Change subject of SmtpAppender programmatically - log4net

Question

I have an SmtpAppender like this:
<appender name="SmtpAppender" type="log4net.Appender.SmtpAppender">
<to value="MyEmail#example.org" />
<from value="SenderEmail#example.org" />
<subject type="log4net.Util.PatternString" value="This is a subject" />
<smtpHost value="smtp.host.value" />
<authentication value="Basic" />
<port value="587" />
<username value="Username" />
<password value="Password" />
<bufferSize value="1" />
<EnableSsl value="true"/>
<lossy value="false" />
<threshold value="ERROR" />
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date [%3thread] %-5level [%class].[%method] - %message%newline" />
</layout>
</appender>
I would like to change the subject of the log mail in my code to a string I would specify so it suits my needs better than a standard subject.
Right now I achieve it like this. First, I find the SmtpAppender by name:
public static IAppender FindAppenderByName(string name)
{
ILoggerRepository rootRep = LogManager.GetRepository();
foreach (IAppender iApp in rootRep.GetAppenders()) {
if (string.Compare(name, iApp.Name, true) == 0) {
return iApp;
}
}
return null;
}
and then I can change the subject like this:
IAppender appender = FindAppenderByName("SmtpAppender");
SmtpAppender smtpAppender = (SmtpAppender)appender;
smtpAppender.Subject = "An error occured trying to convert the values";
log.Error("Error message");
But this seems to be a bit too complicated since every time I send an error mail I first have to find the appender by name and I don't want to use a global IAppender object as well as that seems like bad practice to me.
Is there a way to use the user-specified error message as a subject or is there an extension method I could use?

Answer 1

My proposal is as follows :
Create a new class extending SmtpAppender
Override SendBuffer
Based on your LoggingEvent, dynamically change the base.Subject
public class CustomSmtpAppender : SmtpAppender
{
protected override void SendBuffer(LoggingEvent[] events)
{
PrepareSubject(events);
base.SendBuffer(events);
}
protected virtual void PrepareSubject(IEnumerable<LoggingEvent> events)
{
//here you can eval events and set base.Subject
}
}