An IHttpModule that rewrites all URLs to /app.js (making the original URL available to the Node.js application).

IisNodeUrlRewriter.cs

// Copyright (c) 2014 by David Anson, http://dlaa.me/
// Released under the MIT license, http://opensource.org/licenses/MIT

using System;
using System.Text.RegularExpressions;
using System.Web;

/// <summary>
/// An IHttpModule that rewrites all URLs to /app.js (making the original URL available to the Node.js application).
/// </summary>
/// <remarks>
/// For use with Node.js applications running under iisnode on IIS as an alternative to installing the URL Rewrite module.
/// </remarks>
public class IisNodeUrlRewriter : IHttpModule
{
    /// <summary>
    /// Unique lookup key for the HttpContext.Items dictionary.
    /// </summary>
    private const string ItemsKey_PathAndQuery = "__IisNodeUrlRewriter_PathAndQuery__";

    /// <summary>
    /// Regex matching paths that should not be rewritten.
    /// </summary>
    /// <remarks>
    /// Specifically: /iisnode(/...) /app.js/debug(/...) and /app.js.debug(/...)
    /// </remarks>
    private Regex _noRewritePaths = new Regex(@"^/(iisnode|app\.js[/\.]debug)(/.*)?$", RegexOptions.IgnoreCase);

    /// <summary>
    /// Initializes a module and prepares it to handle requests.
    /// </summary>
    /// <param name="context">An HttpApplication that provides access to the methods, properties, and events common to all application objects within an ASP.NET application.</param>
    public void Init(HttpApplication context)
    {
        context.BeginRequest += HandleBeginRequest;
        context.PreRequestHandlerExecute += HandlePreRequestHandlerExecute;
    }

    /// <summary>
    /// Occurs as the first event in the HTTP pipeline chain of execution when ASP.NET responds to a request.
    /// </summary>
    /// <param name="sender">The source of the event.</param>
    /// <param name="e">An System.EventArgs that contains no event data.</param>
    private void HandleBeginRequest(object sender, EventArgs e)
    {
        // Get context
        var application = (HttpApplication)sender;
        var context = application.Context;

        // Rewrite all paths *except* those to the default log directory or those used for debugging
        if (!_noRewritePaths.IsMatch(context.Request.Path))
        {
            // Save original path
            context.Items[ItemsKey_PathAndQuery] = context.Request.Url.PathAndQuery;

            // Rewrite path
            context.RewritePath("/app.js");
        }
    }

    /// <summary>
    /// Occurs just before ASP.NET starts executing an event handler (for example, a page or an XML Web service).
    /// </summary>
    /// <param name="sender">The source of the event.</param>
    /// <param name="e">An System.EventArgs that contains no event data.</param>
    private void HandlePreRequestHandlerExecute(object sender, EventArgs e)
    {
        // Get context
        var application = (HttpApplication)sender;
        var context = application.Context;

        // Restore original path (if present)
        var originalPath = context.Items[ItemsKey_PathAndQuery] as string;
        if (null != originalPath)
        {
            context.RewritePath(originalPath);
        }
    }

    /// <summary>
    /// Disposes of the resources (other than memory) used by the module that implements IHttpModule.
    /// </summary>
    public void Dispose()
    {
        // Nothing to do here; implementation of this method is required by IHttpModule
    }
}