WCF related Interview Questions

WCF provides a runtime environment for services, enabling you to expose CLR types as services, and to consume other services as CLR types. WCF is part of .NET 3.0 and requires .NET 2.0, so it can only run on systems that support it.

Go here for more WCF related questions.

1.) What is Proxy and how to generate proxy for WCF Services?

The proxy is a CLR class that exposes a single CLR interface representing the service contract. The proxy provides the same operations as service's contract, but also has additional methods for managing the proxy life cycle and the connection to the service. The proxy completely encapsulates every aspect of the service: its location, its implementation technology and runtime platform, and the communication transport.

The proxy can be generated using Visual Studio by right clicking Reference and clicking on Add Service Reference. This brings up the Add Service Reference dialog box, where you need to supply the base address of the service (or a base address and a MEX URI) and the namespace to contain the proxy.

Proxy can also be generated by using SvcUtil.exe command-line utility. We need to provide SvcUtil with the HTTP-GET address or the metadata exchange endpoint address and, optionally, with a proxy filename. The default proxy filename is output.cs but you can also use the /out switch to indicate a different name.

SvcUtil http://localhost/MyService/MyService.svc /out:Proxy.cs

When we are hosting in IIS and selecting a port other than port 80 (such as port 88), we must provide that port number as part of the base address:

SvcUtil http://localhost:88/MyService/MyService.svc /out:Proxy.cs

2.) What attachments protocol will be used in Windows Communication Foundation?

SOAP Message Transmission Optimization Mechanism (MTOM) will be the attachment technology supported in Windows Communication Foundation.

3.) Does Windows Communication Foundation support both synchronous and asynchronous messaging?

Yes. Windows Communication Foundation supports multiple message patterns, including one-way, request/response, two-way (duplex), and queued.

4.) What specifications will Windows Communication Foundation support?

Windows Communication Foundation will support a broad range of Web services standards, including basic standards (XML, XSD, XPath, SOAP, WSDL) and advanced standards and specifications that comprise the WS-* architecture. These include WS-Addressing, WS-Policy, WS-Security, WS-Trust, WS-SecureConversation, WS-ReliableMessaging, WS-AtomicTransaction, WS-Coordination, WS-Policy, and MTOM.

5.) How are Windows Communication Foundation services hosted?

A class implementing a Windows Communication Foundation service is typically compiled into a library. By definition, all libraries need a host application domain and Windows process to run in. Windows Communication Foundation provides two options for hosting libraries that implement services. One is to use a host application domain and process provided by the Windows Activation Service (WAS), while the other allows a service to be hosted in any application domain running in an arbitrary process (such as a Windows Forms application, a console application, an NT Service, etc).

WCF related Interview Questions

WCF is a programming framework used to build applicaions that inter-communicate. It is the part of the .NET Framework dedicated to communications. 

Go here  for more about WCF.

1.) How does Windows Communication Foundation address Service Oriented Architecture (SOA)?

WCF is the first programming model built from the ground up to provide implicit service-oriented application development, enabling developers to work autonomously and build applications that are more version independent, thereby increasing application resilience to change.

2.) How to deal with operation overloading while exposing the WCF services?

By default overload operations  are not supported in WSDL based

 operation. However by using Name property of OperationContract attribute, we can deal with operation overloading scenario. 

[ServiceContract] 

interface Isum 

{ 

[OperationContract(Name = "MultiplyInt")] 

int Multiply(int arg1,int arg2); 

[OperationContract(Name = "MultiplyDouble")] 

double Multiply(double arg1,double arg2); 

} 

Notice that both method name in the above interface is same (Add), however the Name property of the OperationContract is different. In this case client proxy will have two methods with different name MultiplyInt and MultiplyDouble.

3.) Is Windows Communication Foundation going to interoperate with my existing applications?

The current plan is for Windows Communication Foundation to provide wire-level interoperability with WSE3, System.Messaging, .NET Enterprise Services, and ASMX applications. With minimal or no changes to code, applications built with these technologies will be able to call Windows Communication Foundation services and be callable by Windows Communication Foundation services.

4.) How to configure Reliability while communicating with WCF Services?

Reliability can be configured in the client config file by adding reliableSession under binding tag.

Reliability is supported by following bindings only:
NetTcpBinding
WSHttpBindingWSFederationHttpBinding
WSDualHttpBinding

5.) Will Windows Communication Foundation applications interoperate with Web services built with other technologi

es?

Yes. By default,services built with WCF will communicate with other services based on the interoperable Web services specifications. This means that WCF services will communicate with any application built on an infrastructure that also conforms to these standards. Microsoft is deeply committed to p

latform interoperability and is an active member of key standards organizations defining the latest Web services standards. 

6.) How to set the timeout property for the WCF Service client call?

The timeout property can be set for the WCF Service client call using binding tag. If no timeout has been specified, the default is considered as 1 minute.

7.) What are the core components of an Windows Communication Foundation service?

A host environment—an application domain and process—in which the service runs;

A service class, implemented in C# or VB.NET or another CLR-based language that implements one or more methods;

One or more endpoints that allow clients to access the service.

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

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

WCF Interview Questions/Answers:

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. WCF is part of .NET 3.0 and requires .NET 2.0, so it can only run on systems that support it. (Fig source: Wikipedia)

1.) 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.

The Endpoint is the fusion of Address, Contract and Binding.

2.) 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. WCF supports nine types of bindings.

Basic binding:

It 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.

TCP binding :

It 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.

Peer network binding:

It 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:

It 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:

It 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.

Federated WS binding:

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

Duplex WS binding:

It 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:

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

MSMQ integration binding:

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

3.)How to define a service as REST based service in WCF?

WCF 3.5 provides explicit support for RESTful communication using a new binding named WebHttpBinding. The below code shows how to expose a RESTful service [ServiceContract]
interface IStock
{
[OperationContract]
[WebGet]
int GetStock(string StockId);
}

By adding the WebGetAttribute, we can define a service as REST based service that can be accessible using HTTP GET operation.

4.) 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)

5.) What is contracts in WCF?

In WCF, all services expose contracts. The contract is a platform-neutral and standard way of describing what the service does.

WCF defines four types of contracts.

Service contracts:

Describe which operations the client can perform on the service.

Data contracts:

Define which data types are passed to and from the service. WCF defines implicit contracts for built-in types such as int and string, but we can easily define explicit opt-in data contracts for custom types.

Fault contracts:

Define which errors are raised by the service, and how the service handles and propagates errors to its clients.

Message contracts:

Allow the service to interact directly with messages.

Message contracts can be typed or untyped, and are useful in interoperability cases and when there is an existing message format we have to comply with.

6.) What is address in WCF and how many types of transport schemas are there in WCF?

Address is a way of letting client know that where a service is located. In WCF, every service is associated with a unique address. This contains the location of the service and transport schemas.

WCF supports following transport schemas HTTP TCP Peer network IPC (Inter-Process Communication over named pipes) .

7.) 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. Reference:dotNetFunda