[FR] Dedicated initializer function for connecting to the Firebase emulator suite

まず、Admin SDK のエントリポイントである initializeApp、getAuth、getFirestore と、現在の FIRESTORE_EMULATOR_HOST の処理を読みます。要求されているエミュレータの初期化を、既存の Web およびモバイルクライアントのアプローチと比較します。エミュレータ用とリモート用の FirebaseApp インスタンスを、一時的な環境変数なしで分離してサポートし、Auth と Firestore の使用も含められれば完了です。

The use case involves use of two initialized instances of FirebaseApp, one for the emulator and another for an actual project. Specifically, it's desirable to programmatically copy data from one to the other without having to export then import separately.

Currently, the Admin SDK requires that an env var is set with host and port in order to connect to the emulator. This is unnecessarily complex when it comes time to init the app. For example, using Auth and Firestore together (and potentially more products) requires code like this:

import { initializeApp } from "firebase-admin/app"
import { getAuth } from "firebase-admin/auth"
import { getFirestore } from "firebase-admin/firestore"

export const remote = initializeApp()
export const remoteAuth = getAuth(remote)
export const remoteFirestore = getFirestore(remote)

process.env.FIRESTORE_EMULATOR_HOST = 'localhost:8080'
export const local = initializeApp(undefined, "local")
export const localAuth = getFirestore(local)
export const localFirestore = getFirestore(local)
delete process.env.FIRESTORE_EMULATOR_HOST

The use of the temporary env var is clunky here, and it would be more straightforward if there was a dedicated function that allowed the caller to pass the host and port instead:

const host, port = ...
export const local = initializeEmulatorApp(host, port, "local")
export const localAuth = getFirestore(local)
export const localFirestore = getFirestore(local)

Either that, or something similar to the way the web and mobile clients work for connecting to the emulator.