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.

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