Receiving an SMS with PHP

Published June 19, 2018 by Michael Heap
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We’ve previously covered sending an SMS with PHP, but that’s only half of the conversation. In this post we’re going to look at allowing people to send you an SMS.

The source code for this blog post is available on Github.

Prerequisites

To work through this post, you’ll need a Nexmo account. Sign up now if you don’t already have an account. Receiving an SMS is free with Nexmo, but you will need to rent a phone number that people can send messages to.

You’ll need PHP installed before working through this post. I’m running PHP 7.2, but the code here should work on PHP 5.6 and above. You’ll also need Composer to download our dependencies.

Finally, you’ll need the Nexmo CLI installed. We’ll use it to purchase a phone number and configure our Nexmo account to point at our new application.

Receiving an SMS with PHP

When Nexmo receives an SMS for a phone number that you own, they make a HTTP request to a URL that you’ve configured containing all of the information about the SMS. (Don’t worry about configuring this URL yet, we’ll get to it a little later on)

To receive the incoming SMS content, we’re going to be using the Slim framework Let’s install it now with composer:

When we receive an SMS, we’re going to log out all of the information that Nexmo provide to the console. In the real world, you could store this in a file or a database.

Nexmo will make either a GET or a POST request to your application with the data, depending on how your account is configured (you can see this under HTTP Method in the dashboard). In this post, we’ll write an application that can handle both HTTP methods:

Create a file named index.php with the following contents. We bootstrap our Slim app, define a handler that returns a HTTP 204 response and then instruct Slim to use this handler whenever we receive a GET or a POST to /webhook/inbound-sms:

With this code all we’re doing is returning with a 204 response code, which says that everything is OK. To log the parameters we received we need to check if there is any data returned by $request->getParsedBody(). If so, this is a POST request and we can carry on. If not, we call $request->getQueryParams() to read the GET parameters.

At this point, all of the parameters are stored in a variable named $params and we can output them to the terminal using
error_log(print_r($params, true));. Putting that all together, your $hander should look like the following:

Save this file and then open up a new terminal window. Let’s start the built in PHP server and serve our application on port 8000.

If you visit http://localhost:8000/webhook/inbound-sms?from=14155550100&text=Hello+World, you should see from and text in the same terminal that you started the PHP server in.

That’s really all there is to it. Receiving an SMS with Nexmo is really easy due to the fact they transform an SMS in to a HTTP request for us.

Exposing your application with ngrok

Whilst our application is complete, our job isn’t quite finished yet. To send a HTTP request to our application, Nexmo needs to know which URL our application is running on.

We’re going to use ngrok to expose our local application to the internet. Run ngrok http 8000 and make a note of the ngrok URL generated (it’ll look something like http://abc123.ngrok.io).

Configure your Nexmo account

With Nexmo, each phone number you own can have a different callback URL that they use to send inbound SMS to.

Let’s start by purchasing a phone number using the Nexmo CLI that we can use to test:

Take the number you just purchased and link it to your ngrok URL so that Nexmo know where to send the inbound SMS to (replacing the phone number and URL with your own values):

At this point, you can send an SMS to your Nexmo number and watch as it appears in your terminal. It may take a few minutes due to network latency, but it should arrive soon!

Conclusion

In just 20 lines of code, we went from zero to being able to receive inbound SMS messages in our application. If you know which HTTP method you’re using, you can even reduce that to 16 by deleting either getParsedBody or getQueryParams!

Nexmo Developer has more information about receiving inbound SMS messages with PHP, including a description of all of the available parameters that Nexmo may send to you.

If you have any questions about this post feel free to email [email protected] or join the Nexmo community Slack channel, where we’re waiting and ready to help.

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