Sample HttpModule

Now it is time to put everything together into a useful HttpModule. The HttpModule implemented in this chapter is a module to log all unhandled errors to a file. If the log file exceeds a certain size , an event is raised. You then can resize or delete the log file with an event handler implemented in the Global.asax file.

This module logs the time of the error, the error message, and the filename, including the line number that generated the error.

The event raised in the Global.asax file contains extra data in a class derived from the System.EventArgs class. This HttpModule will read its initialization data from either the web.config file or the machine.config file. The initialization data contains the filename, including the path of the file where the log data is to be stored and the maximum size of the log file.

You need to add the entries in Listing 25.5 to the beginning of your web.config file inside the <configuration> section.

Listing 25.5 XML Configuration Entries for the machine.config or the web.config File

 <configSections>      <section name="ErrorLogSettings"      type="System.Configuration.NameValueFileSectionHandler, System" />  </configSections>  <ErrorLogSettings>      <add key="ErrorLogFile" value="c:\ErrorLog\Error.log" />      <add key="MaxFileSize" value="102400" />  </ErrorLogSettings> 

If you place the entries in the machine.config file instead, the <section> definition should go in the existing <configSections> section. The entries in Listing 25.5 provide data to the HttpModule about where the log file should be located and what the maximum size should be.

The entry in the <configSections> section defines a new section for the configuration file. This definition includes the name of the class used to parse the section data. In this HttpModule, I used a standard parser class called NameValueFileSectionHandler . This parser class reads in name-value pairs of data. These name-value pairs can be accessed by a call to the GetConfig static method of the System.Configuration.ConfigurationSettings class.

You also must add the following entry to the <HttpModules> section of either your machine.config or web.config file to register the module. This assumes that you build an assembly called ErrorLoggerCS.

 <add name="ErrorLogger" type="ErrorLoggerCS.ErrorLogModule,ErrorLoggerCS" /> 

Because this example is implemented in both C# and Visual Basic .NET, there are actually two assemblies. The C# assembly is called ErrorLoggerCS and the Visual Basic .NET assembly is called ErrorLoggerVB .

Listing 25.6 is the complete C# source code for this HttpModule. Listing 25.7 is the Visual Basic .NET implementation of the same HttpModule.

Listing 25.6 C# Code for Error-Logging HttpModule

 using System;  using System.IO;  using System.Web;  using System.Configuration;  using System.Collections.Specialized;  namespace ErrorLoggerCS  {      /// <summary>      /// Contains the data for the ErrorLogFull event that will      /// be handled in the Global.asax file.      /// </summary>      public class ErrorLogEventArgs : EventArgs      {          //Private class members          private string m_sFilename;          private long m_nFileSize;          private long m_nMaxSize;          // Property accessors          public string Filename          {              get {   return m_sFilename; }              set {   m_sFilename = value; }          }          public long FileSize          {              get {   return m_nFileSize;     }              set {   m_nFileSize = value;    }          }          public long MaxSize           {              get {   return m_nMaxSize;  }              set {   m_nMaxSize = value; }          }          // Constructor          public ErrorLogEventArgs(string sFilename,long nFileSize,long nMaxSize)          {              m_sFilename=sFilename;              m_nFileSize=nFileSize;              m_nMaxSize=nMaxSize;          }      }      /// <summary>      /// Logs unhandled errors to a file.      /// </summary>      // Delegates for events that are to be handled in the global.asax file      public delegate void ErrorLogFullHandler(object sender, EventArgs e);      public class ErrorLogModule : IHttpModule      {          // Events that can be handled in the global.asax file          public event ErrorLogFullHandler ErrorLogFull;          //Private class members          private string m_sLogFile="";          private long m_nMaxFileSize=0;          // Constructor          public ErrorLogModule()          {          }          // Implement IHttpModule Methods          public void Init(HttpApplication context)          {              context.Error += new EventHandler(OnError);              // Load Setting information              NameValueCollection objConfigData=                  ConfigurationSettings.GetConfig("ErrorLogSettings") as                    NameValueCollection;              if(objConfigData!=null)              {                  string sMaxFileSize="";                  m_sLogFile=objConfigData["ErrorLogFile"];                  sMaxFileSize=objConfigData["MaxFileSize"];                  if(sMaxFileSize.Length==0 )                      m_nMaxFileSize=Convert.ToInt64(sMaxFileSize);                  else                       m_nMaxFileSize=102400; //100K bytes                  if(m_sLogFile.Length==0)                      m_sLogFile=@"c:\Errors.log";              }              else              {                  m_sLogFile=@"c:\Errors.log";                  m_nMaxFileSize=102400; //100K bytes              }          }          public void Dispose()          {          }          public void OnError(object sender, EventArgs args)          {              // Declare variables              HttpApplication app;              Exception objError;              string sDateTime;              string sErrorMessage;              string sErrorLocation;              int nStart,nEnd;              FileInfo objFile;              StreamWriter objWriter;              try              {                  app = sender as HttpApplication;                  objError=app.Context.Error.InnerException;                  sDateTime=DateTime.Now.ToString();                  sErrorMessage=objError.Message;                  sErrorLocation=objError.StackTrace;                  nStart=sErrorLocation.IndexOf("in ")+3;                  nEnd=sErrorLocation.IndexOf("\r\n");                  if(nEnd>nStart)                     sErrorLocation=sErrorLocation.Substring(nStart,nEnd-nStart);                  else                      sErrorLocation=sErrorLocation.Substring(nStart);                  //Open File                  objFile=new FileInfo(m_sLogFile);                  objWriter=objFile.AppendText();                  //Write Data                  objWriter.Write(sDateTime);                  objWriter.Write("\t");                  objWriter.Write(sErrorMessage);                  objWriter.Write("\t");                   objWriter.Write(sErrorLocation);                  objWriter.Write("\r\n");                  objWriter.Close();                  // Check file size.  If too large then raise event.                  objFile.Refresh();                  if(objFile.Length>m_nMaxFileSize)                  {                      if(ErrorLogFull!=null)                      {                          ErrorLogFull(this,                              (EventArgs)(new ErrorLogEventArgs(m_sLogFile,                                objFile.Length,m_nMaxFileSize)));                      }                  }              }              catch(Exception e)              {              }          }      }  } 

Listing 25.7 VB Code for Error-Logging HttpModule

 Imports System.Collections.Specialized  Imports System.IO  Namespace ErrorLoggerVB      Public Class ErrorLogEventArgs          Inherits EventArgs          'Private class members          Private m_sFilename As String          Private m_nFileSize As Long          Private m_nMaxSize As Long          ' Property accessors          Public Property Filename() As String              Get                  Return m_sFilename              End Get              Set(ByVal Value As String)                  m_sFilename = Value              End Set          End Property          Public Property FileSize() As String              Get                  Return m_nFileSize              End Get              Set(ByVal Value As String)                  m_nFileSize = Value              End Set          End Property           Public Property MaxSize() As Long              Get                  Return m_nMaxSize              End Get              Set(ByVal Value As Long)                  m_nMaxSize = Value              End Set          End Property          ' Constructor          Public Sub New(ByVal sFilename As String, ByVal nFileSize As Long,           ByVal nMaxSize As Long)              m_sFilename = sFilename              m_nFileSize = nFileSize              m_nMaxSize = nMaxSize          End Sub      End Class      Public Class ErrorLogModule          Implements IHttpModule          'Private class members          Private m_sLogFile As String          Private m_nMaxFileSize As Long          ' Implement the IHttpModule interface.          Public Sub Init(ByVal context As HttpApplication)          Implements IHttpModule.Init              AddHandler context.Error, AddressOf OnError              'Load Setting information              Dim objConfigData As NameValueCollection              objConfigData = ConfigurationSettings.GetConfig("ErrorLogSettings")              If objConfigData Is Nothing Then                  m_sLogFile = "c:\Errors.log"                  m_nMaxFileSize = 102400              Else                  Dim sMaxFileSize As String                  m_sLogFile = objConfigData.Item("ErrorLogFile")                  sMaxFileSize = objConfigData.Item("MaxFileSize")                  If sMaxFileSize.Length = 0 Then                      m_nMaxFileSize = Convert.ToInt64(sMaxFileSize)                  Else                      m_nMaxFileSize = 102400 '100K bytes                  End If                  If m_sLogFile.Length = 0 Then                      m_sLogFile = "c:\Errors.log"                  End If              End If          End Sub       Public Sub Dispose() Implements IHttpModule.Dispose      End Sub      ' Implement event to be handled in Global.asax file      Event LogUnhandledError(ByVal sender As Object, ByVal e As EventArgs)      ' Implement the event handlers      Public Sub OnError(ByVal sender As Object, ByVal e As EventArgs)          'Declare variables          Dim app As HttpApplication          Dim objError As Exception          Dim sDateTime As String          Dim sErrorMessage As String          Dim sErrorLocation As String          Dim nStart, nEnd As Integer          Dim objFile As FileInfo          Dim objWriter As StreamWriter          Try              app = sender              objError = app.Context.Error.InnerException              sDateTime = DateTime.Now.ToString()              sErrorMessage = objError.Message              sErrorLocation = objError.StackTrace              nStart = sErrorLocation.IndexOf("in ") + 3              nEnd = sErrorLocation.IndexOf(Chr(13) + Chr(10))              If nEnd > nStart Then                  sErrorLocation = sErrorLocation.Substring(nStart,                  nEnd - nStart)              Else                  sErrorLocation = sErrorLocation.Substring(nStart)              End If              'Open File              objFile = New FileInfo(m_sLogFile)              objWriter = objFile.AppendText()              'WriteData              objWriter.Write(sDateTime)              objWriter.Write(Chr(9))              objWriter.Write(sErrorMessage)              objWriter.Write(Chr(9))              objWriter.Write(sErrorLocation)              objWriter.Write(Chr(13) + Chr(10))              objWriter.Close()              'Check file size.  If too large then raise event              objFile.Refresh()              If objFile.Length > m_nMaxFileSize Then                  Dim objEventArgs As ErrorLogEventArgs                  objEventArgs = New ErrorLogEventArgs(m_sLogFile,                  objFile.Length, m_nMaxFileSize)                       RaiseEvent LogUnhandledError(Me, objEventArgs)                  End If              Catch              End Try          End Sub      End Class  End Namespace