firebase-admin.js

const firebaseAdmin = require('firebase-admin');

firebaseAdmin.initializeApp();

exports.firestore = firebaseAdmin.firestore();
exports.auth = firebaseAdmin.auth();
exports.storage = firebaseAdmin.storage();

screenshot.js

const puppeteer = require('puppeteer');
const firebaseAdmin = require('./firebase-admin');

exports.handler = async (req, res) => {

	res.locals.browser = await puppeteer.launch({
		args: ['--no-sandbox']
	});

	const url = req.query.url;
	if (!url) {
		res.status(400).send('Please provide a URL. Example: ?url=https://example.com');
		return;
	}
	const browser = res.locals.browser;
	try {
		const page = await browser.newPage();
		await page.setViewport({ width: 1280, height: 1280 });
		page.on('console', msg => {
			console.info('console', msg._text);
		});
		page.on('error', msg => {
			console.info('error', msg);
		});
		page.on('pageerror', msg => {
			console.info('pageerror', msg);
		});
		page.on('requestfailed', msg => {
			console.info('requestfailed', msg._url);
		});
		await page.goto(url, { waitUntil: 'networkidle2' });

		let date = new Date();
		let timestamp = date.getTime();

		const screenshot = await page.screenshot({ fullPage: true });

		// Instantiate the GCP Storage instance
		var bucket = firebaseAdmin.storage.bucket();

		// Upload the image to the bucket
		var file = bucket.file(`screenshot-${timestamp}.png`);
		
		await file.save(screenshot, {
			metadata: { contentType: 'image/png' },
			public: true,
			validation: 'md5'
		});

		res.send('captured and saved a screenshot');
	} catch (e) {
		console.log(e);
		res.status(500).send(e.toString());
	}
	await browser.close();

}

storage.rules

service firebase.storage {
  match /b/{bucket}/o {
    match /{allPaths=**} {
      allow read, write: if false;
    }

    match /images/{imageId} {
      allow read, write: if request.auth != null;
    }
  }
}