Web Services with Ruby on Rails : Building Web Service Clients

From a high-level view, web service implementations can be broken down into two categories: servers and clients. I'll show how to create both clients and servers throughout this document. But since you're likely to build more clients throughout your career, I'll start with clients.

Most web services are based on one of three architectures: Representational State Transfer (REST), Simple Object Access Protocol (SOAP), or Extensible Markup Language Remote Procedural Calls (XML-RPC). Web services often offer access via two or more of these architectures. For example, we'll be offering both SOAP and XML-RPC access to clients in the ActionWebService server examples later in This Site , so clients can implement the architecture that's easiest for their specific application.

If you're building your web service clients in Ruby and implementing them as part of a Rails application, you are in luck. Building web service clients with Ruby on Rails requires only a few simple steps and involves just a few Ruby libraries. Even better news is that the majority of libraries you use for building clientsCGI, NET, REXML, Soap4r, XSD, and XML-RPCare automatically loaded by your Rails environment. All you have to worry about is knowing when, how, and where to use each library, and that's just what I'll help you figure out throughout the rest of this document.

If you're wondering why I'm talking about Rails (a server platform) and web service clients in the same breath, take a step back. Most web service clients aren't desktop programs or command-line programs. Instead, most web service clients are servers: servers that gather data from other web services and then repackage it for some other purpose. (That other purpose is frequently a human-readable web page, but it could just as well be yet another web service.) That's why the clients we develop here will be part of a Rails application.

I'll cover all three of the most popular types of web services: REST, SOAP, and XML-RPC. And to make things as practical as possible, I'll use three of the most popular, free, and useful web services out there for examples: Yahoo! Search, Google Search, and Flickr. Since I'm a big believer in learning by doing, I'll walk you through the details of building web service clients for Rails by developing real-world, working clients for each of these services.

All this document's examples will focus on building working clients to demonstrate web services concepts, so I won't discuss any one service in detail. My goal isn't to teach you everything you might need to know about a specific web service's interface, or even everything you might need to know about SOAP or REST concepts. Rather, my intention is to show you how to apply web service concepts to your Rails applications. My hope is that you will then take these examples as starting points and go on to build the next great client we've all been waiting for! But before I get too deep into specific examples, I'll cover a few quick basics about Ruby on Rails and web services.