Firebase function to validate Apple receipts

apple-receipt-firebase-validator.ts

import {https} from 'firebase-functions';
import bent = require("bent");

/*
* Docs
* https://firebase.google.com/docs/functions/typescript
* https://developer.apple.com/documentation/appstorereceipts/verifyreceipt
*/

/*
Apple validation status codes
	[0]:     { message: 'Active', valid: true, error: false },
	[21000]: { message: 'App store could not read', valid: false, error: true },
	[21002]: { message: 'Data was malformed', valid: false, error: true },
	[21003]: { message: 'Receipt not authenticated', valid: false, error: true },
	[21004]: { message: 'Shared secret does not match', valid: false, error: true },
	[21005]: { message: 'Receipt server unavailable', valid: false, error: true },
	[21006]: { message: 'Receipt valid but sub expired', valid: true, error: false },
	[21007]: { message: 'Sandbox receipt sent to Production environment', valid: false, error: true, redirect: true },
	[21008]: { message: 'Production receipt sent to Sandbox environment', valid: false, error: true },
*/

const sendToApple = async (data: string) => {
	const body = JSON.stringify({ 'receipt-data': data })
	const post = bent('POST', 'json', 200);

	/* We try production following Apple recommendation */
	try {
		const productionResponse: bent.Json & { status?: number } = await post('https://buy.itunes.apple.com/verifyReceipt', body)
		
		/* If status is 21007, we try sandbox */
		if (productionResponse.status === 21007) {
			return await post('https://sandbox.itunes.apple.com/verifyReceipt', body)
		}

		return productionResponse
	} catch (e) {
		console.error(e);
		return { 'error': JSON.stringify(e) }
	}

	return productionResponse
}

/*
* Postman can be used to test the deployed function.
* Paste a receipt data encoded as base64, without quotes, to a POST request Body as raw Text.
* Check if Content-Type is set to  text/plain in Header.
*
* * A sample receipt, working as of June 2020, can be obtained at
* https://stackoverflow.com/questions/33843281/apple-receipt-data-sample
*/
export const validateReceipt = https.onRequest(async (req, res) => {
	const appleResponse = await sendToApple(req.body)

	if (appleResponse.status === 0) {
		console.info(`Receipt for app ${appleResponse.receipt.bundle_id} decrypted by Apple ${appleResponse.environment} server.`)
	}

	res.header("Content-Type", "application/json")
	res.send(JSON.stringify(appleResponse))
})

package.json

{
  "name": "functions",
  "scripts": {
    "lint": "tslint --project tsconfig.json",
    "build": "tsc",
    "serve": "npm run build && firebase emulators:start --only functions",
    "shell": "npm run build && firebase functions:shell",
    "start": "npm run shell",
    "deploy": "firebase deploy --only functions",
    "logs": "firebase functions:log"
  },
  "engines": {
    "node": "10"
  },
  "main": "lib/index.js",
  "dependencies": {
    "@types/bent": "~7.0.2",
    "bent": "~7.3.2",
    "firebase-admin": "~8.10.0",
    "firebase-functions": "~3.6.1"
  },
  "devDependencies": {
    "tslint": "^5.12.0",
    "typescript": "~3.8.0",
  },
  "private": true
}