Firebase - Handle cloud events within NestJS Framework

Question

I'm using NestJS as my backend Framework and Firebase.

To integrate Nest with Firebase on HTTP requests is simple as attaching the express instance of nest to Firebase:

const server: Express = express();

const bootstrap = async (expressInstance: Express) => {
  const app = await NestFactory.create(AppModule, expressInstance);
  await app.listen(3000);
  await app.init();
};

bootstrap(server);

exports.api = functions.https.onRequest(server);

But what about the other Google Functions (such as pubsub, firestore, auth, etc.)?

I'm building a subscription application, and I depend on functions.pubsub to check at the end of every day which subscriptions should I charge. It requires writing business logic that I want to write withing NestJs.

I'm trying to achieve something like this (in a nutshell):

functions.pubsub
    .topic('topic')
    .onPublish(app.getService(Service).method);

Answer 1

Turns out I was very close to the solution. instead of getService, I had to use get, like so:

const bootstrap = async (expressInstance: Express) => {
  const app = await NestFactory.create(AppModule, expressInstance);
  await app.init();

  return app;
};

const main = bootstrap(server);

export const subscriptions = functions
  .pubsub
  .topic('cron-topic')
  .onPublish((context, message) => main.then(app => {
    return app.get(SubscribeService).initDailyCharges(context, message));
  });

Answer 2

Found a new solution for standalone applications: https://docs.nestjs.com/standalone-applications

You don't need to bootstrap NestJS with Express server to handle PubSub messages.

export const subscriptions = functions
  .pubsub
  .topic('cron-topic')
  .onPublish((context, message) => {
    const app = await NestFactory.create(ApplicationModule);
    return app.get(SubscribeService).initDailyCharges(context, message);
  });