Integrating REST Into an Existing C# Application

Introduction

I was trying to add REST web services to an existing C# application. I could only find information as to how to create a new C# REST app, but very little on retrofitting older apps. The results below are not complicated but are the culmination of an afternoon's research.

The Solution

First, create a new public interface for the service contract:

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

namespace bob
{
    [ServiceContract]
    public interface IService
    {
        [OperationContract]
        [WebGet(UriTemplate = "/GetSoftwareVersion", ResponseFormat=WebMessageFormat.Json)]
        String GetSoftwareVersion();
    }
}

Here, I've defined a new interface called IService. Note the two ServiceModel namespaces I'm using.... very important. Also, you will need to include the references by the same name into your project.

I then defined a new method I want to call via REST called GetSoftwareVersion. The UriTemplate states what you add (/GetSoftwareVersion) to the base URI (spec'ed elsewhere, but currently set to 'http://localhost:10870') to form the URI needed to call this method. The ResponseFormat stipulates that I want the data returned using JSON format, rather than the standard XML.

Next, I define a class to implement this interface and therefore my REST services.

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

namespace bob
{
    public class RestService : IService
    {
        /// <summary>
        /// Gets the version
        /// </summary>
        /// <returns>The Version String</returns>
        public String GetSoftwareVersion()
        {
            return App.Instance.GetSoftwareVersion();
        }
    }
}

My new class, RestService, implements the interface, or service contract, I defined earlier. Again, note the ServiceModel references. Since we also have a gSOAP (C++) interface, rather than completely re-jigging the main App class (which has a singleton for external access) or making the RestService a singleton itself (which might be useful down the road for other reasons), I just point the REST service to the existing method. Simple and it works.

Next, the app.config needs to be tweaked:

<system.serviceModel>
    <services>
        <service name="bob.RestService">
            <endpoint binding="webHttpBinding" contract="bob.IService"
                      behaviorConfiguration="webHttp"/>
        </service>
    </services>
    <behaviors>
        <endpointBehaviors>
            <behavior name="webHttp">
                <webHttp/>
            </behavior>
        </endpointBehaviors>
    </behaviors>
</system.serviceModel>

Things of note are the service name (bob.RestService) and endpoint contract (bob.IService). Point the service name at the REST implementation class and the contract at the interface.

I then "borrowed" the ThreadedServiceHost class from here, changed the ServiceHost class reference to WebServiceHost, updated the project reference, removed the endpoint and associated code (simplified things), and made a call to start it from the App() (constructor) ala:

// Fire up REST web services.
restHost = new ThreadedWebServiceHost<RestService>(Properties.Settings.Default.REST_ENDPOINT);

REST_ENDPOINT is simply the base URI where my services are located (http://localhost:10870/App). Compile and point your browser at http://localhost:10870/App/GetSoftwareVersion. You should see the result on screen.

Refs:

• http://www.codeproject.com/Articles/148762/NET-4-0-RESTful-Web-Service-Introduction
• http://www.codeproject.com/Articles/16299/Hosting-WCF-services-in-a-Windows-Forms-Applicatio
• http://msdn.microsoft.com/en-us/library/system.servicemodel.servicehost.aspx
• http://msdn.microsoft.com/en-us/library/dd203052.aspx
• http://msdn.microsoft.com/en-us/library/system.servicemodel.web.webservicehost.aspx