BotDetect ASP.NET 1.1 CAPTCHA Troubleshooting VB.NET Code Sample
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
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.
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.
Default.aspx.vb
Full Source Code Listing
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.
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.
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.
Current BotDetect Versions
- BotDetect ASP.NET CAPTCHA v2.0.152009–11–23
- BotDetect ASP CAPTCHA v2.0.92009–02–12
