HttpClientFactory 日志不好用，自己扩展一个？

前言

　　.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。

现在的HttpClientFactory以依赖注入的方式集成到.NETCore 框架：

// 截取自Startup.cs文件服务配置部分
public void ConfigureServices(IServiceCollection services)
{
services.AddHttpClient("bce-request", x =>
x.BaseAddress = new Uri(Configuration.GetSection("BCE").GetValue<string>("BaseUrl")))
.ConfigurePrimaryHttpMessageHandler(_ => new BceAuthClientHandler()
{
AccessKey = Configuration.GetSection("BCE").GetValue<string>("AccessKey"),
SerectAccessKey = Configuration.GetSection("BCE").GetValue<string>("SecretAccessKey"),
AllowAutoRedirect = true,
UseDefaultCredentials = true
})
.SetHandlerLifetime(TimeSpan.FromHours(12))
.AddPolicyHandler(GetRetryPolicy(3));
}

static IAsyncPolicy<HttpResponseMessage> GetRetryPolicy(int  retry)
{
var retryPolicy = HttpPolicyExtensions
.HandleTransientHttpError()
.OrResult(msg => msg.StatusCode == System.Net.HttpStatusCode.NotFound)
.WaitAndRetryAsync(retry, retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)));
return retryPolicy;
}

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：

 ① 在高并发使用HttpClient，日志条数众多，没有类似TraceId 这样的机制定位 某次HttpClient调用的完整日志。 

 ②  若是微服务/ 分布式调用，可能还有 将本次HttpClient调用日志与后置api日志 结合分析的需求， 这个日志也支持不了。

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

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

编程实践

   如以上分析，

P1  实现 IHttpMessageHandlerFilter接口，在接口中移除默认的两个日志处理器；

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 HttpClient 日志无法追踪的思路和方案， 思考 + 实践 + UML制图，希望能被大家一些启发。