WCF 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.

WCF Runtime

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

Transport Channels

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

Protocol Channels

– Implements SOAP based protocol by processing and possibly modifying message. e.g. WS-Security and WS-Reliability.

WCF 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

Service Contract

Service contracts describe the operation that service can provide. For Eg, a Service provide 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.

To know more on Service contract see Service contract tutorial.

Data Contract

Data contract describes the custom data type which is exposed to the client. This defines the data types, that 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 e.g. 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.

To know more on DataContract see DataContract tutorial.

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.

To know more on Message Contract see Message contract tutorial.

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 identity, what error has occurred.

To know more on Fault Contract see Fault Contract tutorial.

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();

WCF Binding and Behavior

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 its 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.cording 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.

Example:

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 specifies 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.

WCF EndPoint

WCF Service is a program that exposes a collection of Endpoints. Each Endpoint is a portal for communicating with the world.

All the WCF communications are take place through end point. End point consists of three components.

Address

Basically URL, specifies where this WCF service is hosted .Client will use this url to connect to the service. e.g

http://localhost:8090/MyService/SimpleCalculator.svc

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, or 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

 

 

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

Example:

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>

Difference between WCF and Web service

Web service is a part of WCF. WCF offers much more flexibility and portability to develop a service when comparing to web service. Still we are having more advantages over Web service, following table provides detailed difference between them.

Features Web Service WCF
Hosting It can be hosted in IIS It can be hosted in IIS, windows activation service, Self-hosting, Windows service
Programming [WebService] attribute has to be added to the class [ServiceContraact] attribute has to be added to the class
Model [WebMethod] attribute represents the method exposed to client [OperationContract] attribute represents the method exposed to client
Operation One-way, Request- Response are the different operations supported in web service One-Way, Request-Response, Duplex are different type of operations supported in WCF
XML System.Xml.serialization name space is used for serialization System.Runtime.Serialization namespace is used for serialization
Encoding XML 1.0, MTOM(Message Transmission Optimization Mechanism), DIME, Custom XML 1.0, MTOM, Binary, Custom
Transports Can be accessed through HTTP, TCP, Custom Can be accessed through HTTP, TCP, Named pipes, MSMQ,P2P, Custom
Protocols Security Security, Reliable messaging, Transactions

WCF Fundamentals

Windows Communication Foundation (Code named Indigo) is a programming platform and runtime system for building, configuring and deploying network-distributed services. It is the latest service oriented technology; Interoperability is the fundamental characteristics of WCF. It is unified programming model provided in .Net Framework 3.0. WCF is a combined features of Web Service, Remoting, MSMQ and COM+. WCF provides a common platform for all .NET communication.

 

Advantage

  1. WCF is interoperable with other services when compared to .Net Remoting,where the client and service have to be .Net.
  2. WCF services provide better reliability and security in compared to ASMX web services.
  3. In WCF, there is no need to make much change in code for implementing the security model and changing the binding. Small changes in the configuration will make your requirements.
  4. WCF has integrated logging mechanism, changing the configuration file settings will provide this functionality. In other technology developer has to write the code.