[WebSocketStream] Websocket handshake User-Agent header duplicated

[vinhjaxt]

Version: Deno/2.0.6

Step 1
Websocket Stream client (ws.ts):

const wss = new WebSocketStream('ws://1.1.1.1/' /* over http to see handshake request */, {
    headers: {
      'User-Agent': 'My-UA'
    }
})

const { readable, writable } = await wss.opened
console.log('Connected')

Step 2
Open Wireshark to capture websocket's http handshake request

Step 3
Run client:

deno --allow-net --unstable-net ws.ts

Result
http handshake request

GET / HTTP/1.1
host: 1.1.1.1
upgrade: websocket
connection: Upgrade
sec-websocket-key: ZZPd2TFAskpUnsM+/1fgDQ==
user-agent: Deno/2.0.6
user-agent: My-UA
sec-websocket-version: 13

=> Some web servers will concat duplicate header to one or array that leads to the wrong user-agent header

Reason
Deno set default User-Agent header value (array) into a fetch request
Deno append new headers of WebSocketStream into existing fetch's headers array