Simple Object Access Protocol (SOAP) is an XML-based messaging protocol for exchanging information among computers. SOAP relies on application layer protocols, most often Hypertext Transfer Protocol (HTTP) or Simple Mail Transfer Protocol (SMTP), for message negotiation and transmission. As we are talking about HTTP, which is installed and runs on every operating system, web services implementing SOAP can be called from any platform using any language.

We already know that a SOAP message is an XML document, but let's have a better look by way of a diagram:

The following is a description of the components from the preceding diagram:

• Envelope: Mandatory element of SOAP message structure. Defines the...

REST is an architectural style for providing standards between computer systems on the web, so that systems can communicate with each other easily. Services compliant to the REST style are often called RESTful services.

Let's talk about a few important constraints of a web service when it is tagged as RESTful.

With REST, there is no restriction or dependency between server and client. Both can be independent of each other. It's just the URL by which the client understands the service. The code for a web service on a server can be modified without caring about the clients that are associated with it and vice versa.

This kind of separation helps the client/server architecture...

Before we explore the communication mechanism, let's first set up the development environment. We will use Visual Studio 2017 for our examples.

Open Visual Studio and undertake our favorite step, File | New | Project, which opens up a dialog window with available templates, as shown in the following screenshot:

Select ASP.NET Core Web Application as shown in the preceding screenshot. Don't forget to select .NET Core in the left-hand side panel. Everything looks cool now.

Let's click OK and then we will land on another dialog where we can select more templates related to our web app. Obviously, we will click on Web API and then click OK.

The project is created. Beautifully, it has crafted all the necessary components and created an example controller for us named ValuesController as shown in the following screenshot:

Now, here is one...

Following are some key differences between SOAP and REST:

Traditionally, in a web application, the client requests the server for a web page. Then, the server responds to the client with the requested HTML page after validating and authenticating the request, if necessary. The next request to the server might occur when a user hits some link on the page, submits a form, and so on. The server again processes the request and sends back the response with another HTML page.

Don't you think instead of getting the whole HTML page (which would be mostly the same look and feel as the last loaded page), we should just get the data we need and update the currently loaded page itself without posting back to the server? Yes, modern web development works in that regard. Today, we just need data from the server on demand using Ajax. After receiving the data, we will just update the UI with JavaScript or a client...

Like SPA, Web API plays an important role in service-oriented architecture (SOA). As the name suggests, it is an architecture methodology that deals with separation of responsibility from a business-oriented point of view into independent services. Often, these independent services or components can be designed using RESTful Web APIs.

Consider an e-commerce application that would have different components such as ordering, billing, payment processing, customer profile management, and so on. Each of these components has its own business logic and can be implemented independently.

The following diagram represents a pictorial view of such an application having independent components:

To make them independent, RESTful APIs can be exposed for these components, which can be easily consumed by any client/application including other components as well, as...

We started with some basic knowledge of SOAP and then we moved towards REST gradually.

This chapter shed some light on the fundamental REST building blocks and how they actually work. We explored the different status codes returned by widely used HTTP verbs.

To explore the request and response cycles of Web API, you can use Postman, where you not only have control over what is being sent and received, but also the ability to get code for different languages in order to consume the API.

ASP.NET Core attributes can be tied to controller action methods to make them more expressive and manageable in terms of routing and arguments.

Single-page applications can be easily designed using client-side technologies and consuming ASP.NET Core Web APIs so that pages can be updated as soon as responses are received to have a smooth user experience.

Web APIs can be plugged into the...