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Service Contracts
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A service contract describes the interface to operations implemented by a service endpoint Service contracts reference message formats and describe how they are exchanged Message formats are further described by data contracts and message contracts This section covers the message exchange patterns that service contracts implement Service contracts are used by WCF at design time and runtime At design time, they identify classes in code that should be exposed as endand its methods points in WSDL A class marked with are exposed in WSDL so that they can marked with and the operbe accessed by clients The class is identi ed as At runtime, when the WCF disations are identi ed as name to patcher receives a message, it looks at the should determine which class method marked with receive the deserialized message Figure 21 depicts the high-level translation of code to WSDL
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[ServiceContract] Class A
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WSDL
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service definitions porttype operation action operation input output binding
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[OperationContract] Method 1 [OperationContract] Method 2 [OperationContract] Method 3
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Figure 21 High-level translation of code artifacts to WSDL
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Figure 22 shows the same translation depicted in Figure 21, but shows also the syntax of the C# and WSDL elements for clarity
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2: Contracts
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[ServiceContract] public class StockService { [OperationContract] double GetPrice(string ticker) { return 9485; } }
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WSDL
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<wsdl:definitions > <wsdl:types> </wsdl:types> <wsdl:message name="StockService_GetPrice_InputMessage"> <wsdl:part element="tns:GetPrice" /> </wsdl:message> <wsdl:message name="StockService_GetPrice_OutputMessage"> <wsdl:part element="tns:GetPriceResponse" /> </wsdl:message> <wsdl:portType name="StockService"> <wsdl:operation name="GetPrice"> </wsdl:operation> </wsdl:portType> <wsdl:service name="StockService"> <wsdl:port name="BasicHttpBinding_StockService" <soap:address location="http://localhost/RequestResponse/ StockServicesvc" /> </wsdl:port> </wsdl:service> <wsdl:definitions>
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Figure 22 High-level translation of code syntax to WSDL
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Synchronous Request-Response Operations The synchronous request-response message exchange is the most common pattern for service operations This pattern is familiar to anyone who has programmed in a procedural or object-oriented language The requestresponse pattern is the prototypical local procedure call and is also quite common for remote procedure calls Figure 23 shows a request-response interaction, where a proxy running within a client sends a request to a service and the service responds synchronously back to the client
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WCF Client WCF Service Endpoint A B C
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Figure 23 Synchronous request-response communication
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WCF makes request-response communication between client and service very easy At design time, you use Add Service Reference or to call the service s Metadata Exchange (MEX) endpoint and generate a client-side proxy that mimics the signature of the service operations This allows the client code to call methods on the proxy as local
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Proxy
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function calls The proxy serializes the method name and parameters into a SOAP message, sends the SOAP message to the service, listens for a message to be sent back from the service, and then creates a NET type representing the message response from the service Listing 21 shows a service contract de nition One service contract and one operation contract are de ned in the code The operation contract represents a method that can be called by a client or, more accurately, a message that can be sent by the client and understood by the service Note that the contract is de ned on the interface, not the class de nition
Listing 21 Request-Response Service
Listing 22 shows the client code, using a proxy generated by Add Service Reference that calls the service in Listing 21 This is similar to the code shown in Listing 12
Listing 22 Request-Response Client
2: Contracts
Listing 22 continued
Listing 23 shows the SOAP message that is sent from the client to the service endpoint There are a few points worth noting: The namespace of the SOAP message is http://tempuriorg/, which attribute is the default unless overridden in the If the service is going to be exposed outside an application or outside a relatively small organization, you should override the default because the namespace construct is designed to uniquely identify your service and eliminate ambiguity as multiple services are combined is The method name in the class de nition in Listing 11, used to form the wsa:Action in the SOAP header The full action value is a combination of the contract namespace, the contract name (interface name or the class name, if no explicit service interface is used), the operation name, and an additional string (Response) if the message is a correlated response The SOAP body is controlled by the signature of the method and and the quali ers speci ed with the attributes The SOAP header includes the address to which the message is sent In this case, it s the SVC le hosted on the IIS machine