Logentries.com and F#

I recently was working on a project that has a fair bit of legacy code.  One of the pieces of the project is an logging service whose interface is this:

1 public interface ILoggingRepository 2 { 3 void LogMessage(String message); 4 void LogException(String message, Exception exception); 5 }

 

There are 2 or 3 different implementations of the logging repository – one that covers the windows logs, one that writes to azure service bus, one that writes to nothing (and in-memory one used for testing).  I thought about using Logentries as place to write the messages to.  I created an account and set up my first log

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Note that the log also gets a token (a guid) that I will use to send messages to the log at the bottom of the page.

I then fired up visual studio and created a new FSharp project and added a reference from the CSharp project to the FSharp project.  I then added an associated unit test class to the existing unit test project:

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I then went back to Logentries and read the api documentation about posting to the log here.   They suggested either log4net or NLog.  For no particular reason, I picked NLog.  I fired up Nuget and installed the Logentries.NLog package

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I then read further down the documentation and yuck, there is tons of places where you have to add to the configuration file.  I am trying to maintain a clean separation of concerns in the app and this intertwines the working code with the .config file.  Also, the other implementations don’t use the .config so I would like to keep consistant there.  After bouncing around in the api for a bit, I went to stack overflow and asked if there was a way I could implement without the .config file.  Sure enough, the dev team was kind enough to answer.  I went ahead and implemented their code (after porting it from C#)  in my project like so:

1 namespace ChickenSoftware.LoggingExample.FS 2 3 open NLog 4 open System 5 open NLog.Targets 6 open NLog.Config; 7 open ChickenSoftware.LoggingExample 8 9 type LogEntriesLoggingRepository(logEntriesToken:string) = 10 let target = new LogentriesTarget() 11 let config = new LoggingConfiguration() 12 do target.Token <- logEntriesToken 13 do target.Ssl <- true 14 do target.Debug <- true 15 do target.Name <- "Logentries" 16 let layout = Layouts.Layout.FromString("${date:format=ddd MMM dd} ${time:format=HH:mm:ss} ${date:format=zzz yyyy} ${logger} : ${LEVEL}, ${message}") 17 do target.Layout <- layout 18 do target.HttpPut <- false 19 do config.AddTarget("Logentries2",target) 20 let loggingRule = new LoggingRule("*", LogLevel.Debug, target) 21 do LogManager.Configuration.AddTarget("targetName", target) 22 do LogManager.Configuration.LoggingRules.Add(loggingRule) 23 do LogManager.Configuration.Reload() |> ignore 24 let logger = LogManager.GetCurrentClassLogger() 25 26 interface ILoggingRepository with 27 member this.LogMessage(message) = 28 logger.Log(LogLevel.Warn, message) 29 member this.LogException(message, exn) = 30 logger.LogException(LogLevel.Error,message,exn)

I then went into the unit test and attempted to generate a log message:

1 public class LogEntriesLoggingRepositoryTests 2 { 3 ILoggingRepository _repository = null; 4 public LogEntriesLoggingRepositoryTests() 5 { 6 string logEntriesToken = "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"; 7 _repository = new LogEntriesLoggingRepository(logEntriesToken); 8 } 9 10 [TestMethod] 11 public void LogMessage_ReturnsExpected() 12 { 13 _repository.LogMessage("This is a test"); 14 15 } 16 }

Unfortunately, when I ran it, I got the following exception, even though I marked the .dlls to be copied

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So back to Nuget, where I added in the Logentries.NLog to the Tests project.  I feel really dirty by doing it:

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I then ran the test again but I got this exception:

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When I added a break to the code and stepped through, I found it was on the LogManager.Configuration.

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Apparently, the only way out of this pickle is to add some basic entries to the .config file <sigh>:

1 <?xml version="1.0" encoding="utf-8"?> 2 <configuration> 3 <configSections> 4 <section name="nlog" type="NLog.Config.ConfigSectionHandler, NLog" /> 5 </configSections> 6 <runtime> 7 <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1"> 8 <dependentAssembly> 9 <assemblyIdentity name="NLog" publicKeyToken="5120e14c03d0593c" culture="neutral" /> 10 <bindingRedirect oldVersion="0.0.0.0-2.1.0.0" newVersion="2.1.0.0" /> 11 </dependentAssembly> 12 </assemblyBinding> 13 </runtime> 14 <nlog> 15 <extensions> 16 <add assembly="LogentriesNLog" /> 17 </extensions> 18 <targets> 19 <target name="logentries" type="Logentries" debug="true" httpPut="false" ssl="false" layout="${date:format=ddd MMM dd} ${time:format=HH:mm:ss} ${date:format=zzz yyyy} ${logger} : ${LEVEL}, ${message}" /> 20 </targets> 21 <rules> 22 <logger name="*" minLevel="Debug" appendTo="logentries" /> 23 </rules> 24 </nlog> 25 </configuration>

After I added it, the test ran green.

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Alas, nothing was showing up in the log!

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After some back and forth with the Logentries team, it became clear that the thread was terminating before the Logentries library had a chance to post it to the service.  This was proven by adding a Thread.Sleep to the test:

1 public void LogMessage_ReturnsExpected() 2 { 3 _repository.LogMessage("This is a test"); 4 Thread.Sleep(500); 5 6 }

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So what to do?  The api does not have an async implementation so I can’t await it and if I leave that Thread.Sleep as is, the main thread will be blocked.  I decided to add an async implementation to the interface

1 public interface ILoggingRepository 2 { 3 void LogMessage(String message); 4 Task LogMessageAsync(String message); 5 void LogException(String message, Exception exception); 6 Task LogExceptionAsync(String message, Exception exception); 7 }

I then updated the repository like so:

1 interface ILoggingRepository with 2 member this.LogMessage(message) = 3 logger.Log(LogLevel.Warn, message) 4 member this.LogMessageAsync(message) = 5 Tasks.Task.Run(fun _ -> logger.Log(LogLevel.Warn, message) 6 Thread.Sleep(500)) 7 member this.LogException(message, exn) = 8 logger.LogException(LogLevel.Error,message,exn) 9 member this.LogExceptionAsync(message, exn) = 10 Tasks.Task.Run(fun _ -> logger.LogException(LogLevel.Error,message,exn) 11 Thread.Sleep(500))

And then I added an async unit test like so:

1 [TestMethod] 2 public void LogMessageAsync_ReturnsExpected() 3 { 4 var task = _repository.LogMessageAsync("This is an async test"); 5 task.Wait(); 6 }

And sure enough, green (note that the async test takes longer than 500MS) and the expected side-effect:

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So now another CSharp shop has some FSharp sprinkled into their code base.  Note the code actually used is slightly different b/c  the code as written will keep adding more and more targets, which is not what we want.

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One Response to Logentries.com and F#

  1. Pingback: F# Weekly #5, 2015 | Sergey Tihon's Blog

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