I'm trying to learn WCF to use it as an IPC mechanism for a host/plugin system. The host needs to be able to call the plugin to Start/Stop it, and the plugin needs to call the server back to perform logging.
I made a simple test case where the host creates an endpoint on net.pipe://localhost/SampleServer with the following ServiceContract:
[ServiceContract]
public interface IWcfServer
{
[OperationContract]
void Log(string message);
}
And the plugin creates an endpoint on net.pipe://localhost/SampleClient with the following ServiceContract:
[ServiceContract]
public interface IWcfClient
{
[OperationContract]
string Init();
}
Here's a sample of how I'm setting up each endpoint:
this.server = new ServiceHost(this);
this.server.AddServiceEndpoint(typeof(IWcfServer),
new NetNamedPipeBinding(),
"net.pipe://localhost/SampleServer");
this.server.Open();
And here's a sample of how I'm making the calls:
ChannelFactory<IWcfClient> factory = new ChannelFactory<IWcfClient>(
new NetNamedPipeBinding(),
new EndpointAddress("net.pipe://localhost/SampleClient"));
IWcfClient client = factory.CreateChannel();
using ((IClientChannel)client)
{
client.Init());
}
I already confirmed that the host can call plugin.Init(), and the plugin can call host.Log(message) without issues. However, if this following scenario happens:
Host calls plugin.Init()
During the execution of plugin.Init(), the plugin attempts to call host.Log(message)
The applications freezes, and I get a TimeoutException after 1min. Anyone has any ideas on what I'm doing wrong?
what is the InstanceContextMode of the service host ? If it is a singleton, it will block until Init() returns - resulting in a circular dependency.
1 min is the standard wcf timeout.
Do you have a circular reference?
Also, why do you have 2 contracts, when you make a call to client.init who is listening?
Turn on E2E tracing for WCF to check what exactly is timing out. - http://msdn.microsoft.com/en-us/library/ms733025.aspx. Besides your methods might be causing a deadlock since init might require log and log might require init to happen first or something like that.
"net.pipe://localhost/SampleServer"
"net.pipe://localhost/SampleClient"
You have two different URL for the Server and for the Client. It is a problem!
Related
I am writing a WCF client/service. The service can perform some long operations so I have added a callback contract IProgressCallback. The system I am developing has to run in all kind of environments so I suspect that I will run into an environment where a callback channel cannot be opened (I might be wrong here).
So to be careful I have defined the operation contract like this.
[ServiceContract()]
interface IContract
{ ... }
[ServiceContract(CallbackContract = typeof(IProgress))]
interface IDuplexContract : IContract
{ ... }
This works great on the server side. I can easily configure the service to use either contract.
The problem however arises on the client side. I have manually defined 2 proxies
public class ContractProxy
: ClientBase<IContract>, IContract
{ ... }
public class DuplexContractProxy
: DuplexClientBase<IDuplexContract>, IDuplexContract
{ ... }
Again both proxies work fine.
Now I have a proxy factory which is responsible for creating the correct proxy. It can easily figure out which proxy to instantiate but my problem arises when I try to return the proxy.
The user needs to get an object back that is at least IContract and ICommunicationObject but I haven't been able to find what to return. I have tried to the following:
IContract CreateProxy(...) // The user lacks access to Open, Abort, Close, etc.
ClientBase<IContract> CreateProxy(...) // DuplexClientBase derives from ClientBase but the generic parameter is different and it isn't covariant so this cannot be done.
// First define a generic interface and then make both proxies implement it.
IProxy<TContract> : TContract, ICommunicationObject // TContract cannot be restricted to an interface so I cannot make IProxy derive from TContract
Currently as a workaround I am simply returning the IContract interface but then everyone using the proxy will have to start by casting it to a ICommunicationObject to open the proxy etc.
Does anyone here have a better way to do this or am I simply being overly worried that duplex communication might not work in some environments?
TL;DR:
What is a good and testable way to implement the dependency between the ViewModels and the WCF services in a MVVM client?
Please read the rest of the question for more details about the problems I encountered while trying to do this:
I am working on a silverlight client that connects to a wcf service, and I want to write unit tests for the client.
So I'm looking for a good solution for using the wcf clients in my ViewModels and testing that interaction. I have found two solutions until now:
Solution 1: This is actually how I have implemented it until now:
public class ViewModelExample
{
public ViewModelExample(IServiceClient client)
{
client.DoWorkCompleted += ..
client.DoWorkAsync();
}
}
//This is how the interface looks like
public interface IServiceClient
{
event EventHandler<AsyncCompletedEventArgs> DoWorkCompleted;
void DoWorkAsync();
}
//I was able to put the interface on the generated clients because they are partial classes, like this:
public partial class GeneratedServiceClient : IServiceClient
{
}
The good part: it's relatively easy to mock
The bad part: my service client lives as long as my ViewModel, and when I have concurrent requests I don't know which answer belongs to which request.
Solution 2: Inspired by this answer
WCF Service Client Lifetime.
public class ViewModelExample
{
public ViewModelExample(IServiceFactory factory)
{
var client = factory.CreateClient();
client.DoWorkCompleted += ...
client.DoWorkAsync();
}
}
The good part: each request is on a different client, so no more problems with matching requests with answers.
The bad part: it's more difficult to test. I would have to write mocks for both the factory and the wcf client every time. This is not something I would like to do, since I alreay have 200 tests... :(
So my question is, how do you guys do it? How do your ViewModels talk to the wcf services, where do you inject the dependency, and how do you test that interaction?
I feel that I'm missing something..
Try having a Func<IServiceClient> injected into your VM instead of the a client instance; you'll have a 'language-level factory' injected instead of building a class for this. In the factory method you can instantiate your client however you want (each access could create a new instance for that for example).
The downside is that you'll still have to touch your tests for the most part, but I assume it will be less work:
public ViewModelExample(Func<IServiceClient> factoryMethod)
{
var client = factoryMethod();
client.DoWorkCompleted += ...
client.DoWorkAsync();
}
The WCF service should have it's own tests that confirm the functionality of itself.
You should then be mocking this WCF service and writing unit tests within your consumers.
Unfortunately, it's a pain and something we all have to do. Be pragmatic and get it done, it will save you getting bitten in the future.
Are you using IoC container by a chance? If you had, this problem would be totally mitigated by container (you'll simply register IService dependency to be created as brand new upon each request).
If that's not the case, then
I would have to write mocks for both the factory and the wcf client every time
is how you deal with this kind of "problems". The cost is relatively small, probably 2-3 extra lines of code per test (all you have to do is setup factory mock to return service mock, which you do need either way).
I'm making a WCF service with netTcpBinding which has a main lobby with multiple chatrooms which the clients can enter. The Lobby class implements ILobby as the service contract.
When a client wishes to enter a room I want to callback the client exposing a new Channel containing the InstanceContext for the room he just entered but after much searching I am doubting that this is possible.
For example on the Service side I might have
class Lobby : ILobby
{
Dictionary<string, Chatroom> rooms;
public void JoinRoom(string roomname)
{
if (rooms[roomname].TryEnter()) {}
}
}
class ChatRoom : IChatRoom
{
public bool TryEnter(string username)
{
ILobbyCallback callback =
OperationContext.Current.GetCallbackChannel<ILobbyCallback>();
// How do I do this next bit?
callback.JoinedRoom(pass some instance context here);
return true;
}
}
On the client side callback method I want
public void JoinedRoom(InstanceContext for the room on the service side)
{
// Create a new WCF proxy using above InstanceContext
// Create a WPF UI for the new room passing the proxy so it can communicate
// with the room class directly without going via the root service
}
Is this possible? What's the best practice for spawning new classes with their own contracts on the service side? Or do I just have to bundle everything into one massive MyService class and handle everything myself?
You cannot pass instance context as parameter to any operation contract. It doesn't make sense because that context has local scope. It is called "instance context" = it is context of current service instance. In duplex scenario both client and server has its own service:
Clients calls server's service through its proxy
Server calls client' service through received callback channel
Server's service instance context has meaning only on the server. It is not clear what you are trying to achieve (except very complex architecture).
If you want to share context on client you can try to pass around the instance context used for the very first proxy you created - I'm not sure if it will work but you can try it
If you want to share service instance context between multiple proxies you must develop your own IInstanceContextProvider and perhaps also your own IInstanceProvider (depending on what you want to achieve), wrap them in behavior and add them to the service. That will put whole complexity of session handling and correct instance releasing under your control (it obviously has its pros and cons).
But is it really needed? When I look at your code I see that one service and one proxy is enough. Also your JoinRoom operation doesn't need to use callback at all, it can be just request response method.
I have a Windows Service Application
in which i create WCF services in it.
One of the services is data
services: add, delete,
read , updatte data via
WCF.
WCF use NHibernate for data manipulation
So my guestions are:
Any advice (best practice) for session management for Hibernate using with WCF?
Anybody knows anything about
WcfOperationSessionContext (hibernate 3.0) class?
how to use it with WCF?
Well to make it concrete :
Suppose that i have WCF Service called DataServices
class WCFDataService .....
{
void SaveMyEntity(MyEntity entity)
{
.....................?? // How to do? Best Way
// Should i take one session and use it all times
// Should i take session and dipsose when operation finished then get
//new session for new operations?
// If many clients call my WCF service function at the same time?
// what may go wrong?
// etc....
}
}
And I need a NHibernateServiceProvider class
class NHibernateServiceProvider ....
{
// How to get Session ?? Best way
ISession GetCurrentSession(){.... }
DisposeSession(){ ....}
}
Best Wishes
PS: I have read similiar entries here and other web pages. But can not see "concrete" answers.
The WcfOperationSessionContext, similar to ThreadStaticSessionContext and WebRequestSessionContext is an implementation for a session context. The session context is used to bind (associate) a ISession instance to a particular context.
The session in the current context can be retrieved by calling ISessionFactory.GetCurrentSession().
You can find more information about session context here.
The WcfOperationSessionContext represents a context that spans for the entire duration of a WCF operation. You still need to handle the binding of the session in the begining of the operation and the unbinding/commiting/disposal of the session at the end of the operation.
To get access to the begin/end actions in the wcf pipeline you need to implement a IDispatchMessageInspector. You can see a sample here.
Also regarding WCF integration: if you use ThreadStatic session context it will appear to work on development, but you will hit the wall in production when various components (ex: authorization, authentication ) from the wcf pipeline are executed on different threads.
As for best practices you almost nailed it: Use WcfOperationSessionContext to store the current session and the IDispatchMessageInspector to begin/complete your unit of work.
EDIT - to address the details you added:
If you configured WcfOperationSessionContext and do the binding/unbinding as i explained above, all you have to do to is inject the ISessionFactory into your service and just use factory.GetCurrentSession(). I'll post a sample prj if time permits.
Here is the sample project
The model we use for managing NHibernate sessions with WCF is as follows:
1) We have our own ServiceHost class that inherits from System.ServiceModel.ServiceHost which also implements ICallContextInitializer. We add the service host instance to each of the operations in our service as follows:
protected override void InitializeRuntime()
{
base.InitializeRuntime();
foreach (ChannelDispatcher cd in this.ChannelDispatchers)
{
foreach (EndpointDispatcher ed in cd.Endpoints)
{
foreach (DispatchOperation op in ed.DispatchRuntime.Operations)
{
op.CallContextInitializers.Add(this);
}
}
}
}
public void AfterInvoke(object correlationState)
{
// We don't do anything after the invoke
}
public object BeforeInvoke(InstanceContext instanceContext, IClientChannel channel, Message message)
{
OperationContext.Current.Extensions.Add(new SessionOperationContext());
return null;
}
The BeforeInvoke simply makes sure that the OperationContext for each WCF call has it's own session. We have found problems with IDispatchMessageInspector where the session is not available during response serialisation - a problem if you use lazy loading.
2) Our SessionOperationContext will then be called to attach itself and we use the OperationCompleted event to remove ourselves. This way we can be sure the session will be available for response serialisation.
public class SessionOperationContext : IExtension<OperationContext>
{
public ISession Session { get; private set; }
public static SessionOperationContext Current
{
get
{
OperationContext oc = OperationContext.Current;
if (oc == null) throw new InvalidOperationException("Must be in an operation context.");
return oc.Extensions.Find<SessionOperationContext>();
}
}
public void Attach(OperationContext owner)
{
// Create the session and do anything else you required
this.Session = ... // Whatever instantiation method you use
// Hook into the OperationCompleted event which will be raised
// after the operation has completed and the response serialised.
owner.OperationCompleted += new EventHandler(OperationCompleted);
}
void OperationCompleted(object sender, EventArgs e)
{
// Tell WCF this extension is done
((OperationContext)sender).Extensions.Remove(this);
}
public void Detach(OperationContext owner)
{
// Close our session, do any cleanup, even auto commit
// transactions if required.
this.Session.Dispose();
this.Session = null;
}
}
We've used the above pattern successfully in high-load applications and it seems to work well.
In summary this is similar to what the new WcfOperationSessionContext does (it wasn't around when we figured out the pattern above;-)) but also overcomes issues surrounding lazy loading.
Regarding the additional questions asked: If you use the model outlined above you would simply do the following:
void SaveMyEntity(MyEntity entity)
{
SessionOperationContext.Current.Session.Save(entity);
}
You are guaranteed that the session is always there and that it will be disposed once the WCF operation is completed. You can use transactions if required in the normal way.
Here is a post describing, in detail, all the steps for registering and using the WcfOperationSessionContext. It also includes instructions for using it with the agatha-rrsl project.
Ok, after few days of reading internet posts etc. all approaches shown in the internets seems to be wrong. When we are using UnitOfWork pattern with NH 3^ with nhibernate transaction this all aprochaes are producing exceptions. To test it and proof that we need to create test enviroment with MSMQ transaction queue, special interface with OneWay operation contract with transaction required set on it. This approach should works like this:
1. We put transactionally message in queue.
2. Service is getting transactionally messege from queue.
3. Everything works queue is empty.
In some cases not so obious with internet approaches this does not work properly. So here are expamples which we tested that are wrong and why:
Fabio Maulo approach: Use ICallContextInitializer - open NH session/transaction on BeforeCall, after that WCF is executing service method, on AfterCall in context initializer we call session.Flush + transaction.commit. Automaticly session will be saved when transaction scope will commit operation. In situation when on calling transaction.Complete exception will be thrown WCF service will shutdown! Question can be ok, so take transaction.Complete in try/catch clausule - great! - NO wrong! Then transaction scope will commit transaction and message will be taken from queue but data will not be saved !
Another approach is to use IDispatchMessageInspector - yesterday I thought this is best approach. Here we need to open session/transaction in method AfterReceiveRequest, after WCF invoke service operation on message dispatcher inspector BeforeSendReply is called. In this method we have info about [reply] which in OneWay operation is null, but filled with fault information if it occured on invoking service method. Great I thought - this is this ! but NOT! Problem is that at this point in WCF processing pipe we have no transaction ! So if transaction.Complete throw error or session.Flush will throw it we will have not data saved in database and message will not come back to queue what is wrong.
What is the solution?
IOperationInvoker and only this!
You need to implement this interface as a decorator pattern on default invoker. In method Invoke before call we are openning session/transaction open then we call invoke default invoker and after that call transaction.complete in finally clausule we call session.flush. What types of problem this solves:
1. We have transaction scope on this level so when complete throws exception message will go back to queue and WCF will not shutdown.
2. When invocation will throw exception transaction.complete will not be called what will not change database state
I hope this will clear everyones missinformation.
In some free time I will try to write some example.
Hi
Maybe this look like ridiculous but this is problem at least for me
I wrote duplex WCF service, in my service I need to get active client service and save them, and when with occurred special event I call specific client and send some values for it. So I define dictionary and save client in that. (With this method client calls)
public static Dictionary<int, IServiceCallbak> ActiveClients;
public void IConnect(int SenderId)
{
if (ActiveClients == null)
ActiveClients = new Dictionary<int, IServiceCallbak>();
Client = OperationContext.Current.GetCallbackChannel<IServiceCallbak>();
if (ActiveClients.Count(ac => ac.Key == SenderId) > 0)
ActiveClients.Remove(SenderId);
ActiveClients.Add(SenderId, Client);
}
So then when I need find client from that dictionary and call specific method : Client.DoSomthing().
Also when Client wants to exit, it calls IDisconnect method which will remove client from dictionary.
so I manage Active-client in service!!!
But there is problem in client for managing themselves
After a period time which define in app.config service connection will be closed and you should renew that and then open the service.
So in this case:
1)Is there any solution for recreate and open the service object automatically in client.
2)Or when in server side when service want call clients, check state of client-service-object from that dictionary, and reopen connection from server-side (Ridiculous-solution)
Edit
I think better solution is to handle Suggestion 1, I don't know how!!!.
So for now the question is: Is way exist to do Suggestion 1 Or not? Previously I describe Suggestion 1 in Comment:
"And automatically refer to event for this case(like closing or aborting), but I don't find anything for doing this in Service-Client"
In order to prevent the server side from closing the connection you could set up a Heartbeat() method in the contract that the client could call periodically. This is not ideal however, for one thing because the underlying socket could drop and this does nothing to remedy that.
As far as your suggestion 1) if on the client side you are inheriting from ClientBase you are somewhat stuck in that no indication of a problem may be given until you call a method to route to the service. You would have to wrap the call in a try / catch and then employ some reconnect logic:
public class MyClass : ClientBase<IContract>, IContract
{
public void ServiceMethod(String data) {
try {
base.Channel.ServiceMethod(data);
}
catch (CommunicationException ce) {
// Perform some reconnect logic here
base.Channel.ServiceMethod(data);
}
}
}
Your comment for suggestion 2) is correct, if there are any firewalls between the server side and client they would most likely not allow the connection
Edit:
To expand on my suggestion for 1), you would need to create a new connection when the call to the service fails with a CommunicationException. The simplest approach would be to create the service channel in the constructor and then create another when the call fails:
class ServiceClient {
Service1Client mService; // Class generated by VS tool
public ServiceClient()
: base() {
mService = new Service1Client();
}
#region IService1 Members
public string GetData(int value) {
CommunicationState state = mService.State;
if (state == CommunicationState.Closed || state == CommunicationState.Faulted) {
mService = new Service1Client();
}
try {
// Note: The state checked above may not be accurate,
// hence the try...catch
return mService.GetData(value);
}
catch (CommunicationException) {
mService = new Service1Client(); // Reconnect logic
return mService.GetData(value); // If it fails again we are out of luck...
}
}
#endregion
}
Edit2:
In WCF the session is handled by the client, if the session between the client and the service is lost, I know of no way to restore that session, either from the client or the service. You are, unfortunately, stuck here.
If the service wants to send via the callback with a broken session, simply put, it can't. Because of the way networks work the service may not know the actual client address. This and various other issues (like firewalls) mean that trying to reestablish a connection to the client from the service just isn't practical. The only approach for the service is to store what data it wanted to send to the client and send it when the service detects that the client has reconnected.
There is no guarantee that the client will know of the underlying socket dropping, until the client tries to send something over the socket, hence the try...catch. Recreating the channel from the client once it becomes aware of a broken connection is the only way I know of to handle the issue; which is what the code example does.
The heartbeat idea is a way to proactively deal with broken connection. Its efficiency depends on your requirements as to how fast you need to detect a broken connection and how many clients are present. The more clients connected the longer the heartbeat would have to be so that you don't put a load on the network at the service.
Edit3:
After some additional digging there may be a way to do what you want automatically. You can create what is known as a Reliable Session. Activating this involves creating additional entries in the config:
<netTcpBinding>
<binding>
<reliableSession ordered="Boolean"
inactivityTimeout="TimeSpan"
enabled="Boolean" />
</binding>
</netTcpBinding>
It is also available for Http related bindings, check out the link to the Microsoft documentation on the feature.