HttpClientFactory日志不好用，自己扩展一个？

.NetCore2.1新推出 HttpClientFactory 工厂类， 替代了早期的 HttpClient ，并新增了弹性Http调用机制 (集成 Policy 组件)。

HttpClientFactory 以一种模块化、可命名、弹性可预期的方式重建了HttpClient的使用方式。HttpClientFactory以依赖注入的方式集成到.NETCore 框架：

HttpClientFactory典型用法

使用时从IHttpClientFactory工厂创建所需HttpClient实例，发起业务端请求。

观察Info级别日志：

19/12/04 11:06:46 [Info].[System.Net.Http.HttpClient.bce-request.LogicalHandler].[18}].[]
Start processing HTTP request GET http://localhost:5000/v1/eqid/b827a9400004132a000000065dc26470 19/12/04 11:06:46 [Info].[System.Net.Http.HttpClient.bce-request.ClientHandler].[18}].[]
Sending HTTP request GET http://localhost:5000/v1/eqid/b827a9400004132a000000065dc26470 19/12/04 11:06:46 [Info].[System.Net.Http.HttpClient.bce-request.ClientHandler].[34}].[]
Received HTTP response after 174.5088ms - OK 
19/12/04 11:06:46 [Info].[System.Net.Http.HttpClient.bce-request.LogicalHandler].[34}].[]
End processing HTTP request after 211.1478ms - OK

一切都是那么自然、优雅。

头脑风暴

观察上面 单次请求的日志 ，由外层 LogicHandler 和内层 ClientHandler 日志头组成。这样的日志可以想象到有2个问题：

因此本文打算重新构建 HttpClientFactory日志： 给某次请求的全部日志设置TraceId

结合我给出的典型用法来看IHttpClientFactory组件原理：

示例中 System.Net.Http.HttpClient.bce-request.LogicalHandler ， System.Net.Http.HttpClient.bce-request.ClientHandler  日志头即是来自 LoggingScopeHttpMessageHandler  ，LoggingHttpMessageHandler 两个处理器。

给出手绘的UML类图： 

本次要扩展的入口便是 IHttpMessageHandlerFilter 接口，核心是自定义DelegatingHandler日志处理器。

编程实践

如以上分析，使用aspNetCore2.2需要做如下扩展：

P1

实现IHttpMessageHandlerFilter接口，移除接口中默认的2个日志处理器

public class TraceIdLoggingMessageHandlerFilter : IHttpMessageHandlerBuilderFilter
    {
        private readonly ILoggerFactory _loggerFactory;

        public TraceIdLoggingMessageHandlerFilter(ILoggerFactory loggerFactory)
        {
            _loggerFactory = loggerFactory ?? throw new ArgumentNullException(nameof(loggerFactory));
        }

        public Action<HttpMessageHandlerBuilder> Configure(Action<HttpMessageHandlerBuilder> next)
        {
            if (next == null)
            {
                throw new ArgumentNullException(nameof(next));
            }

            return (builder) =>
            {
                // Run other configuration first, we want to decorate.
                next(builder);

                var outerLogger =_loggerFactory.CreateLogger($"System.Net.Http.HttpClient.{builder.Name}.LogicalHandler");
                builder.AdditionalHandlers.Clear();
                builder.AdditionalHandlers.Insert(0,new CustomLoggingScopeHttpMessageHandler(outerLogger));
            };
        }
    }

P2

实现带有TraceId能力的HttpClient 日志处理器，并加入到IHttpMessageHandlerFilter接口实现类

public class CustomLoggingScopeHttpMessageHandler : DelegatingHandler
    {
        private readonly ILogger _logger;

        public CustomLoggingScopeHttpMessageHandler(ILogger logger)
        {
            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
        }

        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request,
            CancellationToken cancellationToken)
        {
            if (request == null)
            {
                throw new ArgumentNullException(nameof(request));
            }

            using (Log.BeginRequestPipelineScope(_logger, request))
            {
                Log.RequestPipelineStart(_logger, request);
                var response = await base.SendAsync(request, cancellationToken);
                Log.RequestPipelineEnd(_logger, response);

                return response;
            }
        }

        private static class Log
        {
            private static class EventIds
            {
                public static readonly EventId PipelineStart = new EventId(100, "RequestPipelineStart");
                public static readonly EventId PipelineEnd = new EventId(101, "RequestPipelineEnd");
            }

            private static readonly Func<ILogger, HttpMethod, Uri, string, IDisposable> _beginRequestPipelineScope =
                LoggerMessage.DefineScope<HttpMethod, Uri, string>(
                    "HTTP {HttpMethod} {Uri} {CorrelationId}");

            private static readonly Action<ILogger, HttpMethod, Uri, string, Exception> _requestPipelineStart =
                LoggerMessage.Define<HttpMethod, Uri, string>(
                    LogLevel.Information,
                    EventIds.PipelineStart,
                    "Start processing HTTP request {HttpMethod} {Uri} [Correlation: {CorrelationId}]");

            private static readonly Action<ILogger, HttpStatusCode,string,Exception> _requestPipelineEnd =
                LoggerMessage.Define<HttpStatusCode,string>(
                    LogLevel.Information,
                    EventIds.PipelineEnd,
                    "End processing HTTP request - {StatusCode}, [Correlation: {CorrelationId}]");

            public static IDisposable BeginRequestPipelineScope(ILogger logger, HttpRequestMessage request)
            {
                var correlationId = GetCorrelationIdFromRequest(request);
                return _beginRequestPipelineScope(logger, request.Method, request.RequestUri, correlationId);
            }

            public static void RequestPipelineStart(ILogger logger, HttpRequestMessage request)
            {
                var correlationId = GetCorrelationIdFromRequest(request);
                _requestPipelineStart(logger, request.Method, request.RequestUri, correlationId, null);
            }

            public static void RequestPipelineEnd(ILogger logger, HttpResponseMessage response)
            {
                var correlationId = GetCorrelationIdFromRequest(response.RequestMessage);
                _requestPipelineEnd(logger, response.StatusCode, correlationId, null);
            }

            private static string GetCorrelationIdFromRequest(HttpRequestMessage request)
            {
                string correlationId = Guid.NewGuid().ToString();
                if (request.Headers.TryGetValues("X-Correlation-ID", out var values))
                    correlationId = values.First();
                else
                    request.Headers.Add("X-Correlation-ID",correlationId);
                return correlationId;
            }
        }
    }

以上TraceId的实现思路，参考了我前一篇博文《 被忽略的TraceId，可以用起来了 》的思路，为每次HttpClient调用过程设定  全局唯一的GUID标记， 后置api服务可酌情修改以上代码处理。》 其中写入日志的代码Copy自HttpClientFactory源代码。

P3

在DI框架中替换原有的IHttpMessageHandlerFilter实现

services.Replace(ServiceDescriptor.Singleton<IHttpMessageHandlerBuilderFilter, TraceIdLoggingMessageHandlerFilter>());

发起两次HttpClient请求， 输出的日志如下:

19/12/04 12:59:22 [Info].[System.Net.Http.HttpClient.bce-request.LogicalHandler].[17}].[]
Start processing HTTP request GET http://localhost:5000/v1/eqid/ad78deef00444ed7000000035de704e8 [Correlation: 03de676d-680e-4a92-aef5-749bcc3ba499]
19/12/04 12:59:22 [Info].[System.Net.Http.HttpClient.bce-request.LogicalHandler].[4}].[]
End processing HTTP request - OK, [Correlation: 03de676d-680e-4a92-aef5-749bcc3ba499]
19/12/04 12:59:48 [Info].[System.Net.Http.HttpClient.bce-request.LogicalHandler].[17}].[]
Start processing HTTP request GET http://localhost:5000/v1/eqid/8ea0c3b66b60f0ff100000005de704fb [Correlation: 6f14393a-3a2b-45c4-a9b4-0b4ab874ef1d]
19/12/04 12:59:48 [Info].[System.Net.Http.HttpClient.bce-request.LogicalHandler].[42}].[]
End processing HTTP request - OK, [Correlation: 6f14393a-3a2b-45c4-a9b4-0b4ab874ef1d]

可以看到每次请求的开始和结束都带上了设定的GUID TraceId。

That's All， 这是本次解决HttpCl ient日志无法追踪的思路和方案， 思考+实践+UML制图，希望能给 大家一些启发。

+ https://github.com/aspnet/HttpClientFactory/blob/master/src/Microsoft.Extensions.Http/Logging/LoggingHttpMessageHandlerBuilderFilter.cs

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