How to send device to device messages using Firebase Cloud Messaging?

Question

After searching the docs I could not find any info on how to send device to device messages using FCM without the use of an external server.

For example, if I was cr

Answer 1

In my case I use retrofit with this class Message:

public class Message {

    private String to;
    private String collapseKey;
    private Notification notification;
    private Data data;

    public Message(String to, String collapseKey, Notification notification, Data data) {
        this.to = to;
        this.collapseKey = collapseKey;
        this.notification = notification;
        this.data = data;
    }
}

Data

public class Data {

    private String body;
    private String title;
    private String key1;
    private String key2;

    public Data(String body, String title, String key1, String key2) {
        this.body = body;
        this.title = title;
        this.key1 = key1;
        this.key2 = key2;
    }
}

Notification

public class Notification {

    private String body;
    private String title;

    public Notification(String body, String title) {
        this.body = body;
        this.title = title;
    }
}

this the call

private void sentToNotification() {
    String to = "YOUR_TOKEN";
    String collapseKey = "";
    Notification notification = new Notification("Hello bro", "title23");
    Data data = new Data("Hello2", "title2", "key1", "key2");
    Message notificationTask = new Message(to, collapseKey, notification, data);

    Retrofit retrofit = new Retrofit.Builder()
            .baseUrl("https://fcm.googleapis.com/")//url of FCM message server
            .addConverterFactory(GsonConverterFactory.create())//use for convert JSON file into object
            .build();

    ServiceAPI api = new retrofit.create(ServiceAPI.class);

    Call call = api .sendMessage("key=YOUR_KEY", notificationTask);

    call.enqueue(new Callback() {
        @Override
        public void onResponse(Call call, retrofit2.Response response) {
            Log.d("TAG", response.body().toString());
        }

        @Override
        public void onFailure(Call call, Throwable t) {

            Log.e("TAG", t.getMessage());
        }
    });
}

our ServiceAPi

public interface ServiceAPI {
    @POST("/fcm/send")
    Call sendMessage(@Header("Authorization") String token, @Body Message message);
}