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

Irving the procedural ape 2020-11-09 02:35:12
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 It's strange that our request will be sent to the server after 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); } } } else { 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>(); do { KeyValuePair<string, string?> item = e.Current; baggage.Add(new NameValueHeaderValue(WebUtility.UrlEncode(item.Key), WebUtility.UrlEncode(item.Value)).ToString()); } while (e.Mov.........
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