The EDX Software Blog

Sys.WebForms.PageRequestManagerServerErrorException

Intro. My company has a private webpage where subscribers search for some specialized information and then can use the search results to update database records. The page has many textboxes used to allow the user to define search criteria, filter the results, and add and update records. The textboxes are in AJAX UpdatePanels and there are many buttons which submit the data to the webpage server.

The Problem. If the user types a "less than" character ( < ) followed by a letter in any textbox, clicking any of the buttons will result in this popup error message:

Sys.WebForms.PageRequestManagerServerErrorException: An unknown error occurred while processing the request on the server. The status code returned from the server was: 500.

A little research revealed that an error occurs because the system is trying to prevent the user from entering an html tag. And the user get a popup message (instead of a full error page) because the submit button is within an UpdatePanel, and I have no customErrors page defined for a 500 error. Unfortunately, the error message above does not convey to my users that they must put a space after the < .

Rejected Ideas. So how can I fix this problem? Some blogs recommended that I simply turn off the test for html by adding:

ValidateRequest="false"

in the tag < %@ Page ...%>, but I didn't think this was a very good idea because then the page would be open to HTML injection.

I also considered the question, "Can I prevent users from entering html into my textboxes?", and looked at javascript ways to change or remove the < characters.

The Solution. I decided, though, that it is better to let the user fix the problem. A popup error message is perfect, as I don't want my users navigating away from my page. So, I just needed a way to change the text of the error message to something the users will understand. Insert this code in your .aspx just below your asp:ScriptManager line:

< !-- Code to replace text of 500 error -->
< script type="text/javascript">
  Sys.WebForms.PageRequestManager.getInstance().add_endRequest(
    function(sender, e)
    {
     if (e.get_error())
      {
       if (e.get_response().get_statusCode() == 500)
        {
          alert("A potentially dangerous value was detected from the client. Note that every < must have a space after it. ");
      e.set_errorHandled(true);
        }
      }
    }
)
< /script>

This entry was posted on Tuesday, June 16th, 2009 at 09:45 and is filed under AJAX. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

Sys.WebForms.PageRequestManagerServerErrorException

Leave a Reply