Custom Layout Renderer and Custom Header and Footer

In a previous message, i was trying to figure out how to write my own custom xml log format, with header and footer. i was ultimately able to do that, without too much problem, some time and patience is all it took.

I'm posting the code here, in hope it will serve another n00b like me someday.

I was not however able to figure the proper way to use those custom headers and footers. There's probably not much to it either but i ended not using my own technique after finding out that the FileTarget implements the NLog.TargetWithLayoutHeaderAndFooter interface and allowed me to put my own text for header and footer.

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Imports NLog
Imports NLog.Layouts

Namespace AWInterface.ErrorHandling
  <LayoutRenderer("appliweb_error")> _
  Public NotInheritable Class AWErrorRenderer
    Inherits LayoutRenderer

    Private _showSession As Boolean = False

    Public Property ShowSession() As Boolean
    Get
      Return _showSession
    End Get
    Set(ByVal Value As Boolean)
      _showSession = Value
    End Set
    End Property

    Protected Overrides Sub Append(ByVal builder As System.Text.StringBuilder, ByVal logEvent As NLog.LogEventInfo)
      With builder
        .Append(ApplyPadding(vbTab & "<error date=""" & logEvent.TimeStamp & """>" & vbCrLf))
        If Not logEvent.Message Is Nothing And ShowSession Then
          .Append(ApplyPadding(vbTab & vbTab & vbTab & "<session>" & logEvent.Message & "</session>" & vbCrLf))
        End If
        .Append(ApplyPadding(vbTab & vbTab & "<exception>" & vbCrLf))
        .Append(ApplyPadding(vbTab & vbTab & vbTab & "<message>" & logEvent.Exception.Message & "</message>" & vbCrLf))
        .Append(ApplyPadding(vbTab & vbTab & vbTab & "<source>" & logEvent.Exception.Source & "</source>" & vbCrLf))
        .Append(ApplyPadding(vbTab & vbTab & vbTab & "<stackTrace>" & logEvent.Exception.StackTrace & "</stackTrace>" & vbCrLf))
        .Append(ApplyPadding(vbTab & vbTab & vbTab & "<innerException>"))
        If Not logEvent.Exception.InnerException Is Nothing Then
        .Append(ApplyPadding(logEvent.Exception.InnerException.ToString))
        End If
        .Append(ApplyPadding("</innerException>" & vbCrLf))
        .Append(ApplyPadding(vbTab & vbTab & "</exception>" & vbCrLf))
        .Append(ApplyPadding(vbTab & "</error>"))

      End With
    End Sub

    Protected Overrides Function GetEstimatedBufferSize(ByVal logEvent As NLog.LogEventInfo) As Integer
      'More or less 4k characters to display in a AW session
      Return 4000
    End Function
  End Class

  Public MustInherit Class AWLayoutBase : Implements ILayout
    Private myLayout As NLog.Layout

    Protected ReadOnly Property BaseLayout() As NLog.Layout
    Get
      Return myLayout
    End Get
    End Property

    Public Sub New()
      myLayout = New NLog.Layout
    End Sub

    Public Sub Close() Implements NLog.ILayout.Close
      myLayout.Close()
    End Sub

    Public MustOverride Function GetFormattedMessage(ByVal logEvent As NLog.LogEventInfo) As String Implements NLog.ILayout.GetFormattedMessage

    Public Sub Initialize() Implements NLog.ILayout.Initialize
      myLayout.Initialize()
    End Sub

    Public Function IsVolatile() As Boolean Implements NLog.ILayout.IsVolatile
      Return myLayout.IsVolatile
    End Function

    Public Function NeedsStackTrace() As Integer Implements NLog.ILayout.NeedsStackTrace
      Return myLayout.NeedsStackTrace
    End Function

    Public Sub PopulateLayouts(ByVal layouts As NLog.LayoutCollection) Implements NLog.ILayout.PopulateLayouts
      myLayout.PopulateLayouts(layouts)
    End Sub

    Public Sub Precalculate(ByVal logEvent As NLog.LogEventInfo) Implements NLog.ILayout.Precalculate
      myLayout.Precalculate(logEvent)
    End Sub
  End Class

  Public Class AWHeader
    Inherits AWLayoutBase

    Public Overrides Function GetFormattedMessage(ByVal logEvent As NLog.LogEventInfo) As String
      Return "<?xml version=""1.0"" ?><errors>" & vbNewLine
    End Function
  End Class

  Public Class AWFooter
    Inherits AWLayoutBase

    Public Overrides Function GetFormattedMessage(ByVal logEvent As NLog.LogEventInfo) As String
      Return vbNewLine & "</errors>"
    End Function
  End Class
End Namespace