前言

　　.NetCore2.1新推出HttpClientFactory工廠類， 替代了早期的HttpClient，并新增了彈性Http調用機制 (集成Policy組件)。

替換的初衷還是簡單說下：

①? using(var client= new HttpClient()) 調用Dispose()方法，并不會很快釋放底層Socket連接，同時新建Socket需要時間，這在高并發場景下Socket耗盡。?傳送門

②? 由于①很多人會想到用單例或靜態類構建HttpClient實例，但是這里還有一個坑，HttpClient會忽略DNS的變化。?傳送門

HttpClientFactory 以一種模塊化、可命名、彈性可預期的方式重建了HttpClient的使用方式。HttpClientFactory以依賴注入的方式集成到.NETCore 框架：

?HttpClientFactory典型用法

使用時從IHttpClientFactory工廠創建所需HttpClient實例，發起業務端請求。

觀察Info級別日志：

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、優雅。

頭腦風暴

　　觀察上面單次請求的日志，由外層LogicHandler和內層ClientHandler?日志頭組成。這樣的日志可以想象到有2個問題：

① 在高并發使用HttpClient，日志條數眾多，沒有類似TraceId 這樣的機制定位 某次HttpClient調用的完整日志。?

?②? 若是微服務/ 分布式調用，可能還有 將本次HttpClient調用日志與后置api日志 結合分析的需求， 這個日志也支持不了。

因此本文打算重新構建 HttpClientFactory日志：給某次請求的全部日志設置TraceId

結合我給出的典型用法來看IHttpClientFactory組件原理：

示例中System.Net.Http.HttpClient.bce-request.LogicalHandler，System.Net.Http.HttpClient.bce-request.ClientHandler?日志頭即是來自LoggingScopeHttpMessageHandler?，LoggingHttpMessageHandler 兩個處理器。

給出手繪的UML類圖：?

?

本次要擴展的入口便是IHttpMessageHandlerFilter接口，核心是自定義DelegatingHandler日志處理器。

編程實踐

? ?如以上分析，使用aspNetCore2.2需要做如下擴展：

P1

實現IHttpMessageHandlerFilter接口，移除接口中默認的2個日志處理器

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

?實現帶有TraceId能力的HttpClient?日志處理器，并加入到IHttpMessageHandlerFilter接口實現類

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的實現思路，參考了我前一篇博文《被忽略的TraceId，可以用起來了》的思路，為每次HttpClient調用過程設定? 全局唯一的GUID標記， 后置api服務可酌情修改以上代碼處理。》其中寫入日志的代碼Copy自HttpClientFactory源代碼。

P3

?在DI框架中替換原有的IHttpMessageHandlerFilter實現

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

發起兩次HttpClient請求， 輸出的日志如下:

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]

可以看到每次請求的開始和結束都帶上了設定的GUID TraceId。

Tip

?① 這個TraceId 可以使用你業務上獨具一格的標記，這樣在排查時， 能根據上游業務更好的追蹤日志。

?② 目前這個TraceId位于LogMessage，實際上可以為nlog自定義LogoutRenderer，將該TraceId放在顯著位置，便于ETL等日志集成框架過濾。

That's All， 這是本次解決HttpClient日志無法追蹤的思路和方案，思考+實踐+UML制圖，希望能給大家一些啟發。

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

掃一掃左邊二維碼，
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............

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