We are trying to build a Nservicebus service that can communicated with form and wpf based clients using WCF. I have read that you can inherit from WcfService.
like:
public class ThirdPartyWebSvc : WcfService<ThirdPartyCmd, ThirdPartyCmdResponse>
And then you simple create a endpoint in the app.config and you done like described here. but the problem is that i have to create a endpoint for every command.
I would like to have a single endpoint that excepts any command and returns its response.
public class ThirdPartyWebSvc : WcfService<ICommand, IMessage>
Can someone point me in the right direction? Using Nservicebus for client communication can't be done for us and i don't want to build a proxy like server unless thats the only way to do it.
Thanks
So from what I can gather, you want to expose a WCF service operation which consumers can call to polymorphically pass one of a number of possible commands to, and then have the service route that command to the correct NServiceBus endpoint which then handles the command.
Firstly, in order to achieve this you should forget about using the NserviceBus.WcfService base class, because to use this you must closely follow the guidance in the article you linked in your post.
Instead, you could:
design your service operation contract to accept polymorphic requests by using the ServiceKnownType attribute on your operation definition, adding all possible command types,
host the service using a regular System.ServiceModel.ServiceHost(), and then configure an NserviceBus.IBus in the startup of your hosted WCF service, and
define your UnicastBusConfig config section in your service config file by adding all the command types along with the recipient queue addresses
However, you now have the following drawbacks:
Because of the requirement to be able to pass in implementations of ICommand into the service, you will need to recompile your operation contract each time you need to add a new command type.
You will need to manage a large quantity of routing information in the config file, and if any of the recipient endpoints change, you will need to change your service config.
If your service has availability problems then no more messages to any of your NSB endpoints.
You will need to write code to handle what to do if you do not receive a response message from the NSB endpoints in a timely manner, and this logic may depend on the type of command sent.
I hope you are beginning to see how centralizing this functionality is not a great idea.
All the above problems would go away if you could get your clients to send commands to the bus in the standard way, but without msmq how can you do that?
Well, for a start you could look at using one of the other supported transports.
If none of these work for you and you have to use WCF hosted services, then you must follow the guidance in the linked article. This guidance is there to steer you in the correct direction - multiple WCF services sounds like a pain, until you try to centralize them into a single service - then the pain gets bigger, not less.
Related
The project I'm currently working on includes a server that receives C# scripts (partial code) from clients, wraps it to create a complete class, compiles it then load it into a separate AppDomain for execution.
A task (currently running script) can send feedback to the user at any point of it's execution, as defined in the script by the user. And possibly the task might wait for a response from the user (currently assuming it's only right after having sent feedback). And the user might, at any moment, decide to kill a task.
The server is implemented as a Windows Service hosting a WCF Service Library.
As I don't want to overcomplicate the client to make it communicate directly with the dynamically created AppDomains, the (partial) solution that I considered after some research was hosting a second WCF service with named pipe binding to make the dynamic AppDomains use it as a relay between them and the client facing WCF service.
My issue is that now I can't think of a clean way to have the two WCF services interact.
My ideas are:
Having them maintain direct references to each other:
Seeing as Normally both of the services are singletons it shouldn't be hard to do.
But that would be a pain to maintain in the case one of them fails and needs to be restarted. (I'm still new to WCF so I have no idea how common that is, but it's still an issue to consider. I think.)
Introducing some sort of a "message queue" (or two, one for each direction) with properties that can be set and subscribed to. Thus when one service sets a property an event will be triggered in the second. But that feels somewhat hacky to me, even though I can't really think of any clear issues.
I could really use some expert input on what I'm trying to accomplish, be it opinions on my thoughts or new ideas. Even if that involves rethinking the architecture. This project is still in an early enough stage to afford some rework, as long as there is enough reason to do that of course.
Since I've put lots of efforts (read: 2 minutes on paint) to prepare a quick (read: useless) schema of the system, I'll link it here since I don't have the reputation to post images:
Link to schema
Edit:
As I now have the reputation thanks to an upvote:
Still after rereading my question, I feel that perhaps I have been looking at this issue from a too narrow perspective by thinking of the services as something more special than ordinary classes. The more I think about it the more I feel that the observer pattern is probably the best approach to take.
Just for the record, and to avoid leaving my (silly) question unanswered, I've realised that I was looking at this too narrowly by trying to find a solution specific to WCF services.
And finally I ended up using a variation of the observer pattern (based on the IObservable<T>Interface).
I came across the same issue. The way I handled a duplex communication between the two servers is as following:
For each process (AppDomain Seperated Task) create a pair of WCF services. Both services have their Instancing set to PerSession (no need for singleton which may cause problems in the long run like disconnect). This means the Client will be communicating for each process (AppDomain Separated Task) with two distinct Service instances or a service pair (i.e. Service1 and Service2).
We want a duplex communication in between these two services, which means that both can communicate with the other and pass data (in the form of a DataContract class object).
For this:
1- Declare two services (i.e. in a separate class library) and host them (self hosting or else).
2- Create your DataContract class and add any property, collection, enum etc. as you like. Both services must have a get-set property for this class.
3- In the same class library (where the Service1 and 2 classes reside), create another class. This class will act as a depository for the Service pair instances. It has a static List in order to register the service pair instances (you can identify each service with a GUID).
4- We setup the client proxy using svcUtil.exe (or by code). When the client makes a service request, a service (i.e. service1) will be created by the WCF. At service1, create or launch the process (App Domain Separated Task) as client2 and at its constructor create the Service2 proxy by code.
5- Initialize the Service2 instance (i.e. by a call to the service2) and register the service pair instances at static list of the depository (so that it can be retrieved later for duplex communication). Now we have both service instances and both of them are registered as a pair into a static list.
6- Start communication between both services by making a call from Client1 proxy.
7- At Service1 call method, retrieve the service pair from the static list. Deep copy (DeepClone) the Datacontract class object from Service1 to the Service2 using the get-set property mentioned at (2). (Note that you can use one of the many Deep Clone libraries from Nuget like DeepCloner).
8- Make a call back from Service2. Client2 now has the identical DataContract class property values as Client1
9- Repeat steps 6-8 for Client2 proxy for Service2-Service1 communication.
My WCF service is suppose to push a call to MSMQ (queue), which eventually will call another WCF service to perform database operations.
I have created a new project for MSMQ operations, and it has an "xamlx" file for the workflow. How do (or in which event) I initialize objects so that they can be accessible in the destination WCF?
hugh makes a great point. Based on what you've told us, it doesn't seem that workflow is absolutely necessary here.
If it is needed for some other reason (e.g. flowing a distributed transaction), then in your workflow project, you should be able to do Add Service Reference to your destination WCF service. This will generate you activities that match the signature of your destination WCF service. The objects that those activities expect can be initialized via expressions, e.g. directly on the activity in the expression text box, or using a variable that is set via an Assign activity.
Hope that helps,
-- Dave, WF Team
What's the use of action/reply action for service operation in WCF. So far, what I've understood is; action is used by WSDL to identify the service operation to which the message from the client belongs and in return reply action is used by service operation to identify the caller to which reply message belong --> Please correct me if I am wrong with this!
Now, I want to understand; what's the real use (apart from handling anonymous messages by using aster ix [*]), I mean this could well be handled internally by WCF instead of exposing it to the developer.
Also, why is action and replyaction required at all? I mean, we already have a name property for the service operation to identify the method and when I call Proxy.SomeMethod() then somemethod is already mapped to the Name property and it should be enough to identify the destination method for the message and similarly the replyaction. Please clarify.
Can I please get a simple real world scenario/or link to that to understand Action/ReplyAction in real life.
Many Thanks.
Actions are part of the various SOAP and WS-* specifcations.
So the first point is that this is not something unique to WCF it is a standard part of the specification you need to support if you want to have interoperable web services. They are used for message routing and other message handling functions.
Second, WCF DOES manage these by default. You only need to specify them yourself if you wish to customise or manage them in some other way. E.g. WCF will automatically generate them into the WSDL for you. WCF will also use them by default when it is selecting which operation to invoke for an incoming message. Again, WCF provides extension points to customise this behavior if you require.
I have a universal service hosted on IIS7 that accepts a Message and returns Message ( with Action="*"). This service still publishes meta for the clients.
This metadata is explicitly specified using LocationUrl property in ServiceMetadataBehavior.
We have a requirement that the metadata can change during lifetime of the service, so in essence metadata has a lifetime.
I tried adding IWsdlExportExtension to the service endpoint behavior, but the ExportEndpoint method only gets called once (when the service is loaded first time). Is there a way for me to invalidate the loaded metadata so that anytime there is a call for wsdl using HttpGet, the behavior gets called ?
What you are asking for (changing the published service definition at runtime) is not possible - you need to remove the requirement which specifies that the metadata can change over time.
Once you've published a service, the only reason the service specification should change is because the service has been upgraded.
You should look closer at the business requirement which is making this technical requirement necessary, and try to find another way to satisfy it (perhaps post in programmers.stackexchange). Perhaps you can have multiple services available, and switch between the services over time - but this is a bit of a stab in the dark without knowing the business requirement.
No there is no way. Moreover if you needed you are up to your fully custom solution because this is out of scope of web services. Changing metadata means changing the service itself = its internal logic which always result in restarting the hosting process and publishing new metadata.
I'm looking at creating a data query WCF service over a slow satellite connection and I really like WCF Data Services. The problem I see is that HTTP is a very verbose format and since everything I'm doing is internal and .NET, is it possible to use NetTcpBinding instead to reduce some of the overhead?
Is this even possible? Advisable?
While researching this on my own, i ran across the MSDN article on Self-Hosted WCF Data Services. This article notes that you can host the service with DataServiceHost which still requires HTTP (it's derived from WebServiceHost).
But you can also roll your own host using IDataServiceHost. Here's an excerpt from the MSDN article:
For cases where the WCF host
implementation is too restrictive, you
can also define a custom host for a
data service. Any class that
implements IDataServiceHost interface
can be used as the network host for a
data service. A custom host must
implement the IDataServiceHost
interface and be able to handle the
following basic responsibilities of
the data service host:
Provide the data service with the service root path.
Process request and response headers information to the appropriate
IDataServiceHost member implementation.
Handle exceptions raised by the data service.
Validate parameters in the query string.
The article seems to suggest that MS has properly segrated data-service responsibilities from network interface responsibilities. If that's so, then I should be able to write a NetTcpDataServiceHost. Has anyone ever written a IDataServerHost? Any suggestions?
No, WCF Data Services are built on top of REST, and REST itself is very intimately and completely based on the HTTP verbs like GET, PUT, POST etc. - you cannot run those over NetTcp, since those are intrinsically tied to the HTTP protocol stack.
Maybe there are other options for you to reduce the data being transmitted? Tweak your objects - trim the fat, if you can - both on the number of rows retrieved at once, and the number of attributes/data fields transmitted. That's probably you're most promising approach.