使用自定义目标将所有 NLog 输出重定向到 Serilog

Question

作为从 NLog 切换到 Serilog 的一个步骤，我想将 NLog 的 LogManager.GetLogger(name) 的标准布线底层标准调用重定向到桥接任何代码日志记录到 NLog 以立即转发到环境 Serilog Log.Logger - 即我想只需一项配置即可简单地转发消息，而无需像 Log4net.Appender.Serilog 为 Log4net 所做的那样进行缓冲。

任何人都可以编造或指出一个规范的 sn-p 可以正确有效地执行此操作吗？我能想到的要求：

• 保持水平，即nlog.Warn应该等价于serilog.Warning
• Serilog 可以重新生成时间
• 在附加程序中实现消息 - 即，无需维护与“消息”相关的任何属性（Serilog 术语中的 LogEvent）
• 无缓冲
• 我不需要使用任何其他 NLog 目标（即改变/删除消息就可以了）

Answer 1

我认为最好的选择确实是自定义 NLog 目标。像这样的东西：（C#）

using NLog;
using NLog.Targets;
using Serilog;
using Serilog.Events;

namespace MyNamespace
{
    [Target("SerilogTarget")]
    public sealed class SerilogTarget : TargetWithLayout
    {
        protected override void Write(LogEventInfo logEvent)
        {
            var log = Log.ForContext(Serilog.Core.Constants.SourceContextPropertyName, logEvent.LoggerName);
            var logEventLevel = ConvertLevel(logEvent.Level);
            if ((logEvent.Parameters?.Length ?? 0) == 0)
            {
                // NLog treats a single string as a verbatim string; Serilog treats it as a String.Format format and hence collapses doubled braces
                // This is the most direct way to emit this without it being re-processed by Serilog (via @nblumhardt)
                var template = new Serilog.Events.MessageTemplate(new[] { new Serilog.Parsing.TextToken(logEvent.FormattedMessage) });
                log.Write(new Serilog.Events.LogEvent(DateTimeOffset.Now, logEventLevel, logEvent.Exception, template, Enumerable.Empty<Serilog.Events.LogEventProperty>()));
            }
            else
                // Risk: tunneling an NLog format and assuming it will Just Work as a Serilog format
#pragma warning disable Serilog004 // Constant MessageTemplate verifier
                log.Write(logEventLevel, logEvent.Exception, logEvent.Message, logEvent.Parameters);
#pragma warning restore Serilog004
        }

        static Serilog.Events.LogEventLevel ConvertLevel(LogLevel logEventLevel)
        {
            if (logEventLevel == LogLevel.Info)
                return Serilog.Events.LogEventLevel.Information;
            else if (logEventLevel == LogLevel.Trace)
                return Serilog.Events.LogEventLevel.Verbose;
            else if (logEventLevel == LogLevel.Debug)
                return Serilog.Events.LogEventLevel.Debug;
            else if (logEventLevel == LogLevel.Warn)
                return Serilog.Events.LogEventLevel.Warning;
            else if (logEventLevel == LogLevel.Error)
                return Serilog.Events.LogEventLevel.Error;
            return Serilog.Events.LogEventLevel.Fatal;
        }
    }
}

在您的main() 或app_start 中注册：

// Register so it can be used by config file parsing etc
Target.Register<MyNamespace.SerilogTarget>("SerilogTarget"); 

在进行任何日志记录之前，需要连接Target，以便LogManager.GetLogger() 实际上可以触发对SerilogTarget.Write 的调用

    public static void ReplaceAllNLogTargetsWithSingleSerilogForwarder()
    {
        // sic: blindly overwrite the forwarding rules every time
        var target = new SerilogTarget();
        var cfg = new NLog.Config.LoggingConfiguration();
        cfg.AddTarget(nameof(SerilogTarget), target);
        cfg.LoggingRules.Add(new NLog.Config.LoggingRule("*", LogLevel.Trace, target));
        // NB assignment must happen last; rules get ingested upon assignment
        LogManager.Configuration = cfg;
    }

---

另请参阅：https://github.com/nlog/nlog/wiki/How-to-write-a-custom-target

在不引起任何可避免的性能影响等的情况下执行此操作的最佳方法。

这是 NLog 中的最佳方式，对 NLog 的站点没有性能影响。

TargetAttribute 给我买了什么？

好吧，在这种情况下，您不需要它。 TargetAttribute 在注册完整程序集时使用，但因为我们手动注册，所以不需要它。我认为这是最佳做法，但您可以忽略它。

还有Register给我买什么

使用编程方式配置时确实不需要这样做。但是如果你有 XML 配置，你需要注册。

我有编写可在所有方面工作的目标的习惯（手动注册、按程序集注册、从代码配置、从 XML 配置）。我可以理解这可能会令人困惑。

---

F# 端口：

module SerilogHelpers =

    let private mapLevel = function
        | x when x = NLog.LogLevel.Info -> LogEventLevel.Information
        | x when x = NLog.LogLevel.Off || x = NLog.LogLevel.Trace -> LogEventLevel.Verbose
        | x when x = NLog.LogLevel.Debug -> LogEventLevel.Debug
        | x when x = NLog.LogLevel.Warn -> LogEventLevel.Warning
        | x when x = NLog.LogLevel.Error ->  LogEventLevel.Error
        | _ -> LogEventLevel.Fatal

    // via https://stackoverflow.com/a/49639001/11635
    [<NLog.Targets.Target("SerilogTarget")>]
    type SerilogTarget() =
        inherit NLog.Targets.Target()

        static member InitializeAsGlobalTarget() =
            // sic: blindly overwrite the forwarding rules every time
            // necessary as Azure Startup establishes a different config as a bootstrapping step
            // see: LogModule.To.target("rollingFile", create, "*", LogLevel.Trace)
            let cfg, target = NLog.Config.LoggingConfiguration(), SerilogTarget()
            cfg.AddTarget("SerilogTarget", target)
            cfg.LoggingRules.Add(NLog.Config.LoggingRule("*", NLog.LogLevel.Trace, target))
            // NB assignment must happen last; rules get ingested upon assignment
            NLog.LogManager.Configuration <- cfg

        override __.Write(logEvent : NLog.LogEventInfo) =
            let log = Log.ForContext(Serilog.Core.Constants.SourceContextPropertyName, logEvent.LoggerName)
            match logEvent.Parameters with
            | xs when isNull xs || xs.Length = 0 ->
                // NLog treats a single string as a verbatim string; Serilog treats it as a String.Format format and hence collapses doubled braces
                // This is the most direct way to emit this without it being re-processed by Serilog (via @nblumhardt)
                let template = MessageTemplate [| Serilog.Parsing.TextToken(logEvent.FormattedMessage) |]
                log.Write(new LogEvent(DateTimeOffset.Now, mapLevel logEvent.Level, logEvent.Exception, template, Seq.empty<LogEventProperty>))
            | _ ->
                // Risk: tunneling an NLog format and assuming it will Just Work as a Serilog format
                log.Write(mapLevel logEvent.Level, logEvent.Exception, logEvent.Message, logEvent.Parameters)