Web Service Interface

Question

I'm looking to add a web services interface to an existing server application. The set of services to expose is not known at compile time and can change over the runtime life of the server.

From a tech standpoint all the server/web services endpoints will be on Windows.

In our server app a user will have the option to register workflows as 'web services callable'. This will create the WSDL defining this particular workflow service.

For the calling endpoint I'm thinking of an HttpModule that accepts the inbound web service request, unpacks the request and converts the XML data types into our server applications "domain", calls the server and finally converts the server outputs back into XML for return down the http connection.

Does that make sense?

Critical comments welcomed.

Answer 1

an HttpModule that accepts the inbound web service request, unpacks the request and converts the XML data types into our server applications "domain", calls the server and finally converts the server outputs back into XML for return down the http connection.

That is what all web service frameworks do (e.g. Metro, Axis). So I can't see your problem. What's your concern with this approach?

The downside for the client is that, as far as I understand it, availability of your services may change over time. So you should consider a way to inform the client if the service is available (other than getting a time out error because it is not there), e.g. WS-ResourceLifetime or UUDI.

Answer 2

In effect writing your own WS engine. Clearly doable, but quite a bit of work to get right from scratch. I guess if you find some open source implementation, then adapting it should be possible.

A rather dirtier alternative, but one I've seen applied in another context, is to go for a simgle WS interface

String call( String workkFlowName, String payload)

The payload and response are both Strings containing any XML. So the caller needs to undestand the schemas for those XMLs. From the client's perspective the amount of coding effort is not much different. Your coding effort would I think be significantly redcued.

Answer 3

I ended up creating a C# class that implements the IHttpHandler interface. The implementation serves up the WSDL of the services exposed from our app and accepts SOAP posts to invoke the services. In the end most of the work went on converting SOAP types to our types and vice versa.