NLog 4.1 is Now Available!

31 Aug 2015

A new version of NLog has been released!

We fixed around 25 bugs, added some new features and made the migration of NLog 3 to 4 easier. The release can be downloaded from NuGet.

Check for all the details the GitHub 4.1 milestone.


This release contains the following features:

Overhaul variables

Since 4.0 you can read the variables defined in the configuration file. We also claimed you could change the values, but we were wrong… The variables where implemented like a kind of macros and changing them would not give the expected results.

In NLog 4.1, we created a new method to render the variables, which fits a lot better in the NLog library: we created a layout renderer for the variables! With the same syntax you can define the variables, but rendering is a bit different.

In NLog 4.0 you would define:

  <variable name='user' value='admin' />
  <variable name='password' value='realgoodpassword' />
    <target name='debug' type='Debug' layout='${message} and ${user}=${password}' />
    <logger name='*' minlevel='Debug' writeTo='debug' />

In 4.1 you can use the $var{} layout renderer:

  <variable name='user' value='admin' />
  <variable name='password' value='realgoodpassword' />
    <target name='debug' type='Debug' layout='${message} and ${var:user}=${var:password}' />
    <logger name='*' minlevel='Debug' writeTo='debug' />

What’s the real advantage here?

  • It is in line with NLog’s current code
  • Variables can be changed, deleted and created from the API
  • A default value can be configured for a variable, e.g. ${var:password:default=unknown}
  • The old variables can still be used and so this is completely backwards-compatible.

You might wonder: why has the old method not been replaced? The answer is simple: the new method only works on Layout types and not on plain strings.

Object values for GDC, MDC and NDC contexts

The context classes, GCD, MCD and NDC, now support using object values instead of strings. This is mostly beneficial from the API perspective.

The get method still returns a string - for backwards-compatibility reasons. We created a new method: getObject.

When writing to the logs, the object is converted to a string

GlobalDiagnosticsContext.Set("myDataBase","someValue"); //already possible
GlobalDiagnosticsContext.Set("myDataBaseNumber",2); //4.1+

Easier upgrade from NLog 3 to NLog 4

With the release of NLog 4.0 we made some breaking changes. Those breaking changes made upgrading an issue: all the code has to be upgraded to NLog 4 at once.

The main cause was the change of behavior of Log(string message, Exception ex). This call should be replaced by Log(Exception ex, string message) in NLog 4.0.

Changing all those calls can be difficult at once. So we have introduced the following option:

<nlog exceptionLoggingOldStyle='true'>

With this option enabled, you can still use Log(string message, Exception ex) in NLog 4.

So the upgrade path to NLog 4

  1. Enable “exceptionLoggingOldStyle” in the configuration
  2. Upgrade to NLog 4.1+
  3. (this can take some time): replace the calls to Log(string message, Exception ex) etc.
  4. Disable “exceptionLoggingOldStyle” in the configuration

Note: we will remove this feature in NLog 5.0

New JSON options

New options have been added for writing JSON output.

  • More control over spaces: SuppressSpaces. Example:
<layout xsi:type="JsonLayout" SuppressSpaces="false">
  <attribute name="process_name" layout="${processname}" />
  <attribute name="short_message" layout="${message}" />
  • The JSON encoding can be disabled for properties.
<layout xsi:type="JsonLayout">
    <attribute name="Message" layout="${message}" encode="false"/>

Example call:

logger.Info("{ \"hello\" : \"world\" }");

See the wiki

Integrated NLog.Contrib to core

The NLog.Contrib code has been integrated with the core of NLog. The following features are now available on the NLog package:

  • Mapped Diagnostics Context (MDLC): Async version of Mapped Diagnostics Context Allows for maintaining state across asynchronous tasks and call contexts.
  • The Mapped Diagnostics Context Layout renderer: ${mdlc}
  • Trace Activity Id Layout Renderer: ${activityid} write the System.Diagnostics his trace correlation id.

All events layout renderer: optional writing of caller information

The all events layout renderer introduced in NLog 4.0 was unexpectedly writing caller information, like current method etc, to the targets. This is now an option and disabled by default.

For example:

  • ` ${all-event-properties}` writes “Test=InfoWrite, coolness=200%, a=not b”
  • ` ${all-event-properties:includeCallerInformation=true}` writes “Test=InfoWrite, coolness=200%, a=not b, CallerMemberName=foo, CallerFilePath=c:/test/log.cs, CallerLineNumber=1001”

Call site line number layout renderer

Officially introduced in NLog 4.0, but was not available due to a merge fault. The ${callsite-linenumber} writes the line number of the caller.

Easy replacement of newlines

With the ${replace} layout renderer it was already possible to replace the newlines, but it was a bit tricky to use - different systems, different newlines.

The ${replace-newlines} layout renderer fixes this.

WCF Log Receiver Changes

4.0.0 introduced an unattended breaking changing that replaced the WcfLogReceiverClient with the WcfLogReceiverClientFacade (NLog/NLog#783). It was not only a naming issue, but also some functionality was lost and there was a lot of code duplication.

Unfortunately, there was not an easy fix, so the following was done to try to make it less of a breaking change. The changes are still breaking, but minus a recompilation, the changes should be mostly transparent. See NLog/NLog#874 for all of the changes related to WCF Log Receiver.

Changes from 3.2.1

Compared to 3.2.x, these the changes:

  • Use ILogReceiverTwoWayClient instead of ILogReceiverClient. ILogReceiverClient is still in the code, but is marked obsolete.
  • If your code is dependent on ClientBase, then change it to WcfLogReceiverClientBase

Changes from 4.0.0

Compared to 4.0.x, these the changes:

  • The return type for the method CreateWcfLogReceiverClient() in LogReceiverWebServiceTarget is WcfLogReceiverClient again, but is marked obsolete.
  • Use CreateLogReceiver(), which returns IWcfLogReceiverClient to reduce breaking changes in the future.

Event properties - culture and format options

The event properties are object values. When writing them with ${event-properties} to the logs, the values are converted to strings. It’s now possible to control the culture and format.

Examples: ${event-properties:prop1:format=yyyy-M-dd} and ${event-properties:aaa:culture=nl-NL}


Various bugs are fixed in this version. The most notable ones:

UNC path issues

4.0.1 did gave issues with configuration files or binaries hosted on UNC locations.

Fixes in file archiving

Multiple bugs are fixed with file archiving:

  • Archive files where sometimes deleted in the wrong order.
  • DeleteOldDateArchive could delete files not being actual archives. #847

Fixed Mono build

This release finally builds again on Mono! We are busy adding Travis CI integration to keep the Mono build working.

Exception is not correctly logged when calling without message

Writing an exception as only argument to a logger, like logger.Info(new Exception()) was not correctly registering the exception to the log messages.

Internal logger improvements

Some small improved has been made to the internal logger.