Configuring ELMAH with SQL Server logging with encrypted connection string

Question

I'm attempting to configure ELMAH error logging in an ASP.NET 4 application using SQL Server 2008 R2. Is there any way I can tell ELMAH to call our in-house decryption function on the connection string we provide it? Do I need to modify the ELMAH source and rebuild?

<configSections>
  <sectionGroup name="elmah">
    <section name="security" requirePermission="false" type="Elmah.SecuritySectionHandler, Elmah" />
    <section name="errorLog" requirePermission="false" type="Elmah.ErrorLogSectionHandler, Elmah" />
    <section name="errorMail" requirePermission="false" type="Elmah.ErrorMailSectionHandler, Elmah" />
    <section name="errorFilter" requirePermission="false" type="Elmah.ErrorFilterSectionHandler, Elmah" />
  </sectionGroup>
</configSections>

<elmah>
  <security allowRemoteAccess="1" />
  <errorLog type="Elmah.SqlErrorLog, Elmah" connectionStringName="ELMAH" />
</elmah>

<connectionStrings>
  <add name="ELMAH" connectionString="EncryptedConnectionString" providerName="System.Data.SqlClient" />
</connectionStrings>

<system.webServer>
  <handlers>
    <add name="Elmah" verb="POST,GET,HEAD" path="elmah.axd" type="Elmah.ErrorLogPageFactory, Elmah" preCondition="integratedMode" />
  </handlers>
  <modules>
    <add name="ErrorLog" type="Elmah.ErrorLogModule, Elmah" />
  </modules>
</system.webServer>

Answer 1

You can't just tell ELMAH to do something with your connection string. What you can do, however, is tell ELMAH to call you back when it needs an ErrorLog, giving you more control at run-time. You can then read the encrypted connection string, decrypt it with your in-house function and return an SqlErrorLog initialized with it.

To do this, you need to provide a method that is compatible with the ServiceProviderQueryHandler delegate. Here's the definition:

public delegate IServiceProvider ServiceProviderQueryHandler(object context); 

The implementation of the method must return an instance of an object that implements IServiceProvider. If you don't feel like writing one yourself to start with, you can get one for free from the .NET Framework. See System.ComponentModel.Design.ServiceContainer. The service provider's GetService must respond to requests for the ErrorLog type and you can then, for example, return a SqlErrorLog object that has been initialized with a connection string manipulated at runtime. Here's a possible implementation:

var parent = ServiceCenter.Current;
ServiceCenter.Current = context => { 
    var container = new ServiceContainer(parent(context)); 
    var connectionSettings = ConfigurationManager.ConnectionStrings["FOOBAR"];
    var connectionString = Decrypt(connectionSettings.ConnectionString);
    var log = new SqlErrorLog(connectionString); 
    container.AddService(typeof(ErrorLog), log); 
    return container; 
  } ;

This captures the current service point and installs your own instead. The lambda/delegate created pass on service requests to the captured service point when it cannot satisfy it directly, thus creating a chain. You tell ELMAH about your implementation by setting ServiceCenter.Current somewhere during the initialization of your application so that's where the above code will need to sit.

Bear in mind that this is a very simple implementation but it should be good enough to get you started and optimize later if needed.

Prior to this addition in 1.2, the only way to do something similar required subclassing and other gymnastics and still yielded partial results. Now you just need to implement a method and hand it over to ELMAH and which simply responds to queries from ELMAH for objects based on their service type.

Answer 2

As an addition to the post of Atif Aziz, here the VB.NET version (InitializeElmah_VB9 for the .NET 2.0 version [without lamdda], InitializeElmah for VB.NET for .NET 4.0)

Imports System.Web.SessionState

Public Class Global_asax
    Inherits System.Web.HttpApplication


    Public Overrides Sub Init()
        MyBase.Init()

        InitializeElmah_VB9()
        'InitializeElmah()'
    End Sub

    Public parent As Elmah.ServiceProviderQueryHandler = Nothing

    Sub InitializeElmah_VB9()
        ' TODO: Create Table + Functions '
        parent = Elmah.ServiceCenter.Current
        Elmah.ServiceCenter.Current = AddressOf ElmahCallback
    End Sub

    Function ElmahCallback(objContext As Object) As System.IServiceProvider
        Dim container As New System.ComponentModel.Design.ServiceContainer(parent(objContext))
        Dim connectionSettings As System.Configuration.ConnectionStringSettings = ConfigurationManager.ConnectionStrings("FOOBAR")

        Dim strConnectionString As String = connectionSettings.ConnectionString

        Dim x As New System.Data.SqlClient.SqlConnectionStringBuilder(strConnectionString)
        x.Password = CryptStrings.DeCrypt(x.Password)

        strConnectionString = x.ConnectionString

        Dim log As Elmah.SqlErrorLog = New Elmah.SqlErrorLog(strConnectionString)
        container.AddService(GetType(Elmah.ErrorLog), log)
        Return container
    End Function

    Sub InitializeElmah()
        ' TODO: Create Table + Functions '
        Dim parent As Elmah.ServiceProviderQueryHandler = Elmah.ServiceCenter.Current
        Elmah.ServiceCenter.Current = Function(context)
              Dim container As New System.ComponentModel.Design.ServiceContainer(parent(context))
              Dim connectionSettings As System.Configuration.ConnectionStringSettings = ConfigurationManager.ConnectionStrings("Foobar")
              Dim connectionString As String = connectionSettings.ConnectionString

              Dim x As New System.Data.SqlClient.SqlConnectionStringBuilder(connectionString)

              x.Password = CryptStrings.DeCrypt(x.Password)

              connectionString = x.ConnectionString

              Dim log As Elmah.SqlErrorLog = New Elmah.SqlErrorLog(connectionString)
              container.AddService(GetType(Elmah.ErrorLog), log)

              Return container
          End Function

    End Sub


    Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
        ' Wird beim Starten der Anwendung ausgelöst
    End Sub


    Sub Session_Start(ByVal sender As Object, ByVal e As EventArgs)
        ' Wird beim Starten der Sitzung ausgelöst
    End Sub


    Sub Application_BeginRequest(ByVal sender As Object, ByVal e As EventArgs)
        ' Wird zu Beginn jeder Anforderung ausgelöst
    End Sub


    Sub Application_AuthenticateRequest(ByVal sender As Object, ByVal e As EventArgs)
        ' Wird beim Versuch der Benutzerauthentifizierung ausgelöst
    End Sub


    Sub Application_Error(ByVal sender As Object, ByVal e As EventArgs)
        ' Wird bei einem Fehler ausgelöst
    End Sub


    Sub Session_End(ByVal sender As Object, ByVal e As EventArgs)
        ' Wird beim Beenden der Sitzung ausgelöst
    End Sub


    Sub Application_End(ByVal sender As Object, ByVal e As EventArgs)
        ' Wird beim Beenden der Anwendung ausgelöst
    End Sub


End Class