Improve Firebase and Google Cloud function cold starts by using Firestore REST client instead of the default gRPC (time to retrieve a single document down from ~1.5 s to ~250 ms in cold start function)

fast-cold-start-firestore-firebase-function.ts

import {firestore_v1, google} from 'googleapis';
import {convert} from 'firestore-adapter';

let fs: firestore_v1.Firestore;

const getFirestore = async (): Promise<firestore_v1.Firestore> => {
    if (!fs) {
        const auth = new google.auth.GoogleAuth({
                scopes: ['https://www.googleapis.com/auth/cloud-platform']
            }),
            authClient = await auth.getClient();

        fs = new firestore_v1.Firestore({
            auth: authClient
        });
    }

    return fs;
};

export const googleApiFirestoreTest = functions.region('europe-west3').https.onRequest(
    async (request, response) => {
        const path = `projects/${process.env.GCLOUD_PROJECT}/databases/(default)/documents/users/{some-user-uid}`,
            firestore = await getFirestore();

        const result = await firestore.projects.databases.documents.get({
                name: path
            }),
            doc = result.data,
            idRegex = /([^/]+$)/g,
            id = doc.name.match(idRegex)[0],
            fields = doc.fields;

        response.send({
            id,
            data: convert.docToData(fields)
        });
    }
);