Redirect to Firebase Hosting custom domain

Question

I have setup a custom domain with Firebase Hosting (eg. myapp.domain.com).

How can one redirect (or turn off) the default Firebase Hosting URL (eg. myapp.firebaseap

Answer 1

You could use Firebase Functions.

Free for 125K invocations/month - https://firebase.google.com/pricing

An example using Express middleware:

// functions/index.js

const functions = require('firebase-functions');
const express = require('express');
const url = require('url');

const app = express();

// Allowed domains
let domains = ['localhost:5000', 'example.com'];
// Base URL to redirect
let baseurl = 'https://example.com/';

// Redirect middleware
app.use((req, res, next) => {
    if (!domains.includes(req.headers['x-forwarded-host'])) {
        return res.status(301).redirect(url.resolve(baseurl, req.path.replace(/^\/+/, "")));
    }
    return next();
});

// Dynamically route static html files
app.get('/', (req, res) => {
    return res.sendFile('index.html', { root: './html' });
});

// ...

// 404 middleware
app.use((req, res) => {
    return res.status(404).sendFile('404.html', { root: './html' });
});

// Export redirect function
exports.redirectFunc = functions.https.onRequest(app);

The exported function name must be added to rewrites in firebase.json e.g.:

{
    "hosting": {
        "public": "public",
        "rewrites": [
          {
            "source": "**",
            "function": "redirectFunc"
          }
        ]
    }
}