Introduction to WCF
● 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
- WCF is interoperable with other services when compared to .Net Remoting,where the client and service have to be .Net.
- WCF services provide better reliability and security in compared to ASMX web services.
- 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.
- WCF has integrated logging mechanism, changing the configuration file settings will provide this functionality. In other technology developer has to write the code.
Disadvantage
Making right design for your requirement is little bit difficult. I will try to help you on solving these difficulties in the following article.
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 |
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>
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.
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.
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.
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.
Service contract describes the operation that service provide.
A Service can have more than one service contract but it should have at least one Service contract.
Service Contract can be define using [ServiceContract] and [OperationContract] attribute.
[ServiceContract] attribute is similar to the [WebServcie] attribute in the WebService and [OpeartionContract] is similar to the [WebMethod] in WebService.
● It describes the client-callable operations (functions) exposed by the service
● It maps the interface and methods of your service to a platform-independent description
● It describes message exchange patterns that the service can have with another party. Some service operations might be one-way; others might require a request-reply pattern
● It is analogous to the element in WSDL
To create a service contract you define an interface with related methods representative of a collection of service operations, and then decorate the interface with the ServiceContract Attribute to indicate it is a service contract. Methods in the interface that should be included in the service contract are decorated with the OperationContract Attribute.
[ServiceContract()]
public interface ISimpleCalculator
{
[OperationContract()]
int Add(int num1, int num2);
}
Once we define Service contract in the interface, we can create implement class for this interface.
public class SimpleCalculator : ISimpleCalculator
{
public int Add(int num1, int num2)
{
return num1 + num2;
}
}
Without creating the interface, we can also directly created the service by placing Contract in the implemented class. But it is not good practice of creating the service
[ServiceContract()]
public class SimpleCalculator
{
[OperationContract()]
public int Add(int num1, int num2)
{
return num1 + num2;
}
}
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.
A data contract is a formal agreement between a service and a client that abstractly describes the data to be exchanged.
Data contract can be explicit or implicit. Simple type such as int, string etc has an implicit data contract. User defined object are explicit or Complex type, for which you have to define a Data contract using [DataContract] and [DataMember] attribute.
A data contract can be defined as follows:
● It describes the external format of data passed to and from service operations
● It defines the structure and types of data exchanged in service messages
● It maps a CLR type to an XML Schema
● It defines how data types are serialized and deserialized. Through serialization, you convert an object into a sequence of bytes that can be transmitted over a network. Through deserialization, you reassemble an object from a sequence of bytes that you receive from a calling application.
● It is a versioning system that allows you to manage changes to structured data
We need to include System.Runtime.Serialization reference to the project. This assembly holds the DataContract and DataMember attribute.
Create user defined data type called Employee. This data type should be identified for serialization and deserialization by mentioning with [DataContract] and [DataMember] attribute.
[ServiceContract]
public interface IEmployeeService
{
[OperationContract]
Employee GetEmployeeDetails(int EmpId);
}
[DataContract]
public class Employee
{
private string m_Name;
private int m_Age;
private int m_Salary;
private string m_Designation;
private string m_Manager;
[DataMember]
public string Name
{
get { return m_Name; }
set { m_Name = value; }
}
[DataMember]
public int Age
{
get { return m_Age; }
set { m_Age = value; }
}
[DataMember]
public int Salary
{
get { return m_Salary; }
set { m_Salary = value; }
}
[DataMember]
public string Designation
{
get { return m_Designation; }
set { m_Designation = value; }
}
[DataMember]
public string Manager
{
get { return m_Manager; }
set { m_Manager = value; }
}
}
Implementation of the service class is shown below. In GetEmployee method we have created the Employee instance and return to the client. Since we have created the data contract for the Employee class, client will aware of this instance whenever he creates proxy for the service.
public class EmployeeService : IEmployeeService
{
public Employee GetEmployeeDetails(int empId)
{
Employee empDetail = new Employee();
//Do something to get employee details and assign to 'empDetail' properties
return empDetail;
}
}
Client side
On client side we can create the proxy for the service and make use of it. The client side code is shown below.
protected void btnGetDetails_Click(object sender, EventArgs e)
{
EmployeeServiceClient objEmployeeClient = new EmployeeServiceClient();
Employee empDetails;
empDetails = objEmployeeClient.GetEmployeeDetails(empId);
//Do something on employee details
}
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.
Message
Message is the packet of data which contains important information. WCF uses these messages to transfer information from Source to destination.
WCF uses SOAP(Simple Object Access Protocol) Message format for communication. SOAP message contain Envelope, Header and Body.SOAP envelope contails name, namespace,header and body element. SOAP Hear contain important information which are not directly related to message. SOAP body contains information which is used by the target.
Diagram Soap envelope
Message Pattern
It describes how the programs will exchange message each other. There are three way of communication between source and destination
- Simplex - It is one way communication. Source will send message to target, but target will not respond to the message.
- Request/Replay - It is two way communications, when source send message to the target, it will resend response message to the source. But at a time only one can send a message
- Duplex - It is two way communication, both source and target can send and receive message simultaniouly.
What is Message contract?
As I said earlier, WCF uses SOAP message for communication. Most of the time developer will concentrate more on developing the DataContract, Serializing the data, etc. WCF will automatically take care of message. On Some critical issue, developer will also require control over the SOAP message format. In that case WCF provides Message Contract to customize the message as per requirement.
WCF supports either RPC(Remote Procedure Call) or Message style operation model. In the RPC model, you can develop operation with Ref and out parameter. WCF will automatically create the message for operation at run time. In Message style operation WCF allows to customize the message header and define the security for header and body of the message.
Defining Message Contract
Message contract can be applied to type using MessageContract attribute. Custom Header and Body can be included to message using 'MessageHeader' and 'MessageBodyMember'atttribute. Let us see the sample message contract definition.
[MessageContract]
public class EmployeeDetails
{
[MessageHeader]
public string EmpID;
[MessageBodyMember]
public string Name;
[MessageBodyMember]
public string Designation;
[MessageBodyMember]
public int Salary;
[MessageBodyMember]
public string Location;
}
When I use this EmployeeDeatils type in the service operation as parameter. WCF will add extra header call 'EmpID' to the SOAP envelope. It also add Name, Designation, Salary, Location as extra member to the SOAP Body.
Rules :
You have to follow certain rules while working with Message contract
- When using Message contract type as parameter, Only one parameter can be used in service Operation
[OperationContract]
void SaveEmployeeDetails(EmployeeDetails emp);
- Service operation either should return Messagecontract type or it should not return any value
[OperationContract]
EmployeeDetails GetEmployeeDetails();
- Service operation will accept and return only message contract type. Other data types are not allowed.
[OperationContract]
EmployeeDetails ModifyEmployeeDetails(EmployeeDetails emp);
Note: If a type has both Message and Data contract, service operation will accept only message contract.
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.
Service that we develop might get error in come case. This error should be reported to the client in proper manner. Basically when we develop managed application or service, we will handle the exception using try- catch block. But these exceptions handlings are technology specific.
In order to support interoperability and client will also be interested only, what wents wrong? not on how and where cause the error.
By default when we throw any exception from service, it will not reach the client side. WCF provides the option to handle and convey the error message to client from service using SOAP 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 accorded in the service to client. This help as to easy identity the what error has accord. Let us try to understand the concept using sample example.
Step 1: I have created simple calculator service with Add operation which will throw general exception as shown below
//Service interface
[ServiceContract()]
public interface ISimpleCalculator
{
[OperationContract()]
int Add(int num1, int num2);
}
//Service implementation
public class SimpleCalculator : ISimpleCalculator
{
public int Add(int num1, int num2)
{
//Do something
throw new Exception("Error while adding number");
}
}
Step 2: On client side code. Exceptions are handled using try-Catch block. Even though I have capture the exception when I run the application. I got the message that exceptions are not handled properly.
try
{
MyCalculatorServiceProxy.MyCalculatorServiceProxy proxy
= new MyCalculatorServiceProxy.MyCalculatorServiceProxy();
Console.WriteLine("Client is running at " + DateTime.Now.ToString());
Console.WriteLine("Sum of two numbers... 5+5 =" + proxy.Add(5, 5));
Console.ReadLine();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
Console.ReadLine();
}
Step 3: Now if you want to send exception information form service to client, you have to use FaultException as shown below.
public int Add(int num1, int num2)
{
//Do something
throw new FaultException("Error while adding number");
}
Step 4: Output window on the client side is show below.
Step 5: You can also create your own Custom type and send the error information to the client using FaultContract. These are the steps to be followed to create the fault contract.
● Define a type using the data contract and specify the fields you want to return.
● Decorate the service operation with the FaultContract attribute and specify the type name.
● Raise the exception from the service by creating an instance and assigning properties of the custom exception.
Step 6: Defining the type using Data Contract
[DataContract()]
public class CustomException
{
[DataMember()]
public string Title;
[DataMember()]
public string ExceptionMessage;
[DataMember()]
public string InnerException;
[DataMember()]
public string StackTrace;
}
Step 7: Decorate the service operation with the FaultContract
[ServiceContract()]
public interface ISimpleCalculator
{
[OperationContract()]
[FaultContract(typeof(CustomException))]
int Add(int num1, int num2);
}
Step 8: Raise the exception from the service
public int Add(int num1, int num2)
{
//Do something
CustomException ex = new CustomException();
ex.Title = "Error Funtion:Add()";
ex.ExceptionMessage = "Error occur while doing add function.";
ex.InnerException = "Inner exception message from serice";
ex.StackTrace = "Stack Trace message from service.";
throw new FaultException(ex,"Reason: Testing the Fault contract") ;
}
Step 9: On client side, you can capture the service exception and process the information, as shown below.
try
{
MyCalculatorServiceProxy.MyCalculatorServiceProxy proxy
= new MyCalculatorServiceProxy.MyCalculatorServiceProxy();
Console.WriteLine("Client is running at " + DateTime.Now.ToString());
Console.WriteLine("Sum of two numbers... 5+5 =" + proxy.Add(5, 5));
Console.ReadLine();
}
catch (FaultException<MyCalculatorService.CustomException> ex)
{
//Process the Exception
}
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();
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