A few days ago, we released our first beta of Apigility. We've started our documentation effort now, and one question has arisen a few times that I want to address: How can you use Hypermedia Application Language (HAL) in RPC services?

In my previous posts, I covered basics of JSON hypermedia APIs using Hypermedia Application Language (HAL), and methods for reporting errors, including API-Problem and vnd.error.

In this post, I'll be covering documenting your API — techniques you can use to indicate what HTTP operations are allowed, as well as convey the full documentation on what endpoints are available, what they accept, and what you can expect them to return.

While I will continue covering general aspects of RESTful APIs in this post, I will also finally introduce several ZF2-specific techniques.

In my last post, I covered some background on REST and the Richardson Maturity Model, and some emerging standards around hypermedia APIs in JSON; in particular, I outlined aspects of Hypermedia Application Language (HAL), and how it can be used to define a generic structure for JSON resources.

In this post, I cover an aspect of RESTful APIs that's often overlooked: reporting problems.

RESTful APIs have been an interest of mine for a couple of years, but due to circumstances, I've not had much chance to work with them in any meaningful fashion until recently.

Rob Allen and I proposed a workshop for PHP Benelux 2013 covering RESTful APIs with ZF2. When it was accepted, it gave me the perfect opportunity to dive in and start putting the various pieces together.

In previous articles, I've explored building service endpoints and RESTful services with Zend Framework. With RPC-style services, you get to cheat: the protocol dictates the content type (XML-RPC uses XML, JSON-RPC uses JSON, SOAP uses XML, etc.). With REST, however, you have to make choices: what serialization format will you support?

Why not support multiple formats?

There's no reason you can't re-use your RESTful web service to support multiple formats. Zend Framework and PHP have plenty of tools to assist you in responding to different format requests, so don't limit yourself. With a small amount of work, you can make your controllers format agnostic, and ensure that you respond appropriately to different requests.

As a followup to my previous post, I now turn to RESTful web services. I originally encountered the term when attending php|tropics in 2005, where George Schlossnaggle likened it to simple GET and POST requests. Since then, the architectural style — and developer understanding of the architectural style — has improved a bit, and a more solid definition can be made.