Sep 21, 2015

Shareable URLs from Forward and the Twilio service: accessing an API endpoint on a localhost site

How do you have an external service access an API endpoint that is defined on a site that you're running locally?

One of the Drupal 7 sites ( I work on sends out SMS messages to users who register for weekly messages to be delivered to their cellphones.

The site uses the Twilio service to configure a virtual cellphone number from which the messages are apparently sent.

We also use the D7 Twilio module (version 7.x-1.10) to interface with the Twilio API. The module provides Drupal-specific elements such as hooks for implementing the desired functionality.

During local development, this worked fine as long as the site was only calling the Twilio API endpoints.

However, we wanted to enhance the site to define its own endpoints for the Twilio service to call back. For example, we wanted to be notified of and to be able to process STOP messages that our users were texting to our virtual cell number so that we could update the site's database.

For development purposes, I wanted to test as realistically as possible. I wanted my local site to interact with my cellphone via Twilio.

The problem was, I only run Apache on my system as a local server. At first, I thought I'd have to use our development site (it happens to be on Pantheon), constantly pushing code changes to it. That would have been tedious and messy.

Because I find the use of a debugger indispensable, I also would have had to figure out how to do so remotely.

Luckily, I saw a comment in response to a question about how to test the use of Twilio that mentioned "request forwarding utilities", of which Forward is one. The comment is clear and concise, so I'm just going to quote the commenter, Devin Rader.
Basically, request forwarding utilities like ForwardHQ do two things:
  1. It creates a publicly accessible URL, that you can tell Twilio about.
  2. It creates an SSH tunnel between a port on your machine and a server on the internet
When Twilio needs to make an HTTP request because it received an inbound SMS or voice call, it will request the ForwardHQ URL. Forward knows how to take that request and send it to the port running on your local machine. That port maps to your local web development server running in order to process the request and return the result to Twilio.

This sounded like exactly what I wanted. Here are the steps I took.

1.  Signed up for an account with Forward.

2.  Installed their browser extension for Chrome, which puts an icon on the toolbar to Open Forward.

3.  Browsed to the local site. Clicked on the Open Forward icon.

(I probably had to log in to Forward the first time I did this.)

4.  This brought up a special page from the browser extension. Clicked on Start Tunnel to create a tunnel between the site running on my localhost and Forward.

To access the site, the url was provided by default, where the subdomain wholewhale was specified by me.

5.  The Twilio module defines the path /twilio/sms using hook_menu() for processing incoming sms messages.

6.  So under my Twilio account, I specified as the Request URL to notify the local site of incoming sms messages from users.

(On the live site, the endpoint will be

7.  I had an issue with the Twilio module logging the error message "Incoming SMS could not be validated" and not invoking the hook I had implemented.

I hacked around this by temporarily inserting a "return TRUE" statement in the module code so that it would continue as though no error had occurred. This worked fine for what I was doing.
I was now able to run the site and make code changes to it locally, run my debugger locally, and have the site interact with the Twilio service in both directions.




twilio (the service)

Twilio (the Drupal module)

How to test Twilio calling my REST API via POST when a user sends an sms to a short code?

Accessing localhost from Anywhere