When WCF was conceived back in its Indigo and .NET 3 days, the main goal was to support SOAP + WS-* over a wide variety of transports. However, over time it became clear that although SOAP is wide spread and supported on many platforms, it is not the only way to go when creating services. There is also a need to also support non-SOAP services, especially over HTTP, where you can harness the power of the HTTP protocol to create HTTP services: services that are activated by simple GET requests, or by passing plain XML over POST, and respond with non-SOAP content such as plain XML, a JSON string, or any other content that can be used by the consumer. Support for non-SOAP services was very much needed in WCF back then, mostly because some clients, such as web browsers, were not that suitable to handle SOAP messages (plenty of XML parsing and DOM manipulation).
So in WCF 3.5 we got the WebHttpBinding – a new binding that helped us create this kind of non-SOAP service over HTTP, better known as a RESTful service.
The WebHttpBinding was not enough, and after WCF 3.5 was released, a new set of tools was created – the WCF REST Starter Kit. The REST starter kit was an attempt to enrich the support of WCF 3.5 for HTTP services – add better client-side support for .NET apps, extend the server side support for other content types, enable response and request caching, inspection of messages and so forth. Unfortunately, this great toolkit was never officially released and ended its product cycle as “Preview 2”, although it’s still being used today in some of Microsoft’s products that are built with .NET 3.5.
Although not released, some of the service-side features of the REST starter kit were integrated into WCF 4 – we didn’t get any of the client-side libraries, but we did get most of the service-side features (excluding the new inspectors). Some were well-integrated into WCF while others required the use of ASP.NET (by turning on the ASP.NET compatibility mode).
So with WCF 4 we had some support for “Web” HTTP services, but it wasn’t that perfect – to get some of the features you needed IIS hosting and ASP.NET, not all types of requests were supported easily (ever tried posting HTML form data to a WCF HTTP service?), the overuse of CLR attributes to define the POST/GET/PUT/DELETE was tedious, not to mention the configuration required to create this type of services with all of the endpoint behavior. And even after all of that we didn’t actually get full control over the HTTP messages.
That was the main goal of the Web APIs, known back then as the WCF Web APIs: to stop looking at HTTP through the eyes of WCF - as just a transport protocol to pass requests. Rather, it allows us to look at it as the real application-level protocol it is – a rich, interoperable, resource-oriented protocol. The purpose of the Web APIs was to properly use URIs, HTTP headers, and body to create HTTP services for the web, and for everyone else that wished to embrace HTTP as its protocol and lifelong friend.