NLog MailTarget with bufferingwrapper and autoflushwrapper: reverse order of events? - nlog

Question

I'm using the following structure:
<target name="MailOnError" xsi:type="AutoFlushWrapper" condition="level >= LogLevel.Error" flushOnConditionOnly="true">
<target name="MailBuffer" xsi:type="BufferingWrapper" bufferSize="250" overflowAction="Discard">
<-- note: mail config has been removed -->
<target xsi:type="Mail"
name="email"
header="Error in ${processname}:${newline}
Machine: ${machinename}${newline}
Proces: ${processname}${newline}
User: ${environment-user}${newline}
${newline}
${newline}"
layout="${date:format=HH\:mm\:ss}: ${message} (in ${callsite})${newline}"
/>
</target>
This works almost fine to achieve my goal: receiving an e-mail on error, with the most recent log-entries embedded to have some context about the error.
It would be nice if I get the error on the top of my e-mail-message (or, even better, receive the log-entries in descending order).
How can this be done (if possible without writing my own custom target)?

Answer 1

You need something like this:
[Target("ReverseOrderWrapper", IsWrapper = true)]
public class ReverseOrderWrapper : WrapperTargetBase
{
protected override void Write(IList<AsyncLogEventInfo> logEvents)
{
// Some re oder logic
var reorderEvents = logEvents.Reverse().ToArray();
WrappedTarget.WriteAsyncLogEvents(reorderEvents);
}
}
Register (as soon as possible), NLog 4.7+ syntax
NLog.LogManager.Setup().SetupExtensions(s =>
s.RegisterTarget<ReverseOrderWrapper>("ReverseOrderWrapper")
);
Usage:
<target name="MailOnError" xsi:type="AutoFlushWrapper" condition="level >= LogLevel.Error" flushOnConditionOnly="true">
<target name="MailBuffer" xsi:type="BufferingWrapper" bufferSize="250"
overflowAction="Discard">
<target name="Reoder" xsi:type="ReverseOrderWrapper">
<-- note: mail config has been removed -->
<target xsi:type="Mail"
name="email"
header="Error in ${processname}:${newline}
Machine: ${machinename}${newline}
Proces: ${processname}${newline}
User: ${environment-user}${newline}
${newline}
${newline}"
layout="${date:format=HH\:mm\:ss}: ${message} (in ${callsite})${newline}"
/>
</target>
</target>
</target>