22 Essential WCF Interview Questions (SOLVED) That'll Make You Cry

Windows Communication Foundation (WCF) is a framework for building service-oriented applications. Using WCF, you can send data as asynchronous messages from one service endpoint to another. A service endpoint can be part of a continuously available service hosted by IIS, or it can be a service hosted in an application. An endpoint can be a client of a service that requests data from a service endpoint. The messages can be as simple as a single character or word sent as XML, or as complex as a stream of binary data.

Have a look at this mindmap to navigate yourself through WCF service components:

SOA stands for **service-oriented architecture. Service Oriented Architecture is an architectural approach in software development where the application is organized as "Services". Services are a group of methods that contain the business logic to connect a DB or other services. For instance you go to a hotel and order food. Your order first goes to the counter and then it goes to the kitchen where the food is prepared and finally the waiter serves the food.

Some important characteristics of Service Oriented Architecture

• SOA services should be independent of other services. Altering a service should not affect the client calling the service.
• Services should be self-contained. Services should be able to define themselves (in the Web Service Description Language (WSDL)). It should be able to tell the client what all of the operations it does, what are all the data types it uses and what kind of value it will return.

Features of WCF**

Windows Communication Foundation (WCF) is a secure, reliable, and scalable messaging platform for the .NET Framework 3.0,

• Service Orientation
• Interoperability
• Multiple Message Patterns
• Service Metadata
• Data Contracts
• Security
• Multiple Transports and Encodings
• Reliable and Queued Messages
• Durable Messages
• Transactions
• AJAX and REST Support
• Extensibility

Advantages of WCF:

1. Service Oriented
2. Location Independent
3. Language Independent
4. Platform Independent
5. Support Multiple operation
6. WCF can maintain transaction like COM+ Does
7. It can maintain state
8. It can control concurrency
9. It can be hosted on IIS, WAS, Self hosting, Windows services.

A service contract defines the operations which are exposed by the service to the outside world. A service contract is the interface of the WCF service and it tells the outside world what the service can do. It may have service-level settings, such as the name of the service and namespace for the service.

[ServiceContract]
interface IMyContract { 
    [OperationContract]
	string MyMethod();
}

class MyService: IMyContract {
	public string MyMethod() {
		return "Hello World";
	}
}

In the scenarios listed below you should go for WCF:

• If you need to send data on protocols like TCP, MSMQ or MIME
• If the consuming client just knows how to consume SOAP messages WEB API is a framework for developing RESTful/HTTP services.

Consider:

WCF contract specifies the service and its operations. WCF has five types of contracts:

• service contract,
• operation contract,
• data contract,
• message contract
• fault contract.

For a Windows Communication Foundation service to host, we need at least a managed process, a ServiceHost instance and an Endpoint configured. Possible approaches for hosting a service are:

1. Hosting in a Managed Application/Self Hosting
   1. Console Application
   2. Windows Application
   3. Windows Service
2. Hosting on Web Server
   1. IIS 6.0 (ASP.NET Application supports only HTTP)
   2. Windows Process Activation Service (WAS) i.e. IIS 7.0 supports HTTP, TCP, NamedPipes, MSMQ.

Bindings specify how a Windows Communication Foundation (WCF) service endpoint communicates with other endpoints. At its most basic, a binding must specify the transport (for example, HTTP or TCP) to use. You can also set other characteristics, such as security and transaction support, through bindings.

WCF provides nine built-in bindings:

• BasicHttpBinding: Basic web service communication. Exposes WCF services as legacy ASMX web services. Used for interoperability. No security by default.
• WSHttpBinding: Web services with WS-* support. Supports transactions and reliable messaging.
• 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.

Sometimes complete control over the structure of a SOAP message is just as important as control over its contents (that defined by Data Contracts). This is especially true when interoperability is important or to specifically control security issues at the level of the message or message part. In these cases, you can create a message contract that enables you to specify the structure of the precise SOAP message required.

The WCF programming model separates endpoint operations (as expressed in a service contract) from the transport mechanism that connects two endpoints. This gives you the flexibility to decide how to expose your services to the network. The transport layer is at the lowest level of the channel stack. A transport sends or receives the serialized form of a message to or from another application. The main transports used in Windows Communication Foundation (WCF) are:

• HTTP,
• HTTPS,
• TCP
• named pipes.

An operation contract is defined within a service contract. It defines the parameters and return type of an operation. An operation contract can also defines operation-level settings, like as the transaction flow of the operation, the directions of the operation (one-way, two-way, or both ways), and fault contract of the operation.

[ServiceContract]
interface IMyContract { 
    [FaultContract(typeof(MyFaultContract))]
    [OperationContract]
	string MyMethod();
}

When you have a large amount of data to transfer, the streaming transfer mode in WCF is a feasible alternative to the default behavior of buffering and processing messages in memory in their entirety.

In WCF any receiving message is delivered only once the entire message has been received. What I mean here is that first message is buffered at the receiving side and once it is fully received it gets delivered to the receiving end. The main problem with this approach is that the receiver end is unresponsive while the message is getting buffered. So default way of message handling in WCF is ok for small size messages but for the large size messages, this approach is not good. So to overcome this problem Streaming in WCF come into action.