Taking the HttpContext out of the MVC Framework Controller

I really like the MVC Framework. I'm currently working on my third commercial project using it and I just love the flexibility it gives me, especially the opportunity to refactor the framework itself.

Here's an example: one of the things I dislike is the way the default Controller class is overly coupled to the HttpContext. HttpContext in itself is a problematic hangover from ASP.NET and to have it bound into the Controller to such an extent is a design mistake IMHO.

OK, so what do I mean? Take this action code from a controller:

public ActionResult Search()
{
    const int pageSize = 20;

    var criteria = new ArticleSearchCriteria();
    validatingBinder.UpdateFrom(criteria, Request.Form);

    var articles = articleRepository
        .GetAll()
        .ThatMatch(criteria)
        .ToPagedList(PageNumber, pageSize);

    return View("Search", View.Data
        .WithArticleSearchCriteria(criteria)
        .WithArticles(articles));
}

You see the reference to Request.Form there? The HttpRequest (and HttpResponse and HttpContext) are all exposed as properties of the base Controller class. In order to test that code I have to mock the HttpContext which is a real PITA.

Here's an alternative that I've started using. An IHttpContextService interface:

public interface IHttpContextService
{
    HttpContextBase Context { get; }
    HttpRequestBase Request { get; }
    HttpResponseBase Response { get; }
    NameValueCollection FormOrQuerystring { get; }
}

I can now just use Dependency injection in my controller to get a reference to an implementation of IHttpContextService. Note I don't care here how it is implemented:

public class ArticleController : ControllerBase
{
    private readonly IRepository<Article> articleRepository;
    private readonly IHttpContextService httpContextService;
    private readonly IValidatingBinder validatingBinder;

    public ArticleController(
        IRepository<Article> articleRepository, 
        IHttpContextService httpContextService,
        IValidatingBinder validatingBinder)
    {
        this.articleRepository = articleRepository;
        this.httpContextService = httpContextService;
        this.validatingBinder = validatingBinder;
    }

    public ActionResult Search()
    {
        const int pageSize = 20;

        var criteria = new ArticleSearchCriteria();
        validatingBinder.UpdateFrom(criteria, httpContextService.FormOrQuerystring);

        var articles = articleRepository
            .GetAll()
            .ThatMatch(criteria)
            .ToPagedList(PageNumber, pageSize);

        return View("Search", GroupLibView.Data
            .WithArticleSearchCriteria(criteria)
            .WithArticles(articles));
    }
}

And I can set up my IoC container to give me any implementation of IHttpContextService I want. Now because the IHttpContextService is provided by the IoC container, any dependencies that its implementation may require can also be provided by the IoC container which opens up all kinds of interesting opportunities.

Here's my current HttpContextService:

using System.Collections.Specialized;
using System.Web;

namespace Suteki.Common.Services
{
    public class HttpContextService : IHttpContextService
    {
        public HttpContextBase Context
        {
            get
            {
                return new HttpContextWrapper2(HttpContext.Current);
            }
        }

        public HttpRequestBase Request
        {
            get
            {
                return Context.Request;
            }
        }

        public HttpResponseBase Response
        {
            get
            {
                return Context.Response;
            }
        }

        public NameValueCollection FormOrQuerystring
        {
            get
            {
                if(Request.RequestType == "POST")
                {
                    return Request.Form;
                }
                return Request.QueryString;
            }
        }
    }
}