NLog webservice target, slack icon based on log level - nlog

Question

I'm new to NLog, and fighting with finding the solution to what I'm going for.
I'd like warning and up to get pushed to a slack channel with log level specific icons. I have got that working, technically. I have 2 pairs of targets/loggers that are hard coded to catch warnings only, and errors and above, and have 'warning' or 'error' icons hard coded into the layout template.
<target xsi:type="WebService"
name="slackWarningTarget"
url="https://hooks.slack.com/services/xx/xx/xx"
protocol="JsonPost"
encoding="utf-8"
>
<parameter name="text" type="System.String" layout=":warning: ${machinename} ${message}"/>
<parameter name="channel" type="System.String" layout="xx"/>
</target>
and
<logger name="*" minlevel="Warn" maxlevel="Warn" writeTo="slackWarningTarget">
Is there a way to better accomplish this? I want warning level to map to :warning:, etc.
I'd also like some info level stuff pushed there as well. To do this I created a named logger that always logs to the slack channel, but it results in duplicated messages if they are warning or above.
<logger name="noticeLogger" writeTo="slackInfoTarget" />
I'd guess there is a much more elegant way to do both of these things than i have come up with on my own.

Answer 1

You could do that from config with a ${when}, e.g.
layout="${when:when=${level}=='Warn':inner=\:warning\::else:${when:when=${level}== 'Error':inner=\:error\::else:todo}}"
but it get clumsy fast.
Another option is to register a custom layout renderer:
// register in the start of your program (e.g. main, app_start)
// usage ${slackIcon}
LayoutRenderer.Register("slackIcon", logEvent =>
{
if (logEvent.Level == LogLevel.Warn)
{
return ":warning:";
}
if (logEvent.Level == LogLevel.Error)
{
return ":error:";
}
return ":other:";
//etc
});
See How to write a custom layout renderer