WebHttpBinding and Callbacks

I have asp.net site where I call my WCF service using jQuery. Sometimes the WCF service 开发者_C百科must have an ability to ask user with confirmation smth and depend on user choice either continue or cancel working

does callback help me here? or any other idea appreciated!

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Callback contracts won't work in this scenario, since they're mostly for duplex communication, and there's no duplex on WebHttpBinding (there's a solution for a polling duplex scenario in Silverlight, and I've seen one implementation in javascript which uses it, but that's likely way too complex for your scenario).

What you can do is to split the operation in two. The first one would "start" the operation and return an identifier and some additional information to tell the client whether the operation will be just completed, or whether additional information is needed. In the former case, the client can then call the second operation, passing the identifier to get the result. In the second one, the client would again make the call, but passing the additional information required for the operation to complete (or to be cancelled).

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Your architecture is wrong. Why:

• Service cannot callback client's browser. Real callback over HTTP works like reverse communication - client is hosting service called by the client. Client in your case is browser - how do you want to host service in the browser? How do you want to open port for incoming communication from the browser? Solutions using "callback like" functionality are based on pooling the service. You can use JavaScript timer and implement your own pooling mechanism.
• Client browser cannot initiate distributed transaction so you cannot start transaction on the client. You cannot also use server side transaction over multiple operations because it requires per-session instancing which in turn requires sessinoful channel.
• WCF JSON/REST services don't support HTTP callback (duplex communication).
• WCF JSON/REST services don't build pooling solution for you - you must do it yourselves
• WCF JSON/REST services don't support distributed transactions
• WCF JSON/REST services don't support sessionful channels / server side sessions

That was technical aspect of your solution.

Your solution looks more like scenario for the Workflow service where you start the workflow and it runs till some point where it waits for the user input. Until the input is provided the workflow can be persisted to the database so generally user can provide the input several days later. When the input is provided the service can continue. Starting the service and providing each needed input is modelled as separate operation called from the client. This is not usual scenario for something called from JavaScript but it should be possible because you can write custom WebHttpContextBinding to support workflows. It will still not achieve the situation where user will be automatically asked for something - that is your responsibility to find when the popup should appear and handle it.

If you leave standard WCF world you can check solutions like COMET which provides AJAX push/callback.