add-function

name	add-function
description	Scaffold a new Firebase Cloud Function in this repo's exportIfNeeded cold-start pattern. Use when asked to "add a function", "functionを追加", "Cloud Functionをつくって", "callableを追加して", "APIエンドポイントを追加". Creates the functions/src/functions logic + wrappers config, registers it in index.ts, and (for callables) adds the client-side httpsCallable in src/utils/functions.ts.

Add a Cloud Function

Functions are split in two so cold starts stay small and logic stays testable:

• functions/src/functions/<name>.ts — the business logic.
• functions/src/wrappers/<name>.ts — the firebase-functions binding (region, memory, timeout, App Check). Only the invoked wrapper is required at runtime.

Steps

1. Logic — functions/src/functions/<name>.ts

Keep it a plain async function that takes what it needs and returns data. Example:

import { CallableRequest } from "firebase-functions/v2/https";

export const greet = async (request: CallableRequest<{ name: string }>) => {
  const name = request.data.name ?? "world";
  return { message: `Hello, ${name}!` };
};

2. Wrapper — functions/src/wrappers/<name>.ts

Bind region / limits / App Check. Callable (v2) pattern:

import { onCall, HttpsError } from "firebase-functions/v2/https";
import { greet } from "../functions/greet";

const REGION = "asia-northeast1";

export default onCall({ region: REGION, memory: "1GiB", maxInstances: 5 }, async (request) => {
  if (request.app == undefined) {
    throw new HttpsError("failed-precondition", "Call must come from an App Check verified app.");
  }
  return await greet(request);
});

For an HTTP endpoint follow the hono/express wrappers (wrappers/server/hono.ts → onRequest({ region, memory, ... }, handler) from firebase-functions/v2/https), and add a hosting rewrite in firebase.json.

3. Register — functions/src/index.ts

exportIfNeeded("greet", "greet", exports);
// exportIfNeeded(publicFunctionName, wrapperFilePathUnderWrappers, exports)

The 1st arg is the deployed function name; the 2nd is the wrapper path relative to functions/src/wrappers/ (no extension).

4. Client hook (callables only) — src/utils/functions.ts

export const greetFunction = httpsCallable(functions, "greet");

Call it from a component: const { data } = await greetFunction({ name });. The client functions instance is pinned to asia-northeast1 (src/utils/firebase.ts) — the region must match the wrapper.

5. Verify

yarn --cwd functions lint
yarn --cwd functions build
yarn --cwd functions serve   # emulator; exercise the function

Conventions

• No any; type request.data and the return value. Double quotes, semicolons, 2-space indent.
• Set maxInstances / timeoutSeconds / memory deliberately (cost + abuse ceiling).
• Guard callables with the request.app App Check check and, for user data, request.auth.
• Deploy with firebase deploy --only functions (predeploy runs lint + build automatically).