BotDetect ASP.NET 1.1 CAPTCHA Troubleshooting VB.NET Code Sample (BotDetect v2.0)

documentation > asp.net 1.1 captcha > samples

Please Note

The information on this page is out of date and applies to a deprecated version of BotDetect™ CAPTCHA (v2.0).

An up-to-date equivalent page for the latest BotDetect Captcha release (v3) is BotDetect v3 CAPTCHA Troubleshooting code sample.

General information about the major improvements in the current BotDetect release can be found at the What's New in BotDetect v3.0 page.

This BotDetect ASP.NET CAPTCHA code sample shows how to use the BotDetect built-in error logging to troubleshoot CAPTCHA issues. It is equivalent to the result you will get if you are following the How to log internal BotDetect errors to a text file guide. It simulates an exception in BotDetect code and demonstrates how it can be logged and handled.

Please Note

Since this example logs errors and validation attempt details to a text file in the server filesystem, it will only work in full trust environments.

Sample Project Location
Default.aspx
Default.aspx.vb
Global.asax.vb
Web.config

Sample Project Location

By default, this sample project is installed at
C:\Program Files\Lanapsoft\BotDetect\ASP.NET 1.1\v2.0\Samples\VBNetBotDetect2TroubleshootingDemo\.

You can also run it from the Start Menu:
Programs > Lanapsoft > BotDetect > ASP.NET 1.1 > v2.0 > Samples > VB.NET BotDetect CAPTCHA Troubleshooting Sample.

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Default.aspx

Full Source Code Listing

<%@ Page Language="vb" AutoEventWireup="false"
  Codebehind="Default.aspx.vb" Inherits="VBNetBotDetectDemo._Default" 
%>

<%@ Register Assembly="Lanap.BotDetect" Namespace="Lanap.BotDetect" 
  TagPrefix="BotDetect" %>

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>BotDetect Demo</title>
    <link type='text/css' rel='Stylesheet' href="StyleSheet.css" />
</head>
<body>
    <form id="form1" runat="server">
    <fieldset id="Preview">
        <legend>
            lt;span id="PreviewLegend">CAPTCHA Validation Logging</span>
        </legend>
        <div id="PromptDiv">
            <span id="Prompt">Type the characters you see in 
              the picture</span>
        </div>
        <div id="CaptchaDiv">
            <BotDetect:Captcha ID="SampleCaptcha" runat="server" />
        </div>
        <div id="ValidationDiv">
            <asp:TextBox ID="CodeTextBox" runat="server">
            </asp:TextBox>
            <asp:Button ID="ValidateButton" runat="server" />
            <asp:Label ID="MessageCorrectLabel" runat="server">
            </asp:Label>
            <asp:Label ID="MessageIncorrectLabel" runat="server">
            </asp:Label>
        </div>
        <div class="ValidationTroubleshooting">
            <p>All Captcha validation attempts will be logged to the 
              'debug.txt' file in the sample folder.</p>
        </div>
        <div class="Troubleshooting">
            <p>
                <asp:Label ID="DebugLabel" runat="server"></asp:Label>
            </p>
        </div>
    </fieldset>
		
    <fieldset id="TroubleshootingError">
        <legend><span id="TroubleshootingErrorLegend">CAPTCHA Error 
            Logging</span></legend>
        <div class="Troubleshooting">
            <p>Clicking 'Simulate Error' will throw a fake BotDetect 
              exception and log it to the 'error.txt' file in the 
              sample folder.</p>
        </div>
        <asp:Button ID="CauseErrorButton" runat="server" 
            OnClick="CauseErrorButton_Click" />
        <div class="Troubleshooting">
            <p>
                <asp:Label ID="ErrorLabel" runat="server"></asp:Label>
            </p>
        </div>
    </fieldset>

    <div id="Note">
        <span>NOTE: the Trial version will use "LANAP" instead of a 
          random code in 50% of renderings.</span>
    </div>
    </form>
</body>
</html>

Explanation

Beside the usual elements required to add the BotDetect CAPTCHA to an ASP.NET form, this file also contains an extra button used to simulate an internal BotDetect exception and several related presentation elements.

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Default.aspx.vb

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Public Class _Default
    Inherits System.Web.UI.Page

    #Region " Web Form Designer Generated Code "

    'This call is required by the Web Form Designer.
    <System.Diagnostics.DebuggerStepThrough()> Private Sub _
        InitializeComponent()
    End Sub
    
    Protected WithEvents MessageCorrectLabel As _
        System.Web.UI.WebControls.Label
				
    Protected WithEvents MessageIncorrectLabel As _
        System.Web.UI.WebControls.Label
				
    Protected WithEvents SampleCaptcha As _
        Lanap.BotDetect.Captcha
				
    Protected WithEvents CodeTextBox As _
        System.Web.UI.WebControls.TextBox
				
    Protected WithEvents ValidateButton As _
        System.Web.UI.WebControls.Button
				
    Protected WithEvents CauseErrorButton As _
        System.Web.UI.WebControls.Button
				
    Protected WithEvents ErrorLabel As _
        System.Web.UI.WebControls.Label

    Protected WithEvents DebugLabel As _
        System.Web.UI.WebControls.Label

    'NOTE: The following placeholder declaration is required by 
    'the Web Form Designer. Do not delete or move it.
    Private designerPlaceholderDeclaration As System.Object

    Private Sub Page_Init(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles MyBase.Init
        'CODEGEN: This method call is required by the Web Form 
        'Designer. Do not modify it using the code editor.
        InitializeComponent()
    End Sub

    #End Region

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

        ' initial page setup
        If (Not IsPostBack) Then

            'set control text
            ValidateButton.Text = "Validate"
            MessageCorrectLabel.Text = "Correct!"
            MessageIncorrectLabel.Text = "Incorrect!"

            'these messages are shown only after validation
            MessageCorrectLabel.Visible = False
            MessageIncorrectLabel.Visible = False

            CauseErrorButton.Text = "Simulate error"
            ErrorLabel.Text = "An error has been generated. _
                Please check the 'error.log' file."
								
            DebugLabel.Visible = False								
            DebugLabel.Text = "A validation attempt has been logged. _
                Please check the 'debug.txt' file."
								
        End If

        If (Session("error") <> Nothing) Then
            ErrorLabel.Visible = True
            MessageCorrectLabel.Visible = False
            MessageIncorrectLabel.Visible = False
            Session("error") = Nothing
            DebugLabel.Visible = False	
        Else
            ErrorLabel.Visible = False
        End If
				
        ' clear user input on Reload button clicks
        Dim scriptTemplate As String
        scriptTemplate = "<script type='text/javascript'>" & _
          "function LBD_ClearUserInput() {{" & _
          "  var LBD_textBox = document.getElementById('{0}');" & _
          "  if(LBD_textBox) {{" & _
          "    LBD_textBox.value = '';" & _
          "  }}" & _
          "}}" & _
          "LBD_RegisterHandler('PreReloadCaptchaImage', _
            LBD_ClearUserInput);</script>"

        Dim script As String
        script = String.Format(scriptTemplate, CodeTextBox.ClientID)
        If (Not Page.ClientScript.IsStartupScriptRegistered( _
            "CaptchaReloadClearInput")) Then
          Page.ClientScript.RegisterStartupScript(Me.GetType(), _ 
            "CaptchaReloadClearInput", script, True)
        End If
				
        ' automatically lowercase user input	
        CodeTextBox.Attributes.Add("onkeyup", _ 
            "this.value = this.value.toLowerCase();")

        If (IsPostBack) Then
            'validate the input code, and show the 
            'appropriate message 
            Dim code As String = CodeTextBox.Text.Trim().ToUpper()

            If (SampleCaptcha.Validate(code)) Then
                MessageCorrectLabel.Visible = True
                MessageIncorrectLabel.Visible = False
            Else
                MessageCorrectLabel.Visible = False
                MessageIncorrectLabel.Visible = True
            End If
						
            DebugLabel.Visible = True	

            'clear previous user code input
            CodeTextBox.Text = ""
        End If
    End Sub

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

End Class

Explanation

Beside the usual CAPTCHA initialization and validation code, the CauseErrorButton_Click event handler is used to throw a simulated BotDetect internal exception. Since this is a simplified sample project containing only one page which is used both before and after the exception is thrown and handled, we also use a Session flag to handle error information presentation.

There is no error handling code in the form codebehind, since a special HttpModule is registered in the Web.config file, which catches BotDetect internal errors (but not general exceptions) and writes the error information to a text file.

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Global.asax.vb

Full Source Code Listing

Imports System.Web
Imports System.Web.SessionState

Public Class Global
    Inherits System.Web.HttpApplication

#Region " Component Designer Generated Code "

    Public Sub New()
        MyBase.New()

        'This call is required by the Component Designer.
        InitializeComponent()

        'Add any initialization after the InitializeComponent() call

    End Sub

    'Required by the Component Designer
    Private components As System.ComponentModel.IContainer

    'NOTE: The following procedure is required by the Component 
    'Designer. It can be modified using the Component Designer.
    'Do not modify it using the code editor.
    <System.Diagnostics.DebuggerStepThrough()> Private Sub _
        InitializeComponent()
				
        components = New System.ComponentModel.Container()
    End Sub

#End Region

    Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
        ' Fires when the application is started
    End Sub

    Sub Session_Start(ByVal sender As Object, ByVal e As EventArgs)
        ' Fires when the session is started
    End Sub

    Sub Application_BeginRequest(ByVal sender As Object, _
        ByVal e As EventArgs)
				
        ' Fires at the beginning of each request
    End Sub

    Sub Application_AuthenticateRequest(ByVal sender As Object, _
        ByVal e As EventArgs)
				
        ' Fires upon attempting to authenticate the use
    End Sub

    Sub Application_Error(ByVal sender As Object, ByVal e As EventArgs)
        ' Fires when an error occurs
        Response.Redirect("Default.aspx")
    End Sub

    Sub Session_End(ByVal sender As Object, ByVal e As EventArgs)
        ' Fires when the session ends
    End Sub

    Sub Application_End(ByVal sender As Object, ByVal e As EventArgs)
        ' Fires when the application ends
    End Sub

End Class

Explanation

Since the BotDetect internal error logging re-throws any exceptions after logging their details, you can handle all exceptions in your applications in a consistent manner. In this simple example, we just ignore the error and redraw the only page in the application.

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Web.config

Full Source Code Listing

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    
  <configSections>
    <section name="log4net" 
      type="log4net.Config.Log4NetConfigurationSectionHandler, 
      log4net"/>
  </configSections>
	
  <!-- 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>	
	
  <system.web>
  
  <httpHandlers>
    <add verb="*" path="LanapCaptcha.aspx" 
      type="Lanap.BotDetect.CaptchaHandler, Lanap.BotDetect"/>
  </httpHandlers>
	
  <httpModules>
    <add type="Lanap.BotDetect.Troubleshooting.LoggingModule, 
      Lanap.BotDetect.Troubleshooting" name="LoggingModule"/>
  </httpModules>

  <!-- DYNAMIC DEBUG COMPILATION
    Set compilation debug="true" to enable ASPX debugging. Otherwise, 
    setting this value to false will improve runtime performance of 
    this application. Set compilation debug="true" to insert debugging 
    symbols (.pdb information) into the compiled page. Because this 
    creates a larger file that executes more slowly, you should set 
    this value to true only when debugging and to false at all other 
    times. For more information, refer to the documentation about 
    debugging ASP.NET files.
  -->
  <compilation 
    defaultLanguage="vb"
    debug="false"
  />

  <!-- CUSTOM ERROR MESSAGES
    Set customErrors mode="On" or "RemoteOnly" to enable custom error 
    messages, "Off" to disable. 
		
    Add <error> tags for each of the errors you want to handle.

    "On" Always display custom (friendly) messages.
		
    "Off" Always display detailed ASP.NET error information.
		
    "RemoteOnly" Display custom (friendly) messages only to users not 
      running on the local Web server. This setting is recommended for 
      security purposes, so that you do not display application detail 
      information to remote clients.
  -->
  <customErrors 
    mode="RemoteOnly" 
  /> 

  <!-- AUTHENTICATION 
    This section sets the authentication policies of the application. 
    Possible modes are "Windows", "Forms", "Passport" and "None".

    "None" No authentication is performed. 
		
    "Windows" IIS performs authentication (Basic, Digest, or 
    Integrated Windows) according to its settings for the 
    application. Anonymous access must be disabled in IIS. 
		
    "Forms" You provide a custom form (Web page) for users to 
    enter their credentials, and then you authenticate them 
    in your application. A user credential token is stored 
    in a cookie.
		
    "Passport" Authentication is performed via a centralized 
    authentication service provided by Microsoft that offers 
    a single logon and core profile services for member sites.
  -->
  <authentication mode="Windows" /> 

  <!-- AUTHORIZATION 
    This section sets the authorization policies of the 
    application. You can allow or deny access to application 
    resources by user or role. Wildcards: "*" mean everyone, 
    "?" means anonymous (unauthenticated) users.
  -->

  <authorization>
    <allow users="*" /> <!-- Allow all users -->
    <!-- 
    <allow users="[comma separated list of users]"
      roles="[comma separated list of roles]"/>
    <deny users="[comma separated list of users]"
      roles="[comma separated list of roles]"/>
    -->
  </authorization>

  <!-- APPLICATION-LEVEL TRACE LOGGING
    Application-level tracing enables trace log output for 
    every page within an application. 
    Set trace enabled="true" to enable application trace 
    logging. If pageOutput="true", the trace information 
    will be displayed at the bottom of each page. Otherwise, 
    you can view the application trace log by browsing the 
    "trace.axd" page from your web application root. 
  -->
  <trace
    enabled="false"
    requestLimit="10"
    pageOutput="false"
    traceMode="SortByTime"
    localOnly="true"
  />

  <!-- SESSION STATE SETTINGS
    By default ASP.NET uses cookies to identify which requests 
    belong to a particular session. If cookies are not available, 
    a session can be tracked by adding a session identifier to the 
    URL. To disable cookies, set sessionState cookieless="true".
  -->
  <sessionState 
    mode="InProc"
    stateConnectionString="tcpip=127.0.0.1:42424"
    sqlConnectionString="data source=127.0.0.1;Trusted_Connection=yes"
    cookieless="false" 
    timeout="20" 
  />

  <!-- GLOBALIZATION
    This section sets the globalization settings of the application. 
  -->
  <globalization 
    requestEncoding="utf-8" 
    responseEncoding="utf-8" 
  />
   
 </system.web>

</configuration>

Explanation

Beside the usual HttpHandler and Session State declarations required for all BotDetect CAPTCHA applications, two more elements are necessary to enable BotDetect built-in error logging. The first is the HttpModule registration in the <httpModules> section, which activates the special BotDetect LoggingModule.

The second necessary element is the <configSection> declaration, in which we register a special configuration section for log4net (the open-source .NET logging framework used for the actual error logging) settings. Using the log4net configuration syntax, the <log4net> section setups an error logger writing exception details to a text file named error.txt and located in the same folded as the log4net.config file, and a debug logger writing Captcha validation attempt details to a text file named debug.txt.

The log4net framework offers many other logging options, from different log output destinations to different log message levels (trace, debug, and other messages), which can be handled in different ways. For simplicity's sake, this sample project uses a simple file logger – if you are interested in the other options, please consult the log4net documentation.

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