NLog.Web.AspNetCore – make sure you add error message for logging exception

2017-07-09 TPodolakNLog2 Comments

I’ve been using NLog for quite some time already, and it was a natural choice to use it in the ASP.NET Core projects as well. I’ve configured the logger using this tutorial and everything seemed to be working fine. Unfortunately, after some time we’ve noticed that for some reasons some of the errors are not logged. We’ve taken a deeper look at our code base and we’ve found couple logs being written as follows

_logger.LogError(exception.HResult, exception, string.Empty); 
_logger.LogCritical(exception.HResult, exception, string.Empty);

1 2	_logger.LogError(exception.HResult, exception, string.Empty); _logger.LogCritical(exception.HResult, exception, string.Empty);

This piece of code works perfectly fine with ASP.NET Core console logger but it seems it doesn’t for NLog.
We double checked that with following piece of code

[Route("api/[controller]")]
public class ValuesController : Controller
{
    private readonly ILogger<ValuesController> _logger;
        
    public ValuesController(ILogger<ValuesController> logger)
    {
        _logger = logger;
    }

    // GET api/values
    [HttpGet]
    public IEnumerable<string> Get()
    {
        var exception = new Exception();
        _logger.LogTrace("Log trace");
        _logger.LogDebug("Log debug");
        _logger.LogInformation("Log information");
        _logger.LogWarning("Log warning");
        _logger.LogError(exception.HResult, exception, string.Empty); // this one will not be logged
        _logger.LogCritical(exception.HResult, exception, string.Empty); // this one will not be logged as well            

        return new string[] {"value1", "value2"};
    }
}

[Route("api/[controller]")]

public class ValuesController : Controller

{

private readonly ILogger<ValuesController> _logger;

public ValuesController(ILogger<ValuesController> logger)

{

_logger = logger;

}

// GET api/values

[HttpGet]

public IEnumerable<string> Get()

{

var exception = new Exception();

_logger.LogTrace("Log trace");

_logger.LogDebug("Log debug");

_logger.LogInformation("Log information");

_logger.LogWarning("Log warning");

_logger.LogError(exception.HResult, exception, string.Empty); // this one will not be logged

_logger.LogCritical(exception.HResult, exception, string.Empty); // this one will not be logged as well

return new string[] {"value1", "value2"};

}

And as you can see in the picture below, no errors have been reported

Changing the error message to any message (even the one containing only white spaces)

 _logger.LogError(exception.HResult, exception, " "); 
 _logger.LogCritical(exception.HResult, exception, " " );

1 2	_logger.LogError(exception.HResult, exception, " "); _logger.LogCritical(exception.HResult, exception, " " );

fixed the problem.

That looks like a bug for me, so I will create a PR with the fix and see if that will make its way to the “master”

As usual, the source code for this post can be found on my GitHub

ASP.NET Core – tracking flow of requests with NLog

2017-02-18 TPodolakASP.NET Core, NLog3 Comments

1. Introduction

A while ago I wrote an article about using MappedDiagnosticsLogicalContext for tracking request flow in your application. As we are moving our project to ASP.NET Core, I wanted to keep that functionality in place. Unfortunately, MDLC layout renderer is not available in that framework anymore(when targeting .NET Core). Luckily, there are two other renderers which can be used as a replacement:

aspnet-traceidentifier
aspnet-item

2. Configuring NLog

Before I dig into details of layout renderers mentioned above, we have to configure ASP.NET Core to use NLog as a logger. First of all, we need to grab NLog.Web.AspNetCore NuGet package. Once the package is installed we have to manually add NLog.config to the project (the file won’t be added automatically by NuGet installer). The next step is to configure NLog with our config, then configure NLogWeb and finally register NLog in LoggingFactory. All of these steps should be done in Startup class.

public class Startup
{
    public Startup(IHostingEnvironment env)
    {
        // rest of the code omitted for brevity
        env.ConfigureNLog("NLog.config");
        // rest of the code omitted for brevity
    }
	
    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        // rest of the code omitted for brevity
        loggerFactory.AddNLog();
        app.AddNLogWeb();
        // rest of the code omitted for brevity
    }
}

public class Startup

{

public Startup(IHostingEnvironment env)

{