How to Print a Multi-Line Message with NLog.Extensions.Logging (1.6.1)

When working with NLog.Extensions.Logging in your .NET Core 3.1 console application, you may encounter a problem when trying to print multi-line messages. The issue is that the first line of the message is not prefixed as expected. In this guide, we’ll walk you through the steps to resolve this issue and successfully print multi-line messages using NLog.Extensions.Logging (v1.6.1). Let’s get started!

Understanding the Issue

To provide some context, let’s take a look at the current behavior of printing multi-line messages with NLog.Extensions.Logging. In the example you provided, the output looks like this:

code

line 1> Hello world 
line 2> 19:30:45.2313 Hello World , again

As you can see, the second line is correctly prefixed with the timestamp, but the first line is missing the prefix. This can make it difficult to differentiate between different lines in the log.

The Solution

To fix this issue, we need to make some changes to the code and override the Transform method in the ReplaceNewLinesFormatLayoutRendererWrapper class. Here’s the modified code:

code






























using System;
using NLog;
using NLog.Config;
using NLog.LayoutRenderers;
using NLog.LayoutRenderers.Wrappers;
using NLog.Layouts;

namespace My.Namespace
{
    [LayoutRenderer("replace-newlines-withlayout")] 
[ThreadAgnostic] 











    public class ReplaceNewLinesFormatLayoutRendererWrapper : WrapperLayoutRendererBase
    {
        public Layout Replacement { get; set; } = " ";

        protected override string Transform(LogEventInfo logEvent, string text)
        {
            var replacementString = Replacement.Render(logEvent);
            return replacementString + text.Replace(Environment.NewLine, replacementString);
        }
    }
}

By overriding the Transform method, we can ensure that the first line of the multi-line message is correctly prefixed with the timestamp. The modified code adds the replacementString to the beginning of the transformed text, ensuring consistent formatting for all lines.

Implementing the Solution

To implement the solution in your application, follow these steps:

1. Include the modified ReplaceNewLinesFormatLayoutRendererWrapper class in your project.
2. Update your NLog configuration to use the new layout renderer. Here’s an example:

code





















<?xml version="1.0" encoding="utf-8" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd" xsi:schemaLocation="NLog NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      autoReload="true"
      internalLogFile="c:\temp\console-example-internal.log"
      internalLogLevel="Info" >

  <!-- the targets to write to -->
  <targets>
    <!-- write logs to file -->
    <target xsi:type="File" name="target1" fileName="c:\temp\console-example.log"
        layout="${replace-newlines-withlayout:replacement=${newline}${time}:${message}}" />
    <target xsi:type="ColoredConsole" name="target2"
        layout="${replace-newlines-withlayout:replacement=${newline}${time}:${message}}" />
    />
  </targets>

  <!-- rules to map from logger name to target -->
  <rules>
    <logger name="*" minlevel="Trace" writeTo="target1,target2" />
  </rules>
</nlog>

3. In your application, make sure to register the ReplaceNewLinesFormatLayoutRendererWrapper class:

code

var replaceNewLinesFormatLayoutRendererWrapper = new ReplaceNewLinesFormatLayoutRendererWrapper();
replaceNewLinesFormatLayoutRendererWrapper.Register<NLogTest.ReplaceNewLinesFormatLayoutRendererWrapper>("replace-newlines-withlayout");

4. Finally, use the logger to print multi-line messages in your code:

code
Logger.Info($"Hello world {Environment.NewLine} Hello World , again");

With these modifications in place, you should now see correctly prefixed multi-line messages in your log output.

Conclusion

Printing multi-line messages with NLog.Extensions.Logging can be a useful feature in your .NET Core 3.1 console application. By following the steps outlined in this guide, you can overcome the issue of missing prefixes for the first line of your multi-line messages. Enhance your logging capabilities with NLog and improve the readability of your logs. Happy coding!

That’s it! Now you have the knowledge and tools to successfully print multi-line messages using NLog.Extensions.Logging in your .NET Core 3.1 console application. Don’t forget to implement the changes in your code and update your NLog configuration accordingly. Enjoy the benefits of clear and well-formatted log output.