App receives duplicate notification using GCM afte

Question

This question already has an answer here:

• Do old GCM tokens live on even after an uninstall? 2 answers

I'm currently trying to use GCM to send notification to user and currently I'm still studying on how I can maximize it. For now I just use the sample project provided on the documentation here and I use the gcm-client sample to work on it.

Now using this project from Git I tried to push a message using the registration ID created by the app and yes it successfully delivers the message.

Now the problem is that after I uninstalled the application. After I reinstall it it will generate a new registration ID wherein I store it on a server together with the previous one except that I can't tag the previous registration ID to not receive any further message since the uninstall might happen when user has no internet connection. After that I send a message to two registration ID's which is the ID before uninstalling the app and the ID after reinstalling the application. What happen is that I receive two push messages eventhough I expected it to only get one since the app already changes the registration ID.

I expect that the app might receive twoor more duplicate apps if ever I also updated the app since as said on documentation the registration ID might change on update.

Any workaround I can do to handle this duplicate messages?

Answer 1

After reinstal you will get new RegId and prev not valid anymore. So, even if you send push to both RegIds, only last will received it.

You can implement logic for accounts in application.

For example, when user login in application you send his GoogleId + RegId. After reinstall of application and relogin you just update RegId on server. So, you can have only one RegId for every user.

There is problem: only one device will receive push msg (if you login in 2 devices with same account). So, you can send to server GoogleId + RegId + DeviceId after start application.

Answer 2

@KaHel When client app was uninstalled regId will be valid during some time, you are right. But, when client app will be installed again and your push server try to send message on old reg id that message will be successfully sent but GCM server put cannonical_id in response. And you should correct processes this response with cannonical_id. How do this i described at this post and there is not big documentation about cannonical_id. I.e. as soon as you get cannonical_id from GCM server you should immediately replace old reg_id by new one value. It will allow you not to produce a many regIds for one client, just one to one.

Answer 3

From the official documentation:

How uninstalled client app unregistration works

A client app can be automatically unregistered after it is uninstalled. However, this process does not happen immediately. What happens in this scenario is:

1. The end user uninstalls the client app.
2. The app server sends a message to GCM connection server.
3. The GCM connection server sends the message to the GCM client on the device.
4. The GCM client on the device receives the message and detects that the client app has been uninstalled; the detection details depend on the platform on which the client app is running.
5. The GCM client on the device informs the GCM connection server that the client app was uninstalled.
6. The GCM connection server marks the registration token for deletion.
7. The app server sends a message to GCM.
8. The GCM returns a NotRegistered error message to the app server.
9. The app server should delete the registration token.

Note that it might take a while for the registration token to be completely removed from GCM. Thus it is possible that messages sent during step 7 above get a valid message ID as a response, even though the message will not be delivered to the client app. Eventually, the registration token will be removed and the server will get a NotRegistered error, without any further action being required from the app server.

However, it can apparently happen that you still get the notification for the old registration ID, as users state in other questions:

• Android GCM and multiple tokens
• Unregistering and re-registering for GCM messages causes two regId's to be valid. Is this as intended?
• Do old GCM tokens live on even after an uninstall?

For this problem, there is a functionality called "canonical IDs":

Canonical IDs

If a bug in the client app triggers multiple registrations for the same device, it can be hard to reconcile state and the client app might end up with duplicate messages.

Implementing canonical IDs can help you more easily recover from these situations. A canonical registration ID is the registration token of the last registration requested by the client app. This is the ID that the server should use when sending messages to the device.

If you try to send a message using an old registration token, GCM will process the request as usual, but it will include the canonical ID in the registration_id field of the response. Make sure to replace the registration token stored in your server with this canonical ID, as eventually the old registration token will stop working.