WebSocket: wrong subprotocol choose check (response Sec-WebSocket-Protocol header)

[farwayer]

Bug Description

1. client sends Sec-WebSocket-Protocol header with protocol list (separated by ',')
2. server responds with one protocol from this list
3. WebSocket client compares request header (protocol list) with response header (one protocol) value and fails with the error Protocol was not set in the opening handshake

undici/lib/web/websocket/connection.js

Line 179 in c49058b

if (secProtocol !== null && secProtocol !== request.headersList.get('Sec-WebSocket-Protocol')) {

Reproducible By

let ws = new WebSocket('ws://server...', ['msgpack', 'json'])
ws.addEventListener('error', e => console.log(e.error))
// server choses json and responds with `Sec-WebSocket-Protocol: json`
// client failed

Expected Behavior

Correct subprotocol check

Environment

• Node.js v21.6.2
• --experimental-websocket flag

[KhafraDev]

I will have a fix for this soon.

Relevant part of the specification:

   The client can request that the server use a specific subprotocol by
   including the |Sec-WebSocket-Protocol| field in its handshake.  If it
   is specified, the server needs to include the same field and one of
   the selected subprotocol values in its response for the connection to
   be established.

https://datatracker.ietf.org/doc/html/rfc6455#section-1.9

[kettanaito]

@KhafraDev, is there a chance to backport this to Node.js v18? This bug breaks WebSocket connections with multiple protocols.