How do you get client-side firebase cloud messaging token into google cloud function?

Question

I'm working towards implementing push notifications that appear on change to a firebase firestore document. I'm using the react-native-firebase module. My google cloud function listens for changes to the firestore and then sends messages via firebase-admin.

google's reference says you can specify a single device to message with:

// This registration token comes from the client FCM SDKs.
var registrationToken = 'YOUR_REGISTRATION_TOKEN';

var message = {
  data: {
    score: '850',
    time: '2:45'
  },
  token: registrationToken
};

// Send a message to the device corresponding to the provided
// registration token.
admin.messaging().send(message)
  .then((response) => {
    // Response is a message ID string.
    console.log('Successfully sent message:', response);
  })
  .catch((error) => {
    console.log('Error sending message:', error);
  });

client-side in my react-native app I get a token using react-native-firebase:

function getToken() {
  let fcmToken = await AsyncStorage.getItem("fcmToken");
  if (!fcmToken) {
    fcmToken = await firebase.messaging().getToken();
    if (fcmToken) {
      await AsyncStorage.setItem("fcmToken", fcmToken);
    }
  }
}

Do I have to store the google cloud messaging token somewhere other than async storage or is there a way to access it as is, inside my google cloud function? It seems like I should be storing the auth token inside firestore and accessing firestore with cloud functions. is this the best way to do this?

Answer 1

You don't need AsyncStorage to access the token, it is available right from fcmToken = await firebase.messaging().getToken(); in your code.

From there you can either send it to a callback Cloud Function with something like:

var sendMessage = firebase.functions().httpsCallable('sendMessage');
addMessage({ token: fcmToken }).then(function(result) {
  // ...
});

This is based on the example in the documentation here. You can then use this value in your Cloud Functions code to send a message by calling the FCM API through the Admin SDK.

Or store it in a database, such as Cloud Firestore with something like this:

db.collection("tokens").add(docData).then(function() {
    console.log("Token successfully written to database!");
});

Which is based on the example in the documentation here. You can then read this value from the database in your Cloud Function and use it to again send a message by calling the FCM API through the Admin SDK.