Introduction to WCF

Windows Communication Foundation (Code named Indigo) is a programming platform and runtime system for building, configuring and deploying network-distributed services.

Below figures shows the different technology combined to form WCF.

Advantage

1. WCF is interoperable with other services when compared to .Net Remoting,where the client and service have to be .Net.

2. WCF services provide better reliability and security in compared to ASMX web services.

3. In WCF, there is no need to make much change in code for implementing the security model and changing the binding. Small changes in the configuration will make your requirements.

4. WCF has integrated logging mechanism, changing the configuration file settings will provide this functionality. In other technology developer has to write the code.

Disadvantage

Making right design for your requirement is little bit difficult. I will try to help you on solving these difficulties in the following article.

Difference between WCF and Web service

Web service is a part of WCF. WCF offers much more flexibility and portability to develop a service when comparing to web service. Still we are having more advantages over Web service, following table provides detailed difference between them.

Features	Web Service	WCF
Hosting	It can be hosted in IIS	It can be hosted in IIS, windows activation service, Self-hosting, Windows service
Programming	[WebService] attribute has to be added to the class	[ServiceContraact] attribute has to be added to the class
Model	[WebMethod] attribute represents the method exposed to client	[OperationContract] attribute represents the method exposed to client
Operation	One-way, Request- Response are the different operations supported in web service	One-Way, Request-Response, Duplex are different type of operations supported in WCF
XML	System.Xml.serialization name space is used for serialization	System.Runtime.Serialization namespace is used for serialization
Encoding	XML 1.0, MTOM(Message Transmission Optimization Mechanism), DIME, Custom	XML 1.0, MTOM, Binary, Custom
Transports	Can be accessed through HTTP, TCP, Custom	Can be accessed through HTTP, TCP, Named pipes, MSMQ,P2P, Custom
Protocols	Security	Security, Reliable messaging, Transactions

WCF Fundamental

In this part of tutorial you are going to learn about some fundamental concepts in WCF. These concepts and terms will be used throughout this tutorial.

EndPoint

WCF Service is a program that exposes a collection of Endpoints. Each Endpoint is a portal for communicating with the world.

All the WCF communications are take place through end point. End point consists of three components.

Address

Basically URL, specifies where this WCF service is hosted .Client will use this url to connect to the service. e.g

http://localhost:8090/MyService/SimpleCalculator.svc

Binding

Binding will describes how client will communicate with service. There are different protocols available for the WCF to communicate to the Client. You can mention the protocol type based on your requirements.

A binding has several characteristics, including the following:

Transport -Defines the base protocol to be used like HTTP, Named Pipes, TCP, and MSMQ are some type of protocols.
Encoding (Optional) - Three types of encoding are available-Text, Binary, or Message Transmission Optimization Mechanism (MTOM). MTOM is an interoperable message format that allows the effective transmission of attachments or large messages (greater than 64K).
Protocol(Optional) - Defines information to be used in the binding such as Security, transaction or reliable messaging capability

The following table gives some list of protocols supported by WCF binding.

Binding	Description
BasicHttpBinding	Basic Web service communication. No security by default
WSHttpBinding	Web services with WS-* support. Supports transactions
WSDualHttpBinding	Web services with duplex contract and transaction support
WSFederationHttpBinding	Web services with federated security. Supports transactions
MsmqIntegrationBinding	Communication directly with MSMQ applications. Supports transactions
NetMsmqBinding	Communication between WCF applications by using queuing. Supports transactions
NetNamedPipeBinding	Communication between WCF applications on same computer. Supports duplex contracts and transactions
NetPeerTcpBinding	Communication between computers across peer-to-peer services. Supports duplex contracts
NetTcpBinding	Communication between WCF applications across computers. Supports duplex contracts and transactions

Contract

Collection of operation that specifies what the endpoint will communicate with outside world. Usually name of the Interface will be mentioned in the Contract, so the client application will be aware of the operations which are exposed to the client. Each operation is a simple exchange pattern such as one-way, duplex and request/reply.

Below figure illustrate the functions of Endpoint

Example:

Endpoints will be mentioned in the web.config file on the created service.

<system.serviceModel>

<services>

      <service name="MathService"

        behaviorConfiguration="MathServiceBehavior">

       <endpoint

         address="http://localhost:8090/MyService/MathService.svc" contract="IMathService"

          binding="wsHttpBinding"/>

      </service>

    </services>

    <behaviors>

      <serviceBehaviors>

        <behavior name="MathServiceBehavior">

          <serviceMetadata httpGetEnabled="True"/>

          <serviceDebug includeExceptionDetailInFaults="true" />

        </behavior>

      </serviceBehaviors>

    </behaviors>

  </system.serviceModel>

Binding and Behavior

Binding

Simple definition for Binding describes how the client will communicate with service. We can understand with an example.

Consider a scenario say, I am creating a service that has to be used by two type of client. One of the client will access SOAP using http and other client will access Binary using TCP. How it can be done? With Web service it is very difficult to achieve, but in WCF its just we need to add extra endpoint in the configuration file.

<system.serviceModel>

    <services>

      <service name="MathService"

        behaviorConfiguration="MathServiceBehavior">

      <endpoint address="http://localhost:8090/MyService/MathService.svc"

        contract="IMathService"

          binding="wsHttpBinding"/>

<endpoint address="net.tcp://localhost:8080/MyService/MathService.svc"

contract="IMathService"

          binding="netTcpBinding"/>

      </service>

    </services>

    <behaviors>

      <serviceBehaviors>

        <behavior name="MathServiceBehavior">

          <serviceMetadata httpGetEnabled="True"/>

          <serviceDebug includeExceptionDetailInFaults="true" />

        </behavior>

      </serviceBehaviors>

    </behaviors>

  </system.serviceModel>

See how simple it is in WCF. Microsoft is making everything simple.cording to its scope: common behaviors affect all endpoints globally, service behaviors affect only service-related aspects, endpoint behaviors affect only endpoint-related properties, and operation-level behaviors affect particular operations.

Example:

In the below configuration information, I have mentioned the Behavior at Service level. In the service behavior I have mention the servieMetadata node with attribute httGetEnabled='true'. This attribute will specifies the publication of the service metadata. Similarly we can add more behavior to the service.

<system.serviceModel>

    <services>

      <service name="MathService"

        behaviorConfiguration="MathServiceBehavior">

        <endpoint address="" contract="IMathService"

          binding="wsHttpBinding"/>

      </service>

    </services>

    <behaviors>

      <serviceBehaviors>

        <behavior name="MathServiceBehavior">

          <serviceMetadata httpGetEnabled="True"/>

          <serviceDebug includeExceptionDetailInFaults="true" />

        </behavior>

      </serviceBehaviors>

    </behaviors>

  </system.serviceModel>

Note:

Application can be controlled either through coding, configuring or through combination of both. Specification mention in the configuration can also be overwritten in code.

Contracts and Service Host

Contracts

In WCF, all services are exposed as contracts. Contract is a platform-neutral and standard way of describing what the service does. Mainly there are four types of contracts available in WCF

Service Contract

Service contracts describe the operation that service can provide. For Eg, a Service provide to know the temperature of the city based on the zip code, this service is called as Service contract. It will be created using Service and Operational Contract attribute.

To know more on Service contract see Service contract tutorial.

Data Contract

Data contract describes the custom data type which is exposed to the client. This defines the data types, that are passed to and from service. Data types like int, string are identified by the client because it is already mention in XML schema definition language document, but custom created class or data types cannot be identified by the client e.g. Employee data type. By using DataContract we can make client to be aware of Employee data type that are returning or passing parameter to the method.

To know more on DataContract see DataContract tutorial.

Message Contract

Default SOAP message format is provided by the WCF runtime for communication between Client and service. If it is not meeting your requirements then we can create our own message format. This can be achieved by using Message Contract attribute.

To know more on Message Contract see Message contract tutorial.

Fault Contract

Suppose the service I consumed is not working in the client application. I want to know the real cause of the problem. How I can know the error? For this we are having Fault Contract. Fault Contract provides documented view for error occurred in the service to client. This helps us to easy identity, what error has occurred.

To know more on Fault Contract see Fault Contract tutorial.

Service Host

Service Host object is in the process of hosting the WCF service and registering endpoints. It loads the service configuration endpoints, apply the settings and start the listeners to handle the incoming request. System.ServiceModel.ServiceHost namespace hold this object. This object is created while self hosting the WCF service.

In the below example you can find that WCF service is self hosted using console application.

//Creating uri for the hosting the service

Uri uri = new Uri("http://localhost/CategoryService");

//Creating the host object for MathService

  ServiceHost host = new ServiceHost(typeof(CategoryService), uri);

//Adding endpoint to the Host object

  host.AddServiceEndpoint(typeof(ICategoryService),new WSHttpBinding(), uri);

  host.Open(); //Hosting the Service

  Console.WriteLine("Waiting for client invocations");

  Console.ReadLine();

  host.Close();

Message and Channel

Message

WCF Message is the unit of data exchange between client and service. It consists of several parts, including a body and headers.

WCF Runtime

WCF runtime is the set of object responsible for sending and receiving message. For example formatting the message, applying security and transmitting and receiving message using various protocol.

Channels:

Channels are the core abstraction for sending message to and receiving message from an Endpoint. Broadly we can categories channels as

Transport Channels

- Handles sending and receiving message from network. Protocols like HTTP, TCP name pipes and MSMQ.

Protocol Channels

- Implements SOAP based protocol by processing and possibly modifying message. e.g. WS-Security and WS-Reliability.

WCF Client and Metadata

WCF Client

WCF client is a client application creates to expose the service operations as method. Any application can host a WCF client, including an application that host a service. Therefore it is possible to create a service that includes WCF clients of other services.

A client application is a managed application that uses a WCF client to communicate with another application. To create a client application for a WCF service requires the following steps:

1. Get the Proxy class and service end point information

Using SvcUtil.exe we can create proxy class for the service and configuration information for endpoints. Example type the following sentence in the Visual studio command prompt, this will generate the class file and configuration file which contain information about the endpoints.

svcutil /language:vb /out:ClientCode.vb /config:app.config http://localhost:8090/MyService/SimpleCalculator.svc?wsdl

2. Call operations.

Add this class files in the client application. Then create the object for this class and invoke the service operation. Configuration information we got from the above step has to be added to the client application configuration file. When the client application calls the first operation, WCF automatically opens the underlying channel. This underlying channel is closed, when the object is recycled.

//Creating the proxy on client side

MyCalculatorServiceProxy.MyServiceProxy proxy

= new MyCalculatorServiceProxy.MyServiceProxy();

Console.WriteLine("Counter: " + proxy.MyMethod());

3. Close the WCF client object.

After using the object created in the above steps, we have to dispose the object. Channel will be closed with the service, when the object is cleared.

Metadata

Characteristics of the service are described by the metadata. This metadata can be exposed to the client to understand the communication with service. Metadata can be set in the service by enabling the ServiceMetadata node inside the servcieBehaviour node of the service configuration file.

<system.serviceModel>

<service name="MathService"

behaviorConfiguration="MathServiceBehavior">

<endpoint address="" contract="IMathService"

binding="wsHttpBinding"/>

</service>

</services>

</behavior>

</serviceBehaviors>

</behaviors>

</system.serviceModel>

This metadata can be viewed while creating WCF client application using SvcUtil.exe

WCF Architecture

The following figure illustrates the major components of WCF.

Figure 1: WCF Architecture

Contracts

Contracts layer are next to that of Application layer. Developer will directly use this contract to develop the service. We are also going to do the same now. Let us see briefly what these contracts will do for us and we will also know that WCF is working on message system.

Service contracts

- Describe about the operation that service can provide. Example, Service provided to know the temperature of the city based on the zip code, this service we call as Service contract. It will be created using Service and Operational Contract attribute.

Data contract

- It describes the custom data type which is exposed to the client. This defines the data types, are passed to and from service. Data types like int, string are identified by the client because it is already mention in XML schema definition language document, but custom created class or datatype cannot be identified by the client e.g. Employee data type. By using DataContract we can make client aware that we are using Employee data type for returning or passing parameter to the method.

Message Contract

- Default SOAP message format is provided by the WCF runtime for communication between Client and service. If it is not meeting your requirements then we can create our own message format. This can be achieved by using Message Contract attribute.

Policies and Binding

- Specify conditions required to communicate with a service e.g security requirement to communicate with service, protocol and encoding used for binding.

Service Runtime

- It contains the behaviors that occur during runtime of service.

Throttling Behavior- Controls how many messages are processed.
Error Behavior - Specifies what occurs, when internal error occurs on the service.
Metadata Behavior - Tells how and whether metadata is available to outside world.
Instance Behavior - Specifies how many instance of the service has to be created while running.
Transaction Behavior - Enables the rollback of transacted operations if a failure occurs.
Dispatch Behavior - Controls how a message is processed by the WCF Infrastructure.

Messaging

- Messaging layer is composed of channels. A channel is a component that processes a message in some way, for example, by authenticating a message. A set of channels is also known as a channel stack. Channels are the core abstraction for sending message to and receiving message from an Endpoint. Broadly we can categories channels as

Transport Channels

Handles sending and receiving message from network. Protocols like HTTP, TCP, name pipes and MSMQ.

Protocol Channels

Implements SOAP based protocol by processing and possibly modifying message. E.g. WS-Security and WS-Reliability.

Activation and Hosting

- Services can be hosted or executed, so that it will be available to everyone accessing from the client. WCF service can be hosted by following mechanism

Internet information Service provides number of advantages if a Service uses Http as protocol. It does not require Host code to activate the service, it automatically activates service code.

Windows Activation Service

(WAS) is the new process activation mechanism that ships with IIS 7.0. In addition to HTTP based communication, WCF can also use WAS to provide message-based activation over other protocols, such as TCP and named pipes.

Self-Hosting

WCF service can be self hosted as console application, Win Forms or WPF application with graphical UI.

Windows Service

WCF can also be hosted as a Windows Service, so that it is under control of the Service Control Manager (SCM).

WCF Hosting

In this part of the tutorial we are going to see the four different way of hosting the WCF service. WCF service cannot exist on its own; it has to be hosted in windows process called as host process. Single host process can host multiple servers and same service type can be hosted in multiple host process. As we discussed there are mainly four different way of hosting the WCF service.

1. IIS hosting

2. Self hosting

3. Windows Activation Service

4. Windows Service

Multiple hosting and protocols supported by WCF.Microsoft has introduced the WCF concept in order to make distributed application development and deployment simple.

Hosting Environment	Supported protocol
Windows console and form application	HTTP,net.tcp,net.pipe,net.msmq
Windows service application (formerly known as NT services)	HTTP,net.tcp,net.pipe,net.msmq
Web server IIS6	http, wshttp
Web server IIS7 - Windows Process Activation Service (WAS)	HTTP,net.tcp,net.pipe,net.msmq

A summary of hosting options and supported features.

Feature	Self-Hosting	IIS Hosting	WAS Hosting
Executable Process/ App Domain	Yes	Yes	Yes
Configuration	App.config	Web.config	Web.config
Activation	Manual at startup	Message-based	Message-based
Idle-Time Management	No	Yes	Yes
Health Monitoring	No	Yes	Yes
Process Recycling	No	Yes	Yes
Management Tools	No	Yes	Yes

IIS 5/6 Hosting

The main advantage of hosting service in IIS is that, it will automatically launch the host process when it gets the first client request. It uses the features of IIS such as process recycling, idle shutdown, process health monitoring and message based activation. The main disadvantage of using IIS is that, it will support only HTTP protocol.

Let as do some hands on, to create service and host in IIS

Step 1:Start the Visual Studio 2008 and click File->New->Web Site. Select the 'WCF Service' and Location as http. This will directly host the service in IIS and click OK.

Step 2: I have created sample HelloWorld service, which will accept name as input and return with 'Hello' and name. Interface and implementation of the Service is shown below.

IMyService.cs

[ServiceContract]

public interface IMyService

{

[OperationContract]

string HelloWorld(string name);

}

MyService.cs

public class MyService : IMyService

{

#region IMyService Members

public string HelloWorld(string name)

{

return "Hello " + name;

}

#endregion

}

Step 3: Service file (.svc) contains name of the service and code behind file name. This file is used to know about the service.

MyService.svc

<%@ ServiceHost Language="C#" Debug="true"

Service="MyService" CodeBehind="~/App_Code/MyService.cs" %>

Step 4: Server side configurations are mentioned in the config file. Here I have mention only one end point which is configured to 'wsHttpBinding', we can also have multiple end point with differnet binding. Since we are going to hosted in IIS. We have to use only http binding. We will come to know more on endpoints and its configuration in later tutorial. Web.Config

<system.serviceModel>

<endpoint address="http://localhost/IISHostedService/MyService.svc"

binding="wsHttpBinding" contract="IMyService">

</identity>

</endpoint>

</service>

</services>

<!-- To avoid disclosing metadata information,

set the value below to false and remove the

metadata endpoint above before deployment -->

<!-- To receive exception details in faults for

debugging purposes, set the value below to true.

Set to false before deployment to avoid disclosing exception information -->

</behavior>

</serviceBehaviors>

</behaviors>

</system.serviceModel>

Note:

You need to mention the service file name, along with the Address mention in the config file. IIS Screen shot

This screen will appear when we run the application.

Step 5: Now we successfully hosted the service in IIS. Next we have to consume this service in client application. Before creating the client application, we need to create the proxy for the service. This proxy is used by the client application, to interact with service. To create the proxy, run the Visual Studio 2008 command prompt. Using service utility we can create the proxy class and its configuration information.

svcutil http://localhost/IISHostedService/MyService.svc

After executing this command we will find two file generated in the default location.

MyService.cs - Proxy class for the WCF service
output.config - Configuration information about the service.

Step 6: Now we will start creating the Console application using Visual Studio 2008(Client application).

Step 7: Add the reference 'System.ServiceModel'; this is the core dll for WCF.

Step 8: Create the object for the proxy class and call the HelloWorld method.

static void Main(string[] args)

{

//Creating Proxy for the MyService

MyServiceClient client = new MyServiceClient();

Console.WriteLine("Client calling the service...");

Console.WriteLine(client.HelloWorld("Ram"));

Console.Read();

}

Step 9: If we run the application we will find the output as shown below.

I hope you have enjoyed the Service hosted in IIS. Now let start the look on the self hosted service.

Self Hosting

In web service, we can host the service only in IIS, but WCF provides the user to host the service in any application (e.g. console application, Windows form etc.). Very interestingly developer is responsible for providing and managing the life cycle of the host process. Service can also be in-pro i.e. client and service in the same process. Now let's us create the WCF service which is hosted in Console application. We will also look in to creating proxy using 'ClientBase' abstract class.

Note: Host process must be running before the client calls the service, which typically means you have to prelaunch it.

Step 1: First let's start create the Service contract and it implementation. Create a console application and name it as MyCalculatorService. This is simple service which return addition of two numbers.

Step 2: Add the System.ServiceModel reference to the project.

Step 3: Create an ISimpleCalculator interface, Add ServiceContract and OperationContract attribute to the class and function as shown below. You will know more information about these contracts in later session. These contracts will expose method to outside world for using this service.

IMyCalculatorService.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.ServiceModel;

namespace MyCalculatorService

{

[ServiceContract()]

public interface ISimpleCalculator

{

[OperationContract()]

int Add(int num1, int num2);

}

Step 4: MyCalculatorService is the implementation class for IMyCalculatorService interface as shown below.

MyCalculatorService.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace MyCalculatorService

{

class SimpleCalculator : ISimpleCalculator

{

public int Add(int num1, int num2)

{

return num1 + num2;

}

Step 5: Now we are ready with service. Let's go for implementing the hosting process. Create a new console application and name it as 'MyCalculatorServiceHost'

Step 6: ServiceHost is the core class use to host the WCF service. It will accept implemented contract class and base address as contractor parameter. You can register multiple base addresses separated by commas, but address should not use same transport schema.

Uri httpUrl

= new Uri("http://localhost:8090/MyService/SimpleCalculator");

Uri tcpUrl

= new Uri("net.tcp://localhost:8090/MyService/SimpleCalculator");

ServiceHost host

= new ServiceHost(typeof(MyCalculatorService.SimpleCalculator), httpUrl, tcpUrl);

Multiple end points can be added to the Service using AddServiceEndpoint() method. Host.Open() will run the service, so that it can be used by any client.

Step 7: Below code show the implementation of the host process.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.ServiceModel;

using System.ServiceModel.Description;

namespace MyCalculatorServiceHost

{

class Program

{

static void Main(string[] args)

{

//Create a URI to serve as the base address

Uri httpUrl = new Uri("http://localhost:8090/MyService/SimpleCalculator");

//Create ServiceHost

ServiceHost host

= new ServiceHost(typeof(MyCalculatorService.SimpleCalculator), httpUrl);

//Add a service endpoint

host.AddServiceEndpoint(typeof(MyCalculatorService.ISimpleCalculator)

, new WSHttpBinding(), "");

//Enable metadata exchange

ServiceMetadataBehavior smb = new ServiceMetadataBehavior();

smb.HttpGetEnabled = true;

host.Description.Behaviors.Add(smb);

//Start the Service

host.Open();

Console.WriteLine("Service is host at " + DateTime.Now.ToString());

Console.WriteLine("Host is running... Press <Enter> key to stop");

Console.ReadLine();

}

Step 8: Service is hosted, now we need to implement the proxy class for the client. There are different ways of creating the proxy

Using SvcUtil.exe, we can create the proxy class and configuration file with end points.
Adding Service reference to the client application.
Implementing ClientBase<T> class

Of these three methods, Implementing ClientBase<T> is the best practice. If you are using rest two method, we need to create proxy class every time when we make changes in Service implementation. But this is not the case for ClientBase<T>. It will create the proxy only at runtime and so it will take care of everything.

MyCalculatorServiceProxy.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.ServiceModel;

using MyCalculatorService;

namespace MyCalculatorServiceProxy

{

public class MyCalculatorServiceProxy :

//WCF create proxy for ISimpleCalculator using ClientBase

ClientBase<ISimpleCalculator>,

ISimpleCalculator

{

public int Add(int num1, int num2)

{

//Call base to do funtion

return base.Channel.Add(num1, num2);

}

Step 9: In the client side, we can create the instance for the proxy class and call the method as shown below. Add proxy assembly as reference to the project.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.ServiceModel;

namespace MyCalculatorServiceClient

{

class Program

{

static void Main(string[] args)

{

MyCalculatorServiceProxy.MyCalculatorServiceProxy proxy ;

proxy= new MyCalculatorServiceProxy.MyCalculatorServiceProxy();

Console.WriteLine("Client is running at " + DateTime.Now.ToString());

Console.WriteLine("Sum of two numbers... 5+5 ="+proxy.Add(5,5));

Console.ReadLine();

}

Step 10 : End point (same as service) information should be added to the configuration file of the client application.

<?xml version="1.0" encoding="utf-8" ?>

<system.serviceModel>

<endpoint address ="http://localhost:8090/MyService/SimpleCalculator"

binding ="wsHttpBinding"

contract ="MyCalculatorService.ISimpleCalculator">

</endpoint>

</client>

</system.serviceModel>

</configuration>

Step 11: Before running the client application, you need to run the service. Output of the client application is shown below.

This self host shows advantage such as in-Pro hosting, programmatic access and it can be used when there need singleton service. I hope you have enjoyed the Self hosting session, now let go for hosting using Windows Activation service.

Windows Activation Service

Windows Activation service is a system service available with Windows vista and windows server 2008. It is available with IIS 7.0 and it is more powerful compared to IIS 6.0 because it supports Http, TCP and named pipes were IIS 6.0 supports only Http. It can be installed and configured separately.

Hosting WCF in Activation service takes many advantages such as process recycling, isolation, idle time management and common configuration system. WAS hosted service can be created using following steps

1. Enable WCF for non-http protocols

2. Create WAS hosted service

3. Enable different binding to the hosted service

Enable WCF for non-http protocols

Before Start creating the service we need to configure the system to support WAS. Following are the step to configure WAS.

1. Click Start -> Control Panel -> programs and Features and click 'Turn Windows Components On or Off' in left pane.

2. Expand 'Microsoft .Net Framework 3.0' and enable "Windows Communication Foundation HTTP Activation" and "Windows Communication Foundation Non- HTTP Activation".

3. Next we need to add Binding to the Default Web site. As an example, we will bind the default web site to the TCP protocol. Go to the Start menu -> Programs ->Accessories. Right click on the "Command Prompt" item, and select "Run as administrator" from the context menu.

4. Execute the following command

5. C:\Windows\system32\inetsrv> appcmd.exe set site "Default Web Site" -+bindings.[protocol='net.tcp',

bindingInformation='808:*']

 That command adds the net.tcp site binding to the default web site by modifying the applicationHost.config file located in the "C:\Windows\system32\inetsrv\config" directory. Similarly we can add different protocols to the Default Web site.

Create WAS hosted service

Step 1: Next we are going to create the service, Open the Visual Studio 2008 and click New->WebSite and select WCF Service from the template and Location as HTTP as shown below.

Step 2: Create the Contract by creating interface IMathService and add ServiceContract attribute to the interface and add OperationContract attribute to the method declaration.

IMathService.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Runtime.Serialization;

using System.ServiceModel;

using System.Text;

[ServiceContract]

public interface IMathService

{

[OperationContract]

int Add(int num1, int num2);

[OperationContract]

int Subtract(int num1, int num2);

}

Step 3: Implementation of the IMathService interface is shown below.

MathService.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Runtime.Serialization;

using System.ServiceModel;

using System.Text;

public class MathService : IMathService

{

public int Add(int num1, int num2)

{

return num1 + num2;

}

public int Subtract(int num1, int num2)

{

return num1 - num2;

}

Step 4: Service file is shown below.

MathService.svc

<%@ ServiceHost Language="C#" Debug="true" Service="MathService"

CodeBehind="~/App_Code/MathService.cs" %>

Step 5: In web.Config file, create end point with 'netTcpBinding' binding and service metadata will be published using Metadata Exchange point. So create the Metada Exchange end point with address as 'mex' and binding as 'mexTcpBinding'. Without publishing the service Metadata we cannot create the proxy using net.tcp address (e.g svcutil.exe net.tcp://localhost/WASHostedService/MathService.svc )

Web.Config

<system.serviceModel>

<endpoint binding="netTcpBinding"

contract="IMathService" >

</endpoint>

<endpoint address="mex"

binding="mexTcpBinding" contract="IMetadataExchange"/>

</service>

</services>

<!-- To avoid disclosing metadata information, set the value below

to false and remove the metadata endpoint above before deployment -->

<!-- To receive exception details in

faults for debugging purposes, set the value below to true.

Set to false before deployment to avoid disclosing

exception information -->

</behavior>

</serviceBehaviors></behaviors>

</system.serviceModel>

Enable different binding to the hosted service

1. Go to the Start menu -> Programs ->Accessories. Right click on the "Command Prompt" item, and select "Run as administrator" from the context menu.

2. Execute the following command C:\Windows\system32\inetsrv>appcmd set app "Default Web Site/WASHostedServcie" /enabledProtocols:http,net.tcp

Output will be shown below.

Step 6: Now the service is ready to use. Next we can create the proxy class using service uttility and add the proxy class to the client application. Creat the proxy class using Visual Studio Command prompt and execute the command

svcutil.exe net.tcp://localhost/WASHostedService/MathService.svc

Proxy and configuration file are generated in the corresponding location.

Step 6: Create the client application as shown below and add the reference 'System.ServiceModel', this is the core dll for WCF.

Step 8: Add the proxy class and configuration file to the client application. Create the object for the MathServiceClient and call the method.

Program.cs

class Program

{

static void Main(string[] args)

{

MathServiceClient client = new MathServiceClient();

Console.WriteLine("Sum of two number 5,6");

Console.WriteLine(client.Add(5,6));

Console.ReadLine();

}

The output will be shown as below.

So this tutorial clearly explains about the hosting the WCF in Windows Activation Service. So next we can see how to host the service using Windows Service

Windows Service Hosting

In this tutorial we are going to see the hosting WCF service in Windows service. We will use same set of code used for hosting the WCF service in Console application to this. This is same as hosting the service in IIS without message activated. There is some advantage of hosting service in Windows service.

The service will be hosted, when system starts
Process life time of the service can be controlled by Service Control Manager for windows service
All versions of Windows will support hosting WCF service.

Step 1: Now let start create the WCF service, Open the Visual Studio 2008 and click New->Project and select Class Library from the template.

Step 2: Add reference System.ServiceModel to the project. This is the core assembly used for creating the WCF service.

Step 3: Next we can create the ISimpleCalulator interface as shown below. Add the Service and Operation Contract attribute as shown below.

ISimpleCalculator.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.ServiceModel;

namespace WindowsServiceHostedContract

{

[ServiceContract]

public interface ISimpleCalculator

{

[OperationContract]

int Add(int num1, int num2);

[OperationContract]

int Subtract(int num1, int num2);

[OperationContract]

int Multiply(int num1,int num2);

[OperationContract]

double Divide(int num1, int num2);

}

Step 4: Implement the ISimpleCalculator interface as shown below.

SimpleCalulator.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace WindowsServiceHostedService

{

class SimpleCalculator

: ISimpleCalculator

{

public int Add(int num1, int num2)

{

return num1+num2;

}

public int Subtract(int num1, int num2)

{

return num1-num2;

}

public int Multiply(int num1, int num2)

{

return num1*num2;

}

public double Divide(int num1, int num2)

{

if (num2 != 0)

return num1 / num2;

else

return 0;

}

Step 5: Build the Project and get the dll. Now we are ready with WCF service, now we are going to see how to host the WCF Service in Windows service. Note: In this project, I have mention that we are creating both Contract and Service(implementation) are in same project. It is always good practice if you have both in different project.

Step 6: Open Visual Studio 2008 and Click New->Project and select Windows Service.

Step 7: Add the 'WindowsServiceHostedService.dll' as reference to the project. This assembly will going to act as service.

Step 8: OnStart method of the service, we can write the hosting code for WCF. We have to make sure that we are using only one service host object. On stop method you need to close the Service Host. Following code show how to host WCF service in Windows service.

WCFHostedWindowsService.cs

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Diagnostics;

using System.Linq;

using System.ServiceProcess;

using System.Text;

using System.ServiceModel;

using System.ServiceModel.Description;

namespace WCFHostedWindowsService

{

partial class WCFHostedWindowsService : ServiceBase

{

ServiceHost m_Host;

public WCFHostedWindowsService()

{

InitializeComponent();

}

protected override void OnStart(string[] args)

{

if (m_Host != null)

{

m_Host.Close();

}

//Create a URI to serve as the base address

Uri httpUrl = new Uri("http://localhost:8090/MyService/SimpleCalculator");

//Create ServiceHost

m_Host = new ServiceHost

(typeof(WindowsServiceHostedService.SimpleCalculator), httpUrl);

//Add a service endpoint

m_Host.AddServiceEndpoint

(typeof(WindowsServiceHostedService.ISimpleCalculator), new WSHttpBinding(), "");

//Enable metadata exchange

ServiceMetadataBehavior smb = new ServiceMetadataBehavior();

smb.HttpGetEnabled = true;

m_Host.Description.Behaviors.Add(smb);

//Start the Service

m_Host.Open();

}

protected override void OnStop()

{

if (m_Host != null)

{

m_Host.Close();

m_Host = null;

}

static void Main()

{

ServiceBase[] ServicesToRun;

ServicesToRun = new ServiceBase[]

{

new WCFHostedWindowsService()

};

ServiceBase.Run(ServicesToRun);

}

Step 9: In order to install the service we need to have the Installer class for the Windows service. So add new Installer class to the project, which is inherited from the Installer class. Please find the below code for mentioning the Service name, StartUp type etc of the service.

ServiceInstaller.cs

using System;

using System.Collections.Generic;

using System.Text;

using System.ServiceProcess;

using System.Configuration.Install;

using System.ComponentModel;

using System.Configuration;

namespace WCFHostedWindowsService

{

[RunInstaller(true)]

public class WinServiceInstaller : Installer

{

private ServiceProcessInstaller process;

private ServiceInstaller service;

public WinServiceInstaller()

{

process = new ServiceProcessInstaller();

process.Account = ServiceAccount.NetworkService;

service = new ServiceInstaller();

service.ServiceName = "WCFHostedWindowsService";

service.DisplayName = "WCFHostedWindowsService";

service.Description = "WCF Service Hosted";

service.StartType = ServiceStartMode.Automatic;

Installers.Add(process);

Installers.Add(service);

}

Step 10: Build the project, we will get the WCFHostedWindowsService.exe. Next we need to install the service using Visual Studio Command Prompt. So open the command prompt by clicking Start->All Programs-> Microsoft Visual Studio 2008-> Visual Studio Tools-> Visual Studio Command Prompt Using installutil utility application, you can install the service as shown below.

Step 11: Now service is Hosted sucessfully and we can create the proxy class for the service and start using in the client applcaiton.

Binding

Binding has several characteristics, including the following:

Transport

Defines the base protocol to be used like HTTP, Named Pipes, TCP, and MSMQ are some type of protocols.

Encoding (Optional)

Three types of encoding are available-Text, Binary, or Message Transmission Optimization Mechanism (MTOM). MTOM is an interoperable message format that allows the effective transmission of attachments or large messages (greater than 64K).

Protocol(Optional)

Defines information to be used in the binding such as Security, transaction or reliable messaging capability

Bindings and Channel Stacks

In WCF all the communication details are handled by channel, it is a stack of channel components that all messages pass through during runtime processing. The bottom-most component is the transport channel. This implements the given transport protocol and reads incoming messages off the wire. The transport channel uses a message encoder to read the incoming bytes into a logical Message object for further processing.

Figure 1: Bindings and Channel Stacks (draw new diagram)

After that, the message bubbles up through the rest of the channel stack, giving each protocol channel an opportunity to do its processing, until it eventually reaches the top and WCF dispatches the final message to your service implementation. Messages undergo significant transformation along the way.

It is very difficult for the developer to work directly with channel stack architecture. Because you have to be very careful while ordering the channel stack components, and whether or not they are compatible with one other.

So WCF provides easy way of achieving this using end point. In end point we will specify address, binding and contract. To know more about end point. Windows Communication Foundation follows the instructions outlined by the binding description to create each channel stack. The binding binds your service implementation to the wire through the channel stack in the middle.

Types of Binding

Let us see more detailed on predefined binding

BasicHttpBinding

It is suitable for communicating with ASP.NET Web services (ASMX)-based services that comfort with WS-Basic Profile conformant Web services.
This binding uses HTTP as the transport and text/XML as the default message encoding.
Security is disabled by default
This binding does not support WS-* functionalities like WS- Addressing, WS-Security, WS-ReliableMessaging
It is fairly weak on interoperability.

WSHttpBinding

Defines a secure, reliable, interoperable binding suitable for non-duplex service contracts.
It offers lot more functionality in the area of interoperability.
It supports WS-* functionality and distributed transactions with reliable and secure sessions using SOAP security.
It uses HTTP and HTTPS transport for communication.
Reliable sessions are disabled by default.

WSDualHttpBinding

This binding is same as that of WSHttpBinding, except it supports duplex service. Duplex service is a service which uses duplex message pattern, which allows service to communicate with client via callback.

In WSDualHttpBinding reliable sessions are enabled by default. It also supports communication via SOAP intermediaries.

WSFederationHttpBinding

This binding support federated security. It helps implementing federation which is the ability to flow and share identities across multiple enterprises or trust domains for authentication and authorization. It supports WS-Federation protocol.

NetTcpBinding

This binding provides secure and reliable binding environment for .Net to .Net cross machine communication. By default it creates communication stack using WS-ReliableMessaging protocol for reliability, TCP for message delivery and windows security for message and authentication at run time. It uses TCP protocol and provides support for security, transaction and reliability.

NetNamedPipeBinding

This binding provides secure and reliable binding environment for on-machine cross process communication. It uses NamedPipe protocol and provides full support for SOAP security, transaction and reliability. By default it creates communication stack with WS-ReliableMessaging for reliability, transport security for transfer security, named pipes for message delivery and binary encoding.

NetMsmqBinding

This binding provides secure and reliable queued communication for cross-machine environment.
Queuing is provided by using MSMQ as transport.
It enables for disconnected operations, failure isolation and load leveling

NetPeerTcpBinding

This binding provides secure binding for peer-to-peer environment and network applications.
It uses TCP protocol for communication
It provides full support for SOAP security, transaction and reliability.

Binding configuration

Binding can be configured either through configuration file or Programming. Let us see the binding representation in each method.

Administrative (Configuration file):

In the configuration file of the hosting application, you can add the <bindings> element inside the <system.serviceModel> element and add the properties to particular binding type. Properties corresponding to the particular binding type can be mentioned below. Name of the binding properties that you are going to use has to be mention in the end point.

<system.serviceModel>

  <services>

   <service  name="MyService">

                    <endpoint address="http://localhost/IISHostedService/MyService.svc"

                    binding="wsHttpBinding" bindingName="wshttpbind" contract="IMyService">

                    <identity>

                    <dns value="localhost"/>

                    </identity>

                    </endpoint>

                    <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange"/>

    </service>

  </services>

  <bindings>

      <wsHttpBinding>

        <binding name="wshttpbind"  allowCookies="true" closeTimeout="00:01:00"

        receiveTimeout="00:01:00" />

      </wsHttpBinding>

  </bindings>

</system.serviceModel>

Programming Model:

In the following code, I have created the WSHttpBinding object and assign the properties which to be configured. This binding object is added to the Service endpoint for client communication. Similarly you can also create any type of binding and add to endpoint.

//Create a URI to serve as the base address

            Uri httpUrl = new Uri("http://localhost:8090/MyService/SimpleCalculator");

            //Create ServiceHost

            ServiceHost host =

             new ServiceHost(typeof(MyCalculatorService.SimpleCalculator), httpUrl);

            //Create Binding to add to end point

            WSHttpBinding wshttpbind = new WSHttpBinding();

            wshttpbind.AllowCookies = true;

            wshttpbind.CloseTimeout = new TimeSpan(0, 1, 0);

            wshttpbind.ReceiveTimeout  = new TimeSpan(0, 1, 0);

            //Add a service endpoint

            host.AddServiceEndpoint

            (typeof(MyCalculatorService.ISimpleCalculator), wshttpbind, "");

            //Enable metadata exchange

            ServiceMetadataBehavior smb = new ServiceMetadataBehavior();

            smb.HttpGetEnabled = true;

            host.Description.Behaviors.Add(smb);

            //Start the Service

            host.Open();

            Console.WriteLine("Service is host at " + DateTime.Now.ToString());

            Console.WriteLine("Host is running... Press  key to stop");

            Console.ReadLine();

Note: It is always good if you configure the binding properties using configuration file, because while moving to the production you no need to change in the code and recompile it. It is always good practice to represent in the configuration file.

Metadata Exchange

WCF provides rich infrastructure for Exporting, Publishing, retrieving and Importing the metadata. WCF uses the Metadata to describe how to interact with the service endpoint. Using the metadata, client will create the proxy class for the service usingSvcUtil.exe

Exporting Service Metadata

It is the process of describing the service endpoint so that client can understand how to use the service.

Publishing Service Metadata

It is the process publishing metadata. It involves converting CLR type and binding information into WSDL or some other low level representation.

Retrieving Service Metadata

It is the process of retrieving the metadata. It uses WS-MetadataExcahge or HTTP protocol for retrieving the metadata. Importing Service Metadata - It is the process of generating the abstract representation of the service using metadata.

Now we are going to focus mainly on publishing metadata. There are two way to publish metadata, either we can use HTTP-GET or through message exchange endpoint. By default service metadata is turn-off due to security reason. WCF metadata infrastructure resides in System.ServiceModel.Description namespace. Service metadata can be used for following purpose

Automatically generating the client for consuming service
Implementing the service description
Updating the binding for a client

Now let us understand the publishing the metadata using HTTP-GET method.

HTTP_GET Enabled Metadata

We will use ServiceBehaviour to publish the metadata using HTTP-GET. This can be configures either administratively or Programmatically. Http and Https can expose by appending "?wsdl" to the end of the service address. For example service address is http://localhost:9090/MyCalulatorService , HTTP-Get metadata address is given byhttp://localhost:9090/MyCalulatorService?wsdl.

Administrative (Configuration file):

In the below mention configuration information, you can find the behavior section in the ServiceBehavior. You can expose the metadata using ServiceMetadata node with httpGetEnable='True'.

<system.serviceModel>

   <services>

                    <service behaviorConfiguration="ServiceBehavior" name="MyService">

                       <endpoint address="http://localhost/IISHostedService/MyService.svc"

                        binding="wsHttpBinding" contract="IMyService">

                                         <identity>

                                         <dns value="localhost"/>

                                         </identity>

                        </endpoint>

                    </service>

  </services>

  <behaviors>

    <serviceBehaviors>

                    <behavior name="ServiceBehavior">

                                          <!-Setting httpGetEnabled you can publish the metadata -->

                                         <serviceMetadata httpGetEnabled="true"/>

                                         </behavior>

                        </serviceBehaviors>

   </behaviors>

</system.serviceModel>

Progarmming Model:

Using ServiceMetadataBehavior you can enable the metadata exchange. In the following code, I have created the ServiceMetadataBehavior object and assigned HttpGetEnabled property to true. Then you have to add the behavior to host description as shown. This set of code will publish the metadata using HTTP-GET.

 //Create a URI to serve as the base address

            Uri httpUrl = new Uri("http://localhost:8090/MyService/SimpleCalculator");

            //Create ServiceHost

            ServiceHost host = new

            ServiceHost(typeof(MyCalculatorService.SimpleCalculator), httpUrl);

            //Add a service endpoint

            host.AddServiceEndpoint

            (typeof(MyCalculatorService.ISimpleCalculator), new WSHttpBinding(), "");

            //Enable metadata exchange

            ServiceMetadataBehavior smb = new ServiceMetadataBehavior();

            //Enable metadata exchange using HTTP-GET

            smb.HttpGetEnabled = true;

            host.Description.Behaviors.Add(smb);

            //Start the Service

            host.Open();

            Console.WriteLine("Service is host at " + DateTime.Now.ToString());

            Console.WriteLine("Host is running... Press  key to stop");

            Console.ReadLine();

Metadata Exchange Endpoint

Exposing the metadata using HTTP-GET has a disadvantage, such that there is no guarantee that other platforms you interact will support it. There is other way of exposing the using special endpoint is called as Metadata Exchange Endpoint. You can have as many metadata exchange endpoints as you want.

Address

It is basically Uri to identify the metadata. You can specify as address in the endpoint but append with "mex" keyword. For example "http://localhost:9090/MyCalulatorService/mex"

Binding

There are four types of bindings supported for metadata exchange. They are mexHttpBinding, mexHttpsBinding, mexNamedPipesBinding, mexTcpBinding.

Contract

IMetadataExchange is the contract used for MEX endpoint. WCF service host automatically provides the implementation for this IMetadataExcahnge while hosting the service.

You can create the Metadata Exchange Endpoint either Administrative (configuration file) or programmatically.

Administrative (Configuration file):

In the configuration file of the hosting application, you can add metadata exchange endpoint as shown below.

<system.serviceModel>

<services>

                    <service name="MyService">

                    <endpoint address="http://localhost/IISHostedService/MyService.svc"

                    binding="wsHttpBinding" contract="IMyService">

                    <identity>

                    <dns value="localhost"/>

                    </identity>

                    </endpoint>

                    <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange"/>

                    </service>

</services>

</system.serviceModel>

Programming Model:

In the following code I have mention about creating the Metadata Exchange Endpoint through coding. Steps to create the metadata endpoint are

Create the ServiceMetadataBehavior object and add to Service host description.

ServiceMetadataBehavior smb = new ServiceMetadataBehavior();

            host.Description.Behaviors.Add(smb);

Create the metadata binding object using MetadataExchangeBinding

Binding mexBinding = MetadataExchangeBindings.CreateMexHttpBinding ();

3. Add the endpoint to the service host with address, binding and contract.

host.AddServiceEndpoint(typeof(IMetadataExchange), mexBinding, "mex");

Complete code for hosting the service with metadata exchange endpoint is shown below.

//Create a URI to serve as the base address

            Uri httpUrl = new Uri("http://localhost:8090/MyService/SimpleCalculator");

            //Create ServiceHost

            ServiceHost host = new

            ServiceHost(typeof(MyCalculatorService.SimpleCalculator), httpUrl);

            //Add a service endpoint

            host.AddServiceEndpoint

            (typeof(MyCalculatorService.ISimpleCalculator), new WSHttpBinding(), "");

            //Enable metadata exchange

            ServiceMetadataBehavior smb = new ServiceMetadataBehavior();

            host.Description.Behaviors.Add(smb);

            Binding mexBinding = MetadataExchangeBindings.CreateMexHttpBinding ();

            //Adding metadata exchange endpoint

            host.AddServiceEndpoint(typeof(IMetadataExchange), mexBinding, "mex");

            //Start the Service

            host.Open();

            Console.WriteLine("Service is host at " + DateTime.Now.ToString());

            Console.WriteLine("Host is running... Press  key to stop");

            Console.ReadLine();

Contracts

Windows Communication Foundation (WCF, formerly known as Indigo) is built upon the foundation of web services messaging and related standards, while at the same time makes it possible to serialize messages in a more compact binary format, or in a more proprietary way. Still, the core message can always be represented in XML, therefore be considered compatible with any platform that understands XML, and agrees on the contract that defines said messaging between systems.

The contract is a platform-neutral and standard way of describing what the service does. WCF defines four types of contracts:

Service Contract

Service contract describes the operation that service provide. A Service can have more than one service contract but it should have at least one Service contract.

Service Contract can be define using [ServiceContract] and [OperationContract] attribute. [ServiceContract] attribute is similar to the [WebServcie] attribute in the WebService and [OpeartionContract] is similar to the [WebMethod] in WebService.

It describes the client-callable operations (functions) exposed by the service
It maps the interface and methods of your service to a platform-independent description
It describes message exchange patterns that the service can have with another party. Some service operations might be one-way; others might require a request-reply pattern
It is analogous to the element in WSDL

To create a service contract you define an interface with related methods representative of a collection of service operations, and then decorate the interface with the ServiceContract Attribute to indicate it is a service contract. Methods in the interface that should be included in the service contract are decorated with the OperationContract Attribute.

[ServiceContract()]

public interface ISimpleCalculator

{

[OperationContract()]

int Add(int num1, int num2);

}

Once we define Service contract in the interface, we can create implement class for this interface.

public class SimpleCalculator : ISimpleCalculator

{

public int Add(int num1, int num2)

{

return num1 + num2;

}

With out creating the interface, we can also directly created the service by placing Contract in the implemented class. But it is not good practice of creating the service

[ServiceContract()]

public class SimpleCalculator

{

[OperationContract()]

public int Add(int num1, int num2)

{

return num1 + num2;

}

Now you have some fundamental idea on Service contract. Next we will look into Data Contract.

Data Contract

A data contract is a formal agreement between a service and a client that abstractly describes the data to be exchanged.

Data contract can be explicit or implicit. Simple type such as int, string etc has an implicit data contract. User defined object are explicit or Complex type, for which you have to define a Data contract using [DataContract] and [DataMember] attribute.

A data contract can be defined as follows:

It describes the external format of data passed to and from service operations
It defines the structure and types of data exchanged in service messages
It maps a CLR type to an XML Schema
t defines how data types are serialized and deserialized. Through serialization, you convert an object into a sequence of bytes that can be transmitted over a network. Through deserialization, you reassemble an object from a sequence of bytes that you receive from a calling application.
It is a versioning system that allows you to manage changes to structured data

We need to include System.Runtime.Serialization reference to the project. This assembly holds the DataContract andDataMember attribute.

Create user defined data type called Employee. This data type should be identified for serialization and deserialization by mentioning with [DataContract] and [DataMember] attribute.

[ServiceContract]

public interface IEmployeeService

{

[OperationContract]

Employee GetEmployeeDetails(int EmpId);

}

[DataContract]

public class Employee

{

private string m_Name;

private int m_Age;

private int m_Salary;

private string m_Designation;

private string m_Manager;

[DataMember]

public string Name

{

get { return m_Name; }

set { m_Name = value; }

}

[DataMember]

public int Age

{

get { return m_Age; }

set { m_Age = value; }

}

[DataMember]

public int Salary

{

get { return m_Salary; }

set { m_Salary = value; }

}

[DataMember]

public string Designation

{

get { return m_Designation; }

set { m_Designation = value; }

}

[DataMember]

public string Manager

{

get { return m_Manager; }

set { m_Manager = value; }

}

Implementation of the service class is shown below. In GetEmployee method we have created the Employee instance and return to the client. Since we have created the data contract for the Employee class, client will aware of this instance whenever he creates proxy for the service.

public class EmployeeService : IEmployeeService

{

public Employee GetEmployeeDetails(int empId)

{

Employee empDetail = new Employee();

//Do something to get employee details and assign to 'empDetail' properties

return empDetail;

}

Client side

On client side we can create the proxy for the service and make use of it. The client side code is shown below.

protected void btnGetDetails_Click(object sender, EventArgs e)

{

EmployeeServiceClient objEmployeeClient = new EmployeeServiceClient();

Employee empDetails;

empDetails = objEmployeeClient.GetEmployeeDetails(empId);

//Do something on employee details

}

Message Contract

Message

Message is the packet of data which contains important information. WCF uses these messages to transfer information from Source to destination.

WCF uses SOAP(Simple Object Access Protocol) Message format for communication. SOAP message contain Envelope, Header and Body.SOAP envelope contails name, namespace,header and body element. SOAP Hear contain important information which are not directly related to message. SOAP body contains information which is used by the target.

Diagram Soap envelope

Message Pattern

It describes how the programs will exchange message each other. There are three way of communication between source and destination

1. Simplex - It is one way communication. Source will send message to target, but target will not respond to the message.

2. Request/Replay - It is two way communications, when source send message to the target, it will resend response message to the source. But at a time only one can send a message

3. Duplex - It is two way communication, both source and target can send and receive message simultaniouly.

What is Message contract?

As I said earlier, WCF uses SOAP message for communication. Most of the time developer will concentrate more on developing the DataContract, Serializing the data, etc. WCF will automatically take care of message. On Some critical issue, developer will also require control over the SOAP message format. In that case WCF provides Message Contract to customize the message as per requirement.

WCF supports either RPC(Remote Procedure Call) or Message style operation model. In the RPC model, you can develop operation with Ref and out parameter. WCF will automatically create the message for operation at run time. In Message style operation WCF allows to customize the message header and define the security for header and body of the message.

Defining Message Contract

Message contract can be applied to type using MessageContract attribute. Custom Header and Body can be included to message using 'MessageHeader' and 'MessageBodyMember'atttribute. Let us see the sample message contract definition.

[MessageContract]

public class EmployeeDetails

{

[MessageHeader]

public string EmpID;

[MessageBodyMember]

public string Name;

[MessageBodyMember]

public string Designation;

[MessageBodyMember]

public int Salary;

[MessageBodyMember]

public string Location;

}

When I use this EmployeeDeatils type in the service operation as parameter. WCF will add extra header call 'EmpID' to the SOAP envelope. It also add Name, Designation, Salary, Location as extra member to the SOAP Body.

Rules :

You have to follow certain rules while working with Message contract

1. When using Message contract type as parameter, Only one parameter can be used in servicie Operation

2. [OperationContract]

3. void SaveEmployeeDetails(EmployeeDetails emp);

4. Service operation either should return Messagecontract type or it should not return any value

5. [OperationContract]

6. EmployeeDetails GetEmployeeDetails();

7. Service operation will accept and return only message contract type. Other data types are not allowed.

8. [OperationContract]

9. EmployeeDetails ModifyEmployeeDetails(EmployeeDetails emp);

Note: If a type has both Message and Data contract, service operation will accept only message contract.

MessageHeaderArray Attribute

Consider the Message contract type definition as shown below.

[MessageContract]

    public class Department

        [MessageHeader]

        public string DepartmentID;

        [MessageHeader]

        public string DepartmentName;

        [MessageHeader]

        public Employees Employee();

In this we are having array of Employee type as message header. When this converted to SOAP Header it looks as shown below.

<Department>

  <DepartmentID>PRO1243</DepartmentID>

  <DepartmentName>Production</DepartmentName>

  <Employees>

    <Employee>Sam</Employee>

    <Employee>Ram</Employee>

    <Employee>Raja</Employee>

  </Employees>

</Department>

Suppose you want to show the all employee detail in same level. We can use MessageHeaderArray attribute which will serialize the array element independently. If you use the MessageHeaderArray attribute of Employees, SOAP message will look as shown below.

<Department>

  <DepartmentID>PRO1243</DepartmentID>

  <DepartmentName>Production</DepartmentName>

  <Employee>Sam</Employee>

  <Employee>Ram</Employee>

  <Employee>Raja</Employee>

</Department>

Note: MessageHeaderArray Attribute is applicable only for Array, not for collection.

Message Contract Properties

ProtectionLevel

You can mention the MessageHeader or MessageBodyMember to be signed or Encrypted using ProtectionLevel property.

Example

using System.Net.Security;

[MessageContract]

public class EmployeeDetails

{

[MessageHeader(ProtectionLevel=ProtectionLevel.None)]

public string EmpID;

[MessageBodyMember(ProtectionLevel = ProtectionLevel.Sign )]

public string Name;

[MessageBodyMember(ProtectionLevel = ProtectionLevel.Sign )]

public string Designation;

[MessageBodyMember(ProtectionLevel=ProtectionLevel.EncryptAndSign)]

public int Salary;

}

In the above type definition, we have made the different protection level for body. But the protection level of the body is determind by the highest ProtectionLevel property. By default if you are not specifying the protection level it takes 'EncryptAndSign'. So it good if you specify minimum ProtectionLevel required.

Name and Namespace:

SOAP representation of the message element can be change by mentioning Name and Namespace property of the Header and Body member. By default namespace is the same as the namespace of the service contract that the message is participating. In the below example, I have mention the Name property to the EmpID and Name.

[MessageContract]

public class EmployeeDetails

{

[MessageHeader(Name="ID")]

public string EmpID;

[MessageBodyMember(Name="EmployeeName")]

public string Name;

[MessageBodyMember()]

public string Designation;

[MessageBodyMember()]

public int Salary;

}

When SOAP message representation, its name is changed to ID and EmployeeName.

<Designation>Software Engineer</Designation>

</EmployeeDetails>

Order

The order of the body elements are alpehabetical by default. But you can control the order, usiing Order property in theMessageBody attribute.

[MessageContract]

public class EmployeeDetails

{

[MessageHeader()]

public string EmpID;

[MessageBodyMember(Order=2)]

public string Name;

[MessageBodyMember(Order=3)]

public string Designation;

[MessageBodyMember(Order=1)]

public int Salary;

}

Fault Contract

Service that we develop might get error in come case. This error should be reported to the client in proper manner. Basically when we develop managed application or service, we will handle the exception using try- catch block. But these exceptions handlings are technology specific.

In order to support interoperability and client will also be interested only, what wents wrong? not on how and where cause the error.

By default when we throw any exception from service, it will not reach the client side. WCF provides the option to handle and convey the error message to client from service using SOAP Fault contract.

Suppose the service I consumed is not working in the client application. I want to know the real cause of the problem. How I can know the error? For this we are having Fault Contract. Fault Contract provides documented view for error accorded in the service to client. This help as to easy identity the what error has accord. Let us try to understand the concept using sample example.

Step 1: I have created simple calculator service with Add operation which will throw general exception as shown below

//Service interface

[ServiceContract()]

public interface ISimpleCalculator

{

[OperationContract()]

int Add(int num1, int num2);

}

//Service implementation

public class SimpleCalculator : ISimpleCalculator

{

public int Add(int num1, int num2)

{

//Do something

throw new Exception("Error while adding number");

}

Step 2: On client side code. Exceptions are handled using try-Catch block. Even though I have capture the exception when I run the application. I got the message that exceptions are not handled properly.

try

{

MyCalculatorServiceProxy.MyCalculatorServiceProxy proxy

= new MyCalculatorServiceProxy.MyCalculatorServiceProxy();

Console.WriteLine("Client is running at " + DateTime.Now.ToString());

Console.WriteLine("Sum of two numbers... 5+5 =" + proxy.Add(5, 5));

Console.ReadLine();

}

catch (Exception ex)

{

Console.WriteLine(ex.Message);

Console.ReadLine();

}

Step 3: Now if you want to send exception information form service to client, you have to use FaultException as shown below.

public int Add(int num1, int num2)

{

//Do something

throw new FaultException("Error while adding number");

}

Step 4: Output window on the client side is show below.

Step 5: You can also create your own Custom type and send the error information to the client using FaultContract. These are the steps to be followed to create the fault contract.

Define a type using the data contract and specify the fields you want to return.
Decorate the service operation with the FaultContract attribute and specify the type name.
Raise the exception from the service by creating an instance and assigning properties of the custom exception.

Step 6: Defining the type using Data Contract

[DataContract()]

public class CustomException

{

[DataMember()]

public string Title;

[DataMember()]

public string ExceptionMessage;

[DataMember()]

public string InnerException;

[DataMember()]

public string StackTrace;

}

Step 7: Decorate the service operation with the FaultContract

[ServiceContract()]

public interface ISimpleCalculator

{

[OperationContract()]

[FaultContract(typeof(CustomException))]

int Add(int num1, int num2);

}

Step 8: Raise the exception from the service

public int Add(int num1, int num2)

{

//Do something

CustomException ex = new CustomException();

ex.Title = "Error Funtion:Add()";

ex.ExceptionMessage = "Error occur while doing add function.";

ex.InnerException = "Inner exception message from serice";

ex.StackTrace = "Stack Trace message from service.";

throw new FaultException(ex,"Reason: Testing the Fault contract") ;

}

Step 9: On client side, you can capture the service exception and process the information, as shown below.

try

{

MyCalculatorServiceProxy.MyCalculatorServiceProxy proxy

= new MyCalculatorServiceProxy.MyCalculatorServiceProxy();

Console.WriteLine("Client is running at " + DateTime.Now.ToString());

Console.WriteLine("Sum of two numbers... 5+5 =" + proxy.Add(5, 5));

Console.ReadLine();

}

catch (FaultException<MyCalculatorService.CustomException> ex)

{

//Process the Exception

}

Instance Management

Instance management refers to the way a service handles a request from a client. Instance management is set of techniques WCF uses to bind client request to service instance, governing which service instance handles which client request. It is necessary because application will differ in their need for scalability, performance, durability, transaction and queued calls.

Basically there are three instance modes in WCF:

Configuration:

Instance mode can be configured using ServiceBehavior attribute. This can be specified at implementing the service contract as shown below.

[ServiceContract()]

public interface IMyService

{

[OperationContract]

int MyMethod();

}

[ServiceBehavior(InstanceContextMode=InstanceContextMode.Single)]

public class MyService:IMyService

{

public int MyMethod()

{

//Do something

}

Per-Call Service

When WCF service is configured for Per-Call instance mode, Service instance will be created for each client request. This Service instance will be disposed after response is sent back to client.

Following diagram represent the process of handling the request from client using Per-Call instance mode.

Let as understand the per-call instance mode using example.

Step 1: Create the service contract called IMyService and implement the interface. Add service behavior attribute to the service class and set the InstanceContextMode property to PerCall as show below.

[ServiceContract()]

public interface IMyService

{

[OperationContract]

int MyMethod();

}

Step 2: In this implementation of MyMethod operation, increment the static variable(m_Counter). Each time while making call to the service, m_Counter variable is incremented and return the value to the client.

[ServiceBehavior(InstanceContextMode=InstanceContextMode.PerCall)]

public class MyService:IMyService

{

static int m_Counter = 0;

public int MyMethod()

{

m_Counter++;

return m_Counter;

}

Step 3: Client side, create the proxy for the service and call "myMethod" operation multiple time.

static void Main(string[] args)

{

Console.WriteLine("Service Instance mode: Per-Call");

Console.WriteLine("Client making call to service...");

//Creating the proxy on client side

MyCalculatorServiceProxy.MyServiceProxy proxy =

new MyCalculatorServiceProxy.MyServiceProxy();

Console.WriteLine("Counter: " + proxy.MyMethod());

Console.ReadLine();

}

Surprisingly, all requests to service return '1', because we configured the Instance mode to Per-Call. Service instance will created for each request and value of static variable will be set to one. While return back, service instance will be disposed. Output is shown below.

Fig: PercallOutput.

Per-Session Service

When WCF service is configured for Per-Session instance mode, logical session between client and service will be maintained. When the client creates new proxy to particular service instance, a dedicated service instance will be provided to the client. It is independent of all other instance.

Following diagram represent the process of handling the request from client using Per-Session instance mode.

Let as understand the Per-Session instance mode using example.

[ServiceContract()]

public interface IMyService

{

[OperationContract]

int MyMethod();

}

Step 2: In this implementation of MyMethod operation, increment the static variable (m_Counter). Each time while making call to the service, m_Counter variable will be incremented and return the value to the client.

[ServiceBehavior(InstanceContextMode=InstanceContextMode.PerSession)]

public class MyService:IMyService

{

static int m_Counter = 0;

public int MyMethod()

{

m_Counter++;

return m_Counter;

}

Step 3: Client side, create the proxy for the service and call "myMethod" operation multiple time.

static void Main(string[] args)

{

Console.WriteLine("Service Instance mode: Per-Session");

Console.WriteLine("Client making call to service...");

//Creating the proxy on client side

MyCalculatorServiceProxy.MyServiceProxy proxy =

new MyCalculatorServiceProxy.MyServiceProxy();

Console.WriteLine("Counter: " + proxy.MyMethod());

Console.ReadLine();

}

All request to service return incremented value (1, 2, 3, 4), because we configured the instance mode to Per-Session. Service instance will be created once the proxy is created at client side. So each time request is made to the service, static variable is incremented. So each call to MyMethod return incremented value. Output is shown below.

Fig: PersessionOutput.

Singleton Service

When WCF service is configured for Singleton instance mode, all clients are independently connected to the same single instance. This singleton instance will be created when service is hosted and, it is disposed when host shuts down.

Following diagram represent the process of handling the request from client using Singleton instance mode.

Let as understand the Singleton Instance mode using example.

[ServiceContract()]

public interface IMyService

{

[OperationContract]

int MyMethod();

}

[ServiceBehavior(InstanceContextMode=InstanceContextMode.Single)]

public class MyService:IMyService

{

static int m_Counter = 0;

public int MyMethod()

{

m_Counter++;

return m_Counter;

}

Step 3: Client side, create the two proxies for the service and made a multiple call to MyMethod.

static void Main(string[] args)

{

Console.WriteLine("Service Instance mode: Singleton");

Console.WriteLine("Client 1 making call to service...");

//Creating the proxy on client side

MyCalculatorServiceProxy.MyServiceProxy proxy =

new MyCalculatorServiceProxy.MyServiceProxy();

Console.WriteLine("Counter: " + proxy.MyMethod());

Console.WriteLine("Client 2 making call to service...");

//Creating new proxy to act as new client

MyCalculatorServiceProxy.MyServiceProxy proxy2 =

new MyCalculatorServiceProxy.MyServiceProxy();

Console.WriteLine("Counter: " + proxy2.MyMethod());

Console.ReadLine();

}

When two proxy class made a request to service, single instance at service will handle it and it return incremented value (1, 2, 3, 4), because instance mode is configured to 'Single'. Service instance is created when it is hosted. So this instance will remain till host is shutdown. Output is shown below.

Fig: SingletonOutput.

Instance Deactivation

In Instance Management System tutorial, you learn how to create sessionful service instance. Basically service instance is hosted in a context. Session actually correlated the client message not to the instance, but to the context that host it. When session starts, context is created and when it closes, context is terminated. WCF provides the option of separating the two lifetimes and deactivating the instance separately from its context.

ReleaseInstanceMode property of the OberationalBehavior attribute used to control the instance in relation to the method call.

Followings are the list Release mode available in the ReleaseInstanceMode

1. RealeaseInstanceMode.None

2. RealeaseInstanceMode.BeforeCall

3. RealeaseInstanceMode.AfterCall

4. RealeaseInstanceMode.BeforeAndAfterCall

Below code show, how to add the 'ReleaseInstanceMode' property to the operational behavior.

[ServiceContract()]

public interface ISimpleCalculator

{

[OperationContract()]

int Add(int num1, int num2);

}

[OperationBehavior(ReleaseInstanceMode=ReleaseInstanceMode.BeforeCall]

public int Add(int num1, int num2)

{

return num1 + num2;

}

ReleaseInstanceMode.None

This property means that it will not affect the instance lifetime. By default ReleaseInstanceMode property is set to 'None'.

ReleaseInstanceMode.BeforeCall

This property means that it will create new instance before a call is made to the operation.

If the instance is already exist,WCF deactivates the instance and calls Dispose() before the call is done. This is designed to optimize a method such as Create()

ReleaseInstanceMode.AfterCall

This property means that it will deactivate the instance after call is made to the method.

This is designed to optimize a method such a Cleanup()

ReleaseInstanceMode.BeforeAndAfterCall

This is means that it will create new instance of object before a call and deactivates the instance after call. This has combined effect of using ReleaseInstanceMode.BeforeCall and ReleaseInstanceMode.AfterCall

Explicit Deactivate

You can also explicitly deactivate instance using InstanceContext object as shown below.

[ServiceContract()]

public interface IMyService

{

[OperationContract]

void MyMethod();

}

[ServiceBehavior(InstanceContextMode=InstanceContextMode.Single)]

public class MyService:IMyService

{

public void MyMethod()

{

//Do something

OperationContext.Current.InstanceContext.ReleaseServiceInstance();

}

Durable Service

Durable services are WCF services that persist service state information even after service host is restarted or Client. It means that durable services have the capability to restore their own state when they are recycled. It can use data store like SQL database for maintain instance state. It is new feature in .Net 3.5

You might think that we can also maintain session using WCF sessions, but content in the session environment is not persisted by default. If the service is shut down or client closes the proxy, data will be lost. But in case of Durable service it is still maintained.

Working:

When Durable service is created with database as data store, it will maintain all its state information in the table.

When a client make a request to the service, instance of the service is serialized, a new GUID is generated. This serialized instance xml and key will be saved in the database. We will call this GUID as instanceID. Service will send the instanceID to the client, so later it can use this id to get the instance state back. Even when client is shut down, instanceId will be saved at the client side. So when ever client opening the proxy, it can get back the previous state.

Defining the Durable Service

Durable service can be implemented using [DurableService()] attribute. It takes 'CanCreateInstance' and 'CompletesInstance' property to mention on which operation instance state has to be saved and destroyed.

CanCreateInstance = true: Calling this operation results in creating the serialization and inserting it into the datastore.
CompletesInstance = true: Calling this operation results in deleting the persisted instance from the datastore.

[Serializable]

[DurableService()]

public class MyService :IMyservice

{

[DurableOperation(CanCreateInstance = true)]

public int StartPersistance()

{

//Do Something

}

[DurableOperation(CompletesInstance = true)]

public void EndPersistence()

{

//Do Something

}

How to Create Durable Service

Let us understand more about the durable service by creating Simple Calculator service which persist the instance state in SQL server database.

Step 1: Start the Visual Studio 2008 and click File->New->Web Site. Select the 'WCF Service' as shown below.

Step 2: Create interface and decorate with Service and Operation contract.

[ServiceContract()]

public interface ISimpleCalculator

{

[OperationContract]

int Add(int num);

[OperationContract]

int Subtract(int num);

[OperationContract]

int Multiply(int num);

[OperationContract]

void EndPersistence();

}

Step 3: You need to add [Serializable] And [DurableService()] attribute to the service implementation. Set CanCreateInstance = true property to the operation in which instance state has to be persisted and set CompletesInstance = true when state has to be destroyed. In this implementation, we are going to persist the 'currentValue' variable value to the database.

using System.Runtime.Serialization;

using System.ServiceModel;

using System.Text;

using System.ServiceModel.Description;

[Serializable]

[DurableService()]

public class SimpleCalculator :ISimpleCalculator

{

int currentValue = default(int);

[DurableOperation(CanCreateInstance = true)]

public int Add(int num)

{

return (currentValue += num);

}

[DurableOperation()]

public int Subtract(int num)

{

return (currentValue -= num);

}

[DurableOperation()]

public int Multiply(int num)

{

return (currentValue *= num);

}

[DurableOperation(CompletesInstance = true)]

public void EndPersistence()

{

}

Step 4: Before configuring the database information in the durable service, you need to set up DataStore environment. Microsoft provides inbuilt sqlPersistance provider. To set up the database environment, run the these sql query located at following location 'C:\Windows\Microsoft.NET\Framework\v3.5\SQL\EN'

SqlPersistenceProviderSchema.sql
SqlPersistenceProviderLogic.sql

Step 5: In order to support durable service, you need to use Context binding type. <persistenceProvider> tag is used to configure the persistence provider.

<system.serviceModel>

<endpoint address="" binding="wsHttpContextBinding"

bindingConfiguration="browConfig" contract="ISimpleCalculator">

</identity>

</endpoint>

<endpoint address="mex" binding="mexHttpBinding"

contract="IMetadataExchange"/>

</service>

</services>

<persistenceProvider

type="System.ServiceModel.Persistence.SqlPersistenceProviderFactory,

System.WorkflowServices, Version=3.5.0.0, Culture=neutral,

PublicKeyToken=31bf3856ad364e35" connectionStringName="DurableServiceStore"

persistenceOperationTimeout="00:00:10"

lockTimeout="00:01:00"

serializeAsText="true"/>

</behavior>

</serviceBehaviors>

</behaviors>

</binding>

</wsHttpContextBinding>

</bindings>

</system.serviceModel>

<add name="DurableServiceStore"

connectionString="Data Source=saravanakumar;Initial Catalog

=DurableServiceStore;Integrated Security=True"/>

</connectionStrings>

Step 6: Create the console client application and name it as DurableServiceClient

Step 7: Add following reference to client application

System.ServiceModel
System.WorkflowService

Step 8: Add WCF service as Service Reference to the project and name it as SimpleCalculatorService

Step 9: Create the Helper class called it as Helper.cs. This helper class is used to Store, Retrieve and set the context at the client side. Context information will be saved in 'token_context.bin' file. Copy and paste the below code to your helper file.

Helper.cs

using System.ServiceModel.Channels;

using System.ServiceModel;

using System.Net;

using System.IO;

using System.Runtime.Serialization.Formatters.Binary;

public class Helper

{

static readonly String TokenContextFileName = "token_context.bin";

public static IDictionary<String, String> LoadContext()

{

IDictionary<String, String> ctx = null;

try

{

using (FileStream fs = new

FileStream(TokenContextFileName, FileMode.Open, FileAccess.Read))

{

BinaryFormatter bf = new BinaryFormatter();

ctx = bf.Deserialize(fs) as IDictionary<String, String>;

fs.Close();

}

catch (Exception ex)

{

}

return ctx;

}

public static void SaveContext(IClientChannel channel)

{

IDictionary<String, String> ctx = null;

IContextManager cm = channel.GetProperty<IContextManager>();

if (cm != null)

{

ctx = cm.GetContext() as IDictionary<String, String>;

try

{

using (FileStream fs

= new FileStream(TokenContextFileName, FileMode.CreateNew))

{

BinaryFormatter bf = new BinaryFormatter();

bf.Serialize(fs, ctx);

fs.Close();

}

catch (Exception ex)

{

}

public static void DeleteContext()

{

try

{

File.Delete(TokenContextFileName);

}

catch (Exception ex)

{

}

public static void SetContext(IClientChannel channel,

IDictionary<String, String> ctx)

{

IContextManager cm = channel.GetProperty<IContextManager>();

if (cm != null)

{

cm.SetContext(ctx);

}

Step 10: In the main method, I was creating the proxy for the service and calling the Add operation. Call to this method will add instance state to the database. Now I have closed the proxy and creating new proxy instance. When I call the Subtract and Multiply operation, it will operate on the previously saved value (instance state).

static void Main(string[] args)

{

//Create the proxy for the service

SimpleCalculatorService.SimpleCalculatorClient client

= new SimpleCalculatorService.SimpleCalculatorClient

"WSHttpContextBinding_ISimpleCalculator");

int currentValue = 0;

//Call the Add method from the service

currentValue = client.Add(10000);

Console.WriteLine("The current value is {0}", currentValue);

//Save the Context from the service to the client

Helper.SaveContext(client.InnerChannel);

//Close the proxy

client.Close();

//Create new Instance of the proxy for the service

client = new SimpleCalculatorService.SimpleCalculatorClient

("WSHttpContextBinding_ISimpleCalculator");

//Load the context from the client to start from saved state

IDictionary<string,string> cntx=Helper.LoadContext();

//Set Context to context manager

Helper.SetContext(client.InnerChannel, cntx);

//Call the Subtract and Multiply method from service

currentValue = client.Subtract(2);

Console.WriteLine("The current value is {0}", currentValue);

currentValue = client.Multiply(5);

Console.WriteLine("The current value is {0}", currentValue);

//Delete the context from the client

Helper.DeleteContext();

//Remove persistance state from the server

client.EndPersistence();

Console.WriteLine("Press <ENTER> to shut down the client.");

Console.ReadLine();

client.Close();

}

End of the proxy 1, service instance saved in the database as shown below.

Serialized XML instance state save in the database is shown below.

Output of the client application.

Throttling

WCF throttling provides some properties that you can use to limit how many instances or sessions are created at the application level. Performance of the WCF service can be improved by creating proper instance.

Attribute	Description
maxConcurrentCalls	Limits the total number of calls that can currently be in progress across all service instances. The default is 16.
maxConcurrentInstances	The number of InstanceContext objects that execute at one time across a ServiceHost. The default is Int32.MaxValue.
maxConcurrentSessions	A positive integer that limits the number of sessions a ServiceHost object can accept. The default is 10.

Service Throttling can be configured either Adminstractive or Programatically

Administrative(configuration file)

Using <serviceThrottling> tag of the Service Behavior, you can configure the maxConcurrentCalls, maxConcurrentInstances ,maxConcurrentSessions property as shown below.

<system.serviceModel>

</identity>

</endpoint>

</service>

</services>

<serviceThrottling maxConcurrentCalls="500"

maxConcurrentInstances ="100"

maxConcurrentSessions ="200"/>

</behavior>

</serviceBehaviors>

</behaviors>

</system.serviceModel>

Programming Model

Use ServiceThrottlingBehavior object to set concurrent calls, session and instance property.

ServiceHost host = new ServiceHost(typeof(MyService));

ServiceThrottlingBehavior throttle

= host.Description.Behaviors.Find();

if (throttle == null)

{

throttle = new ServiceThrottlingBehavior();

throttle.MaxConcurrentCalls = 500;

throttle.MaxConcurrentSessions = 200;

throttle.MaxConcurrentInstances = 100;

host.Description.Behaviors.Add(throttle);

}

host.Open();

Operations

In classic object or component- oriented programming model offered only single way for client to call a method. Client will issue a call, block while the call was in progress, and continue executing once the method returned.

WCF will support classical Request-Replay model, along with that it also supports One-Way call(call and forget operation) and callback(service to call back the client)

Three modes of communication between client and service are

1. Request- Replay

2. One-Way

3. Callback

Request-Reply

By default all WCF will operated in the Request-Replay mode. It means that, when client make a request to the WCF service and client will wait to get response from service (till receiveTimeout). After getting the response it will start executing the rest of the statement. If service doesn't respond to the service within receiveTimeout, client will receive TimeOutException.

Apart from NetPeerTcpBinding and the NetMsmqBinding all other bindings will support request-reply operations.

One-Way

In One-Way operation mode, client will send a request to the server and does not care whether it is success or failure of service execution. There is no return from the server side, it is one-way communication.

Client will be blocked only for a moment till it dispatches its call to service. If any exception thrown by service will not reach the server.

Client can continue to execute its statement, after making one-way call to server. There is no need to wait, till server execute. Sometime when one-way calls reach the service, they may not be dispatched all at once but may instead be queued up on the service side to be dispatched one at a time, according to the service's configured concurrency mode behavior. If the number of queued messages has exceeded the queue's capacity, the client will be blocked even if it's issued a one-way call. However, once the call is queued, the client will be unblocked and can continue executing, while the service processes the operation in the background.

Definition :

One-way operation can be enabled by setting IsOneWay property to true in Operation contract attribute.

[ServiceContract]

public interface IMyService

{

[OperationContract(IsOneWay=true)]

void MyMethod(EmployeeDetails emp);

}

One-Way Operations and Sessionful Services

Let us see the example, what will happen when you use the one-way communication with Sessionful service.

[ServiceContract(SessionMode = SessionMode.Required)]

interface IMyContract

{

[OperationContract(IsOneWay = true)]

void MyMethod();

}

As per above configuration, when client makes one-way call using MyMethod() operation and if it close the proxy. Client will be blocked until operation completes. It will be good practice, that one-way operation should be applied on per-call and singleton service.

Suppose If you want to make use of One-way operation in Sessionful service, use in the last operation of the service which will terminate the session. This operation should not return any value.

[ServiceContract(SessionMode = SessionMode.Required)]

interface IMyContract

{

[OperationContract]

void MyMethod1();

[OperationContract]

string MyMethod2();

[OperationContract(IsOneWay = true, IsInitiating = false,

IsTerminating = true)]

string CloseSessionService(int id);

}

One-Way Operations and Exceptions

Suppose when we are using BasicHttpBinding or WSHttpBinding, i.e. no transport session is used, if any exception throw by service will not affect the client. Client can make a call to the service using same proxy

[ServiceContract]

interface IMyContract

{

[OperationContract(IsOneWay = true)]

void MethodWithError( );

[OperationContract]

void MethodWithoutError( );

}

//Client side without transport session

MyContractClient proxy = new MyContractClient( );

proxy.MethodWithError( ); //No exception is thrown from serivce

proxy.MethodWithoutError( ); //Operation will execute properly

proxy.Close( );

In the presence of transport session, any exception thrown by service will fault the client channel. Client will not be able to make new call using same proxy instance.

//Client side transport session

MyContractClient proxy = new MyContractClient( );

proxy.MethodWithError( );

proxy.MethodWithoutError( ); //Can not executre because channel is faulted

proxy.Close( );

Callback Service

Till now we have seen that the all clients will call the service to get the things done. But WCF also provides the service to call the client. In which, service will act as client and client will act as service.

HTTP protocols are connectionless nature, so it is not supported for callback operation. So BasicHttpBinding and WSHttpBinding cannot be used for this operation.
WCF support WSDualHttpBinding for call back operation.
All TCP and IPC protocols support Duplex communication. So all these binding will be used for callback operation.

Defining and configuring a callback contract

Callback service can be enabled by using CallbackContract property in the ServiceContract attribute. In the below example you can find the decalration of the callback contract and it is configured in the ServiceContract attribute.

public interface IMyContractCallback

{

[OperationContract]

void OnCallback();

}

[ServiceContract(CallbackContract = typeof(IMyContractCallback))]

public interface IMyContract

{

[OperationContract()]

void MyMethod();

}

Client Callback Setup

As I said earlier, in callback operation client will act as service and service will act as client. So client has to expose a callback endpoint to the service to call. In the earlier part of the tutorial I have mention that InstanceContext is the execution scope of inner most service instance. It provides a constructor that takes the service instance to the host.

IMyContractCallback callback=new MyCallback();

InstanceContext cntx=new InstanceContext(callback);

MyServiceClient proxy = new MyServiceClient(cntx);

proxy.MyMethod();

The client must use a proxy that will set up the bidirectional communication and pass the callback endpoint reference to the service. This can be achieved by creating the proxy using DuplexClientBase

class MyServiceClient:DuplexClientBase,IMyContract

{

public MyServiceClient(InstanceContext callbackCntx)

: base(callbackCntx)

{

}

public void MyMethod()

{

base.Channel.MyMethod();

}

Service-Side Callback Invocation

The client-side callback endpoint reference is passed along with every call the client makes to the service, and it is part of the incoming message. The OperationContext class provides the service with easy access to the callback reference via the generic method GetCallbackChannel<T>( ). Service can call the client side callback method using reference e to the client side callback instance. The following code shows the callback method invocation.

IMyContractCallback

callbackInstance=OperationContext.Current.GetCallbackChannel();

callbackInstance.OnCallback();

How to Create Callback Service in WCF

This tutorial gives hands-on to create a sample Callback service.

Step 1: Create the sample Classlibrary project using Visual Studio 2008 and name it as CallbackService

Step 2 : Add System.ServiceModel reference to the project

Step 3: Create the Callback and Service contract as shown below. You need to mention CallbackContract property in theServiceContract attribute. Implementation of the Callback contract will be done on the client side.

IMyContract.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.ServiceModel;

namespace CallbackService

{

public interface IMyContractCallback

{

[OperationContract]

void OnCallback();

}

[ServiceContract(CallbackContract = typeof(IMyContractCallback))]

public interface IMyContract

{

[OperationContract()]

void MyMethod();

}

Step 4: Implement the Service contract as shown below. In the below code you will find using OperationContext is used to receive the reference to Callback instance. Using that instance we are calling the OnCallback() method from client side.

MyService.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.ServiceModel;

namespace CallbackService

{

[ServiceBehavior(ConcurrencyMode=ConcurrencyMode.Multiple )]

public class MyService:IMyContract

{

public void MyMethod()

{

//Do something

IMyContractCallback callbackInstance

=OperationContext.Current.GetCallbackChannel();

callbackInstance.OnCallback();

}

You can also note that We have set the ConcurrencyMode to Multile. If you are not using ConcurrencyMode to Multiple or Reentent, you will be end up with deadlock exception as shown below. This is because when a client made a call to the service, channel is created and lock by WCF service. If you are calling the Callback method inside the service method. Service will try to access the lock channel, this may leads to deadlock. So you can set ConcurrencyMode to Multiple or Reentent so it will release the lock silently.

Step 5: Create a Console application using Visual Studio 2008 and name it a CallbackServiceHost. This application is used to self-host the WCF service

Step 6: Main method

static void Main(string[] args)

{

Uri httpUrl = new Uri("http://localhost:8090/MyService/");

ServiceHost host = new ServiceHost(typeof(CallbackService.MyService), httpUrl);

host.Open();

Console.WriteLine("Service is Hosted at {0}", DateTime.Now.ToString());

Console.WriteLine("Host is running...Press key to stop the service.");

Console.ReadLine();

host.Close();

}

Step 7: Use Duplex binding to support Callback operation.

Web.Config

<system.serviceModel>

<service behaviorConfiguration="ServiceBehavior"

name="CallbackService.MyService">

<endpoint address="http://localhost:8090/MyService"

binding="wsDualHttpBinding" contract="CallbackService.IMyContract">

</identity>

</endpoint>

<endpoint address="mex"

binding="mexHttpBinding" contract="IMetadataExchange"/>

</service>

</services>

</behavior>

</serviceBehaviors>

</behaviors>

</system.serviceModel>

Step 8: Run the host application

Step 9: Create Console Application using Visual Studio 2008 and name it as CallbackClient. This is the client application which contain Callback implementation.

Step10: Add System.ServiceModel and CallbackService as reference to the project

Step 11: Create the proxy class as shown below. Use DuplexClientBase to create the proxy, because it will support bidirectional communication. Create the contractor which will accept InstanceContext as parameter.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.ServiceModel;

using CallbackService;

namespace CallbackClient

{

class MyServiceClient:DuplexClientBase<IMyContract>,IMyContract

{

public MyServiceClient(InstanceContext callbackCntx)

: base(callbackCntx)

{

}

public void MyMethod()

{

base.Channel.MyMethod();

}

Step12: Create the implementation for Callback Contract

class MyCallback : IMyContractCallback

{

public void OnCallback()

{

Console.WriteLine("Callback method is called from client side.");

}

Step 13: Implementation of main method

static void Main(string[] args)

{

IMyContractCallback callback=new MyCallback();

InstanceContext cntx=new InstanceContext(callback);

MyServiceClient proxy = new MyServiceClient(cntx);

Console.WriteLine("Client call the MyMethod Operation from Service.");

proxy.MyMethod();

Console.ReadLine();

}

Step14: Run the client application. In the output, you can see the OnCallback method called by the service

Events

Events allow the client or clients to be notified about something that has occurred on the service side. An event may result from a direct client call, or it may be the result of something the service monitors. The service firing the event is called the publisher, and the client receiving the event is called the subscriber.

Publisher will not care about order of invocation of subscriber. Subscriber can be executed in any manner.
Implementation of subscriber side should be short duration. Let us consider the scenario in which you what to publish large volume of event. Publisher will be blocked, when subscriber is queued on previous subscription of the event. These make publishers to put in wait state. It may lead Publisher event not to reach other subscriber.
Large number of subscribers to the event makes the accumulated processing time of each subscriber could exceed the publisher's timeout
Managing the list of subscribers and their preferences is a completely service-side implementation. It will not affect the client; publisher can even use .Net delegates to manage the list of subscribers.
Event should always one-Way operation and it should not return any value

Definition

public interface IMyEvents

{

[OperationContract(IsOneWay = true)]

void Event1();

}

Let us understand more on Event operation by creating sample service

Step 1 : Create ClassLibrary project in the Visual Studio 2008 and name it as WCFEventService as shown below.

Step 2:

Add reference System.ServiceModel to the project

Create the Event operation at the service and set IsOnwWay property to true. This operation should not return any value. Since service has to communicate to the client, we need to use CallbackContract for duplex communication. Here we are using one operation to subscribe the event and another for firing the event.

public interface IMyEvents

{

[OperationContract(IsOneWay = true)]

void Event1();

}

[ServiceContract(CallbackContract = typeof(IMyEvents))]

public interface IMyContract

{

[OperationContract]

void DoSomethingAndFireEvent();

[OperationContract]

void SubscribeEvent();

}

Step 3: Implementation of the Service Contract is shown below.

In the Subscription operation, I am using Operationcontext to get the reference to the client instance and Subscription method is added as event handler to the service event. DoSomethingAndFireEvent operation will fire the event as shown.

MyPublisher.cs

[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall)]

public class MyPublisher : IMyContract

{

static Action m_Event1 = delegate { };

public void SubscribeEvent()

{

IMyEvents subscriber = OperationContext.Current.GetCallbackChannel();

m_Event1 += subscriber.Event1;

}

public static void FireEvent()

{

m_Event1();

}

public void DoSomethingAndFireEvent()

{

MyPublisher.FireEvent();

}

Step 4: Create the Console application using Visual Studio 2008 and name it as WcfEventServiceHost. This application will be used to self-host the service.

Step 5: Add System.ServiceModel and WcfEventService as reference to the project.

static void Main(string[] args)

{

Uri httpUrl = new Uri("http://localhost:8090/MyPublisher/");

ServiceHost host = new ServiceHost(typeof(WcfEventService.MyPublisher), httpUrl);

host.Open();

Console.WriteLine("Service is Hosted at {0}", DateTime.Now.ToString());

Console.WriteLine("Host is running...Press key to stop the service.");

Console.ReadLine();

host.Close();

}

Step 6: Use Duplex binding to support Callback operation.

Web.Config

<system.serviceModel>

<service behaviorConfiguration="ServiceBehavior"

name="WcfEventService.MyPublisher">

<endpoint address="http://localhost:8090/MyPublisher"

binding="wsDualHttpBinding" contract="WcfEventService.IMyContract">

</identity>

</endpoint>

<endpoint address="mex" binding="mexHttpBinding"

contract="IMetadataExchange"/>

</service>

</services>

</behavior>

</serviceBehaviors>

</behaviors>

</system.serviceModel>

Step7: Run the host application as shown below.

Step 8: Create the console application using visual studio and name it as WcfEventServiceClient as shown below. This application will act a client which is used to subscribe the event from service.

Step 9: Create the proxy class as shown below. Use DuplexClientBase to create the proxy, because it will support bidirectional communication. Create the contractor which will accept InstanceContext as parameter.

EventServiceClient.cs

class EventServiceClient:DuplexClientBase<IMyContract>,IMyContract

{

public EventServiceClient(InstanceContext eventCntx)

: base(eventCntx)

{

}

public void DoSomethingAndFireEvent()

{

base.Channel.DoSomethingAndFireEvent();

}

public void SubscribeEvent()

{

base.Channel.SubscribeEvent();

}

Step 10: Implementation of IMyEvents at client side is shown below. This method will be called when service publish the event.

class MySubscriber : IMyEvents

{

public void Event1()

{

Console.WriteLine("Event is subscribed from the

service at {0}",DateTime.Now.ToString() );

}

Step 11: Main method of the client side you can find the creating Subscription instance and it passed to service usingInstanceContext

static void Main(string[] args)

{

IMyEvents evnt = new MySubscriber();

InstanceContext evntCntx = new InstanceContext(evnt);

EventServiceClient proxy = new EventServiceClient(evntCntx);

Console.WriteLine("Client subscribe the event

from the service at {0}",DateTime.Now.ToString());

proxy.SubscribeEvent();

Console.WriteLine("Client call operation which will fire the event");

proxy.DoSomethingAndFireEvent();

Console.ReadLine();

}

Step 12: Run the client application and you see the when event is fired from the service. Subscriber got notification.

Transfer mode

In our normal day today life, we need to transfer data from one location to other location. If data transfer is taking place through WCF service, message size will play major role in performance of the data transfer. Based on the size and other condition of the data transfer, WCF supports two modes for transferring messages

Buffer transfer

When the client and the service exchange messages, these messages are buffered on the receiving end and delivered only once the entire message has been received. This is true whether it is the client sending a message to the service or the service returning a message to the client. As a result, when the client calls the service, the service is invoked only after the client's message has been received in its entirety; likewise, the client is unblocked only once the returned message with the results of the invocation has been received in its entirety.

Stream transfer

When client and Service exchange message using Streaming transfer mode, receiver can start processing the message before it is completely delivered. Streamed transfers can improve the scalability of a service by eliminating the requirement for large memory buffers. If you want to transfer large message, streaming is the best method.

StreamRequest

In this mode of configuration, message send from client to service will be streamed

StreamRespone

In this mode of configuration, message send from service to client will be streamed.

Configuration

<system.serviceModel>

<endpoint address="" binding="netTcpBinding"

bindingConfiguration="MyService.netTcpBinding" contract="IMyService">

</identity>

</endpoint>

<endpoint address="mex" binding="mexHttpBinding"

contract="IMetadataExchange"/>

</service>

</services>

</behavior>

</serviceBehaviors>

</behaviors>

<binding name="MyService.netTcpBinding"

transferMode="Buffered" closeTimeout ="0:01:00" openTimeout="0:01:00"></binding>

</netTcpBinding>

</bindings>

</system.serviceModel>

Differences between Buffered and Streamed Transfers

Buffered	Streamed
Target can process the message once it is completely received.	Target can start processing the data when it is partially received
Performance will be good when message size is small	Performance will be good when message size is larger(more than 64K)
Native channel shape is IDuplexSessionChannel	Native channels are IRequestChannel and IReplyChannel

Streaming

Client and Service exchange message using Streaming transfer mode, receiver can start processing the message before it is completely delivered. Streamed transfers can improve the scalability of a service by eliminating the requirement for large memory buffers. If you want to transfer large message, streaming is the best method.

Supported Bindings

BasicHttpBinding
NetTcpBinding
NetNamedPipeBinding

Restrictions

There are some restriction, when streaming is enabled in WCF

Digital signatures for the message body cannot be performed
Encryption depends on digital signatures to verify that the data has been reconstructed correctly.
Reliable sessions must buffer sent messages on the client for redelivery if a message gets lost in transfer and must hold messages on the service before handing them to the service implementation to preserve message order in case messages are received out-of-sequence.
Streaming is not available with the Message Queuing (MSMQ) transport
Streaming is also not available when using the Peer Channel transport

I/O Streams

WCF uses .Net stream class for Streaming the message. Stream in base class for streaming, all subclasses like FileStream,MemoryStream, NetworkStream are derived from it. Stream the data, you need to do is, to return or receive a Stream as an operation parameter.

[ServiceContract]

public interface IMyService

{

[OperationContract]

void SaveStreamData(Stream emp);

[OperationContract]

Stream GetStreamData();

}

Note:

1. Stream and it's subclass can be used for streaming, but it should be serializable

2. Stream and MemoryStream are serializable and it will support streaming

3. FileStream is non serializable, and it will not support streaming

Streaming and Binding

Only the TCP, IPC, and basic HTTP bindings support streaming. With all of these bindings streaming is disabled by default.TransferMode property should be set according to the desired streaming mode in the bindings.

public enum TransferMode

{

Buffered, //Default

Streamed,

StreamedRequest,

StreamedResponse

}

public class BasicHttpBinding : Binding,...

{

public TransferMode TransferMode

{get;set;}

//More members

}

StreamedRequest - Send and accept requests in streaming mode, and accept and return responses in buffered mode
StreamResponse - Send and accept requests in buffered mode, and accept and return responses in streamed mode
Streamed - Send and receive requests and responses in streamed mode in both directions
Buffered -Send and receive requests and responses in Buffered mode in both directions

Streaming and Transport

The main aim of the Streaming transfer mode is to transfer large size data, but default message size is 64K. So you can increase the message size using maxReceivedMessageSize attribute in the binding element as shown below.

<system.serviceModel>

<binding name="MyService.netTcpBinding"

transferMode="Buffered" maxReceivedMessageSize="1024000">

</binding>

</netTcpBinding>

</bindings>

</system.serviceModel>

Transaction

A transaction is a collection or group of one or more units of operation executed as a whole. It provides way to logically group single piece of work and execute them as a single unit. In addition, WCF allows client applications to create transactions and to propagate transactions across service boundaries.

Recovery Challenge

Let us discuss more on challenge we will phased and how to recover from it.

1. Consider a system maintained in consistent state, when application fail to perform particular operation, you should recover from it and place the system in the consistent state.

2. While doing singe operation, there will be multiple atomic sub operation will happen. These operations might success or fail. We are not considering about sub operation which are failed. We mainly consider about the success operation. Because we have to recover all these state to its previous consistence state.

3. Productivity penalty has to be payee for all effort required for handcrafting the recovery logic

4. Performance will be decreased because you need to execute huge amount of code.

Solution

Best way to maintain system consistence and handling error-recovery challenge is to use transactions. Below figure gives idea about transaction.

Committed transaction: Transaction that execute successfully and transfer the system from consistence state A to B.
Aborted transaction: Transaction encounters an error and rollback to Consistence State A from intermediate state.
In-doubt transaction: Transactions fail to either in commit or abort.

Transaction Resources

Transactional programming requires working with a resource that is capable of participating in a transaction, and being able to commit or roll back the changes made during the transaction. Such resources have been around in one form or another for decades. Traditionally, you had to inform a resource that you would like to perform transactional work against it. This act is called enlisting. Some resources support auto-enlisting.

Transaction Properties

Transaction can be said as pure and successful only if meets four characteristics.

Atomic - When transaction completes, all the individual changes made to the resource while process must be made as to they were all one atomic, indivisible operation.
Consistent - transaction must leave the system in consistent state.
Isolated - Resources participating in the transaction should be locked and it should not be access by other third party.
Durable - Durable transactions must survive failures.

· Two-phase committed protocol

· Consider the scenario where I am having single client which use single service for communication and interacting with single database. In which service starts and manage the transaction, now it will be easy for the service to manage the transaction.

· Consider for example client calling multiple service or service itself calling another service, this type of system are called as Distributed Service-oriented application. Now the questions arise that which service will begin the transaction? Which service will take responsibility of committing the transaction? How would one service know what the rest of the service feels about the transaction? Service could also be deployed in different machine and site. Any network failure or machine crash also increases the complexity for managing the transaction.

· In order to overcome these situations, WCF come up with distributed transaction using two way committed protocol and dedicated transaction manager.

· Transaction Manager is the third party for the service that will manage the transaction using two phase committed protocol.

· Let us see how Transaction manager will manage the transaction using two-phase committed protocols.

· Transaction Propagation

· In WCF, transaction can be propagated across service boundary. This enables service to participate in a client transaction and it includes multiple services in same transaction, Client itself will act as service or client.

· We can specify whether or not client transaction is propagated to service by changing Binding and operational contract configuration

· <bindings>

· <netTcpBinding>

· <binding transactionFlow="true"></binding>

· </netTcpBinding>

· </bindings>

· Even after enabling transaction flow does not mean that the service wants to use the client’s transaction in every operation. We need to specify the “TransactionFlowAttribute” in operational contract to enable transaction flow.

· [ServiceContract]

· public interface IService

· {

· [OperationContract]

· [TransactionFlow(TransactionFlowOption.Allowed)]

· int Add(int a, int b);

· [OperationContract]

· int Subtract(int a, int b);

· }

· Note: TransactionFlow can be enabled only at the operation level not at the service level.

TransactionFlowOption	Binding configuration
NotAllowed	transactionFlow="true" ortransactionFlow="false"	Client cannot propagate its transaction to service even client has transaction
Allowed	transactionFlow="true"	Service will allow to flow client transaction. It is not necessary that service to use client transaction.
Allowed	transactionFlow="false"	If service disallows at binding level, client also should disable at binding level else error will be occurred.
Mandatory	transactionFlow="true"	Both Service and client must use transaction aware binding
Mandatory	transactionFlow="false"	InvalidOperationException will be throw when serice binding disables at binding level. FaultException will be thrown when client disable at its binding level.

Transaction Protocols

As a developer we no need to concern about transaction protocols and transaction manager used by WCF. WCF itself will take care of what kind of transaction protocols should be used for different situation. Basically there are three different kinds of transaction protocols used by WCF.

Handling Exception in Silverlight application from WCF

Attachment:

Silverlight_WCF_Exception.zip

This article explains about handling the exception in Silverlight application from WCF. I have created the sample Silverlight application, which uses the WCF service for process the data. While testing the application I came to know that exception message thrown from WCF cannot be received at the client side(Silverlight application) even after using the FaultException. I was always getting System.ServiceModel.CommunicationException: The remote server returned an error: NotFound.

Later I came to know that WCF throws the HTTP 500 series Fault message but Silverlight can handle only 200 series. So we need to convert the 500 series to 200 error message for Silverlight. Here is the sample application for exception handling between WCF and Silverlight.

Step 1: We can customize the Endpoint behavior of the WCF service by inheriting the Beha and implementing theIEndpointBehavior. Actual code for converting the 500 error serice to 200 serivce in BeforeSendReply method.

Create a ClassLibrary project and name it as “Silverlight_WCF_FaultBehavior” and name the class as “SilverlightFaultBehavior”. Copy and paste the follwing code inside the SilverlightFaultBehavior class.

Imports System.ServiceModel.ConfigurationrviceModel.Configuration

Imports System.ServiceModel.Description

Imports System.ServiceModel.Dispatcher

Imports System.ServiceModel.Channels

Imports System.ServiceModel

Public Class SilverlightFaultBehavior

Inherits BehaviorExtensionElement

Implements IEndpointBehavior

Public Overrides ReadOnly Property BehaviorType() As System.Type

Get

Return GetType(SilverlightFaultBehavior)

End Get

End Property

Protected Overrides Function CreateBehavior() As Object

Return New SilverlightFaultBehavior

End Function

Public Sub AddBindingParameters(ByVal endpoint As ServiceEndpoint,

ByVal bindingParameters As BindingParameterCollection)

Implements IEndpointBehavior.AddBindingParameters

End Sub

Public Sub ApplyClientBehavior(ByVal endpoint As ServiceEndpoint,

ByVal clientRuntime As ClientRuntime)

Implements IEndpointBehavior.ApplyClientBehavior

End Sub

Public Sub ApplyDispatchBehavior(ByVal endpoint As ServiceEndpoint,

ByVal endpointDispatcher As EndpointDispatcher)

Implements IEndpointBehavior.ApplyDispatchBehavior

Dim inspector As New SilverlightFaultMessageInspector()

endpointDispatcher.DispatchRuntime.MessageInspectors.Add(inspector)

End Sub

Public Sub Validate(ByVal endpoint As ServiceEndpoint)

Implements IEndpointBehavior.Validate

End Sub

Public Class SilverlightFaultMessageInspector

Implements IDispatchMessageInspector

Public Function AfterReceiveRequest(ByRef request As Message,

ByVal channel As IClientChannel,

ByVal instanceContext As InstanceContext) As Object

Implements IDispatchMessageInspector.AfterReceiveRequest

' Do nothing to the incoming message.

Return Nothing

End Function

Public Sub BeforeSendReply(ByRef reply As System.ServiceModel.Channels.Message,

ByVal correlationState As Object)

Implements IDispatchMessageInspector.BeforeSendReply

If reply.IsFault Then

Dim [property] As New HttpResponseMessageProperty()

' Here the response code is changed to 200.

[property].StatusCode = System.Net.HttpStatusCode.OK

reply.Properties(HttpResponseMessageProperty.Name) = [property]

End If

End Sub

End Class

Note: Highlighted code shows the conversion for 500 serices to 200 series error code.

Step 2: Build the project

Step 3: Create a new WCF service with Interface and implementation class as follows

Interface

<ServiceContract()> _

Public Interface IService

<OperationContract()> _

Function Add(ByVal num1 As Integer, ByVal num2 As Integer) As Integer

<OperationContract()> _

Function Subtract(ByVal num1 As Integer, ByVal num2 As Integer) As Integer

End Interface

Implementation

Public Class Service

Implements IService

Public Sub New()

End Sub

Public Function Add(ByVal num1 As Integer, ByVal num2 As Integer)

As Integer Implements IService.Add

Throw New FaultException("Error thrown by user for Add operation")

'Return num1 + num2

End Function

Public Function Subtract(ByVal num1 As Integer,

ByVal num2 As Integer) As Integer Implements IService.Subtract

Return num1 - num2

End Function

End Class

< Add the Silverlight_WCF_FaultBehavior project dll as reference to WCF Service

Step 5:

Step 5: In WCF we can extend the binding and behavior by using <extention> tag. In our case also we are extending the custom endpoint behavior as shown below. In the <behaviorExtensions> tag we need specify the fully qualified name of the cutom behaviour assembly.

Modify the Web.config file as shown bellow

<system.serviceModel>

<endpoint address="" binding="basicHttpBinding" contract="IService"

behaviorConfiguration="SilverlightFaultBehavior">

<!--

Upon deployment, the following identity element should be removed or replaced

to reflect the identity under which the deployed service runs. If removed,

WCF will infer an appropriate identity automatically.-->

</identity>

</endpoint>

</service>

</services>

<!-- To avoid disclosing metadata information, set the value below to false and

remove the metadata endpoint above before deployment -->

<!-- To receive exception details in faults for debugging purposes, set the value

below to true. Set to false before deployment to avoid disclosing exception

information -->

</behavior>

</serviceBehaviors>

</behavior>

</endpointBehaviors>

</behaviorss=“BlueCode”>>

<add name="silverlightFaults"

type="Silverlight_WCF_FaultBehavior.SilverlightFaultBehavior,

Silverlight_WCF_FaultBehavior, Version=1.0.0.0, Culture=neutral,

PublicKeyToken=null"/>

</behaviorExtensions>

</extensionss=“BlueCode”>>

</system.serviceModel>

Step 6: Create the any sample silverlight application as “Silverlight_WCF_Exception” and add this WCF service as Service Reference.

url: http://localhost/MathService/Service.svc

Step 7: Add a button to the MainPage.xaml and call the WCF method as shown below

Private Sub Button_Click(ByVal sender As System.Object,

ByVal e As System.Windows.RoutedEventArgs)

Dim proxy As New ServiceProxy.ServiceClient

AddHandler proxy.AddCompleted, AddressOf AddOperationCompleted

proxy.AddAsync(5, 6)

End Sub

Private Sub AddOperationCompleted(ByVal sender As Object,

ByVal e As ServiceProxy.AddCompletedEventArgs)

If e.Error IsNot Nothing Then

MessageBox.Show(e.Error.Message)

Else

MessageBox.Show(e.Result)

End If

End Sub

Step 8: Output will look like this

Conclution: This article explains about handling the exception in Silverlight application from WCF

Custom message header

Attachment:

CustomMessageHeader.zip

This article explains about customizing the wcf message flowing between service and client.

There are certain scenario in which you to pass some information from client to service, but not as parameter in operation contracts. Example, logging system at the service we need to log user or machine information, which made request to the service. In this kind of scenario we should not pass user or machine information as parameter in operation contract. Instead we can pass the information through message flowing between client and service vice versa. The information we need to send can be appended with message header and it can be received at the server side.

Let as create sample service and client application, in which client will send “User name” information through request message and service will respond with confirmation message.

I have created Math service with Add and Subtract functionality. Client consuming this service will send his user name information as string with requested message. Once request reached the service, it will read the information from the message header and display using console window. When service responding to the client, along with operation result, it will also send confirmation message to client through message header.

Step 1: Create IMathService interface decorated with Service and Operational contract attribute

IMathService.vb

<ServiceContract()> _

Public Interface IMathService

<OperationContract()> _

Function Add(ByVal a As Integer, ByVal b As Integer) As Integer

<OperationContract()> _

Function Subtract(ByVal a As Integer, ByVal b As Integer) As Integer

End Interface

Step 2:In this class, we have implemented Add and Subtract functionality.

PrintRequestedUserID() method will read the “UserID” message header from incoming message using OperationContext. This User information is displayed in console window.

SendResponseWithMessage() method will send a confirmation message to the client as Message header through Operation context.

MathService.vb

Public Class MathService

Implements IMathService

Public Function Add(ByVal a As Integer, ByVal b As Integer) As Integer

Implements IMathService.Add

'This method call will retrive message send from client using MessageHeader

PrintRequestedUserID()

'This method call will send message to client using MessageHeader

SendResponseWithMessage()

Return a + b

End Function

Public Function Subtract(ByVal a As Integer, ByVal b As Integer) As Integer

Implements IMathService.Subtract

'This method call will retrive message send from client using MessageHeader

PrintRequestedUserID()

'This method call will send message to client using MessageHeader

SendResponseWithMessage()

Return a - b

End Function

Private Sub PrintRequestedUserID()

Dim userID As String = String.Empty

'Read the message header using "Name" and "NameSpace"

userID = OperationContext.Current.IncomingMessageHeaders

.GetHeader(Of String)("UserID", "ns")

Console.WriteLine("Requested user: " + userID)

End Sub

Private Sub SendResponseWithMessage()

'Creating new message header with "Content" value assigned in constructor

Dim mess As New MessageHeader(Of String)("This is sample message from service")

'Assigning Name and NameSpace to the message header value at server side

Dim header As System.ServiceModel.

Channels.MessageHeader = mess.GetUntypedHeader("ServiceMessage", "ns")

'Adding message header with OperationContext

'which will be received at the client side

OperationContext.Current.OutgoingMessageHeaders.Add(header)

End Sub

End Class

Step 3: Hosting the MathService using console application

MyServiceHost.vb

Module MyServiceHost

Sub Main()

'Hosting the Math service using console application

Dim host As New ServiceHost(GetType(MyService.MathService))

host.Open()

Console.WriteLine("Service is running... Press to exit.")

Console.ReadLine()

End Sub

End Module

Web.Config

<system.serviceModel>

<services><service name="MyService.MathService"

behaviorConfiguration="MyServiceBehavior">

<endpoint address ="MathService" binding="basicHttpBinding"

contract="MyService.IMathService"/>

<endpoint address="mex" binding="mexHttpBinding"

contract="IMetadataExchange"/>

<host>

</baseAddresses>

</host>

</service>

</services>

</behavior>

</serviceBehaviors>

</behaviors>

</system.serviceModel>

Step 4: Created console client application which add “UserID” as message header to service using Operation context before calling Add() functionality. Once the response is received from the service, it is trying to read the confirmation message from service using Operation context.

Sub Main()

'Creating proxy class for service

Dim proxy As IMathService = Nothing

proxy = ChannelFactory(Of IMathService).CreateChannel(New BasicHttpBinding(),

New EndpointAddress("http://localhost:8090/MyService/MathService"))

'Lifetime of OperationContextScope defines the scope for OperationContext.

Dim scope As OperationContextScope = Nothing

scope = New OperationContextScope(proxy)

'Creating new message header with "Content" value assigned in constructor

Dim mess As New MessageHeader(Of String)

(System.Security.Principal.WindowsIdentity.GetCurrent().Name)

'Assigning Name and NameSpace to the message header value at client side

Dim header As System.ServiceModel.Channels.MessageHeader

= mess.GetUntypedHeader("UserID", "ns")

'Adding message header with OperationContext

'which will be received at the server side

OperationContext.Current.OutgoingMessageHeaders.Add(header)

'Making service call

Console.WriteLine("Sum of {0},{1}={2}", 1, 2, proxy.Add(1, 2))

'Displaying confrimation message from service

Console.WriteLine("Response Message: " + OperationContext.Current.

IncomingMessageHeaders.GetHeader(Of String)("ServiceMessage", "ns"))

Console.ReadLine()

End Sub

End Module

<ServiceContract()> _

Public Interface IMathService

Inherits IClientChannel

<OperationContract()> _

Function Add(ByVal a As Integer, ByVal b As Integer) As Integer

<OperationContract()> _

Function Subtract(ByVal a As Integer, ByVal b As Integer) As Integer

End Interface

Step 5: Run the MyServiceHost

Step 6: Run the MyClientApplication

Below figure shows the message flowing between service and client

Client application output

Console hosted service output screen

Conclusion:

This article explain about customizing the wcf message header

Pages

WCF

EndPoint

Address

Binding

Contract

Example:

Binding and Behavior

Binding

Example:

Note:

Contracts and Service Host

Contracts

Service Contract

Data Contract

Message Contract

Fault Contract

Service Host

Message and Channel

Message

WCF Runtime

Channels:

Transport Channels

Protocol Channels

Binding configuration

Administrative (Configuration file):

Programming Model:

HTTP_GET Enabled Metadata

Administrative (Configuration file):

Progarmming Model:

Metadata Exchange Endpoint

Address

Binding

Contract

Administrative (Configuration file):

Programming Model:

MessageHeaderArray Attribute

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