feat(functions): Add emulator support for integration tests (#1897)

* feat(functions): Add emulator support for integration tests

- Modernize package.json dependencies in integration tests for functions, app_check, and messaging.
- Resolve vulnerability in uuid via dependency overrides.
- Introduce start.js to spin up local functions emulator dynamically on port 5005.
- Strip http:// and https:// prefixes from emulator host strings for iOS to prevent crashes on native iOS client initialization.
- Parse FUNCTIONS_EMULATOR_HOST environment variable and --functions_emulator_host flag, and connect functions clients in integration tests to the emulator.

* docs: Add release notes for Cloud Functions emulator support

* chore: Incorporate PR review feedback and apply formatting

* docs: Update integration test backend readmes with emulator instructions

Author: inlined

.gitignore

@@ -88,3 +88,6 @@ src/firebase_test_framework.h
 src/ios/.clang-format
 src/ios/ios_app_framework.mm
 src/ios/ios_firebase_test_framework.mm
+
+# Node dependencies
+node_modules/

app_check/integration_test/functions/README.md

@@ -1,4 +1,23 @@
-Cloud functions used by the integration test.
-Instructions to deploy:
-1. From the innermost functions directory run `npm install`
-2. From this directory, run `firebase deploy --only functions`
+# Cloud Functions for App Check Integration Tests
+
+This directory contains the Cloud Functions backend used by the App Check integration tests.
+
+## Running Locally via Emulator
+
+To run these functions locally using the Firebase emulator:
+
+1. Navigate to the nested `functions/` directory and install dependencies:
+   ```bash
+   cd functions && npm install && cd ..
+   ```
+
+2. Start the Firebase emulator:
+   ```bash
+   npx firebase emulators:start --only functions --project functions-integration-test
+   ```
+
+3. Run the integration test client app, specifying the emulator host:
+   - Command-line flag: `--functions_emulator_host=localhost:5005`
+   - Environment variable: `FUNCTIONS_EMULATOR_HOST=localhost:5005`
+
+   *(Note: On Android, `localhost` or `127.0.0.1` will be automatically mapped to `10.0.2.2` to route requests to the host machine.)*

app_check/integration_test/functions/firebase.json

@@ -1,4 +1,10 @@
 {
+  "functions": {
+    "source": "functions"
+  },
+  "emulators": {
     "functions": {
+      "port": 5005
     }
+  }
 }