Send massage to group devices in Firebase Cloud Messaging - firebase

Question

I am building a chat and I want to send message in FCM to 1000 clients in a group. The message would sent from client to group of 1000 clients (the message not pass through server). I can use the topic method, but if I want to remove a client by the group admin it's not possible. Anyone can propose a solution?
Help me please.

Answer 1

Topics are indeed public: you (as the developer/administrator of the app) cannot prevent your app's users from subscribing to a topic.
If you want to control the devices that do (and don't) receive your messages, you'll have to send the message to those specific devices. You do this by tracking the instance ID tokens for those devices in a database and then targeting the list of tokens when you send the downstream message.
There is an example of how to manage device tokens and send messages in the Cloud Messaging for Firebase documentation.

Answer 2

If you simply want to remove (unsubscribe) some specific members, you can make use of the InstanceID API, specifically batchRemove.
Manage relationship maps for multiple app instances
Using the Instance ID service's batch methods, you can perform batch management of app instances. For example, you can perform bulk addition or removal of app instances to an FCM or GCM topic. To manage app instances, call the Instance ID service at this endpoint, providing the app instance tokens in the JSON body:
https://iid.googleapis.com/iid/v1:batchAdd
https://iid.googleapis.com/iid/v1:batchRemove
Parameters
Authorization: key=YOUR_API_KEY. Set this parameter in the header.
to : The topic name.
registration_tokens : The array of IID tokens for the app instances you want to add or remove.
Results
On success the call returns HTTP status 200. Empty results indicate successful subscription for the token. For failed subscriptions, the result contains one of these error codes:
NOT_FOUND — The registration token has been deleted or the app has been uninstalled.
INVALID_ARGUMENT — The registration token provided is not valid for the Sender ID.
INTERNAL — The backend server failed for unknown reasons. Retry the request.
TOO_MANY_TOPICS — Excessive number of topics per app instance.
Example POST request
https://iid.googleapis.com/iid/v1:batchAdd
Content-Type:application/json
Authorization:key=API_KEY
{
"to": "/topics/movies",
"registration_tokens": ["nKctODamlM4:CKrh_PC8kIb7O...", "1uoasi24:9jsjwuw...", "798aywu:cba420..."],
}
Example result
HTTP 200 OK
{
"results":[
{},
{"error":"NOT_FOUND"},
{},
]
}