WCF Basic information in dotnet

WCF

• Windows Communication Foundation (Code named Indigo) is a programming platform and runtime system for building, configuring and deploying network-distributed services.
• It is unified programming model provided in .Net Framework 3.0. WCF is a combined feature of Web Service, Remoting, MSMQ and COM+.
• WCF provides a common platform for all .NET communication.

Difference between WCF and Web service

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	[ServiceContract] 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

Different bindings supported by WCF

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

Different contracts 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, which 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.

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");

        }

ABC of Windows Communication Foundation

What are the ABCs of WCF? "ABC" stands for address, binding and contract.

1.       Address (Where)

It specifies the location of the service means, where the service is hosted. The service hosting URL may be like http://server/wcfService. Clients will use this location to communicate with your service.

2.       Binding (How)

It specifies how the client will communicate to the service. We have different protocols (like http,tcp,named pipe,msmq) for the WCF to communicate to the client.

3.       Contract (What)

It specifies what the service will do. For this purpose we have different contract like as Data Contract, Operation Contract, Message Contract, Fault Contract.

WCF Hosting

A WCF service is a component that can be called by other applications. It must be hosted in an environment in order to be discovered and used by others. The WCF host is an application that controls the lifetime of the service. With .NET 3.0 and beyond, there are several ways to host the service.

1.       Self hosting

A WCF service can be self-hosted, which means that the service runs as a standalone application and controls its own lifetime. This is the most flexible and easiest way of hosting a WCF service, but its availability and features are limited.

2.       Windows services hosting

A WCF service can also be hosted as a Windows service. A Windows service is a process managed by the operating system and it is automatically started when Windows is started (if it is configured to do so). However, it lacks some critical features (such as versioning) for WCF services.

3.       IIS hosting

A better way of hosting a WCF service is to use IIS. This is the traditional way of hosting a web service. IIS, by nature, has many useful features, such as process recycling, idle shutdown, process health monitoring, message-based activation, high availability, easy manageability, versioning, and deployment scenarios. All of these features are required for enterprise-level WCF services.

4.       Windows Activation Services hosting

The IIS hosting method, however, comes with several limitations in the service-orientation world; the dependency on HTTP is the main culprit. With IIS hosting, many of WCF's flexible options can't be utilized. This is the reason why Microsoft specifically developed a new method, called Windows Activation Services, to host WCF services.

Windows Process Activation Service (WAS) is the new process activation mechanism for Windows Server 2008 that is also available on Windows Vista. WAS hosting is possible only with IIS 7.0.Additional WCF components also plug into WAS to provide message-based activation over the other protocols that WCF supports, such as TCP, MSMQ, and named pipes. This allows applications that use the non-HTTP communication protocols to use the IIS features such as process recycling, rapid fail protection, and the common configuration systems that were only available to HTTP-based applications.

Security Modes in WCF:

Many WCF services will require secure communication, where it is necessary to authenticate the sender of a message, and to ensure that messages have not been read or tampered with by unauthorized third parties. 

 WCF can provide authentication, privacy, and integrity for messages by using two mechanisms.

The Security Modes are stated below

• Transport Mode
• Message Mode
• Mixed Mode

Let us now explain each one of them in details

Transport Mode 

1. Transport mode, which uses the security features of a transport layer such as HTTPS. 
2. This mode has performance benefits due to the optimized nature of the underlying protocols, but it has a restricted set of credential or claim types. 
3. This mode also only works between two transport endpoints

Message Mode

1. Message mode, which protects the message itself by using a protocol such as WS-Security. 
2. Credential information is embedded within the message so that this mode can support a richer set of claim types at the expense of performance. 
3. This mode provides end-to-end security for the message.

Mixed Mode 

1. WCF also supports a mixed mode, where integrity and privacy are provided by the transport, while authentication is handled by using credentials in the message. 
2. This can give the best balance of performance and flexibility.
3. You can specify the security for a binding by setting its SecurityMode property.
4. By default, the BasicHttpBinding has no security configured. Other HTTP bindings use WS-Security, and TCP and Named Pipe bindings use Windows security

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>

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.

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:

• Per-Call instance mode
• Per-Session instance mode
• Singleton Instance Mode

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

        }       

    }

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>

    <services >

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

        <endpoint address="" binding="netTcpBinding"

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

          <identity>

            <dns value="localhost"/>

          </identity>

        </endpoint>

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

        contract="IMetadataExchange"/>

      </service>

    </services>

    <behaviors>

      <serviceBehaviors>

        <behavior name="ServiceBehavior">

          <serviceMetadata httpGetEnabled="true"/>

          <serviceDebug includeExceptionDetailInFaults="true "/>

        </behavior>

      </serviceBehaviors>

    </behaviors>

    <bindings >

      <netTcpBinding>

        <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