Building an api

Ever thought about building an api for your web app? Not sure where to start, or perhaps the best practices for a rails app? This post will explore some of the choices I made when building a new API for Change:Healthcare.

Versioning

One of the key things I knew needed to happen was versioning. Having used many other APIs before, un-versioned APIs like twitter can be very frustrating. They require you to stay lock and step with the development team, especially breaking API changes. I won’t go into the how too much, I followed John Barnette’s advice.

Versioning covers a lot of pain points in deal with APIs, but it definitely falls flat in a few spots. RESTifarians argue that using versioning in your url means you break with strict RESTful routing and principals. There is also the matter of just doing a straight copy from one version to the next, it creates a lot of extra code to get that versioned benefit.

Encrypt for security

Another key concern when writing this API was to ensure passing sensitive data was as secure as possible. We already require SSL for all API interactions, but we needed to take it farther. We quickly settled on a two way encryption scheme, using AES 256 Bit.

Why AES 256 bit? We wanted something well supported and well documented. We use ruby to build our apps, but not everyone does. A quick search turned up easy ways to deal with AES in Java, Php, etc. One other key point to remember is to use AES256-CBC, as it requires a initialization variable (ivar) to start the encryption and is more secure than just using all 0’s to start encrypting all the blocks.

Supporting JSON

The decision of what formats to support was left up to me, and I decided we would start with JSON, as it is so easy to implement and support. Since rails 2.3 switched to rack, it is very easy to switch out your own Param Parser if you need it, but the built in one works nicely.

In some spots we used the built in .to_json support for objects, and it worked out very nice - we implemented some of those methods very quickly. In other areas we needed custom output, so we wrote helpers to take the object and output the strict JSON we needed. Note the use of .to_json in our helper method below - we used it to easily output proper null when ruby had a nil piece of data.

Write documentation

API adoption relies on a few different factors, but none of more important than good documentation. Having worked with other APIs from eBay, amazon, and twitter - it is easy to realize you can’t get started without good docs. I made the decision to follow a format similar to twitter’s wiki documentation for their API.

We really liked twitter’s inclusion of example return values and curl examples. The example return values are great because you can easily copy and paste them into tests/fixtures/factories when writing your tests. The curl examples are super helpful as well because you can actually figure out how to play around with the API without writing a single line of code.

Bringing it all together

If you glean only one thing from this post, I hope it is that writing an API should be something you put a real effort into. Don’t half ass it, people will be able to tell. Spend the time to figure out your approach, your input and output formats, and above all write documentation!