Dynamic C#.NET Webservice

Question

I am using a class in a C# ASP.NET project to allow a script written in some random scripting language to expose webservice methods dynamically - in other words, the script should be able to expose a method of any name with any signature (as long as it's valid, anyway) to the outside world through this SOAP interface (able to add and remove them at will, without needing a hard code change), and as such I need to be able to create a webservice class in C# while being able to dynamically add and remove methods at runtime.

Now, the best plan I've been able to come up with so far is (runtime) generating C# code to represent the webservice, using System.Reflection.Emit to compile it and then loading the assembly at runtime - all whenever the script adds or removes a method to/from the service (should not happen very often, mind).

Does anyone have a better idea than this?

Answer 1

You can modify WSDL by using SoapExtensionReflector class. From Kirk Evans Blog:

The SoapExtensionReflector is called when your type is being reflected over to provide the WSDL definition for your service. You can leverage this type to intercept the reflection call and modify the WSDL output.

The following example removes the first method out of 2 web service methods:

[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
[System.ComponentModel.ToolboxItem(false)]
public class Service1 : System.Web.Services.WebService
{
   [WebMethod]
   public string HelloWorld()
   {
      return "Hello World";
   }

   [WebMethod]
   public int Multiply(int a, int b)
   {
      return a * b;
   }
}

Create a class inherited from SoapExtensionReflector:

namespace TestWebservice
{
   public class MyReflector : SoapExtensionReflector
   {
      public override void ReflectMethod()
      {
         //no-op
      }

      public override void ReflectDescription()
      {
         ServiceDescription description = ReflectionContext.ServiceDescription;
         if (description.PortTypes[0].Operations.Count == 2)
            description.PortTypes[0].Operations.RemoveAt(0);
         if (description.Messages.Count == 4)
         {
            description.Messages.RemoveAt(0);
            description.Messages.RemoveAt(0);
         }
         foreach (Binding binding in description.Bindings)
         {
            if (binding.Operations.Count == 2)
               binding.Operations.RemoveAt(0);
         }
         if (description.Types.Schemas[0].Items.Count == 4)
         {
            description.Types.Schemas[0].Items.RemoveAt(0);
            description.Types.Schemas[0].Items.RemoveAt(0);
         }
      }
   }
}

Add this to configuration/system.web section in web.config:

<webServices>
   <soapExtensionReflectorTypes>
      <add type="TestWebservice.MyReflector, TestWebservice" />
   </soapExtensionReflectorTypes>
</webServices>

This should give you a starting point to dynamically removing methods from WSDL document. You would also need to throw NotImplementedException from web method if it is disabled.

Finally, you need to disable web service documentation produced by invoking .asmx endpoint without ?WSDL parameter. Set href attribute of wsdlHelpGenerator element to some URL. You can use DefaultWsdlHelpGenerator.aspx as a starting point for your own documentation handler. See question on web service documentation in XML Files, August 2002.

Answer 2

XMLRPC is fairly dead, isn't it?

SOAP implies a WSDL. How do you generate the WSDL dynamically?

You should look into using WCF. I expect you'll be able to take control of the process of generating the WSDL (and other metadata), yet you should also be able to take control of the processing of incoming messages. In particular, you will be able to examine the incoming messages to determine which script to run, what parameters to pass, etc.

Answer 3

You could create a WCF service with an input and output type of xs:any and handle the incoming request as a raw Message. That would allow you to accept any type of data and return any type of data. You would not use data contracts or static types, just a Message in and a Message out.

The problem with this approach is that generating a proxy from the WSDL really does nothing to help the consumer other than provide a wrapper to call the method. Providing data that is acceptable to the method would require hand-rolling data types, etc which is not that hard, it is just not as intuitive as a hard, typed contract.

Answer 4

Does it have to be a SOAP interface? That sounds like it might be more suitable to a route/REST/etc based API. You could do something in ASP.NET MVC (with a custom IController.Execute method that resolves the action to the method) pretty easily (in fact, I'm working on something very similar for some of my own code at the moment).

For example, you might have routes:

http://myserver/myservice/mymethod

that accepts (either in the body or args) the payload (parameters), and returns the result in the response. In non-MVC you should be able to do something similar with a wildcard-mapped generic handler.