id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
32586	ASGI responses from Django do not provide lowercased HTTP headers as required by the spec	Myers Carpenter	nobody	"Every time HTTP headers are talked about in the ASGI spec it always says: ""Header names must be lowercased."" 

They never explain why they should be in lowercase, which maybe is a bug in the spec, but it turns out http headers are to be treated case insensitively https://stackoverflow.com/questions/5258977/are-http-headers-case-sensitive

Using Django 3.1.7 and uvicorn and adding a ASGI middleware like this:

{{{
class SpamMiddleware:
    def __init__(self, app):
        self.app = app

    async def __call__(self, scope, receive, send):
        print(f""start {scope!r}"")
        async def send_wrapper(message):
            print(f""send {message!r}"")
            return await send(message)
        async def receive_wrapper():
            message = await receive()
            print(f""receive {message!r}"")
            return message

        return await self.app(scope, receive_wrapper, send_wrapper)
}}}

you can see that django does not follow the spec:

{{{
send {'type': 'http.response.start', 'status': 200, 'headers': [(b'Content-Type', b'application/javascript; charset=""utf-8""'), (b'X-Frame-Options', b'DENY'), (b'Vary', b'Cookie'), (b'Content-Length', b'189761')]}
}}}

A possible fix (and I would be happy to make a PR) is to add a call to {{{.lower()}}} on the header name on https://github.com/django/django/blob/76c0b32f826469320c59709d31e2f2126dd7c505/django/core/handlers/asgi.py#L227

The upside, beyond being spec compliant, would be that middleware that need to filter/modify headers wouldn't need to apply {{{.lower()}}} themselves.

This all came up because I'm attempting to add the zerocopysend extension to uvicorn and middleware to translate the X-Sendfile header from django-sendfile2 to using zerocopysend.
"	Bug	closed	HTTP handling	3.1	Normal	invalid		Andrew Godwin Carlton Gibson	Unreviewed	0	0	0	0	0	0