Serilog简介

与其他许多.NET库一样，Serilog还提供了对文件，控制台等的基本诊断日志记录。它易于设置，具有简洁的API，并且可以在最新的.NET平台之间移植。

使用和配置、自定义Enricher

由于 serilog 配置信息比较多，避免硬编码代码中，我们在 appsetting.jgon 同级目录中新建一个 serilogsetting.json 的日志配置文件，简单内容如下:

{
	"Serilog": {
		"Using": [ "Serilog.Sinks.Console", "Serilog.Sinks.Seq" ],
		"MinimumLevel": {
			"Default": "Information",
			"Override": {
				"System": "Error",
				"Microsoft": "Error"
			}
		},
		"WriteTo": [
			{
				"Name": "Console"
			},
			{
				"Name": "Seq",
				"Args": {
					"serverUrl": "http://localhost:5341/",
					"apiKey": "L2on8gpgjose5uldhdch"
				}
			}
		]
	}
}

更多配置内容请参考：serilog wiki 文档

接下来，在 Program.cs 中添加一个方法，初始化这些配置，然后重写下构建主机的代码：

public class Program
{
    public static int Main(string[] args)
    {
        var logConfig = GetLogConfig();
        Log.Logger = new LoggerConfiguration()
                     .ReadFrom.Configuration(logConfig)
                     .Enrich.FormLogContext()
                     .CreateLogger(); 
        try
        {
            // web host 初始化
            var host = BuildWebHost(args);
            host.Run();
            return 0;
        }
        catch(Exception e)
        {
            Log.Fatal(ex, "{ApplicationContext} 出现错误:{messsage} !", AppName, ex.Message);
            return 1;
        }
        finally
        {
            Log.CloseAndFlush();
        }
    }
    
    /// <summary>
    /// 读取日志配置
    /// </summary>
    /// <returns></returns>
    private static IConfiguration GetLogConfig()
    {
        var builder = new ConfigurationBuilder()
                      .AddJsonFile("serilogsetting.json", optional: false, reloadOnChange: true);
        return builder.Build();
    
    }
}

然后，添加一个自定义Enircher,用来记录HttpContext，的数据。_enrichAction则可以自定义，默认记录ip，请求路径，请求方法，和返回响应码：

public class HttpContextEnricher:ILogEventEnricher
{
    private readonly IServiceProvider _serviceProvider;
    private readonly Action<LogEvent, ILogEventPropertyFactory, HttpContext> _enrichAction;
    
    public HttpContextEnricher(IServiceProvider serviceProvider) : this(serviceProvider, null)
    {}
      
    public HttpContextEnricher(IServiceProvider serviceProvider, Action<LogEvent, ILogEventPropertyFactory, HttpContext> enrichAction)
    {
        _serviceProvider = serviceProvider;
        if (enrichAction == null)
        {
            _enrichAction = (logEvent, propertyFactory, httpContext) =>{
                var x_forwarded_for = new StringValues();
                if (httpContext.Request.Headers.ContainsKey("X-Forwarded-For"))
                {
                   x_forwarded_for = httpContext.Request.Headers["X-Forwarded-For"];
                }
                logEvent.AddPropertyIfAbsent(propertyFactory.CreateProperty("client_ip", JsonConvert.SerializeObject(x_forwarded_for)));
                logEvent.AddPropertyIfAbsent(propertyFactory.CreateProperty("request_path", httpContext.Request.Path));
                logEvent.AddPropertyIfAbsent(propertyFactory.CreateProperty("request_method", httpContext.Request.Method));
                 if (httpContext.Response.HasStarted)
                 {
                     logEvent.AddPropertyIfAbsent(propertyFactory.CreateProperty("response_status", httpContext.Response.StatusCode));
                 }
            }
        }else{
            _enrichAction = enrichAction;
        }
    }
    
    
    public void Enrich(LogEvent logEvent, ILogEventPropertyFactory propertyFactory)
    {
        var httpContext = _serviceProvider.GetService<IHttpContextAccessor>()?.HttpContext;
         if (null != httpContext){
             _enrichAction.Invoke(logEvent, propertyFactory, httpContext);
         }
    }
    
}

现在，我们添加了一个记录HttpContext的Enricher，但是怎么用起来呢，怎么添加到日志对象中呢。就要靠asp.net core的中间件了。新建一个HttpContextLogMiddleware中间件：

public class HttpContextLogMiddleware
{
    private readonly RequestDelegate _next;

    public HttpContextLogMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        var serviceProvider = context.RequestServices;
        // 将我们自定义的Enricher添加到LogContext中。
        // LogContext功能很强大，可以动态添加属性，具体使用介绍，参见官方wiki文档
        using (LogContext.Push(new HttpContextEnricher(serviceProvider)))
        {
            await _next(context);
        }
    }
}

// 使用扩展方法形式注入中间件
public static IApplicationBuilder UseHttpContextLog(
    this IApplicationBuilder builder)
{
    return builder.UseMiddleware<HttpContextLogMiddleware>();
}

这样，我们就建立了一个中间件，接下来在Startup.cs的Configure方法中app.UseHttpContextLog();即可。

此处需要注意中间件的顺序，参见官方ASP.NET CORE的中间件介绍

这样，我们就添加了一个自定义的Enricher来记录请求的上下文信息。启动应用程序，看下输出结果：

asp.net core中使用Serilog以及自定义Enricher