DotNet

Saturday, June 9, 2012

WCF Interview Questions and Answers

Q1. What is WCF?

WCF stands for Windows Communication Foundation. It is a Software development kit for developing services on Windows. WCF is introduced in .NET 3.0. in the System.ServiceModel namespace. WCF is based on basic concepts of Service oriented architecture (SOA)

Q2. What is endpoint in WCF service?

The endpoint is an Interface which defines how a client will communicate with the service. It consists of three main points: Address,Binding and Contract.

Q3. Explain Address,Binding and contract for a WCF Service?

Address:Address defines where the service resides.

Binding:Binding defines how to communicate with the service.

Contract:Contract defines what is done by the service.

Q4. What are the various address format in WCF?

a)HTTP Address Format:--> http://localhost:

b)TCP Address Format:--> net.tcp://localhost:

c)MSMQ Address Format:--> net.msmq://localhost:

Q5. What are the types of binding available in WCF?

A binding is identified by the transport it supports and the encoding it uses. Transport may be HTTP,TCP etc and encoding may be text,binary etc. The popular types of binding may be as below:

a)BasicHttpBinding

b)NetTcpBinding

c)WSHttpBinding

d)NetMsmqBinding

Q6. What are the types of contract available in WCF?

The main contracts are:

a)Service Contract:Describes what operations the client can perform.

b)Operation Contract : defines the method inside Interface of Service.

c)Data Contract:Defines what data types are passed

d)Message Contract:Defines wheather a service can interact directly with messages

Q7. What are the various ways of hosting a WCF Service?

a)IIS b)Self Hosting c)WAS (Windows Activation Service)

Q8. WWhat is the proxy for WCF Service?

A proxy is a class by which a service client can Interact with the service.

By the use of proxy in the client application we are able to call the different methods exposed by the service

Q9. How can we create Proxy for the WCF Service?

We can create proxy using the tool svcutil.exe after creating the service.

We can use the following command at command line.

svcutil.exe *.wsdl *.xsd /language:C# /out:SampleProxy.cs /config:app.config

Q10.What is the difference between WCF Service and Web Service?

a)WCF Service supports both http and tcp protocol while webservice supports only http protocol.

b)WCF Service is more flexible than web service.

Q11.What is DataContract and ServiceContract?Explain

Data represented by creating DataContract which expose the

data which will be transefered /consumend from the serive

to its clients.

Q12.What is .NET 3.0?

In one simple equation .NET 3.0 = .NET 2.0 + Windows Communication Foundation + Windows

Presentation Foundation + Windows Workflow Foundation + Windows Card Space.

Q13.What is WCF?

Windows Communication Foundation (WCF) is an SDK for developing and deploying services on Windows. WCF provides a runtime environment for services, enabling you to expose CLR types as services, and to consume other services as CLR types.

First let us give a short answer to this: - “WCF (Indigo was the code name for WCF) is a

unification of .NET framework communication technologies

“.WCF is a unification technology,

Q14.which unites the following technologies:-

• NET remoting

• MSMQ

• Web services

• COM+.

Q15.What was the code name for WCF?

The code name of WCF was Indigo .

WCF is a unification of .NET framework communication technologies which unites the following technologies:-

1.Web services

2.MSMQ

3.NET remoting

4.COM+

Q16.What are the main components of WCF?

The main components of WCF are

1. Service class

2. Hosting environment

3. End point

Q17.Where we can host WCF services?

Every WCF services must be hosted somewhere. There are three ways of hosting WCF services.

They are

1. IIS

2. Self Hosting

3. WAS (Windows Activation Service)

Q18.What is service and client in perspective of data communication?

A service is a unit of functionality exposed to the world.

The client of a service is merely the party consuming the service.

Q19.What are different elements of WCF Srevices Client configuration file?

WCF Services client configuration file contains endpoint, address, binding and contract.

A sample client config file looks like

Q20.What is endpoint in WCF?

Every service must have Address that defines where the service resides, Contract that defines what the service does and a Binding that defines how to communicate with the service. In WCF the relationship between Address, Contract and Binding is called Endpoint.

Q21.What are ends, contract, address, and bindings?

The above terminologies are the core on which SOA stands. Every service must expose one or more ends by which the service can be available to the client. End consists of three important things where, what and how:-

• Contract (What)

Contract is an agreement between two or more parties. It defines the protocol how client should communicate with your service. Technically, it describes parameters and return values for a method.

• Address (Where)

An Address indicates where we can find this service. Address is a URL, which points to the

location of the service.

• Binding (How)

Bindings determine how this end can be accessed. It determines how communications is done.

For instance, you expose your service, which can be accessed using SOAP over HTTP or

BINARY over TCP. So for each of these communications medium two bindings will be created.

Below figure, show the three main components of end. You can see the stock ticker

is the service

class, which has an end hosted on http://www.soa.com with HTTP and TCP binding support and using

Stock Ticker interface type.

Q22.What is binding and how many types of bindings are there in WCF?

A binding defines how an endpoint communicates to the world. A binding defines the transport (such as HTTP or TCP) and the encoding being used (such as text or binary). A binding can contain binding elements that specify details like the security mechanisms used to secure messages, or the message pattern used by an endpoint.

Q23.WCF supports nine types of bindings?

Basic binding

Offered by the BasicHttpBinding class, this is designed to expose a WCF service as a legacy ASMX web service, so that old clients can work with new services. When used by the client, this binding enables new WCF clients to work with old ASMX services.

This binding is used when we need to use SOAP over HTTP. This binding

can also be configured to be used as HTTPS. It can be also configured to send data in plain text or in optimized form like MTOM.

TCP binding

Offered by the NetTcpBinding class, this uses TCP for cross-machine communication on the intranet. It supports a variety of features, including reliability, transactions, and security, and is optimized for WCF-to-WCF communication. As a result, it requires both the client and the service to use WCF.

This binding sends binary-encoded SOAP, including support for reliable

message transfer, security, and transactions, directly over TCP. The biggest disadvantage of

NetTcpBinding is that both server and client should be also made in .NET language.

Peer network binding

Offered by the NetPeerTcpBinding class, this uses peer networking as a transport. The peer network-enabled client and services all subscribe to the same grid and broadcast messages to it.

IPC binding

Offered by the NetNamedPipeBinding class, this uses named pipes as a transport for same-machine communication. It is the most secure binding since it cannot accept calls from outside the machine and it supports a variety of features similar to the TCP binding.

Web Service (WS) binding

Offered by the WSHttpBinding class, this uses HTTP or HTTPS for transport, and is designed to offer a variety of features such as reliability, transactions, and security over the Internet.

It is same like BasicHttpBinding. In short, it uses SOAP over HTTP. But with

it also supports reliable message transfer, security and transaction. WS-Reliable Messaging,

security with WS-Security, and transactions with WS-Atomic Transaction supports reliable

message.

Federated WS binding

Offered by the WSFederationHttpBinding class, this is a specialization of the WS binding, offering support for federated security.

Duplex WS binding

Offered by the WSDualHttpBinding class, this is similar to the WS binding except it also supports bidirectional communication from the service to the client.

MSMQ binding

Offered by the NetMsmqBinding class, this uses MSMQ for transport and is designed to offer support for disconnected queued calls.

MSMQ integration binding

Offered by the MsmqIntegrationBinding class, this converts WCF messages to and from MSMQ messages, and is designed to interoperate with legacy MSMQ clients.

This binding sends binary-encoded SOAP over MSMQ. This binding can

only be used for WCF-to-WCF communication.

Q24.What are the different concurreny modes available in WCF?

1. Single

2. Reentrant

3. Multiple

Q25.Are WCF services protected from concurrent access by default?

Yes, WCF services are protected from concurrent access by default, as the concurrency mode of a WCF service is set to Single by default.

Q26.Explain Single Concurrency Mode?

In a Single concurrency mode only one request is processed by the same service instance. A lock is acquired while a request is processed by a service instance. Other threads, if any, are queued, until they timeout. Once the lock is released when the current request completes, next thread in the queue can then access the objects.

Q27.What effect does Single concurreny mode setting have on PerCall, PerSession and Singleton services?

PerCall services and Single Concurreny mode : A new service instance is allocated for each thread. Here, concurrency is not an issue and Single mode setting has no impact on the throughput and concurrent calls can be processed.

Q28.PerSession services and Single Concurreny mode : Service instances are protected against multithreaded clients. Single mode impacts throughput of single client but multiple clients can get through and concurrent calls can be processed.

Q29.Singleton services and Single Concurreny mode : Service instances are protected against any concurrent calls. Single concurrency mode impacts throughput of singleton. Multiple threads and clients cannot get through and no concurrent calls can be processed.

Q30.Explain Reentrant Concurrency Mode?

Reentrant concurrency mode is useful when services issue callbacks to clients, If callback operations are not one-way. Services release the acquired lock upon exit to make the callback and another thread is able to acquire the lock. In this case, return from callback will queue.

Q31.What effect does Reentrant concurreny mode setting have on PerCall, PerSession and Singleton services?

PerCall services and Reentrant Concurreny mode : In a case where PerCall services may need reentrancy, if we set the concurrency mode to Single, deadlock is guaranteed, where as if it is In Reentrant mode, we will have no problem.

Q32.PerSession services and Reentrant Concurreny mode : PerSession services allow a multithreaded client to access the service instance

Q33.Singleton services and Reentrant Concurreny mode : Singleton services allow any threads to access the service instance

Q34.What is the effect of Multiple concurrency mode on PerSession services with multithreaded clients?

PerSession services with multithreaded clients can have increased throughput, with Multiple concurrency mode, as no locks are acquired when requests are being processed by a service instance. However, care should be taken to protect shared resources.

Q35.What are different .NET multithreading techniques available to protect a shared resource?

1. Monitor

2. Mutex

3. Semaphore

4. ReadWriterLock

5. Interlocked

Q36.What are the factors that can influence overall throughput for a service, when multiple concurrency mode is enabled?

1. Instancing mode

2. Concurrency mode

3. Throttling behavior

Q37.What is ServiceThrottleBehavior?

ServiceThrottleBehavior provides several settings for throughput control, as shown below.

MaxConcurrentCalls: Maximum concurrent requests allowed. The default is 16 .

MaxConcurrentInstances: Maximum concurrent service instances allowed . The default is int.MaxValue.

MaxConcurrentSessions: Maximum concurrent active sessions. This includes transport, reliable, secure, and application sessions. The default is 10.

Hosting WCF Services in IIS

To host a WCF Service in IIS, you need a new physical file with the .svc extension. The file associates a service with its implementation and is the means for IIS to create ServiceHost for you. IIS takes over the interaction between your service and ServiceHost; you no longer have to instantiate and start ServiceHost yourself. The first line of the .svc file contains a directive enclosed in the ASP.NET <% Page %> directive that tells the hosting environment to which service this file points. The service code can then reside inline and it is a separate assembly registered in the GAC, in an assembly that resides in the application's Bin folder, or in a C# file that resides under the application's App_Code folder. The most common scenario is to define endpoints in a configuration file. In IIS, you have to define your endpoints in the Web.config file.

The most rich hosting option for WCF is IIS[ from IIS 7.0 onwords] and all hosting requirements for any good service is provided by IIS.

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 2010 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.

Remove Service.cs,IService.cs and Service.svc from our IIHostingService Project

Step 2: I have created sample MyService service, which will display 'Hello Wolrd ' and returning "Service is running..". Interface and implementation of the Service is shown below.

write the following code under IMyService.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Runtime.Serialization;

using System.ServiceModel;

using System.Text;

// NOTE: You can use the "Rename" command on the "Refactor" menu to change the interface name "IMyService" in both code and config file together.

[ServiceContract]

public interface IMyService

{

[OperationContract]

string GetMessage();

}

write the following code under MyService.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Runtime.Serialization;

using System.ServiceModel;

using System.Text;

// NOTE: You can use the "Rename" command on the "Refactor" menu to change the class name "MyService" in code, svc and config file together.

public class MyService : IMyService

{

public void DoWork()

{

}

public string GetMessage()

{

Console.WriteLine("Hello World");

return "Service is running ";

}

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>
  <services>
   <service behaviorConfiguration="ServiceBehavior" 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>
 <behaviors>
  <serviceBehaviors>
    <behavior name="ServiceBehavior">
 <!-- To avoid disclosing metadata information, 
 set the value below to false and remove the 
 metadata endpoint above before deployment -->
      <serviceMetadata httpGetEnabled="true"/>
 <!-- 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 -->
 <serviceDebug includeExceptionDetailInFaults="false"/>
 </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
IIS view

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 2010(Client application).
Client project create

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

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.
Output

WCF Hosting

The service-host application is the program that holds the service that has the actual objects. This is the server if you like to call it that.

WCF Hosting are three Types:

Self-hosting in any managed .NET application
Hosting in a Windows service
Hosting in different versions of IIS

Windows Communication Foundation (WCF) Services can be hosted with Internet Information Services (IIS); with the new Windows Activation Service (WAS) installed with IIS 7.0; or with any managed application process including console, Windows Forms, Windows Presentation Foundation (WPF), or managed Windows service applications. Selecting the right hosting environment for your services is a choice driven largely by deployment requirements related to transport protocol and operating platform.

Hosting Environment Features

A .NET application requires a hosting Windows process. Inside that Windows process, you can host multiple .NET application domains. An application domain is the means for the .NET CLR to isolate the managed code from Windows. The CLR automatically creates one default application domain in each worker process where it is initialized in a process. The default application domain is not unloaded until the process in which it runs shuts down. The CLR controls the shutdown of the default application domain. In most hosts, no code is running inside the default application domain. Instead, hosts (or processes) create a new application domain so the application domain can be closed independently of the process. In a lot of applications, it is desirable that the client-side code and server-side code execute in different application domains. Often, these desires stem from reasons such as security and isolation.

The relationship between processes and application domains is similar to the relationship between applications and application domains and the WCF ServiceHost. Bellow image illustrates, every process has at least one application domain, and each application domain can host zero or more WCF ServiceHost instances. WCF requires at least an application domain hosted inside a Windows process.

To be able to determine which host is the most applicable host for your scenario, you should refer to your nonfunctional requirements. Typically, nonfunctional requirements state technical requirements for your application to ensure they meet the quality and maintainability of your application. For WCF applications, this comes down to the following topics:

Availability: When do you want to be able to reach your service?
Reliability: What happens when your service somehow breaks? How does this affect other consumers?
Manageability: Do you need easy access to information about what is happening on the host where WCF services live?
Versioning: Do you need to support older versions of the service? Do you know who is consuming your services?
Deployment: What is your deployment model? Are you installing through the Microsoft Installer process and Visual Studio deployment packages, or is xcopy sufficient?
State: Are your services stateless? Do you need sessions?

Based on these nonfunctional requirements, you can decide which host meets your needs. To help you with this choice, for the remaining part of this chapter you will look at the different hosting environments, including their advantages and disadvantages.

Note The WCF programming model is agnostic to where it is running, so switching to a different host later is always possible and doesn't mean you have to change your service implementation. Typically, you'll start with a self-hosted scenario in a console application to test-drive and prototype your services.

Developing WCF Service using VS.Net Support

Microsoft VisualStudio Net provides many templates for developing as well as consuming wcf services.It has to two important/core templates for developing wcf service.These templates not only make our work easier but also they help us in developing wcf service in standard approach.

Apart from these templates we have other concepts/Projects related wcf templates also means wcf azure template...wcf cloud based service,wcf ajax template...wcf ajax based service...many more like this.

It is highly recommended to use these templates and develop the require projects instead of manually handling them.

BasicHttpBinding => SOAP+HTTP
wsHttpBinding => SOAP+Security+Performance+HTTP

WCF Service Library

A sample wcf interface and derived class.
It provides app config file,where all service endpoints and behavior are written as follows:

<system.serviceModel>

</identity>

</endpoint>

<host>

</baseAddresses>

</host>

</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>

Devolping wcf Service Jobservice:
To develop jobservice first we have download pubs database .

write the following code under IJobs.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Runtime.Serialization;

using System.ServiceModel;

using System.Text;

using System.Data;

namespace JobService

{

// NOTE: You can use the "Rename" command on the "Refactor" menu to change the interface name "IJobs" in both code and config file together.

[ServiceContract]

public interface IJobs

{

[OperationContract]

Job GetJobInfo(int jobid);

[OperationContract]

DataSet GetJobs();

[OperationContract]

List<Job> GetAllJobs();

[OperationContract]

void Dowoker();

}

2.write the following code under Jobs.cs

using System.Collections.Generic;

using System.Linq;

using System.Runtime.Serialization;

using System.ServiceModel;

using System.Text;

using System.Data.SqlClient;

using System.Data;

namespace JobService

{

// NOTE: You can use the "Rename" command on the "Refactor" menu to change the class name "Jobs" in both code and config file together.

public class Jobs : IJobs

{

string cnstr = @"Data Source=SUDHAKAR-PC;Initial Catalog=Pubs;User ID=sa;Password=#sa#";

public void DoWork()

{

}

public Job GetJobInfo(int jobid)

{

SqlConnection con = new SqlConnection(cnstr);

SqlCommand cmd = new SqlCommand("select * from jobs where job_id="+jobid,con);

Job jobdata = new Job();

con.Open();

SqlDataReader dr=cmd.ExecuteReader();

if (dr.Read())

{

jobdata.Description = dr[1].ToString();

jobdata.JobID = jobid;

jobdata.MinLevel = Convert.ToInt32(dr[2]);

jobdata.MaxLevel = Convert.ToInt32(dr[3]);

}

else {

jobdata.JobID = -1;

}

con.Close();

return jobdata;

}

public System.Data.DataSet GetJobs()

{

SqlConnection con = new SqlConnection(cnstr);

SqlDataAdapter da = new SqlDataAdapter("select * from jobs",con);

DataSet ds = new DataSet();

da.Fill(ds,"jobs");

return ds;

}

public List<Job> GetAllJobs()

{

//JobsDataDataContext dc=new JobsDataDataContext();

//List<job> obj = new List<job>();

//obj = dc.jobs.ToList();

//return obj;

throw new NotImplementedException();

}

public void Dowoker()

{

throw new NotImplementedException();

}

3. write the following code under Job.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Runtime.Serialization;

namespace JobService

{

[DataContract]

public class Job

{

[DataMember]

public int JobID { get; set; }

[DataMember]

public string Description { get; set; }

[DataMember]

public int MinLevel { get; set; }

[DataMember]

public int MaxLevel { get; set; }

}

DotNet

Saturday, June 9, 2012

WCF for Beginners

What Is WCF REST?

WCF Interview Questions and Answer

Hosting WCF Services in IIS

WCF Hosting

Developing WCF Service using VS.Net Support