proxy_config.go

package main

import (
	"context"
	"log"

	firebase "firebase.google.com/go"
	"firebase.google.com/go/messaging"
)

func main() {
	ctx := context.Background()
	app, err := firebase.NewApp(ctx, nil)
	if err != nil {
		log.Fatal(err)
	}

	db, err := app.Firestore(ctx)
	if err != nil {
		log.Fatal(err)
	}
	snapshot, err := db.Collection("users").Doc("alice").Get(ctx)
	if err != nil {
		log.Fatal(err)
	}
	topic, err := snapshot.DataAt("topicName")
	if err != nil {
		log.Fatal(err)
	}

	fcm, err := app.Messaging(ctx)
	if err != nil {
		log.Fatal(err)
	}
	resp, err := fcm.Send(ctx, &messaging.Message{
		Topic:        topic.(string),
		Notification: &messaging.Notification{
			Title: "Hello from the other side",
			Body: "I must have called this proxy a thousand times",
		},
	})
	if err != nil {
		log.Fatal(err)
	}
	log.Println(resp)
}