Consider introducing rack.protocol env variable.

[ioquatix]

To correctly handle WebSockets, HTTP/1 requires the use of the upgrade headers, while HTTP/2 requires the use of :protocol pseudo header.

We don't have any mechanism like we discussed in #1878 for putting these pseudo headers into env.

Therefore, I've been using rack.protocol and mapping it specially.

• In HTTP/1, the upgrade header is mapped to rack.protocol, can contain multiple values, and the 101 response should include the specific protocol upgrade. Response should include rack.protocol to indicate an upgrade.
• In HTTP/2, the :protocol pseudo header is mapped to rack.protocol, can only contain a single value, and the 200 response indicates that the stream will transport that protocol.

Another option is to map HTTP/2 :protocol header to env["HTTP_UPGRADE"] although this feels a little ugly, and the same with the response header. HTTP/2 RFCs explicitly call out that this is invalid, that the headers are not the same. However, if we consider rack through the lens of a CGI gateway, this is probably acceptable - except that we don't do this strictly for other features.

If we can discuss this and get agreement on a specification, I'll create a PR. This is not urgent, but it would be nice to have, and to be compatible with Falcon's existing behaviour where possible. If not, it's okay to change.

[ioquatix]

Another example of this problem: socketry/falcon#202