动态设置每个记录器实例的 Nlog 日志级别 ASP.Net Core 2.x

客观的：动态选择我想要详细日志记录的 HTTP 请求（不同的日志级别）。

Overview：我有一个正在运行的 ASP.Net core 2.1 Web 服务器，一旦投入生产，如果我需要调试问题，我希望能够更改日志级别。我已经找到了如何全局更改日志级别 https://stackoverflow.com/questions/10302561/reconfiguring-nlog-programmatically;但是，更改日志级别是持久的...也就是说，每次调用我的控制器后都不会重置。

    [HttpGet]
    public async Task<IEnumerable<string>> Get()
    {
        this.Logger.LogTrace("This should NOT get logged");
        SetMinLogLevel(LogLevel.Trace);
        this.Logger.LogTrace("This should be logged");

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

   public static void SetMinLogLevel(LogLevel NewLogLevel)
    {
        foreach (var rule in LogManager.Configuration.LoggingRules)
        {
            rule.EnableLoggingForLevel(NewLogLevel);
        }

        //Call to update existing Loggers created with GetLogger() or 
        //GetCurrentClassLogger()
        LogManager.ReconfigExistingLoggers();
    }

我希望请求者能够在其 HTTP 请求（标头或 cookie）中设置一个标志，以便对每个请求进行更详细的日志记录。这样我就不会用请求者的详细日志淹没我的日志。

Question：如何动态设置每个记录器实例的日志级别？ （我相信这是正确的措辞）

我目前使用 NLog 包 4.5。

我们知道 NLog 4.6.7 添加了对使用 NLog Layout 的支持，例如${gdc:globalLevel} to 在运行时动态更改级别属性 https://github.com/nlog/NLog/wiki/Configure-from-code。更好的解决方案是如果可能的话升级您的 NLog。

更新：新解决方案 我在 4.5 版本上尝试了这段代码，效果很好。看来你不需要升级你的NLog版本。在这种情况下，所有配置均以编程方式设置。您可以在标题中发送您想要的级别：loglevel。如果您发送loglevel在标题中，它将被使用。否则，logLevel 将为Error. See here https://github.com/NLog/NLog/wiki/Tutorial#configure-nlog-targets-for-output， 请。

注意：只需使用using NLog;。你不需要using Microsoft.Extensions.Logging;

[Route("api/[controller]/[action]")]
    [ApiController]
    public class HomeController : ControllerBase
    {
        private readonly Logger _log = LogManager.GetCurrentClassLogger();

        [HttpGet]
        public async Task<IEnumerable<string>> Get()
        {
            var requestLogLevel = Request.Headers.SingleOrDefault(x => x.Key == "loglevel");
            LogLevel logLevel = LogLevel.Error;
            switch (requestLogLevel.Value.ToString().ToLower())
            {
                case "trace":
                    logLevel = LogLevel.Trace;
                    break;
                case "debug":
                    logLevel = LogLevel.Debug;
                    break;
                case "info":
                    logLevel = LogLevel.Info;
                    break;
                case "warn":
                case "warning":
                    logLevel = LogLevel.Warn;
                    break;
                case "error":
                    logLevel = LogLevel.Error;
                    break;
                case "fatal":
                    logLevel = LogLevel.Fatal;
                    break;
            }

            var config = new NLog.Config.LoggingConfiguration();
            var defaultMode = new NLog.Targets.FileTarget("defaultlog") { FileName = "log.txt" };
            config.AddRule(logLevel, LogLevel.Fatal, defaultMode);
            NLog.LogManager.Configuration = config;

            _log.Trace("Some logs");

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

解决方案1）升级NLog到4.6.7或更高版本：

var config = new NLog.Config.LoggingConfiguration();

// Targets where to log to: File and Console
var logfile = new NLog.Targets.FileTarget("logfile") { FileName = "file.txt" };
var logconsole = new NLog.Targets.ConsoleTarget("logconsole");
            
// Rules for mapping loggers to targets            
config.AddRule(LogLevel.Info, LogLevel.Fatal, logconsole);
config.AddRule(LogLevel.Debug, LogLevel.Fatal, logfile);
            
// Apply config           
NLog.LogManager.Configuration = config;

解决方案 2) 以编程方式更改配置文件：因为你的版本NLog不支持自动更改配置，我们将以编程方式更改它：

[Route("api/[controller]/[action]")]
[ApiController]
public class HomeController : ControllerBase
{
    private readonly Logger _log = LogManager.GetCurrentClassLogger();

    // Special Authorization needed
    public bool ChangeToDebugMode()
    {
        try
        {
            XmlDocument doc = new XmlDocument();
            doc.Load(AppDomain.CurrentDomain.BaseDirectory +  "nlog.config");
            XmlNode root = doc.DocumentElement;
            XmlNode myNode = root["include"].Attributes["file"];
            myNode.Value = "debugmode.config";
            doc.Save(AppDomain.CurrentDomain.BaseDirectory + "nlog.config");
        }
        catch (Exception)
        {
            return false;
        }

        return true;
    }

    // Special Authorization needed
    public bool RestToDefault()
    {
        try
        {
            XmlDocument doc = new XmlDocument();
            doc.Load(AppDomain.CurrentDomain.BaseDirectory + "nlog.config");
            XmlNode root = doc.DocumentElement;
            XmlNode myNode = root["include"].Attributes["file"];
            myNode.Value = "defaultmode.config";
            doc.Save(AppDomain.CurrentDomain.BaseDirectory + "nlog.config");
        }
        catch (Exception)
        {
            return false;
        }

        return true;
    }

    [HttpGet]
    public async Task<IEnumerable<string>> Get()
    {
        _log.Trace("Some logs");

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

在这种情况下，您需要对配置文件进行一些更改。 你需要添加autoReload=true到配置。现在，当任何配置发生更改时，NLog 会自动重新加载配置，您无需重新启动应用程序。你需要看看autoReload and include here https://github.com/nlog/NLog/wiki/Configure-from-code

nlog配置文件

<?xml version="1.0" encoding="utf-8"?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" autoReload="true">
  <include file="defaultmode.config" />
</nlog>

默认模式配置

<?xml version="1.0" encoding="utf-8" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

  <targets>
    <target name="logfile" xsi:type="File" fileName="file.txt" />
  </targets>

  <rules>
    <logger name="*" minlevel="Debug" writeTo="logfile" />
  </rules>
  <!-- ... -->
</nlog>

调试模式配置

<?xml version="1.0" encoding="utf-8" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

  <targets>
    <target name="logfile" xsi:type="File" fileName="file.txt" />
  </targets>

  <rules>
    <logger name="*" minlevel="Trace" writeTo="logfile" />
  </rules>
  <!-- ... -->
</nlog>

我制作了另外两个配置文件。debugmode.config and defaultmode.config。默认情况下nlog.config file, deafultmode.config已经包括了。什么时候ChangeToDebugMode被调用，它变为debugmode.config什么时候RestToDefault被调用，它变为defaultmode.config。我用了include为了简单起见，将配置分成两个文件。

解决方案3）根据您的问题：在这种情况下，我使用了您在问题中提供的代码。如果您在请求标头中发送日志级别，它将被考虑。如果您不发送，它将使用您在配置中设置的默认值。因此，您无需在客户端更改应用程序。效果很好。调试时只需发送您想要的日志级别即可。

[Route("api/[controller]/[action]")]
[ApiController]
public class HomeController : ControllerBase
{
    private readonly Logger _log = LogManager.GetCurrentClassLogger();

    [HttpGet]
    public async Task<IEnumerable<string>> Get()
    {
        var requestLogLevel = Request.Headers.SingleOrDefault(x => x.Key == "loglevel");
        LogLevel logLevel = LogLevel.Error;
        switch (requestLogLevel.Value.ToString().ToLower())
        {
            case "trace":
                logLevel = LogLevel.Trace;
                break;
            case "debug":
                logLevel = LogLevel.Debug;
                break;
            case "info":
                logLevel = LogLevel.Info;
                break;
            case "warn":
            case "warning":
                logLevel = LogLevel.Warn;
                break;
            case "error":
                logLevel = LogLevel.Error;
                break;
            case "fatal":
                logLevel = LogLevel.Fatal;
                break;
        }
        SetMinLogLevel(logLevel);               

        _log.Trace("Some logs.");

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

    public static void SetMinLogLevel(LogLevel NewLogLevel)
    {
        foreach (var rule in LogManager.Configuration.LoggingRules)
        {
            rule.EnableLoggingForLevel(NewLogLevel);
        }

        //Call to update existing Loggers created with GetLogger() or 
        //GetCurrentClassLogger()
        LogManager.ReconfigExistingLoggers();
    }
}

The problem is, this situation needs to send the log level every time. In these screenshots, you see how to send log level in debugging mode.