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  • What is the advantage of WSDualHttpBinding in WCF?

    - by schmoopy
    How much benefit would there be to using WSDualHttpBinding with IIS hosted service vs. a client poll that calls the WCF service, assuming in the latter the service cached the data in question? This scenerio would be for a notify type of service where the clients need to be notified by the service when an event occurs. Specifically, what advantages would WSDualHttpBinding provide over polling? ie: Less network traffic, faster to design, easier to maintain, more control ??? From what i understand, WSDualHttpBinding is less scalable than client polling, so why use it at all? Edit: As Matt supplied, time critical can be one reason for the duplex binding. Here is what i have so far: WSDualHttpBinding adv: can get immediate response w/o waiting on polling timer dis: less scalable than WsHttpBinding dis: less firewall friendly I'll add to this based on comments, please let me know if i state anything incorrectly. thanks for you input :-)

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  • WCF Test Client Service Failed to Invoke

    - by renjucool
    I'm connection IBM.Iseries database in a c# application using ADO.NET iSeries drivers. My WCF service is throwing the error as "HTTP could not register URL http://+:80/Temporary_Listen_Addresses/771be107-8fa3-46f9-ac01-12c4d503d01e/ because TCP port 80 is being used by another application." <system.serviceModel> <client> <endpoint address="http://localhost:8080/Design_Time_Addresses/DataAccessLayer/POEngine/" binding="wsDualHttpBinding" bindingConfiguration="" contract="POServiceReference.IPOEngine" name="MyPoBindings"> <identity> <dns value="localhost" /> </identity> </endpoint> <endpoint address="http://localhost:8080/Design_Time_Addresses/DataAccessLayer/POEngine/" binding="wsDualHttpBinding" bindingConfiguration="PoBindings1" contract="POServiceReference.IPOEngine" name="PoBindings"> <identity> <dns value="localhost" /> </identity> </endpoint> </client> <bindings> <wsDualHttpBinding> <binding name="PoBindings1" 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> <wsHttpBinding> <binding name="PoBindings" /> </wsHttpBinding> </bindings> <services> <service behaviorConfiguration="DataAccessLayer.POEngineBehavior" name="DataAccessLayer.POEngine"> <endpoint address="" binding="wsDualHttpBinding" bindingConfiguration="" name="PoBindings" contract="DataAccessLayer.IPOEngine"> <identity> <dns value="localhost" /> </identity> </endpoint> <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange" /> <host> <baseAddresses> <add baseAddress="http://localhost:8080/Design_Time_Addresses/DataAccessLayer/POEngine/" /> </baseAddresses> </host> </service> </services> <behaviors> <endpointBehaviors> <behavior name="NewBehavior" /> </endpointBehaviors> <serviceBehaviors> <behavior name="DataAccessLayer.Service1Behavior"> <serviceMetadata httpGetEnabled="true" /> <serviceDebug includeExceptionDetailInFaults="false" /> </behavior> <behavior name="DataAccessLayer.POEngineBehavior"> <serviceMetadata httpGetEnabled="true" /> <serviceDebug includeExceptionDetailInFaults="false" /> </behavior> </serviceBehaviors> </behaviors> </system.serviceModel> Having the problem also without using any IBM data access. A normal Hello World is also throwing the error.Where i need to change the port address

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  • WCF with No security

    - by james.ingham
    Hi all, I've got a WCF service setup which I can consume and use as intendid... but only on the same machine. I'm looking to get this working over multiple computers and I'm not fussed about the security. However when I set (client side) the security to = none, I get a InvalidOperationException: The service certificate is not provided for target 'http://xxx.xxx.xxx.xxx:8731/Design_Time_Addresses/WcfServiceLibrary/ManagementService/'. Specify a service certificate in ClientCredentials. So I'm left with: <security mode="Message"> <message clientCredentialType="None" negotiateServiceCredential="false" algorithmSuite="Default" /> </security> But this gives me another InvalidOperationException: The service certificate is not provided for target 'http://xxx.xxx.xxx.xxx:8731/Design_Time_Addresses/WcfServiceLibrary/ManagementService/'. Specify a service certificate in ClientCredentials. Why would I have to provide a certificate if security was turned off? Server app config: <system.serviceModel> <services> <service name="Server.WcfServiceLibrary.CheckoutService" behaviorConfiguration="Server.WcfServiceLibrary.CheckoutServiceBehavior"> <host> <baseAddresses> <add baseAddress = "http://xxx:8731/Design_Time_Addresses/WcfServiceLibrary/CheckoutService/" /> </baseAddresses> </host> <endpoint address ="" binding="wsDualHttpBinding" contract="Server.WcfServiceLibrary.ICheckoutService"> <identity> <dns value="localhost"/> </identity> </endpoint> <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange"/> </service> <service name="Server.WcfServiceLibrary.ManagementService" behaviorConfiguration="Server.WcfServiceLibrary.ManagementServiceBehavior"> <host> <baseAddresses> <add baseAddress = "http://xxx:8731/Design_Time_Addresses/WcfServiceLibrary/ManagementService/" /> </baseAddresses> </host> <endpoint address ="" binding="wsDualHttpBinding" contract="Server.WcfServiceLibrary.IManagementService"> <identity> <dns value="localhost"/> </identity> </endpoint> <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange"/> </service> </services> <behaviors> <serviceBehaviors> <behavior name="Server.WcfServiceLibrary.CheckoutServiceBehavior"> <serviceMetadata httpGetEnabled="True"/> <serviceDebug includeExceptionDetailInFaults="False" /> <serviceThrottling maxConcurrentCalls="100" maxConcurrentSessions="50" maxConcurrentInstances="50" /> </behavior> <behavior name="Server.WcfServiceLibrary.ManagementServiceBehavior"> <serviceMetadata httpGetEnabled="True"/> <serviceDebug includeExceptionDetailInFaults="False" /> </behavior> </serviceBehaviors> </behaviors> </system.serviceModel> Client app config: <system.serviceModel> <bindings> <wsDualHttpBinding> <binding name="WSDualHttpBinding_IManagementService" closeTimeout="00:01:00" openTimeout="00:01:00" receiveTimeout="00:10:00" sendTimeout="00:00:10" 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="http://xxx:8731/Design_Time_Addresses/WcfServiceLibrary/ManagementService/" binding="wsDualHttpBinding" bindingConfiguration="WSDualHttpBinding_IManagementService" contract="ServiceReference.IManagementService" name="WSDualHttpBinding_IManagementService"> <identity> <dns value="localhost" /> </identity> </endpoint> </client> </system.serviceModel> Thanks

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  • TimoutException occurs over a network but not locally

    - by Gibsnag
    I have a program with three WCF services and when I run them locally (i.e: Server and Clients are all on localhost) everything works. However when I test them across a network I get a TimoutException on two services but not the other. I've disabled the firewalls on all the machines involved in the test. I can both ping the server and access the wsdl "You have created a service" webpage from the client The service that works uses a BasicHttpBinding with streaming and the two which don't work use WSDualHttpBinding. The Services that use WSDualHttpBinding both have CallbackContracts. I apologise for the vagueness of this question but I'm not really sure what code to include or where to even start looking for the solution to this. Non-working bindings: public static Binding CreateHTTPBinding() { var binding = new WSDualHttpBinding(); binding.MessageEncoding = WSMessageEncoding.Mtom; binding.MaxBufferPoolSize = 2147483647; binding.MaxReceivedMessageSize = 2147483647; binding.Security.Mode = WSDualHttpSecurityMode.None; return binding; } Exception Stack Trace: Unhandled Exception: System.TimeoutException: The open operation did not complete within the allotted timeout of 00:01:00. The time allotted to this operation may have been a portion of a longer timeout. Server stack trace: at System.ServiceModel.Channels.ReliableRequestor.ThrowTimeoutException() at System.ServiceModel.Channels.ReliableRequestor.Request(TimeSpan timeout) at System.ServiceModel.Channels.ClientReliableSession.Open(TimeSpan timeout) at System.ServiceModel.Channels.ClientReliableDuplexSessionChannel.OnOpen(TimeSpan timeout) at System.ServiceModel.Channels.CommunicationObject.Open(TimeSpan timeout) at System.ServiceModel.Channels.ServiceChannel.OnOpen(TimeSpan timeout) at System.ServiceModel.Channels.CommunicationObject.Open(TimeSpan timeout) at System.ServiceModel.Channels.ServiceChannel.CallOpenOnce.System.ServiceModel.Channels.ServiceChannel.ICallOnce.Call(ServiceChannel channel, TimeSpan timeout) at System.ServiceModel.Channels.ServiceChannel.CallOnceManager.CallOnce(TimeSpan timeout, CallOnceManager cascade) at System.ServiceModel.Channels.ServiceChannel.EnsureOpened(TimeSpan timeout) at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout) at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs) at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation) at System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message) Exception rethrown at [0]: at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg) at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type) at IDemeService.Register() at DemeServiceClient.Register() at DemeClient.Client.Start() at DemeClient.Program.Main(String[] args)

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  • WCF configuration file: why do we need clientBaseAddress in Binding section?

    - by Captain Comic
    Hi, There are three sections in WCF configuration for service client: Look at bindings = clientBaseAddress Why do we need to specify callback address? Is this field required? Why .NET is unable to determine the address of client? Does it mean that i can specify callback service that is located on some other machine? <configuration> <system.serviceModel> <client> <endpoint address= </client> <bindings> <wsDualHttpBinding> <binding name= clientBaseAddress= maxBufferPoolSize="2147483647" maxReceivedMessageSize="2147483647" </binding> </wsDualHttpBinding> </bindings> <behaviors> <endpointBehaviors> <behavior name=> </behavior> </endpointBehaviors> </behaviors> </system.serviceModel>

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  • WCF: connecting to service over internet times out

    - by Shaul
    Still on the WCF learning curve: I've set up a self-hosted WCF Service (WSDualHttpBinding), which works fine on my own computer, which resides behind a firewall. If I run the client on my own computer, everything works great. Now I installed the client on a computer outside my network, and I'm trying to access the service via a dynamic DNS, like so: http://mydomain.dyndns.org:8000/MyService. My port forwarding issues were taken care of in a previous question; I can now see the service is up in my browser. But now when I try to run the client on the other machine, I get the following error message: "The open operation did not complete within the allotted timeout of 00:01:00. The time allotted to this operation may have been a portion of a longer timeout." I have disabled security on the service, so that's not it. What else might be preventing the connection from happening?

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  • Bi-directional WCF Client-Server Communication

    - by Bill
    I have been working for weeks on creating a client/server to control a music-server application located on the server-side that is controlled by several client apps located across the LAN. I've been successful in getting the client-side to communicate with the Server, sending commands to operate the music-server, and through the use of callbacks, reply to the clients so that all of the client UI's can be appropriately updated. My problem is however, that I unable to figure-out how to broadcast other messages that need to be sent from the server app to the clients. I was hoping to utilize the callback method; however I have not been able to access it from the server side. Do I need to modify or create another contract that provides for communication from the server to the clients? Does the binding require modification? As I mentioned earlier, I have truly been working on this for weeks (which is beginning to feel like 'years'), and hope to get this last piece of the application working. Would someone please steer me in the right direction? Client Side SERVICE REFERENCE: <?xml version="1.0" encoding="utf-8"?> <ServiceReference> <ProxyGenerationParameters ServiceReferenceUri="http://localhost:8001/APService/mex" Name="APGateway" NotifyPropertyChange="True" UseObservableCollection="False"> </ProxyGenerationParameters> <EndPoints> <EndPoint Address="net.tcp://localhost:8000/APService/service" BindingConfiguration="TcpBinding" Contract="APClient.APGateway.APUserService" > </EndPoint> <EndPoint Address="http://localhost:8001/APService/service" BindingConfiguration="HttpBinding" Contract="APClient.APGateway.APUserService" > </EndPoint> </EndPoints> </ServiceReference> Client Side AP CONFIG <?xml version="1.0" encoding="utf-8" ?> <configuration> <configSections> <sectionGroup name="applicationSettings" type="System.Configuration.ApplicationSettingsGroup, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" > <section name="APClient.Properties.Settings" type="System.Configuration.ClientSettingsSection, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" /> </sectionGroup> </configSections> <system.serviceModel> <client> <endpoint address="net.tcp://localhost:8000/APService/service" binding="netTcpBinding" contract="APClient.APGateway.APUserService" name="TcpBinding" /> <endpoint address="http://localhost:8001/APService/service" binding="wsDualHttpBinding" contract="APClient.APGateway.APUserService" name="HttpBinding" /> </client> </system.serviceModel> <applicationSettings> <APClient.Properties.Settings> <setting name="pathToDatabase" serializeAs="String"> <value>C:\Users\Bill\Documents\APData\</value> </setting> </APClient.Properties.Settings> </applicationSettings> Server Side AP.CONFIG <?xml version="1.0" encoding="utf-8" ?> <configuration> <system.serviceModel> <behaviors> <serviceBehaviors> <behavior name="MetadataBehavior"> <serviceMetadata httpGetEnabled="true" httpGetUrl="http://localhost:8001/APService/mex" /> </behavior> </serviceBehaviors> </behaviors> <services> <service behaviorConfiguration="MetadataBehavior" name="APService.APService"> <endpoint address="service" binding="netTcpBinding" name="TcpBinding" contract="APService.IAPServiceInventory" /> <endpoint address="service" binding="wsDualHttpBinding" name="HttpBinding" contract="APService.IAPServiceInventory" /> <endpoint address="mex" binding="mexHttpBinding" name="MexBinding" contract="IMetadataExchange" /> <host> <baseAddresses> <add baseAddress="net.tcp://localhost:8000/APService/" /> <add baseAddress="http://localhost:8001/APService/" /> </baseAddresses> </host> </service> </services> </system.serviceModel> </configuration> Server Side APSERVICE.CS namespace APService { [ServiceBehavior(ConcurrencyMode=ConcurrencyMode.Single,InstanceContextMode=InstanceContextMode.PerCall)] public class APService : IAPServiceInventory { private static List<IClientCallback> _callbackList = new List<IClientCallback>(); private static int _beerInventory = Convert.ToInt32(System.Configuration.ConfigurationManager.AppSettings["InitialBeerInventory"]); public APService() {} public int SubscribeToServer(string guestName) { IClientCallback guest = OperationContext.Current.GetCallbackChannel<IClientCallback>(); if(!_callbackList.Contains(guest)) { _callbackList.Add(guest); } else { Console.WriteLine(guest + " is already logged onto the Server."); } _callbackList.ForEach(delegate(IClientCallback callback) { callback.NotifyGuestJoinedParty(guestName); }); } public void UpdateClients(string guestName,string UpdateInfo) { _callbackList.ForEach(delegate(IClientCallback callback) { callback.NotifyUpdateClients(guestName,UpdateInfo); }); } public void SendRequestToServer(string guestName, string request) { _callbackList.ForEach(delegate(IClientCallback callback) { callback.NotifyRequestMadeToServer(guestName,request); }); if(request == "Play") { APControl.Play(); } else if(request == "Stop") { APControl.Stop(); } else if(request == "Pause") { APControl.PlayPause(); } else if(request == "Next Track") { APControl.NextTrack(); } else if(request == "Previous Track") { APControl.PreviousTrack(); } else if(request == "Mute") { APControl.Mute(); } else if(request == "Volume Up") { APControl.VolumeUp(5); } else if(request == "Volume Down") { APControl.VolumeDown(5); } } public void CancelServerSubscription(string guestName) { IClientCallback guest = OperationContext.Current.GetCallbackChannel<IClientCallback>(); if(_callbackList.Contains(guest)) { _callbackList.Remove(guest); } _callbackList.ForEach(delegate(IClientCallback callback) { callback.NotifyGuestLeftParty(guestName); }); } } Server Side IAPSERVICE.CS namespace APService { [ServiceContract(Name="APUserService",Namespace="http://AP.com/WCFClientServer/",SessionMode=SessionMode.Required, CallbackContract=typeof(IClientCallback))] public interface IAPServiceInventory { [OperationContract()] int SubscribeToServer(string guestName); [OperationContract(IsOneWay=true)] void SendRequestToServer(string guestName,string request); [OperationContract(IsOneWay=true)] void UpdateClients(string guestName,string UpdateInfo); [OperationContract(IsOneWay=true)] void CancelServerSubscription(string guestName); } } Server side - IAPServiceCallback.cs namespace APService { public interface IClientCallback { [OperationContract(IsOneWay=true)] void NotifyGuestJoinedParty(string guestName); [OperationContract(IsOneWay=true)] void NotifyUpdateClients(string guestName,string UpdateInfo); [OperationContract(IsOneWay=true)] void NotifyRequestMadeToServer(string guestName,string request); [OperationContract(IsOneWay=true)] void NotifyGuestLeftParty(string guestName); }

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  • Setting custom WCF-binding behaviour via .config file - why doesn't this work?

    - by Andrew Shepherd
    I am attempting to insert a custom behavior into my service client, following the example here. I appear to be following all of the steps, but I am getting a ConfigurationErrorsException. Is there anyone more experienced than me who can spot what I'm doing wrong? Here is the entire app.config file. <?xml version="1.0" encoding="utf-8" ?> <configuration> <system.serviceModel> <behaviors> <endpointBehaviors> <behavior name="ClientLoggingEndpointBehaviour"> <myLoggerExtension /> </behavior> </endpointBehaviors> </behaviors> <extensions> <behaviorExtensions> <add name="myLoggerExtension" type="ChatClient.ClientLoggingEndpointBehaviourExtension, ChatClient, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null"/> </behaviorExtensions> </extensions> <bindings> </bindings> <client> <endpoint behaviorConfiguration="ClientLoggingEndpointBehaviour" name="ChatRoomClientEndpoint" address="http://localhost:8016/ChatRoom" binding="wsDualHttpBinding" contract="ChatRoomLib.IChatRoom" /> </client> </system.serviceModel> </configuration> Here is the exception message: An error occurred creating the configuration section handler for system.serviceModel/behaviors: Extension element 'myLoggerExtension' cannot be added to this element. Verify that the extension is registered in the extension collection at system.serviceModel/extensions/behaviorExtensions. Parameter name: element (C:\Documents and Settings\Andrew Shepherd\My Documents\Visual Studio 2008\Projects\WcfPractice\ChatClient\bin\Debug\ChatClient.vshost.exe.config line 5) I know that I've correctly written the reference to the ClientLoggingEndpointBehaviourExtensionobject, because through the debugger I can see it being instantiated.

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  • WCF 3.5 to 3.0 backwards compatibility with callback services

    - by Miral
    I have a set of existing WCF services hosted in a .NET 3.0 app. They're using the WSHttp bindings and no security. I need to connect to these from a .NET 3.5 client. This seems to be working fine for the one-way services, but I also have some callback services (with CallbackContract and SessionMode = Required, using WSDualHttpBinding); these fail to connect with a timeout somewhere in the ReliableSession code. The service side cannot be changed (it's a historic version issue). Can I modify something on the client side to get this working? (I can connect with a .NET 3.0 client just fine, but I'd rather not be forced to try that path.) The open operation did not complete within the allotted timeout of 00:00:09.9410000. The time allotted to this operation may have been a portion of a longer timeout. Server stack trace: at System.ServiceModel.Channels.ReliableRequestor.ThrowTimeoutException() at System.ServiceModel.Channels.ReliableRequestor.Request(TimeSpan timeout) at System.ServiceModel.Channels.ClientReliableSession.Open(TimeSpan timeout) at System.ServiceModel.Channels.ClientReliableDuplexSessionChannel.OnOpen(TimeSpan timeout) at System.ServiceModel.Channels.CommunicationObject.Open(TimeSpan timeout) at System.ServiceModel.Channels.ServiceChannel.OnOpen(TimeSpan timeout) at System.ServiceModel.Channels.CommunicationObject.Open(TimeSpan timeout)

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  • Setting custom behaviour via .config file - why doesn't this work?

    - by Andrew Shepherd
    I am attempting to insert a custom behavior into my service client, following the example here. I appear to be following all of the steps, but I am getting a ConfigurationErrorsException. Is there anyone more experienced than me who can spot what I'm doing wrong? Here is the entire app.config file. <?xml version="1.0" encoding="utf-8" ?> <configuration> <system.serviceModel> <behaviors> <endpointBehaviors> <behavior name="ClientLoggingEndpointBehaviour"> <myLoggerExtension /> </behavior> </endpointBehaviors> </behaviors> <extensions> <behaviorExtensions> <add name="myLoggerExtension" type="ChatClient.ClientLoggingEndpointBehaviourExtension, ChatClient, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null"/> </behaviorExtensions> </extensions> <bindings> </bindings> <client> <endpoint behaviorConfiguration="ClientLoggingEndpointBehaviour" name="ChatRoomClientEndpoint" address="http://localhost:8016/ChatRoom" binding="wsDualHttpBinding" contract="ChatRoomLib.IChatRoom" /> </client> </system.serviceModel> </configuration> Here is the exception message: An error occurred creating the configuration section handler for system.serviceModel/behaviors: Extension element 'myLoggerExtension' cannot be added to this element. Verify that the extension is registered in the extension collection at system.serviceModel/extensions/behaviorExtensions. Parameter name: element (C:\Documents and Settings\Andrew Shepherd\My Documents\Visual Studio 2008\Projects\WcfPractice\ChatClient\bin\Debug\ChatClient.vshost.exe.config line 5) I know that I've correctly written the reference to the ClientLoggingEndpointBehaviourExtensionobject, because through the debugger I can see it being instantiated.

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  • Duplex Contract GetCallbackChannel always returns a null-instance

    - by Yaroslav
    Hi! Here is the server code: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.ServiceModel; using System.Runtime.Serialization; using System.ServiceModel.Description; namespace Console_Chat { [ServiceContract(SessionMode = SessionMode.Required, CallbackContract = typeof(IMyCallbackContract))] public interface IMyService { [OperationContract(IsOneWay = true)] void NewMessageToServer(string msg); [OperationContract(IsOneWay = false)] bool ServerIsResponsible(); } [ServiceContract] public interface IMyCallbackContract { [OperationContract(IsOneWay = true)] void NewMessageToClient(string msg); [OperationContract(IsOneWay = true)] void ClientIsResponsible(); } [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)] public class MyService : IMyService { public IMyCallbackContract callback = null; /* { get { return OperationContext.Current.GetCallbackChannel<IMyCallbackContract>(); } } */ public MyService() { callback = OperationContext.Current.GetCallbackChannel<IMyCallbackContract>(); } public void NewMessageToServer(string msg) { Console.WriteLine(msg); } public void NewMessageToClient( string msg) { callback.NewMessageToClient(msg); } public bool ServerIsResponsible() { return true; } } class Server { static void Main(string[] args) { String msg = "none"; ServiceMetadataBehavior behavior = new ServiceMetadataBehavior(); ServiceHost serviceHost = new ServiceHost( typeof(MyService), new Uri("http://localhost:8080/")); serviceHost.Description.Behaviors.Add(behavior); serviceHost.AddServiceEndpoint( typeof(IMetadataExchange), MetadataExchangeBindings.CreateMexHttpBinding(), "mex"); serviceHost.AddServiceEndpoint( typeof(IMyService), new WSDualHttpBinding(), "ServiceEndpoint" ); serviceHost.Open(); Console.WriteLine("Server is up and running"); MyService server = new MyService(); server.NewMessageToClient("Hey client!"); /* do { msg = Console.ReadLine(); // callback.NewMessageToClient(msg); } while (msg != "ex"); */ Console.ReadLine(); } } } Here is the client's: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.ServiceModel; using System.Runtime.Serialization; using System.ServiceModel.Description; using Console_Chat_Client.MyHTTPServiceReference; namespace Console_Chat_Client { [ServiceContract(SessionMode = SessionMode.Required, CallbackContract = typeof(IMyCallbackContract))] public interface IMyService { [OperationContract(IsOneWay = true)] void NewMessageToServer(string msg); [OperationContract(IsOneWay = false)] bool ServerIsResponsible(); } [ServiceContract] public interface IMyCallbackContract { [OperationContract(IsOneWay = true)] void NewMessageToClient(string msg); [OperationContract(IsOneWay = true)] void ClientIsResponsible(); } public class MyCallback : Console_Chat_Client.MyHTTPServiceReference.IMyServiceCallback { static InstanceContext ctx = new InstanceContext(new MyCallback()); static MyServiceClient client = new MyServiceClient(ctx); public void NewMessageToClient(string msg) { Console.WriteLine(msg); } public void ClientIsResponsible() { } class Client { static void Main(string[] args) { String msg = "none"; client.NewMessageToServer(String.Format("Hello server!")); do { msg = Console.ReadLine(); if (msg != "ex") client.NewMessageToServer(msg); else client.NewMessageToServer(String.Format("Client terminated")); } while (msg != "ex"); } } } } callback = OperationContext.Current.GetCallbackChannel(); This line constanly throws a NullReferenceException, what's the problem? Thanks!

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