Designing Evolvable Web APIs with ASP.NET

Chapter 12. Controllers and Routing

Knowing how home plumbing works is unnecessary much of the time—but when you need to know it, you really need to know it.

While ASP.NET Web API provides a litany of helpful high-level features ranging from serialization and model binding to support for OData-style queries, the core job of all Web APIs, and ASP.NET Web API as a result, is to process HTTP requests and provide appropriate responses. Therefore, it is critical to understand the core mechanics of how an HTTP request flows from a client through the various elements of the ASP.NET Web API infrastructure and programming model, ultimately resulting in an HTTP response that can be sent back to the client.

This chapter focuses on that message flow, exploring the fundamental mechanics and supporting the programming model behind request handling and response generation. In addition, this chapter will look at the key types and insertion points that enable the framework to be extended to support custom message flow and processing schemes.

HTTP Message Flow Overview

The precise message flow through ASP.NET Web API will vary somewhat depending on the choice of host, and hosting is discussed in much greater detail in Chapter 10. However, at a high level, the framework components that participate in the HTTP message flow fall into two categories (as illustrated in Figure 12-1):

• Components that rely only on the HTTP message for context
• Components that rely on the higher-level programming model for context ...