Namitha's Pensieve: 2014

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. WCF is part of .NET 3.0 and requires .NET 2.0, so it can only run on systems that support it.

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.

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 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.

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";

}

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.

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.

Where we can host WCF services?

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

1. IIS

2. Self Hosting

3. WAS (Windows Activation Service)

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: 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: 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 : 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.

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.

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.

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 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

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 different elements of WCF Services Client configuration file?

WCF Services client configuration file contains endpoint, address, binding and contract. A sample client config file looks like

<system.serviceModel>

</client>

</system.serviceModel>

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.

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>

</service>

</services>

</binding>

</netTcpBinding>

</bindings>

</system.serviceModel>

Reliability is supported by following bindings only

NetTcpBinding

WSHttpBinding

WSFederationHttpBinding

WSDualHttpBinding

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.

<endpoint

...

binding = "wsHttpBinding"

bindingConfiguration = "LongTimeout"

...

</client>

</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.

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:-

· NET remoting

· MSMQ

· Web services

· COM+

What are the main components of WCF?

The main components of WCF are

1. Service class

2. Hosting environment

3. End point

What are various ways of hosting WCF Services?

There are three major ways of hosting a WCF services

• Self-hosting the service in its own application domain. The service comes in to existence when you create the object of Service Host class and the service closes when you call the Close of the Service Host class.

• 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 the difference WCF and Web services?

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

What is three major points in WCF?

We should remember ABC.

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.

Difference between WCF and Web services?

Web Services

1. It can be accessed only over HTTP

2. It works in stateless environment

3. Web Services Use XmlSerializer

WCF

1. WCF is flexible because its services can be hosted in different types of applications.

2. State management is possible

3. WCF uses DataContractSerializer which is better in Performance as Compared to XmlSerializer

Important difference between DataContractSerializer and XMLSerializer.

1. A practical benefit of the design of the DataContractSerializer is better performance over Xmlserializer.

2. 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.

3. The DataContractSerializer can translate the HashTable into XML.

4. DataContractSerializer is the default serializer fot the WCF

5. DataContractSerializer is very fast.

6. DataContractSerializer is basically for very small, simple subset of the XML infoset.

7. XMLSerializer is used for complex schemas.

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.

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

1. 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)

2. 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)

3. 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)

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.

What is the Messaging Pattern? Which Messaging Pattern WCF supports?

Messaging Pattern : 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)

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"

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 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.

E.g.

<system.servicemodel>

<host>

</baseAddresses>

</host>

</service>

</system.servicemodel>

</configuration>

Which protocol is used for platform-independent communication?

SOAP (Simple Object Access Protocol), which is directly supported from WCF (Windows Communication Foundation).

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.

Ex.

[ServiceBehavior(ConcurrencyMode=ConcurrencyMode.Single)]

Public class ServiceClass : IServiceInterface{

//Implementation Code

}

There are 3 possible values of ConcurrencyMode enumeration

Single

Reentrant

Multiple

Which are the 3 types of transactions manager WCF supports?

WCF supports following 3 types of transactions managers:

a. LightWeight

b. OLE Transactions

c. WS-Atomic Transactions

How to set the instancing mode in WCF service?

In WCF, instancing mode is set at service level. For ex.

//Setting PerSession instance mode

[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)]

class MyService : IMyService

{

//Implementation goes there

}

What are the 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?

1. Service host factory is the mechanism by which we can create the instances of service host dynamically as the request comes in.

2. This is useful when we need to implement the event handlers for opening and closing the service.

3. WCF provides ServiceFactory class for this purpose.

What does a Windows Communication Foundation, or WCF, service application use to present exception information to clients by default?

However, 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.

What is the use of Is Required Property in Data Contracts?

Data Contracts, is used to define Required or NonRequired data members. It can be done with a property named IsRequired on DataMember attribute.

[DataContract]

public class test

{

[DataMember(IsRequired=true)]

public string NameIsMust;

[DataMember(IsRequired=false)]

public string Phone;

}

What is Asynchronous Messaging ?

Asynchronous messaging describes a way of communications that takes place between two applications or systems, where the system places a message in a message queue and does not need to wait for a reply to continue processing.

Why in WCF, the "httpGetEnabled" attribute is essential ?

The attribute "httpGetEnabled" is essential because we want other applications to be able to locate the metadata of this service that we are hosting.

Without the metadata, client applications can't generate the proxy and thus won't be able to use the service.

What is "Automatic activation" in WCF ?

Automatic Activation means that the service is not necessary to be running in advance. When any message is received by the service it then launches and fulfills the request. But in case of self hosting the service should always be running.

What is a proxy class for WCF Service ?

It is a class by which a service client can interact with the service. The client will make an object of the proxy class and by the help of it will call different methods exposed by the service.

Explain briefly the three way of communication between source and destination in WCF ?
Simplex - Also known as one way communication. Source will send a message to the target, but target will not respond to the message.

Request/Replay - It is two way communications, source send message to the target, target will resend the response message to the source. But in this scenario at a time only one can send a message (that is), either source or destination.

Duplex -Also known as two way communication, both source and target can send and receive message simultaneously.

State 3 primary aspects of WCF ?

(1) Inter-operability with applications built on differnet technologies.

(2) Unification of the original Dotnet Framework communication Technologies.

(3) Support for Service Oriented Architecture (SOA).

If you have a Dotnet Web Service and a Java Client Application, then which Communication technology will you use other than WCF ?

Web Service (that is), ASMX will be the most likely way to achieve cross-vender inter-operability.

Suppose you have created a WCF service. You have an interface stating your methods that must be exposed to the clients. But you have forgotten to specify "[OperationContract]" attribute in any of your method. What will happen ?

If you do not specify "[OperationContract] " in any of the methods in your interface then you will get the following error :-

IService1' has zero operations; a contract must have at least one operation

Here, Iservice is the name of my Interface. you can have your own name.

So, it is mandatory to label "[OperationContract] " attribute to at least one method while declaring your interface methods or ServiceContract.

In WCF, can a struct be used as a DataContract ?

Yes, a struct can be used as a DataContract. For example :-

[DataContract]

struct EmployeeInfo

{

[DataMember]

public int id;

[DataMember]

public string name;

[DataMember]

public DateTime joining_date;

}

How can I encrypt sensitive data in the WCF configuration file?

To encrypt sensitive data in WCF configuration file, use aspnet_regiis.exe tool.

Example: If you want to encrypt Connection String section of WCF config file, use -pe that means provider encryption .

aspnet_regiis -pe "connectionStrings" -app "/MachineDPAPI"

-prov "DataProtectionConfigurationProvider"

-pe means provider encryption of configuration section.

-app means your application's virtual path.

-prov means provider name

Briefly explain WCF Data Services ?

WCF Data Services are used when you want to expose your data model and associated logic through a RESTful interface. It includes a full implementation of theOpen Data (OData) Protocol for .NET to make this process very easy.

WCF Data Services was originally released as ‘ADO.NET Data Services’ with the release of .NET Framework 3.5.

Explain in brief, WCF One Way Contract ?

WCF One Way Contract are methods/operations which are invoked on the service by the client or the server in which either of them do not expect a reply back. For example :-

If a client invokes a method on the service then it will not expect a reply back from the service.

What is the most primary reason to use WCF One Way Contract ?

One way contract is used to ensure that the WCF client does not go in a blocking mode . If your WCF operation contracts are returning nothing and they are doing some heavy process then it is better to use one way contract.

How is WCF One Way Contract implemented?

WCF one way contract is implemented via "IsOneWay = true/false" attribute.

For example :-

[ServiceContract]

interface IMyContract

{

[OperationContract(IsOneWay = true)]

void MyMethod( );

}

What is Sessionful Services in WCF One Way Contract ?

[ServiceContract(SessionMode = SessionMode.Required)]

interface IService

{

[OperationContract(IsOneWay = true)]

void Method1();

}

If the client issues a one-way call and then closes the proxy while the method executes, the client will still be blocked until the operation completes.

What is duplex contract in WCF?

In Duplex contract, clients and servers can communicate with each other independently.

Duplex contracts consists of two one-way contracts so that parallel communication is achieved.

What are the 3 message patterns available in WCF ?

Three message patterns available in WCF are :-

(1) One Way Contract

(2) Duplex Contract

(3) Request-Reply Contract

What is the primary reason for which Duplex Contract is used in WCF ?

Duplex Contracts are needed when the service queries the client for some additional information or the service wants to explicitly raise events on the client.

In WCF, can data contract classes inherit from one another?

[DataContract]

public class A

{

[DataMember]

public MyCustomType AValue1{ get; set; }

[DataMember]

public MyCustomType AValue2 { get; set; }

}

[DataContract]

public class B: A

{

[DataMember]

public double BValue1{ get; set; }

[DataMember]

public double BValue2 { get; set; }

}

The metadata fails to load when testing the services.

What needs to be done to load both super and sub class.

We must add KnownType Attribute.

[DataContract]

[KnownType(typeof(B))]

public class A

{

[DataMember]

public string Value { get; set; }

}

[DataContract]

public class B : A

{

[DataMember]

public string OtherValue { get; set; }

}

In what are the different ways a WCF Metadata can be accessed ?

WCF Metadata can be accessed in two ways :-

(1) WSDL document can be generated which represents the endpoints and protocols

(2) Or the ServiceHost can expose a metadata exchange endpoint to access metadata at runtime

Difference between reliable messaging and reliable sessions in WCF ?

Reliable messaging is concerned with ensuring that messages are delivered exactly once.

Reliable session provides a context for sending and receiving a series of reliable messages. reliable sessions have a dependency on reliable messaging.

You have to use reliable messaging to provide an end-to-end reliable session between a client application and a service.

What is Windows Server AppFabric?

It is a set of extensions to the Windows OS aimed at making it easier for developers to build faster, scalable, and more-easily managed services.

It provides a distributed in-memory caching service and replication technology that helps developers improve the speed and availability of .NET Web applications and WCF services.

If you are hosting WCF services by using IIS or WAS in a production environment, you might want to consider implementing Windows Server AppFabric.

What is the difference between RIA and WCF services?

Some points are as under

1) WCF is concerned with technical aspects of communication between servers across tiers and message data management whereas RIA Web Services delegates this functionality to WCF.

2) WCF is a generic service that could be used in Windows Forms for example whereas RIA Web Services is focused on Silverlight and ASP.NET clients

3) WCF does not generate source code to address class business logic such as validation that may need to be shared across tiers like RIA Web Services does.

4) The RIA Services can either exist on top of WCF or replace the WCF layer with RIA Services using alternatice data source e.g. an ORM layer(EF/NHibernate etc.)

5) RIA Services allow serializing LINQ queries between the client and server.

How many different types of authorization supported by WCF ?

Role-based : Map users to roles and check whether a role can perform the requested operation.

• Identity-based : Authorize users based on their identity.

• Claims-based : Grant or deny access to the operation or resources based on the client’s claims.

• Resource-based : Protect resources using access control lists (ACLs)

What are the benefits of WCF?

The benefits include the following

1. Transactional support

2. Asynchronous one-way messaging

3. Interoperability

4. Independent versioning

5. Platform Consolidation

What are the principles WCF implement?

WCF services effectively communicates with the clients through these principles.

1. Explicit boundaries

WCF services function using the defined interfaces to identify the communications between server and client that flow outside the boundaries of the service

2. Independent services

WCF services are deployed and managed independently and each service interaction is independent of other interactions. They are independent of deployment, installation and version issues.

3. Schema and contract based communication

WCF services communicate with clients by providing only the schema of the message and not its implementation classes. The service implementation can be changed if required without impacting the clients

4. Policy based compatibility

Compatibility between WCF services and clients at runtime is determined using published policies. Policies help separate the description of the service fro its implementation details.

What are the four layers in WCF architecture?

SOA based WCF architecture has four layers.

1. Contracts

It describe the WCF message system. This is achieved by three contracts with policies and bindings.

1. Service Contract - Describes the method signature of the service using C# or VB

2. Data Contract - Enables .NET types to be in XML

3. Message Contract - Defines the structure os the SOAP message exchanged between the service and client

4. Policies and Bindings - Defines the security level required by the clients

2. Service Runtime

This includes the behaviors that occur when service is running.

3. Messaging

This layer contains the channels that process messages and operate on messages and message headers

4. Hosting

Describes the ways in which WCF service can be hosted.

List the behaviors included in Service Runtime of the WCF layer?

The following behaviors are included in the WCF Service Runtime layer..

1. Throttling behavior

Throttling behavior provides the options to limit how many instances or sessions are created at the application level.

2. Error behavior

By implementing IErrorHandler interface WCF allows an implementer to control the fault message returned to the caller and also it performs custom error processing such as logging

3. Metadata behavior

Through the metadata behavior we can publish metadata of the service by configuring an endpoint to expose the IMetadataExchange contract as an implementation of a WS-MetadataExchange (MEX) protocol. By default it is disabled.

4. Instance behavior

This behavior specifies how many instance of the service has to be created while running WCF.

5. Transaction behavior

This is used to enables the rollback of transacted operations if a failure occurs.

6. Dispatch behavior

This behavior controls how a message is processed by the WCF Infrastructure.

7. Concurrency behavior

Concurrency behavior measures how many tasks can be performed simultaneously

9. Parameter Filtering

This demonstrates how to validate the parameters passed to a method before it is invoked.

Explain the functionality of the Message layer in WCF.

The Messaging layer contains channels that process messages and operate on messages and message headers. The messaging layer has eight channels which defines the possible formats and data exchange patterns.

The eight channels are divided into two categories.

1. Transport Channels

These channels helps reads and write messages from the network.

1. WS Security Channel

2. WS Reliable MessagingChannel

3. Encoders:Binary/ MTOM/ Text/ XML

2. Protocol Channels

These channels implement message processing protocols.

1. HTTP Channel

2. TCP Channel

3. TransitionFlow Channel

4. NamedPipe Channel

5. MSMQ Channel

What is a Throttling behavior in WCF?

Throttling behavior of the WCF service holds the configuration for three limitations that control the amount of resources that your service hosting can allocate to deal with the client request. Thus it enables to

1. Manages resource Usage

2. Balances performance load

How can we specify the throttling behavior for a WCF service?

Throttling behavior is specified by the following three parameters.

1. MaxConcurrentCalls - Total no of concurrent calls service will accept

2. MaxConcurrentSessions - Total no of sessionful channels service will accept

3. MaxConcurrentInstances - Total no of service instances will be created for servicing requests.

It can be specifed either through code or configuration file. It requires the "System.SystemModel.Behavior" namespace to be included.

What is a metadata export?

Metadata Export is the process of describing the service endpoints and projecting them into a parallel, standardized representation that clients can use to understand how to use the service.

How to publish service metadata?

WCF services publish its metadata by exposing one or more metadata endpoints. Publishing service metadata makes service metadata available using standardized protocols, such as MEX and HTTP/GET requests.

Metadata endpoints are the same as other service endpoints and have an address, a binding, and a contract.

You can add metadata endpoints to a service host in configuration or in code.

In WCF, suppose you have a derived class inherited from a datacontract class, will the derived class automatically have a datacontract as well ?

The Data contract is not inherited, so any derived class, would have to be explicitly declared as having a Data contract attribute as well.

In WCF, if your service wants an authentication before it is used then what is the best way to handle an authentication mechanism with WCF?

The best way to handle this would be to design a Message contract that accepts these authentication tokens in the header of the message.

What is meant by WS Addressing Standard in WCF ?

The address for an endpoint is a unique URL that identifies the location of the service. The address should follow the Web Service Addressing (WS-Addressing) standard, and they are:-

(1) Scheme - This is typically “http” followed by a colon.

(2) Machine - Identifies the machine name, which can be a public URL such as “www.google.com" or a local identifier such as “localhost”.

(3) Port - The optional port number, preceded by a colon.

(4) Path - The path used to locate the service files. Typically, this is just the service name, but the path can consist of more than one level when a service resides in a directory structure.

What namespace is used by ASMX and WCF respectively for serialization ?

For serialization, WCF uses the System.Runtime.Serialization namespace for serialization.

Web service(i.e), ASMX uses System.Xml.serialization namespace.

State 3 Duplex contract problems in WCF ?

(1) Threading problems can occur if either of the Callback channels are not empty.

(2) If the client and service has a long running work then this pattern doesn't scale very well. It can block the client or the service until the process is completes !

(3) It requires a connection back to the client. And there may be a chance to not connect back due to firewall and Network Address Translation problems.

Note :- It is always better to use Request / Response MEP rather than using Duplex method.

Which command is used to convert WSDL to a proxy

svcutil.exe command will convert the WSDL to a proxy class for our client

Open visual studio command prompt window

click on visual studio command prompt,set the current folder to the location where you want the generated proxy and configuration files to be created.

Run SvcUtil.exe to generate the output files.

What is MTOM?

MTOM stands for Message Transmission Optimization Mechanism and is an Interoperable standard that reduces the overhead for transfer large binary data in WCF. Its a mechanism for transmitting large binary attachments with SOAP messages as raw bytes.

What is the purpose of ExtensionDataObject in WCF? or How to make DataContract forward compatible?

A .NET serialization system supports backward-compatibility on custom data types naturally. However, sometimes we also need forward-compatibility for data types used in a WCF service.ExtensionDataObject property is used to achieve the Forward compatible in WCF.

What is RoundTripping ?

A client with an older version (v1.0) of a data contract can communicate with a service with a newer version(v2.0) of the same data contract, or a client with a newer version of a data contract can communicate with an older version of the same data contract. this new-to-old-to-new interaction is called versioning roundtrip.

Round-tripping guarantees that no data is lost. WCF does have some built-in support it (IExtensibleDataObject interface).

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Saturday, October 18, 2014

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