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 topublic, to avoid any hurdles when making your HTTP calls:
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 theServerless Toolkit as explained below:
If you prefer a UI-driven approach, creating and deploying a Function can be done entirely using the Twilio Console and the following steps:
- Log in to the Twilio Console and navigate to theFunctions tab. If you need an account, you can sign up for a free Twilio accounthere!
- Functions are contained withinServices. Create aService by clicking theCreate Service button and providing a name such astest-function.
- Once you've been redirected to the new Service, click theAdd + button and selectAdd Function from the dropdown.
- This will create a newProtected Function for you with the option to rename it. The name of the file will be path it is accessed from.
- 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.
- ClickSave to save your Function's contents.
- ClickDeploy All to build and deploy the Function. After a short delay, your Function will be accessible from:
https://<service-name>-<random-characters>-<optional-domain-suffix>.twil.io/<function-path>
For example:test-function-3548.twil.io/hello-world
.
TheServerless Toolkit enables you with local development, project deployment, and other functionality via theTwilio CLI. To get up and running with these examples using Serverless Toolkit, follow this process:
- From the CLI, run
twilio serverless:init <your-service-name> --empty
to bootstrap your local environment. - Navigate into your new project directory using
cd <your-service-name>
- 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 aProtected Function intended to handle incoming SMS. - 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 likengrok), or by deploying the Function and executing against the deployed url(s).
Run your Function in local development
Runtwilio serverless:start
from your CLI to start the project locally. The Function(s) in your project will be accessible fromhttp://localhost:3000/sms-reply
- If you want to test a Function as aTwilio webhook, run:
twilio phone-numbers:update <your Twilio phone number> --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 thevoice-url
flag instead if you want to test withTwilio Voice. - If your code doesnot 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), runtwilio 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://<service-name>-<random-characters>-dev.twil.io/<function-path>
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 thewebhook of a Twilio phone number, invoked by a Twilio StudioRun 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.
1exports.handler=(context,event,callback)=>{2constjoke='How many apples grow on a tree? They all do!';3returncallback(null, joke);4};
Copy the above code into the Twilio Functions code editor. Please, change the joke to something better. Press theSave button to save that code, andDeploy All to deploy your Function.
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!
We can use the standard iOS library to call our Twilio Function. TheURLSession
(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, theData
/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 theData
and print it out. Be sure to call resume on the task to initiate the HTTP Request—this step is commonly forgotten.
1NSString*functionURL=@"https://yourdomain.twil.io/joke";2NSURL*url=[NSURL URLWithString:functionURL];3NSURLSessionDataTask*task=[[NSURLSessionsharedSession]dataTaskWithURL:urlcompletionHandler:^(NSData*_Nullable data,NSURLResponse*_Nullable response,NSError*_Nullable error) {4if(error) {5NSLog(@"Error:%@",error);6}else{7NSString*responseString=[[NSString alloc]initWithData:dataencoding:NSUTF8StringEncoding];8NSLog(@"Response:%@", responseString);9}10}];11[taskresume];
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 thePlaygroundSupport
framework, and then include this line of code at the bottom:
PlaygroundPage.current.needsIndefiniteExecution = true
Our previous example Function returned plain text. You can also return JSON from a Twilio Function, by passing a JavaScript object or array to thecallback
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
.
1exports.handler=(context,event,callback)=>{2constknockKnock={ id:1, text:'Knock, knock', favorited:37};3constchicken={4id:2,5text:'Why did the chicken cross the road?',6favorited:12,7};8constjokes=[knockKnock, chicken];9returncallback(null, jokes);10};
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 aString
/NSString
from data, we will use iOS's built-in JSON Serialization to parse the response data into an array.
1NSString*functionURL=@"https://yourdomain.twil.io/jokes";2NSURL*url=[NSURL URLWithString:functionURL];3NSURLSessionDataTask*task=[[NSURLSessionsharedSession]dataTaskWithURL:urlcompletionHandler:^(NSData*_Nullable data,NSURLResponse*_Nullable response,NSError*_Nullable error) {4if(error) {5NSLog(@"Error:%@",error);6}else{7NSError*error;8idresponseObject=[NSJSONSerializationJSONObjectWithData:dataoptions:0 error:&error];9NSLog(@"Response:%@", responseObject);10}11}];12[taskresume];
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 theProgrammable SMS Quickstart for Twilio Functions andProgrammable Voice Quickstart for Twilio Functions for more quick introductions to these key features of Functions.