HttpClient.DefaultRequestHeaders.Add('X-Request-Id', "...") difference between .NET Framework and .NET Core

[vsfeedback]

This issue has been moved from a ticket on Developer Community.

---

Here's an example to reproduce the problem:

HttpClient client = new HttpClient();
var reuqestId = Guid.NewGuid();
client. DefaultRequestHeaders.Add("X-Request-Id", reuqestId.ToString());

In .NET Framework, the result of test is:

But in .NET Core (including . NET 5), 'Id' becomes 'ID':

I want to know what makes the difference. Is there any way to prevent ‘id’ become 'ID'?

---

Original Comments

Feedback Bot on 4/13/2021, 03:51 AM:

Thank you for taking the time to provide your suggestion. We will do some preliminary checks to make sure we can proceed further. We'll provide an update once the issue has been triaged by the product team.

[ghost]

Tagging subscribers to this area: @dotnet/ncl
See info in area-owners.md if you want to be subscribed.

Issue Details

---

This issue has been moved from a ticket on Developer Community.

---

Here's an example to reproduce the problem:

            HttpClient client = new HttpClient();
            var reuqestId = Guid.NewGuid();
            client. DefaultRequestHeaders.Add("X-Request-Id", reuqestId.ToString());

In .NET Framework, the result of test is :
! [1.png] (https://aka.ms/dc/image?name=Bb4265a7992364f4ab1533e53bb754885637538798104237677_1.png&tid=b4265a7992364f4ab1533e53bb754885637538798104237677)
But in .NET Core(including . NET5), 'Id' becomes 'ID':
! [2.png] (https://aka.ms/dc/image?name=B7a5a4c7bb9024fcdbb464a8c69409c7b637538800662076541_2.png&tid=7a5a4c7bb9024fcdbb464a8c69409c7b637538800662076541)
I want to know what makes the difference．
Is there any way to prevent ‘id’ become 'ID'?

---

Original Comments

Feedback Bot on 4/13/2021, 03:51 AM:

Thank you for taking the time to provide your suggestion. We will do some preliminary checks to make sure we can proceed further. We'll provide an update once the issue has been triaged by the product team.

Author:	vsfeedback
Assignees:	-
Labels:	area-System.Net, untriaged
Milestone:	-

[MihaZupan]

X-Request-ID is a known header internally, so we use a cached value of the name.
As per RFC, the name should be considered as case-insensitive.

Closing as a duplicate of #50325. That one is about TryAddWithoutValidation instead of Add, but the cause of the behaviour is the same.