google-cloud-node: Automatically create topic / subscription if not found.

I would like to share code to solve this problem.

import 'dotenv/config';
import {PubSub} from '@google-cloud/pubsub';

process.env.PUB_SUB_PREFIX = process.env.PUB_SUB_PREFIX || 'local';

process.env.SEARCH_REQUESTS_TOPIC = process.env.SEARCH_REQUESTS_TOPIC || 'search.requests';
process.env.SEARCH_REQUESTS_SUBSCRIPTION = process.env.SEARCH_REQUESTS_SUBSCRIPTION || process.env.SEARCH_REQUESTS_TOPIC + '-sub';

process.env.SEARCH_RESPONSES_TOPIC = process.env.SEARCH_RESPONSES_TOPIC || 'search.responses';
process.env.SEARCH_RESPONSES_SUBSCRIPTION = process.env.SEARCH_RESPONSES_SUBSCRIPTION || process.env.SEARCH_RESPONSES_TOPIC + '-sub';

process.env.CREATE_INDEX_REQUESTS_TOPIC = process.env.CREATE_INDEX_REQUESTS_TOPIC || 'index.create.requests';
process.env.CREATE_INDEX_REQUESTS_SUBSCRIPTION = process.env.CREATE_INDEX_REQUESTS_SUBSCRIPTION || process.env.CREATE_INDEX_REQUESTS_TOPIC + '-sub';

process.env.TRUNCATE_INDEX_REQUESTS_TOPIC = process.env.TRUNCATE_INDEX_REQUESTS_TOPIC || 'index.truncate.requests';
process.env.TRUNCATE_INDEX_REQUESTS_SUBSCRIPTION = process.env.TRUNCATE_INDEX_REQUESTS_SUBSCRIPTION || process.env.TRUNCATE_INDEX_REQUESTS_TOPIC + '-sub';

process.env.UPSERT_DOCUMENT_REQUESTS_TOPIC = process.env.UPSERT_DOCUMENT_REQUESTS_TOPIC || 'document.upsert.requests';
process.env.UPSERT_DOCUMENT_REQUESTS_SUBSCRIPTION = process.env.UPSERT_DOCUMENT_REQUESTS_SUBSCRIPTION || process.env.UPSERT_DOCUMENT_REQUESTS_TOPIC + '-sub';

process.env.DELETE_DOCUMENT_REQUESTS_TOPIC = process.env.DELETE_DOCUMENT_REQUESTS_TOPIC || 'document.delete.requests';
process.env.DELETE_DOCUMENT_REQUESTS_SUBSCRIPTION = process.env.DELETE_DOCUMENT_REQUESTS_SUBSCRIPTION || process.env.DELETE_DOCUMENT_REQUESTS_TOPIC + '-sub';


process.env.PUBSUB_EMULATOR_HOST = process.env.PUBSUB_EMULATOR_HOST || '0.0.0.0:8085';
process.env.PUBSUB_PROJECT_ID = process.env.PUBSUB_PROJECT_ID || 'pure-plaform';

const createTopicAndSubscription = async (pubsub: PubSub, {topic: topicName, subscription: subscriptionName}: {topic: string, subscription: string}) => {
    let topic = pubsub.topic(topicName);

    const [topicExists] = await topic.exists();

    if(!topicExists) {
        [topic] =  await pubsub.createTopic(topicName);
        console.log(`Topic created ${topicName}`);
    } else {
        console.log(`Topic exists ${topicName}`);
    }

    let subscription = topic.subscription(subscriptionName);

    const [subscriptionExists] = await subscription.exists()

    if(!subscriptionExists) {
        [subscription] = await topic.createSubscription(subscriptionName)
        console.log(`Subscription created ${topicName}`);
    } else {
        console.log(`Subscription exists ${topicName}`);
    }

    return {topic, subscription};
}

const main = async (): Promise<string> => {
    console.log("Creating pub/sub topics and subscriptions on project %s.", process.env.PUBSUB_PROJECT_ID);

    const client = new PubSub({projectId: process.env.PUBSUB_PROJECT_ID});

    const pubsubs = [
        { topic: process.env.SEARCH_REQUESTS_TOPIC, subscription: process.env.SEARCH_REQUESTS_SUBSCRIPTION },
        { topic: process.env.SEARCH_RESPONSES_TOPIC, subscription: process.env.SEARCH_RESPONSES_SUBSCRIPTION },
        { topic: process.env.CREATE_INDEX_REQUESTS_TOPIC, subscription: process.env.CREATE_INDEX_REQUESTS_SUBSCRIPTION },
        { topic: process.env.TRUNCATE_INDEX_REQUESTS_TOPIC, subscription: process.env.TRUNCATE_INDEX_REQUESTS_SUBSCRIPTION },
        { topic: process.env.UPSERT_DOCUMENT_REQUESTS_TOPIC, subscription: process.env.UPSERT_DOCUMENT_REQUESTS_SUBSCRIPTION },
        { topic: process.env.DELETE_DOCUMENT_REQUESTS_TOPIC, subscription: process.env.DELETE_DOCUMENT_REQUESTS_SUBSCRIPTION },
    ]

    for(const pubsub of pubsubs) {
        await createTopicAndSubscription(client, pubsub)
    }

    return 'Done';
}

main().then(console.log).catch(console.error);

After run it by

 ts-node .scripts/init-pubsub.ts

you can go to pages

http://localhost:8085/v1/projects/pure-plaform/topics http://localhost:8085/v1/projects/pure-plaform/subscriptions

and see

The approach we have taken for every object in this library is that you can create one or reference an existing one. If we changed this, it would need to be changed everywhere and would require two API requests rather than one, causing increased delays for responses.

Now actually, the latest pubsub v1beta2 (in this library master branch) call to create a topic/subscription is a PUT call meaning its idempotent (basically no matter how many times you call it, it won’t cause more effects than if you call it just once). This means that you can effectively “create or get” by always creating the topic regardless of whether it exists or not. If we know we don’t need to create it, it would be silly to try to every time we want to do something with it, this would multiply every request time by a factor of two and provide less stability overall.

Hope this makes sense. Let me know if there’s a smart compromise that could be made here.