ASP.NET CAPTCHA Troubleshooting VB.NET Code Sample (BotDetect v3.0; deprecated)

The ASP.NET Captcha troubleshooting sample project shows how to use BotDetect CAPTCHA built-in error logging and Captcha event tracing, using the BotDetect Troubleshooting utility based on log4net.

First Time Here?

Check the BotDetect Developer Crash Course for key integration steps.

The logging requires the <captchaLogging> element and BotDetectTroubleshooting Module registration in the web.config file, as well as the log4net.config file defining log4net settings (in this case, logging to simple text files).

Such logging techniques can be used as a foundation for effective diagnosis and resolution of any BotDetect issues you might encounter on your servers.

The sample demonstrates the effects of following the How To Troubleshoot BotDetect ASP.NET CAPTCHA Issues guide.

  • C#
  • VB.NET

Visual Studio 2013 / Visual Studio 2012 / .NET 4.5

By default, the .NET 4.5 VB.NET version of the ASP.NET Captcha troubleshooting sample project is installed at:
C:\Program Files\Lanapsoft\BotDetect 3 CAPTCHA Component\Asp.Net\v4.5\WebApp\CaptchaTroubleshootingSample\CSharp

You can also run it from the BotDetect Start Menu:
Programs > Lanapsoft > BotDetect 3 CAPTCHA Component > ASP.NET > DotNET 4.5 Web Applications > Run

Default.aspx

<%@ Page Language="VB" AutoEventWireup="true"  CodeFile="Default.aspx.vb" 
  Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" 
  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
  <title>BotDetect ASP.NET CAPTCHA Troubleshooting Sample</title>
  <link type="text/css" rel="Stylesheet" href="StyleSheet.css" />
</head>
<body>
<form id="form1" runat="server">
  <h1>BotDetect ASP.NET CAPTCHA Troubleshooting Sample</h1>
  <fieldset id="TroubleshootingDebug">
    <legend>CAPTCHA Debug Logging</legend>
    <p class="prompt">
      <label for="CaptchaCodeTextBox">Retype the characters from the picture:</label>
    </p>
    <BotDetect:Captcha ID="SampleCaptcha" runat="server" />
    <div class="validationDiv">
      <asp:TextBox ID="CaptchaCodeTextBox" runat="server"></asp:TextBox>
      <asp:Button ID="ValidateCaptchaButton" runat="server" />
      <asp:Label ID="CaptchaCorrectLabel" runat="server" CssClass="correct">
      </asp:Label>
      <asp:Label ID="CaptchaIncorrectLabel" runat="server" CssClass="incorrect">
      </asp:Label>
    </div>
    <p class="validationTroubleshooting">A detailed trace of all 
      CAPTCHA events will be logged to the 'debug.txt' file in the 
      sample folder.</p>
    <div class="troubleshooting">
      <asp:Label ID="DebugLabel" runat="server"></asp:Label>
    </div>
  </fieldset>
  <fieldset id="TroubleshootingError">
    <legend>CAPTCHA Error Logging</legend>
    <p class="troubleshooting">Clicking 'Simulate Error' will throw a 
      fake BotDetect CAPTCHA exception and log it to the 'error.txt' 
      file in the sample folder.</p>
    <asp:Button ID="CauseErrorButton" runat="server" OnClick="CauseErrorButton_Click"/>
    <div class="troubleshooting">
      <asp:Label ID="ErrorLabel" runat="server"></asp:Label>
    </div>
  </fieldset>
</form>
</body>
</html>

[back to the top of the page]

Default.aspx.vb

Imports BotDetect

Partial Class _Default
    Inherits System.Web.UI.Page

    Protected Sub Page_PreRender(ByVal sender As Object, _
      ByVal e As System.EventArgs) Handles Me.PreRender

        ' initial page setup
        If Not IsPostBack Then
            ' set control text
            ValidateCaptchaButton.Text = "Validate"
            CaptchaCorrectLabel.Text = "Correct!"
            CaptchaIncorrectLabel.Text = "Incorrect!"

            ' these messages are shown only after validation
            CaptchaCorrectLabel.Visible = False
            CaptchaIncorrectLabel.Visible = False

            CauseErrorButton.Text = "Simulate error"
            ErrorLabel.Text = "An error has been generated. Please check the 
              'error.txt' file."

            DebugLabel.Text = "A validation attempt has been logged. Please check the 
              'debug.txt' file."
              
            DebugLabel.Visible = False
        End If

        If Session("error") IsNot Nothing Then
            ErrorLabel.Visible = True
            CaptchaCorrectLabel.Visible = False
            CaptchaIncorrectLabel.Visible = False
            Session("error") = Nothing
            DebugLabel.Visible = False
        Else
            ErrorLabel.Visible = False
        End If

        SampleCaptcha.UserInputClientID = CaptchaCodeTextBox.ClientID

        If IsPostBack Then
            ' validate the Captcha to check we're not dealing with a bot
            Dim code As String, isHuman As Boolean
            code = CaptchaCodeTextBox.Text.Trim().ToUpper()
            isHuman = SampleCaptcha.Validate(code)
            CaptchaCodeTextBox.Text = "" ' clear previous user input

            If isHuman Then
                CaptchaCorrectLabel.Visible = True
                CaptchaIncorrectLabel.Visible = False
            Else
                CaptchaCorrectLabel.Visible = False
                CaptchaIncorrectLabel.Visible = True
            End If

            DebugLabel.Visible = True
        End If

    End Sub

    Protected Sub CauseErrorButton_Click(ByVal sender As Object, _
      ByVal  e As System.EventArgs) Handles CauseErrorButton.Click
        Session("error") = True
        Throw New CaptchaControlException("Simulated exception")
    End Sub
End Class

[back to the top of the page]

Global.asax

<%@ Application Language="VB" %>

<script runat="server">

    Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
        ' Code that runs on application startup
    End Sub
    
    Sub Application_End(ByVal sender As Object, ByVal e As EventArgs)
        ' Code that runs on application shutdown
    End Sub
        
    Sub Application_Error(ByVal sender As Object, ByVal e As EventArgs)
        ' Code that runs when an unhandled error occurs
        Response.Redirect("Default.aspx")
    End Sub

    Sub Session_Start(ByVal sender As Object, ByVal e As EventArgs)
        ' Code that runs when a new session is started
    End Sub

    Sub Session_End(ByVal sender As Object, ByVal e As EventArgs)
        ' Code that runs when a session ends. 
        ' Note: The Session_End event is raised only when the 
        sessionstate mode
        ' is set to InProc in the Web.config file. If session mode is 
        set to StateServer 
        ' or SQLServer, the event is not raised.
    End Sub
       
</script>

[back to the top of the page]

log4net.config

<?xml version="1.0"?>

<!-- This section contains the log4net configuration settings -->
<log4net debug="false">

  <!-- Errors are logged to a 'error.txt' file -->
  <appender name="ErrorFileAppender" type="log4net.Appender.FileAppender">
    <file value="error.txt" />
    <appendToFile value="true" />
    <lockingModel type="log4net.Appender.FileAppender+MinimalLock" />
    <layout type="log4net.Layout.PatternLayout,log4net">
      <conversionPattern value="%date [%thread] %type - %n%n%message%n%n" />
    </layout>
  </appender>

  <!-- Error logging is enabled, comment-out to disable -->
  <logger name="ErrorLogger">
    <level value="ERROR" />
    <appender-ref ref="ErrorFileAppender" />
  </logger>

  
  <!-- Debug info is logged to a 'debug.txt' file -->
  <appender name="DebugFileAppender" type="log4net.Appender.FileAppender">
    <file value="debug.txt" />
    <appendToFile value="true" />
    <lockingModel type="log4net.Appender.FileAppender+MinimalLock" />
    <layout type="log4net.Layout.PatternLayout,log4net">
      <conversionPattern value="%date [%thread] %type - %n%n%message%n%n" />
    </layout>
  </appender>

  <!-- Debug logging is enabled, comment-out to disable -->
  <logger name="DebugLogger">
    <level value="DEBUG" />
    <appender-ref ref="DebugFileAppender" />
  </logger>

</log4net>

[back to the top of the page]

Web.config

<?xml version="1.0"?>
<!--
  For more information on how to configure your ASP.NET application, please visit
  http://go.microsoft.com/fwlink/?LinkId=169433
  -->
<configuration>
  <configSections>
    <!-- Register the log4net configuration section -->
    <section name="log4net" requirePermission="false"
      type="log4net.Config.Log4NetConfigurationSectionHandler, log4net" />
    <!-- Register the BotDetect configuration section -->
    <section name="botDetect" requirePermission="false" 
      type="BotDetect.Configuration.BotDetectConfigurationSection, BotDetect" />
  </configSections>
  <appSettings>
    <add key="aspnet:UseTaskFriendlySynchronizationContext" value="true" />
    <add key="ValidationSettings:UnobtrusiveValidationMode" value="None" />
  </appSettings>
  <!-- log4net settings are loaded from a separate config file -->
  <log4net configSource="log4net.config"/>
  <!-- BotDetect Captcha settings can be configured in this section -->
  <botDetect>
    <!-- Register the log4net BotDetect logging provider -->
    <captchaLogging errorLoggingEnabled="true" traceEnabled="true" eventFilter=".*" 
      loggingProvider="BotDetect.Logging.Log4NetLoggingProvider, 
        BotDetect.Troubleshooting"/>
    <captchaImage>
      <helpLink enabled="true" mode="image" />
    </captchaImage>
  </botDetect>
  <system.web>
    <httpHandlers>
      <!-- Register the HttpHandler used for BotDetect Captcha requests -->
      <add verb="GET" path="BotDetectCaptcha.ashx" 
        type="BotDetect.Web.CaptchaHandler,  BotDetect"/>
    </httpHandlers>
    <httpModules>
      <!-- Register the HttpModule used for BotDetect error logging (IIS 5.0, 5.1, 6.0)
      -->
      <add name="BotDetectTroubleshootingModule" 
        type="BotDetect.Web.CaptchaTroubleshootingModule, BotDetect"/>
    </httpModules>
    <!-- Register a custom SessionIDManager for BotDetect Captcha requests -->
    <sessionState mode="InProc" cookieless="AutoDetect" timeout="20" 
      sessionIDManagerType="BotDetect.Web.CustomSessionIdManager, BotDetect"/>
    <!-- Session state is required for BotDetect storage; you can also turn if off 
      globally and only enable for BotDetect-protected pages if you prefer -->
    <pages enableSessionState="true" controlRenderingCompatibilityVersion="4.5">
      <controls>
        <!-- Register the BotDetect tag prefix for easier use in all pages -->
        <add assembly="BotDetect" namespace="BotDetect.Web.UI" tagPrefix="BotDetect"/>
      </controls>
    </pages>
    <compilation debug="false" targetFramework="4.5" />
    <httpRuntime requestValidationMode="4.5" targetFramework="4.5" 
      encoderType="System.Web.Security.AntiXss.AntiXssEncoder, System.Web, 
        Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
    <machineKey compatibilityMode="Framework45" />
    <trace enabled="false" localOnly="true"/>
    <httpCookies httpOnlyCookies="true"/>
    <trust level="Medium" originUrl=""/>
    <authentication mode="None"/>
    <customErrors mode="RemoteOnly"/>
  </system.web>
  <system.webServer>
    <validation validateIntegratedModeConfiguration="false"/>
    <handlers>
      <!-- Register the HttpHandler used for BotDetect Captcha requests (IIS 7.0+) -->
      <remove name="BotDetectCaptchaHandler"/>
      <add name="BotDetectCaptchaHandler" preCondition="integratedMode" verb="GET" 
        path="BotDetectCaptcha.ashx" type="BotDetect.Web.CaptchaHandler, BotDetect"/>
    </handlers>
    <modules>
      <!-- Register the HttpModule used for BotDetect error logging (IIS 7.0+) -->
      <remove name="BotDetectTroubleshootingModule"/>
      <add name="BotDetectTroubleshootingModule" preCondition="integratedMode" 
        type="BotDetect.Web.CaptchaTroubleshootingModule, BotDetect"/>
    </modules>
  </system.webServer>
</configuration>

[back to the top of the page]

Visual Studio 2010 / .NET 4.0

By default, the .NET 4.0 VB.NET version of the ASP.NET Captcha troubleshooting sample project is installed at:
C:\Program Files\Lanapsoft\BotDetect 3 CAPTCHA Component\Asp.Net\v4.0\WebApp\CaptchaTroubleshootingSample\CSharp

You can also run it from the BotDetect Start Menu:
Programs > Lanapsoft > BotDetect 3 CAPTCHA Component > ASP.NET > DotNET 4.0 Web Applications > Run

The Visual Studio 2010 / .NET 4.0 source has no essential differences from the Visual Studio 2013 / Visual Studio 2012 / .NET 4.5 source.

[back to the top of the page]

Visual Studio 2008 / .NET 3.5

By default, the .NET 3.5 VB.NET version of the ASP.NET Captcha troubleshooting sample project is installed at:
C:\Program Files\Lanapsoft\BotDetect 3 CAPTCHA Component\Asp.Net\v3.5\WebApp\CaptchaTroubleshootingSample\CSharp

You can also run it from the BotDetect Start Menu:
Programs > Lanapsoft > BotDetect 3 CAPTCHA Component > ASP.NET > DotNET 3.5 Web Applications > Run

The Visual Studio 2008 / .NET 3.5 source has no essential differences from the Visual Studio 2013 / Visual Studio 2012 / .NET 4.5 source.

[back to the top of the page]

Visual Studio 2005 / .NET 2.0

By default, the .NET 2.0 VB.NET version of the ASP.NET Captcha troubleshooting sample project is installed at:
C:\Program Files\Lanapsoft\BotDetect 3 CAPTCHA Component\Asp.Net\v2.0\WebApp\CaptchaTroubleshootingSample\CSharp

You can also run it from the BotDetect Start Menu:
Programs > Lanapsoft > BotDetect 3 CAPTCHA Component > ASP.NET > DotNET 2.0 Web Applications > Run

The Visual Studio 2005 / .NET 2.0 source has no essential differences from the Visual Studio 2013 / Visual Studio 2012 / .NET 4.5 source.

[back to the top of the page]


Please Note

The information on this page is out of date and applies to a deprecated version of BotDetect™ CAPTCHA (v3.0).

An up-to-date equivalent page for the latest BotDetect Captcha release (v4) is BotDetect v4 Captcha documentation index.

General information about the major improvements in the current BotDetect release can be found at the What's New in BotDetect v4.0 page.

© Captcha, Inc. 2004-2023. All rights reserved.

BotDetect, BotDetect CAPTCHA, Lanap, Lanap CAPTCHA, Lanap BotDetect, Lanap BotDetect CAPTCHA, Lanapsoft, Lanapsoft CAPTCHA, Lanapsoft BotDetect, Lanapsoft BotDetect CAPTCHA, and Lanap Software are trademarks of Captcha, Inc. All other product, brand, and company names are mentioned for identification purposes only and are trademarks or registered trademarks of their respective owners.

Captcha, Inc. -- formerly: Lanapsoft, Inc. / Lanap, Inc.