NLog plugin: report custom properties like application name

[ygavrishov]

Hi team!
I did not find a very important possibility - to attach custom properties to error reports. The most typical case is to attach the application name. We have multiple applications that report to the same Rollbar project and only stack trace can help to distinguish applications.

[snakefoot]

The NLog RollbarTarget inherits from TargetWithContext that support context-capture.

Example:

<?xml version="1.0" encoding="utf-8" ?>
<nlog throwConfigExceptions="true">

  <extensions>
    <add assembly="Rollbar.PlugIns.NLog"/>
  </extensions>

  <targets>
    <target name="logrollbar" type="Rollbar.PlugIns.NLog">
      <contextproperty name="HostName" layout="${machinename}" />
      <contextproperty name="ApplicationName" layout="MySuperApplication" />
      <contextproperty name="ProcessName" layout="${processname}" />
      <contextproperty name="AppDomainName" layout="${appdomain:cached=true:format=\{1\}}" />
    </target>
  </targets>

  <rules>
    <logger name="*" minlevel="Info" writeTo="logrollbar" />
  </rules>
</nlog>

See also: https://github.com/rollbar/Rollbar.NET/tree/master/Samples/Sample.PlugIns.NLog