Introduction to Web API: Yes, It’s That Easy
REST Web Services Are Fundamental
In my career, I’ve sort of drifted like a wraith among various technology stacks and platforms, working on web sites, desktop apps, drivers, or even OS/kernel level stuff. Anything that you might work on has its enthusiasts, its peculiar culture, and its best practices and habits. It’s interesting to bop around a little and get some cross-pollination so that you can see concepts that are truly transcendent and worth knowing. In this list of concepts, I might include Boolean logic, the DRY principle, a knowledge of data structures, the publish/subscribe pattern, resource contention, etc. I think that no matter what sort of programmer you are, you should be at least aware of these things as they’re table stakes for reasoning well about computer automation at any level.
Add REST services to that list. That may seem weird when compared with the fundamental concepts I’ve described above, but I think it’s just as fundamental. At its core, REST embodies a universal way of saying, “here’s a thing, and here’s what you can do to that thing.” When considered this way, it’s not so different from “DRY,” or “data structures,” or “publish/subscribe” (“only define something once,” “here are different ways to organize things,” and, “here’s how things can do one way communication,” respectively). REST is a powerful reasoning concept that’s likely to be at the core of our increasing connectedness and our growing “internet of things.”
So even if you write kernel code or Winforms desktop apps or COBOL or something, I think it’s worth pausing, digressing a little, and understanding a very shallow-dive into how this thing works. It’s worth doing once, quickly, so you at least understand what’s possible. Seriously. Spend three minutes doing this right now. If you stumbled across this on google while looking for an introduction to Web API, skim no further, because here’s how you can create your very own REST endpoint with almost no work.
Getting Started with Web API
Prerequisites for this exercise are as follows:
- Visual Studio (I’m using 2012 Professional)
With just these two tools, you’re going to create a REST web service, run it in a server, make a valid request, and receive a valid response. This is going to be possible and stupid-easy by virtue of a framework called Web API.
- Fire up Visual Studio and click “New->Project”.
- Select “Web” under Visual C# and then Choose “ASP.NET MVC 4 Web Application”
- Now, choose “Web API” as the template and click “OK” to create the project.
- You will see a default controller file created containing this class:
- Hit F5 to start IIS express and your web service. It will launch a browser window that takes you to the default page and explains a few things to you about REST. Copy the URL, which will be http://localhost:12345, where 12345 is your local port number that the server is running on.
- Now launch fiddler and paste the copied URL into the URL bar next to the dropdown showing “GET” and add api/values after it. Go to the request header section and add “Content-Type: application-json” and press Execute (near top right)
(Note — I corrected the typo in the screenshots after I had already taken and uploaded them)
- A 200 result will appear in the results panel at the left. Double click it and you’ll see a little tree view with a JSON and “value1” and “value2” under it as children. Click on the “Raw” view to see the actual text of the response.
- What you’re looking at is the data returned by the “Get()” method in your controller as a raw HTTP response. If you switch to “TextView”, you’ll see just the JSON [“value1″,”value2”] which is what this thing will look like to most JSON-savvy parsing tools.
So what’s all of the fuss about? Why am I so enamored with this concept?
Well, think about what you’ve done here without actually touching a line of code. Imagine that I deployed this thing to http://www.daedtech.com/api/values. If you want to know what values I had available for you, all you’d need to do is send a GET request to that URL, and you’d get a bare-bones response that you could easily parse. It wouldn’t be too much of a stretch for me to get rid of those hard-coded values and read them from a file, or from a database, or the National Weather Service, or from Twitter hashtag “HowToGetOutOfAConversation,” or anything at all. Without writing any code at all, I’ve defined a universally accessible “what”–a thing–that you can access.
We generally think of URLs in the context of places where we go to get HTML, but they’re rapidly evolving into more than that. They’re where we go to get a thing. And increasingly, the thing that they get is dictated by the parameters of the request and the HTTP verb supplied (GET, POST, etc.–I won’t get too detailed here). This is incredibly powerful because we’re eliminating the question “where” and decoupling “how” from “what” on a global scale. There’s only one possible place on earth you can go to get the Daedtech values collection, and it’s obviously at daedtech.com/api/values. You want a particular value with id 12? Well, clearly that’s at daedtech.com/api/values/12–just send over a GET if you want it. (I should note you’ll just 404 if you actually try these URLs.)
So take Web API for a test drive and kick the tires. Let the powerful simplicity of it wash over you a bit, and then let your mind run wild with the architectural possibilities of building endpoints that can talk to each other without caring about web server, OS, programming language, platform, device-type, protocol setup and handshaking, or really anything but the simple, stateless HTTP protocol. No matter what kind of programming you do at what level, I imagine that you’re going to need information from the internet at some point in the next ten years–you ought to learn the basic mechanics of getting it.