Deploy ASP.NET MVC on IIS 6, solve 404, compression and performance problems

There are several problems with ASP.NET MVC application when deployed on IIS 6.0:

  • Extensionless URLs give 404 unless some URL Rewrite module is used or wildcard mapping is enabled
  • IIS 6.0 built-in compression does not work for dynamic requests. As a result, ASP.NET pages are served uncompressed resulting in poor site load speed.
  • Mapping wildcard extension to ASP.NET introduces the following problems:
    • Slow performance as all static files get handled by ASP.NET and ASP.NET reads the file from file system on every call
    • Expires headers doesn't work for static content as IIS does not serve them anymore. Learn about benefits of expires header from here. ASP.NET serves a fixed expires header that makes content expire in a day.
    • Cache-Control header does not produce max-age properly and thus caching does not work as expected. Learn about caching best practices from here.
  • After deploying on a domain as the root site, the homepage produces HTTP 404.

Problem 1: Visiting your website's homepage gives 404 when hosted on a domain

You have done the wildcard mapping, mapped .mvc extention to ASP.NET ISAPI handler, written the route mapping for Default.aspx or default.aspx (lowercase), but still when you visit your homepage after deployment, you get:

image

You will find people banging their heads on the wall here:

Solution is to capture hits going to "/" and then rewrite it to Default.aspx:

image

You can apply this approach to any URL that ASP.NET MVC is not handling for you and it should handle. Just see the URL reported on the 404 error page and then rewrite it to a proper URL.

Problem 2: IIS 6 compression is no longer working after wildcard mapping

When you enable wildcard mapping, IIS 6 compression no longer works for extensionless URL because IIS 6 does not see any extension which is defined in IIS Metabase. You can learn about IIS 6 compression feature and how to configure it properly from my earlier post.

Solution is to use an HttpModule to do the compression for dynamic requests.

Problem 3: ASP.NET ISAPI does not cache Static Files

When ASP.NET's DefaultHttpHandler serves static files, it does not cache the files in-memory or in ASP.NET cache. As a result, every hit to static file results in a File read. Below is the decompiled code in DefaultHttpHandler when it handles a static file. As you see here, it makes a file read on every hit and it only set the expiration to one day in future. Moreover, it generates ETag for each file based on file's modified date. For best caching efficiency, we need to get rid of that ETag, produce an expiry date on far future (like 30 days), and produce Cache-Control header which offers better control over caching.

image

So, we need to write a custom static file handler that will cache small files like images, Javascripts, CSS, HTML and so on in ASP.NET cache and serve the files directly from cache instead of hitting the disk. Here are the steps:

  • Install an HttpModule that installs a Compression Stream on Response.Filter so that anything written on Response gets compressed. This serves dynamic requests.
  • Replace ASP.NET's DefaultHttpHandler that listens on *.* for static files.
  • Write our own Http Handler that will deliver compressed response for static resources like Javascript, CSS, and HTML.

image

Here's the mapping in ASP.NET's web.config for the DefaultHttpHandler. You will have to replace this with your own handler in order to serve static files compressed and cached.

Solution 1: An Http Module to compress dynamic requests

First, you need to serve compressed responses that are served by the MvcHandler or ASP.NET's default Page Handler. The following HttpCompressionModule hooks on the Response.Filter and installs a GZipStream or DeflateStream on it so that whatever is written on the Response stream, it gets compressed.

image

These are formalities for a regular HttpModule. The real hook is installed as below:

image

Here you see we ignore requests that are handled by ASP.NET's DefaultHttpHandler and our own StaticFileHandler that you will see in next section. After that, it checks whether the request allows content to be compressed. Accept-Encoding header contains "gzip" or "deflate" or both when browser supports compressed content. So, when browser supports compressed content, a Response Filter is installed to compress the output.

Solution 2: An Http Module to compress and cache static file requests

Here's how the handler works:

  • Hooks on *.* so that all unhandled requests get served by the handler
  • Handles some specific files like js, css, html, graphics files. Anything else, it lets ASP.NET transmit it
  • The extensions it handles itself, it caches the file content so that subsequent requests are served from cache
  • It allows compression of some specific extensions like js, css, html. It does not compress graphics files or any other extension.

Let's start with the handler code:

image

Here you will find the extensions the handler handles and the extensions it compresses. You should only put files that are text files in the COMPRESS_FILE_TYPES.

Now start handling each request from BeginProcessRequest.

image

Here you decide the compression mode based on Accept-Encoding header. If browser does not support compression, do not perform any compression. Then check if the file being requested falls in one of the extensions that we support. If not, let ASP.NET handle it. You will see soon how.

image

Calculate the cache key based on the compression mode and the physical path of the file. This ensures that no matter what the URL requested, we have one cache entry for one physical file. Physical file path won't be different for the same file. Compression mode is used in the cache key because we need to store different copy of the file's content in ASP.NET cache based on Compression Mode. So, there will be one uncompressed version, a gzip compressed version and a deflate compressed version.

Next check if the file exits. If not, throw HTTP 404. Then create a memory stream that will hold the bytes for the file or the compressed content. Then read the file and write in the memory stream either directly or via a GZip or Deflate stream. Then cache the bytes in the memory stream and deliver to response. You will see the ReadFileData and CacheAndDeliver functions soon.

image

This function delivers content directly from ASP.NET cache. The code is simple, read from cache and write to the response.

When the content is not available in cache, read the file bytes and store in a memory stream either as it is or compressed based on what compression mode you decided before:

image

Here bytes are read in chunk in order to avoid large amount of memory allocation. You could read the whole file in one shot and store in a byte array same as the size of the file length. But I wanted to save memory allocation. Do a performance test to figure out if reading in 8K chunk is not the best approach for you.

Now you have the bytes to write to the response. Next step is to cache it and then deliver it.

image

Now the two functions that you have seen several times and have been wondering what they do. Here they are:

image

WriteResponse has no tricks, but ProduceResponseHeader has much wisdom in it. First it turns off response buffering so that ASP.NET does not store the written bytes in any internal buffer. This saves some memory allocation. Then it produces proper cache headers to cache the file in browser and proxy for 30 days, ensures proxy revalidate the file after the expiry date and also produces the Last-Modified date from the file's last write time in UTC.

How to use it

Get the HttpCompressionModule and StaticFileHandler from:

http://code.msdn.microsoft.com/fastmvc

Then install them in web.config. First you install the StaticFileHandler by removing the existing mapping for path="*" and then you install the HttpCompressionModule.

image

That's it! Enjoy a faster and more responsive ASP.NET MVC website deployed on IIS 6.0.

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ensure - Ensure relevant Javascript and HTML are loaded before using them

ensure allows you to load Javascript, HTML and CSS on-demand, whenever they are needed. It saves you from writing a gigantic Javascript framework up front so that you can ensure all functions are available whenever they are needed. It also saves you from delivering all possible html on your default page (e.g. default.aspx) hoping that they might some day be needed on some user action. Delivering Javascript, html fragments, CSS during initial loading that is not immediately used on first view makes initial loading slow. Moreover, browser operations get slower as there are lots of stuff on the browser DOM to deal with. So, ensure saves you from delivering unnecessary javascript, html and CSS up front, instead load them on-demand. Javascripts, html and CSS loaded by ensure remain in the browser and next time when ensure is called with the same Javascript, CSS or HTML, it does not reload them and thus saves from repeated downloads.

Ensure supports jQuery, Microsoft ASP.NET AJAX and Prototype framework. This means you can use it on any html, ASP.NET, PHP, JSP page that uses any of the above framework.

For example, you can use ensure to download Javascript on demand:

ensure( { js: "Some.js" }, function()
{
    SomeJS(); // The function SomeJS is available in Some.js only
});

The above code ensures Some.js is available before executing the code. If the SomeJS.js has already been loaded, it executes the function write away. Otherwise it downloads Some.js, waits until it is properly loaded and only then it executes the function. Thus it saves you from deliverying Some.js upfront when you only need it upon some user action.

Similarly you can wait for some HTML fragment to be available, say a popup dialog box. There's no need for you to deliver HTML for all possible popup boxes that you will ever show to user on your default web page. You can fetch the HTML whenever you need them.

ensure( {html: "Popup.html"}, function()
{
    // The element "Popup" is available only in Popup.html
    document.getElementById("Popup").style.display = "";   
});

The above code downloads the html from "Popup.html" and adds it into the body of the document and then fires the function. So, you code can safely use the UI element from that html.

You can mix match Javascript, html and CSS altogether in one ensure call. For example,

ensure( { js: "popup.js", html: "popup.html", css: "popup.css" }, function()
{
    PopupManager.show();
});

You can also specify multiple Javascripts, html or CSS files to ensure all of them are made available before executing the code:

ensure( { js: ["blockUI.js","popup.js"], html: ["popup.html", "blockUI.html"], css: ["blockUI.css", "popup.css"] }, function()
{
    BlockUI.show();
    PopupManager.show();
});

You might think you are going to end up writing a lot of ensure code all over your Javascript code and result in a larger Javascript file than before. In order to save you javascript size, you can define shorthands for commonly used files:

var JQUERY = { js: "jquery.js" };
var POPUP = { js: ["blockUI.js","popup.js"], html: ["popup.html", "blockUI.html"], css: ["blockUI.css", "popup.css"] };
...
...
ensure( JQUERY, POPUP, function() {
    $("DeleteConfirmPopupDIV").show();
});
...
...
ensure( POPUP, function()
{
    $("SaveConfirmationDIV").show();
);

While loading html, you can specify a container element where ensure can inject the loaded HTML. For example, you can say load HtmlSnippet.html and then inject the content inside a DIV named "exampleDiv"

ensure( { html: ["popup.html", "blockUI.html"], parent: "exampleDiv"}, function(){});

You can also specify Javascript and CSS that will be loaded along with the html. 

How ensure works

The following CodeProject article explains in detail how ensure it built. Be prepared for a high dose of Javascript techniques:

http://www.codeproject.com/KB/ajax/ensure.aspx

If you find ensure useful, please vote for me.

Download Code

Download latest source code from CodePlex: www.codeplex.com/ensure

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UFrame: goodness of UpdatePanel and IFRAME combined

UFrame combines the goodness of UpdatePanel and IFRAME in a cross browser and cross platform solution. It allows a DIV to behave like an IFRAME loading content from any page either static or dynamic. It can load pages having both inline and external Javascript and CSS, just like an IFRAME. But unlike IFRAME, it loads the content within the main document and you can put any number of UFrame on your page without slowing down the browser. It supports ASP.NET postback nicely and you can have DataGrid or any other complex ASP.NET control within a UFrame. UFrame works perfectly with ASP.NET MVC making it an replacement for UpdatePanel. Best of all, UFrame is implemented 100% in Javascript making it a cross platform solution. As a result, you can use UFrame on ASP.NET, PHP, JSP or any other platform.

<div class="UFrame" id="UFrame1" src="SomePage.aspx?ID=UFrame1" >
  <p>This should get replaced with content from Somepage.aspx</p>
</div>

Response from SomePage.aspx is rendered directly inside the UFrame. Here you see two UFrame's are used to load the same SomePage.aspx as if they are loaded inside IFRAME. Another UFrame is used to load AnotherPage.aspx that shows photos from Flickr.

image

See it in action!

You can test UFrame from:

What is UFrame?

UFrame can load and host a page (ASP.NET, PHP or regular html) inside a DIV. Unlike IFRAME which loads the content inside a browser frame that has no relation with the main document, UFrame loads the content within the same document. Thus all the Javascripts, CSS on the main document flows through the loaded content. It's just like UpdatePanel with IFRAME's src attribute.

The above UFrames are declared like this:

<div id="UFrame1" src="SomePage.aspx" >
    <p>This should get replaced with content from Somepage.aspx</p>
</div>

The features of UFrame are:

  • You can build regular ASP.NET/PHP/JSP/HTML page and make them behave as if they are fully AJAX enabled! Simple regular postback will work as if it's an UpdatePanel, or simple hyperlinks will behave as if content is being loaded using AJAX.
  • Load any URL inside a DIV. It can be a PHP, ASP.NET, JSP or regular HTML page.
  • Just like IFRAME, you can set src property of DIVs and they are converted to UFrames when UFrame library loads.
  • Unlike IFRAME, it loads the content within the main document. So, main document's CSS and Javascripts are available to the loaded content.
  • It allows you to build parts of a page as multiple fully independent pages.
  • Each page is built as standalone page. You can build, test and debug each small page independently and put them together on the main page using UFrames.
  • It loads and executes both inline and external scripts from loaded page. You can also render different scripts during UFrame postback.
  • All external scripts are loaded before the body content is set. And all inline scripts are executed when both external scripts and body has been loaded. This way the inline scripts execute when the body content is already available.
  • It loads both inline and external CSS.
  • It handles duplicates nicely. It does not load the same external Javascript or CSS twice.

Download the code

You can download latest version of UFrame along with the VS 2005 and VS 2008 (MVC) example projects from CodePlex:

www.codeplex.com/uframe

Please go to the "Source Code" tab for the latest version. You are invited to join the project and improve it or fix bugs.

Read the article about UFrame

I have published an article about UFrame at CodeProject:

http://www.codeproject.com/KB/aspnet/uframe.aspx

The article explains in details how the UFrame is built. Be prepared for a big dose of Javascript code.

If you find UFrame or the article useful, please vote for me at CodeProject.

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Fast ASP.NET web page loading by downloading multiple javascripts in batch

A web page can load a lot faster and feel faster if the javascripts on the page can be loaded after the visible content has been loaded and multiple javascripts can be batched into one download. Browsers download one external script at a time and sometimes pause rendering while a script is being downloaded and executed. This makes web pages load and render slow when there are multiple javascripts on the page. For every javascript reference, browser stops downloading and processing of any other content on the page and some browsers (like IE6) pause rendering while it processes the javascript. This gives a slow loading experience and the web page kind of gets 'stuck' frequently. As a result, a web page can only load fast when there are small number of external scripts on the page and the scripts are loaded after the visible content of the page has loaded.

Here's an example, when you visit Dropthings.com, you see a lot of Javascripts downloading. Majority of these are from the ASP.NET AJAX framework and the ASP.NET AJAX Control Toolkit project.

Andysnap_003
Figure: Many scripts downloaded on a typical ASP.NET AJAX page having ASP.NET AJAX Control Toolkit

As you see, browser gets stuck for 15 times as it downloads and processes external scripts. This makes page loading "feel" slower. The actual loading time is also pretty bad because these 15 http requests waste 15*100ms = 1500ms on the network latency inside USA. Outside USA, the latency is even higher. Asia gets about 270ms and Australia gets about 380ms latency from any server in USA. So, users outside USA wastes 4 to 6 seconds on network latency where no data is being downloaded. This is an unacceptable performance for any website.

You pay for such high number of script downloads only because you use two extenders from AJAX Control Toolkit and the UpdatePanel of ASP.NET AJAX.

If we can batch the multiple individual script calls into one call like Scripts.ashx as shown in the picture below and download several scripts together in one shot using an HTTP Handler, it saves us a lot of http connection which could be spent doing other valuable work like downloading CSS for the page to show content properly or downloading images on the page that is visible to user.

Andysnap_002
Figure: Download several javascripts over one connection and save call and latency

The Scripts.ashx handler can not only download multiple scripts in one shot, but also has a very short URL form. For example:

/scripts.ashx?initial=a,b,c,d,e&/

Compared to conventional ASP.NET ScriptResource URLs like:

/ScriptResource.axd?d=WzuUYZ-Ggi7-B0tkhjPDTmMmgb5FPLmciWEXQLdjNjt
bmek2jgmm3QETspZjKLvHue5em5kVYJGEuf4kofrcKNL9z6AiMhCe3SrJrcBel_c1
&amp;t=633454272919375000

The benefits of downloading multiple Javascript over one http call are:

  • Saves expensive network roundtrip latency where neither browser nor the origin server is doing anything, not even a single byte is being transmitted during the latency
  • Create less "pause" moments for the browser. So, browser can fluently render the content of the page and thus give user a fast loading feel
  • Give browser move time and free http connections to download visible artifacts of the page and thus give user a "something's happening" feel
  • When IIS compression is enabled, the total size of individually compressed files is greater than multiple files compressed after they are combined. This is because each compressed byte stream has compression header in order to decompress the content.
  • This reduces the size of the page html as there are only a few handful of script tag. So, you can easily saves hundreds of bytes from the page html. Especially when ASP.NET AJAX produces gigantic WebResource.axd and ScriptResource.axd URLs that have very large query parameter

The solution is to dynamically parse the response of a page before it is sent to the browser and find out what script references are being sent to the browser. I have built an http module which can parse the generated html of a page and find out what are the script blocks being sent. It then parses those script blocks and find the scripts that can be combined. Then it takes out those individual script tags from the response and adds one script tag that generates the combined response of multiple script tags.

For example, the homepage of Dropthings.com produces the following script tags:

<script type="text/javascript">
...
//]]>
</script>
<script src="/Dropthings/WebResource.axd?d=_w65Lg0FVE-htJvl4_zmXw2&amp;t=633403939286875000" 
type="text/javascript"></script> ... <script src="Widgets/FastFlickrWidget.js" type="text/javascript"></script> <script src="Widgets/FastRssWidget.js" type="text/javascript"></script> <script src="/Dropthings/ScriptResource.axd?d=WzuUYZ-Ggi7-B0tkhjPDTmMmgb5FPLmciWEXQLdj
Njtbmek2jgmm3QETspZjKLvHue5em5kVYJGEuf4kofrcKNL9z6AiMhCe3SrJrcBel_c1
&amp;t=633454272919375000"
type="text/javascript"></script> <script type="text/javascript"> //<![CDATA[ ... </script> <script src="/Dropthings/ScriptResource.axd?d=WzuUYZ-Ggi7-B0tkhjPDTmMmgb5FPLmciWEXQLdjNjtbmek2j
gmm3QETspZjKLvHIbaYWwsewvr_eclXZRGNKzWlaVj44lDEdg9CT2tyH-Yo9jFoQij_XIWxZNETQkZ90
&amp;t=633454272919375000"
type="text/javascript"></script> <script type="text/javascript"> ... </script> <script type="text/javascript"> ... </script> <script type="text/javascript" charset="utf-8"> ... </script> <script src="Myframework.js" type="text/javascript"></script> <script type="text/javascript"> ... </script> <script type="text/javascript">if( typeof Proxy == "undefined" ) Proxy = ProxyAsync;</script> <script type="text/javascript"> ... </script> <script src="/Dropthings/ScriptResource.axd?d=WzuUYZ-Ggi7-B0tkhjPDTmMmgb5FPLmciWEXQLdjN
jtbmek2jgmm3QETspZjKLvH-H5JQeA1OWzBaqnbKRQWwc2hxzZ5M8vtSrMhytbB-Oc1
&amp;t=633454272919375000"
type="text/javascript"></script> <script src="/Dropthings/ScriptResource.axd?d=BXpG1T2rClCdn7QzWc-HrzQ2ECeqBhG6oiVakhRAk
RY6YSaFJsnzqttheoUJJXE4jMUal_1CAxRvbSZ_4_ikAw2
&amp;t=633454540450468750"
type="text/javascript"></script> <script src="/Dropthings/ScriptResource.axd?d=BXpG1T2rClCdn7QzWc-HrzQ2ECeqBhG6oiVakhRA
kRYRhsy_ZxsfsH4NaPtFtpdDEJ8oZaV5wKE16ikC-hinpw2
&amp;t=633454540450468750"
type="text/javascript"></script> <script src="/Dropthings/ScriptResource.axd?d=BXpG1T2rClCdn7QzWc-HrzQ2ECeqBhG6oiVakhRAk
RZbimFWogKpiYN4SVreNyf57osSvFc_f24oloxX4RTFfnfj5QsvJGQanl-pbbMbPf01
&amp;t=633454540450468750"
type="text/javascript"></script>
...

<script type="text/javascript"> ... </script> </body> </html>

As you see, there are lots of large script tags, in total 15 of them. The solution I will show here will combine the script links and replace with two script links that download 13 of the individual scripts. I have left two scripts out that are related to ASP.NET AJAX Timer extender.

<script type="text/javascript"> ... </script>


<script type="text/javascript" src="Scripts.ashx?initial=a,b,c,d,e,f&/dropthings/"></script>
<script type="text/javascript"> ... </script> <script type="text/javascript"> ... </script> <script type="text/javascript"> ... </script> <script type="text/javascript"> ... </script> <script type="text/javascript">if( typeof Proxy == "undefined" ) Proxy = ProxyAsync;</script> <script type="text/javascript"> ... </script> <script src="/Dropthings/ScriptResource.axd?d=WzuUYZ-..." type="text/javascript"></script> <script src="/Dropthings/ScriptResource.axd?d=BXpG1T2..." type="text/javascript"></script>
<script type="text/javascript" src="Scripts.ashx?post=C,D,E,F,G,H,I,J&/dropthings/"></script> <script type="text/javascript"> ... </script>

As you see, 13 of the script links have been combined into two script links. The URL is also smaller than majority of the script references.

There are two steps involved here:

  1. Find out all the script tags being emitted inside generated response HTML and collect them in a buffer. Move them after the visible artifacts in the HTML, especially the <form> tag that contains the generated output of all ASP.NET controls on the page
  2. Parse the buffer and see which script references can be combined into one set. The sets are defined in a configuration file. Replace the individual script references with the combined set reference.

The whole solution is explained in this CodeProject article:

Fast ASP.NET web page loading by downloading multiple javascripts after visible content and in batch
http://www.codeproject.com/KB/aspnet/fastload.aspx

You should be able to use this approach in any ASP.NET (even better if AJAX) application and give your site a big performance boost.

If you like the idea, please vote for me.

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Fast, Streaming AJAX proxy - continuously download from cross domain

Due to browser's prohibition on cross domain XMLHTTP call, all AJAX websites must have server side proxy to fetch content from external domain like Flickr or Digg. From client side javascript code, an XMLHTTP call goes to the server side proxy hosted on the same domain and then the proxy downloads the content from the external server and sends back to the browser. In general, all AJAX websites on the Internet that are showing content from external domains are following this proxy approach except some rare ones who are using JSONP. Such a proxy gets a very large number of hits when a lot of component on the website are downloading content from external domains. So, it becomes a scalability issue when the proxy starts getting millions of hits. Moreover, web page's overall load performance largely depends on the performance of the proxy as it delivers content to the page. In this article, we will take a look how we can take a conventional AJAX Proxy and make it faster, asynchronous, continuously stream content and thus make it more scalable.

You can see such a proxy in action when you go to Pageflakes.com. You will see flakes (widgets) loading many different content like weather feed, flickr photo, youtube videos, RSS from many different external domains. All these are done via a Content Proxy. Content Proxy served about 42.3 million URLs last month which is quite an engineering challenge for us to make it both fast and scalable. Sometimes Content Proxy serves megabytes of data, which poses even greater engineering challenge. As such proxy gets large number of hits, if we can save on an average 100ms from each call, we can save 4.23 million seconds of download/upload/processing time every month. That's about 1175 man hours wasted throughout the world by millions of people staring at browser waiting for content to download.

Such a content proxy takes an external server's URL as a query parameter. It downloads the content from the URL and then writes the content as response back to browser.

image
Figure: Content Proxy working as a middleman between browser and external domain

The above timeline shows how request goes to the server and then server makes a request to external server, downloads the response and then transmits back to the browser. The response arrow from proxy to browser is larger than the response arrow from external server to proxy because generally proxy server's hosting environment has better download speed than the user's Internet connectivity.

Such a content proxy is also available in my open source Ajax Web Portal Dropthings.com. You can see from its code how such a proxy is implemented.

The following is a very simple synchronous, non-streaming, blocking Proxy:

[WebMethod]
[ScriptMethod(UseHttpGet=true)]
public string GetString(string url)
{
using (WebClient client = new WebClient())
{
string response = client.DownloadString(url);
return response;
}
}
}

Although it shows the general principle, but it's no where close to a real proxy because:

  • It's a synchronous proxy and thus not scalable. Every call to this web method causes the ASP.NET thread to wait until the call to the external URL completes.
  • It's non streaming. It first downloads the entire content on the server, storing it in a string and then uploading that entire content to the browser. If you pass MSDN feed URL, it will download that gigantic 220 KB RSS XML on the server and store it on a 220 KB long string (actually double the size as .NET strings are all Unicode string) and then write 220 KB to  ASP.NET Response buffer, consuming another 220 KB UTF8 byte array in memory. Then that 220 KB will be passed to IIS in chunks so that it can transmit it to the browser.
  • It does not produce proper response header to cache the response on the server. Nor does it deliver important headers like Content-Type from the source.
  • If external URL is providing gzipped content, it decompresses the content into a string representation and thus wastes server memory.
  • It does not cache the content on the server. So, repeated call to the same external URL within the same second or minute will download content from the external URL and thus waste bandwidth on your server.

So, we need an asynchronous streaming proxy that transmits the content to the browser while it downloads from the external domain server. So, it will download bytes from external URL in small chunks and immediately transmit that to the browser. As a result, browser will see a continuous transmission of bytes right after calling the web service. There will be no delay while the content is fully downloaded on the server.

Before I show you the complex streaming proxy code, let's take an evolutionary approach. Let's build a better Content Proxy that the one shown above, which is synchronous, non-streaming but does not have the other problems mentioned above. We will build a HTTP Handler named RegularProxy.ashx which will take url as a query parameter. It will also take cache as a query parameter which it will use to produce proper response headers in order to cache the content on the browser. Thus it will save browser from downloading the same content again and again.

<%@ WebHandler Language="C#" Class="RegularProxy" %>

using System;
using System.Web;
using System.Web.Caching;
using System.Net;
using ProxyHelpers;
public class RegularProxy : IHttpHandler {

public void ProcessRequest (HttpContext context) {
string url = context.Request["url"];
int cacheDuration = Convert.ToInt32(context.Request["cache"]?? "0");
string contentType = context.Request["type"];

// We don't want to buffer because we want to save memory
context.Response.Buffer = false;

// Serve from cache if available
if (context.Cache[url] != null)
{
context.Response.BinaryWrite(context.Cache[url] as byte[]);
context.Response.Flush();
return;
}
using (WebClient client = new WebClient())
{
if (!string.IsNullOrEmpty(contentType))
client.Headers["Content-Type"] = contentType;

client.Headers["Accept-Encoding"] = "gzip";
client.Headers["Accept"] = "*/*";
client.Headers["Accept-Language"] = "en-US";
client.Headers["User-Agent"] =
"Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.8.1.6) Gecko/20070725 Firefox/2.0.0.6";

byte[] data = client.DownloadData(url);

context.Cache.Insert(url, data, null,
Cache.NoAbsoluteExpiration,
TimeSpan.FromMinutes(cacheDuration),
CacheItemPriority.Normal, null);

if (!context.Response.IsClientConnected) return;


// Deliver content type, encoding and length as it is received from the external URL
context.Response.ContentType = client.ResponseHeaders["Content-Type"];
string contentEncoding = client.ResponseHeaders["Content-Encoding"];
string contentLength = client.ResponseHeaders["Content-Length"];

if (!string.IsNullOrEmpty(contentEncoding))
context.Response.AppendHeader("Content-Encoding", contentEncoding);
if (!string.IsNullOrEmpty(contentLength))
context.Response.AppendHeader("Content-Length", contentLength);

if (cacheDuration > 0)
HttpHelper.CacheResponse(context, cacheDuration);

// Transmit the exact bytes downloaded
context.Response.BinaryWrite(data);
}
}

public bool IsReusable {
get {
return false;
}
}

}

There are two enhancements in this proxy:

  • It allows server side caching of content. Same URL requested by a different browser within a time period will not be downloaded on server again, instead it will be served from cache.
  • It generates proper response cache header so that the content can be cached on browser.
  • It does not decompress the downloaded content in memory. It keeps the original byte stream intact. This saves memory allocation.
  • It transmits the data in non-buffered fashion, which means ASP.NET Response object does not buffer the response and thus saves memory

However, this is a blocking proxy. We need to make a streaming asynchronous proxy for better performance. Here's why:

image 
Figure: Continuous streaming proxy

As you see, when data is transmitted from server to browser while server downloads the content, the delay for server side download is eliminated. So, if server takes 300ms to download something from external source, and then 700ms to send it back to browser, you can save up to 300ms Network Latency between server and browser. The situation gets even better when the external server that serves the content is slow and takes quite some time to deliver the content. The slower external site is, the more saving you get in this continuous streaming approach. This is significantly faster than blocking approach when the external server is in Asia or Australia and your server is in USA.

The approach for continuous proxy is:

  • Read bytes from external server in chunks of 8KB from a separate thread (Reader thread) so that it's not blocked
  • Store the chunks in an in-memory Queue
  • Write the chunks to ASP.NET Response from that same queue
  • If the queue is finished, wait until more bytes are downloaded by the reader thread

image

The Pipe Stream needs to be thread safe and it needs to support blocking Read. By blocking read it means, if a thread tries to read a chunk from it and the stream is empty, it will suspend that thread until another thread writes something on the stream. Once a write happens, it will resume the reader thread and allow it to read. I have taken the code of PipeStream from CodeProject article by James Kolpack and extended it to make sure it's high performance, supports chunks of bytes to be stored instead of single bytes, support timeout on waits and so on.

A did some comparison between Regular proxy (blocking, synchronous, download all then deliver) and Streaming Proxy (continuous transmission from external server to browser). Both proxy downloads the MSDN feed and delivers it to the browser. The time taken here shows the total duration of browser making the request to the proxy and then getting the entire response.

image
Figure: Time taken by Streaming Proxy vs Regular Proxy while downloading MSDN feed

Not a very scientific graph and response time varies on the link speed between the browser and the proxy server and then from proxy server to the external server. But it shows that most of the time, Streaming Proxy outperformed Regular proxy.

image
Figure: Test client to compare between Regular Proxy and Streaming Proxy

You can also test both proxy's response time by going to http://labs.dropthings.com/AjaxStreamingProxy. Put your URL and hit Regular/Stream button and see the "Statistics" text box for the total duration. You can turn on "Cache response" and hit a URL from one browser. Then go to another browser and hit the URL to see the response coming from server cache directly. Also if you hit the URL again on the same browser, you will see response comes instantly without ever making call to the server. That's browser cache at work.

Learn more about Http Response caching from my blog post:
Making best use of cache for high performance website

A Visual Studio Web Test run inside a Load Test shows a better picture:

image 
Figure: Regular Proxy load test result shows Average Requests/Sec 0.79 and Avg Response Time 2.5 sec

image
Figure: Streaming Proxy load test result shows Avg Req/Sec is 1.08 and Avg Response Time 1.8 sec.

From the above load test results, Streaming Proxy is 26% better Request/Sec and Average Response Time is 29% better. The numbers may sound small, but at Pageflakes, 29% better response time means 1.29 million seconds saved per month for all the users on the website. So, we are effectively saving 353 man hours per month which was wasted staring at browser screen while it downloads content.

Building the Streaming Proxy

The details how the Streaming Proxy is built is quite long and not suitable for a blog post. So, I have written a CodeProject article:

Fast, Scalable, Streaming AJAX Proxy - continuously deliver data from cross domain

Please read the article and please vote for me if your find it useful.  

Reduce website download time by heavily compressing PNG and JPEG

PNG and JPEG are two most popular formats for web graphics. JPEG is used for photographs, screenshots and backgrounds where PNG is used for all other graphics need including cliparts, buttons, headers, footers, borders and so on. As a result, these two types of graphics file usually take up 80% of the total graphics used in a website. Of course, there's the GIF, which is very popular. But as it supports only 256 colors, it is losing its popularity day by day. PNG seems to be a all rounder winner for all kinds of graphics need. As all browsers support PNG well enough and PNG supports alpha transparency, it's surely the best format so far on the web for all purpose graphics need for websites. So, if you can optimize all PNG and JPEG on your website and compress them rigorously, you can easily shed off several seconds of load time from your website without doing any coding. Especially if your website is graphics rich like Pageflakes, 30% reduction in total size of graphics throughout the website is a big performance win.

Optimize all PNG on your website

PNG has a lot of scope for optimization. Generally regular graphics tools like Photoshop, Paintshop pro, Paint.NET all generate PNG using a moderate compression. So, PNG can be compressed further by using advanced compression tools. OptiPNG is such a tool that can compress PNG and sometimes produce 50% smaller output. At Pageflakes, we have around 380 PNG which when compressed using OptiPNG, gives us 40% reduction in total size. This is a big win for us.

Here's what wikipedia says about OptiPNG:

OptiPNG is an open source command line computer program that reduces the size of PNG files. The compression is lossless, meaning that the resulting image will have exactly the same appearance as the source image.

The main purpose of OptiPNG is to reduce the size of the PNG IDAT data stream by trying various filtering and compression methods. It also performs automatic bit depth, color type and color palette reduction where possible, and can correct some data integrity errors in input files.

Here's a poweshell script that you can run from the root folder of your website. It will scan through all the PNG files in the webtree and run OptiPNG on each file. This takes quite some time if you have hundreds of files. So, you should make it a part of your build script.

gci -include *.png -recurse | foreach
 { $fileName = $_.FullName; cmd /c "C:\soft\png\optipng.exe -o7 `"$fileName`"" }

Here I have stored the optipng.exe on the c:\soft\png folder.

OptiPNG gives very good compression. But there's even more scope for compression. AdvanceCOMP is the ultimate in compression technology for PNG as it uses the mighty 7zip compression algorithm. It can squeeze down PNG even further after being compressed by OptiPNG using its maximum compression mode. PNG files are compressed using DEFLATE algorithm. DEFLATE has 0 to 9 compression level, where 9 is the highest. AdvanceCOMP uses 7zip DEFLATE encoder, that extends the compression factor even more. During 7zip compression, a much more detailed search of compression possibilities is performed, at the expense of significant further processor time spent on searching. Effectively, the 10-point scale used in gzip is extended to include extra settings above 9, the previous maximum search level. There will be no difference in decompression speed, regardless of the level of compressed size achieved or time taken to encode the data.

Here's a poweshell script that you can run from the root folder of your website. It will scan through all the PNG files in the webtree and run AdvanceCOMP on each file. You need to run AdvanceCOMP after running OptiPNG.

gci -include *.png -recurse | foreach
 { $fileName = $_.FullName; cmd /c "C:\soft\png\advpng.exe 
 --shrink-insane -z `"$fileName`"" }

I have collected both optipng and advpng in this zip file.

Optimize all JPEG on your website

Unfortunately, there's not much powerful tool like OptiPNG for jpeg that you can run on all your jpeg files and compress them rigorously. JPEG file is compressed when it is saved. Generally all graphics applications provide you an option to select what's the quality ratio of the jpeg being saved. So, you have to consciously make the best compression vs quality choice while saving the jpeg file. However, libjpeg project has a jpeg optimizer tool that does some optimization on jpeg files. It has a jpegtran utility which does the optimization according to wikipedia:

jpegtran - a utility for lossless transcoding between different JPEG formats. The jpegtran command-line program is useful to optimize the compression of a JPEG file, convert between progressive and non-progressive JPEG formats, eliminate non-standard application-specific data inserted by some image programs, or to perform certain transformations on a file — such as grayscaling, or rotating and flipping (within certain limits) — all done "losslessly" (i.e. without decompressing and recompressing the data, and so causing a reduction of image quality due to generation loss).

However, when we ran jpegtran on all the jpeg files in Pageflakes, we are able to reduce about 20% total size of all jpeg. So, that was not too bad.

Here's how you run jpegtran to get all the jpeg files within your website directory optimized:

gci -include *.jpg -recurse | foreach
 { $fileName = $_.FullName; $newFileName = $fileName + ".tmp"; 
cmd /c "C:\soft\jpeg\jpegtran.exe -optimize -outfile `"$newFileName`" `"$fileName`""; 
copy $newFileName $fileName; del $newFileName; }

The libjpeg binaries are uploaded here for your convenience.

Warning: You have to run all these powershell commands in a single line. I have broken the commands in multiple line for better readability.

Let's save global bandwidth, go green.

Fast page loading by moving ASP.NET AJAX scripts after visible content

ASP.NET ScriptManager control has a property LoadScriptsBeforeUI, when set to false, should load all AJAX framework scripts after the content of the page. But it does not effectively push down all scripts after the content. Some framework scripts, extender scripts and other scripts registered by Ajax Control Toolkit still load before the page content loads. The following screen taken from www.dropthings.com shows several script tags are still added at the beginning of <form> which forces them to download first before the page content is loaded and displayed on the page. Script tags pause rendering on several browsers especially in IE until the scripts download and execute. As a result, it gives user a slow loading impression as user stares at a white screen for some time until the scripts before the content download and execute completely. If browser could render the html before it downloads any script, user would see the page content immediately after visiting the site and not see a white screen. This will give user an impression that the website is blazingly fast (just like Google homepage) because user will ideally see the page content, if it's not too large, immediately after hitting the URL.

image
Figure: Script blocks being delivered before the content

From the above screen shot you see there are some scripts from ASP.NET AJAX framework and some scripts from Ajax Control Toolkit that are added before the content of the page. Until these scripts download, browser don't see anything on the UI and thus you get a pause in rendering giving user a slow load feeling. Each script to external URL adds about 200ms avg network roundtrip delay outside USA while it tries to fetch the script. So, user basically stares at a white screen for at least 1.5 sec no matter how fast internet connection he/she has.

These scripts are rendered at the beginning of form tag because they are registered using Page.ClientScript.RegisterClientScriptBlock. Inside Page class of System.Web, there's a method BeginFormRender which renders the client script blocks immediately after the form tag.

   1: internal void BeginFormRender(HtmlTextWriter writer, string formUniqueID)
   2: {
   3:     ...
   4:         this.ClientScript.RenderHiddenFields(writer);
   5:         this.RenderViewStateFields(writer);
   6:         ...
   7:         if (this.ClientSupportsJavaScript)
   8:         {
   9:             ...
  10:             if (this._fRequirePostBackScript)
  11:             {
  12:                 this.RenderPostBackScript(writer, formUniqueID);
  13:             }
  14:             if (this._fRequireWebFormsScript)
  15:             {
  16:                 this.RenderWebFormsScript(writer);
  17:             }
  18:         }
  19:         this.ClientScript.RenderClientScriptBlocks(writer);
  20: }

Figure: Decompiled code from System.Web.Page class

Here you see several script blocks including scripts registered by calling ClientScript.RegisterClientScriptBlock are rendered right after form tag starts.

There's no easy work around to override the BeginFormRender method and defer rendering of these scripts. These rendering functions are buried inside System.Web and none of these are overridable. So, the only solution seems to be using a Response Filter to capture the html being written and suppress rendering the script blocks until it's the end of the body tag. When the </body> tag is about to be rendered, we can safely assume page content has been successfully delivered and now all suppressed script blocks can be rendered at once.

In ASP.NET 2.0, you to create Response Filter which is an implementation of a Stream. You can replace default Response.Filter with your own stream and then ASP.NET will use your filter to write the final rendered HTML. When Response.Write is called or Page's Render method fires, the response is written to the output stream via the filter. So, you can intercept every byte that's going to be sent to the client (browser) and modify it the way you like. Response Filters can be used in variety ways to optimize Page output like stripping off all white spaces or doing some formatting on the generated content, or manipulating the characters being sent to the browser and so on.

I have created a Response filter which captures all characters being sent to the browser. It it finds that script blocks are being rendered, instead of rendering it to the Response.OutputStream, it will extract the script blocks out of the buffer being written and render the rest of the content. It stores all script blocks, both internal and external, in a string buffer. When it detects </body> tag is about to be written to the response, it flushes all the captured script blocks from the string buffer.

   1: public class ScriptDeferFilter : Stream
   2: {
   3:     Stream responseStream;
   4:     long position;
   5:  
   6:     /// <summary>
   7:     /// When this is true, script blocks are suppressed and captured for 
   8:     /// later rendering
   9:     /// </summary>
  10:     bool captureScripts;
  11:  
  12:     /// <summary>
  13:     /// Holds all script blocks that are injected by the controls
  14:     /// The script blocks will be moved after the form tag renders
  15:     /// </summary>
  16:     StringBuilder scriptBlocks;
  17:     
  18:     Encoding encoding;
  19:  
  20:     public ScriptDeferFilter(Stream inputStream, HttpResponse response)
  21:     {
  22:         this.encoding = response.Output.Encoding;
  23:         this.responseStream = response.Filter;
  24:  
  25:         this.scriptBlocks = new StringBuilder(5000);
  26:         // When this is on, script blocks are captured and not written to output
  27:         this.captureScripts = true;
  28:     }

Here's the beginning of the Filter class. When it initializes, it takes the original Response Filter. Then it overrides the Write method of the Stream so that it can capture the buffers being written and do it's own processing.

   1: public override void Write(byte[] buffer, int offset, int count)
   2: {
   3:     // If we are not capturing script blocks anymore, just redirect to response stream
   4:     if (!this.captureScripts)
   5:     {
   6:         this.responseStream.Write(buffer, offset, count);
   7:         return;
   8:     }
   9:  
  10:     /* 
  11:      * Script and HTML can be in one of the following combinations in the specified buffer:          
  12:      * .....<script ....>.....</script>.....
  13:      * <script ....>.....</script>.....
  14:      * <script ....>.....</script>
  15:      * <script ....>.....</script> .....
  16:      * ....<script ....>..... 
  17:      * <script ....>..... 
  18:      * .....</script>.....
  19:      * .....</script>
  20:      * <script>.....
  21:      * .... </script>
  22:      * ......
  23:      * Here, "...." means html content between and outside script tags
  24:     */
  25:  
  26:     char[] content = this.encoding.GetChars(buffer, offset, count);
  27:  
  28:     int scriptTagStart = 0;
  29:     int lastScriptTagEnd = 0;
  30:     bool scriptTagStarted = false;
  31:  
  32:     for (int pos = 0; pos < content.Length; pos++)
  33:     {
  34:         // See if tag start
  35:         char c = content[pos];
  36:         if (c == '<')
  37:         {
  38:             int tagStart = pos;
  39:             // Check if it's a tag ending
  40:             if (content[pos+1] == '/')
  41:             {
  42:                 pos+=2; // go past the </ 
  43:  
  44:                 // See if script tag is ending
  45:                 if (isScriptTag(content, pos))
  46:                 {
  47:                     /// Script tag just ended. Get the whole script
  48:                     /// and store in buffer
  49:                     pos = pos + "script>".Length;
  50:                     scriptBlocks.Append(content, scriptTagStart, pos - scriptTagStart);
  51:                     scriptBlocks.Append(Environment.NewLine);
  52:                     lastScriptTagEnd = pos;
  53:  
  54:                     scriptTagStarted = false;
  55:                     continue;
  56:                 }
  57:                 else if (isBodyTag(content, pos))
  58:                 {
  59:                     /// body tag has just end. Time for rendering all the script
  60:                     /// blocks we have suppressed so far and stop capturing script blocks
  61:  
  62:                     if (this.scriptBlocks.Length > 0)
  63:                     {
  64:                         // Render all pending html output till now
  65:                         this.WriteOutput(content, lastScriptTagEnd, tagStart - lastScriptTagEnd);
  66:  
  67:                         // Render the script blocks
  68:                         byte[] scriptBytes = this.encoding.GetBytes(this.scriptBlocks.ToString());
  69:                         this.responseStream.Write(scriptBytes, 0, scriptBytes.Length);
  70:  
  71:                         // Stop capturing for script blocks
  72:                         this.captureScripts = false;
  73:  
  74:                         // Write from the body tag start to the end of the inut buffer and return
  75:                         // from the function. We are done.
  76:                         this.WriteOutput(content, tagStart, content.Length - tagStart);
  77:                         return;
  78:                     }
  79:                 }
  80:                 else
  81:                 {
  82:                     // some other tag's closing. safely skip one character as smallest
  83:                     // html tag is one character e.g. <b>. just an optimization to save one loop
  84:                     pos++;
  85:                 }
  86:             }
  87:             else
  88:             {
  89:                 if (isScriptTag(content, pos+1))
  90:                 {
  91:                     /// Script tag started. Record the position as we will 
  92:                     /// capture the whole script tag including its content
  93:                     /// and store in an internal buffer.
  94:                     scriptTagStart = pos;
  95:  
  96:                     // Write html content since last script tag closing upto this script tag 
  97:                     this.WriteOutput(content, lastScriptTagEnd, scriptTagStart - lastScriptTagEnd);
  98:  
  99:                     // Skip the tag start to save some loops
 100:                     pos += "<script".Length;
 101:  
 102:                     scriptTagStarted = true;
 103:                 }
 104:                 else
 105:                 {
 106:                     // some other tag started
 107:                     // safely skip 2 character because the smallest tag is one character e.g. <b>
 108:                     // just an optimization to eliminate one loop 
 109:                     pos++;
 110:                 }
 111:             }
 112:         }
 113:     }
 114:     
 115:     // If a script tag is partially sent to buffer, then the remaining content
 116:     // is part of the last script block
 117:     if (scriptTagStarted)
 118:     {
 119:         
 120:         this.scriptBlocks.Append(content, scriptTagStart, content.Length - scriptTagStart);
 121:     }
 122:     else
 123:     {
 124:         /// Render the characters since the last script tag ending
 125:         this.WriteOutput(content, lastScriptTagEnd, content.Length - lastScriptTagEnd);
 126:     }
 127: }

There are several situations to consider here. The Write method is called several times during the Page render process because the generated HTML can be quite big. So, it will contain partial HTML. So, it's possible the first Write call contains a start of a script block, but no ending script tag. The following Write call may or may not have the ending script block. So, we need to preserve state to make sure we don't overlook any script block. Each Write call can have several script block in the buffer as well. It can also have no script block and only page content.

The idea here is to go through each character and see if there's any starting script tag. If there is, remember the start position of the script tag. If script end tag is found within the buffer, then extract out the whole script block from the buffer and render the remaining html. If there's no ending tag found but a script tag did start within the buffer, then suppress output and capture the remaining content within the script buffer so that next call to Write method can grab the remaining script and extract it out from the output.

There are two other private functions that are basically helper functions and does not do anything interesting:

   1: private void WriteOutput(char[] content, int pos, int length)
   2: {
   3:     if (length == 0) return;
   4:  
   5:     byte[] buffer = this.encoding.GetBytes(content, pos, length);
   6:     this.responseStream.Write(buffer, 0, buffer.Length);
   7: }
   8:  
   9: private bool isScriptTag(char[] content, int pos)
  10: {
  11:     if (pos + 5 < content.Length)
  12:         return ((content[pos] == 's' || content[pos] == 'S')
  13:             && (content[pos + 1] == 'c' || content[pos + 1] == 'C')
  14:             && (content[pos + 2] == 'r' || content[pos + 2] == 'R')
  15:             && (content[pos + 3] == 'i' || content[pos + 3] == 'I')
  16:             && (content[pos + 4] == 'p' || content[pos + 4] == 'P')
  17:             && (content[pos + 5] == 't' || content[pos + 5] == 'T'));
  18:     else
  19:         return false;
  20:  
  21: }
  22:  
  23: private bool isBodyTag(char[] content, int pos)
  24: {
  25:     if (pos + 3 < content.Length)
  26:         return ((content[pos] == 'b' || content[pos] == 'B')
  27:             && (content[pos + 1] == 'o' || content[pos + 1] == 'O')
  28:             && (content[pos + 2] == 'd' || content[pos + 2] == 'D')
  29:             && (content[pos + 3] == 'y' || content[pos + 3] == 'Y'));
  30:     else
  31:         return false;
  32: }

The isScriptTag and isBodyTag functions may look weird. The reason for such weird code is pure performance. Instead of doing fancy checks like taking a part of the array out and doing string comparison, this is the fastest way of doing the check. Best thing about .NET IL is that it's optimized, if any of the condition in the && pairs fail, it won't even execute the rest. So, this is  as best as it can get to check for certain characters.

There are some corner cases that are not handled here. For example, what if the buffer contains a partial script tag declaration. For example, "....<scr" and that's it. The remaining characters did not finish in the buffer instead next buffer is sent with the remaining characters like "ipt src="..." >.....</scrip". In such case, the script tag won't be taken out. One way to handle this would be to make sure you always have enough characters left in the buffer to do a complete tag name check. If not found, store the half finished buffer somewhere and on next call to Write, combine it with the new buffer sent and do the processing.

In order to install the Filter, you need to hook it in in the Global.asax BeginRequest or some other event that's fired before the Response is generated.

   1: protected void Application_BeginRequest(object sender, EventArgs e)
   2: {
   3:     if (Request.HttpMethod == "GET")
   4:     {
   5:         if (Request.AppRelativeCurrentExecutionFilePath.EndsWith(".aspx"))
   6:         {
   7:             Response.Filter = new ScriptDeferFilter(Response);
   8:         }
   9:     }
  10: }

Here I am hooking the Filter only for GET calls to .aspx pages. You can hook it to POST calls as well. But asynchronous postbacks are regular POST and I do not want to do any change in the generated JSON or html fragment. Another way is to hook the filter only when ContentType is text/html.

When this filter is installed, www.dropthings.com defers all script loading after the <form> tag completes.

image
Figure: Script tags are moved after the <form> tag when the filter is used

You can grab the Filter class from the App_Code\ScriptDeferFilter.cs of the Dropthings project. Go to CodePlex site and download the latest code for the latest filter.

Posted by omar with