Why does the. NETCORE httpclient automatically bring a requestid header when sending a request?

Agile.Zhou 2020-11-09 01:26:14
the. netcore httpclient automatically bring

Strange question

Recently, there is a system in the company that needs to call a third party webservice. Originally called a very simple thing , Use HttpClient Construct a SOAP Please send it out and get it XML That's it .
It's strange that our request will be sent to the server after running for a period of time 504 It was rejected . Make the system unusable , Users complain .
Weirdness is weird. It doesn't happen every time , It's a random query , Every time I modify the code, I release it and think it's OK ,
Two days later, it didn't work , It's so overwhelming .

Postman test

In the case of repeated debugging code failure , I suspect it's the other server's problem . So he took it out Postman Send a request test to the opposite server .
postman The problem was detected as soon as the test was carried out , No matter what you send , The server gives all of them 504 Response . Because it's accessed in the browser webservice The home page is OK , But why postman It doesn't work on the top ?
So I started checking it over and over again postman What's the difference between the requests for , It's not far from finding the problem here . After checking it over and over again, I began to suspect that postman A head problem :

Postman-Token: 4d407574-636b-9343-8216-7f2845cbeef1

postman Every time you send a request, you bring a name called postman-token The head of . So I disabled the head and tried again , Decisive success .
After repeated tests, I finally understood , The other server should be protected , as long as http Request with a custom header will be given directly 504 Response , Reject request directly .
At this point, the reason why the server refused the request finally became clear .

fiddler monitor

however , Our code sent the request without any custom headers . Should not .NET Core Do you take any headers with you when you send a request ?
So install it on the server fiddler, Pass the request fiddler Agent forward , And then monitor http The head of the request . When the system goes wrong again
Go up and check it decisively fiddler. After a look, we found the problem , All rejected requests carry a name called “Request-Id” The head of .
I was shocked ,.NetCore He even talks to himself and adds a head to me ?
If it wasn't discovered in person , I won't believe it if I kill you . Maybe you don't believe it when you see it here , I was thinking that I must be wrong .

Request-Id Where the hell did the head come from ?

This is a question that can't be solved , So he began to ask for advice google. Soon .net core runtime Of github Upper issues Found the same problem :
HttpClient automatically adds Request-Id HTTP header
The questioner said to use HttpClient The request was sent with an inexplicable addition of Request-Id, It's the same as me .
So some people began to discuss it . Some people say HttpClient It's impossible to add it yourself Request-Id This head , The elder brother below is directly in the face , say : In fact, it will , The location of the source code is also given . Smile to cry ! Later, some developers replied that this function was built-in , It's for distributed tracking .
Since the source code has been given out , Directly from the source location given by the elder brother above, start to chase the source code . Here is a general description of the source code :
HttpClient Default constructor :

 public HttpClient()
: this(new HttpClientHandler())

Keep looking inside HttpClientHandler:

 protected internal override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request,
CancellationToken cancellationToken)
return DiagnosticsHandler.IsEnabled() ?
_diagnosticsHandler.SendAsync(request, cancellationToken) :
_socketsHttpHandler.SendAsync(request, cancellationToken);

HttpClientHandler When sending a request, it will determine whether to use diagnosticsHandler To send a request . Continue to look at diagnosticsHandler Code for :

 private static void InjectHeaders(Activity currentActivity, HttpRequestMessage request)
if (currentActivity.IdFormat == ActivityIdFormat.W3C)
if (!request.Headers.Contains(DiagnosticsHandlerLoggingStrings.TraceParentHeaderName))
request.Headers.TryAddWithoutValidation(DiagnosticsHandlerLoggingStrings.TraceParentHeaderName, currentActivity.Id);
if (currentActivity.TraceStateString != null)
request.Headers.TryAddWithoutValidation(DiagnosticsHandlerLoggingStrings.TraceStateHeaderName, currentActivity.TraceStateString);
if (!request.Headers.Contains(DiagnosticsHandlerLoggingStrings.RequestIdHeaderName))
request.Headers.TryAddWithoutValidation(DiagnosticsHandlerLoggingStrings.RequestIdHeaderName, currentActivity.Id);
// we expect baggage to be empty or contain a few items
using (IEnumerator<KeyValuePair<string, string?>> e = currentActivity.Baggage.GetEnumerator())
if (e.MoveNext())
var baggage = new List<string>();
KeyValuePair<string, string?> item = e.Current;
baggage.Add(new NameValueHeaderValue(WebUtility.UrlEncode(item.Key), WebUtility.UrlEncode(item.Value)).ToString());
while (e.MoveNext());
request.Headers.TryAddWithoutValidation(DiagnosticsHandlerLoggingStrings.CorrelationContextHeaderName, baggage);
private static readonly DiagnosticListener s_diagnosticListener =
new DiagnosticListener(DiagnosticsHandlerLoggingStrings.DiagnosticListenerName);

Finally found the key position, there is a name InjectHeaders There is such a sentence in the method request.Headers.TryAddWithoutValidation(DiagnosticsHandlerLoggingStrings.RequestIdHeaderName, currentActivity.Id); among DiagnosticsHandlerLoggingStrings.RequestIdHeaderName It's a constant , Its value is "Request-Id".
Who brought it here Request-Id The problem with the head is finally hammered .

Repetition problem

The reason is found , So we started testing the solution . The first step in solving the problem is to reproduce the problem first . You use it normally HttpClient You don't take this header with you when you send a request . It's not easy to have local requests with this header . After looking at the source code, we found that it was actually with .net core Of Diagnostics Mechanisms related to . Because of the complexity of the source code logic , Directly give the code with the header :
So let's define a Observer:

 public class MyObserver<T> : IObserver<T>
private Action<T> _next;
public MyObserver(Action<T> next)
_next = next;
public void OnCompleted()
public void OnError(Exception error)
public void OnNext(T value) => _next(value);

subscribe HttpHandlerDiagnosticListener:

 DiagnosticListener.AllListeners.Subscribe(new MyObserver<DiagnosticListener>(listener =>
// Determine the name of the publisher
if (listener.Name == "HttpHandlerDiagnosticListener")
// Get subscription information
listener.Subscribe(new MyObserver<KeyValuePair<string, object>>(listenerData =>
System.Console.WriteLine($" Listen to the name :{listenerData.Key}");
dynamic data = listenerData.Value;

When we subscribe HttpHandlerDiagnosticListener When HttpClient The request sent will take this header with it . This design is really abnormal , because DiagnosticListener.AllListeners Is static , So its impact is global . In other words, I subscribe to a monitor here , It will cause all of the HttpClient They all started to wear this head .
This also explains why our program has been running for some time before it comes with Request-Id The head of . Because other modules in our program , Or the referenced third-party library will start to subscribe when it reaches a certain state HttpHandlerDiagnosticListener This monitor , Cause me to ask webservice This header is also included in the code .

solve the problem

The cause of the problem has also been found , It's happening here , Now we're going to start really solving the problem . after google Follow the source code , Must let HttpClient Don't send this Request-Id There are several ways to head .

  1. Method 1

Set up System.Net.Http.EnableActivityPropagation The switch is false

string switchName = "System.Net.Http.EnableActivityPropagation";
AppContext.SetSwitch(switchName, false);
  1. Method 2
    Configure environment variables DOTNET_SYSTEM_NET_HTTP_ENABLEACTIVITYPROPAGATIO=false

  2. Method 3

 public class DisableActivityHandler : DelegatingHandler
public DisableActivityHandler(HttpMessageHandler innerHandler) : base(innerHandler)
protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
Activity.Current = null;
return await base.SendAsync(request, cancellationToken);
var httpClient = new HttpClient(new DisableActivityHandler(new HttpClientHandler()));

This method defines a DisableActivityHandler Reconstruct HttpClient, Send the request every time Activity.Current empty .


Recently, by this Request-Id It's been a long time . I can't help but make complaints about it. , Is this built-in feature really good , Force insert custom header , Have you considered the feeling of firewall ? Or is it possible for developers to choose whether to include Diagnostic Statistics , Instead of adding headers to all requests at the beginning of a subscription somewhere , After all, we can't control whether the third-party library has any operation . If you want to turn this off Diagnostic Is it possible to be in HttpClient Instance directly gives a clear switch for developers to turn it off , Rather than what environment variables need to be configured .

ps: If using HttpWebRequest Class sending requests has the same problem , because HttpWebRequest When you send a request, you use HttpClient.

Pay attention to my official account and play with technology


  1. 【计算机网络 12(1),尚学堂马士兵Java视频教程
  2. 【程序猿历程,史上最全的Java面试题集锦在这里
  3. 【程序猿历程(1),Javaweb视频教程百度云
  4. Notes on MySQL 45 lectures (1-7)
  5. [computer network 12 (1), Shang Xuetang Ma soldier java video tutorial
  6. The most complete collection of Java interview questions in history is here
  7. [process of program ape (1), JavaWeb video tutorial, baidu cloud
  8. Notes on MySQL 45 lectures (1-7)
  9. 精进 Spring Boot 03:Spring Boot 的配置文件和配置管理,以及用三种方式读取配置文件
  10. Refined spring boot 03: spring boot configuration files and configuration management, and reading configuration files in three ways
  11. 精进 Spring Boot 03:Spring Boot 的配置文件和配置管理,以及用三种方式读取配置文件
  12. Refined spring boot 03: spring boot configuration files and configuration management, and reading configuration files in three ways
  13. 【递归,Java传智播客笔记
  14. [recursion, Java intelligence podcast notes
  15. [adhere to painting for 386 days] the beginning of spring of 24 solar terms
  16. K8S系列第八篇(Service、EndPoints以及高可用kubeadm部署)
  17. K8s Series Part 8 (service, endpoints and high availability kubeadm deployment)
  18. 【重识 HTML (3),350道Java面试真题分享
  19. 【重识 HTML (2),Java并发编程必会的多线程你竟然还不会
  20. 【重识 HTML (1),二本Java小菜鸟4面字节跳动被秒成渣渣
  21. [re recognize HTML (3) and share 350 real Java interview questions
  22. [re recognize HTML (2). Multithreading is a must for Java Concurrent Programming. How dare you not
  23. [re recognize HTML (1), two Java rookies' 4-sided bytes beat and become slag in seconds
  24. 造轮子系列之RPC 1:如何从零开始开发RPC框架
  25. RPC 1: how to develop RPC framework from scratch
  26. 造轮子系列之RPC 1:如何从零开始开发RPC框架
  27. RPC 1: how to develop RPC framework from scratch
  28. 一次性捋清楚吧,对乱糟糟的,Spring事务扩展机制
  29. 一文彻底弄懂如何选择抽象类还是接口,连续四年百度Java岗必问面试题
  30. Redis常用命令
  31. 一双拖鞋引发的血案,狂神说Java系列笔记
  32. 一、mysql基础安装
  33. 一位程序员的独白:尽管我一生坎坷,Java框架面试基础
  34. Clear it all at once. For the messy, spring transaction extension mechanism
  35. A thorough understanding of how to choose abstract classes or interfaces, baidu Java post must ask interview questions for four consecutive years
  36. Redis common commands
  37. A pair of slippers triggered the murder, crazy God said java series notes
  38. 1、 MySQL basic installation
  39. Monologue of a programmer: despite my ups and downs in my life, Java framework is the foundation of interview
  40. 【大厂面试】三面三问Spring循环依赖,请一定要把这篇看完(建议收藏)
  41. 一线互联网企业中,springboot入门项目
  42. 一篇文带你入门SSM框架Spring开发,帮你快速拿Offer
  43. 【面试资料】Java全集、微服务、大数据、数据结构与算法、机器学习知识最全总结,283页pdf
  44. 【leetcode刷题】24.数组中重复的数字——Java版
  45. 【leetcode刷题】23.对称二叉树——Java版
  46. 【leetcode刷题】22.二叉树的中序遍历——Java版
  47. 【leetcode刷题】21.三数之和——Java版
  48. 【leetcode刷题】20.最长回文子串——Java版
  49. 【leetcode刷题】19.回文链表——Java版
  50. 【leetcode刷题】18.反转链表——Java版
  51. 【leetcode刷题】17.相交链表——Java&python版
  52. 【leetcode刷题】16.环形链表——Java版
  53. 【leetcode刷题】15.汉明距离——Java版
  54. 【leetcode刷题】14.找到所有数组中消失的数字——Java版
  55. 【leetcode刷题】13.比特位计数——Java版
  56. oracle控制用户权限命令
  57. 三年Java开发,继阿里,鲁班二期Java架构师
  58. Oracle必须要启动的服务
  59. 万字长文!深入剖析HashMap,Java基础笔试题大全带答案
  60. 一问Kafka就心慌?我却凭着这份,图灵学院vip课程百度云