HttpContextAccessor is null in AspNetLayoutRendererBase

[jholovacs]

• Bug

I've got NLog wired into DI like so:

		public static IApplicationBuilder StartLogging(this IApplicationBuilder app,
			IConfiguration config)
		{
			var loggerFactory = app.ApplicationServices.GetService<ILoggerFactory>();
			loggerFactory.AddNLog(new NLogAspNetCoreOptions
			{
				RegisterHttpContextAccessor = true,
				IgnoreEmptyEventId = true,
				IncludeScopes = true
			});
			LogManager.LoadConfiguration("nlog.config");
			LogManager.Configuration.Variables["appDbConnectionString"] =
				config["ConnectionStrings:ApplicationContext"];
			return app;
		}

		public static IServiceCollection ConfigureLogging(this IServiceCollection services,
			IConfiguration config)
		{
			services.AddLogging();
			return services;
		}

I've made my own test renderer (off of AspNetLayoutRendererBase) and registered it just to see why I could not get the user info to work.

The ClaimsPrincipal is properly filled out with the user claims. The ClaimsIdentity has the proper username. The protected override void DoAppend(StringBuilder builder, LogEventInfo logEvent) method in the layout renderer was never reached... so I dug a bit further back and found that the protected override void Append(StringBuilder builder, LogEventInfo logEvent) method was being hit. However, the HttpContextAccessor property was null, so it never got to the DoAppend method.

I see this method is populated with a ServiceLocator, but I don't know if maybe that can't figure out how to access the ServiceProvider in .NET Core 2.1, or do I need to configure something that I'm missing?

NLog version: 4.5.10

NLog.Web/NLog.Web.AspNetCore version: 4.7.0

NLog.Extensions.Logging version: 1.3.0

Platform: .NET Core 2.1

Current NLog config (xml or C#, if relevant)

<?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"
      throwExceptions="true"
      internalLogIncludeTimestamp="true"
      internalLogFile="nlog-internal.log"
      internalLogLevel="Error">
  <extensions>
    <add assembly="NLog.Web.AspNetCore"/>
  </extensions>
  <targets>
    <target xsi:type="File"
            name="fileSystem"
            fileName="cfcommunity.log"
            layout="${date}|${level:uppercase=true}|${message} ${exception}|${logger}|${all-event-properties}"
            cleanupFileName="true" enableFileDelete="true"
            maxArchiveFiles="5" archiveAboveSize="1000000" archiveOldFileOnStartup="true" />
    <target xsi:type="ColoredConsole"
            name="console"
            layout="${date}|${level:uppercase=true}|${message} ${exception}|${logger}|${all-event-properties}" />
    <target xsi:type="Database"
            name="database"
            commandType="Text"
            dbProvider="Npgsql.NpgsqlConnection, Npgsql"
            connectionString="${var:appDbConnectionString}"
            commandText="Layout">
      <commandText>
        insert into "logs" ("application", "user", "level", "message", "exception", "logger")
        values (@application, @user, @level, @message, @exception, @logger);
      </commandText>
      <parameter name="@application" layout="MyApp" />
      <parameter name="@user" layout="${aspnet-user-identity}" />
      <parameter name="@level" layout="${level}" />
      <parameter name="@message" layout="${message}" />
      <parameter name="@exception" layout="${exception:format=tostring}" />
      <parameter name="@logger" layout="${logger}" />
    </target>
  </targets>
  <rules>
    <logger name="MyApp.*" minlevel="Info" writeTo="database" final="true" />
    <logger name="*" minlevel="Error" writeTo="fileSystem,database" final="true"/>
    <logger name="*" minlevel="Warn" writeTo="database" final="true"/>
  </rules>
</nlog>

In case of a BUG:

• What is the current result? User column stored to db is blank.
• What is the expected result? User column displays the logged-in user.
• Did you checked the Internal log? even when set to debug, it is not producing any results. CORRECTION When setting output to console with Debug level I do see the message "Missing serviceProvider, so no HttpContext".
• Please post full exception details (message, stacktrace, inner exceptions)
• Are there any workarounds? not that I can find
• Is there a version in which it did work? not that I can find
• Can you help us by writing an unit test? With a static ServiceLocator pattern, I don't think that I can. The IHttpContextAccessor is registered as a Singleton in the application already, and it still not able to find it.

[snakefoot]

If wanting to configure NLog in Startup.cs using AddNLog (ASP NET Core v1 style):

NLog/NLog#2859 (comment)

But the recommended way is UseNLog in Program.cs: https://github.com/NLog/NLog.Web/wiki/Getting-started-with-ASP.NET-Core-2#4-update-programcs

Please do not apply both approaches at the same time.

[jholovacs]

Now that is a buried nugget of gold. That did indeed solve my issue. Thank you.

[snakefoot]

@jholovacs Remember not to use both AddNLog (ver. 1) and UseNLog (ver. 2) at the same time.

[jholovacs]

@snakefoot Thanks, but it's not clear how I would be able to use the connection string in my appsettings from Program.cs before DI is configured. Can you point me to where I'd find that info?

[snakefoot]

NLog variables should not be assigned at runtime. Instead use GDC see also: https://github.com/NLog/NLog/wiki/Gdc-layout-renderer

[jholovacs]

I don't see how that would work to load a connection string that's stored in an appsettings.json file. I need the IConfiguration object loaded before setting the value.

[snakefoot]

You just have to assign the GDC at any point at runtime. Before or after loading the NLog config.