Creating Custom HTTP Handlers

Hi all, 

I am now at the stage in my project where I need to find ways of fine tune the loading times. Of course I have used tools like Firbug etc to run diagnosis on what is taking a long time to load etc. One thing I did find, was that a lot of the time I was using .ASPX files to load something that really only need a method call, and not all the overhead that comes with an ASPX page. So what else to use, but a custom HTTP Handler!

I decided that I would use a ASHX file to load my CSS into the pag

e instead of just adding a reference within the ASPX page and making .net do all the work. The payoff, was a load time of the CSS that was about half!!!!

Here is how you do it.

Create a Generic Handler file in your Website or Web Application.

Call the file "CSSHttpHandler"

You will be presented with the following code :

By default you only have to implement one method and a property when implementing the IHttpHandler interface

public void ProcessRequest (HttpContext context) {

        context.Response.ContentType = "text/plain";

        context.Response.Write("Hello World");

    }

 

    public bool IsReusable {

        get {

            return false;

        }

    }

Replace the code with this :

using System.IO;

using System.Text;

using System.Text.RegularExpressions;

using System.Web;

using System.IO.Compression;

public class CSSHttpHandler : IHttpHandler {

    private const string PrefixAllImagesWith = "~/";

    private readonly static TimeSpan KeepInCache = TimeSpan.FromDays(15);

    private readonly static Regex UrlCheck = new Regex(@"http(s)?://([\w-]+\.)+[\w-]+(/[\w- ./?%&=]*)?", RegexOptions.Compiled);

    public void ProcessRequest(HttpContext context)

    {

        context.Response.ContentType = "text/css";

        var themeName = context.Request["theme"];

        var themeFileNames = context.Request["files"];

        var version = context.Request["version"];

        var isCompressed = CanGZip(context.Request);

        var encoding = new UTF8Encoding(false);

        if (WriteFromCache(context, themeName, version, isCompressed)) return;

        using (var memoryStream = new MemoryStream(5000))

        {

            using (var writer = isCompressed ? (Stream)(new GZipStream(memoryStream, CompressionMode.Compress)) : memoryStream)

            {

                if (!string.IsNullOrEmpty(themeName))

                {

                    var themeCssNames = themeFileNames.Split(',');

                    foreach (var fileName in themeCssNames)

                    {

                        var fileBytes = GetCss(context,

                                                  "~/App_Themes/" + themeName + "/" + fileName,

                                                  PrefixAllImagesWith, version, encoding);

                        writer.Write(fileBytes, 0, fileBytes.Length);

                    }

                }

                writer.Close();

            }

            var responseBytes = memoryStream.ToArray();

            context.Cache.Insert(GetCacheKey(themeName, version, isCompressed),

                                 responseBytes, null, System.Web.Caching.Cache.NoAbsoluteExpiration,

                                 KeepInCache);

            WriteBytes(responseBytes, context, isCompressed);

        }

    }

    private static bool WriteFromCache(HttpContext context, string themeName,

        string version, bool isCompressed)

    {

        var responseBytes = context.Cache[GetCacheKey(themeName,

            version, isCompressed)] as byte[];

        if (null == responseBytes) return false;

        WriteBytes(responseBytes, context, isCompressed);

        return true;

    }

    private static void WriteBytes(byte[] bytes, HttpContext context, bool isCompressed)

    {

        var response = context.Response;

        response.AppendHeader("Content-Length", bytes.Length.ToString());

        response.ContentType = "text/css";

        if (isCompressed)

            response.AppendHeader("Content-Encoding", "gzip");

        context.Response.Cache.SetCacheability(HttpCacheability.Public);

        context.Response.Cache.SetExpires(DateTime.Now.Add(KeepInCache));

        context.Response.Cache.SetMaxAge(KeepInCache);

        context.Response.Cache.AppendCacheExtension("must-revalidate, proxy-revalidate");

        response.OutputStream.Write(bytes, 0, bytes.Length);

        response.Flush();

    }

    private static bool CanGZip(HttpRequest request)

    {

        var acceptEncoding = request.Headers["Accept-Encoding"];

        return !string.IsNullOrEmpty(acceptEncoding) &&

               (acceptEncoding.Contains("gzip") || acceptEncoding.Contains("deflate"));

    }

    private static byte[] GetCss(HttpContext context, string virtualPath,

        string imagePrefix, string version, Encoding encoding)

    {

        var physicalPath = context.Server.MapPath(virtualPath);

        var fileContent = File.ReadAllText(physicalPath, encoding);

        var imagePrefixUrl = imagePrefix +

            VirtualPathUtility.GetDirectory(virtualPath).TrimStart('~').TrimStart('/');

        var cssContent = UrlCheck.Replace(fileContent,

            new MatchEvaluator(delegate(Match m)

            {

                var imgPath = m.Groups["path"].Value.TrimStart('\'').TrimEnd('\'').TrimStart('"').TrimEnd('"');

                if (!imgPath.StartsWith("http://"))

                {

                    return "url('" + imagePrefixUrl 

                        + imgPath 

                        + (imgPath.IndexOf('?') > 0 ? "&version=" + version : "?version=" + version)

                        + "')";

                }

                else

                {

                    return "url('" + imgPath + "')";

                }

            }));

        return encoding.GetBytes(cssContent);

    }

    private static string GetCacheKey(string themeName, string version, bool isCompressed)

    {

        return "CssHttpHandler." + themeName + "." + version + "." + isCompressed;

    }

    public bool IsReusable

    {

        get

        {

            return true;

        }

    }

}

Then in the Render Method of the Page you are loading e.g. Default.aspx simply use this code

 var themeName = Page.Theme;

        if (string.IsNullOrEmpty(themeName)) return;

        var linksToRemove = new List();

        foreach (Control c in Page.Header.Controls)

            if (c is HtmlLink)

                if ((c as HtmlLink).Href.Contains("App_Themes/" + themeName))

                    linksToRemove.Add(c as HtmlLink);

        string themeCssNames = "";

        linksToRemove.ForEach(delegate(HtmlLink link)

                                  {

                                      Page.Header.Controls.Remove(link);

                                      themeCssNames += VirtualPathUtility.GetFileName(link.Href) + ',';

                                  });

        var linkTag = new Literal();

        var cssPath = CSS_PREFIX + "CssHttpHandler.ashx?theme=" + themeName

                      + "&files=" + HttpUtility.UrlEncode(themeCssNames.TrimEnd(','))

                      + "&version=" + CSS_VERSION;

        linkTag.Text = string.Format(@"&ltlink href=""{0}"" type=""text/css"" rel=""stylesheet"" /%gt", cssPath);

        Page.Header.Controls.Add(linkTag);

Hope this Helps, 

 - Tim