log4net smtpappender custom email recipients

Question

I am able to use log4net to send logging information to an email address using the smtpappender and a Gmail account in a VB solution (Visual Studio 2010). The recipient is configured in the log4net config file, however I would like to be able to change the recipient email address dynamically.

Is it possible without having to write a custom smtpappender?

Wether the answer is yes or no, please give me an example, preferably in VB.

Answer 1

It's not possible, the current SmtpAppender won't allow it. But you're lucky, the SendBuffer in the SmtpAppender can be overridden, so you can easily add some behavior to it. I think your best bet is to use the LoggingEvent properties to set the recipient:

public class MySmtpAppender : SmtpAppender
{
    protected override void SendBuffer(log4net.Core.LoggingEvent[] events)
    {
        var Recipients = events
            .Where(e => e.Properties.Contains("recipient"))
            .Select(e => e.Properties["recipient"])
            .Distinct();
        var RecipientsAsASingleLine = string.Join(";", Recipients.ToArray()); // or whatever the separator is
        var PreviousTo = To;
        To = RecipientsAsASingleLine;
        base.SendBuffer(events);
        To = PreviousTo;
    }
}

You may want to change the way to select recipients, your call.

edit The tool recommended by stuartd works quite well (well, it is quite a simple class, but still):

Public Class MySmtpAppender
    Inherits SmtpAppender
    Protected Overrides Sub SendBuffer(events As log4net.Core.LoggingEvent())
        Dim Recipients = events.Where(Function(e) e.Properties.Contains("recipient")).[Select](Function(e) e.Properties("recipient")).Distinct()
        Dim RecipientsAsASingleLine = String.Join(";", Recipients.ToArray())
        ' or whatever the separator is
        Dim PreviousTo = [To]
        [To] = RecipientsAsASingleLine
        MyBase.SendBuffer(events)
        [To] = PreviousTo
    End Sub
End Class