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Answer 1

+8 A:

Why don't you migrate your ASMX webservice to WCF?

The WCF API in .NET Framework 3.5 supports JSON web services natively.

In addition Microsoft declared ASMX as "legacy technology", and suggests "Web services and XML Web service clients should now be created using Windows Communication Foundation (WCF)". (Source).

You may want to check out these links to get started:

In addition, you may also want to read through the following example which I "extracted" from a self-hosted WCF project of mine. Self-hosted WCF services do not require IIS, but can be served from any managed .NET application. This example is being hosted in a very simple C# Console Application:

IContract.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Runtime.Serialization;
using System.ServiceModel;
using System.ServiceModel.Web;

namespace MyFirstWCF
{
    [ServiceContract] 
    public interface IContract
    {
        [OperationContract]
        [WebGet(ResponseFormat = WebMessageFormat.Json, UriTemplate = "/CustomerName/{CustomerID}")]
        string GET_CustomerName(string CustomerID);
    }
}

Service.cs

using System;
using System.Collections.Generic;
using System.Runtime.Serialization;
using System.ServiceModel;
using System.ServiceModel.Activation;
using System.ServiceModel.Syndication;
using System.ServiceModel.Web;

namespace MyFirstWCF
{
    [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single, ConcurrencyMode = ConcurrencyMode.Multiple)]
    [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.NotAllowed)]
    public class Service : IContract
    {
        public string GET_CustomerName(string CustomerID)
        {
            return "Customer Name: " + CustomerID;
        }
    }
}

WCFHost.cs (Console Application)

using System;
using System.Collections.Generic;
using System.ServiceModel;
using System.ServiceModel.Web;
using System.ServiceModel.Description;
using System.Threading;
using System.Text;

namespace MyFirstWCF
{
    class Program
    {
        private static WebServiceHost M_HostWeb = null;

        static void Main(string[] args)
        {
            M_HostWeb = new WebServiceHost(typeof(MyFirstWCF.Service));

            M_HostWeb.Open();

            Console.WriteLine("HOST OPEN");
            Console.ReadKey();

            M_HostWeb.Close();
        }
    }
}

app.config

<?xml version="1.0" encoding="utf-8" ?>

<configuration>
  <system.serviceModel>
    <services>
      <service name="MyFirstWCF.Service">

        <endpoint address="http://127.0.0.1:8000/api"
                  binding="webHttpBinding"
                  contract="MyFirstWCF.IContract" />

      </service>
    </services>

  </system.serviceModel>
</configuration>

The above example is very basic. If you build a request with Fiddler to http://127.0.0.1:8000/api/CustomerName/1000 it will simply return "Customer Name: 1000".

Make sure to set the content-type: application/json in the request header. To return more complex data structures, you will have to use Data Contracts. These are constructed as follows:

[DataContract]
public class POSITION
{
    [DataMember]
    public int      AssetID { get; set; }

    [DataMember]
    public decimal  Latitude { get; set; }

    [DataMember]
    public decimal  Longitude { get; set; }
}

You need to add .NET References to System.RuntimeSerialization, System.ServiceModel and System.ServiceModel.Web for this example project to compile.

Daniel Vassallo 2009-12-14 19:57:25

Hmmm. Seems something is FUBAR on my machine. I do not have an option to create an AJAX WFC Service. Is there something I should install on top of VS2008?

Keith Barrows 2009-12-14 21:14:33

You can just create a normal WCF service; you can decorate your interface with attributes to indicate that the ResponseFormat will be JSON.

Jan Jongboom 2009-12-14 21:34:27

I don't have an option to create *any* WCF service. http://screencast.com/t/OGQwMDlk

Keith Barrows 2009-12-14 21:50:27

Can you try to create a new solution, to check if the WCF option appears? When you add a new project, you should have the choice of framework version, as shown here: http://www.techbubbles.com/net-framework/wcf-sample-in-visual-studio-2008/. Make sure you have .NET 3.5 selected wherever prompted.

Daniel Vassallo 2009-12-14 22:00:01

OK. Going that route I do have the option for a WCF project. Any references on building a .NET WCF JSON enabled WS *AND* calling it from a seperate (non .NET) web site? Maybe a pure HTML site with JS as the calling method?

Keith Barrows 2009-12-14 22:58:39

I would suggest checking out the links I have posted in my answer, and google a bit on WCF RESTful web services. You should be using the webHttpBinding. Methods will respond in JSON if their interface is decorated with `[WebGet(ResponseFormat = WebMessageFormat.Json]`.

Daniel Vassallo 2009-12-14 23:18:21

Been working through all the links you posted (TYVM!). Still not getting a simple service to run correctly. Getting brain wiped at this point. I created a seperate project for the WS. Now trying to figure out the "correct" way to merge it back into my Web project...

Keith Barrows 2009-12-14 23:57:59

Keith, give a look to the example I've included in the answer. This is from a self-hosted WCF project, so it was not being served from IIS.

Daniel Vassallo 2009-12-15 00:51:56

The example described above will return pure JSON, as you requested. It should work perfectly with your external JavaScript application. Obviously you will need to construct your Data Contracts according to the JSON format of your spec.

Daniel Vassallo 2009-12-15 01:07:42

If the JSON request is cross domain, you'll need to look into JSONP. You can implement it in .NET 2 using an extension - http://msdn.microsoft.com/en-us/library/cc716898.aspx. It's also supporting in .NET 4 - http://bendewey.wordpress.com/2009/11/24/using-jsonp-with-wcf-and-jquery/

Richard Szalay 2009-12-15 13:27:00

You can also use a very simple reverse proxy to get around the cross-domain limitation. However this is a problem of the client-side, and it appears to be outside Keith's control/responsibility.

Daniel Vassallo 2009-12-15 13:40:40

Answer 2

+2 A:

What's the "Content-Type" set to on the request to the method?

From what I've done with the ASP.NET, if it's set to text/xml, you'll get back XML; but if it's set to application/json, you'll get JSON back.

Chris Waters 2009-12-14 22:35:06

application/json in JS. Note: The JS is not on our pages! THe WS needs to respond to a foreign JS request.

Keith Barrows 2009-12-14 23:58:47

I think the point is that it will return the response in the type that is requested, which seems to be 'text/xml' in your example.Even if it's not a request from something you wrote, you could easily write a small JS script of your own to test it with 'application/json'

Chris Waters 2009-12-15 16:35:34

The content type is very important. Thanks!

Keith Barrows 2009-12-17 00:18:16

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