In #6778 we found that AWS forwards HTTP headers to Lambdas from clients without modifying their casing. Since users are relying on this behavior, it effectively renders a web server that lowercases headers unusable as proxy for localstack. In general, I think there is a case to be made that web servers should not manipulate the casing of request headers, so that they can function as application-layer proxy to backends that make assumptions about header casing.

The issue of header casing for HTTP/1.1 in hypercorn was addressed with https://github.com/pgjones/hypercorn/issues/66, but later reverted with https://github.com/pgjones/hypercorn/issues/77. Apparently the relevant ASGI spec is being discussed here https://github.com/django/asgiref/issues/246 where I think we should make that case.

If this is a fundamental limitation of ASGI and we cannot get this into hypercorn, then we will be forced to either
- apologize to lambda users and tell them that they need to re-write their lambda code in a way that treats headers in a case-insensitive way
- fork hypercorn and maintain our own version
- use another webserver that does not manipulate HTTP headers, or at least allows access to the raw headers in some way
config = Config()
        config.bind = f"localhost:{net.get_free_tcp_port()}"
        loop = asyncio.new_event_loop()
        srv = HypercornServer(AsgiGateway(gateway, event_loop=loop), config, loop=loop)
        _servers.append(srv)
        srv.start()
        assert srv.wait_is_up(timeout=10), "gave up waiting for server to start up"
        return srv
    yield _create
    for server in _servers:
        server.shutdown()
        assert poll_condition(
            lambda: not server.is_up(), timeout=10
        ), "gave up waiting for server to shut down"
def test_gateway_served_through_hypercorn_preserves_client_headers(serve_gateway_hypercorn):