FCM very slow and unreliable when sending to a group of recipients through Cloud Function - firebase

Question

I have the following Function that:
Listens for document (text message) creation
Grab IDs of members of a group chat
Get the FCM Tokens for each member
With a for-loop, send messages to group members
exports.sendChatMessage = functions.firestore
.document("chats/{mealID}/messages/{messageID}")
.onCreate((snap, context) => {
const data = snap.data();
const mealID = context.params.mealID;
const senderID = data.senderID;
const senderName = data.senderName;
const messageContent = data.content;
var docRef = db.collection("chats").doc(mealID);
docRef
.get()
.then((doc) => {
if (doc.exists) {
const docData = doc.data();
const mealName = docData.name;
const userStatus = docData.userStatus;
var users = docData.to;
var eligibleUsers = users.filter(
(user) => userStatus[user] == "accepted"
);
eligibleUsers.push(docData.from);
// get fcmTokens from eligibleUsers and send the messagme
db.collection("users")
.where("uid", "in", eligibleUsers)
.get()
.then((snapshot) => {
var fcmTokens = [];
var thumbnailPicURL = "";
// get thumbnailpic of the sender and collect fcmTokens
snapshot.forEach((doc) => {
if (doc.data().uid == senderID) {
thumbnailPicURL =
doc.data().thumbnailPicURL == null
? "https://i.imgur.com/8wSudUk.png"
: doc.data().thumbnailPicURL;
} else {
fcmTokens.push(doc.data().fcmToken);
}
});
// send the message fcmTokens
fcmTokens.forEach((token) => {
if (token != "") {
const fcmMessage = {
message: {
token: token,
notification: {
title: mealName,
body: senderName + ": " + messageContent,
image: thumbnailPicURL,
},
apns: {
payload: {
aps: {
category: "MESSAGE_RECEIVED",
},
MEAL_ID: mealID,
},
},
},
};
tokenManger.sendFcmMessage(fcmMessage);
}
});
return true;
});
} else {
// doc.data() will be undefined in this case
console.log("No such document!");
return false;
}
})
.catch((error) => {
console.log("Error getting document:", error);
return false;
});
return true;
});
My send function comes from a helper file that uses the HTTP V1 protocol to build the send-request:
const { google } = require("googleapis");
const https = require("https");
const MESSAGING_SCOPE = "https://www.googleapis.com/auth/firebase.messaging";
const SCOPES = [MESSAGING_SCOPE];
const PROJECT_ID = MY_PROJECT_ID;
const HOST = "fcm.googleapis.com";
const PATH = "/v1/projects/" + PROJECT_ID + "/messages:send";
exports.getAccessToken = () => {
return new Promise(function (resolve, reject) {
const key = require("./service-account.json");
var jwtClient = new google.auth.JWT(
key.client_email,
null,
key.private_key,
SCOPES,
null
);
jwtClient.authorize(function (err, tokens) {
if (err) {
reject(err);
return;
}
resolve(tokens.access_token);
});
});
};
//send message
exports.sendFcmMessage = (fcmMessage) => {
this.getAccessToken().then(function (accessToken) {
var options = {
hostname: HOST,
path: PATH,
method: "POST",
headers: {
Authorization: "Bearer " + accessToken,
},
// … plus the body of your notification or data message
};
var request = https.request(options, function (resp) {
resp.setEncoding("utf8");
resp.on("data", function (data) {
console.log("Message sent to Firebase for delivery, response:");
console.log(data);
});
});
request.on("error", function (err) {
console.log("Unable to send message to Firebase");
console.log(err);
});
request.write(JSON.stringify(fcmMessage));
request.end();
});
};
It worked all fine in the emulator but once deployed, there're significant delays (~3 mins):
I also noticed that the console says the cloud function finishes execution BEFORE sendFcmMessage logs success messages.
I did some research online, it appears that it might have something to do with the usage of Promise but I wasn't sure if that's the sole reason or it has something to do with my for-loop.

Answer 1

The Problem
To summarize the issue, you are creating "floating promises" or starting other asynchronous tasks (like in sendFcmMessage) where you aren't returning a promise because they use callbacks instead.
In a deployed function, as soon as the function returns its result or the Promise chain resolves, all further actions should be treated as if they will never be executed as documented here. An "inactive" function might be terminated at any time, is severely throttled and any network calls you make (like setting data in database or calling out to FCM) may never be executed.
An indicator that you haven't properly chained the promises is when you see the function completion log message ("Function execution took...") before other messages you are logging. When you see this, you need to look at the code you are running and confirm whether you have any "floating promises" or are using callback-based APIs. Once you have changed the callback-based APIs to use promises and then made sure they are all chained together properly, you should see a significant boost in performance.
The fixes
Sending the message data to FCM
In your tokenManger file, getAccessToken() could be reworked slightly and sendFcmMessage should be converted to return a Promise:
exports.getAccessToken = () => {
return new Promise(function (resolve, reject) {
const key = require("./service-account.json");
const jwtClient = new google.auth.JWT(
key.client_email,
null,
key.private_key,
SCOPES,
null
);
jwtClient.authorize(
(err, tokens) => err ? reject(err) : resolve(tokens.access_token)
);
});
};
//send message
exports.sendFcmMessage = (fcmMessage) => {
// CHANGED: return the Promise
return this.getAccessToken().then(function (accessToken) {
const options = {
hostname: HOST,
path: PATH,
method: "POST",
headers: {
Authorization: "Bearer " + accessToken,
},
// … plus the body of your notification or data message
};
// CHANGED: convert to Promise:
return new Promise((resolve, reject) => {
const request = https.request(options, (resp) => {
resp.setEncoding("utf8");
resp.on("data", resolve);
resp.on("error", reject);
});
request.on("error", reject);
request.write(JSON.stringify(fcmMessage));
request.end();
});
});
};
However, the above code was built for googleapis ^52.1.0 and google-auth-library ^6.0.3. The modern versions of these modules are v92.0.0 and v7.11.0 respectively. This means you should really update the code to use these later versions like so:
// Import JWT module directly
const { JWT } = require('google-auth-library');
// FIREBASE_CONFIG is a JSON string available in Cloud Functions
const PROJECT_ID = JSON.parse(process.env.FIREBASE_CONFIG).projectId;
const FCM_ENDPOINT = `https://fcm.googleapis.com/v1/projects/${PROJECT_ID}/messages:send`;
const FCM_SCOPES = ["https://www.googleapis.com/auth/firebase.messaging"];
exports.sendFcmMessage = (fcmMessage) => {
const key = require("./service-account.json"); // consider moving outside of function (so it throws an error during deployment if its missing)
const client = new JWT({
email: key.client_email,
key: key.private_key,
scopes: FCM_SCOPES
});
return client.request({ // <-- this uses `gaxios`, Google's fork of `axios` built for Promise-based APIs
url: FCM_ENDPOINT,
method: "POST",
data: fcmMessage
});
}
Better yet, just use the messaging APIs provided by the Firebase Admin SDKs that handle the details for you. Just feed it the message and tokens as needed.
import { initializeApp } from "firebase-admin/app";
import { getMessaging } from "firebase-admin/messaging";
initializeApp(); // initializes using default credentials provided by Cloud Functions
const fcm = getMessaging();
fcm.send(message) // send to one (uses the given token)
fcm.sendAll(messagesArr) // send to many at once (each message uses the given token)
fcm.sendMulticast(message) // send to many at once (uses a `tokens` array instead of `token`)
The Cloud Function
Updating the main Cloud Function, you'd get:
exports.sendChatMessage = functions.firestore
.document("chats/{mealID}/messages/{messageID}")
.onCreate((snap, context) => {
const mealID = context.params.mealID;
const { senderID, senderName, content: messageContent } = snap.data();
const docRef = db.collection("chats").doc(mealID);
/* --> */ return docRef
.get()
.then((doc) => {
if (!doc.exists) { // CHANGED: Fail fast and avoid else statements
console.log(`Could not find "chat:${mealID}"!`);
return false;
}
const { userStatus, to: users, name: mealName, from: fromUser } = doc.data();
const eligibleUsers = users.filter(
(user) => userStatus[user] == "accepted"
);
eligibleUsers.push(fromUser);
// get fcmTokens from eligibleUsers and send the message
/* --> */ return db.collection("users")
.where("uid", "in", eligibleUsers) // WARNING: This will only work for up to 10 users! You'll need to break it up into chunks of 10 if there are more.
.get()
.then(async (snapshot) => {
const fcmTokens = [];
let thumbnailPicURL = "";
// get thumbnailpic of the sender and collect fcmTokens
snapshot.forEach((doc) => {
if (doc.get("uid") == senderID) {
thumbnailPicURL = doc.get("thumbnailPicURL"); // update with given thumbnail pic
} else {
fcmTokens.push(doc.get("fcmToken"));
}
});
const baseMessage = {
notification: {
title: mealName,
body: senderName + ": " + messageContent,
image: thumbnailPicURL || "https://i.imgur.com/8wSudUk.png", // CHANGED: specified fallback image here
},
apns: {
payload: {
aps: {
category: "MESSAGE_RECEIVED",
},
MEAL_ID: mealID,
},
}
}
// log error if fcmTokens empty?
// ----- OPTION 1 -----
// send the message to each fcmToken
const messagePromises = fcmTokens.map((token) => {
if (!token) // handle "" and undefined
return; // skip
/* --> */ return tokenManger
.sendFcmMessage({
message: { ...baseMessage, token }
})
.catch((err) => { // catch the error here, so as many notifications are sent out as possible
console.error(`Failed to send message to "fcm:${token}"`, err);
})
});
await Promise.all(messagePromises); // wait for all messages to be sent out
// --------------------
// ----- OPTION 2 -----
// send the message to each fcmToken
await getMessaging().sendAll(
fcmTokens.map((token) => ({ ...baseMessage, token }))
);
// --------------------
return true;
})
.catch((error) => {
console.log("Error sending messages:", error);
return false;
});
})
.catch((error) => {
console.log("Error getting document:", error);
return false;
});
});

Answer 2

I found out that the culprit is my queries to db. Like #samthecodingman commented, I was creating floating Promises.
Originally, I have codes like:
db.collection("users")
.where("uid", "in", eligibleUsers)
.get()
.then((snapshot) => {...}
All I needed to do is to return that call:
return db.collection("users")
.where("uid", "in", eligibleUsers)
.get()
.then((snapshot) => {...}
Although it's still not instant delivery, it's much faster now.