Connectivity issues to firebase emulator

[lhrolim]

Quick Question: Functions Emulator Connection Issues

TL;DR: Cannot connect to Firebase Functions emulator from iOS Simulator and Android physical device, despite trying multiple approaches. Android Simulator works perfectly.

Problem

• ✅ Emulator accessible from browser (localhost:5002)
• ❌ React Native Firebase calls fail on both iOS Simulator and Android physical device. It works fine from the Android Simulator.
• we get a basic connection error. Error: java.util.concurrent.ExecutionException: 1 out of 2 underlying tasks failed

What We've Tried

1. Both APIs: functions().useEmulator() and connectFunctionsEmulator()
2. Multiple hosts: localhost, 127.0.0.1, 10.0.2.2, network IP 192.168.1.147:5002
3. Android fixes: Network Security Config, ADB forwarding, android_bypass_emulator_url_remap
4. Connection timing: Calling immediately after getFunctions()
5. adb reverse tcp:5002 tcp:5002
6. Multiple LLM models and web research.

Questions

1. Which API is recommended: useEmulator() instance method or connectFunctionsEmulator() modular API?
2. Should localhost work on iOS Simulator? (It works in Safari)
3. Known issues with Android physical devices? (Tried network IP, ADB, security config)
4. How to verify emulator connection is actually established?

RN Firebase version: 23.4.0
Expo version: 54.0.20
React Native version: 0.81.5
Emulator port: 5002

Related: #6475

[ismaildasci]

for iOS Simulator localhost should work but there are quirks. for Android physical device its trickier.

1. iOS Simulator fix:
   localhost should work but try this order:

import { getFunctions, connectFunctionsEmulator } from "firebase/functions";

const functions = getFunctions();
if (__DEV__) {
  connectFunctionsEmulator(functions, "127.0.0.1", 5002);
}

2. Android physical device:
   needs your machines local IP, not localhost:

connectFunctionsEmulator(functions, "192.168.1.147", 5002);

also make sure emulator is binding to 0.0.0.0:

firebase emulators:start --host 0.0.0.0

3. check firewall:
   macOS firewall might block incoming connections on port 5002

4. verify connection:

try {
  const result = await httpsCallable(functions, "yourFunction")({});
  console.log("connected!", result);
} catch (e) {
  console.log("error:", e.code, e.message);
}

5. timing issue:
   call connectFunctionsEmulator immediately after getFunctions, before any httpsCallable

6. for physical android also check:

• both devices on same wifi network
• phones mobile data is off
• firebase.json has functions host as 0.0.0.0