Tuesday, December 27, 2011

WCF



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)


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


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.


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:


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.
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.
WCF supports nine types of bindings:


1. 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.

2. 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.

3. 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.

4. 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.

5. 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.

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

7. 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.

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

9. 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.


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


What are the various ways of hosting a WCF Service?
a) IIS
b) Self Hosting
c) WAS (Windows Activation Service))


What 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


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


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.


What does a Windows Communication Foundation, or WCF, service application use to present exception information to clients by default?
The service cannot return a .NET exception to the client. The WCF service and the client communicate by passing SOAP messages. If an exception occurs, the WCF runtime serializes the exception into XML and passes that to the client.


Can we overload methods in WCF Service or Web Service?
Yes for a WCF Service use the Name property of OperationContractAttribute class
Example:
    [ServiceContract]
    interface ddd
    {
        [OperationContract(Name = "one")]
        int calc(int a,int b);
        [OperationContract(Name = "two")]
        double calc(double a,double b);
    }
1)For a Web Service use the MessageName property of WebMethodAttribute class
2)Please comment the following line in the .cs file of the Web Service
    //[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [WebMethod]
    public string HelloWorld(string a)
    {
        return "Hello"+" "+a;
    }
    [WebMethod(MessageName="second")]
    public string HelloWorld()
    {
        return "Hello second";
    }

What are advantages of Hosting WCF in IIS?
  • Provides process activation and recycling ability thereby increasing reliability
  • It is a simplified way of deployment and development of hosted services.
  • Hosting WCF services in IIS can take advantage of scalability and density features of ASP.NET
What are the different WCF binding available?
  • BasicHttpBinding
  • WSHttpBinding
  • WSDualHttpBinding
  • WSFederationHttpBinding
  • NetTcpBinding
  • NetNamedPipeBinding
  • NetMsmqBinding
  • NetPeerTcpBinding
  • MsmqIntegrationBinding
What are the different platforms where we can host WCF service ?
WCF Services can be hosted on following platforms
1. WAS(Windows Activation Service)
2. Self Hosting
3. IIS


What is Address Header in WCF?
Address Header contains the information which is sent with every request, it can be used by either end point service or any intermediate device for determining any routing logic or processing logic.
WCF provides AddressHeader class for this purpose.
Example :

AddressHeader addressHeader= AddressHeader.CreateAddressHeader("Name of the header", "Information included in header ");

Once the AddressHeader instance is created, it can be associated with end point instance as follows :

EndpointAddress endpoint = new EndpointAddress(new Uri("http://myserver/myservice"), addressHeader);


In WCF which bindings supports the reliable session?
In WCF, following bindings supports the reliable session
1. wsHttpBinding
2. wsDualHttpBinding
3. wsFederationHttpBinding
4. netTcpBinding


What are tha advantages of hosting WCF service in WAS?
WAS (Windows Activation Service) is a component of IIS 7.0. Following are few advantages :
1. We are not only limited to HTTP protocol. We can also use supported protocols like TCP, named pipes and MSMQ
2. No need to completely install IIS. We can only install WAS component and keep away the WebServer.


What is service host factory in WCF?
Service host factory is the mechanism by which we can create the instances of service host dynamically as the request comes in. This is useful when we need to implement the event handlers for opening and closing the service. WCF provides ServiceFactory class for this purpose.


Which bindings in WCF support the message streaming?
Following bindings supports the streaming in WCF:
1. basicHttpBinding
2. netTcpBinding
3. netNamedPipeBinding

Which is the default mode for Instancing in WCF?
1.PerCall
2.PerSession
3.Singleton


How can we set the instancing mode in WCF service?
In WCF, instancing mode is set at service level. Example:
//Setting PerSession instance mode
[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)]
class MyService : IMyService
{
    //Implementation goes there
}

Which are the 3 types of transactions manager WCF supports?
WCF supports following 3 types of transactions managers:
1. LightWeight
2. OLE Transactions
3. WS-Atomic Transactions


How the concurrency mode is specified in WCF service?
The concurrency mode is specified using the ServiceBehavior attribute on the class that implements the service.
Example
[ServiceBehavior(ConcurrencyMode=ConcurrencyMode.Single)]
Public class ServiceClass : IServiceInterface
{
    //Implementation Code
}

There are three possible values of ConcurrencyMode enumeration:
1. Single
2. Reentrant
3. Multiple


What is ABC of WCF?
ABC is the three building blocks of WCF:
A - Address (Where): Address tells us where to find the services, like url
B - Bindings (How) : Bindings tells us how to find the services or using which protocols finds the services (SOAP, HTTP, TCT etc.)
C - Contacts (What): Contracts are an agreement between the consumer and the service providers that explains what parameters the service expects and what return values it gives.
Which protocol is used for platform-independent communication?
SOAP (Simple Object Access Protocol), which is directly supported from WCF (Windows Communication Foundation).

What is Fault Contracts in WCF?
Fault Contracts is the way to handle exceptions in WCF. The problem with exceptions is that those are technology specific and therefore cannot be passed to other end because of interoperability issue. (Means either from Client to Server or vice-versa). There must be another way representing the exception to support the interoperability. And here the SOAP Faults comes into the picture.
SOAP faults are not specific to any particular technology and they are based on industry standards.
To support SOAP Faults WCF provides FaultException class. This class has two forms:
a) FaultException : to send untyped fault back to consumer
b) FaultException: to send typed fault data to the client
WCF service also provides FaultContract attribute so that developer can specify which fault can be sent by the operation (method). This attribute can be applied to operations only.


What is the difference between XMLSerializer and the DataContractSerializer?
DataContractSerializer is the default serializer fot the WCF. It is very fast and is basically for very small, simple subset of the XML infoset. While XMLSerializer is used for complex schemas.
What is the purpose of base address in WCF service? How it is specified?
When multiple endpoints are associated with WCF service, base address (one primary address) is assigned to the service, and relative addresses are assigned to each endpoint. Base address is specified in <host> element for each service.
<configuration>
    <system.servicemodel>
      <Services>
<service name=”MyService>
  <host>
  <baseAddresses>
 <add baseAddress =”http://localhost:6070/MyService”>
</baseAddresses>
</host>
</service>
<services>
</system.servicemodel>
</configuration>

What are the various ways of hosting a WCF Service?
1. IIS
2. Self Hosting
3. WAS (Windows Activation Service)


What is DataContractSerializer in WCF?
DataContractSerializer is new WCF serializer. This is serialization engine in WCF. DataContractSerializer translate the .NET framework objects into XML and vice-versa. By default WCF uses DataContractSeriazer.


What is Message Contract in WCF?
Message Contract is the way to control the SOAP messages, sent and received by the client and server. It can be used to add and to get the custom headers in SOAP message Because of Message Contract we can customize the parameters sent using SOAP message between the server and client.

What is XML Infoset?
The XML Information Set defines a data model for XML. It is an abstract set of concepts such as attributes and entities that can be used to describe a valid XML document. According to the specification, "An XML document's information set consists of a number of information items; the information set for any well-formed XML document will contain at least a document information item and several others."


What is .svc file in WCF?
.svc file is a text file. This file is similar to our .asmx file in web services.
This file contains the details required for WCF service to run it successfully.
This file contains following details :
1. Language (C# / VB)
2. Name of the service
3. Where the service code resides
Example of .svc file
<%@ ServiceHost Language="C#/VB" Debug="true/false" CodeBehind="Service code files path" Service="ServiceName" %>
We can also write our service code inside but this is not the best practice.


What is the Messaging Pattern? Which Messaging Pattern WCF supports?
Messaging patterns describes how client and server should exchange the message. There is a protocol between client and server for sending and receiving the message. These are also called Message Exchange Pattern.
WCF supports following 3 types of Message Exchange Patterns:
1. request - reply (default message exchange pattern)
2. OneWay (Simplex / datagram)
3. Duplex(CallBack)


In WCF, Which contract is used to document the errors occurred in the service to client?
Fault Contract is used to document the errors occurred in the service to client.


Which is the default Message Exchange Pattern (MEP) ?
1. Request/Response
2. OneWay
3. Duplex


What is difference between Web Services and WCF?
  • Web services can only be invoked by HTTP (traditional webservice with .asmx). While WCF Service or a WCF component can be invoked by any protocol (like http, tcp etc.) and any transport type.
  • Second web services are not flexible. However, WCF Services are flexible. If you make a new version of the service then you need to just expose a new end. Therefore, services are agile and which is a very practical approach looking at the current business trends.
  • We develop WCF as contracts, interface, operations, and data contracts. As the developer we are more focused on the business logic services and need not worry about channel stack. WCF is a unified programming API for any kind of services so we create the service and use configuration information to set up the communication mechanism like HTTP/TCP/MSMQ etc
  • Major Difference is That Web Services Use XmlSerializer But WCF Uses DataContractSerializer which is better in Performance as Compared to XmlSerializer. Key issues with XmlSerializer to serialize .NET types to XML.
    •  Only Public fields or Properties of .NET types can be translated into XML.
    • Only the classes which implement IEnumerable interface.
    • Classes that implement the IDictionary interface, such as Hash table can not be serialized.
  • The DataContractAttribute can be applied to the class or a strcture. DataMemberAttribute can be applied to field or a property and theses fields or properties can be either public or private.
  • Important difference between DataContractSerializer and XMLSerializer.
    • A practical benefit of the design of the DataContractSerializer is better performance over Xmlserializer.
    • XML Serialization does not indicate the which fields or properties of the type are serialized into XML where as DataCotratSerializer Explicitly shows the which fields or properties are serialized into XML.
    • The DataContractSerializer can translate the HashTable into XML.
Web Services
1. It Can be accessed only over HTTP
2. It works in stateless environment

WCF
WCF is flexible because its services can be hosted in different types of applications. The following lists several common scenarios for hosting WCF services:
1. IIS
2. WAS
3. Self-hosting
4. Managed Windows Service


Which namespace is required in a class to use DataContract or DataMember attribute for a class or properties?
1. Using System.Runtime.Serialization;
2. Using System.ServiceModel;
3. Using System.ServiceModel.Web


What is the use of ServiceBehavior attribute in WCF?
ServiceBehaviour attribute is used to specify the InstanceContextMode for the WCF Service class (This can be used to maintained a state of the service or a client too)
There are three instance Context Mode in the WFC
  • PerSession: This is used to create a new instance for a service and the same instance is used for all method for a particular client. (eg: State can be maintained per session by declaring a variable)
  • PerCall: This is used to create a new instance for every call from the client whether same client or different. (eg: No state can be maintained as every time a new instance of the service is created)
  • Single: This is used to create only one instance of the service and the same instance is used for all the client request. (eg: Global state can be maintained but this will be applicable for all clients)
What is a SOA Service?
SOA is Service Oriented Architecture. SOA service is the encapsulation of a high level business concept. A SOA service is composed of three parts.
1. A service class implementing the service to be provided.
2. An environment to host the service.
3. One or more endpoints to which clients will connect.


Which namespace is used to access WCF service?
1. System.Service
2. System.Data
3. System.ServiceModel
4. System.Web


What are the various ways of hosting a WCF service?
  • Self hosting the service in his own application domain.
  • Host in application domain or process provided by IIS Server.
  • Host in Application domain and process provided by WAS (Windows Activation Service) Server.
What is three major points in WCF?
The three major points in WCF are:
Address - Specifies the location of the service which will be like http://Myserver/MyService.Clients will use this location to communicate with our service.
Binding - Specifies how the two paries will communicate in term of transport and encoding and protocols
Contract - Specifies the interface between client and the server.It's a simple interface with some attribute.


What was the code name for WCF?
The code name of WCF was Indigo.


What are the main components of WCF?
The main components of WCF are
1. Service class
2. Hosting environment
3. End point


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.
<client>
   <endpoint      ...
      binding = "wsHttpBinding"
      bindingConfiguration = "LongTimeout"
      ...
   />
</client>
<bindings>
   <wsHttpBinding>
      <binding name = "LongTimeout" sendTimeout = "00:04:00"/>
   </wsHttpBinding>
</bindings>
If no timeout has been specified, the default is considered as 1 minute.

How to deal with operation overloading while exposing the WCF services?
By default overload operations (methods) are not supported in WSDL based operation. However by using Name property of OperationContract attribute, we can deal with operation overloading scenario.
    [ServiceContract]
    interface ICalculator
    {
       [OperationContract(Name = "AddInt")]
       int Add(int arg1,int arg2);

       [OperationContract(Name = "AddDouble")]
       double Add(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 AddInt and AddDouble.

How to configure Reliability while communicating with WCF Services?
Reliability can be configured in the client config file by adding reliableSession under binding tag.
<system.serviceModel>
   <services>
      <service name = "MyService">
         <endpoint
            address  = "net.tcp://localhost:8888/MyService"
            binding  = "netTcpBinding"
            bindingConfiguration = "ReliableCommunication"
            contract = "IMyContract"
         />
      </service>
   </services>
   <bindings>
      <netTcpBinding>
         <binding name = "ReliableCommunication">
            <reliableSession enabled = "true"/>
         </binding>
      </netTcpBinding>
   </bindings>
</system.serviceModel>

Reliability is supported by following bindings only
NetTcpBinding
WSHttpBinding
WSFederationHttpBinding
WSDualHttpBinding


What is Transport and Message Reliability?
Transport reliability (such as the one offered by TCP) offers point-to-point guaranteed delivery at the network packet level, as well as guarantees the order of the packets. Transport reliability is not resilient to dropping network connections and a variety of other communication problems.

Message reliability deals with reliability at the message level independent of how many packets are required to deliver the message. Message reliability provides for end-to-end guaranteed delivery and order of messages, regardless of how many intermediaries are involved, and how many network hops are required to deliver the message from the client to the service.


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
<system.serviceModel>
   <client>
      <endpoint name = "MyEndpoint"
         address  = "http://localhost:8000/MyService/"
         binding  = "wsHttpBinding"
         contract = "IMyContract"
      />
   </client>
</system.serviceModel>

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


What are 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.

1. Service Contracts
Describe which operations the client can perform on the service. There are two types of Service Contracts. ServiceContract - This attribute is used to define the Interface. OperationContract - This attribute is used to define the method inside Interface.
   [ServiceContract]
    interface IMyContract
    {
       [OperationContract]
       string MyMethod( );
    }
    class MyService : IMyContract
    {
       public string MyMethod( )
       {
          return "Hello World";
       }
    }

2. 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.
There are two types of Data Contracts:
DataContract - attribute used to define the class
DataMember - attribute used to define the properties.
    [DataContract]
    class Contact
    {
       [DataMember]
       public string FirstName;

       [DataMember]
       public string LastName;
    }

If DataMember attributes are not specified for a properties in the class, that property can't be passed to-from web service.

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

4. 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.


What is the address formats of the WCF transport schemas?
Address format of WCF transport schema always follow

[transport]://[machine or domain][:optional port] format.
for example:

HTTP Address Format
http://localhost:8888
the way to read the above url is

"Using HTTP, go to the machine called localhost, where on port 8888 someone is waiting" When the port number is not specified, the default port is 80.

TCP Address Format
net.tcp://localhost:8888/MyService
When a port number is not specified, the default port is 808:
net.tcp://localhost/MyService
NOTE: Two HTTP and TCP addresses from the same host can share a port, even on the same machine.
IPC Address Format
net.pipe://localhost/MyPipe
We can only open a named pipe once per machine, and therefore it is not possible for two named pipe addresses to share a pipe name on the same machine.
MSMQ Address Format
net.msmq://localhost/private/MyService
net.msmq://localhost/MyService


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.

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)
  • MSMQ
The sample address for above transport schema may look like
http://localhost:81
http://localhost:81/MyService
net.tcp://localhost:82/MyService
net.pipe://localhost/MyPipeService
net.msmq://localhost/private/MyMsMqService
net.msmq://localhost/MyMsMqService

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. 






Thanks,
Anil Kr. Singh

4 comments:

Shyam Ji Srivastava said...

Nice article to understand WCF

varuni said...

I was searching fir inotify in C# and got proper answer in ur site and from then onwards,I began to use this site for preparing for the interviews..I feel the font to be a bit large...pleas change the font
But nice notes.....!

Anil's Blog said...

Thanks for suggestion!!!!!!!

Rakesh said...

Nice article really helping for beginners.