Log4net EventLogAppender Log Event ID - log4net

Question

Is there a way to log an event into the windows event log with a specified eventid per message? I am using log4net v 1.2.10.

Answer 1

Based on what I see in the EventLogAppender source code the following should do the trick:
log4net.ThreadContext.Properties["EventID"] = 5;
Just call this before you write your log messages (if you do not set it for all messages you should remove the "EventID" again from the Properties.
N.B the property key is case sensitive.

Answer 2

When one uses the native .net Event Log APIs in System.Diagnostics, the WriteEntry methods allow setting the eventID and category. In these APIs:
eventID is a 32 bit int, but its value must be between 0 and 65535
category is a 16 bit int, but its value must be positive. If the
event source includes a category resource file, the event viewer will
use the integer category value to lookup a localized “Task category”
string. Otherwise, the integer value is displayed.
The categories must be numbered consecutively, beginning with the
number 1
Log4net supports writing an EventID and a Category, but it isn’t straight forward. When log4net’s EventLogAppender logs an event, it looks at a dictionary of properties. The named properties "EventID" and "Category" are automatically mapped by the EventLogAppender to the corresponding values in the event log. I’ve seen a few good suggested ways to use log4net’s EventLogAppender and set the EventID and Category in the Windows event log.
a. Using log4net’s appender filtering, a filter may be registered that can add the EventID and Category properties. This method has a nice benefit that the standard log4net wrappers are used and so this can be implemented without changing existing logging code. The difficulty in this method is some mechanism has to be created to calculate the EventID and Category from the logged information. For instance, the filter could look at the exception source and map that source to a Category value.
b. Log4net may be extended so custom logging wrappers can be used that can include EventID and Category parameters. Adding EventID is demonstrated in the log4net sample “Extensibility – EventIDLogApp” which is included in the log4net source. In the extension sample a new interface (IEventIDLog) is used that extends the standard ILog interface used by applications to log. This provides new logging methods that include an eventId parameter. The new logging methods add the eventId to the Properties dictionary before logging the event.
public void Info(int eventId, object message, System.Exception t)
{
if (this.IsInfoEnabled)
{
LoggingEvent loggingEvent = new LoggingEvent(ThisDeclaringType, Logger.Repository, Logger.Name, Level.Info, message, t);
loggingEvent.Properties["EventID"] = eventId;
Logger.Log(loggingEvent);
}
}
c. Log4net supports a ThreadContext object that contains a Properties dictionary. An application could set the EventID and Category properties in this dictionary and then when the thread calls a logging method, the values will be used by the EventLogAppender.
log4net.ThreadContext.Properties["EventID"] = 5;
Some helpful references:
Log4net home page
Log4net SDK reference
Log4net samples
Log4net source
Enhancing log4net exception logging
Log4Net Tutorial pt 6: Log Event Context
Customizing Event Log Categories
EventSourceCreationData.CategoryResourceFile Property
Event Logging Elements
EventLog.WriteEntry Method

Answer 3

Well, the solution was to build the extension project "log4net.Ext.EventID" and to use its types: IEventIDLog, EventIDLogImpl and EventIDLogManager.

Answer 4

Another solution is to add a custom Filter as described here: Enhancing log4net exception logging (direct link to the Gist just in case).
As the author points out:
... EventLogAppender uses inline consts to check them. Once they are added they will be used by the mentioned EventLogAppender to mark the given entries with EventId and Category.
The filter implementation will look like the code below (stripped down gist) with the added benefit that if you make GetEventId method public, you can write some tests against it
public class ExceptionBasedLogEnhancer : FilterSkeleton
{
private const string EventLogKeyEventId = "EventID";
public override FilterDecision Decide(LoggingEvent loggingEvent)
{
var ex = loggingEvent.ExceptionObject;
if (ex != null)
{
loggingEvent.Properties[EventLogKeyEventId] = GetEventId(ex);
}
return FilterDecision.Neutral;
}
private static short GetEventId(Exception ex)
{
// more fancy implementation, like getting hash of ex properties
// can be provided, or mapping types of exceptions to eventids
// return no more than short.MaxValue, otherwise the EventLog will throw
return 0;
}
}

Answer 5

Extend ILog.Info() to take an event ID:
public static class LogUtils
{
public static void Info(this ILog logger, int eventId, object message)
{
log4net.ThreadContext.Properties["EventID"] = eventId;
logger.Info(message);
log4net.ThreadContext.Properties["EventID"] = 0; // back to default
}
}
Then call it like this:
using LogUtils;
private static readonly log4net.ILog _logger = log4net.LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
_logger.Info(3, "First shalt thou take out the Holy Pin, then shalt thou count to three.");