Include header only once at the top of a rolling file

Question

Is it possible to only include header information at the top of a rolling file?

I have the following config file:

<appender name="RollingFileAppender" type="log4net.Appender.RollingFileAppender">
            <file value="d:\temp\TTTest.log"/>
            <layout type="log4net.Layout.PatternLayout">
                <header value="[Header]&#13;&#10;" />
                <param name="ConversionPattern" value="%-25utcdate{dd/MM/yyyy HH:mm:ss.fff}%-20property{log4net:HostName}%-30logger%-30thread%-7level%message%newline"/>
            </layout>
            <lockingModel type="log4net.Appender.FileAppender+MinimalLock"/>
            <maximumFileSize value="5MB"/>
            <rollingStyle value="Size"/>
            <maxSizeRollBackups value="-1"/>
            <countDirection value="1"/>
        </appender>

When I run my application, for example twice I get header information twice e.g.

 [Header] 
 The Log line
 [Header]
 The Log line 
 etc

I am looking to achieve the following:

 [Header] 
 The Log line
 The Log line 
 etc

Answer 1

The easiest way I've found to do this is to create a class that inherits from RollingFileAppender and overwrites like this the WriteHeader method :

using System.IO;
using System.Text;
using log4net.Core;
using log4net.Layout;
using log4net.Util;
using log4net.Appender;

namespace CsvLogging
{
    public class HeaderOnceAppender : RollingFileAppender 
    {
        protected override void WriteHeader()
        {
            try
            {
                if (LockingModel.AcquireLock().Length == 0)
                {
                    base.WriteHeader();
                }
            }
            finally
            {
                LockingModel.ReleaseLock();
            }
        }
    }
}

then use this class as appender :

<appender name="CsvFileAppender" type="CsvLogging.HeaderOnceAppender">

Answer 2

Create a concrete implementation of the log4net.Layout.PatternLayout :

namespace MyApplication
{
    using log4net.Layout;

    public class MyConcretePatternLayout : PatternLayout
    {
        public override string Header => "My Header text here"
    }
}

Modify your log4net.config file to use this new custom pattern layout :

    <appender name="MyFileAppender" type="log4net.Appender.RollingFileAppender">
      ...
      <layout type="MyApplication.MyConcretePatternLayout">
        <conversionPattern...
      </layout>

    </appender>

Now whenever the file rolls due to your criteria you should see "My Header text here" at the top of each file.