WCF Tutorial

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.

coding to its scope:

• Common behaviors affect all endpoints globally

• Service behaviors affect only service-related aspects

• Endpoint behaviors affect only endpoint-related properties

• 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>

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.

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.

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.

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.

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

   1. 1. 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.

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

2. Call operations.

• 1. 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.

     1. 1. //Creating the proxy on client side MyCalculatorServiceProxy.MyServiceProxy proxy  = new MyCalculatorServiceProxy.MyServiceProxy();  Console.WriteLine("Counter: " + proxy.MyMethod());

3. Close the WCF client object.

• 1. 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>     <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> 

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

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.

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.

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

• IIS

  • 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).