How do you send a Firebase Notification to all devices via CURL?

Question

I'm attempting to send out a notification to all app users (on Android), essentially duplicating what happens when a notification is sent via the Firebase admin console. Here is the CURL command I begin with:

curl --insecure --header "Authorization: key=^dummy_key^" --header "Content-Type:application/json" -d "{\"notification\":{\"title\":\"note-Title\",\"body\":\"note-Body\"}}" https://fcm.googleapis.com/fcm/send

Here's that JSON parsed out to be easier on your eyes:

{
"notification":{
    "title":"note-Title",
    "body":"note-Body"
    }
}

The response that comes back is just two characters:

to

That's it, the word "to". (Headers report a 400) I suspect this has to do with not having a "to" in my JSON. What would one even put for a "to"? I have no topics defined, and the devices have not registered themselves for anything. Yet, they are still able to receive notifications from the Firebase admin panel.

I'm want to attempt a "data only" JSON package due to the amazing limitation of Firebase notification processing whereby if your app is in the foreground, the notification gets processed by YOUR handler, but if your app is in the background, it gets processed INTERNALLY by the Firebase service and never passed to your notification handler. APPARENTLY this can be worked around if you submit your notification request via the API, but ONLY if you do it with data-only. (Which then breaks the ability to handle iOS and Android with the same message.) Replacing "notification" with "data" in any of my JSON has no effect.

Ok, then I attempted the solution here: Firebase Java Server to send push notification to all devices which seems to me to say "Ok, even though notifications to everyone is possible via the Admin console... it's not really possible via the API." The workaround is to have each client subscribe to a topic, and then push out the notification to that topic. So first the code in onCreate:

FirebaseMessaging.getInstance().subscribeToTopic("allDevices");

then the new JSON I send:

{
"notification":{
    "title":"note-Title",
    "body":"note-Body"
    },
"to":"allDevices"
}

So now I'm getting a real response from the server at least. JSON response:

{
"multicast_id":463numbersnumbers42000,
"success":0,
"failure":1,
"canonical_ids":0,
"results":
    [
    {
    "error":"InvalidRegistration"
    }
    ]
}

And that comes with a HTTP code 200. Ok... according to https://firebase.google.com/docs/cloud-messaging/http-server-ref a 200 code with "InvalidRegistration" means a problem with the registration token. Maybe? Because that part of the documentation is for the messaging server. Is the notification server the same? Unclear. I see elsewhere that the topic might take hours before it's active. It seems like that would make it useless for creating new chat rooms, so that seems off as well.

I was pretty excited when I could code up an app from scratch that got notifications in just a few hours when I had never used Firebase before. It seems like it has a long way to go before it reaches the level of, say, the Stripe.com documentation.

Bottom line: does anyone know what JSON to supply to send a message out to all devices running the app to mirror the Admin console functionality?

Answer 1

EDIT: It appears that this method is not supported anymore (thx to @FernandoZamperin). Please take a look at the other answers!

Instead of subscribing to a topic you could instead make use of the condition key and send messages to instances, that are not in a group. Your data might look something like this:

{
    "data": {
        "foo": "bar"
    },
    "condition": "!('anytopicyoudontwanttouse' in topics)"
}

See https://firebase.google.com/docs/cloud-messaging/send-message#send_messages_to_topics_2