An Abstract Boilerplate HttpHandler

My last project involved writing a lot of HttpHandlers to respond to HTTP requests originating from a cell phone. To simplify my life, I created an abstract base handler that handled a lot of the repetitive tasks in writing an HTTP handler.

So today, I read Scott Hanselman’s post about the boilerplate HttpHandler he uses. He says one day he’ll get more organized and make an abstract base class to handle this kind of boilerplate stuff.

I’ve got your back Scott.

I went ahead and took my base class and quickly (about 10 minutes) incorporated some of the things he has in his boilerplate and voila! An abstract base class! Enjoy.

/// <summary>
/// An abstract base Http Handler for all your
/// <see cref="IHttpHandler"/> needs.
/// </summary>
/// <remarks>
/// <p>
/// For the most part, classes that inherit from this
/// class do not need to override <see cref="ProcessRequest"/>.
/// Instead implement the abstract methods and
/// properties and put the main business logic
/// in the <see cref="HandleRequest"/>.
/// </p>
/// <p>
/// HandleRequest should respond with a StatusCode of
/// 200 if everything goes well, otherwise use one of
/// the various "Respond" methods to generate an appropriate
/// response code.  Or use the HttpStatusCode enumeration
/// if none of these apply.
/// </p>
/// </remarks>
public abstract class BaseHttpHandler : IHttpHandler
{
    /// <summary>
    /// Creates a new <see cref="BaseHttpHandler"/> instance.
    /// </summary>
    public BaseHttpHandler() {}
 
    /// <summary>
    /// Processs the incoming HTTP request.
    /// </summary>
    /// <param name="context">Context.</param>
    public void ProcessRequest(HttpContext context)
    {
        SetResponseCachePolicy(context.Response.Cache);
 
        if(!ValidateParameters(context))
        {
            RespondInternalError(context);
            return;
        }
 
        if(RequiresAuthentication
            && !context.User.Identity.IsAuthenticated)
        {
            RespondForbidden(context);
            return;
        }
 
        context.Response.ContentType = ContentMimeType;
 
        HandleRequest(context);
    }
 
    /// <summary>
    /// Indicates whether or not this handler can be
    /// reused between successive requests.
    /// </summary>
    /// <remarks>
    /// Return true if this handler does not maintain
    /// any state (generally a good practice).  Otherwise
    /// returns false.
    /// </remarks>
    public bool IsReusable
    {
        get
        {
            return true;
        }
    }
 
    /// <summary>
    /// Handles the request.  This is where you put your
    /// business logic.
    /// </summary>
    /// <remarks>
    /// <p>This method should result in a call to one 
    /// (or more) of the following methods:</p>
    /// <p><code>context.Response.BinaryWrite();</code></p>
    /// <p><code>context.Response.Write();</code></p>
    /// <p><code>context.Response.WriteFile();</code></p>
    /// <p>
    /// <code>
    /// someStream.Save(context.Response.OutputStream);
    /// </code>
    /// </p>
    /// <p>etc...</p>
    /// <p>
    /// If you want a download box to show up with a 
    /// pre-populated filename, add this call here 
    /// (supplying a real filename).
    /// </p>
    /// <p>
    /// </p>
    /// <code>Response.AddHeader("Content-Disposition"
    /// , "attachment; filename=\"" + Filename + "\"");</code>
    /// </p>
    /// </remarks>
    /// <param name="context">Context.</param>
    public abstract void HandleRequest(HttpContext context);
 
    /// <summary>
    /// Validates the parameters.  Inheriting classes must
    /// implement this and return true if the parameters are
    /// valid, otherwise false.
    /// </summary>
    /// <param name="context">Context.</param>
    /// <returns><c>true</c> if the parameters are valid,
    /// otherwise <c>false</c></returns>
    public abstract bool ValidateParameters(HttpContext context);
 
    /// <summary>
    /// Gets a value indicating whether this handler
    /// requires users to be authenticated.
    /// </summary>
    /// <value>
    ///    <c>true</c> if authentication is required
    ///    otherwise, <c>false</c>.
    /// </value>
    public abstract bool RequiresAuthentication {get;}
 
    /// <summary>
    /// Gets the content MIME type.
    /// </summary>
    /// <value></value>
    public abstract string ContentMimeType {get;}
 
    /// <summary>
    /// Sets the cache policy.  Unless a handler overrides
    /// this method, handlers will not allow a respons to be
    /// cached.
    /// </summary>
    /// <param name="cache">Cache.</param>
    public virtual void SetResponseCachePolicy
        (HttpCachePolicy cache)
    {
        cache.SetCacheability(HttpCacheability.NoCache);
        cache.SetNoStore();
        cache.SetExpires(DateTime.MinValue);
    }
 
    /// <summary>
    /// Helper method used to Respond to the request
    /// that the file was not found.
    /// </summary>
    /// <param name="context">Context.</param>
    protected void RespondFileNotFound(HttpContext context)
    {
        context.Response.StatusCode 
            = (int)HttpStatusCode.NotFound;
        context.Response.End();
    }
 
    /// <summary>
    /// Helper method used to Respond to the request
    /// that an error occurred in processing the request.
    /// </summary>
    /// <param name="context">Context.</param>
    protected void RespondInternalError(HttpContext context)
    {
        // It's really too bad that StatusCode property
        // is not of type HttpStatusCode.
        context.Response.StatusCode =
            (int)HttpStatusCode.InternalServerError;
        context.Response.End();
    }
 
    /// <summary>
    /// Helper method used to Respond to the request
    /// that the request in attempting to access a resource
    /// that the user does not have access to.
    /// </summary>
    /// <param name="context">Context.</param>
    protected void RespondForbidden(HttpContext context)
    {
        context.Response.StatusCode 
            = (int)HttpStatusCode.Forbidden;
        context.Response.End();
    }
}