Windows Communication Foundation (Code named Indigo) is a programming platform and runtime system for building, configuring and deploying network-distributed services. It is the latest service oriented technology; Interoperability is the fundamental characteristics of WCF. It is unified programming model provided in .Net Framework 3.0. WCF is a combined features of Web Service, Remoting, MSMQ and COM+. WCF provides a common platform for all .NET communication.
Below figures shows the different technology combined to form WCF.
- WCF is interoperable with other services when compared to .Net Remoting, where the client and service have to be .Net.
- WCF services provide better reliability and security in compared to ASMX web services.
- 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.
- WCF has integrated logging mechanism, changing the configuration file settings will provide this functionality. In other technology developer has to write the code.
Making right design for your requirement is little bit difficult. I will try to help you on solving these difficulties in the following article.
WCF application can be developed by the Microsoft Visual Studio. Visual studio is available at different edition. You can use Visual Studio 2008 Expression edition for the development.
Visual Studio 2008 SDK 1.1
Microsoft Visual Studio 2008
Microsoft Visual studio 2008 provides new features for WCF compared to Visual Studio 2005. These are the new features added to VS 2008.
You can create application in different framework like Framework 2.0, 3.0 and 3.5
2. Default template is available for WCF
3. WCF – Test Client tools for testing the WCF service.
Microsoft provides inbuilt application to test the WCF application. This can be done by opening the Visual Studio command prompt and type the wcfClient Serviceurl shows below. This will help the developer to test the service before creating the client application.
4. WCF services can be debugged now in Visual Studio 2008. Wcfsvchost.exe will do it for you because service will be self hosted when you start debugging.
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.
|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|
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.
- End Point
- Bindings and Behavior
- Contracts and Service host
- Message and Channel
- WCF client and Metadata
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.
Basically URL, specifies where this WCF service is hosted .Client will use this url to connect to the service. e.g
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.
|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|
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
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
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.
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
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 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 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.
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.
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 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
WCF Message is the unit of data exchange between client and service. It consists of several parts, including a body and headers.
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 are the core abstraction for sending message to and receiving message from an Endpoint. Broadly we can categories channels as
– Handles sending and receiving message from network. Protocols like HTTP, TCP name pipes and MSMQ.
– Implements SOAP based protocol by processing and possibly modifying message. e.g. WS-Security and WS-Reliability.
WCF Client and Metadata
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:
- 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
- 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
= new MyCalculatorServiceProxy.MyServiceProxy();
Console.WriteLine(“Counter: ” + proxy.MyMethod());
- 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.
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.
<endpoint address=”” contract=”IMathService”
<serviceDebug includeExceptionDetailInFaults=”true” />
This metadata can be viewed while creating WCF client application using SvcUtil.exe
The following figure illustrates the major components of WCF.
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.
– 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.
– 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.
– 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.
– 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 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.
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).
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.
Multiple hosting and protocols supported by WCF.Microsoft has introduced the WCF concept in order to make distributed application development and deployment simple.
|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.
|Executable Process/ App Domain||Yes||Yes||Yes|
|Activation||Manual at startup||Message-based||Message-based|