Properly respond with sec-websocket-protocol under http/2

[coolreader18]

Motivation

Was looking at the ws code and noticed that the subprotocol never gets properly communicated to the client if the connection is HTTP/2.

Solution

Add the sec-websocket-protocol header irrespective of HTTP version. A response with that header is still a valid HTTP/2 websocket handshake, as per RFC8441.

[jplatte]

cc @SabrinaJewson

[SabrinaJewson]

Ah, looks good! Can you modify the http2 test to check for this as well? (Or write a new test)

[Turbo87]

I could click on "Approve" but I have very little knowledge about WebSocket internals, so I'd rather have those with more experience in this area chime in 😅

[yanns]

Same here, no knowledge in WS in HTTP2.
@SabrinaJewson would be more knowledgeable?

@Turbo87 You haven't approved AFAIS:

[Turbo87]

You haven't approved AFAIS

yeah, that was intentional. I didn't want to approve anything I don't have a clue about :D

[SabrinaJewson]

Yeah, sorry I didn’t say before but this looks good.

[yanns]

Should we add a changelog entry for this?

[jplatte]

We probably should, but I merged because I think asking the original author to update their PR after it previously being stuck for a month is a bit annoying.

Feel free to open a PR; otherwise I'll do it myself at some point.