Get GCM canonical registration ID without sending a message

Question

I have a problem with an app using GCM, the scenario is this:

1. the app is installed
2. the app calls the GCM register method getting the registration id "RID-1"
3. the app is uninstalled
4. the app is installed again
5. the app calls the GCM register method again getting the registration id "RID-2"

In step 5, I need to get the previous registration id so I can update my model.

Limitations:
- I am trying to do this without using the external storage
- I can't update the model when the server sends a message, it should be done after the registration because a new profile is created in the app for each new device

I know that this information is in Google servers because it is sent to you when you send a message to the old registration id. For example, if I send a message to "RID-1", in the response I get that the new (canonical) registration id is "RID-2". What I need is a way to get this information without sending a message.

Let me know if you need more context.

---

I found several related questions but the answers doesn't apply to this scenario:
Registration ID duplication for GCM
gcm canonical id should be updated or not
Persistance of gcm registration id
Google Cloud Messaging - Registration ID status
Android GCM: How to detect registered canonical ids in my own server?
Handling registration ID changes in Google Cloud Messaging on Android
(all answered by @eran)

Answer 1

You can specify "dry_run": true option in /send request.

I found that devices do not receive any push notifications with "dry_run": true option, while a server get canonical_ids response.

Here is a sample code in Ruby. You may have to install gcm Gem beforehand.

$ gem install gcm

ask_canonical_ids.rb

require 'gcm'
require 'json'

API_KEY = "YourApiKey"
gcm = GCM.new(API_KEY)

registration_ids = [
  'OldRegistrationId',
]

option = { data: { 'message' => 'Hello Gcm!' }, dry_run: true }
response = gcm.send_notification(registration_ids, option)

p response[:canonical_ids]

output of $ ruby ask_canonical_ids.rb (formatted)

[{
  :old => "OldRegistrationId",
  :new => "NewRegistrationId"
}]

Again, your device will not receive any push notifications.