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We interrupt this series to take a side trip concerning application logging.  The series begins here. NLog is an excellent open source logging project available from NuGet and other sources.   The sample code for this blog post can be found HERE. Although this is a kitchen sink implementation (Log to files, event logs, database, SMTP whatever) I will be using it as a simple way to log text information to files.  Once you have created a Visual Studio Project open Tools / NuGet Package  Manager/Package Manager Console.  From Here you can add NLog to your object with the command:

PM> Install-Package NLog

This will install NLog, modify your project and add a project reference for NLog.  Although NLog targets and rules can be managed programmatically, I 

normally user the configuration file: 

NLog.Config

You can set this up using the Package Manager Console with the command:

PM> Install-Package NLog.Config

Configuration File Setup

The NLog config file is then modified to define “targets” and “rules”.  The former defines where log entries are written and the latter define which log 

levels are written to which targets.  A file based target section might look like:

<targets>

   DLR.Flickr/Debug.txt” archiveNumbering=”Rolling”   archiveEvery=”Day” maxArchiveFiles=”7″ ConcurrentWrites=”true”/>

<target name=”logfile” xsi:type=”File” layout=”${message}”    fileName=”C:/temp/DLR.Flickr/Info.txt”  archiveNumbering=”Rolling”  archiveEvery=”Day” maxArchiveFiles=”7″ ConcurrentWrites=”true”/>

<target name=”Errorsfile” xsi:type=”File” layout=”${message}” fileName=”C:/temp/DLR.Flickr/Error.txt” archiveNumbering=”Rolling”  archiveEvery=”Day” maxArchiveFiles=”7″ ConcurrentWrites=”true”/>

<target name=”Fatalfile” xsi:type=”File” layout=”${message}”  fileName=”C:/temp/DLR.Flickr/Fatal.txt” archiveNumbering=”Rolling”  archiveEvery=”Day” maxArchiveFiles=”7″ ConcurrentWrites=”true”/>

</targets>

where name is the symbolic name of the target xsi:type defines this as a file target.  If you are controlling the layout of the log entry set layout to “${message}”.  Given that we are using xsi:type as File we can use fileName to set the physical location of the log file.  The value of fileName can be changed programmatically at runtime but I will not give examples here.

NLog defines five Log levels:  Debug, Info, Warn, Error and Fatal.  These levels are defined in an enum and have the names have no special significance except as you define them.  The Rules section of the config file defines which Log Levels are written to which targets. A given level can be written to zero to many targets.  My Rules section typically looks like:

<rules>

<logger name=”*” minlevel=”Debug” maxlevel=”Debug” writeTo=”debugfile” />

<logger name=”*” minlevel=”Info” maxlevel= “Info” writeTo=”logfile” />

<logger name=”*” minlevel=”Warn” maxlevel=”Warn” writeTo=”Warnfile” />

<logger name=”*” minlevel=”Error” maxlevel=”Error” writeTo=”Errorfile” />

<logger name=”*” minlevel=”Fatal” maxlevel=”Fatal” writeTo=”Fatalfile” />
  </rules>

More complex rules like the following are possible:

    <logger name=”*” minlevel=”Error” maxlevel=”Error” writeTo=”Errorfile” />

       <logger name=”*” minlevel=”Error” maxlevel=”Fatal” writeTo=”Fatalfile” />

NLog initialization at runtime is very simple.  Typically you can you a single line like:

using NLog;

static Logger _LogEngine = LogManager.GetLogger(“Log Name”);

this need only be called once.

The simplest NLog log call (given the definition layout=”${message}”  ) would look like:

_LogEngine.Log(NLog.LogLevel.Info, “Info Message”);

We can extend this quite simply.  I have a single class extension providing a simple extension of NLog on Git Hub.  You can find it here.  Specifically I have provided wrapper methods for each NLog.LogLevel and support for Exception Stack Dumps.  Include this file in your project (after installing NLog and NLog config) then you can write:

using DLR.Util;

namespace DLR.CCDB.ConsoleApp

{

    class Program

{

static void Main(string[] args)

{

string _CorrelationID=System.Guid.NewGuid().ToString();

CCDB cbase = new CCDB { CorrelationID = _CorrelationID };

cbase.Client = CouchbaseManager.Instance;

NLS.Info(_CorrelationID, “Helllo, CouchBase”);

try{

throw new ApplicationException(“My Exception”);

}catch(Exception x){

NLS.Error(_CorrelationID,”Error”,x.Message);

//OR

NLS.Error(_CorrelationID,”Error”,x);

}

_CorrelationID is supported here so in multiuser situations (like WebAPI) we can identify which messages where written by which task.  In a console app this is not strictly necessary.  The call to NLS.Info results in an output log line like:

DLR|20140909-152031037|2f8f89ce-51de-4269-9ae0-9313ad2a0243|Helllo, CouchBase|

where:

• DLR is the Log Engine name (more than one engine can write to a given log file);
• 20140909-152031037 is the terse timestamp of the form: YYYYMMDD-HHMMSSmmm; and
• Hello, CouchBase is our text message

My call:

NLS.Error(_CorrelationID,”Error”,x);

would result in a log line like:

DLR|20140909-152544801|46e656cd-4e17-4285-a5f3-e1484dad2995|Error|Error Data. Message: [My Exception]Stack Trace:  DLR.CCDB.ConsoleApp.Program.MainString args|

where Error is my message;

Error Data. Message: [My Exception] is the Message in ApplicationException; and

Stack Trace:  DLR.CCDB.ConsoleApp.Program.MainString args| is the stack dump.

NLS will handle nested exceptions and stack dumps but we are only showing a single un-nested exception in this example.

OK! That’s it for this post.  We will, hopefully return to couchBase and the Flickr API in the next post.