bytes in C2DM.

The code level changes to be done on client and server sides are well documented in the GCM documentation. So, I will just fast-forward to some specific things that I had to address:

   a) Migration approach: C2DM and GCM are not interoperable. So, an application can’t push to a C2DM-registered device through a GCM endpoint, and vice-versa. On the server-side, we need to know whether we are dealing with C2DM-registered devices or GCM-registered devices and push events through the respective endpoints. Hopefully, soon our userbase will switch over to GCM-enabled version of the Android application client, and when it reaches the point when there are no registrations marked as C2DM, we can drop the support for it and complete the migration.

   b) Eclipse specific issues:

  • Installation of the Helper libraries under Android SDK : The option to use for installing these libraries, “Extras > Google Cloud Messaging for Android Library”, does not show-up under the Android SDK Manager until you have Android SDK Tools updated to revision 20 and Android Platform SDK Tools updated to revision 12. This also necessitates the update of ADT plugin to v20.
  • NoClassDefFoundError errors post ADT plugin update : After updating the ADT plugin from v15 to v20, we started getting NoClassDefFoundError for classes coming from external libraries referenced. These jars existed under “/lib” folder. It seems the new ADT plugin looks for them under “/libs” folder. So the jars existing in “/lib” folder are not picked up for dalvik conversion by the new ADT plugin. More details are available here.

Other than these few issues, the migration has been quite an smooth exercise – helper libraries made it much easier.

Hope this information helps someone in C2DM-to-GCM migration. For more assistance, the GCM forum is here.