Providing New Services

The final topic for this presentation regarding adding new services for your Drupal site. Before we dive in to the code, I wanted to take a moment to discuss why such services might be useful and to warn about several potential pitfalls regarding these APIs.

Adding your own web services allows you to share data and functionality easily amongst your applications, whether they be Drupal or otherwise. For example, say you have a dozen client sites which are configured to alert another, master site whenever they have problems. You could have either your client sites all provide services so that your master site could poll them, or you could have the master site services enabled and allow the client sites to push to it (I favor the latter). As another example, I should note that I work on a non-Drupal PHP application which is complex enough to warrant often-changing help documentation. Since each of our clients has their own instance of our application and we want to make sure they all have the same documentation, we centralize this in a single Drupal site, which our client sites pull from nightly.

Another common use for adding your own web services involves making desktop and mobile apps. You may want users to post comments or upload data from their phones without having to deal with your web interface. In these situations, creating a new web service may be essential so that you (or other app developers) can access your site without a browser. Further, by publishing an API for users, you join the ranks of Twitter, Facebook, and Meetup.com; you will be officially Web 2.0 ready.

When you are designing your API, you will want to keep a few things in mind. First, remember that you need to escape your SQL, avoid cross-site scripting, and pay attention to permission escalation bugs just as you would with any other module you develop. You shouldn’t trust web services users any more than you would trust your HTML users (which should be not-at-all,) because although accessing web services is a bit more complicated, it’s just an extra hurdle for a determined user. When designing your API, remember also to require the hash-based authentication whenever creating/modifying data. The added security confirms that the user is who he/she claims to be and provides a tidy audit trail should anything go wrong.

Finally, be sure to think your API through before you start developing it. Creating an API and then altering it is not only a hassle, but will surely cost some customers. Before any user can write his/her own application on top of your API, he/she must believe that your API is stable; changing method names or parameters will break this stability.

© C.M. Lubinski 2008-2021