WCF Exclusive Interview Questions and Answers (54) - Page 3

<system.diagnostics>

<sources>

<source name="System.ServiceModel"

switchValue="Information, ActivityTracing">

............

............

............

............

<system.serviceModel> 

<diagnostics>

<messageLogging

logEntireMessage="true"

logMalformedMessages="false"

logMessagesAtServiceLevel="false"

logMessagesAtTransportLevel="true"

maxMessagesToLog="3000"

maxSizeOfMessageToLog="10000"/>

</diagnostics>

</system.serviceModel>

WCF is a unification technology, which unites the following technologies:-
     NET remoting
     MSMQ
     Web services
     COM+.

Below figure depicts WCF fundamentals pictorially.

Regards,

Address(Where):- An Address indicates where we can find the service. Address is a URL, which points to the location of the service.

Binding(How):- Bindings determine how the endpoints interacts(communicate) with the services.In other words it determines how communications is done.

Contract(What):-It defines, what kind of protocol your service is using currently.

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WCF  service can be hosted by three diffrent way as below.

1. Self-hosting.


2. IIS Server.


3. WAS (Windows Activation Service).

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The following steps are followed to do Self-hosting.

Step1:    //Create a URI to serve as the base address
            // Address as well binding

Uri httpUrl = new Uri("http://localhost:8010/MyService/HelloWorld");

Step2: //Create ServiceHost           

 ServiceHost host = new ServiceHost(typeof(ClassLibrary1.HelloWorldService),httpUrl);

Step3: //Add a service endpoint      

host.AddServiceEndpoint(typeof(ClassLibrary1.IHelloWorldService) , new WSHttpBinding(), "");

Step4: //Enable metadata exchange

ServiceMetadataBehavior smb = new ServiceMetadataBehavior();

smb.HttpGetEnabled = true;           

host.Description.Behaviors.Add(smb);

Step5: //Start the Service           

host.Open();

Step6:

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

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

Console.ReadLine();

Regards,

Service Contract:-Service Contract is used to define the service name.

Operation Contract:-Operation contract defines the methods in the services.

Data Contract:-Data contract defines custom data types in the services.

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IIS-Hosting is done using .SVC file.

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Basic Httpbinding:In httpbinding Data is sent as a plain text.In other words,there is no security provided for the message when the client calls happen.
This is aimed for clients who do not have .NET 3.0 installed and it supports wider ranges of clients. Many of the clients like Windows 2000 still do not run .NET 3.0. So older version of .NET can consume this service.
It uses SOAP1.1 version.

WShttpbinding:As WsHttBinding supports WS-*, it has WS-Security enabled by default. So the data is not sent in plain text.
As its built using WS-* specifications, it does not support wider ranges of client and it cannot be consumed by older .NET version less than 3 version.
It uses SOAP 1.2 and WS-Addressing specification.

Regards,

In WCF there are two types of Security,transport level security and message level security.

Transport Security:Transport level security happens at the channel level. Transport level security is the easiest to implement as it happens at the communication level. WCF uses transport protocols like TCP, HTTP, MSMQ etc and every of these protocols have their own security mechanisms. One of the common implementation of transport level security is HTTPS. HTTPS is implemented over HTTP protocols with SSL providing the security mechanism. No coding change is required it’s more of using the existing security mechanism provided by the protocol.

Message Security:Message level security is implemented with message data itself. Due to this it is independent of the protocol. Some of the common ways of implementing message level security is by encrypting data using some standard encryption algorithm.

Below Diagram illustrate the concept of security in WCF.

Regards,

We need WCF when we want to expose a service which can be consumed by clients, which are in different technologies.

Regards,

Three ways by which you can handle concurrency in WCF is Single, multiple and reentrant. To specify WCF concurrency we need to use the ‘ServiceBehavior’ tag as shown below with appropriate ‘ConCurrencyMode’ property value.

Figure:

Single: - A single request has access to the WCF service object at a given moment of time. So only one request will be processed at any given moment of time. The other requests have to wait until the request processed by the WCF service is not completed.

Multiple: - In this scenario multiple requests can be handled by the WCF service object at any given moment of time. In other words request are processed at the same time by spawning multiple threads on the WCF server object. So you have great a throughput here but you need to ensure concurrency issues related to WCF server objects.

Reentrant: - A single request thread has access to the WCF service object, but the thread can exit the WCF service to call another WCF service or can also call WCF client through callback and reenter without deadlock.

You can also view video on WCF one way contract as follows: -

Before we define WCF REST, lets define REST. REST is an architectural style built on certain principles using the current “Web” fundamentals.

It has five important principle: -

• Everything is a resource.
• Every resource is identified by a unique identifier
• Use simple and uniform interfaces.
• Communication are done by representation.
• Be Stateless.

To implement WCF REST we need to use first enable webhttp bindings in behavior as shown in the below code snippet: -

 <endpointBehaviors>

        <behavior name="NewBehavior0">

          <webHttp />

        </behavior>

</endpointBehaviors>

We can then use WebGet or WebInvoke to ensure that our URL is invoked by using HTTP POST or GET: -

[OperationContract]

[WebGet(UriTemplate = "/Students/{id}")]

string getStudents(string id);

Also see our following video on explanation of REST: -

Many developers would answer this question as Yes because C# is used in WCF and C# is Object oriented, so a natural thinking would be WCF should also support method overloading.

The fact is it does not, surprised right :-). If you have a method which is overloaded you need to use the "Name" parameter in the "OperationContract" to ensure that the proxy class generates different names.

See the below code for more details. In the below code we have "GetData" which is overloaded but we are saying to the client to generate the methods with name "GetData" and "GetData1".

[ServiceContract]

    public interface IService1

    {



        [OperationContract(Name="GetData")]

        string GetData(int value);



        [OperationContract(Name="GetData1")]

        string GetData(int value, int value1);



       

        // TODO: Add your service operations here

    }

Do also see the below video why practically we can not do method overloading in WCF service: -