firebase serve: From a locally served app, call locally served functions

Question

How can I properly simulate a cloud function locally so that it has all data as when being invoked on firebase servers? (e.g. the context.auth)

I am serving my project with firebase serve, it runs ok on http://localhost:5000/, however, my cloud functions are being called from https://us-central1-<my-app>.cloudfunctions.net/getUser. (The function is not even deployed.)

To avoid XY problem, I am trying to debug my function, but calling it from firebase shell results in context.auth being undefined, same when calling via postman from http://localhost:5000/<my-app>/us-central1/getUser.

This is my ./functions/src/index.ts file

import * as functions from 'firebase-functions'
import admin from 'firebase-admin'
import { inspect } from 'util'

admin.initializeApp()

export const getUser = functions.https.onCall((data, context) => {
  console.debug('== getUser called =========================================')
  console.log('getUser', inspect(data), inspect(context.auth))
  return admin.database().ref('userRights/admin').child(context.auth.uid).once('value', snapshot => {
    console.log(snapshot.val())
    if (snapshot.val() === true) {
      return 'OK'
      // return {status: 'OK'}
    } else {
      return 'NOK'
      // return {status: 'error', code: 401, message: 'Unauthorized'}
    }
  })
})

file ./firebase.functions.ts

import { functions } from '~/firebase'
export const getUser = functions.httpsCallable('getUser')

Consumer ./src/pages/AdminPanel/index.tsx

import { getUser } from '~/firebase.functions'
//...
getUser({myDataX: 'asd'}).then(response => console.debug('response', response))

Answer 1

UPDATE - April/2021

As of April/2021, method useFunctionsEmulator has been deprecated. It is suggested to use method useEmulator(host, port) instead.

---

Original post:

By default, firebase serve sends queries to CLOUD function instead of localhost, but it is possible to change it to to point to localhost.

@gregbkr found a workaround for that at this github thread.

You basically add this after firebase initialization script (firebase/init.js) in html head.

<script>
   firebase.functions().useFunctionsEmulator("http://localhost:5001");
</script>

Make sure to REMOVE it when deploying to SERVER