Firebase Cloud Function Nutrition Lookup Proxy

A Firebase Cloud Function nutrition lookup proxy is the fastest path for mobile teams already on Firebase Auth and Firestore. Your Flutter, React Native, or native apps call https://us-central1-PROJECT.cloudfunctions.net/foodSearch while the Calorie API key lives in Firebase secrets.

Why Firebase for Nutrition Lookup

Compare with Supabase Edge Functions or Next.js routes.

Step 1: Initialize Functions

firebase init functions
cd functions
npm install firebase-functions firebase-admin

Set secret:

firebase functions:secrets:set CALORIE_API_KEY

Step 2: HTTP Function (Gen 2)

functions/index.js:

const { onRequest } = require('firebase-functions/v2/https');
const { defineSecret } = require('firebase-functions/params');

const calorieApiKey = defineSecret('CALORIE_API_KEY');
const UPSTREAM = 'https://api.calorieapi.com/api/v1';

exports.foodSearch = onRequest(
  { secrets: [calorieApiKey], cors: true },
  async (req, res) => {
    const q = String(req.query.q ?? '').trim();
    const limit = Math.min(parseInt(req.query.limit, 10) || 10, 25);

    if (q.length < 2 || q.length > 100) {
      return res.status(400).json({ error: 'Invalid query' });
    }

    const url = `${UPSTREAM}/search/foods?q=${encodeURIComponent(q)}&limit=${limit}`;
    const upstream = await fetch(url, {
      headers: { 'X-API-Key': calorieApiKey.value() },
    });
    const data = await upstream.json();
    res.status(upstream.status).json(data);
  }
);

Step 3: Barcode Lookup Function

exports.foodBarcode = onRequest(
  { secrets: [calorieApiKey], cors: true },
  async (req, res) => {
    const upc = String(req.query.upc ?? '').trim();
    if (!/^\d{8,14}$/.test(upc)) {
      return res.status(400).json({ error: 'Invalid barcode' });
    }
    const url = `${UPSTREAM}/search/barcode/${upc}`;
    const upstream = await fetch(url, {
      headers: { 'X-API-Key': calorieApiKey.value() },
    });
    const data = await upstream.json();
    res.status(upstream.status).json(data);
  }
);

Step 4: Require Firebase Auth (Recommended)

const admin = require('firebase-admin');
admin.initializeApp();

async function verifyAuth(req) {
  const header = req.headers.authorization || '';
  const token = header.startsWith('Bearer ') ? header.slice(7) : null;
  if (!token) throw new Error('Unauthorized');
  return admin.auth().verifyIdToken(token);
}

// Call verifyAuth(req) before upstream fetch

Attach Firebase ID token from mobile clients.

Step 5: Client Call (Flutter Example)

final token = await FirebaseAuth.instance.currentUser!.getIdToken();
final uri = Uri.parse('https://us-central1-APP.cloudfunctions.net/foodSearch?q=banana');
final res = await http.get(uri, headers: {'Authorization': 'Bearer $token'});

Step 6: Deploy

firebase deploy --only functions

Cost and Quota Tips

1. Cache hot searches in Firestore or Memorystore
2. Debounce mobile search input
3. Monitor Calorie API dashboard alongside Firebase usage
4. Upgrade Calorie API plan before viral launch

Related Guides

• Hide nutrition API key mobile proxy
• Flutter integration tutorial
• Backend proxy pattern

Get API key | Docs