System.Net.Http.DiagnosticsHandler.InjectHeaders does not add baggage to the existing header in the request header

[efanovroman]

Description

1. DiagnosticsHandler the class has a method InjectHeaders, which is executed when transferring activity fields to the request header

{
    _propagator.Inject(currentActivity, request, static (carrier, key, value) =>
    {
        if (carrier is HttpRequestMessage request &&
            key is not null &&
            HeaderDescriptor.TryGet(key, out HeaderDescriptor descriptor) &&
            !request.Headers.TryGetHeaderValue(descriptor, out _))
        {
            request.Headers.TryAddWithoutValidation(descriptor, value);
        }
    );
}

2. I have a custom SamplePropagator : DistributedContextPropagator which has overridden the InjectBaggage method

   {
   using var e = baggage.GetEnumerator();
   if (e.MoveNext())
   {
       var baggageList = new StringBuilder();
       do
       {
           KeyValuePair<string, string> item = e.Current;
           baggageList.Append(WebUtility.UrlEncode(item.Key))
           .Append('=')
           .Append(WebUtility.UrlEncode(item.Value))
           .Append(CommaWithSpace);
       } while (e.MoveNext());
       setter(carrier, HeaderNames.Baggage, baggageList.ToString(0, baggageList.Length - 2));
   }
   }

Thus the activity baggage is transferred to the request headers baggage

3. If at the time of calling DiagnosticsHandler.InjectHeaders there is already baggage in the request header (in my case I use the Sentry package Sentry.AspNetCore, which adds various values ​​to the baggage header before this) then the DiagnosticsHandler code on line 474 request.Headers.TryAddWithoutValidation(descriptor, value); is not executed because the condition !request.Headers.TryGetHeaderValue(descriptor, out _) on line 372 is not satisfied.

4. However, the HttpRequestHeaders.TryAddWithoutValidation method handles the case of adding a new header to an existing value

   HttpRequestMessage t = new HttpRequestMessage();
   t.Headers.TryAddWithoutValidation(HeaderNames.Baggage, "sentry=123");
   t.Headers.TryAddWithoutValidation(HeaderNames.Baggage, "id=123");

result: "[baggage, System.String[]]";baggage;"[sentry=123, id=123]"

Problems I am losing baggage from the current activity because it is not added to the existing header in the request

Configuration .NET Core 8, on windows 10 Propagator SamplePropagator.txt DiagnosticSample DiagnosticSample.txt RequestIdController RequestIdController.txt Startup

{
    services.AddHttpClient("myApi");
    services
        .AddControllers()
        .AddNewtonsoftJson(options =>
        {
            options.SerializerSettings.Converters.Add(new Newtonsoft.Json.Converters.StringEnumConverter());
        })
        .AddDefaultMvcServices();
    services.TryAddEnumerable(ServiceDescriptor.Singleton<IDiagnosticObserver, DiagnosticSample>());
    SamplePropagator.Init();
}

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