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A Remoting Event (Simple and Efficient for Enterprise Solutions)

, 21 Aug 2006 CPOL
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This article contains the simplest solutions for: the security problem for DelegateSerializationHolder, the IO problem, and the messaging speed problem. Note: Messaging speed problem will appear when your application has worked for a long time.

demo project Image

Background

I always had an interest in socket programming. I have created several chat applications and complex socket based applications. When I learned about events in Remoting I was so glad, and the first thing that I thought about was creating a chat application. But in the test, I met with some problems.

Problem 1

The first problem was a security exception:

System.Security.SecurityException: Type System.DelegateSerializationHolder 
and the types derived from it (such as System.DelegateSerializationHolder) 
are not permitted to be deserialized at this security level.

Security Exception Image

Solution 1

This problem was solved by adding the typeFilterLevel attribute with Full value to the formatter element of both configuration files.

<formatter ref="soap" typeFilterLevel="Full" />

Problem 2

But again, it did not work and an IO exception occurred:

System.Reflection.TargetInvocationException: 
Exception has been thrown by the target of an invocation. ---> 
System.IO.FileNotFoundException: Could not load file or assembly 
'Client, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' 
or one of its dependencies. The system cannot find the file specified.

This exception occurs while the request is deserialized at the server. The server tries to call the event handler whereas the event handler exists in the client assembly. Because the client assembly is not available at the server, the exception is thrown.

IO exception Image

Solution 2

An intermediate wrapper class, MarshalByRefObject will solve this problem. This wrapper class is located in the shared assembly, accessible for both the client and the server; therefore, a delegate can resolve the method's signature. In the client application, we will associate the shared object event with the WrapperMessageReceivedHandler method of the wrapper class and associate an event handler on the client with the MessageReceived event of the wrapper class.

Sequense of events Image

Why [OneWay] Attribute

Without defining the remote method as [OneWay], an exception will occur when the client is unreachable or has been disconnected without disassociating the event handler. By using [OneWay], no exception will occur on the client, but it will be in the invocation list of the server and, in longtime, will make your server slower to respond.

Solution 3

Instead of using the normal event invocation mechanism, you must invoke each delegate on your own, and if an exception occurs, you must disassociate the delegate from the invocation list of the event. In the end, you can remove the [OneWay] attribute.

Shared Class

/// <span class="code-SummaryComment"><summary></span>
/// Represents the method that will handle
/// the Remotable.RemoteClass.MessageReceived event.
/// <span class="code-SummaryComment"></summary></span>
/// <span class="code-SummaryComment"><param name="message">Received message</param></span>

[Serializable]
public delegate void MessageHandler(string message);

/// <span class="code-SummaryComment"><summary></span>
/// Shared remoting class that orchestrate messaging tasks 
/// <span class="code-SummaryComment"></summary></span>

public class RemoteClass:MarshalByRefObject
{

    /// <span class="code-SummaryComment"><summary></span>
    /// Occurs when a broadcast message received.
    /// <span class="code-SummaryComment"></summary></span>

    public event MessageHandler MessageReceived;
    /// <span class="code-SummaryComment"><summary></span>
    /// Initializes a new instance of the Remotable.RemoteClass class.
    /// <span class="code-SummaryComment"></summary></span>

    public RemoteClass()
    {
       
    }

    /// <span class="code-SummaryComment"><summary></span>
    /// Obtains a lifetime service object to control the lifetime policy for this
    /// instance.
    /// <span class="code-SummaryComment"></summary></span>
    /// <span class="code-SummaryComment"><returns></span>
    ///An object of type 
    ///System.Runtime.Remoting.Lifetime.ILease used to control
    ///the lifetime policy for this instance. This is the current lifetime service
    ///object for this instance if one exists; otherwise, a new lifetime service
    ///object initialized to the value of the 
    ///System.Runtime.Remoting.Lifetime.LifetimeServices.LeaseManagerPollTime
    ///property.
    ///null value means this object has to live forever.
    /// <span class="code-SummaryComment"></returns></span>

    public override object InitializeLifetimeService()
    {
        return null;
    }

    /// <span class="code-SummaryComment"><summary></span>
    /// Broadcast message to all clients
    /// <span class="code-SummaryComment"></summary></span>
    /// <span class="code-SummaryComment"><param name="message">message string</param></span>

    public void Send(string message)
    {
        if (MessageReceived != null)
        {
            MessageHandler messageDelegate = null;
            Delegate[] invocationList_ = null;
            try
            {
                invocationList_ = MessageReceived.GetInvocationList();
            }
            catch (MemberAccessException ex)
            {
                throw ex;
            }
            if (invocationList_ != null)
            {
                lock (this)
                {
                    foreach (Delegate del in invocationList_)
                    {
                        try
                        {
                            messageDelegate = (MessageHandler)del;
                            messageDelegate(message);
                        }
                        catch (Exception e)
                        {
                            MessageReceived -= messageDelegate;
                        }
                    }
                }
            }
        }
    }

Client Application

RemoteClass remoteClass;
WrapperClass wrapperClass;

private void Form1_Load(object sender, EventArgs e)
{
    //Configure remoting.

    RemotingConfiguration.Configure(Application.StartupPath + 
                          "\\Client.exe.config",false);

    // Create a proxy from remote object.

    remoteClass = (RemoteClass)Activator.GetObject(typeof(RemoteClass), 
                   "http://localhost:8080/Chat");
    //Create an instance of wrapper class.

    wrapperClass = new WrapperClass();
  
    //Associate remote object event with wrapper method.

    remoteClass.MessageReceived += new 
          MessageHandler(wrapperClass.WrapperMessageReceivedHandler);
    //Associate wrapper event with current form event handler.

    wrapperClass.WrapperMessageReceived += new 
           MessageHandler(MessageReceivedHandler);
}

Wrapper Class

/// <span class="code-SummaryComment"><summary></span>
/// Occurs when a broadcast message received.
/// <span class="code-SummaryComment"></summary></span>

public event MessageHandler WrapperMessageReceived;
/// <span class="code-SummaryComment"><summary></span>
/// Wrapper method for sending message to the clients.
/// <span class="code-SummaryComment"></summary></span>
/// <span class="code-SummaryComment"><param name="sender">Caller object</param></span>
/// <span class="code-SummaryComment"><param name="args">Message data</param></span>

public void WrapperMessageReceivedHandler(string message)
{
    // forward the message to the client

    if(WrapperMessageReceived != null)
        WrapperMessageReceived(message);
}

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Hossein Ghahvei Araghi
Program Manager System Group
Iran (Islamic Republic Of) Iran (Islamic Republic Of)
Hossein Ghahvei Araghi
Birth date: 1978
Birth place: Iran
Academic Credentials : BS(Tehran University)
Microsoft Credentials : MCP, MCAD, MCTS 2.0, MCTS 3.5, MCPD 2.0, MCPD 3.5
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Comments and Discussions

 
GeneralMultiple Event Pinmemberborchanii7-Sep-10 0:10 
GeneralRe: Multiple Event Pinmemberysgepl27-Jul-11 19:49 
GeneralSerilizable tag Pinmemberxandy197926-Nov-08 14:02 
GeneralThat's what I really need! Pinmemberxandy197920-Nov-08 13:50 
GeneralTrying to do this without the app.config files PinmemberObsidianPC10-Nov-08 14:09 
GeneralRe: Trying to do this without the app.config files PinmemberObsidianPC10-Nov-08 14:44 
GeneralRe: Trying to do this without the app.config files [modified] PinmemberObsidianPC10-Nov-08 14:51 
QuestionQuestion about broadcasting PinmemberMazdak22-Jul-07 20:43 
AnswerRe: Question about broadcasting PinmemberObsidianPC11-Nov-08 7:08 
Generalconvert to VB.NET Pinmemberfyclinic23-May-07 23:47 
QuestionWrapper Woes. Please Help PinmemberRoey9928-Oct-06 8:57 
GeneralRemoting Pinmemberhariram2811-Oct-06 7:07 
QuestionREmoting Pinmemberhariram2811-Oct-06 6:57 
QuestionAny new client do not communicate to the existing one PinmemberJeetu00725-Sep-06 14:50 
GeneralUsing Across a network PinmembermcstarSatx20-Sep-06 6:32 
I've setup your Asynch code on a machine and it works great on that machine. However, if I copy the client code to another machine on the same network, and edit the url in the client's config to point to the ip address of the server machine, an error is thrown by the client (the target machine actively refused the connection). I've turned off firewalls on both machines, and I'm even able to telnet to the server's port from the client machine. Have you tried this example code across a network? Here's a copy of the client's config....
 




<!--You can replace localhost with your server ip address or host name-->





<formatter ref="soap" />


<formatter ref="soap" typeFilterLevel="Full" />






 
thanks for any help, I'm trying to learn from this source.
GeneralRe: Using Across a network Pinmembergio_ch28-Jul-11 7:25 
GeneralRe: Using Across a network PinmemberHossein Ghahvei Araghi30-Jul-11 21:07 
GeneralRequested service not found PinmemberJeetu0075-Sep-06 14:38 
GeneralRe: Requested service not found PinmemberJeetu00713-Sep-06 15:34 
QuestionRe: Requested service not found Pinmembercamariei11-Dec-06 11:40 
GeneralVB.Net PinmemberFuSe51224-Aug-06 16:19 
GeneralRe: VB.Net PinmemberFuSe51224-Aug-06 16:58 
Questionabout the NAT Pinmemberyonking23-Aug-06 22:41 
AnswerRe: about the NAT Pinmembershahrul6s20-Nov-07 21:37 
GeneralRe: about the NAT Pinmembergio_ch28-Jul-11 7:37 

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