fix header casing for Twisted WebSockets

[bentsku]

Motivation

While implementing a service that uses WebSockets, I realized we were not keeping header casing with WebSockets served over Twisted, but we would in ASGI.

This was due to a workaround with the saved rolo.headers that is not executed in this code path while creating the WebSocketRequest.

I've ported the fix over there, and it's exactly the same code that is living in wsgi.py. However, there isn't really a place for those kind of... utils? So for now it is duplicated.

While testing the fix, I realized it was actually fixing the issue in my code served over LocalStack, but was still failing in the unit tests.
This is because the test was served over a simple Site, when you are supposed to serve it over a WsgiGateway, which contains some logic to preserve header casing. In order to not complicate the unit tests by requiring everything to be a rolo Gateway, I've applied the fix for the WebSockets Site fixture by adding the site.protocol = HeaderPreservingHTTPChannel.protocol_factory like we would in the twisted.WsgiGateway.

Changes

• update the tests to cover cased headers
• update the serve_twisted_websocket_listener to be closer to how Twisted should actually be used (with the Gateway)
• fix the logic by adding the restoration of header casing before creating the SansIO Request

[alexrashed]

Awesome! Thanks for jumping on this and fixing the header casing in the Websocket implementation! I added some PR comments with some questions I have, once we discussed those we should be good to go! 🚀 🦸🏽

[alexrashed]

Thanks for the detailed explanations on the questions! The changes are looking great! Kudos for proactively jumping on fixing the issue here in rolo! 🦸🏽 💯