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

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