As you all know, Windows services run in the background, and users can start or configure them through the services panel in Windows. In order to do the logging to check what the service is doing, you can log messages in the database, message queues, event logs etc. But sending messages back and forth between any Windows application to show real time task execution is only possible via TCP socket connection, remoting etc.

In this post I will show you ways of logging messages from Windows Services to Windows form based Monitor application using WCF Duplex Messaging.

Step 1: Creating WCF Service Library

1. Create a WCF Service Library project from Visual Studio
2. Add a Service Contract interface named as "IMonitorService"

  [ServiceContract(Name = "IMonitorService",SessionMode = SessionMode.Required,CallbackContract = typeof(IMonitorServiceCallback))]

public interface IMonitorService
{
   [OperationContract]
   void Login();

   [OperationContract]
   void Logout();

   [OperationContract]
   void LogMessages(String message);
}

In the above code, I have created an interface and provided three methods of signature: Login, Logout and LogMessages. Login and Logout will be used to connect or disconnect to the Service and LogMessages will be used to log messages to the client. You will notice that in the ServiceContract attribute I have specified CallbackContract which actually holds the type of information of the Call back contract interface through which when the client invokes any of the login, logout or log messages, the server can get the callbackcontract object and sends the response back to client itself.

3. Here is the code for IMonitorServiceCallback contract interface.

public interface IMonitorServiceCallback
{
 [OperationContract]
 void NotifyClient(String message);
}

 In the above code there is a callback contract interface which holds one method signature "NotifyClient" which takes string as a parameter. Server can call NotifyClient method and send messages to the connected clients.

4. Now create another class MonitorService and implement IMonitorService interface. Following code shows the complete.

5. Below code shows the complete implementation. 

[ServiceBehavior(
        ConcurrencyMode = ConcurrencyMode.Reentrant,
        InstanceContextMode = InstanceContextMode.PerCall)]
    public class MonitorService : IMonitorService
    {
        public static List<IMonitorServiceCallback> callBackList = new List<IMonitorServiceCallback>();

        public MonitorService()
        {
        }
        public void Login()
        {
            IMonitorServiceCallback callback = OperationContext.Current.GetCallbackChannel<IMonitorServiceCallback>();
            if (!callBackList.Contains(callback))
            {
                callBackList.Add(callback);

            }
         }

        public void Logout()
        {
            IMonitorServiceCallback callback = OperationContext.Current.GetCallbackChannel<IMonitorServiceCallback>();
            if (callBackList.Contains(callback))
            {
                callBackList.Remove(callback);

            }

            callback.NotifyClient("You are Logged out");
        }

        public void LogMessages(string message)
        {
            foreach (IMonitorServiceCallback callback in callBackList)
            {
                callback.NotifyClient(message);
            }
        }

 The above code shows the implementation of the IMonitorService interface.

Step 2: Create Windows Service project and use WCF Service Library

1. Create a new "Windows Service" project using Visual Studio.
2. In the Start menu, write some code to let service app do some work.
3. Add a project reference of the WCF Service Application
4. Initialize the ServiceHost object of WCF framework 
   
   

   ServiceHost host = new ServiceHost(typeof(MonitorService));
      host.Open();
   

   5. Implement the LogMessage method and notify callback contracts.

  foreach (IMonitorServiceCallback callback in MonitorService.callBackList)
  {
        callback.NotifyClient(message);
  }

       6. App.config for Windows Service

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <system.web>
    <compilation debug="true" />
  </system.web>
  <system.serviceModel>
    <bindings>
      <netTcpBinding>
        <binding name="DefaultNetTCPBinding" receiveTimeout="Infinite">
          <reliableSession inactivityTimeout="Infinite" />
        </binding>
      </netTcpBinding>
    </bindings>
    <services>
      <service name="MonitorService">
        <host>
          <baseAddresses>
            <add baseAddress="net.tcp://localhost:9909/MonitorService/" />
          </baseAddresses>
        </host>
        <!-- Service Endpoints -->
        <!-- Unless fully qualified, address is relative to base address supplied above -->
        <endpoint
         address="service"
         binding="netTcpBinding" bindingConfiguration="DefaultNetTCPBinding"
         contract="IMonitorService"
         name="TcpBinding" />
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior>
          <!-- To avoid disclosing metadata information, 
          set the value below to false and remove the metadata endpoint above before deployment -->
          <serviceMetadata httpGetEnabled="False"/>
          <!-- To receive exception details in faults for debugging purposes, 
          set the value below to true.  Set to false before deployment 
          to avoid disclosing exception information -->
          <serviceDebug includeExceptionDetailInFaults="False" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
  </system.serviceModel>

</configuration>

 Step 3: Developing Monitor Application

1. Create a new Windows Application project using Visual Studio.
2. Add RichTextBox control to log messages
3. Add two buttons connect and disconnect.
4. Now Add the WCF Service reference
5. Implement Login, Logout and NotifyClient messages
6. Add following code in the Login method

            try
            {
                client = new MonitorServiceClient(new InstanceContext(this), "TcpBinding");
                client.Open();
                client.Login();
                WriteTextMessage("Monitor App successfully connected to the Windows Service for logging messages");
            }
            catch (Exception ex)
            {
                WriteTextMessage("Couldn't connect to the Service, cause " + ex.Message); 
            }

       7. Add the following code in the Logout nethod

   client.Close();

       8. Add the following code in the NotifyClient method. 

public void LogMessage(string message)
        {

            if (this.InvokeRequired == false)
            {

                this.BeginInvoke(new WriteMessage(WriteTextMessage),message);
            }
            else
            {
                this.Invoke(new WriteMessage(WriteTextMessage), message);
            }
        }

9. Since the application thread is different, so we need to invoke the WriteTextMessage using BeginInvoke. In that case I have declared a delegate with the same method signature as of WriteTextMessage and set messages in the RichTextBox control. 

public delegate void WriteMessage(String str);

        public void WriteTextMessage(String str)
        {
            rchTextBox.Text += str + "\n";
            rchTextBox.ScrollToCaret();
        }

        10. App.config for Monitor App

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="DatabaseServer" value=".\sqlexpress"/>

  </appSettings>
  <system.serviceModel>
    <bindings>
      <netTcpBinding>
        <binding name="TcpBinding" closeTimeout="00:01:00" openTimeout="00:01:00"
          receiveTimeout="00:10:00" sendTimeout="00:01:00" transactionFlow="false"
          transferMode="Buffered" transactionProtocol="OleTransactions"
          hostNameComparisonMode="StrongWildcard" listenBacklog="10" maxBufferPoolSize="524288"
          maxBufferSize="65536" maxConnections="10" maxReceivedMessageSize="65536">
          <readerQuotas maxDepth="32" maxStringContentLength="8192" maxArrayLength="16384"
            maxBytesPerRead="4096" maxNameTableCharCount="16384" />
          <reliableSession ordered="true" inactivityTimeout="00:10:00"
            enabled="false" />
          <security mode="Transport">
            <transport clientCredentialType="Windows" protectionLevel="EncryptAndSign" />
            <message clientCredentialType="Windows" />
          </security>
        </binding>
      </netTcpBinding>
      <wsDualHttpBinding>
        <binding name="WSDualHttpBinding_IMonitorService" closeTimeout="00:01:00"
          openTimeout="00:01:00" receiveTimeout="00:10:00" sendTimeout="00:01:00"
          bypassProxyOnLocal="false" transactionFlow="false" hostNameComparisonMode="StrongWildcard"
          maxBufferPoolSize="524288" maxReceivedMessageSize="65536" messageEncoding="Text"
          textEncoding="utf-8" useDefaultWebProxy="true">
          <readerQuotas maxDepth="32" maxStringContentLength="8192" maxArrayLength="16384"
            maxBytesPerRead="4096" maxNameTableCharCount="16384" />
          <reliableSession ordered="true" inactivityTimeout="00:10:00" />
          <security mode="Message">
            <message clientCredentialType="Windows" negotiateServiceCredential="true"
              algorithmSuite="Default" />
          </security>
        </binding>
      </wsDualHttpBinding>
    </bindings>
    <client>
      <endpoint address="net.tcp://localhost:9909/MonitorService/service"
        binding="netTcpBinding" bindingConfiguration="TcpBinding" contract="IMonitorService"
        name="TcpBinding">
        <identity>
          <userPrincipalName value="ovais" />
        </identity>
      </endpoint>
      <endpoint address="http://localhost:8732/Design_Time_Addresses/MonitorService/"
        binding="wsDualHttpBinding" bindingConfiguration="WSDualHttpBinding_IMonitorService"
        contract="IMonitorService" name="WSDualHttpBinding_IMonitorService">
        <identity>
          <dns value="localhost" />
        </identity>
      </endpoint>
    </client>
  </system.serviceModel>
</configuration>

 Step 4: Running solution

1. Install the service and start it
2. Start the Monitor app and click on connect
3. Once the service start it will send messages to client and real time logging is achieved.