Choose websocket subprotocol preffered by client

[KSDaemon]

From the Websocket RFC6455:

For client side:

|Sec-WebSocket-Protocol| header field, with a list of values indicating which protocols the client would like to speak, ordered by preference.

And for server side:

Either a single value representing the subprotocol the server is ready to use or null. The value chosen MUST be derived from the client's handshake, specifically by selecting one of the values from the |Sec-WebSocket-Protocol| field that the server is willing to use for this connection (if any).

So if the client provides a few options for subprotocol. The server should choose the first one it supports.

Right now, if client provides a few options, Nexus choose the first one it supports (and not the first one from the client). And first in list is json.

So if the client sends Sec-WebSocket-Protocol: wamp.2.cbor, wamp.2,json → Nexus will choose json and not the cbor

[KSDaemon]

As I figured out, the problem is in the underlying gorilla/websocket library.
Made a fix PR there...

Refs:

• [bug] Websocket subprotocol is not chosen on client preferance gorilla/websocket#822
• Fixes subprotocol selection (aling with rfc6455) gorilla/websocket#823

[KSDaemon]

So even the original author agrees that that is bug and fix is ok. But as there is no maintainer in websocket project (4 years looking for new maintainer) — fix can stuck for ages.....

@gammazero What do you think? Maybe we can switch to fork with bugfix temporarily? As websocket library development is mostly frozen,  I don't expect any new features to come soon (and even bugfixes are very slow to get into the codebase). So we won't lose much with bugfix-fork dependency.

[KSDaemon]

So maybe we can switch someday to something else, like https://github.com/lesismal/nbio. (We use it internally, pretty good XP, speed)

[KSDaemon]

@gammazero what do you think? Please have a look when you have time. This one is pretty small but important question

[om26er]

gorilla project has been archived since last year. So now we are on our own for this one https://github.com/gorilla/websocket

[gammazero]

I am fine with switching to another websocket implementation if we need to, but it looks like gorilla/websocket is now actively maintained again so would prefer to stay with it.

[KSDaemon]

Wow! It took just about 1 year and few weeks till my PR with the Web Socket subprotocol fix landed in the upstream library! Now we can finally update the dependency!)