WCF- Part1

WCF
WCF is a unified programming model for building service-oriented applications.It unites the following technologies
   •  NET remoting
   •  MSMQ
   •  Web services
   •  COM+

Service-Oriented Application

A service is a program that performs a task and that a client application can communicate with through well-defined messages.

SOAP defines the format of XML request and reply messages and how clients and services encode the data in the messages.

Service-oriented applications are loosely coupled. All communication occurs through messages. SOAP defines the format of messages. 

Endpoint 

An endpoint expresses all the information needed by a client to communicate with a service. An endpoint consists of an address, a binding, a contract and optional behaviours.

Contract – (What)

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

Address - (Where)

The address specifies where the service is located (Address/URL). Clients will use this location to communicate with WCF service.

Bindings - (How)

Bindings Determine how Client and Server will communicate in term of transport and encoding and protocols. Bindings are objects that are used to specify the communication details that are required to connect to the endpoint of a Windows Communication Foundation (WCF) service. Each endpoint in a WCF service requires a binding to be well-specified.

Difference between WCF and Web services

• Support for sending messages using not only HTTP, but also TCP and other network protocols. 
• Support for hosting services on hosts other than a Web server. 
• Built-in support for the latest Web services standards (SOAP 1.2 and WS-*) and the ability to easily support new ones. 
• Support for security, transactions and reliability.
• Support for sending messages using formats other than SOAP, such as Representational State Transfer (REST). 

What are the various ways of hosting a WCF service

The following lists several common scenarios for hosting WCF services:

• IIS
• WAS (Windows Activation Service)
• Self-hosting
• Managed Windows Service

Four types of contracts in WCF

1. Service contracts : Describe which operations the client can perform on the service.
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.
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 Message Exchange Patterns (MEPs) supported by WCF

1. Request/Response

It’s the default pattern. In this pattern, a response message will always be generated to consumer when the operation is called, even with the void return type. In this scenario, response will have empty SOAP body.

2. One Way

In some cases, we are interested to send a message to service in order to execute certain business functionality but not interested in receiving anything back. OneWay MEP will work in such scenarios.

If we want queued message delivery, OneWay is the only available option.

3. Duplex

The Duplex MEP is basically a two-way message channel. In some cases, we want to send a message to service to initiate some longer-running processing and require a notification back from service in order to confirm that the requested process has been completed.

 What is DataContractSerializer and How its different from XmlSerializer?

Serialization is the process of converting an object instance to a portable and transferable format. So, whenever we are talking about web services, serialization is very important.

Windows Communication Foundation has DataContractSerializer that is new in .NET 3.0 and uses opt-in approach as compared to XmlSerializer that uses opt-out. Opt-in means specify whatever we want to serialize while Opt-out means you don’t have to specify each and every property to serialize, specify only those you don’t want to serialize.

DataContractSerializer is about 10% faster than XmlSerializer but it has almost no control over how the object will be serialized. If we wanted to have more control over how object should be serialized that XmlSerializer is a better choice.

Choosing the appropriate WCF binding

(Ref:http://www.topwcftutorials.net/2012/07/WCF-Service-Bindings.html)

Interoperability Scenario:

If we are going to develop a WCF service that will be consumed by non-WCF client applications, then we can expose our service using BasicHttpBinding or WsHttpBinding. So, how these two bindings differ from each other is explain as:

1. BasicHttpBinding is designed to replace ASMX Web services. It supports both HTTP and Secure HTTP. As far as encoding is concerned, it provides support for Text as well as MTOM encoding methods. BasicHttpBinding doesn’t support WS-* standards like WS-Addressing, WS-Security and WS-ReliableMessaging.

2. WsHttpBinding also supports interoperability. With this binding, the SOAP message is, by default, encrypted. It supports HTTP and HTTPS. In terms of encoding, it provides support for Text as well as MTOM encoding methods. It supports WS-* standards like WS-Addressing, WS-Security and WS-ReliableMessaging. By default, reliable sessions are disabled because it can cause a bit of performance overhead. 

3. WsDualHttpBinding has all features of WsHttpBinding with addition that it supports Duplex MEP (Message Exchange Pattern). In this MEP, service can communicate with client via callback. Its basically a two way communication.

4. WsFederationHttpBinding is a specialized form of WS Binding that offers support for federated security.

Single Computer Scenario:

If our WCF service resides on a single computer, then netNamedPipeBinding will be the best choice.

5. NetNamedPipeBinding is secure and reliable binding on a single WCF computer across process communication. It provides support for binary encoding which is the best choice in this scenario and uses named pipes as transport for SOAP messages.

Intranet/Cross Computers .NET Communication Scenario:

If we need to communicate across computers with same .NET technology on intranet, then netTcpBinding or netPeerTcpBinding options are available. It’s basically the replacement or enhancement of earlier .NET Remoting technology.

6. NetTcpBinding supports reliability, transactions and security. It also supports TCP protocol and binary as encoding method. We can say that it’s the most optimized or fastest binding because both client and service are on the same WCF technology. 

7. NetPeerTcpBinding supports features as that of netTcpBinding but it provides secure binding for peer-to-peer environment with WCF Services.

Disconnected Queued Scenario:

8. NetMsmqBinding is required in a cross machine environment with secure and reliable queued communication. This uses MSMQ as transport.

Refer the following

 For further details on WS-* Standards, refer the following article

http://blogs.jinishans.com/2007/03/what-ws-standards-supported-by-wcf.html

References

1. http://www.topwcftutorials.net/2012/07/WCF-Service-Bindings.html

2. http://blogs.jinishans.com/2007/03/what-ws-standards-supported-by-wcf.html

3. http://www.pradyblog.com/index.php/2012/09/03/wcf-faqs-part-1/