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How to call Functions from iOS

Twilio Functions are a perfect fit for mobile app developers. You can focus on writing your app, and let Twilio host and run the server code you need.

You don't need a special SDK to call Twilio Functions from your mobile app—your Function will respond to a normal HTTP call, making it accessible from standard iOS Networking code.

In this guide, we'll show you how to set up a Twilio Function, call it from a web browser, and then call that function from an iOS application. Our Function will return a joke as a string. You could extend it to make it choose a random joke from a list, or by category. We'll keep it brief, and just return a hard coded string.

Let's start by creating a Function and giving it the path of /joke. Be sure to set the visibility of this Function to public, to avoid any hurdles when making your HTTP calls:

Create and host a Function

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Before you run any of the examples on this page, create a Function and paste the example code into it. You can create a Function in the Twilio Console or by using the Serverless Toolkit.

ConsoleServerless Toolkit

If you prefer a UI-driven approach, complete these steps in the Twilio Console:

  1. Log in to the Twilio Console(link takes you to an external page) and navigate to Develop > Functions & Assets. If you're using the legacy Console, open the Functions tab(link takes you to an external page).
  2. Functions are contained within Services. Click Create Service(link takes you to an external page) to create a new Service.
  3. Click Add + and select Add Function from the dropdown.
  4. The Console creates a new protected Function that you can rename. The filename becomes the URL path of the Function.
  5. Copy one of the example code snippets from this page and paste the code into your newly created Function. You can switch examples by using the dropdown menu in the code rail.
  6. Click Save.
  7. Click Deploy All to build and deploy the Function. After deployment, you can access your Function at https://<service-name>-<random-characters>-<optional-domain-suffix>.twil.io/<function-path>
    For example: test-function-3548.twil.io/hello-world.

You can now invoke your Function with HTTP requests, configure it as the webhook for a Twilio phone number, call it from a Twilio Studio Run Function Widget, and more.

With the Function created, we'll need to edit the boilerplate code that is generated for the Function—by default, it comes with some code to return TwiML. We're only going to return a joke. And it's a bad joke.

Return a Joke with a Twilio Function

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exports.handler = (context, event, callback) => {

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  const joke = 'How many apples grow on a tree? They all do!';

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  return callback(null, joke);

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};

Copy the above code into the Twilio Functions code editor. Please, change the joke to something better. Press the Save button to save that code, and Deploy All to deploy your Function.

Call a Twilio Function from the Web

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To call your new Function from the web, get the Function's URL by clicking the Copy URL icon next to the path, and then paste that URL into any web browser (you don't have to be authenticated with Twilio). You'll get a text response containing whatever you return from your Function!

Call a Twilio Function from iOS

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We can use the standard iOS library to call our Twilio Function. The URLSession (NSURLSession with Objective-C) class lets us create a data task that takes a URL and a closure (completion block in Objective-C) as an argument. Your closure will get the HTTP response, the Data/NSData returned by the server, and an error (if there was one) as arguments. We check to see if the error exists, and if it does not, we create a string from the Data and print it out. Be sure to call resume on the task to initiate the HTTP Request—this step is commonly forgotten.

Call a Twilio Function from iOSLink to code sample: Call a Twilio Function from iOS
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NSString* functionURL = @"https://yourdomain.twil.io/joke";

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NSURL *url = [NSURL URLWithString:functionURL];

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NSURLSessionDataTask *task = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {

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    if (error) {

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        NSLog(@"Error: %@",error);

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    } else {

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        NSString *responseString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

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        NSLog(@"Response: %@", responseString);

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    }

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}];

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[task resume];
(warning)

Warning

If you are calling Twilio Functions from an Xcode Playground with Swift, you will need to tell the Playground to run indefinitely (so the HTTP call can return).

To do this, you will need to import the PlaygroundSupport framework, and then include this line of code at the bottom:

PlaygroundPage.current.needsIndefiniteExecution = true

Return JSON from a Twilio Function

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Our previous example Function returned plain text. You can also return JSON from a Twilio Function, by passing a JavaScript object or array to the callback function. For instance, we can create another Twilio Function to return a list of jokes, along with an id and a favorite count. Create a new Function with a path of /jokes.

A Twilio Function that Returns a JSON Array

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exports.handler = (context, event, callback) => {

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  const knockKnock = { id: 1, text: 'Knock, knock', favorited: 37 };

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  const chicken = {

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    id: 2,

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    text: 'Why did the chicken cross the road?',

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    favorited: 12,

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  };

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  const jokes = [knockKnock, chicken];

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  return callback(null, jokes);

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};

Parse JSON from a Twilio Function

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From iOS, we call this Function the same way that we did our first Function (don't forget to change the path to /jokes). Instead of creating a String/NSString from data, we will use iOS's built-in JSON Serialization to parse the response data into an array.

Call a Twilio Function that returns JSON from iOSLink to code sample: Call a Twilio Function that returns JSON from iOS
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NSString* functionURL = @"https://yourdomain.twil.io/jokes";

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NSURL *url = [NSURL URLWithString:functionURL];

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NSURLSessionDataTask *task = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {

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    if (error) {

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        NSLog(@"Error: %@",error);

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    } else {

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        NSError *error;

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        id responseObject = [NSJSONSerialization JSONObjectWithData:data options:0 error:&error];

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        NSLog(@"Response: %@", responseObject);

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    }

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}];

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[task resume];

You've now seen how to run Node.js code as a Twilio Function, and how your mobile application can use this as a serverless backend to provide data for your application.

Where to go next? You could extend the Function to choose a random joke from that array. You can also use Twilio functionality from inside your Function, for instance to send an SMS, or to return an access token for Video, Chat, or Sync. Check out the Programmable SMS Quickstart for Twilio Functions and Programmable Voice Quickstart for Twilio Functions for more quick introductions to these key features of Functions.