Archive for March, 2010

I’m using the ASP.NET MVC REST Toolkit for a REST API I’m building for a mobile infrastructure. Long story short, it will be responsible for service hundreds of thousands (if not millions) of users through their mobile phones and rich applications (Android, iPhone and eventually the WP7 Phones).

The one thing that the Toolkit did not provide out of the box was a way to use a container in the controller factory. Therefore I altered the ResourceControllerFactory to use Windsor Container as its default container. The code works great and I’m able to utilize dependency injection all throughout my app now.

The code for this is below:

//----------------------------------------------------------------
// Copyright (c) Microsoft Corporation.  All rights reserved.
//----------------------------------------------------------------

using Castle.MicroKernel;

namespace System.Web.Mvc.Resources
{
    using System.Collections.Generic;
    using System.Globalization;
    using System.Net;
    using System.Net.Mime;
    using System.Text;
    using System.Web.Routing;

    /// <summary>
    /// Specialized ControllerFactory that augments the base controller factory to make it RESTful - specifically, adding
    /// support for multiple formats, HTTP method based dispatch to controller methods and HTTP error handling
    /// </summary>
    public class ResourceControllerFactory : IControllerFactory
    {
        // Note: This has been changed from the regular controller factory provided
        // by the ASP.NET Team so that we can use Windsor Container to resolve
        // container dependencies.

        readonly IKernel _kernel;
        const string restActionToken = "$REST$";

        public ResourceControllerFactory(IKernel kernel)
        {
            _kernel = kernel;
        }

        public IController CreateController(RequestContext requestContext, string controllerName)
        {
            IController ic = _kernel.Resolve<IController>(controllerName.ToLowerInvariant() + "controller");
            Controller c = ic as Controller;
            if (c != null && WebApiEnabledAttribute.IsDefined(c))
            {
                IActionInvoker iai = c.ActionInvoker;
                ControllerActionInvoker cai = iai as ControllerActionInvoker;
                if (cai != null)
                {
                    c.ActionInvoker = new ResourceControllerActionInvoker();

                    string actionName = requestContext.RouteData.Values["action"] as string;
                    if (string.IsNullOrEmpty(actionName))
                    {
                        // set it to a well known dummy value to avoid not having an action as that would prevent the fixup
                        // code in ResourceControllerActionInvoker, which is based on ActionDescriptor, from running
                        requestContext.RouteData.Values["action"] = restActionToken;
                    }
                }
            }
            return ic;
        }

        public void ReleaseController(IController controller)
        {
            _kernel.ReleaseComponent(controller);
        }

        // This ActionInvoker allows us to dispatch to a controller when no action was provided by the routing
        // infrastructure, but the information is available in the request's HTTP verb (GET/PUT/POST/DELETE)
        class ResourceControllerActionInvoker : ControllerActionInvoker
        {
            public ResourceControllerActionInvoker()
            {
            }

            protected override ActionDescriptor FindAction(ControllerContext controllerContext, ControllerDescriptor controllerDescriptor, string actionName)
            {
                if (actionName == restActionToken)
                {
                    // cleanup the restActionToken we set earlier
                    controllerContext.RequestContext.RouteData.Values["action"] = null;

                    List<ActionDescriptor> matches = new List<ActionDescriptor>();
                    foreach (ActionDescriptor ad in controllerDescriptor.GetCanonicalActions())
                    {
                        object[] acceptVerbs = ad.GetCustomAttributes(typeof(AcceptVerbsAttribute), false);
                        if (acceptVerbs.Length > 0)
                        {
                            foreach (object o in acceptVerbs)
                            {
                                AcceptVerbsAttribute ava = o as AcceptVerbsAttribute;
                                if (ava != null)
                                {
                                    if (ava.Verbs.Contains(controllerContext.RequestContext.GetHttpMethod().ToUpperInvariant()))
                                    {
                                        matches.Add(ad);
                                    }
                                }
                            }
                        }
                    }
                    switch (matches.Count)
                    {
                        case 0:
                            break;
                        case 1:
                            ActionDescriptor ad = matches[0];
                            actionName = ad.ActionName;
                            controllerContext.RequestContext.RouteData.Values["action"] = actionName;
                            return ad;
                        default:
                            StringBuilder matchesString = new StringBuilder(matches[0].ActionName);
                            for (int index = 1; index < matches.Count; index++)
                            {
                                matchesString.Append(", ");
                                matchesString.Append(matches[index].ActionName);
                            }
                            return new ResourceErrorActionDescriptor(controllerDescriptor, HttpStatusCode.Conflict, string.Format(CultureInfo.CurrentCulture, "Error dispatching on controller {0}, conflicting actions matched: (1)", controllerDescriptor.ControllerName, matchesString.ToString()));
                    }
                }
                return base.FindAction(controllerContext, controllerDescriptor, actionName) ??
                    new ResourceErrorActionDescriptor(controllerDescriptor, HttpStatusCode.NotFound, string.Format(CultureInfo.CurrentCulture, "Error dispatching on controller {0}, no actions matched", controllerDescriptor.ControllerName));
            }

            // This class is used when we don't find an ActionDescriptor or find multiple matches
            // in this case we want to return an error response but throwing an HttpException from
            // FindAction bypasses the InvokeExceptionFilters, so instead we throw in this custom ActionDescriptor
            class ResourceErrorActionDescriptor : ActionDescriptor
            {
                ControllerDescriptor controllerDescriptor;
                string message;
                HttpStatusCode statusCode;

                public ResourceErrorActionDescriptor(ControllerDescriptor controllerDescriptor, HttpStatusCode statusCode, string message)
                {
                    this.message = message;
                    this.statusCode = statusCode;
                    this.controllerDescriptor = controllerDescriptor;
                }

                public override string ActionName
                {
                    get { return restActionToken; }
                }

                public override ControllerDescriptor ControllerDescriptor
                {
                    get { return this.controllerDescriptor; }
                }

                public override object Execute(ControllerContext controllerContext, IDictionary<string, object> parameters)
                {
                    HttpException he = new HttpException((int)this.statusCode, this.message);
                    ResourceErrorActionResult rear;
                    if (!WebApiEnabledAttribute.TryGetErrorResult2(controllerContext.RequestContext, he, out rear))
                    {
                        rear = new ResourceErrorActionResult(new HttpException((int)this.statusCode, this.message), new ContentType("text/plain"));
                    }
                    return rear;
                }

                public override ParameterDescriptor[] GetParameters()
                {
                    return new ParameterDescriptor[0];
                }
            }
        }
    }
}

You can easily replace the Windsor stuff with StructureMap, NInject, Autofac, etc.

Enjoy.