Handling Calls from Code

---slug: /guides/voice/compatibility-api/handling-calls-from-codesidebar_position: 0x-custom: author: danieleds---# Handling Calls from Codeimport Tabs from @theme/Tabs;import TabItem from @theme/TabItem;In [Making and Receiving Phone Calls](guides/voice-api/getting-started-with-voice/making-and-receiving-phone-calls/index.mdx) welearned how to use Compatibility XML bins to control outbound and inbound calls. Inparticular, we showed how to play a simple audio message.Handling calls from code gives us more flexibility. Instead of serving astatic XML bin, we can use a custom web server to decide the content of the XMLdepending on the state of the call, on the caller, on the time, etc.In this guide, we will show how to create a simple phone service which will tellthe user the current day, with a variation on weekends.## Setting up the environmentWe are going to use a few libraries to make our job easier. In particular, wellneed the SignalWire Compatibility SDK and, depending on the language youreusing, well also need a web server. Lets install them:shellpip install flask signalwireshellcomposer require signalwire-community/signalwireshellnpm install express @signalwire/compatibility-api## Producing XMLWed like to set up an endpoint (our own dynamic XML bin) which emits an XML document, like this one:xml Welcome! Today is Friday.The XML will be sent back to the client as a response to their request.In principle, we could manually create such XML by means of string concatenationor interpolation. However, if you are using one of our supported languages, youcan use our libraries to more easily produce the same XML:pythonfrom twilio.twiml.voice_response import VoiceResponseresponse = VoiceResponse()response.say(Welcome! Today is Friday.)# Prints the XML string.print(response.to_xml())phpsay(Welcome! Today is Friday.);# Prints the XML string.echo $response->asXML();javascriptimport { RestClient } from @signalwire/compatibility-api;const response = new RestClient.LaML.VoiceResponse();response.say(Welcome! Today is Friday.);// Prints the XML string.console.log(response.toString());## Serving the XMLNow that we know how to generate a proper Compatibility XML document, lets seehow to set up a web server to serve those documents.### Setting up a web serverHow you set up the web server is mostly specific to the language and frameworkof your choosing. A basic skeleton might be the following:python title=main.pyfrom flask import Flask, request, Responsefrom twilio.twiml.voice_response import VoiceResponseapp = Flask(__name__)@app.route(/, methods=[GET, POST])def call_handler(): This endpoint will be queried by SignalWire whenever an incoming call is received. We respond with an XML document which specifies the next instructions. print(request.values) # The logic goes here returnphp title=index.phpjavascript title=index.jsimport express from express;import { RestClient } from @signalwire/compatibility-api;const app = express();app.use(express.urlencoded({ extended: true }));/** * @param {express.Request} req * @param {express.Response} res */function callHandler(req, res) { // This endpoint will be queried by SignalWire whenever an incoming call is received. // We respond with an XML document which specifies the next instructions. console.log(req.body); // The logic goes here.}app.get(/, callHandler);app.post(/, callHandler);app.listen(8080);In the next section we will configure a phone number so that, when it receives amessage, SignalWire makes an HTTP request to our message handler endpoint. TheHTTP request will contain as parameters values such as the source number or thebody of the incoming message.For our simple subscription service demo, our message handler needs to look atthe body of the message to determine whether it contains the word START orSTOP. Depending on the word, we will emit an XML document which will producedifferent messages.python title=main.pyfrom flask import Flask, request, Responsefrom twilio.twiml.voice_response import VoiceResponsefrom datetime import datetimeapp = Flask(__name__)@app.route(/, methods=[GET, POST])def call_handler(): This endpoint will be queried by SignalWire whenever an incoming call is received. We respond with an XML document which specifies the next instructions. print(request.values) # Get the callers number caller = request.values.get(From) now = datetime.now() response = VoiceResponse() response.say(fWelcome! Today is {now.strftime(%A)}.) response.say(fYour phone number ends in {caller[-2:]}.) if now.weekday() >= 5: response.say(fEnjoy the weekend.) return Response(response.to_xml(), mimetype=text/xml)php title=index.phpsay(Welcome! Today is . date(l));$response->say(Your phone number ends in . substr($caller, -2));if (date(w) == 0 || date(w) == 6) { $response->say(Enjoy the weekend.);}header(Content-type: text/xml);echo $response->asXML();javascript title=index.jsimport express from express;import { RestClient } from @signalwire/compatibility-api;const app = express();app.use(express.urlencoded({ extended: true }));/** * @param {express.Request} req * @param {express.Response} res */function callHandler(req, res) { // This endpoint will be queried by SignalWire whenever an incoming call is received. // We respond with an XML document which specifies the next instructions. /** @type string */ const caller = req.body?.[From] ?? ; const now = new Date(); const response = new RestClient.LaML.VoiceResponse(); response.say(Welcome! Today is + now.toLocaleString(en-us, { weekday: long })); response.say(Your phone number ends in + caller.slice(-2)); if (now.getDay() === 0 || now.getDay() === 6) { response.say(Enjoy the weekend.); } res.set(Content-Type, text/xml); res.send(response.toString());}app.get(/, callHandler);app.post(/, callHandler);app.listen(8080);This simple message handler works like a dynamic XML bin, whose content dependson the received message.Try running the application, which will listen on port 8080:bashpython3 -m flask --app main.py run --host=0.0.0.0 --port 8080bashdocker run --rm -it -p 8080:80 -v $PWD:/var/www/html php:8.1-apachebashnode index.jsSince you are likely behind a NAT, to test this application on your localmachine you need a public IP address that SignalWire can reach. We suggest using[ngrok](https://ngrok.com/): refer to our [guide onngrok](guides/administration/guides/technical-troubleshooting/how-to-test-webhooks-with-ngrok/index.mdx)for more information.In short, while the application is up and listening on port 8080, run ngrok from a new terminal like this:bashngrok http 8080Youll get a public random URL (such as https://983f-93-41-16-193.ngrok.io/)that you can use to access your local application.### Configuring the numberNow that the code is ready and the HTTP endpoint is reachable from the web, weneed to configure our SignalWire number to access it.If you dont have a phonenumber yet, make sure to [buyone](guides/numbers-api/getting-started/buying-a-phone-number/index.mdx). Youwill need at least one number to receive messages.Then, open the settings for the number. Under Voice and Fax Settings, chooseto handle incoming calls using LaML Webhooks, then paste the public ngrok URLwhich connects to your application.

Try dialing the configured phone number: after a few seconds youll receive anautomated reply, whose content will be different depending on the day of theweek.## ConclusionWe have shown how to handle calls from code, by emitting XMLdocuments whose content depends on external factors. We did all this in thecontext of the [Compatibility API](pathname:///compatibility-api).For more advanced, real-time applications, youll want to check outour [Realtime SDK](sdks/reference/realtime-sdk/00-realtime-sdk-reference.mdx). Find more detailsin the guide about [First Steps with Voice in the Realtime SDK](guides/voice-api/guides/realtime-api/first-steps-with-voice/index.mdx).