How to use Firebase Cloud functions to send push notifications

This article provides a quick introduction on how to use Firebase Cloud Functions to send push notifications. There are 2 main advantages in using them:

1. A small amount of code can send iOS and Android push notifications at the same time.
2. There is no need for server-side coding as it is a server-less solution.

Before starting, we need to complete the configuration of the development environment:

1. Create the Firebase project

In the Firebase console, click Add project and select or enter a Project name (for example: firebase-cloudfunction-demo).

2. Add the Cloud messaging config

Complete the configuration of Firebase Cloud messaging:

• iOS instructions
• Android instructions

When the configuration is done, we also need to save the FCMToken (Firebase Cloud Messaging) in the realtime database or Firestore, to be used for push notifications.

3. Set up Node.js and the Firebase CLI

Open your own command line and create a new folder, then use:

npm install firebase-functions@latest firebase-admin@latest --save
npm install -g firebase-tools

4. Initialize your project

Run the following command:

firebase login

Your browser will open and you can use your Firebase account login and wait for the redirect. Then you will be able to see this:

Waiting for authentication...
✔  Success! Logged in as *******

Run the following command:

firebase init functions

Select JavaScript and when the Cloud functions setup is finished, this is how your folder will look like:

+- .firebaserc
 +- firebase.json
 +- functions/
      +- package.json
      +- index.js
      +- node_modules/

5. Add Cloud functions for push notifications

We only need to edit the functions/index.js file.

There are two ways to send push notifications, through HTTP request or by adding a listener to the realtime database or Firestore.

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

//http request method
exports.sendHttpPushNotification = functions.https.onRequest((req, res) => {
    const userId = req.body.userId; //get params like this
    	...

//listener method
exports.sendListenerPushNotification = functions.database.ref('/sendMessage/{userId}/').onWrite((data, context) => {
	const userId = context.params.userId; //get params like this
		...

Assume that the FCMToken is stored in this location of the realtime database：

/FCMToken/${userId}

You could get the FCMToken like this:

const FCMToken = admin.database().ref(`/FCMTokens/${userId}`).once('value');

To send a notification, use the following code:

const payload = {
	token: FCMToken,
    notification: {
        title: 'cloud function demo',
        body: message
    },
    data: {
        body: message,
    }
};

admin.messaging().send(payload).then((response) => {
    // Response is a message ID string.
    console.log('Successfully sent message:', response);
    return {success: true};
}).catch((error) => {
    return {error: error.code};
});

6. Deploy the functions to a production environment

Run this command to deploy your functions:

firebase deploy --only functions

If you add HTTP request functions, a function URL you should see:

Function URL (sendHttpPushNotification): https://us-central1-firebase-cloudfunction-demo.cloudfunctions.net/sendHttpPushNotification

If you want to debug your cloud functions, you could use this command:

firebase emulators:start

When the Cloud functions are deployed, you can send push notifications by making a request to the Function URL, or just set the data into the Firebase realtime database and the Cloud functions will be triggered by the data listener.

Resources

• Cloud Functions for Firebase
• Firebase Cloud Messaging