C# 2008 Programmer's Reference

Data	The type of data used and required by the service.

Messaging Patterns

Traditional ASMX Web Services use the request/response communication model. This model has some disadvantages. In some cases, the client might want to call the service without waiting for a response from the service. For example, you might want to call a service rapidly to turn on and off a switch and you do not need a response from the service. Using the request/response model, all requests made by the client have to wait for a reply from the service (even if the request does not return a result). The result is unnecessary blocking on the client side, especially if there are many queued requests on the service's end.

WCF supports three communication models (also known as messaging patterns):

□ Request/response

□ One-way (simplex)

□ Two-way (duplex)

The one-way messaging pattern allows clients to fire off a request and forget about it; no response is needed from the service. The two-way messaging pattern allows both the service and the client to send and receive messages.

Hosting Web Services

As mentioned earlier, WCF services can be hosted using different forms:

□ Web Servers — IIS; similar to Web Services

□ Executable — Console application, Windows Forms, WPF, and so on

□ Windows Service — Runs in the background

□ Windows Activation Service (WAS) — Simpler version of IIS

In the earlier example, the WCF service is hosted by the WCF Service Host (see Figure 20-19), a utility provided by Visual Studio 2008.

Figure 20-19

If you host a WCF service using an executable or Windows service, that WCF service is said to be self- hosted.

Building WCF Services

This section explores more sophisticated WCF services that illustrate the various theories presented earlier. Let's start off with creating a WCF that exposes multiple endpoints.

Exposing Multiple Endpoints

A WCF service can expose multiple endpoints. Follow along to build a WCF service that exposes endpoints using two different bindings: WSHttpBinding and BasicHttpBinding.

Creating the WCF Service

Using Visual Studio 2008, create a new WCF Service Application and name it MultipleEndpointsService (see Figure 20-20).

Figure 20-20

In this example, the WCF service is hosted by the ASP.NET Development Server, a web server shipped with Visual Studio 2008. Because the service is hosted by a web server, the NetTcpBinding binding is not supported.

Edit the Web.config file by right-clicking it in Solution Explorer and selecting Edit WCF Configuration. (You can also launch the WCF Service Configuration Editor by selecting Tools→WCF Service Configuration Editor.)

Expand the Endpoints node, and select the first endpoint. Name it WS (see Figure 20-21).

Figure 20-21

Right-click on the Endpoints node, and select New Service Endpoint to add a new endpoint to the service (see Figure 20-22).

Figure 20-22

Name the new endpoint BASIC, and set its various properties as indicated (see Figure 20-23).

Figure 20-23 

Property	Value
Address	asmx
Binding	basicHttpBinding
Contract	MultipleEndpointsService.IService1

Save and close the Web.config file. Build the MultipleEndpointsService