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wcf callback reference

I have a desktop app with a duplex WCF service, but I have some troubles using the callback.
The service is started as following in main of program.cs:
ServiceHost svcHost = new ServiceHost(typeof(PeriodicService));
svcHost.Open();
Console.WriteLine("Available Endpoints :\n");
svcHost.Description.Endpoints.ToList().ForEach(endpoint => Console.WriteLine(endpoint.Address.ToString() + " -- " + endpoint.Name));
For the service I created a subscribe function where the callbackchannel is saved in a global variable, then the callback uses that global variable to talk back to the client (there will be only one client connecting).
IPeriodicCallback callbackClient;
public IPeriodicCallback Proxy
{
get
{
return this.callbackClient;
}
}
public void joinPeriodicService()
{
Console.WriteLine("Client subscribe");
this.callbackClient = OperationContext.Current.GetCallbackChannel<IPeriodicCallback>();
}
The thing I want to do now is call the callbackclient from an other class.
In the other class I created the service as:
private PeriodicService periodicService = new PeriodicService();
And I try to write data to it using:
if(this.periodicService.Proxy != null)
{
this.periodicService.Proxy.On1MinuteDataAvailable(tmpPeriod);
}
However the proxy stays null, I also tried to move the proxy part to the class but this also results in it staying null.
When the client connects I nicely get the message "Client Subscribe" but it seems there are two instances running of the periodicservice.
But my problem is I don't see an other way to access the periodicservice then creating it in my class, or is it also already created by the svcHost?
Can ayone point me in the right direction?

This repository shows the a duplex WCF imeplementation I made to answer a similar question a while ago, its a full working example with as little extra stuff as possible.
https://github.com/Aelphaeis/MyWcfDuplexPipeExample
Lets say we have a Service Contract like this :
[ServiceContract(CallbackContract = typeof(IMyServiceCallback),SessionMode = SessionMode.Required)]
public interface IMyService
{
[OperationContract(IsOneWay=true)]
void DoWork();
}
Note that I specified a CallbackContract.
If you want to make a duplex, you would want to perhaps make your Service Behavior implementation of the above contract like this :
[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)]
public class MyService : IMyService
{
public void DoWork()
{
Console.WriteLine("Hello World");
Callback.WorkComplete();
}
IMyServiceCallback Callback
{
get
{
return OperationContext.Current.GetCallbackChannel<IMyServiceCallback>();
}
}
}
The important thing here is the Callback. This is how your service would allow you to access specified to you by the Client.
You also need to define the callback interface, In my case its quite simple :
[ServiceContract]
public interface IMyServiceCallback
{
[OperationContract(IsOneWay = true)]
void WorkComplete();
}
Now I want to create a client to use this Duplex Service. The first thing I need to do is implement the IMyServiceCallback. I need to do this on the client. In this case the implementation is this:
class Callback : IMyServiceCallback
{
public void WorkComplete()
{
Console.WriteLine("Work Complete");
}
}
Now when I want to open my duplex connection with the services I would create a proxy class like this something like this:
public class MyServiceClient: IMyService, IDisposable
{
DuplexChannelFactory<IMyService> myServiceFactory { get; set; }
public MyServiceClient(IMyServiceCallback Callback)
{
InstanceContext site = new InstanceContext(Callback);
NetNamedPipeBinding binding = new NetNamedPipeBinding();
EndpointAddress endpointAddress = new EndpointAddress(Constants.myPipeService + #"/" + Constants.myPipeServiceName);
myServiceFactory = new DuplexChannelFactory<IMyService>(site, binding, endpointAddress);
}
public void DoWork()
{
myServiceFactory.CreateChannel().DoWork();
}
public void Dispose()
{
myServiceFactory.Close();
}
}
Notice that I specified an InstanceContext. That Instance Context will be an instance of the object I created that implements IMyServiceCallback.
That's all you need to do! Simple as that!
Update :
Callback objects are just like any other object. You can store them into a collection and iterate through them and based on some condition.
One way is to create a property in the IMyServiceCallback that can uniquely identify it. When a client connects to the service it can call a method which specifies a callback object which can then be cached or saved for later use. You can then iterate the callbacks and based on some condition you can call a method for a specific client.
This is certainly more complicated; however, it is certainly manageable. I will add an example in a bit.
Update 2
This is a working example of exactly what you want; however, its a lot more complicated. I'll try to explain as simply as I can : https://github.com/Aelphaeis/MyWcfDuplexPipeExample/tree/MultiClient
Here is a list of the changes:
I've modified the client proxy (and service) so that when initialized it calls the init Method
I've also modified the Service implementation so that now it is a single instance dealing with all requests (for convenience).
I added a new OperationContract in the Service interface called Msg
I've added a new Method in the IMyServiceCallback called RecieveMessage.
I've added a way to identify the client.
In the proxy class I have the following :
public MyServiceClient(IMyServiceCallback Callback)
{
InstanceContext site = new InstanceContext(Callback);
NetNamedPipeBinding binding = new NetNamedPipeBinding();
EndpointAddress endpointAddress = new EndpointAddress(Constants.myPipeService + #"/" + Constants.myPipeServiceName);
myServiceFactory = new DuplexChannelFactory<IMyService>(site, binding, endpointAddress);
Init();
}
public void Init()
{
myServiceFactory.CreateChannel().Init();
}
In my service I have the following :
public class MyService : IMyService
{
public List<IMyServiceCallback> Callbacks { get; private set; }
public MyService(){
Callbacks = new List<IMyServiceCallback>();
}
public void Init()
{
Callbacks.Add(Callback);
}
// and so on
My IMyServiceCallback has been redefined to :
[ServiceContract]
public interface IMyServiceCallback
{
[OperationContract]
int GetClientId();
[OperationContract(IsOneWay = true)]
void WorkComplete();
[OperationContract(IsOneWay = true)]
void RecieveMessage(String msg);
}
By specifying a number, you can contact the client that corresponds with that number. If two clients have the same Id, both clients will be contacted.

WCF ServiceHosts, ServiceEndpoints and Bindings

I currently am running some WCF REST services in a Windows Service (not IIS), using the WebServiceHost. I have a separate interface and class defined for each service, but I'm having some issues understanding how WebServiceHost, ServiceEndpoint and ServiceContracts can be used together to create a selfhosted solution.
The way that I currently set things up is that I create a new WebServiceHost for each class which implements a service and use the name of the class as part of the URI but then define the rest of the URI in the interface.
[ServiceContract]
public interface IEventsService
{
[System.ServiceModel.OperationContract]
[System.ServiceModel.Web.WebGet(UriTemplate = "EventType", ResponseFormat=WebMessageFormat.Json)]
List<EventType> GetEventTypes();
[System.ServiceModel.OperationContract]
[System.ServiceModel.Web.WebGet(UriTemplate = "Event")]
System.IO.Stream GetEventsAsStream();
}
public class EventsService: IEventsService
{
public List<EventType> GetEventTypes() { //code in here }
public System.IO.Stream GetEventsAsStream() { // code in here }
}
The code to create the services looks like this:
Type t = typeof(EventService);
Type interface = typeof(IEventService);
Uri newUri = new Uri(baseUri, "Events");
WebServicesHost host = new WebServiceHost(t, newUri);
Binding binding = New WebHttpBinding();
ServiceEndpoint ep = host.AddServiceEndpoint(interface, binding, newUri);
This works well and the service endpoint for each service is created at an appropriate url.
http://XXX.YYY.ZZZ:portnum/Events/EventType
http://XXX.YYY.ZZZ:portnum/Events/Event
I then repeat for another service interface and service class. I would like to remove the Events in the Url though but if I do that and create multiple WebServiceHosts with the same base URL I get the error:
The ChannelDispatcher at 'http://localhost:8085/' with contract(s) '"IOtherService"' is unable to open its IChannelListener
with the internal Exception of:
"A registration already exists for URI 'http://localhost:8085/'."
I'm trying to understand how the WebServiceHost, ServiceEndpoint and ServiceContract work together to create the ChannelListener.
Do I need a separate WebServiceHost for each class which implements a service? I don't see a way to register multiple types with a single WebServiceHost
Secondly, I'm passing in the interface to the AddServceEndpoint method and I assume that method checks the object for all of the OperationContract members and adds them, the problem is how does the WebServiceHost know which class should map to which interface.
What I would love would be an example of creating a WCF self hosted service which runs multiple services while keeping the interface and the implementation classes separate.

Sounds to me like the problem that you are having is you are trying to register more than one service on the same service URI. This will not work, as you have noticed, each service must have a unique endpoint.
Unique By
IP
Domain
Port Number
Full URL
Examples
http://someserver/foo -> IFoo Service
http://someserver/bar -> IBar Service
http://somedomain -> IFoo Service
http://someotherdomain -> IBar Service
http://somedomain:1 -> IFoo Service
http://somedomain:2 -> IBar Service
You get the idea.
So to directly address your question, if you want more than once service to be at the root url for you site, you will have to put them on different ports. So you could modify your code to be something like
public class PortNumberAttribute : Attribute
{
public int PortNumber { get; set; }
public PortNumberAttribute(int port)
{
PortNumber = port;
}
}
[PortNumber(8085)]
public interface IEventsService
{
//service methods etc
}
string baseUri = "http://foo.com:{0}";
Type iface = typeof(IEventsService);
PortNumberAttribute pNumber = (PortNumberAttribute)iface.GetCustomAttribute(typeof(PortNumberAttribute));
Uri newUri = new Uri(string.Format(baseUri, pNumber.PortNumber));
//create host and all that

I think it might be useful for you to re-think about your URI approach. Uri is a unique resource identifier.
Each your endpoint says that you try to expose outside a different kind of resource it's "Events" and "OtherResource". Thus you need to change your UriTemplates a bit.
I would make it so:
[ServiceContract]
public interface IEventTypesService
{
[OperationContract]
[WebGet(UriTemplate = "", ResponseFormat=WebMessageFormat.Json)]
IList<EventType> GetEventTypes();
[OperationContract]
[WebGet(UriTemplate = "{id}")]
EventType GetEventType(string id);
}
[ServiceContract]
public interface IEventsService
{
[OperationContract]
[WebGet(UriTemplate = "")]
Stream GetEventsAsStream();
[OperationContract]
[WebGet(UriTemplate = "{id}")]
Event GetEvent(string id);
}
public class EventsService: IEventsService, IEventTypesService
{
public IList<EventType> GetEventTypes() { //code in here }
public EventType GetEventType(string id) { //code in here }
public Stream GetEventsAsStream() { // code in here }
public EventType GetEventType(string id) { // code in here }
}
Type t = typeof(EventService);
Type interface1 = typeof(IEventsService);
Type interface2 = typeof(IEventTypesService);
var baseUri = new Uri("http://localhost");
Uri eventsUri= new Uri(baseUri, "Events");
Uri eventTypesUri= new Uri(baseUri, "EventTypes");
WebServicesHost host = new WebServiceHost(t, baseUri);
Binding binding = New WebHttpBinding();
host.AddServiceEndpoint(interface1, binding, eventsUri);
host.AddServiceEndpoint(interface2, binding, eventTypesUri);
And yes, you are right - you have to have different addresses, but it's really different resources. To understand it better you can refer: RESTful API Design, best-practices-for-a-pragmatic-restful-api
To finish, there is a way to use the same address, but the approach a bit weird:
Using the same address

The following solution:
allows a single object to handle a specific endpoint
no part of the path is in the URI template
uses the same port for all of the services
It does requires more than one WebServiceHost - one per object that handles requests. Another difficulty is that adding deeper endpoints (like /events/2014) means they either need to have unique parameters or the URI template must include part of the path, if you go convention over configuration that shouldn't be a problem.
A WebServiceHost can only host one thing (class) but that object can have multiple interfaces to handle multiple different types of requests on different URLs. How can different WebServiceHosts bind to the same domain:port? They can't so I guess WebServiceHost wraps an underlying static object that routes requests to the right object. This doesn't technically answer your question but I think this implementation allows you to do what you want right?
A console app that hosts the web services.
public class Program
{
static void Main (string[] args)
{
var venueHost = new WebServiceHost (typeof (Venues));
venueHost.AddServiceEndpoint (typeof (IVenues), new WebHttpBinding (), "http://localhost:12345/venues");
venueHost.Open ();
var eventHost = new WebServiceHost (typeof (Events));
eventHost.AddServiceEndpoint (typeof (IEvents), new WebHttpBinding (), "http://localhost:12345/events");
eventHost.Open ();
while (true)
{
var k = Console.ReadKey ();
if (k.KeyChar == 'q' || k.KeyChar == 'Q')
break;
}
}
}
The Venues class implements IVenues and handles any requests to http://localhost:12345/venues/
[ServiceContract]
public interface IVenues
{
[WebInvoke (Method = "GET", UriTemplate = "?id={id}")]
string GetVenues (string id);
}
public class Venues : IVenues
{
public string GetVenues (string id)
{
return "This would contain venue data.";
}
}
The Events class implements IEvents and handles any requests to http://localhost:12345/events/
[ServiceContract]
public interface IEvents
{
[WebInvoke (Method = "GET", UriTemplate = "?venue={venue}")]
string GetEvents (string venue);
}
public class Events : IEvents
{
public string GetEvents (string venue)
{
return "This would contain event data.";
}
}

WCF self hosting can be done in many ways like Console application hosting, Windows service hosting, etc.
I had tried to host two services using a single console application. The structure of the services was similar to what you mentioned, that is, separate classes and interfaces for both the services.
You might want to have a look at this link:
Hosting two WCf services using one console app

WCF client fields are losing values

I have a WCF service hosted on a console application the code is:
public interface ITestService
{
[OperationContract]
void SetField(string data);
[OperationContract]
string GetField();
}
public class TestService : ITestService
{
private string myData;
public string GetField()
{
retrun myData;
}
public void SetField(string data)
{
myData = data;
}
}
then I hosted it on a console application:
ServiceHost host = new ServiceHost(typeof(TestService));
host.Open();
Console.WriteLine("Test Service Host");
Console.WriteLine("Service Started!");
foreach (Uri address in host.BaseAddresses)
{
Console.WriteLine("Listening on " + address);
}
Console.WriteLine("Press any key to close the host...");
Console.ReadLine();
host.Close();
I started the console host then In an other console app I referenced the service and used it:
TestService client = new TestService();
client.SetField("test");
Console.WriteLine( client.GetField() );
this print nothing means the field is still null
What is wrong with this service?

What's wrong is that you're expecting that state will be persisted between calls - it is NOT. By default, WCF are absolutely stateless (and they should be! That's a good thing!)
If you need to persist information - store it into a persistent store (a.k.a a database).
Each WCF call will (by default) get a brand new, freshly created instance of TestService.
So your second call's instance knows nothing about the first instance (used by SetField) and therefore cannot return that value that you set in the first call.

Try this:
Use string as static.
public interface ITestService
{
[OperationContract]
void SetField(string data);
[OperationContract]
string GetField();
}
public class TestService : ITestService
{
private static string myData;
public string GetField()
{
retrun myData;
}
public void SetField(string data)
{
myData = data;
}
}

You should mark your service class with the attribute:
[ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)]
public class TestService : ITestService
{
//...
}
This means that your service must have only one instance. And you must create the host like this:
var host = new ServiceHost(new TestService()); // or get a singleton..
host.Open();
Pay your attantion that you use an instance to create a service instead type. Then your code should work.

Getting the WCF SessionID in the Client

I am writing a WCF client and am using a ChannelFactory to create my proxy to my Service:
[ServiceContract]
interface Service {
[OperationContract]
void Operation();
}
var proxy = ChannelFactory<MyServiceInterface>.CreateChannel(
new BasicHttpBinding(),
new EndpointAddress("http://localhost:8000/"));
How would I go about getting the SessionID? The proxy only has the basic Object methods as well as the ones defined in MyServiceInterface.
Thank you in advance.

Try this:
In your WCF Service file (.svc) add the following:
[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)]
public class Service1 : IService1
{
public string SessionId()
{
return OperationContext.Current.SessionId;
}
}
In your WCF Service interface add the following:
[ServiceContract(SessionMode = SessionMode.Required)]
public interface IService1
{
[OperationContract]
string SessionId();
}
In your client, do the following:
ChannelFactory<IService1> factory = new ChannelFactory<IService1>(
new WSHttpBinding(), new EndpointAddress("http://localhost:4213/Service1.svc"));
IService1 proxy = factory.CreateChannel();
Console.WriteLine(proxy.SessionId());
((IClientChannel)proxy).Close();
factory.Close();
Console.Read();
By doing this you can get the proxy session created at service side. Just to know, when ((IClientChannel)proxy).Close(); and factory.Close(); were invoked, then proxy will get new session.

It wasn't what I was looking for to make the SessionId() an OperationContract. If, instead of using the ChannelFactory, I created my own proxy by extending ClientBase<>, and that gave me access to the InnerChannel.SessionId property.

my first WCF Server - why OperationContext.Current is null?

I'm tring to implement my first WCF call-back server. This is my code:
[ServiceContract(SessionMode = SessionMode.Required, CallbackContract = typeof(ILogCallback))]
public interface ILog
{
}
public interface ILogCallback
{
[OperationContract(IsOneWay = true)]
void Push(string callbackValue);
}
public class MyLog : ILog
{
}
class Log
{
public static void initialize()
{
using (ServiceHost host = new ServiceHost(
typeof (MyLog),
new Uri[]
{
new Uri("net.pipe://localhost")
}))
{
host.AddServiceEndpoint(typeof (ILog),
new NetNamedPipeBinding(),
"PipeReverse");
host.Open();
// TODO: host.Close();
}
}
public static void Push(string s)
{
ILogCallback callbacks = OperationContext.Current.GetCallbackChannel<ILogCallback>();
callbacks.Push(s);
}
}
then I try to use my server using this code:
Log.initialize();
while (true)
{
Log.Push("Hello");
System.Threading.Thread.Sleep(1000);
}
But I got NPE, because OperationContext.Current is null. Why, what's wrong and how to fix that?

Because you are NOT in the context of an operation.
You're simply calling a static method of the Log class.
For you to be in an Operation Context your call MUST have been come from a client that is being serviced by your WCF server.

OperationContext.Current is a thread-static property that is initialized when request arrives to the server. Here's what you do to call the callback
[ServiceContract(SessionMode = SessionMode.Required, CallbackContract = typeof(ILogCallback))]
public interface ILog
{
void PushOnTheClient();
}
public class MyLog : ILog
{
void PushOnTheClient()
{
ILogCallback callbacks = OperationContext.Current.GetCallbackChannel<ILogCallback>();
callbacks.Push(s);
}
}

You are missing the subscriber's subscription. The way you do this is to create a [oneway] operation in your MyLog WCF server called something like: "void SendMeLogs()".
This will open the client callback channel. You Then have to implement SendMeLogs() in lines of something like:
void SendMeLogs()
{
while(CheckLogsForNewData())
{
PushOnTheClient();
}
}
Since the SendMeLogs() function is oneway, the client will not block, but will start the subscription to your log server. (you can search the net for sample code for duplex calculator in wcf for a good example of this architecture).
The key however is that you must have a nice unsubscribe method like "StopSendingMeLogs" to break the loop, and also make the PushOnTheClient function fail safe, in case the client terminates or the specific client connection goes down.
The "CheckLogsForNewData" function should ideally be a shared (static) implementation in your case