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Practical WCF Part 1

Mahesh Krishnan, Senior Consultant, Readify. Practical WCF Part 1. Agenda. Introduction to WCF What is it? Why use it? Fundamentals and the ABCs of WCF Hosting Tooling Support Passing data around in WCF Handling faults. Introduction to WCF. What is WCF?.

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Practical WCF Part 1

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  1. Mahesh Krishnan, Senior Consultant, Readify Practical WCFPart 1

  2. Agenda • Introduction to WCF • What is it? Why use it? • Fundamentals and the ABCs of WCF • Hosting • Tooling Support • Passing data around in WCF • Handling faults

  3. Introduction to WCF

  4. What is WCF? • Stands for Windows Communication Foundation • One of the 4 pillars of .NET 3.0 • Microsoft’s unified programming model (the service model) for building Service-Oriented Applications

  5. WCF provides: an SDK for creating SOA a runtime for running Services on Windows Services send and receive messages All messages are SOAP messages WCF takes care of all the plumbing Windows Communication Foundation

  6. Why use WCF? • Interoperable and Standards based • Supports WS-* protocols • Unified Programming Model • Unifies previous models like .NET Remoting, ASMX web services, COM+ etc • Productive Programming Model • Declarative • Imperative • Configuration based

  7. WCF: How does it work? SOAP Message Client Service SOAP Message

  8. WCF End points A = Address (Where) B = Binding (How) C = Contract (What) A B C Client Service Message A B C A B C C B A

  9. Every service has Address Where the service is Binding How to talk to the service Contract What the service can do WCF Endpoints

  10. The EndPointAnology GetBalance() TransferMoney() Address Binding Contract

  11. Address • Combination of transport, server name, port & path • Transport is determined by the binding • Examples http://localhost:8001 net.tcp://localhost:8002/MyService net.pipe://localhost/MyPipe net.msmq://localhost/private/MyService net.msmq://localhost/MyService http://server:345/Service

  12. Transport HTTP TCP MSMQ Message formats and encoding Plain text Binary Message Transmission Optimization Mechanism (MTOM) Communication security No security Transport security Message security Authenticating and authorizing callers Bindings

  13. Out of the box Bindings • BasicHttpBinding • WSHttpBinding • WS2007HttpBinding • WSDualHttpBinding • WSFederationHttpBinding • WS2007FederationHttpBinding • NetTcpBinding • NetNamedPipeBinding • NetMsmqBinding • NetPeerTcpBinding • WebHttpBinding • MsmqIntegrationBinding

  14. Service contracts Defines operations, communications and behaviours. Data contracts Defines data entities and parameter types. Fault contracts Defines error types Message contracts Defines message formats Contracts

  15. Service Contracts • [ServiceContract] – Defines a ‘set’ of operations • [OperationContract] – Defines a single method [ServiceContract] public interface IService { [OperationContract] string GetData(int value); } public class ConcreteService : IService { public string GetData(int value) { ... } public string OtherMethod() { ... } }

  16. Data Contracts • [DataContract] – Specifies type as a data contract • [DataMember] – Members that are part of contract [DataContract] public class CustomType { [DataMember] public boolMyFlag { get; set; } [DataMember] public string MyString { get; set; } }

  17. Metadata Exchange • Service can also expose endpoint for Metadata Exchange (MEX) • It provides a mechanism for clients to find out about: • Address of other end points • Bindings that are used • Contracts used – Service, Operation, Data, etc

  18. Hosting • IIS • HTTP only • WAS (Windows Activation Service) • Can use any transport • Vista and Windows Server 2008 only • Self hosting • Can use any transport • Can be hosted within Console, WinForms, etc Applications

  19. Tooling Support

  20. Tooling Support • Visual Studio • Separate projects for WCF • “Add Service reference” menu • WCF Configuration Editor • WCF Service Host • WCF Test Tool • SvcUtil – To generate proxies • SvcTraceViewer – To view logs

  21. Demonstration WCF in Action

  22. Passing data around in WCF

  23. Passing data around • To pass data across boundaries, they need to be serialized • .NET Framework already contains an attribute for serialization [Serializable] public class Person { public string LastName; public string FirstName; }

  24. Passing data around • Serializable Attribute has some limitations – • Includes some type information in serialized data – not suited for true SOA • Does not support aliases • Does not support versioning • Does not support ordering • Explicit opt-out is needed to leave out some properties that shouldn’t be serialized

  25. Alternative – DataContract • DataContract: created specifically for WCF to serialize types • Attribute contains Name and Namespace properties • DataMember is needed to specify which properties/fields will form part of the contract • Contains EmitDefaultValue, IsRequired, Name, Order properties

  26. DataContract [DataContract(Name="Contact")] public class Person { [DataMember(IsRequired=true, Name="SurName")] public string LastName; public string FirstName; //Not included in contract }

  27. Versioning of data contracts • Three different scenarios: • New fields have been added • Existing fields have been deleted • Fields have been renamed

  28. Alternate way of looking at it: • Older version data [v1] passed to Service accepting newer version of data [v2] • Newer version data [v2] passed to Service accepting older version of data [v1] • New [v2]-> Old [v1]-> New [v2]

  29. New -> Old -> New

  30. Proxy code to hold [DataContract] public class MyDataContract: IExtensibleDataObject { public ExtensionDataObjectExtensionData { get; set; } }

  31. Inheritance with Data Contracts [DataContract] public class Employee { ... } [DataContract] public class Manager : Employee { ... } [ServiceContract] public interface IEmployeeService { [OperationContract] public void AddEmployee(Employee e); }

  32. Inheritance with Data Contracts [DataContract] [KnownType(typeof(Manager))] public class Employee { ... } [DataContract] public class Manager : Employee { ... } [ServiceContract] public interface IEmployeeService { [OperationContract] public void AddEmployee(Employee e); }

  33. Handling Faults

  34. SOAP Faults • Three main kinds of Exceptions can occur: • Communication errors • Unexpected error on the service • Errors thrown by the service on purpose • .NET Exceptions are technology specific • All Exceptions come across the wire as SOAP Faults

  35. Faults • In WCF, SOAP faults are passed in as FaultException objects • Rather than throwing Exceptions, services should throw FaultExceptions • Or better still FaultException<T> • Throwing FaultExceptions will not fault the proxy and the channel

  36. FaultContracts • Specifies what kind of Exceptions, an operation can throw [ServiceContract] public interface IEmployeeService { [OperationContract] [FaultContract(typeof(ValidationException))] public void AddEmployee(Employee e); }

  37. Server side code • Always throw Exceptions as Fault Exceptions public class EmployeeService { public void AddEmployee(Employee e) { ... throw new FaultException<ValidationException> (new ValidationException(errorMsg)); } }

  38. Client side code EmployeeServiceProxy proxy = new EmployeeServiceProxy(); try { ... proxy.AddEmployee(emp); } catch(FaultException<ValidationException> e) { //Do stuff with exception here } catch(FaultException e) { //Will catch all other types of Fault exceptions... }

  39. Exceptions while developing <system.serviceModel> <services> <service name = "EmployeeService" behaviorConfiguration ="Debugging"> ... </service> </services> <behaviors> <serviceBehaviors> <behavior name ="Debugging"> <serviceDebug includeExceptionDetailInFaults = "true"/> </behavior> </serviceBehaviors> </behaviors></system.serviceModel>

  40. Summary • WCF provides a runtime for creating Service Oriented Apps • Provides a productive programming model. Takes care of: • Messaging and Exchange formats • All Plumbing: Transaction, Reliability, Security, etc • Supports Declarative (via attributes), Imperative (via code) and Configuration based (via config files) programming model • ABCs of Endpoints • Address: Where to go? • Binding: How to get there? • Contract: What to do? • Hosting • IIS, WAS, Self-hosting

  41. Summary (contd) • ServiceContract and OperationContract specify Service and operation information • DataContracts and DataMembers are used for specifying the data that is passed across the wire • Use KnownType attribute for specifying class hierarchy information in Data contracts • FaultContracts specify what Exceptions may be thrown by the operations

  42. Questions?

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