falcon: request.headers['Host'] is missing

The latest release of falcon now uses http-protocol which doesn’t delete the host header.

https://github.com/socketry/http-protocol/blob/42d6bcb1d68e4e725048f6503a96b52403ed50fe/lib/http/protocol/http11/connection.rb#L128

That being said, the situation with HTTP/2 is far from clear: https://http2.github.io/http2-spec/#rfc.section.8.1.2.3

I think that #authority is a good baseline for HTTP/2 and I think that while it’s optional, it was very close to being mandatory. Some more details here:

We did not mandate use of :authority so that proxies and gateways could provide perfect fidelity in their translation from 1.1 to 2.

https://www.ietf.org/mail-archive/web/httpbisa/current/msg28630.html

I will leave this issue until we have actually confirmed that this is fixed and then I believe we should figure out ultimately what the behaviour should be like going forward:

• Should falcon serve add a host header so that rack apps that expect it continue to work? (alternatively document the current behaviour).
• Should async-http allow :authority to be optional (e.g. nil)?

I think the best option is indeed the second one: not deleting the Host header, but still extracting it for authority. I don’t think that adding it for HTTP/2 makes a lot of sense, although I guess it can be useful for compatibility.