Custom Errors Module - Proof of Concept

Global.asax.cs

protected void Application_Error(object sender, EventArgs e)
{
    // check to see if something horrible is going on...
    if (Request.Headers["Custom-Error-Request"] != null)
    {
        // looks like a request to grab an error page ended up here. let's bail.
        return;
    }

    // get the last error
    HttpException err = Server.GetLastError() as HttpException;

    Server.ClearError();

    // try to skip using any other custom error settings
    Response.TrySkipIisCustomErrors = true;

    // check to see if we need to send back something pretty
    var acceptsHtml = Request.Headers["Accept"].Contains("text/html");

    // we're on!
    if (err != null && acceptsHtml)
    {
        // get the language from the visitor's browser settings
        string lang = (Request.UserLanguages ?? Enumerable.Empty<string>()).FirstOrDefault();
        var culture = CultureInfo.GetCultureInfo(lang);

        // set the culture to match the browser language
        Thread.CurrentThread.CurrentUICulture = culture;

        PageManager pageManager = PageManager.GetManager();

        PageNode pNode = null;

        // this is where we would put a manager to do some fancy lookups based on the error codes
        switch (err.GetHttpCode())
        {
            case 404:
                pNode = pageManager.GetPageNodes().Where(pN => pN.Title == "404").FirstOrDefault();
                break;
            case 500:
            default:
                pNode = pageManager.GetPageNodes().Where(pN => pN.Title == "Generic").FirstOrDefault();
                break;
        }

        // grab the URL of the error page we're going to display to the visitor
        string url = pNode.GetFullUrl(culture, true);
        url = UrlPath.ResolveUrl(url, true, true);

        // grab the entire HTML of the page
        WebClient client = new WebClient { Encoding = Encoding.UTF8 };
        client.Headers.Add("Custom-Error-Request", "");

        string html = err.GetHttpCode().ToString();

        try
        {
            html = client.DownloadString(url);
        }
        catch (WebException ex)
        {
            // the error page is probably blowing up. maybe do some logging...or send an email?
        }

        // send back the the best response we got for the error and a status code
        Response.Write(html);
        Response.StatusCode = err.GetHttpCode();
    }
    else if (err != null)
    {
        // just fire back a basic message and the status 
        Response.Write(err.GetHttpCode().ToString());
        Response.StatusCode = err.GetHttpCode();
    }
}

web.config

<customErrors mode="On">
  <error statusCode="404" redirect="~/8ec96125-02ce-47e2-a545-0eba4192dc7d" />
</customErrors>

<httpErrors errorMode="Custom">
  <remove statusCode="404" subStatusCode="-1" />
  <error statusCode="404" prefixLanguageFilePath="" path="/CustomErrorPages/8ec96125-02ce-47e2-a545-0eba4192dc7d.aspx" responseMode="ExecuteURL" />
</httpErrors>

I hadn't thought about the accept header thing, good call.

The language sniffing was done because I want to grab the page and return it under the same URL, along with the error code. Because I'm not doing a redirect (spinning up the WebRequest manually) I didn't think I could rely on Sitefinity to return the correct page. I admit that I might be over-complicating it though. 😄

If WebClient is faster and returns the same result, I'm totally making the switch.