CODEWITHSUNDEEP
exceptionfilterlog4net
Nick Swarr
Nick Swarr

Reputation: 1322

log4net filtering on exception message?

How can I filter logging based on a logged exception's message?

Code looks like this:

try { 
    someService.DoSomeWorkflow(); 
} catch(Exception e) {
    log.Error("Hey I have an error", e);
}

Config looks like this:

<appender name="EventLogger" type="log4net.Appender.EventLogAppender">
    <applicationName value="foo" />
    <layout type="log4net.Layout.PatternLayout" value="PID:%P{pid}: %message" />
    <filter type="log4net.Filter.StringMatchFilter">
        <stringToMatch value="TextInsideTheException" />
    </filter>
</appender>

I'm finding that I can filter only on the logged message ("Hey I have an error") but it seemingly ignores the exception's message. Since this is in our production environment I can't make any code changes so I can't change the logged message. Is there some configuration that would specify to also check the exception's message?

Upvotes: 3

Views: 2222

Answers (3)

Claude Ducharme
Claude Ducharme

Reputation: 301

Here are basic implementations based on Peter's accepted answer

using System;
using log4net.Core;

namespace log4net.Filter
{
    public abstract class ExceptionFilterBase : FilterSkeleton
    {
        public override FilterDecision Decide(LoggingEvent loggingEvent)
        {
            if (loggingEvent == null)
                throw new ArgumentNullException("loggingEvent");

            var str = GetString(loggingEvent);
            if (StringToMatch == null || string.IsNullOrEmpty(str) || !str.Contains(StringToMatch))
                return FilterDecision.Neutral;
            return AcceptOnMatch ? FilterDecision.Accept : FilterDecision.Deny;
        }

        protected abstract string GetString(LoggingEvent loggingEvent);

        public string StringToMatch { get; set; }

        public bool AcceptOnMatch { get; set; }
    }

    public class ExceptionMessageFilter : ExceptionFilterBase
    {
        protected override string GetString(LoggingEvent loggingEvent)
        {
            return loggingEvent.ExceptionObject == null
                ? null : loggingEvent.ExceptionObject.Message;
        }
    }

    public class ExceptionTypeFilter : ExceptionFilterBase
    {
        protected override string GetString(LoggingEvent loggingEvent)
        {
            return loggingEvent.ExceptionObject == null
                ? null : loggingEvent.ExceptionObject.GetType().FullName;
        }
    }

    public class ExceptionStackFilter : ExceptionFilterBase
    {
        protected override string GetString(LoggingEvent loggingEvent)
        {
            return loggingEvent.ExceptionObject == null
                ? null : loggingEvent.ExceptionObject.StackTrace;
        }
    }
}

Configuration file

<appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
  <file value="Client.log" />
  <layout type="log4net.Layout.PatternLayout">
   <conversionPattern value="%date{yyyy/MM/dd HH:mm:ss,fff} [%-5level] %logger - %message%newline" />
  </layout>
  <filter type="log4net.Filter.StringMatchFilter">
    <stringToMatch value="Token is not valid." />
    <acceptOnMatch value="false" />
  </filter>
  <filter type="log4net.Filter.ExceptionMessageFilter, YourAssembly">
    <stringToMatch value="Application is not installed." />
    <acceptOnMatch value="false" />
  </filter>
  <filter type="log4net.Filter.ExceptionTypeFilter, YourAssembly">
    <stringToMatch value="System.Deployment.Application.DeploymentException" />
    <acceptOnMatch value="false" />
  </filter>
  <filter type="log4net.Filter.ExceptionStackFilter, YourAssembly">
    <stringToMatch value="at System.Deployment.Application.ComponentStore.GetPropertyString(DefinitionAppId appId, String propName)" />
    <acceptOnMatch value="false" />
  </filter>
</appender>

Upvotes: 1

Peter Lillevold
Peter Lillevold

Reputation: 33910

By subclassing FilterSkeleton, you can implement a filter that evaluates the exception text. Or exception type for that matter.

Upvotes: 2

Simon Linder
Simon Linder

Reputation: 3428

Try this:

log.Error("Hey I have an error: " + e.Message);

Edit: Sorry, didn't see that you cannot change that line...

Upvotes: -2

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