Send push notifications using Cloud Functions for Firebase

Question

I am trying to make a cloud function that sends a push notification to a given user.

The user makes some changes and the data is added/updated under a node in firebase database (The node represents an user id). Here i want to trigger a function that sends a push notification to the user.

I have the following structure for the users in DB.

Users

 - UID
 - - email
 - - token

 - UID
 - - email
 - - token

Until now i have this function:

exports.sendNewTripNotification = functions.database.ref('/{uid}/shared_trips/').onWrite(event=>{
const uuid = event.params.uid;

console.log('User to send notification', uuid);

var ref = admin.database().ref('Users/{uuid}');
ref.on("value", function(snapshot){
        console.log("Val = " + snapshot.val());
        },
    function (errorObject) {
        console.log("The read failed: " + errorObject.code);
});

When i get the callback, the snapshot.val() returns null. Any idea how to solve this? And maybe how to send the push notification afterwards?

Solution 1

I managed to make this work. Here is the code that sends a notification using Cloud Functions that worked for me.

exports.sendNewTripNotification = functions.database.ref('/{uid}/shared_trips/').onWrite(event=>{
    const uuid = event.params.uid;

    console.log('User to send notification', uuid);

    var ref = admin.database().ref(`Users/${uuid}/token`);
    return ref.once("value", function(snapshot){
         const payload = {
              notification: {
                  title: 'You have been invited to a trip.',
                  body: 'Tap here to check it out!'
              }
         };

         admin.messaging().sendToDevice(snapshot.val(), payload)

    }, function (errorObject) {
        console.log("The read failed: " + errorObject.code);
    });
})

Solution 2

Just answering the question from Jerin A Mathews... Send message using Topics:

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

admin.initializeApp(functions.config().firebase);

//Now we're going to create a function that listens to when a 'Notifications' node changes and send a notificcation
//to all devices subscribed to a topic

exports.sendNotification = functions.database.ref("Notifications/{uid}")
.onWrite(event => {
    //This will be the notification model that we push to firebase
    var request = event.data.val();

    var payload = {
        data:{
          username: request.username,
          imageUrl: request.imageUrl,
          email: request.email,
          uid: request.uid,
          text: request.text
        }
    };

    //The topic variable can be anything from a username, to a uid
    //I find this approach much better than using the refresh token
    //as you can subscribe to someone's phone number, username, or some other unique identifier
    //to communicate between

    //Now let's move onto the code, but before that, let's push this to firebase

    admin.messaging().sendToTopic(request.topic, payload)
    .then((response) => {
        console.log("Successfully sent message: ", response);
        return true;
    })
    .catch((error) => {
        console.log("Error sending message: ", error);
        return false;
    })
})
//And this is it for building notifications to multiple devices from or to one.

Solution 3

Return this function call.

return ref.on("value", function(snapshot){
        console.log("Val = " + snapshot.val());
        },
    function (errorObject) {
        console.log("The read failed: " + errorObject.code);
});

This will keep the cloud function alive until the request is complete. Learn more about returning promises form the link give by Doug in the comment.

Comments

[Jen Person]

Does the console.log of the uuid show the correct value?

[Tudor Lozba]

Yes, the uuid is correct.

[Bob Snyder]

Use back-ticks to substitute the value of uuid in your ref: admin.database().ref(`Users/${uuid}`). Also you should use once() instead of on(). on() leaves the listener attached; not something you want in a cloud function.

[Doug Stevenson]

Also, your function should return a promise that indicates to Cloud Functions when your work is done and it's safe to clean up. If you do async work without returning a promise, it will not work the way you want. It might be a good idea to go over these video tutorials to learn more: youtube.com/playlist?list=PLl-K7zZEsYLkPZHe41m4jfAxUi0JjLgSM

[Andrew Breen]

Doug is correct - with Cloud Functions you should be returning a promise so that it can watch the chain execute and then stop the instance when it is done. Because it has no way of knowing that async work is happening in this case, the function is completing before the async work is actually completed.

[Tudor Lozba]

Thank you all for your answers. Combining them helped me to achieve what i wanted!

[Aawaz Gyawali]

Its my pleasure, please accept the answer if it helped your problem. @TudorLozba

[Jerin A Mathews]

is there any way to send messages to a topic using firebase cloud function?

[Deepak Gautam]

will this code send notification to all the users? What if I wants to send notification to only one user like whatsapp message notification.

[Codelicious]

@DeepakGautam This will only send to one specific device. Note sendToDevice is a legacy method. See firebase.google.com/docs/cloud-messaging/admin/send-messages

[Joseph Wambura]

Hello, what if I have a specific topic I want to send to? Say, like some people subscribed to GoodMorning topic and another group NoonTopic. Kindly assist.

[Arjun]

I'm using the above cloud function to send notification, but I don't know how to receive for iOS. Could somebody please let me know how to receive the above notification and display its content to the user?

[DevAS]

@Gsilveira can you check this,stackoverflow.com/questions/56656303/…