Friday, November 20, 2009

HtmlFilter - The ultimate SharePoint and .Net code hack

If you've ever run into a wall of closed classes or inaccessible functionality within or SharePoint, then I have good news for you. When you can't interface with out of the box server side objects, you can always fall back on the HtmlFilter to save you.

The code I wrote will allow you to intercept whatever HTML the server outputs to the browser and filter it via REGEX expressions returning whatever you would like. It works via the page.response.filter property.

You can add the filter at any point (before pre-render) in your server-side code.  This allows you to selectively apply filters based on server side code and to insert server-side parameters.
Warning: Regular Expressions will increase the server processor load.  Each page request implementng this tool will add some overhead as it searches the html.  You may need to load test your expressions and possibly optimize them.  Note that there is also a property that will bypass the filter on asynchronous page loads, although the performance hit of an asynchronous page load will already be reduced since only the updated html will be filtered.  On the other hand, the overhead on the server will probably be less than the overhead that would be created on the client and via increased content bandwidth if a javascript solution was used.

The HtmlFilter is now available on CodePlex.
Refer to the CodePlex project for future updates and usage examples.

  • Add the HtmlFilter.vb file to the App_Code\VBCode folder

    • See here for how to configure separate VBCode and CSCode folders using CodeSubdirectories in the web.config

  • In your UserControl or Page CodeBehind, add the following code in the Page_Load event handler

    • For VB

      Dim FilterReplaceValues As New Specialized.NameValueCollection
      FilterReplaceValues.Add("Your Regex Expression", "Your Replacement Expression")
      HtmlFilter.SetHtmlFilter(Page, FilterReplaceValues, 10000)

    • For C#

      Specialized.NameValueCollection FilterReplaceValues = new Specialized.NameValueCollection();
      FilterReplaceValues.Add("Your Regex Expression", "Your Replacement Expression");
      HtmlFilter.SetHtmlFilter(Page, FilterReplaceValues, 10000);

  • The number 10000 in the code above should be at least the length of any replaceable string.

    • This is used in the stream to reduce buffer size.
    • Example:  If you will be replacing strings up to 20 characters, you would put 20 or more there.

  • Fill in the appropriate Regex and Replacement expressions according to your needs.

    • You may add multiple FilterReplaceValues to the collection.  It will parse each one in order.
    • Examples (VB)

      • Remove all UserControl prepended Identifier strings from Form elements, for use in a custom cross-page post scenario.

        "(name|id)=""[^""]*" & Me.ID & "[\$_]", "$1="""

      • SharePoint: Remove the Edit and Export Web Part Edit items from the Edit Menu

        "(?s:<ie:menuitem type=""separator"" /><ie:menuitem title(?!.*separator.*id=""MSOMenu_Edit"").*MSOMenu_Edit.*Export\.\.\.(\r|\n|\s)*</ie:menuitem>)", ""

  • For help creating your own expressions, use some of these tools


  1. Also available on CodePlex:

    A sample project is available there.

  2. Nice post. Might well use this for a SharePoint project I'm working on. On a different note, I have an HTML site that I need to amend - any way this filter can be implemented on a .Net website that is just rendering HTML files (i.e. no code behind as such). b . weeks at

  3. Yes. This can be used on any .net based site. You can use inline server-side code to add the HtmlFilter if you don't want to use code behind.

  4. I just have static HTML files with .html extensions. Might convert your code to run as an httpHandler if that's ok.

  5. Yes, you could modify it as a HttpHandler. If you do, let me know and you can add it to the codeplex project.