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Posts Tagged ‘WCF


Though Performance blocking and Sluggishness are the tailbacks for any application, we can easily overcome these bottlenecks by using asynchronous programming. But old-style practice for asynchronous programming is not way easy enough to write, debug and maintain. So what is the contemporary approach??

Well, In my view, this is Task based asynchronous programming, which is updated in .Net 4.5 through the use of keywords await and async. But what do async and await do? async and await are the way of controlling continuation. When a method uses the async keyword, it means it is an asynchronous method, which might have an await keyword inside, and if it has an await keyword, async will activate it. So, simply async activates the await, from which point, the asynchronous has been started. There is a nice explanation that has been given here.

In WCF we can also consider an asynchronous operation while the service operation creates a delaying call. There are three ways to implement asynchronous operations

In this post I am going to use task-based asynchronous operation since this is the most contemporary strategy.

Okay. Let’s move to the code,

A very simple Service contract such as,

 [ServiceContract]
 public interface IMessage
 {
     [OperationContract]
     Task<string> GetMessages(string msg);
 }

With this simple contract, the implementation is just straight forward,

 public class MessageService : IMessage
 {
    async Task<string> IMessage.GetMessages(string msg)
    {
       var task = Task.Factory.StartNew(() =>
                                      {
                                          Thread.Sleep(10000);
                                          return "Return from Server : " + msg;
                                      });
      return await task.ConfigureAwait(false);
    }
 }

Here, the method is marked with the async keyword, which means it might use await keyword inside. It also means that the method will be able to suspend and then resume asynchronously at await points. Moreover, it points the compiler to boost the outcome of the method or any exceptions that may happen into the return type.

Service hosting,

 class Program
 {
     static void Main(string[] args)
     {
        var svcHost = new ServiceHost(typeof (MessageService));
        Console.WriteLine("Available Endpoints :\n");
        svcHost.Description.Endpoints.ToList().ForEach(endpoints=> Console.WriteLine(endpoints.Address.ToString()));
        svcHost.Open();
        Console.ReadLine();
     }
 }

Finally Service Configuration,

<?xml version="1.0"?>
 <configuration>
     <system.serviceModel>
       <services>
          <service name="Rashim.RND.WCF.Asynchronous.ServiceImplementation.MessageService">
             <host>
                 <baseAddresses>
                     <add baseAddress="net.Tcp://localhost:8732/"/>
                     <add baseAddress="http://localhost:8889/"/>
                 </baseAddresses>
             </host>
             <endpoint address="Tcp" binding="netTcpBinding" contract="Rashim.RND.WCF.Asynchronous.Services.IMessage"/>
             <endpoint address="Http" binding="basicHttpBinding" contract="Rashim.RND.WCF.Asynchronous.Services.IMessage">
                 <identity>
                      <dns value="localhost"/>
                 </identity>
             </endpoint>
             <endpoint address="mex" binding="mexTcpBinding" contract="IMetadataExchange"/>
             <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange"/>
          </service>
       </services>
       <behaviors>
          <serviceBehaviors>
             <behavior>
                 <serviceMetadata/>
             </behavior>
          </serviceBehaviors>
       </behaviors>
     </system.serviceModel>
     <startup><supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5"/></startup>
</configuration>

After Configuring the service,we need to configure the client app to consume the service.

A simple Console Application(Client),

class Program
 {
    static void Main(string[] args)
    {
       GetResult();
       Console.ReadLine();
    }

    private async static void GetResult()
    {
       var client = new Proxy("BasicHttpBinding_IMessage");
       var task = Task.Factory.StartNew(() => client.GetMessages("Hello"));
       var str = await task;
       str.ContinueWith(e =>
       {
          if (e.IsCompleted)
           {
              Console.WriteLine(str.Result);
           }
       });
      Console.WriteLine("Waiting for the result");
    }
 }

Client Configuration,

<?xml version="1.0"?>
 <configuration>
   <system.serviceModel>
     <bindings>
       <basicHttpBinding>
         <binding name="BasicHttpBinding_IMessage" />
       </basicHttpBinding>
     </bindings>
     <client>
       <endpoint address="http://localhost:8889/Http" binding="basicHttpBinding"
          bindingConfiguration="BasicHttpBinding_IMessage" contract="Rashim.RND.WCF.Asynchronous.Services.IMessage"
           name="BasicHttpBinding_IMessage" />
     </client>
   </system.serviceModel>
 </configuration>

Finally,proxy class is given below through which the client will consume the services.

public class Proxy : ClientBase<IMessage>, IMessage
 {
    public Proxy()
    {
    }
    public Proxy(string endpointConfigurationName) :
    base(endpointConfigurationName)
    {
    }
    public Task<string> GetMessages(string msg)
    {
      return Channel.GetMessages(msg);
    }
 }

That’s it. Very easy stuff though. You can download the source code from here.

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In WCF, a service can call back to its clients. That is to say that, at the time of call back, the service behaves as a client as well as the client becomes the service, and the client must assist hosting the call back object. To support call back, the underlying transport of the binding must support bidirectional. So, for the nature of connectionless, we cannot use all bindings for the call back operation. For instance, BasicHttpBinding or WsHttpBinding does not support callback while WsDualHttpBinding supports it, because this binding establishes two HTTP channel to do that; one for client to service another for service to client. Also, NetTcpBinding and NetNamedPipeBinding supports callback since their underlying transport is bidirectional.

Callback service can be supported by using CallbackContract property in the ServiceContract attribute. Only one callback contract is allowed for a service contract. After defining a callback contract, we require to set up the client for up keeping the callback and also to offer the callback endpoint to the service for each and every call.

In the example given below, the callback contract defines the operations to which the service can call on the client endpoint

public interface INotificationServiceCallBack
{
    [OperationContract(IsOneWay = true)]
    void OnNotificationSend(string message);
}

The implementation of this Service Contract,

[CallbackBehavior(ConcurrencyMode = ConcurrencyMode.Reentrant)]
public class NotificationServiceCallBack : INotificationServiceCallBack
{
    public void OnNotificationSend(string message)
    {
        Console.WriteLine(message);
        Console.ReadLine();
    }
}

Here CallbackBehavior refers how the callback of this operation will act which is similar to ServiceBehavior.

And the service contract has been defined like the way given below,

[ServiceContract(CallbackContract = typeof(INotificationServiceCallBack))]
public interface INotificationServices
{
    [OperationContract]
    void SendNotification(string message);
}

To make a way around for the service to call, clients must expose an endpoint to the service. This has been done by the following way,

public class Program
{
    public static INotificationServices Proxy
    {
        get
        {
            var ctx = new InstanceContext(new NotificationServiceCallBack());
            return new DuplexChannelFactory<INotificationServices>(ctx, "WSDualHttpBinding_INotificationServices").CreateChannel();
        }
    }
    static void Main(string[] args)
    {
        Proxy.SendNotification("Are u ready?");
        Console.ReadLine();
    }
}

Here InstanceContext is the execution scope of inner most service instance. It provides a constructor that takes the service instance to the host.

And now service implementation,

public class NotificationService : INotificationServices
{
    public INotificationServiceCallBack Proxy
    {
        get
        {
            return OperationContext.Current.GetCallbackChannel<INotificationServiceCallBack>();
        }
    }
    public void SendNotification(string message)
    {
        Console.WriteLine("\nClient says :" + message);
        Proxy.OnNotificationSend("Yes");
    }
}

In the above example, we see that the service has the proxy of INotificationServiceCallBack and call its operation which the clients will handle.

That’s it. Now the total code portion that i have used here has been given,

Services and Implementations,

public interface INotificationServiceCallBack
{
    [OperationContract(IsOneWay = true)]
    void OnNotificationSend(string message);
}

 

[ServiceContract(CallbackContract = typeof(INotificationServiceCallBack))]
public interface INotificationServices
{
    [OperationContract]
    void SendNotification(string message);
}
[CallbackBehavior(ConcurrencyMode = ConcurrencyMode.Reentrant)]
public class NotificationServiceCallBack : INotificationServiceCallBack
{
    public void OnNotificationSend(string message)
    {
        Console.WriteLine(message);
        Console.ReadLine();
    }
}
public class NotificationService : INotificationServices
{
    public INotificationServiceCallBack Proxy
    {
        get
        {
            return OperationContext.Current.GetCallbackChannel<INotificationServiceCallBack>();
        }
    }

    public void SendNotification(string message)
    {
        Console.WriteLine("\nClient says :" + message);
        Proxy.OnNotificationSend("Yes");
    }
}

Server and its configuration,

class Program
{
    static void Main(string[] args)
    {
        var svcHost = new ServiceHost(typeof(NotificationService));
        svcHost.Open();
        Console.WriteLine("Available Endpoints :\n");
        svcHost.Description.Endpoints.ToList().ForEach(endpoint => Console.WriteLine(endpoint.Address.ToString()));
        Console.ReadLine();
        svcHost.Close();
    }
}
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <system.web>
    <compilation debug="true" />
  </system.web>
  <system.serviceModel>
    <services>
      <service name="Rashim.RND.WCF.CallBack.Services.NotificationService">
        <host>
          <baseAddresses>
            <add baseAddress = "net.Tcp://localhost:8732/"/>
            <add baseAddress="http://localhost:8888"/>
          </baseAddresses>
        </host>
        <endpoint address="CallbackService" binding="netTcpBinding" contract="Rashim.RND.WCF.CallBack.Interfaces.INotificationServices"/>
        <endpoint address="CallbackService" binding="wsDualHttpBinding" contract="Rashim.RND.WCF.CallBack.Interfaces.INotificationServices"/>
        <endpoint address="mex" binding="mexTcpBinding" contract="IMetadataExchange" />
        <endpoint address="http://localhost:8888/mex" binding="mexHttpBinding" contract="IMetadataExchange" />
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior>
          <serviceMetadata />
          <serviceDebug includeExceptionDetailInFaults="False" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
  </system.serviceModel>
</configuration>

Client and its Configuration,

public class Program
{
    public static INotificationServices Proxy
    {
        get
        {
            var ctx = new InstanceContext(new NotificationServiceCallBack());
            return new DuplexChannelFactory<INotificationServices>(ctx, "WSDualHttpBinding_INotificationServices").CreateChannel();
        }
    }
    static void Main(string[] args)
    {
        Proxy.SendNotification("Are u ready?");
        Console.ReadLine();
    }
}
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <system.serviceModel>
    <client>
      <endpoint address="http://localhost:8888/CallbackService" binding="wsDualHttpBinding" contract="Rashim.RND.WCF.CallBack.Interfaces.INotificationServices" name="WSDualHttpBinding_INotificationServices">
      </endpoint>
      <endpoint address="net.tcp://localhost:8732/CallbackService" binding="netTcpBinding"
 contract="Rashim.RND.WCF.CallBack.Interfaces.INotificationServices" name="NetTcpBinding_INotificationServices">
      </endpoint>
    </client>
  </system.serviceModel>
</configuration>

When working with distributed application, securing communication between the client and the service is a very vital issue. Windows Communication Foundation provides the facility of transfer security which is responsible for ensuring the integrity and confidentiality of service messages, and also responsible for providing authentication. Transfer security in WCF is achieved through the use of either transport security or message security. Transport-layer security provides integrity and confidentiality, while message-layer security provides a variety of passes which are not possible with transport security mechanisms. When using transport security, user credentials are transport-dependent, which allows fewer authentication options compared to message security. And each transport protocol has its own way for passing credentials and handling message guard. But SSL is the most common approach for encrypting and signing the contents sent over HTTPS. Here I will explain how to configure WCF Services and Clients to communicate over HTTPS by using self-signed Certificates.

When I intend to write any technical stuff, my intention always goes to start with a very simple example as well as gives an overview with the necessary things related to it. There is no difference this time as well. So for the purposes of this blog post I am going to organize it with Self-Signed Certificate Creation, Services and its Configuration, Clients and its Configuration. Please be noted that I would like to use custom binding for the code examples given here.

Self-Signed Certificate Creation

In Certificate based communication, we need to use two certificates for the client and server to authenticate each other. To make those certificates I would like to use the “MakeCert.exe” utility with the following arguments

makecert -pe -ss My -sr LocalMachine -a sha1 -sky exchange -n CN=ServerCertificate

makecert -pe -ss MY -sr LocalMachine -a sha1 -sky exchange -n CN=ClientCerttificate

Image

The complete specification of this is available here

Now,

First bring up the Microsoft Management Console by launching mmc.exe which allows us to browse the local machine’s cache of certificates.

Image

Next add the Certificates MMC Snap-in and select Computer account

Image

Navigate to the “Personal” node to see ClientCertificate and ServerCertificate.

Image

It is also required to export the certificates from the certificate store and import the copies of those into the TrustedPeople store so that WCF can find them for validation purposes.

Since I would like to use IIS hosting, we need to configure IIS for https. To do that,

  • Open IIS Manager
  • Select Default Web site and open its property window
  • Click the Edit Binding.

Image

Click Add and select HTTPS and then Select ServerCertificate that you have created earlier

Image

Okay done .Everything is okay now.

Service and its Configuration

I have used here very simple service which is “Feedback” service. The service contract looks like,

[ServiceContract]
public interface IFeedback
{
    [OperationContract]
    string GiveFeedback(string question);
}

With such a simple contract the implementation is just straight forward

public class Feedback : IFeedback
{
    public string GiveFeedback(string question)
    {
        var feedback = question + " : This is very funny stuff";
        return feedback;
    }
}

The configuration file for this Service is given below,

<configuration>
  <system.web>
    <compilation debug="true" targetFramework="4.0" />
  </system.web>
  <system.serviceModel>
    <services>
      <service
      name="Rashim.RND.WCF.SecureCommunication.WcfService.Feedback"
      behaviorConfiguration="MyCustomBehavior">
        <endpoint address=""
        binding="customBinding"
        contract="Rashim.RND.WCF.SecureCommunication.Interfaces.IFeedback"
        bindingConfiguration="MyCustomBinding"/>
        <endpoint
        address="mex"
        binding="mexHttpsBinding"
        contract="IMetadataExchange" />
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name="MyCustomBehavior">
          <serviceMetadata httpsGetEnabled="true" />
          <serviceCredentials>
            <clientCertificate>
              <authentication
              certificateValidationMode="PeerTrust"
              trustedStoreLocation="LocalMachine" />
            </clientCertificate>
            <serviceCertificate
            findValue="ServerCert"
            x509FindType="FindBySubjectName"
            storeLocation="LocalMachine"
            storeName="My"/>
          </serviceCredentials>
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <bindings>
      <customBinding>
        <binding name="MyCustomBinding"
        closeTimeout="00:20:00"
        openTimeout="00:20:00"
        receiveTimeout="00:20:00"
        sendTimeout="00:20:00">
          <security
          authenticationMode="CertificateOverTransport"
          requireSecurityContextCancellation="true"/>
          <httpsTransport/>
        </binding>
      </customBinding>
    </bindings>
    <serviceHostingEnvironment
    multipleSiteBindingsEnabled="false" />
  </system.serviceModel>
  <system.webServer>
    <modules runAllManagedModulesForAllRequests="false" />
    <directoryBrowse enabled="true" />
  </system.webServer>
</configuration>

To get a better idea about the different sections of this configuration file I would like to explain it a bit more,

<services>
  <service
  name="Rashim.RND.WCF.SecureCommunication.WcfService.Feedback"
  behaviorConfiguration="MyCustomBehavior">
    <endpoint
    address="" binding="customBinding"
    contract="Rashim.RND.WCF.SecureCommunication.Interfaces.IFeedback"
    bindingConfiguration="MyCustomBinding"/>
    <endpoint address="mex"
    binding="mexHttpsBinding"
    contract="IMetadataExchange" />
  </service>
</services>

In this above section we see that Custom behavior configuration and custom binding configuration has been used.

The custom behavior section is given below,

<behavior name="MyCustomBehavior">
  <serviceMetadata httpsGetEnabled="true" />
  <serviceCredentials>
    <clientCertificate>
      <authentication
      certificateValidationMode="PeerOrChainTrust"
      trustedStoreLocation="LocalMachine" />
    </clientCertificate>
    <serviceCertificate
    findValue="ServerCert"
    x509FindType="FindBySubjectName"
    storeLocation="LocalMachine"
    storeName="My"/>
  </serviceCredentials>
</behavior>

Here clientCertificate describes an X.509 certificate which has been used to validate a client to a service. At the same time, serviceCertificate specify an X.509 certificate that will be used to authenticate the service to clients. There is a detail explanations about this has been given here [^] [^].

And the custom binding configuration section is,

<binding name="MyCustomBinding"
closeTimeout="00:20:00"
openTimeout="00:20:00"
receiveTimeout="00:20:00"
sendTimeout="00:20:00">
  <security
  authenticationMode="CertificateOverTransport"
  requireSecurityContextCancellation="true">
  </security>
  <sslStreamSecurity requireClientCertificate="true"/>
  <httpsTransport/>
</binding>

We know that, WCF provides several modes by which clients and services verify to each other. We can create binding for these authentication modes through configuration or by code. Here I have used CertificateOverTransport which means the service is valid using an X.509 certificate at the transport layer.  And requireSecurityContextCancellation specifies whether security context should be cancelled and terminated when it is no longer required.

That’s it.Now try to  browse https://localhost/Feedback/Feedback.svc and you will get the following page

Image

Client and its Configuration

Once services have been implemented, the implementation of client is pretty simple. The client code has been given below,

System.Net.ServicePointManager.ServerCertificateValidationCallback += (se, cert, chain, sslerror) => true;

        var channel = new ChannelFactory<IFeedback>("FeedbackEndpoint");

        var client = channel.CreateChannel();

        var input = Console.ReadLine();

        while (input != null && input.ToLower() != "exit")
        {
            var feedback = client.GiveFeedback(input);
            Console.WriteLine(feedback);
            input = Console.ReadLine();
        }

The code above will trust any security certificate handed back from the server since it bypasses the SSL certificate validation. As the certificate I have used here is a self-signed certificate and it is not signed by a trusted CA, I need to make own validation logic to check for it .

So the configuration file for the client is,

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <system.serviceModel>
    <bindings>
      <customBinding>
        <binding name="MyCustomBinding">
          <security authenticationMode="CertificateOverTransport"/>
          <textMessageEncoding />
          <httpsTransport />
        </binding>
      </customBinding>
    </bindings>
    <behaviors>
      <endpointBehaviors>
        <behavior name="MyCustomBehavior">
          <clientCredentials>
            <clientCertificate
            findValue="ClientCert"
            storeLocation="LocalMachine"
            storeName="My"
            x509FindType="FindBySubjectName" />
            <serviceCertificate>
              <authentication
              certificateValidationMode="PeerOrChainTrust"/>
            </serviceCertificate>
          </clientCredentials>
        </behavior>
      </endpointBehaviors>
    </behaviors>
    <client>
      <endpoint
      address="https://localhost/FeedbackService/Feedback.svc"
      binding="customBinding"
      bindingConfiguration="MyCustomBinding"
      contract="Rashim.RND.WCF.SecureCommunication.Interfaces.IFeedback"
      behaviorConfiguration="MyCustomBehavior"
      name="FeedbackEndpoint"/>
    </client>
  </system.serviceModel>
</configuration>

That’s it. I think this would help you while you will be working with the Certificate based communication.

Source code is available here.


Routing is the process of picking and directs messages to the proper endpoints through transitional. That is, the purpose of the Routing Service is to receive messages from clients and frontward those messages to the suitable downstream services. Downstream services may be hosted on the same machine or distributed across several machines in a server farm. Routing provides the facility of isolating these services directly accessible from the client application through router. Client application have knowledge of only one service which further routes request from the client to the specific service.

WCF 4.0 introduces a new service called Routing Service that acts as a message router which has a built-in way for routing WCF service calls. This Routing Service is available under the new assembly System.ServiceModel.Routing.  You will find the complete article here.

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