CloudFunctions: Request is sending twice - firebase

Question

I have an issue and I need help since I'm learning.
I have a flutter app that saves on Firebase/Firestore data, when a user requests a friendship I add it on both sender and target user, changing the IDs of sendTo and sentBy.
My problem is that CloudFunctions detect well that 2 collections from different users have been changed and notify me 2x (target user). So code is fine but should only notify once/target user
I'm using FCM to send local notifications.
exports.sendRequestNotification = functions.firestore
.document('users/{userId}/requests/{requestId}')
.onCreate((snap, context) => {
const docReq = snap.data()
/*console.log(docReq)*/
const sentBy = docReq.sentBy
const sentTo = docReq.sentTo
const contentRequest = docReq.code
if(contentRequest !== null){
// Get push token user to (receive)
admin
.firestore()
.collection('users')
.where('userId', '==', sentTo)
.get()
.then(querySnapshot => {
querySnapshot.forEach(userTo => {
/*console.log(`Found request user to: ${userTo.data().userId}`)*/
if (userTo.data().pushToken) {
// Get info user from (sent)
admin
.firestore()
.collection('users')
.where('userId', '==', sentBy)
.get()
.then(querySnapshot2 => {
querySnapshot2.forEach(userFrom => {
/*console.log(`Found request user from: ${userFrom.data().userId}`)*/
const payload = {
notification: {
title: `${userFrom.data().nickname}`,
body: contentRequest,
badge: '1',
sound: 'default'
}
}
// Let push to the target device
admin
.messaging()
.sendToDevice(userTo.data().pushToken, payload)
.then(response => {
/*console.log('Successfully sent request:', response)*/
})
.catch(error => {
console.log('Error sending request:', error)
})
})
})
} else {
console.log('User request or token not found')
}
})
})
return null
}
})

Answer 1

It is not very clear from your code why it would send the notification twice (since you check that userTo.data().userId !== sentBy). But what is sure is that you are not returning a Promise that resolves when all the asynchronous operations (get() and sendToDevice()) are completed.
I would suggest you watch the official Video Series (https://firebase.google.com/docs/functions/video-series/) which explain very well this point about returning Promises for background functions (in particular the ones titled "Learn JavaScript Promises").
In particular, you will see in the videos that if you don't return a Promise, the Cloud Function may terminate before asynchronous operations are completed, potentially resulting in some inconsistent (not logical) results .
So, you should give a try with the following adapted code, which returns the promises chain:
exports.sendRequestNotification = functions.firestore
.document('users/{userId}/requests/{requestId}')
.onCreate((snap, context) => {
const db = admin.firestore();
const docReq = snap.data();
/*console.log(docReq)*/
const sentBy = docReq.sentBy;
const sentTo = docReq.sentTo;
// Get push token user to (receive)
return db.collection('users')
.where('userId', '==', sentTo)
.get()
.then(querySnapshot => {
//We know there is only one document (i.e. one user with this Id), so lets use the docs property
//See https://firebase.google.com/docs/reference/js/firebase.firestore.QuerySnapshot.html#docs
const userTo = querySnapshot.docs[0];
if (userTo.data().pushToken && userTo.data().userId !== sentBy) {
// Get info user from (sent)
return db.collection('users')
.where('userId', '==', sentBy)
.get();
} else {
console.log('User request or token not found')
throw new Error('User request or token not found');
}
})
.then(querySnapshot => {
const userFrom = querySnapshot.docs[0];
const payload = {
notification: {
title: `${userFrom.data().nickname}`,
body: `requestNotify`,
badge: '1',
sound: 'default'
}
}
return admin
.messaging()
.sendToDevice(userTo.data().pushToken, payload);
})
.catch(error => {
console.log('Error:', error);
return false;
})
})