How to remove logging of 404-request from EPiServers logfiles

When a user request a file or url that does not exist in a EPiServer-site they will get a 404 response back and that is fine. The problem is that EPiServer also report this as a Error to Log4Net with the error “1.2.5 Unhandled exception in ASP.NET System.Web.HttpException (0x80004005): Not Found. at EPiServer.Web.StaticFileHandler.ProcessRequest(HttpContext context)”.

This is no problem for the end user since they are getting the right response but for the developers of the site it can lead to problems when they are looking for errors in the site and all they see is 404’s in the log. I have tried to solve this for a while, I even have a support ticket open with EPiServer support on how to be able to not log this and have not got or find any good ways until right now. Luckily I find a answer on stackowerflow on why “log4net.Filter.StringMatchFilter” not working with errors (it only locks in the message, not in the error description). Read it here: http://goo.gl/U3zBJn

To solve this I did like this:
First create a class named: ExceptionMessageToMatchFilter

using System;
using log4net.Core;
using log4net.Filter;

namespace EPiServer.Templates.Alloy.Business.Core
{
    public class ExceptionMessageToMatchFilter : StringMatchFilter
    {
        public override FilterDecision Decide(LoggingEvent loggingEvent)
        {
            if (loggingEvent == null)
                throw new ArgumentNullException("loggingEvent");

            if (loggingEvent.ExceptionObject == null)
                return FilterDecision.Neutral;

            var exceptionMessage = loggingEvent.GetExceptionString();

            if (m_regexToMatch != null)
            {
                if (!m_regexToMatch.Match(exceptionMessage).Success)
                    return FilterDecision.Neutral;

                return m_acceptOnMatch ? FilterDecision.Accept : FilterDecision.Deny;
            }

            if (m_stringToMatch == null || exceptionMessage.IndexOf(m_stringToMatch) == -1)
            {
                return FilterDecision.Neutral;
            }

            return m_acceptOnMatch ? FilterDecision.Accept : FilterDecision.Deny;
        }
    }
}

After that set up a filter in your EPiServerLog.config on the appender you like to be filtered. In this example I filter away both files/friendly url’s and also url’s with a aspx-extension. When you add the filter set the path attribute to the path to the class (EPiServer.Templates.Alloy.Business.Core) and then a comma and the name of the assambly the class is in (EPiServer.Templates.Alloy).

<?xml version="1.0" encoding="utf-8"?>
<log4net>
    <appender name="errorFileLogAppender" type="log4net.Appender.RollingFileAppender" >
        <!-- Consider moving the log files to a location outside the web application -->
        <file value="App_Data\EPiServerErrors.log" />
        <encoding value="utf-8" />
        <staticLogFileName value="true"/>
        <datePattern value=".yyyyMMdd.'log'" />
        <rollingStyle value="Date" />
        <lockingModel type="log4net.Appender.FileAppender+MinimalLock" />
        <appendToFile value="true" />
        <layout type="log4net.Layout.PatternLayout">
            <conversionPattern value="%date [%thread] %level %logger: %message%n" />
        </layout>
      <filter type="EPiServer.Templates.Alloy.Business.Core.ExceptionMessageToMatchFilter, EPiServer.Templates.Alloy" >
        <stringToMatch value="System.Web.HttpException (0x80004005): Not Found" />
        <acceptOnMatch value="false" />
      </filter>
      <filter type="EPiServer.Templates.Alloy.Business.Core.ExceptionMessageToMatchFilter, EPiServer.Templates.Alloy" >
        <regexToMatch value="System.Web.HttpException \(0x80004005\): The file '[^']*' does not exist\." />
        <acceptOnMatch value="false" />
      </filter>
    </appender>
    <appender name="outputDebugStringAppender" type="log4net.Appender.OutputDebugStringAppender" >
        <layout type="log4net.Layout.PatternLayout">
            <conversionPattern value="[%thread] %level %logger: %message%n" />
        </layout>
    </appender>

    <root>
        <level value="warn" />
        <appender-ref ref="errorFileLogAppender" />
    </root>
</log4net>

Save, compile and voila then you do not have any 404-requests in the log file anymore!

Happy coding!

Henrik Fransas