ScottGu kindly called out our Validator Module on Sunday and it's getting more and more popular. So now seems like a good time to talk about how it can be extended.

There are three rendering modes built-in to the Validator Module:

Html (displays a report at the bottom of the page)

HtmlFloat (displays a floating report at the top of the page)

Comments (writes comments at the bottom of your HTML source)

Additionally, there is a fourth setting:

Custom (up to you :)

To demonstrate how to implement your own renderer we'll create a quick and simple SmtpRenderer class that sends an e-mail whenever an invalid document is rendered.

First we create a new class library project (in .NET 2.0) and we'll need to add a reference to the Validator Module assembly itself (download it here).

Next we add our class and implement the IValidationRenderer interface (in the Tjoc.Web.Validator namespace).

using System;
using System.Collections.ObjectModel;
using System.Web;
using System.Text;
using System.Net.Mail;
using System.Configuration;
using Tjoc.Web.Validator;

namespace MyValidatorExtension
{
    public class SmtpRenderer : IValidationRenderer
    {
    }
}

The IValidationRenderer interface has one method, Render, which is passed the current HttpResponse object, a Collection of ValidationRecords and the time it took to validate the response. The code here is very simplistic and for demonstration purposes; the comments should explain what's going on:

public void Render(
HttpResponse response,
Collection<ValidationRecord> errors,
TimeSpan validationDuration)
{
    // Guard clause to see if validation failed
    if (errors.Count == 0)
    {
        return;
    }
    
    // Use a string builder to create the message body
    StringBuilder body = new StringBuilder();
    
    // Note the page in which the error occured...
    body.Append("XHTML Validation Error in page ");
    body.AppendLine(HttpContext.Current.Request.RawUrl);
    body.AppendLine();
    
    // ... and the details of each error
    foreach (ValidationRecord error in errors)
    {
        body.AppendLine(error.ToString());
        body.AppendLine();
    }
    
    // Finally, note how long validation took
    body.AppendFormat("Validation took {0}", validationDuration);
    
    // Create the message and read the addressee from appSettings
    MailMessage message = new MailMessage(
        "Validator Module <validator@example.com>",
        ConfigurationManager.AppSettings["validatorMailAddress"]);
    message.Subject = "Validator Report";
    message.Body = body.ToString();
    SmtpClient client = new SmtpClient();
    // Send the mail!
    client.Send(message);

}

Finally, We need to add the target mail address to web.config, setup the SMTP Host and specify our custom renderer

<validatorModule enabled="true" mode="Custom" customRenderer="MyValidatorExtension.SmtpRenderer, MyAssembly">

...

<appSettings>
    <add key="validatorMailAddress" value="josh@thejoyofcode.com"/>
</appSettings>
<system.net>
    <mailSettings>
        <smtp>
            <network host="smtp.yourhosthere.co.uk"/>
        </smtp>
    </mailSettings>
</system.net>

And Bingo! An SMTP renderer for the Validation Module that sends e-mails like the one below:

If I was to write this for real I'd want to make sure that I wasn't inundated with mails so I'd probably make sure I was only sent an e-mail once every n minutes per page, which should be easy enough. Maybe somebody out there wants to put such an example together? If you do, let me know and I'll post a link.