kubectl-proxy changes http-header-keys to capitalized

[faxjiangyi]

What happened:
When I am using kubectl proxy, the past proxy http request header keys are converted to initial capital.

What you expected to happen:
HTTP/1.1
According to RFC 7230, section 3.2:

Each header field consists of a case-insensitive field name followed by a colon (":"), optional leading whitespace, the field value, and optional trailing whitespace.

HTTP/2.0
Quoting RFC 7540, section 8.1.2:

Just as in HTTP/1.x, header field names are strings of ASCII
characters that are compared in a case-insensitive fashion.

How to reproduce it (as minimally and precisely as possible):
Use kubectl proxy and log all headers in svc-pods

Anything else we need to know?:
Happened both in aks and local k3s.
I'm not sure if this is a bug or intended?

Environment:
aks

Client Version: v1.29.4
Kustomize Version: v5.0.4-0.20230601165947-6ce0bf390ce3
Server Version: v1.28.9

local

Client Version: v1.29.4
Kustomize Version: v5.0.4-0.20230601165947-6ce0bf390ce3
Server Version: v1.29.3+orb1

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[ardaguclu]

Since the headers are case-insensitive, does it matter that these headers are capitalized or not?. Wouldn't eventually all be considered as same?.

[faxjiangyi]

Since the headers are case-insensitive, does it matter that these headers are capitalized or not?. Wouldn't eventually all be considered as same?.

Thanks for your reply.
I don't think it's a serious problem, but I would like to understand why kubectl proxy capitalizes headers.

[ChetHosey]

Looking through the code, the proxy command's RunProxy method calls Server.ServeOnListener, which itself starts an http.Server instance listening for requests on the requested address and port or Unix socket. When a request is received the http.Server instance creates an http.Request object and passes it to a handler.

Go's http package defines a canonical header format, in which the first letter and any letter immediately following a hyphen are upper-cased and all others are converted to lowercase. Methods on the Header type automatically convert names to canonical form.

So this looks like a Go implementation detail rather than something done deliberately by kubectl proxy.

[sftim]

/priority awaiting-more-evidence

per #1673 (comment)