Duplex Contract/Communication

A duplex Contract defines two logical sets of operations: A set that the Service exposes for the Client to call and a set that the Client exposes for the Service to call. The programming model for defining a duplex Contract is to split each set in a separate type (each type must be a class or an interface) and annotate the contract that represents the service's operations with ServiceContractAttribute, referencing the contract that defines the client (or callback) operations. In addition, ContractDescription contains a reference to each of the types thereby grouping them into one duplex Contract.

Similar to Bindings, each Contract has a Name and Namespace that uniquely identify it in the Service's metadata.

Each Contract also has a collection of ContractBehaviors that are modules that modify or extend the contract's behavior.

Duplex Communication

 Some Important Points to note:

• Sender and Receiver can exchange multiple messages.
• Sender and Receiver establishes  a socket for to communication.
• A duplex service contract is a message exchange pattern which both endpoints can send messages to the other independently. 
• It gives Rich Communication[One-Way Communication ].
• It uses dual channel Binding.eg: WsdualBinding.
• Decalre the Callback interfece.
• Add callbackcontract property of ServiceContractAttribute to indicate the callback interface
• CallOperationcontext.Current.GetcallbackChannel to get the callback interface.
• Fire callback interface methods in free your time.

  The following is an example of a duplex contract.

 Steps for developing duplex contract:

1. Start new website -->wcf service.
2. Delete the default wcf service and add new wcf service.In interface file create service contract with methods to run at server and an additional interface which is a callbackinterface for  this service wcf provides optio in servicecontract and other areas to specify perticular communication.
3. Implement the main inteface according to requirement.
4. Goto Config file and change wsHttpBinding to wsDualBinding because this binding only provides the Duplex style of communication.

          Write following code  in  ICourierTrack.cs

            using System;

            using System.Collections.Generic;

            using System.Linq;

            using System.Runtime.Serialization;

            using System.ServiceModel;

            using System.Text;

           [ServiceContract(SessionMode=SessionMode.Required,CallbackContract

               =typeof(ICourierTrackcallback))]

            public interface ICourierTrack

           {

               [OperationContract]

             void PlaceOrder(int value);

            }

               //callback interface

             public interface ICourierTrackcallback

             {

                        [OperationContract(IsOneWay=true)]

              void Result(string info);

            }

          Write following code  in  CourierTrack.cs

             using System;

             using System.Collections.Generic;

             using System.Linq;

             using System.Runtime.Serialization;

             using System.ServiceModel;

             using System.Text;

            [ServiceBehavior(InstanceContextMode=InstanceContextMode.PerSession)]

           public class CourierTrack : ICourierTrack

           {

           public ICourierTrackcallback callback

           {

            get

           {

            return OperationContext.Current.GetCallbackChannel<ICourierTrackcallback>();

            }

          }

          public void PlaceOrder(int value)

         {

            callback.Result("Special Order Accepted by Manager");

           System.Threading.Thread.Sleep(7000);

           callback.Result("Order Dispatched by dispatch team-ref- a23sd-");

           System.Threading.Thread.Sleep(7000);

           callback.Result("Order in Air-ref-accecing-"+value.ToString());

           System.Threading.Thread.Sleep(4000);

           callback.Result("Order recd by local client- Thanks U");

          }

        }

   Write following code  in  CourierTrack.svc

       <%@ ServiceHost Language="C#" Debug="true" Service="CourierTrack"                      CodeBehind="~/App_Code/CourierTrack.cs" %>
 

   Write following code  in  webconfig file

       <system.serviceModel>
       <services>
       <service behaviorConfiguration="ServiceBehavior" name="Service">
       <endpoint address="" binding="wsDualHttpBinding" contract="IService">
       <identity>
       <dns value="localhost"/>
       </identity>
       </endpoint>
       <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange"/>
        </service>
        <service behaviorConfiguration="CourierTrackBehavior" name="CourierTrack">
        <endpoint address="" binding="wsDualHttpBinding" contract="ICourierTrack">
         <identity>
         <dns value="localhost"/>
         </identity>
            </endpoint>
          <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange"/>
           </service>
         </services>
          <behaviors>
           <serviceBehaviors>
          <behavior name="ServiceBehavior">
          <serviceMetadata httpGetEnabled="true"/>
           <serviceDebug includeExceptionDetailInFaults="false"/>
           </behavior>
          <behavior name="CourierTrackBehavior">
         <serviceMetadata httpGetEnabled="true"/>
        <serviceDebug includeExceptionDetailInFaults="false"/>
        </behavior>
        </serviceBehaviors>
       </behaviors>
       </system.serviceModel>

• To Consume this service  Goto Duplex Client Program.

ScreenShots for Developing Duplex service: