Firebase Messaging

Push notifications are shown and tapped through Notifications in @ng-native/expo, as with any other push. This package only adds the registration.

Install

npx expo install @ng-native/firebase-messaging expo-notifications

Add the plugin and Firebase's config files to app.json, then rebuild the app. It needs a development build, not Expo Go.

{
  "expo": {
    "plugins": ["@ng-native/firebase-messaging"],
    "ios": { "googleServicesFile": "./GoogleService-Info.plist" },
    "android": { "googleServicesFile": "./google-services.json" }
  }
}

Expo copies each file into the app at prebuild, and prebuild fails when one is missing. When the files are not in the repository (each developer supplies their own, or EAS provides them as file environment variables), set each path in app.config.js only when its file is there:

const { existsSync } = require('node:fs');

const file = (variable, path) => process.env[variable] ?? (existsSync(path) ? path : undefined);

module.exports = ({ config }) => ({
  ...config,
  ios: {
    ...config.ios,
    googleServicesFile: file('GOOGLE_SERVICE_INFO_PLIST', './GoogleService-Info.plist'),
  },
  android: {
    ...config.android,
    googleServicesFile: file('GOOGLE_SERVICES_JSON', './google-services.json'),
  },
});

A build without the file runs, and register() rejects with the code ERR_NO_FIREBASE_CONFIG on iOS and Android.

The plugin turns on FCM registration by installation ID, which both platforms leave off. On iOS it also turns off Firebase's app delegate proxy, which would take over the push methods expo-notifications already handles, and gives the GoogleUtilities pod modules in the Podfile, which Firebase's Swift pods need to link as static libraries.

Register

import { Service, effect, inject } from '@angular/core';
import { FirebaseMessaging } from '@ng-native/firebase-messaging';

@Service()
export class Push {
  private readonly messaging = inject(FirebaseMessaging);
  private readonly api = inject(Api);

  constructor() {
    effect(() => {
      const fid = this.messaging.installationId();
      if (fid) void this.api.savePushTarget(fid);
    });
  }

  enable(): Promise<string | null> {
    return this.messaging.register();
  }
}

• register() asks for the notification permission when it has not been answered, registers the installation with FCM and answers its FID. On iOS FCM delivers over APNs, so it registers with the APNs token Notifications reports. It answers null without the permission.
• installationId is the FID each registration answers. Once it has registered, when the platform rolls the push token while the app runs, the installation is registered again with the new token and this is set again, so an effect on it keeps the backend up to date. Firebase can also replace the FID by itself, so once registered, the FID is read again each time the app comes back to the front, and this follows it.
• getInstallationId() answers the FID without registering it.

Without the native module, in Expo Go, on the web host or in a test that provides nothing, every call answers null. A test provides a fake through FirebaseMessaging.SOURCE. Until register() runs, the service reads nothing from Notifications, so a test's fake of Notifications needs only the members the test uses.

Unregister

When the app's pushes belong to the signed-in user, call unregister() on sign-out. Otherwise the backend still holds the FID against the old user, and their pushes keep arriving after someone else signs in on the same device.

async signOut(): Promise<void> {
  await this.messaging.unregister();
  await this.auth.signOut();
}

unregister() deletes the installation, so FCM answers UNREGISTERED for its FID, and sets installationId to null. A roll of the push token or a return to the front registers and reads nothing until register() runs again, which registers a new FID for the effect to send to the backend.

Send from a backend

A backend sends to the FID with FCM's HTTP v1 messages.send, authorized with an OAuth 2.0 token for a service account of the Firebase project:

curl -X POST "https://fcm.googleapis.com/v1/projects/$PROJECT_ID/messages:send" \
  -H "Authorization: Bearer $ACCESS_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{ "message": { "fid": "'"$FID"'", "notification": { "title": "Hello", "body": "From FCM" } } }'

A response of 404 with UNREGISTERED means the installation is not registered: the app has not called register() yet, it called unregister(), or it was uninstalled, and the backend can drop that FID.