RealtimeLogger - An NLog Companion for Real-Time Logging

A C# class that works in conjunction with the NLog 'MethodCall' logging target to expose log messages via an event in real time.

Installation

Install from the NuGet gallery GUI or with the Package Manager Console using the following command:

Install-Package NLog.RealtimeLogger

Usage

NLog Configuration

Note that the following instructions are applicable if you aren't using the NuGet package (e.g. you compiled the code yourself, or inserted the source in your project).

Copy the RealtimeLogger.cs file into your project and rename the namespace to fit your application. In the example below we'll pretend we named it MyNamespace.

In your NLog configuration, add the following target:

<target name="method" xsi:type="MethodCall" className="MyNamespace.RealtimeLogger, MyNamespace" methodName="AppendLog">
  <parameter layout="${threadid}"/>
  <parameter layout="${longdate}"/>
  <parameter layout="${level}"/>
  <parameter layout="${logger}"/>
  <parameter layout="${message} ${exception:format=tostring}"/>
</target>

Note that in the className attribute, the fully qualified name of the RealtimeLogger class is used. This includes the namespace, which in this case is MyNamespace. The second part of the attribute must be set to the name of your assembly. This will be defined in Properties\AssemblyInfo.cs within the AssemblyTitle attribute.

Next, add a logger for the method call to your NLog configuration:

<logger name="*" minlevel="Info" writeTo="method"/>

Change the minlevel attribute to whichever logging level you'd like to catch.

When you are finished, your NLog configuration should look something like this:

<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    autoReload="true" 
    throwExceptions="false" 
    internalLogLevel="Off" 
    internalLogFile="c:\temp\nlog-internal.log"
  >
  <targets>
    <target name="method" xsi:type="MethodCall" className="Example.RealtimeLogger, Example" methodName="AppendLog">
	  <parameter layout="${threadid}"/>
      <parameter layout="${longdate}"/>
      <parameter layout="${level}"/>
      <parameter layout="${logger}"/>
      <parameter layout="${message} ${exception:format=tostring}"/>
    </target>
  </targets>
  <rules>
    <logger name="*" minlevel="Info" writeTo="method"/>
  </rules>
</nlog>

NuGet Package Configuration

If you downloaded and installed the library from NuGet, your target should match the following:

  <targets>
    <target name="method" xsi:type="MethodCall" className="NLog.RealtimeLogger.RealtimeLogger, NLog.RealtimeLogger" methodName="AppendLog">
	  <parameter layout="${threadid}"/>
      <parameter layout="${longdate}"/>
      <parameter layout="${level}"/>
      <parameter layout="${logger}"/>
      <parameter layout="${message} ${exception:format=tostring}"/>
    </target>
  </targets>

Event Handler

Next, create a method that can be bound to the RealtimeLogger's LogAppended event, like so:

private void AppendLog(object sender, RealtimeLoggerEventArgs e)
{
  Console.WriteLine("New log: " + e.Message);
}

Bind this event handler to the LogAppended event:

RealtimeLogger.LogAppended += AppendLog;

Generally you'll want to put the statement above in Main(). Note that any number of handlers can be added.

That's it! Your handler should be invoked each time a new log is added to the logger.

RealtimeLoggerEventArgs

The properties of the event arguments RealtimeLoggerEventArgs for the LogAppended event are as follows:

Property	Type	Description
ThreadID	int	The ID of the tread from which the log message originated.
DateTime	DateTime	The DateTime corresponding to the instant the log was added to the logger.
Level	LogLevel	The logging level used to add the log to the logger.
Logger	string	The name of the logger.
Message	string	The log message.

Note that the constructor for RealtimeLoggerEventArgs parses the ThreadID, DateTime and LogLevel passed from NLog from strings. If parsing fails the code will prefix the log message with an error before adding it to the log queue.

If the specified ThreadID value from NLog fails to be parsed, the ThreadID property will be set to 0 and the following message will be prepended to the log message:

[Invalid ThreadID; substituted with default]

If the specified DateTime value from NLog fails to be parsed, the DateTime property will be set to DateTime.Now and the following message will be prepended to the log message:

[Invalid DateTime; substituted with DateTime.Now]

The DateTime property for the log message will also be set to DateTime.Now.

If the specified LogLevel fails to be parsed, the LogLevel property will be set to LogLevel.Info and the following message will be prepended to the log message:

[Invalid LogLevel; substituted with LogLevel.Info]

Log Queue

A queue of log messages is provided and may be accessed using the LogHistory property of type Queue<RealtimeLoggerEventArgs>. Logs will accumulate in the queue until it reaches the size specified in the LogHistoryLimit property, after which point logs will be dequeued when new logs are enqueued.

The variable logHistoryLimit is used to initialize the value of the LogHistoryLimit property. This can be changed by editing the class, or LogHistoryLimit can be changed programmatically at runtime.

Notes

If the async option is used for the logging target the log event will not fire precisely in real time. It would be a good idea to use the AsyncWrapper functionality described here to limit the asynchronous execution to only those targets that need it, rather than adding the async attribute to the <targets> node of the config file.

Configuration

Create and modify the NLog configuration variable "RealtimeLogger.LogHistoryLimit" to change the number of logs saved in the log history. The default is 300.

  <variable name="RealtimeLogger.LogHistoryLimit" value="300"/>