Add support for Sec-WebSocket-Protocol to HTTP::WebSocketHandler

[antondalgren]

Closes #15547

[Sija]

Suggestion: prefer early returns.

Suggested change

	requested_protocols = request.headers["Sec-WebSocket-Protocol"]?
	return nil unless requested_protocols
	if supported_protocols = @protocols
	requested_protocols.split(",").each do |protocol|
	protocol = protocol.strip
	if supported_protocols.includes? protocol
	return protocol
	end
	end
	end
	return unless requested_protocols = request.headers["Sec-WebSocket-Protocol"]?
	return unless supported_protocols = @protocols
	requested_protocols.split(',').each do |protocol|
	protocol = protocol.strip
	return protocol if protocol.in?(supported_protocols)
	end

[spuun]

I'd like to see the possibility to have regex in the supported protocol list. Sometimes you'd like to "catch all", like ^mqtt.

I have a feeling that even though we have the IANA WebSocket Subprotocol Name Registry not all implementations will follow this strictly. E.g. a client will send mqtt for mqtt 5, another will send mqtt for mqtt 3.1.1 and a third will send mqtt5 for mqtt 5`.

If I can configure the handler to accept any matching ^mqtt and the response header will be set to the request header, it's up the sub-protocol to handle the version check.

[straight-shoota]

@spuun I'm not sure about this... It seems like a relatively simple addition. But then it also adds a bit of complexity and I find it hard to assess. Maybe we could defer this to a follow-up discussion?

Websocket subprotocol matching is intentionally very simple. Adding regex to that makes it carry quite a bit more weight and seems overpowered. It may also open opportunities for DoS.

Potential alternatives would be to allow specifying a custom handler for subprotocol matching. That would give users full flexibility to implement matching however they want. It might be even more overpowered, though.
Instead of full regex support, it seems your described use case could be met with prefix matching. Maybe we could only implement that instead of full regex support to keep things simpler?

[ysbaddaden]

A customizable subprotocol handler proc actually sounds great 🤔
But let's see that in a follow up.

[Sija]

Suggestion: simplification

Suggested change

	if supported_protocols.includes? protocol
	return protocol
	end
	return protocol if protocol.in?(supported_protocols)