add snippets to demonstrate fcm registration tokens best practices

messaging/app/build.gradle

@@ -11,6 +11,7 @@ android {
         versionCode 1
         versionName "1.0"
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
+        multiDexEnabled true
     }
     buildTypes {
         release {
@@ -30,8 +31,14 @@ dependencies {
     // for Google Analytics. This is recommended, but not required.
     implementation 'com.google.firebase:firebase-analytics:21.2.0'
 
+    // Used to store FCM Registration Token.
+    // This is recommended, but not required.
+    // See: https://firebase.google.com/docs/cloud-messaging/manage-tokens
+    implementation 'com.google.firebase:firebase-firestore-ktx:24.4.3'
+
     implementation "com.google.android.gms:play-services-auth:20.4.1"
     implementation 'androidx.work:work-runtime-ktx:2.7.1'
+    implementation 'androidx.lifecycle:lifecycle-runtime-ktx:2.5.1'
 }
 
 apply plugin: 'com.google.gms.google-services'

messaging/app/src/main/java/com/google/firebase/example/messaging/kotlin/MainActivity.kt

@@ -1,6 +1,7 @@
 package com.google.firebase.example.messaging.kotlin
 
 import android.Manifest
+import android.content.Context
 import android.content.pm.PackageManager
 import android.os.Build
 import android.os.Bundle
@@ -10,11 +11,19 @@ import androidx.activity.result.contract.ActivityResultContracts
 import androidx.annotation.RequiresApi
 import androidx.appcompat.app.AppCompatActivity
 import androidx.core.content.ContextCompat
+import androidx.lifecycle.lifecycleScope
+import com.google.firebase.Timestamp
 import com.google.firebase.example.messaging.MainActivity
+import com.google.firebase.firestore.FieldValue
+import com.google.firebase.firestore.ktx.firestore
 import com.google.firebase.ktx.Firebase
 import com.google.firebase.messaging.ktx.messaging
 import com.google.firebase.messaging.ktx.remoteMessage
+import java.util.Calendar
+import java.util.Date
 import java.util.concurrent.atomic.AtomicInteger
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.tasks.await
 
 class MainActivity : AppCompatActivity() {
 
@@ -130,4 +139,20 @@ class MainActivity : AppCompatActivity() {
     }
     // [END ask_post_notifications]
 
+    // [START get_store_token]
+    private suspend fun getAndStoreRegToken(): String {
+        val token = Firebase.messaging.token.await()
+        // Add token and timestamp to Firestore for this user
+        val deviceToken = hashMapOf(
+            "token" to token,
+            "timestamp" to FieldValue.serverTimestamp(),
+        )
+
+        // Get user ID from Firebase Auth or your own server
+        Firebase.firestore.collection("fcmTokens").document("myuserid")
+            .set(deviceToken).await()
+        return token
+    }
+    // [END get_store_token]
+
 }

messaging/functions/index.js

@@ -0,0 +1,44 @@
+'use strict';
+
+const functions = require('firebase-functions');
+const admin = require('firebase-admin');
+
+admin.initializeApp();
+
+const EXPIRATION_TIME = 1000 * 60 * 60 * 24 * 30; // 30 days
+
+/**
+ * Scheduled function that runs once a month. It updates the last refresh date for
+ * tokens so that a client can refresh the token if the last time it did so was
+ * before the refresh date.
+ */
+// [START refresh_date_scheduled_function]
+exports.scheduledFunction = functions.pubsub.schedule('0 0 1 * *').onRun((context) => {
+    admin.firestore().doc('refresh/refreshDate').set({ lastRefreshDate : Date.now() });
+});
+// [END refresh_date_scheduled_function]
+
+/**
+ * Scheduled function that runs once a day. It retrieves all stale tokens then
+ * unsubscribes them from 'topic1' then deletes them.
+ *
+ * Note: weather is an example topic here. It is up to the developer to unsubscribe
+ * all topics the token is subscribed to.
+ */
+// [START remove_stale_tokens]
+exports.pruneTokens = functions.pubsub.schedule('every 24 hours').onRun(async (context) => {
+    const staleTokensResult = await admin.firestore().collection('fcmTokens')
+        .where("timestamp", "<", Date.now() - EXPIRATION_TIME)
+        .get();
+
+    const staleTokens = staleTokensResult.docs.map(staleTokenDoc => staleTokenDoc.id);
+
+    await admin.messaging().unsubscribeFromTopic(staleTokens, 'weather');
+
+    const deletePromises = [];
+    for (const staleTokenDoc of staleTokensResult.docs) {
+        deletePromises.push(staleTokenDoc.ref.delete());
+    }
+    await Promise.all(deletePromises);
+});
+// [END remove_stale_tokens]