Asp.net core default headers

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Hey there.

I am having a very interesting scenario, when asp.net core app adds something additional to my headers. I am inspecting all incoming requests and using the middleware to to inspect headers before processing the request:

public async Task Invoke(HttpContext httpContext)
{
    if (httpContext.Request.Headers.Keys.ToArray()[0] != "UserKey")
    {
        throw new Exception("Wrong header order");
    }

    await _next(httpContext);
}

I have also set this in startup.cs:

<pre>public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }

    // do this before others
    app.UseMiddleware<HeaderHandlingMiddleware>();

    app.UseMvc();
}

Though for some reason when I try to inspect the headers during the time request is in middleware I can see that some default headers been added for "Connection" and "Keep-Alive". And these were set on top (meaning they are first in the header collection).
I tried doing manual request with Fiddler like that:

GET http://localhost:49669/headers HTTP/1.1
Key_1: Value_1
Key_2: Value_2
Key_3: Value_3
Host: localhost:49669
Connection: Close

But still - when I inspect the headers I can see that Connection was set to "Keep-Alive" and the header ordering has been lost.
Any idea where to look?
Maybe there is some additional event I can attach to (without using the middleware)?

br,
m

What I have tried:

Tried using middleware class but that did not quiet help.

Posted 7-Jun-18 0:47am

MK-Gii

Updated 7-Jun-18 4:45am

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Richard Deeming · Answer 1 · 2018-06-07T04:47:00

That's nothing to do with ASP.NET; those headers are being sent the client.

RFC2616, section 4.2[^]:
The order in which header fields with differing field names are received is not significant. However, it is "good practice" to send general-header fields first, followed by request-header or response-header fields, and ending with the entity-header fields.

Most clients will put "general" headers - like Connection and Keep-Alive - before any other headers.

Relying on headers being sent in a specific order is extremely fragile, and will break almost immediately.

Instead, you should test whether the headers dictionary contains the expected header:

C#

public async Task Invoke(HttpContext httpContext)
{
    if (!httpContext.Request.Headers.ContainsKey("UserKey"))
    {
        throw new InvalidOperationException("Required header is missing.");
    }

    await _next(httpContext);
}