# Manage application state with cookies Due to the ephemeral nature of Functions, application state for purely serverless apps has previously been difficult to manage, or required storing such information in a remote database. Luckily, with access to [cookies](/docs/serverless/functions-assets/functions/headers-and-cookies) with [Runtime Handler](/docs/serverless/functions-assets/handler) version 1.2.1 and later, you can now maintain limited state in your apps through cookies! Let's create a Function named `state` that leverages per-phone number cookies to store some application state, just like you would with a [more traditional, server-based solution](/docs/messaging/tutorials/how-to-create-sms-conversations/node-js#using-http-cookies-with-webhooks)! Use the following directions to create a Service and your `state` Function: ## Create and host a Function In order to run any of the following examples, you will first need to create a Function into which you can paste the example code. You can create a Function using the Twilio Console or the [Serverless Toolkit](/docs/labs/serverless-toolkit) as explained below: ## Console If you prefer a UI-driven approach, creating and deploying a Function can be done entirely using the Twilio Console and the following steps: 1. Log in to the Twilio Console and navigate to the [Functions tab](https://www.twilio.com/console/functions/overview). If you need an account, you can sign up for a free Twilio account [here](https://www.twilio.com/try-twilio)! 2. Functions are contained within **Services**. Create a **[Service](/docs/serverless/functions-assets/functions/create-service)** by clicking the **[Create Service](https://www.twilio.com/console/functions/overview/services)** button and providing a name such as *test-function*. 3. Once you've been redirected to the new Service, click the **Add +** button and select **Add Function** from the dropdown. 4. This will create a new [Protected](/docs/serverless/functions-assets/visibility) Function for you with the option to rename it. The name of the file will be path it is accessed from. 5. Copy any one of the example code snippets from this page that you want to experiment with, and paste the code into your newly created Function. You can quickly switch examples by using the dropdown menu of the code rail. 6. Click **Save** to save your Function's contents. 7. Click **Deploy All** to build and deploy the Function. After a short delay, your Function will be accessible from: `https://--.twil.io/`\ For example: `test-function-3548.twil.io/hello-world`. ## Serverless Toolkit The [Serverless Toolkit](/docs/labs/serverless-toolkit) enables you with local development, project deployment, and other functionality via the [Twilio CLI](/docs/twilio-cli/quickstart). To get up and running with these examples using Serverless Toolkit, follow this process: 1. From the CLI, run `twilio serverless:init --empty` to bootstrap your local environment. 2. Navigate into your new project directory using `cd ` 3. In the `/functions` directory, create a new JavaScript file that is named respective to the purpose of the Function. For example, `sms-reply.protected.js` for a [Protected](/docs/serverless/functions-assets/visibility) Function intended to handle incoming SMS. 4. Populate the file using the code example of your choice and save. **Note** A Function can only export a single handler. You will want to create separate files if you want to run and/or deploy multiple examples at once. Once your Function(s) code is written and saved, you can test it either by running it locally (and optionally tunneling requests to it via a tool like [ngrok](https://ngrok.com/)), or by deploying the Function and executing against the deployed url(s). ### Run your Function in local development Run `twilio serverless:start` from your CLI to start the project locally. The Function(s) in your project will be accessible from `http://localhost:3000/sms-reply` * If you want to test a Function as a [Twilio webhook](/docs/usage/webhooks/getting-started-twilio-webhooks), run: `twilio phone-numbers:update --sms-url "http://localhost:3000/sms-reply"`\ This will automatically generate an ngrok tunnel from Twilio to your locally running Function, so you can start sending texts to it. You can apply the same process but with the `voice-url` flag instead if you want to test with [Twilio Voice](/docs/voice). * If your code does *not* connect to Twilio Voice/Messages as a webhook, you can start your dev server and start an ngrok tunnel in the same command with the `ngrok` flag. For example: `twilio serverless:start --ngrok=""` ### Deploy your Function To deploy your Function and have access to live url(s), run `twilio serverless:deploy` from your CLI. This will deploy your Function(s) to Twilio under a development environment by default, where they can be accessed from: `https://--dev.twil.io/` For example: `https://incoming-sms-examples-3421-dev.twil.io/sms-reply` Your Function is now ready to be invoked by HTTP requests, set as the [webhook](/docs/usage/webhooks/getting-started-twilio-webhooks) of a Twilio phone number, invoked by a Twilio Studio **[Run Function Widget](/docs/studio/widget-library/run-function)**, and more! ## Store application state in a cookie Now that you have your `state` Function, copy over the following code sample, save the Function, and deploy your Service. ```js title="Add counter state to an SMS response" exports.handler = (context, event, callback) => { // Initialize a new Response and some TwiML const response = new Twilio.Response(); const twiml = new Twilio.twiml.MessagingResponse(); // Cookies are accessed by name from the event.request.cookies object // If the user doesn't have a count yet, initialize it to zero. Cookies are // always strings, so you'll need to convert the count to a number const count = Number(event.request.cookies.count) || 0; // Return a dynamic message based on if this is the first message or not const message = count > 0 ? `Your current count is ${count}` : 'Hello, thanks for the new message!'; twiml.message(message); response // Add the stringified TwiML to the response body .setBody(twiml.toString()) // Since we're returning TwiML, the content type must be XML .appendHeader('Content-Type', 'text/xml') // You can increment the count state for the next message, or any other // operation that makes sense for your application's needs. Remember // that cookies are always stored as strings .setCookie('count', (count + 1).toString()); return callback(null, response); }; ``` For Twilio SMS, cookies are scoped to the "conversation" between two parties — you can have a unique cookie for each To/From phone number pair. For example, you can store a unique cookie for any messages sent between 415-555-2222 (your number, for example) and 415-555-1111 (the phone number your Function is a webhook for), which will be different from the cookie used between 415-555-3333 and 415-555-1111. The code here is accepting an incoming Message webhook request, and checking for an incoming cookie named `count`. If that cookie is not present, `count` is initialized to 0, the user message is formatted to indicate the start of a conversation, and the count is incremented then set as a cookie along with the response to the sender. If `count` is already present, its value is included in the message, incremented, and set so that subsequent messages can continue to store the ever-increasing value of `count`. To test this and observe your stateless Function managing to track state with cookies, you'll need to set your deployed `state` Function as the webhook for your Twilio phone number, as shown next. > \[!WARNING] > > Cookies created in this [specific scenario](https://help.twilio.com/hc/en-us/articles/223136287-How-do-Twilio-cookies-work) (Twilio forwarding SMS messages to your Function or server) are limited to a maximum lifetime of **four hours**, so if a conversation remains idle for more than four hours, it will be automatically cleared. If you require longer-lasting state, you will need to store it in an external source such as a database. > > In any other scenario, cookies set by your Function are only subject to the usual [limitations](/docs/serverless/functions-assets/functions/headers-and-cookies/limitations#maximum-header-size). ## Set a Function as a webhook In order for your Function to react to incoming SMS and/or voice calls, it must be set as a [webhook](/docs/usage/webhooks) for your Twilio number. There are a variety of methods to set a Function as a webhook, as detailed below: ![Setting a Function as a Messaging webhook using the webhook dropdown option.](https://docs-resources.prod.twilio.com/bf4eae4ac40fe7d47003a93bca295d5c232e0b372358e73ceff931fee3ccdc4f.png) ## Validate that it works Now that your Twilio phone number is directing incoming SMS messages to your Function, try sending a short message to your Twilio phone number. You will receive an initial response of `Hello, thanks for the new message!`, and any subsequent messages you send will then receive a response of `Your current count is 1`, `Your current count is 2`, and so on. ## Set state attributes Cookies support several [attributes](https://developer.mozilla.org/en-US/docs/Web/HTTP/Cookies#define_the_lifetime_of_a_cookie), which allow you to define aspects such as duration, security, and more. You can set these using the third parameter to `setCookie`. For example, given the existing call: ```javascript response.setCookie('count', (count + 1).toString()); ``` You could modify the `count` cookie to last for a maximum of 30 minutes (1800 seconds) by setting the `Max-Age` attribute like so: ```javascript response.setCookie('count', (count + 1).toString(), ['Max-Age=1800']); ``` ## Remove or reset state By default, session cookies persisted by Twilio SMS only last for four hours at most, and you cannot exceed this limit. However, it's perfectly valid to *remove* a cookie at any time to fit your application's needs. For example, you could clear the count from the previous example once a condition is met, as shown in this sample: ```js title="Clear counter state from an SMS conversation" // !mark(14,15,16,17,18,19,20,21) exports.handler = (context, event, callback) => { // Initialize a new Response and some TwiML const response = new Twilio.Response(); const twiml = new Twilio.twiml.MessagingResponse(); // Since we're returning TwiML, the content type must be XML response.appendHeader('Content-Type', 'text/xml'); // Cookies are accessed by name from the event.request.cookies object // If the user doesn't have a count yet, initialize it to zero. Cookies are // always strings, so you'll need to convert the count to a number const count = Number(event.request.cookies.count) || 0; if (count > 5) { twiml.message("You've reached the end of the count!"); // In this case we want to remove the count and let the user begin // a new conversation response.setBody(twiml.toString()).removeCookie('count'); // Use an early return to respond to the user and avoid other logic paths return callback(null, response); } // Return a dynamic message based on if this is the first message or not const message = count > 0 ? `Your current count is ${count}` : 'Hello, thanks for the new message! Message again to see your count update.'; twiml.message(message); response.setBody(twiml.toString()).setCookie('count', (count + 1).toString()); return callback(null, response); }; ``` ## Validate state reset If you save and deploy this new code instead, you should have a very similar interaction with your Twilio phone number. After sending a message, you will receive an initial response, and any subsequent messages you send will then receive a response of `Your current count is 1`, `Your current count is 2`, and so on. The difference is that after reaching a count of five and sending another message, you'll receive `You've reached the end of the count!`. If you try to message again, you'll find yourself in a completely new conversation. This is a handy way to end interactions, such as if your application has successfully helped a customer, or if your application is a game that the user has won or lost. > \[!WARNING] > > These examples demonstrate adding a single state value as a cookie, but you are free to add more to support your application needs! > > Keep in mind, there are [limitations](/docs/serverless/functions-assets/functions/headers-and-cookies/limitations#maximum-header-size) on how many cookies can be set, how large they can be, and how long they can persist until expiring. > \[!NOTE] > > Curious about what else you can build by using cookies to add statefulness to your Functions? Check out this [blog article](/blog/build-wordle-like-sms-game-serverless) to see how you can build your own Wordle clone purely with [Functions](/docs/serverless/functions-assets/functions) and [Assets](/docs/serverless/functions-assets/assets)!