Can I listen to a WCF event from a web client? Is this possible? I am not talking about call backs, I want the WCF service to raise and event and the web client to be able to listen. Is there a good example of this in C#?
There are no events in WCF. If you want mimic event you still have to call some operation exposed on all clients = you must call WCF service or callback exposed on client.
What do you mean by web client? Do you mean javascript code running in web browser? In such case no you can't achieve that with WCF. You can only use AJAX calls from borowser and continuously poll the service for possible "event".
If you mean ASP.NET application then the answer is theoretically yes, practiacally it will be pretty hard. The reason is that in ASP.NET you handle only current HTTP request by some handler - for example Page. The lifetime of the handler is only for serving the single request. Due to that using duplex service doesn't make to much sense because for receiving callbacks by duplex service your client proxy must live. If you open the proxy in Page it will die after serving the request. If you open the proxy in separate thread you must somehow corelate incomming callbacks to actual client but the client still have to poll the web server to be notified about callbacks. Similar situation will be with exposing the service on ASP.NET application.
Difference between asynchronnous and duplex calls is big. In asynchronnous pattern single request always have single response. Resonse is not sent without request. In duplex pattern you can make single request and receive thousands callback from server.
Related
I have system like this:
Windows service (WCF, data/events) <-> Web app <-> Web client
I need simultaneous response for clients requests. I have some events from service for clients too. So duplex channel is the way to go. But I need high throughput, because clients calls simultaneously.
Request/reply approach
In order not to serialize channel requests I need more channels for parallel calls, right? But how to handle callback channel then? Ho to keep it still open for receiving events, even on channel errors?
OneWay approach
On channel should be enough (no waiting for data preparation), but how to link data sent to callback with original request, to be able to compose response for client?
What is the way to go? Thank you.
In a simple case, when a web client sends a request to the web app, and web app (possibly) sends a request(s) to WCF service, there's no need in duplex binding at all.
As for events, raised by the service to be fired in Web client, I'd suggest to use a message broker which supports WebSockets - for example RabbitMQ. It has a plugin compatible with WebSockets and WCF binding.
Putting things together, one can create a RabbitMQ server, which accepts messages from WCF service and sends it to Web client, which subscribes to the event feed from Javascript.
How can I build a synchronous WCF service that wraps asynchronous MSMQ communications?
Let us have a simple scenario. I have a client which supports only synchronous web service calls. I need to send a synchronous request for "Order", but the back end system exposes this as an asynchronous request and response MSMQs. The WCF does not need to have any logic just wrap the MSMQ asych communication and pass parameters back and forth.
Grateful for your help
Let us have a simple scenario. I have a client which supports only synchronous web service calls
Synchronous call means you are using same link (end point url) or channel for your communication between client and server, so according to your assumption no.
Reason: Every time your client will send a request, it will keep waiting for response from server and will produce error.
Alternatively,You can define two services (different end point url) in your wsdl or webservice, one for request and one for response.
At client side you need to invoke these end point url saperately for sending request and receiving response,so it will appear as synchronous but ultimately it will be asynch. Thats all you can do in this scenario.
As per my understanding.
I am currently developing a WCF duplex Service for 2 clients. The first client would be an asp.net webpage which upon receiving a posting, it will send the data over to the service. When the service receives the data, it will then AUTOMATICALLY send it to the second client which is a winform app through the callback channel...
To make it simpler.
Asp.net will invoke the wcf
The wcf will reside on the iis server, same as the asp.net
WCF will require to send a data to the windows form application that is running on a client side. Only 1 instance of this application will be run at a time.
Your service should know nothing about the clients attached to it. Doing so pretty much breaks the intention of WCF.
A better solution might be to have your clients subscribe to "events" that your service can fire off. Or maybe the client can provide some information in their requests that indicates a service and method to call back to when needed.
I have a WCF service hosted as Windows Service with most of its methods currently defined as:
[OperationContract(IsOneWay = true)]
But, now I need to send response back to the calling Web application for these service methods.
Now, because service methods are bit heavy (FYI, they are reporting methods that needs to do mail merge for a no. of records), I am thinking to either queue them or to process asynchronously, so essentially when the request is sent to the service it should save the request to database/queue, returning Request-Id to calling Web application.
In the mean-time, WCF service can just process incompleted requests from the queue or database.
Then either calling Web application can ping WCF service for status of request because it has Request-Id or
WCF service can ping back to calling app when the process corresponding to a Request-Id is completed.
To achieve above, can anyone please guide what changes I need to make to my WCF service (which currently has all one way operation)?
Also, please guide me whether I need to go for Asynch operation or message queuing?
Thank you!
Of course, going Async is simple:
remove the OneWay on the OperationContract in question and regenerate your Service WITH Async methods. There's a reason why Silverlight forces you to use Async operations. They do force you to rethink your UI.
Is there any way to enforce that a method call in soap based wcf is called as an HTTP get? I'm not sure if this would be handled on the client or server side. We wanted to have the wcf call process as a get vs. post for cacheability, etc.
I'm also not sure how to monitor a wcf service to determine if calls are doing gets or posts (or if it always does one or the other). Can I use fiddler for this?
I would imagine I could use a restful wcf service to wrap the call, but I wasn't sure if there was a way to do it straight in a soap based service.
Out of the box WCF functionality does not support SOAP HTTP GET. But WCF is extensible so you can try to develop custom binding (with cutom channel or behavior) supporting this feature.
Caching is supported in WCF 4 REST services. REST services allow all basic HTTP methods.
You can use Fiddler to monitor the gets and posts.
Check out this post about calling a WCF service with an HTTP GET.