[鐵人賽 Day19] ASP.NET Core 2 系列 - NLog & Log4net

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[鐵人賽 Day19] ASP.NET Core 2 系列 - NLog & Log4net

ASP.NET Core 提供的 Logging API，不僅可以方便調用 Logger，且支援多種 Log 輸出，也能把 Log 發送到多個地方，並支援第三方的 Logging Framework 套件。
本篇將介紹 ASP.NET Core 的 Logging 搭配第三方 Logging Framework 套件，NLog 及 Log4net 的範例。

iT 邦幫忙 2018 鐵人賽 - Modern Web 組參賽文章：
[Day19] ASP.NET Core 2 系列 - NLog & Log4net

NLog

NLog 是 .NET 的熱門 Logging Framework；而且還是 ASP.NET Core 官方第三方 Logging Framework 推薦名單之一。

安裝套件

ASP.NET Core 使用 NLog 需要安裝 NLog 及 NLog.Web.AspNetCore 套件。
透過 .NET Core CLI 在專案資料夾執行安裝指令：

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dotnet add package NLog -v 4.5.0-rc02
dotnet add package NLog.Web.AspNetCore -v 4.5.0-rc2

.NET Core 的版本目前還是 RC 版。

組態設定檔

新增一個 nlog.config 的檔案如下：

nlog.config

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<?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" 
  internalLogLevel="info" 
  internalLogFile="C:\Logs\MyWebsite\nlog-internal.txt">
  <targets>
    <!-- write logs to file  -->
    <target xsi:type="File" name="ALL" 
      fileName="C:\Logs\MyWebsite\nlog-all_${shortdate}.log" 
      layout="${longdate}|${event-properties:item=EventId.Id}|${uppercase:${level}}|${logger}|${message} ${exception}" />
  </targets>
  <rules>
    <logger name="*" minlevel="Trace" writeTo="ALL" />
  </rules>
</nlog>

NLog 組態設定可以參考：NLog Configuration file

在 Program.Main 啟動時載入 NLog 組態設定檔，並在 WebHost Builder 注入 NLog 服務。

Program.cs

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using Microsoft.AspNetCore;
using Microsoft.AspNetCore.Hosting;
using NLog.Web;

namespace MyWebsite
{
    public class Program
    {
        public static void Main(string[] args)
        {
            NLogBuilder.ConfigureNLog("nlog.config").GetCurrentClassLogger();
            BuildWebHost(args).Run();
        }

        public static IWebHost BuildWebHost(string[] args)
        {
            return WebHost.CreateDefaultBuilder(args)
                .UseStartup<Startup>()
                .UseNLog()
                .Build();
        }
    }
}

Log 輸出範例延續前篇[鐵人賽 Day18] ASP.NET Core 2 系列 - Logging
以下 Log 輸出都是以前篇的 Home.Index() 做為範例。

輸出結果如下：

C:\Logs\MyWebsite\nlog-all_2018-01-07.log

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2018-01-07 00:27:32.6339||INFO|Microsoft.AspNetCore.DataProtection.KeyManagement.XmlKeyManager|User profile is available. Using 'C:\Users\john.wu\AppData\Local\ASP.NET\DataProtection-Keys' as key repository and Windows DPAPI to encrypt keys at rest. 
2018-01-07 00:27:33.1149||INFO|Microsoft.AspNetCore.Hosting.Internal.WebHost|Request starting HTTP/1.1 GET http://localhost:5000/   
2018-01-07 00:27:33.1969||INFO|Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker|Executing action method MyWebsite.HomeController.Index (MyWebsite) with arguments ((null)) - ModelState is Valid 
2018-01-07 00:27:33.1999||INFO|MyWebsite.HomeController|This information log from Home.Index() 
2018-01-07 00:27:33.1999||WARN|MyWebsite.HomeController|This warning log from Home.Index() 
2018-01-07 00:27:33.1999||ERROR|MyWebsite.HomeController|This error log from Home.Index() 
2018-01-07 00:27:33.1999||FATAL|MyWebsite.HomeController|This critical log from Home.Index() 
2018-01-07 00:27:33.2219||INFO|Microsoft.AspNetCore.Mvc.Internal.ObjectResultExecutor|Executing ObjectResult, writing value Microsoft.AspNetCore.Mvc.ControllerContext. 
2018-01-07 00:27:33.2459||INFO|Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker|Executed action MyWebsite.HomeController.Index (MyWebsite) in 56.8935ms 
2018-01-07 00:27:33.2519||INFO|Microsoft.AspNetCore.Hosting.Internal.WebHost|Request finished in 137.5115ms 200 text/plain; charset=utf-8

安裝完套件後，只要加一個設定檔及兩行程式碼就完成，可說是非常的友善使用。

Log4net

從網路上各方訊息看來，Log4net 應該是 .NET 最熱門的 Logging Framework，我個人也是習慣用 Log4net。

安裝套件

.NET Core 使用 Log4net 需要安裝 log4net 套件。
透過 .NET Core CLI 在專案資料夾執行安裝指令：

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dotnet add package log4net

組態設定檔

新增一個 log4net.config 的檔案如下：

log4net.config

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<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <log4net>
    <appender name="All" type="log4net.Appender.RollingFileAppender">
      <file value="C:\Logs\MyWebsite\log4net-all" />
      <appendToFile value="true" />
      <rollingStyle value="Composite" />
      <datePattern value="_yyyy-MM-dd.lo\g" />
      <maximumFileSize value="5MB" />
      <maxSizeRollBackups value="15" />
      <staticLogFileName value="false" />
      <PreserveLogFileNameExtension value="true" />
      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%date [%thread] %level %logger - %message%newline" />
      </layout>
    </appender>
    <root>
      <appender-ref ref="All" />
    </root>
  </log4net>
</configuration>

Log4net 組態設定可以參考：Apache log4net Manual - Configuration

在 Program.Main 啟動時載入 Log4net 組態設定檔。

Program.cs

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using System.IO;
using System.Reflection;
using log4net;
using log4net.Config;
using Microsoft.AspNetCore;
using Microsoft.AspNetCore.Hosting;

namespace MyWebsite
{
    public class Program
    {
        private readonly static ILog _log = LogManager.GetLogger(typeof(Program));

        public static void Main(string[] args)
        {
            LoadLog4netConfig();
            _log.Info("Application Start");
            BuildWebHost(args).Run();
        }

        public static IWebHost BuildWebHost(string[] args)
        {
            return WebHost.CreateDefaultBuilder(args)
                .UseStartup<Startup>()
                .Build();
        }

        private static void LoadLog4netConfig()
        {
            var repository = LogManager.CreateRepository(
                    Assembly.GetEntryAssembly(),
                    typeof(log4net.Repository.Hierarchy.Hierarchy)
                );
            XmlConfigurator.Configure(repository, new FileInfo("log4net.config"));
        }
    }
}

載入 Log4net 組態設定後，就可以直接操作 _log 物件寫 Log，用法就跟過去 .NET Framework 一樣。
但 Log4net 沒有實作 ASP.NET Core 的 Logging API，所以沒辦法透過注入 ILogger 寫 Log4net 的 Log。

難怪 ASP.NET Core 官方不推 Log4net…

ILogger

既然 Log4net 沒有實作 ILogger，就自己做吧！
建立一個 Log4netLogger.cs，內容如下：

Log4netLogger.cs

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using System;
using System.IO;
using System.Reflection;
using log4net;
using log4net.Config;
using Microsoft.Extensions.Logging;

namespace MyWebsite
{
    public class Log4netLogger : ILogger
    {
        private readonly ILog _log;

        public Log4netLogger(string name, FileInfo fileInfo)
        {
            var repository = LogManager.CreateRepository(
                    Assembly.GetEntryAssembly(),
                    typeof(log4net.Repository.Hierarchy.Hierarchy)
                );
            XmlConfigurator.Configure(repository, fileInfo);
            _log = LogManager.GetLogger(repository.Name, name);
        }

        public IDisposable BeginScope<TState>(TState state)
        {
            return null;
        }

        public bool IsEnabled(LogLevel logLevel)
        {
            switch (logLevel)
            {
                case LogLevel.Critical: return _log.IsFatalEnabled;
                case LogLevel.Debug:
                case LogLevel.Trace: return _log.IsDebugEnabled;
                case LogLevel.Error: return _log.IsErrorEnabled;
                case LogLevel.Information: return _log.IsInfoEnabled;
                case LogLevel.Warning: return _log.IsWarnEnabled;
                default: 
                    throw new ArgumentOutOfRangeException(nameof(logLevel));
            }
        }

        public void Log<TState>(LogLevel logLevel, EventId eventId, TState state,
            Exception exception, Func<TState, Exception, string> formatter)
        {
            if (!IsEnabled(logLevel))
            {
                return;
            }
            if (formatter == null)
            {
                throw new ArgumentNullException(nameof(formatter));
            }
            string message = null;
            if (null != formatter)
            {
                message = formatter(state, exception);
            }
            if (!string.IsNullOrEmpty(message) || exception != null)
            {
                switch (logLevel)
                {
                    case LogLevel.Critical: _log.Fatal(message); break;
                    case LogLevel.Debug:
                    case LogLevel.Trace: _log.Debug(message); break;
                    case LogLevel.Error: _log.Error(message); break;
                    case LogLevel.Information: _log.Info(message); break;
                    case LogLevel.Warning: _log.Warn(message); break;
                    default: 
                        _log.Warn($"Unknown log level {logLevel}.\r\n{message}"); 
                        break;
                }
            }
        }
    }
}

由於 Log4net 的 Log Level 跟 ASP.NET Core Logger API 的級別不一致，所以要將 Log Level 的事件做相對的對應。

ILoggerProvider。

ILogger 主要是透過 Logger Provider 產生，所以需要實作 ILoggerProvider。
建立一個 Log4netProvider.cs，內容如下：

Log4netProvider.cs

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using System.IO;
using Microsoft.Extensions.Logging;

namespace MyWebsite
{
    public class Log4netProvider : ILoggerProvider
    {
        private readonly FileInfo _fileInfo;

        public Log4netProvider(string log4netConfigFile)
        {
            _fileInfo = new FileInfo(log4netConfigFile);
        }

        public ILogger CreateLogger(string name)
        {
            return new Log4netLogger(name, _fileInfo);
        }

        public void Dispose()
        {
        }
    }
}

將 Log4netProvider 註冊到 WebHost 的 ConfigureLogging 中。

Program.cs

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using Microsoft.AspNetCore;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Logging;

namespace MyWebsite
{
    public class Program
    {
        public static void Main(string[] args)
        {
            BuildWebHost(args).Run();
        }

        public static IWebHost BuildWebHost(string[] args)
        {
            return WebHost.CreateDefaultBuilder(args)
                .ConfigureLogging(logging => {
                    logging.AddProvider(new Log4netProvider("log4net.config"));
                })
                .UseStartup<Startup>()
                .Build();
        }
    }
}

如此一來，也能透過 ASP.NET Core 的 Logger API 寫出 Log4net 的 Log 了。

輸出結果如下：

C:\Logs\MyWebsite\log4net-all_2018-01-07.log

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2018-01-07 00:56:46,673 [1] INFO Microsoft.AspNetCore.DataProtection.KeyManagement.XmlKeyManager - User profile is available. Using 'C:\Users\john.wu\AppData\Local\ASP.NET\DataProtection-Keys' as key repository and Windows DPAPI to encrypt keys at rest.
2018-01-07 00:56:47,167 [17] INFO Microsoft.AspNetCore.Hosting.Internal.WebHost - Request starting HTTP/1.1 GET http://localhost:5000/  
2018-01-07 00:56:47,261 [17] INFO Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker - Executing action method MyWebsite.HomeController.Index (MyWebsite) with arguments ((null)) - ModelState is Valid
2018-01-07 00:56:47,265 [17] INFO MyWebsite.HomeController - This information log from Home.Index()
2018-01-07 00:56:47,266 [17] WARN MyWebsite.HomeController - This warning log from Home.Index()
2018-01-07 00:56:47,268 [17] ERROR MyWebsite.HomeController - This error log from Home.Index()
2018-01-07 00:56:47,269 [17] FATAL MyWebsite.HomeController - This critical log from Home.Index()
2018-01-07 00:56:47,278 [17] INFO Microsoft.AspNetCore.Mvc.Internal.ObjectResultExecutor - Executing ObjectResult, writing value Microsoft.AspNetCore.Mvc.ControllerContext.
2018-01-07 00:56:47,303 [17] INFO Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker - Executed action MyWebsite.HomeController.Index (MyWebsite) in 52.7449ms
2018-01-07 00:56:47,305 [17] INFO Microsoft.AspNetCore.Hosting.Internal.WebHost - Request finished in 141.4295ms 200 text/plain; charset=utf-8

參考

Introduction to Logging in ASP.NET Core
NLog - Getting started with ASP.NET Core 2
How to use Log4Net with ASP.NET Core for logging

ASP.NET Core iT 邦幫忙 2018 鐵人賽 NLog Log4net