MSDN Magazine - April 2008 - (Page 107)

Building a WCF Router, Part 1 MICHELE LEROUX BUSTAMANTE H osting and consuming a Windows® Communication Foundation (WCF) service usually requires a few fundamental steps: implement the service, configure endpoints where the service can be reached, host the service, generate a Web Services Description Language (WSDL) file or enable metadata exchange so that clients can generate a proxy to call the service, write code to instantiate the proxy with its associated configuration, and start calling service operations. You rarely need to take a look under the hood, but even in the simplest case, both the client and service channels rely on compatible configuration to handle addressing semantics and message filtering to ensure the correct operation is invoked. Sometimes it is useful to introduce an intermediary or router service between a client and a target service to receive messages that flow between them and perform additional activities such as logging, priority routing, online/offline routing, load balancing, or to introduce a security boundary. When such an intermediate service is introduced, it becomes necessary to tweak some addressing and message filtering behaviors to accommodate. So let’s take a closer look at how you work with intermediate services, which for simplicity I’ll refer to collectively as routers. In this issue, I’ll explain WCF addressing and message filtering concepts while focusing on the router scenario, and I’ll also explain some opFigure 1 Service Contract and Endpoint Configuration Service Contract [ServiceContract(Namespace = “http://www.thatindigogirl.com/samples/2008/01”)] public interface IMessageManagerService { [OperationContract] string SendMessage(string msg); [OperationContract] void SendOneWayMessage(string msg); tions for routing configuration along with the appropriate settings. In Part 2 of this series, I’ll show you how to leverage this foundation for more advanced, practical routing implementations. Default Addressing Semantics WCF handles logical and physical endpoint addressing, addressing headers, and message filtering. In this section, I Sometimes it is useful to will review some of those introduce a router service fundamental addressing between a client and a features and how they impact routing scenarios—but target service to receive you will also find Aaron’s messages and perform column useful for addiadditional activities. tional details behind these WCF features. Typically, clients send messages directly to the target service using a proxy generated from the service description. In order for the client and service to be compatible, they share equivalent contracts and endpoint configurations. Considering the service contract and configuration shown in Figure 1, you can derive several important addressing requirements for the service. First, the expected Action addressing header for a request to the SendMessage operation is: http://www.thatindigogirl.com/samples/2008/01/IMessageManagerService/ SendMessage dnmag/issues/07/06/ServiceStation), Aaron Skonnard explained how In the June 2007 Service Station column (msdn.microsoft.com/ms- } Endpoint Configuration Since OperationContractAttribute doesn’t specify an Action, this value is derived from the service contract namespace, the contract name (which defaults to the interface name), and the operation name (which defaults to the method name). Second, the expected Action header for a response from SendMessage is: http://www.thatindigogirl.com/samples/2008/01/IMessageManagerService/ SendMessageResponse Since the OperationContractAttribute doesn’t specify a ReplyAction, this value is derived in the same way as the Action property, with the suffix “Response” appended. Finally, the expected To header for messages targeting the service endpoint is: http://localhost:8000/MessageManagerService This value is derived from the address attribute for the endpoint eleapril2008 107 http://msdn.microsoft.com/msdnmag/issues/07/06/ServiceStation http://msdn.microsoft.com/ms-dnmag/issues/07/06/ServiceStation

Table of Contents Feed for the Digital Edition of MSDN Magazine - April 2008

MSDN Magazine - April 2008 Contents Toolbox CLR Inside Out Basic Instincts Cutting Edge Foundations Test Run Service Station Windows with C++ Going Places { End Bracket }

MSDN Magazine - April 2008

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