Support layouts (e.g. JSON) and inner text in <variable>

[304NotModified]

fixes #1577 and fixes #1312

[304NotModified]

@snakefoot I have the idea you don't like this change 👼

[snakefoot]

Think it is good idea. Just need to do it right so the same variable is not used multiple places when not threadsafe.

[snakefoot]

The problem with not being threadsafe. Is NOT that multiple threads can get in trouble by "updating" the layout-value (no longer a issue) . But the problem is when multiple targets uses the same thread-unsafe layout, then you get unexpected output when two targets shares the same layout object. So your warning comment in variable-layout-renderer is misleading.

[304NotModified]

thanks for the feedback -> #3462

[snakefoot]

After seeing you have implemented a breaking change in the config-element-interface that is not compatible with appsettings json then I must agree with you that I don't like this PR. You have enforced XML-behavior by adding value-property. Please remove this change. I like the idea of Json-Layout in variable. But not like this. Please fix

[304NotModified]

The value property could just return null in the case of JSON

[snakefoot]

Then you suddenly have something that only works with XML-config

[304NotModified]

'Value' isn't xml specific?

Anyway, do you have a proposal how to solve this different? One way or another, this needs a breaking change.

[snakefoot]

Yes it will always be a breaking change for the Variables-container. Anyway created #3466

[snakefoot]

Btw. could be nice if one could make a static reference to a JsonLayout. So one is not required to use "${var:myjson}" but could just write:

    <variable name='myJson'>
        <layout type='JsonLayout'>
            <attribute name='short date' layout='${shortdate}' />
            <attribute name='message' layout='${message}' />
        </layout>
    </variable>
    <targets>
         <target type='file' name='myfile' layout='${myJson}' />
    <targets>

Then one could skip a dictionary lookup for every logevent-write. And one would be able to make use of optimizations like ThreadAgnostic.

[oskaremil]

Can I use

"variables": {
      "varDefaultLayout": {
          "type": "JsonLayout",
          "Attributes": [
            {
              "name": "timestamp",
              "layout": "${date:format=o}"
            }
            ]
        }
    },

and then

"targets": {
      "logfile": {
        "layout": "${varDefaultLayout}"

in my target when reading configuration from appsettings.json ?

[snakefoot]

Maybe add example to wiki-page, when NLog 5 is released:

NLog JsonLayout as NLog Config Variable Example

<nlog>
  <variable name="defaultJsonLayout" >
    <layout type="JsonLayout">
       <attribute name="message" value="${messsage}">
    </layout>
  </variable>
  <targets>
    <target name="debug" type="Debug" layout="${var:defaultJsonLayout}" />
  </targets>
  <rules>
    <logger name="*" minlevel="Debug" writeTo="debug" />
  </rules>
</nlog>

API

var newJsonLayout = new NLog.Layouts.JsonLayout() { IncludeAllProperties = true };
LogManager.Configuration.Variables["defaultJsonLayout"] = newJsonLayout;

[snakefoot]

Updated wiki: https://github.com/NLog/NLog/wiki/Configuration-file#variables