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Tuesday, December 4, 2012

Anything but restful

Last week I was asked to integrate some "webservices" into a .NET application. I say "webservices", but that word can mean anything from SOAP to custom format XML to some icky CSV that uses the asterisk for a delimiter.
I was lucky though: the url made obvious that this webservice was WCF-based, some methods returning json, and equivalent methods returning xml. All request parameters are to be sent as json through the querystring.
I'm an optimistic fool, so I simply use the "Add Service Reference" to add a link to the service, and all seems well. Until I try to actually use the service: my application throws up the following:

Could not find default endpoint element that references contract 'IServiceInterface' in the ServiceModel client configuration section. This might be because no configuration file was found for your application, or because no endpoint element matching this contract could be found in the client element. 

Sure enough, when I check in my configuration file, the following has been helpfully added:


Well thank you very much, Visual Studio. You're a great help.
Google turns out to be more of a help, and points me to the following article telling me: what you're trying to do does not work and will not work. Because they're so RESTful. Instead I should be using the WebChannelFactory class to generate a channel and use that to call the webservice.
No problem.
I  re-use the proxy classes generated in my non-working service reference (but delete the wrapper classes), and point the WebChannelFactory to the generated service interface. Does that work now?
No of course it doesn't work: "405 http method POST is not supported by this url".
Sure enough, Fiddler shows that the service is being called using a POST of the request paremeter serialized as xml. "Stupid boy, " Google tells me again, "you should be adding the WebGet attribute to your method, and if you want json, you need to add a behavior to your endpoint that selects the JsonQueryStringConverter". "And while you're on it, " Google continues, "don't forget to define a UriTemplate for your WebGet attribute".
Done, done and done.
Now does it work? No of course it bloody well doesn't work. No more errors, but no deserialized data either. The json serialized data appears to be wrapped in a single key 'd' for all requests. The class structure doesn't match up to the json hierarchy, so nothing gets deserialized. So I wrap all my return types in a small generic class:

  public class JsonWrapper<T>
    private T _d;
    public T d {
      get { return _d; }
      set { _d = value; }

Finally I start seeing data. WCF and the one side, WCF on the other side and nothing works by itself. Some of the articles I was reading had the gall to tell me this was because WCF has great extensibility. Is "extensible" newspeak for "does nothing useful out of the box"?
Sure, it is very extensible, but in the time it took me to figure out how to get it to call a simple json webservice, I could just as easily have used the WebClient class to call the url, and run the return data  through  NewtonSoft's Json.NET. In fact, I could have done it three times.
If the service reference is able to properly generate proxy classes, why can't the service reference also send the necessary metadata to configure all that stuff I had to do manually? Where was the added value in all that WCF stuff? Is this a useful abstraction, or needless obfuscation?
Now that I've got a bit more of a handle on how it works, I'll give it another chance. But I'm not sold.


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