.NET 6中通过中间件将Correlation ID传入Serilog文件日志的问题

以下是针对性的解决步骤，按顺序排查调整即可：

1. 启用Serilog的LogContext增强 #

Serilog默认不会自动读取LogContext中的属性，必须在配置里显式开启这个功能。在Program.cs的Serilog配置代码中添加Enrich.FromLogContext()：

var builder = WebApplication.CreateBuilder(args);

builder.Host.UseSerilog((context, config) =>
    config
        .ReadFrom.Configuration(context.Configuration)
        .Enrich.FromLogContext() // 关键配置：开启LogContext属性采集
        .Enrich.WithMachineName()
        .Enrich.WithEnvironmentName()
        .WriteTo.File("logs/log-.txt", rollingInterval: RollingInterval.Day));

2. 调整中间件注册顺序 #

CorrelationIdHandler必须在Serilog请求日志中间件（UseSerilogRequestLogging()）以及路由、端点中间件之前注册，这样才能确保记录日志前，Correlation ID已经被放入LogContext。

修改Program.cs中的中间件顺序：

var app = builder.Build();

// 先注册CorrelationId中间件
app.UseMiddleware<CorrelationIdHandler>();

// 再注册Serilog请求日志中间件
app.UseSerilogRequestLogging();

// 后续是其他业务中间件
app.UseRouting();
app.UseAuthorization();

app.MapControllers();

app.Run();

3. 修正CorrelationIdHandler的类型兼容性问题 #

原代码中使用StringValues作为Correlation ID的类型，虽然可以隐式转换为字符串，但显式转换能避免潜在的序列化问题，确保LogContext能正确识别属性值：

修改后的CorrelationIdHandler代码：

using AspNet.CorrelationIdGenerator;
using Serilog.Context;

namespace MyService.Middlewares.CorrelationId;

public class CorrelationIdHandler
{
    private readonly RequestDelegate _next;
    private const string _correlationIdHeader = "X-Correlation-Id";

    public CorrelationIdHandler(RequestDelegate next) => _next = next;

    public async Task Invoke(HttpContext context, ICorrelationIdGenerator correlationIdGenerator)
    {
        var correlationId = GetCorrelationId(context, correlationIdGenerator);
        AddCorrelationIdHeaderToResponse(context, correlationId);
        using (LogContext.PushProperty(_correlationIdHeader, correlationId))
        {
            await _next(context);
        }
    }

    private static string GetCorrelationId(HttpContext context, ICorrelationIdGenerator correlationIdGenerator)
    {
        if (context.Request.Headers.TryGetValue(_correlationIdHeader, out var correlationId))
        {
            var id = correlationId.ToString();
            correlationIdGenerator.Set(id);
            return id;
        }
        else
        {
            return correlationIdGenerator.Get().ToString();
        }
    }

    private static void AddCorrelationIdHeaderToResponse(HttpContext context, string correlationId)
        => context.Response.OnStarting(() =>
        {
            context.Response.Headers.Add(_correlationIdHeader, correlationId);
            return Task.CompletedTask;
        });
}

验证结果 #

完成以上修改后重启API，发起请求后查看日志文件，就能在Properties字段中看到X-Correlation-Id的记录：

{
  "Timestamp": "2022-08-19T23:22:04.1299119+00:00",
  "Level": "Information",
  "MessageTemplate": "{\"Id\":\"-1\"}",
  "RenderedMessage": "{\"Id\":\"-1\"}",
  "Properties": {
    "X-Correlation-Id": "1ff3d20e-e8a3-4cb3-a5ab-3b0f3c50b2fc",
    "MachineName": "VMA",
    "ApplicationName": "MyService",
    // 其他原有属性...
  }
}

内容的提问来源于stack exchange，提问作者tRuEsAtM