Saturday, 17 January 2015

WCF Fundamental



In this part of tutorial you are going to learn about some fundamental concepts in WCF. These concepts and terms will be used throughout this tutorial.
1)    End Point


End Point

WCF Service is a program that exposes a collection of Endpoints. Each end point is a portal for communicating with the world.
All the WCF communications are take place through end point. End point consists of three components.

1. Address

Basically URL specifies where this WCF service is hosted. Client will use this URL to connect to the service. Ex.

 

2. Binding

Binding will describes how client will communicate with service. There are different protocols available for the WCF to communicate to the Client. You can mention the protocol type based on your requirements.
A binding has several characteristics, including the following:
  • Transport - Defines the base protocol to be used like HTTP, Named Pipes, TCP, and MSMQ are some type of protocols.
  • Encoding (Optional) - Three types of encoding are available - Text, Binary, and Message Transmission Optimization Mechanism (MTOM). MTOM is an interoperable message format that allows the effective transmission of attachments or large messages (greater than 64K).
  • Protocol (Optional) - Defines information to be used in the binding such as Security, transaction or reliable messaging capability.
The following table gives some list of protocols supported by WCF binding.
Binding
Description
BasicHttpBinding
Basic Web service communication. No security by default
WSHttpBinding
Web services with WS-* support. Supports transactions
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

 

3. Contract

Collection of operation that specifies what the endpoint will communicate with outside world. Usually name of the Interface will be mentioned in the Contract, so the client application will be aware of the operations which are exposed to the client. Each operation is a simple exchange pattern such as one-way, duplex and request/reply.
Below figure illustrate the functions of Endpoint


Endpoints will be mentioned in the web.config file on the created service.
<system.serviceModel>
<services>
      <service name="MathService"
        behaviorConfiguration="MathServiceBehavior">
       <endpoint
address=http://localhost:8090/MyService/MathService.svc contract="IMathService"
binding="wsHttpBinding"/> 
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name="MathServiceBehavior">
          <serviceMetadata httpGetEnabled="True"/>
          <serviceDebug includeExceptionDetailInFaults="true" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
  </system.serviceModel>


Binding and Behavior

1. Binding

Simple definition for Binding describes how the client will communicate with service. We can understand with an example.
Consider a scenario say, I am creating a service that has to be used by two type of client. One of the client will access SOAP using http and other client will access Binary using TCP. How it can be done? With Web service it is very difficult to achieve, but in WCF it’s just we need to add extra endpoint in the configuration file.
<system.serviceModel>
    <services>
      <service name="MathService"
                behaviorConfiguration="MathServiceBehavior">
        <endpoint address="http://localhost:8090/MyService/MathService.svc" 
               contract="IMathService"
               binding="wsHttpBinding"/>
        <endpoint address="net.tcp://localhost:8080/MyService/MathService.svc" 
               contract="IMathService"
               binding="netTcpBinding"/> 
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name="MathServiceBehavior">
          <serviceMetadata httpGetEnabled="True"/>
          <serviceDebug includeExceptionDetailInFaults="true" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
  </system.serviceModel>
  
See how simple it is in WCF. Microsoft is making everything simple according to its scope: common behaviors affect all endpoints globally, service behaviors affect only service-related aspects, endpoint behaviors affect only endpoint-related properties, and operation-level behaviors affect particular operations.

 

Ex:

In the below configuration information, I have mentioned the Behavior at Service level. In the service behavior I have mention the servieMetadata node with attribute httGetEnabled='true'. This attribute will specify the publication of the service metadata. Similarly we can add more behavior to the service.
<system.serviceModel>
    <services>
      <service name="MathService"
        behaviorConfiguration="MathServiceBehavior">
        <endpoint address="" contract="IMathService"
          binding="wsHttpBinding"/>
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name="MathServiceBehavior">
          <serviceMetadata httpGetEnabled="True"/>
          <serviceDebug includeExceptionDetailInFaults="true" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
  </system.serviceModel>

 

Note:

Application can be controlled either through coding, configuring or through combination of both. Specification mention in the configuration can also be overwritten in code.


Contracts and Service Host

Contracts:

In WCF, all services are exposed as contracts. Contract is a platform-neutral and standard way of describing what the service does. Mainly there are four types of contracts available in WCF:

1. Service Contract

Service contracts describe the operation that service can provide. For Ex, a Service provides to know the temperature of the city based on the zip code, this service is called as Service contract. It will be created using Service and Operational Contract attribute.

2. Data Contract

Data contract describes the custom data type which is exposed to the client. This defines the data types, which are passed to and from service. Data types like int, string are identified by the client because it is already mention in XML schema definition language document, but custom created class or data types cannot be identified by the client ex. Employee data type. By using DataContract we can make client to be aware of Employee data type that are returning or passing parameter to the method.

3. Message Contract

Default SOAP message format is provided by the WCF runtime for communication between Client and service. If it is not meeting your requirements then we can create our own message format. This can be achieved by using Message Contract attribute.

4. Fault Contract

Suppose the service I consumed is not working in the client application. I want to know the real cause of the problem. How I can know the error? For this we are having Fault Contract. Fault Contract provides documented view for error occurred in the service to client. This helps us to easy identify, what error has occurred.

 

Service Host:

Service Host object is in the process of hosting the WCF service and registering endpoints. It loads the service configuration endpoints, apply the settings and start the listeners to handle the incoming request. System.ServiceModel.ServiceHost namespace hold this object. This object is created while self-hosting the WCF service.
In the below example you can find that WCF service is self-hosted using console application.
//Creating uri for the hosting the service
Uri uri = new Uri("http://localhost/CategoryService");
 
//Creating the host object for MathService
ServiceHost host = new ServiceHost(typeof(CategoryService), uri);
 
//Adding endpoint to the Host object
host.AddServiceEndpoint(typeof(ICategoryService),new WSHttpBinding(), uri);
host.Open(); //Hosting the Service
Console.WriteLine("Waiting for client invocations");
Console.ReadLine();
host.Close();


Message and Channel

Message:

WCF Message is the unit of data exchange between client and service. It consists of several parts, including a body and headers.

1. WCF Runtime

WCF runtime is the set of object responsible for sending and receiving message. For example formatting the message, applying security, transmitting and receiving message using various protocol.

Channels:

Channels are the core abstraction for sending message to and receiving message from an Endpoint. Broadly we can categories channels as:

1. Transport Channels

Handles sending and receiving message from network. Protocols like HTTP, TCP name pipes and MSMQ.

2. Protocol Channels

Implements SOAP based protocol by processing and possibly modifying message. Ex. WS-Security and WS-Reliability.


WCF Client and Metadata

WCF Client:

WCF client is a client application creates to expose the service operations as method. Any application can host a WCF client, including an application that host a service. Therefore it is possible to create a service that includes WCF clients of other services.
A client application is a managed application that uses a WCF client to communicate with another application. To create a client application for a WCF service requires the following steps:
1.    Get the Proxy class and service end point information:
Using SvcUtil.exe we can create proxy class for the service and configuration information for endpoints. Example type the following sentence in the Visual studio command prompt, this will generate the class file and configuration file which contain information about the endpoints.
svcutil /language:vb /out:ClientCode.vb /config:app.config http://localhost:8090/MyService/SimpleCalculator.svc?wsdl
2.    Call operations:
Add this class files in the client application. Then create the object for this class and invoke the service operation. Configuration information we got from the above step has to be added to the client application configuration file. When the client application calls the first operation, WCF automatically opens the underlying channel. This underlying channel is closed, when the object is recycled.
//Creating the proxy on client side
MyCalculatorServiceProxy.MyServiceProxy proxy 
         = new MyCalculatorServiceProxy.MyServiceProxy();
Console.WriteLine("Counter: " + proxy.MyMethod());
3.    Close the WCF client object:
After using the object created in the above steps, we have to dispose the object. Channel will be closed with the service, when the object is cleared.

 

Metadata:

Characteristics of the service are described by the metadata. This metadata can be exposed to the client to understand the communication with service. Metadata can be set in the service by enabling the ServiceMetadata node inside the servcieBehaviour node of the service configuration file.
<system.serviceModel>
    <services>
      <service name="MathService"
        behaviorConfiguration="MathServiceBehavior">
        <endpoint address="" contract="IMathService"
          binding="wsHttpBinding"/>
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name="MathServiceBehavior">
    <serviceMetadata httpGetEnabled="True"/>
          <serviceDebug includeExceptionDetailInFaults="true" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
  </system.serviceModel>

This metadata can be viewed while creating WCF client application using SvcUtil.exe




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