WebSocketStream throws internal error when cannot open an connection

[piotr-cz]

Bug Description

WebSocketStream throws fatal error when it fails to open an connection

Reproducible By

import { WebSocketStream } from 'undici'

const stream = new WebSocketStream('https://not-a-ws-server.com/')

Expected Behavior

Package should not throw an error that is not possible to catch

Logs & Screenshots

TypeError: Cannot read properties of undefined (reading 'closingInfo')
    at #onSocketClose (xxx\node_modules\undici\lib\web\websocket\stream\websocketstream.js:373:33)
    at Object.onSocketClose (xxx\node_modules\undici\lib\web\websocket\stream\websocketstream.js:65:45)
    at failWebsocketConnection (xxx\node_modules\undici\lib\web\websocket\connection.js:318:13)
    at Object.processResponse (xxx\node_modules\undici\lib\web\websocket\connection.js:103:11)
    at xxx\node_modules\undici\lib\web\fetch\index.js:1078:19
    at node:internal/process/task_queues:151:7
    at AsyncResource.runInAsyncScope (node:async_hooks:214:14)
    at AsyncResource.runMicrotask (node:internal/process/task_queues:148:8)
    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)

Environment

Windows, Node v24.4.0, undici v7.18.2

Additional context

This is because this.#parser is being set after connection has been established:

undici/lib/web/websocket/stream/websocketstream.js

Lines 258 to 265 in 7e5cb2d

	#onConnectionEstablished (response, parsedExtensions) {
	this.#handler.socket = response.socket
	const parser = new ByteParser(this.#handler, parsedExtensions)
	parser.on('drain', () => this.#handler.onParserDrain())
	parser.on('error', (err) => this.#handler.onParserError(err))
	this.#parser = parser

but is being accessed before:

undici/lib/web/websocket/stream/websocketstream.js

Line 373 in 7e5cb2d

const result = this.#parser.closingInfo

This behavior has been introduced by #4521 and has also been described here: #3546 (comment)

[piotr-cz]

When running similar code in Chrome browser, there is no error thrown, just promises are rejected:

await stream.opened
// Uncaught WebSocketError: WebSocket closed before handshake complete.

await stream.closed
// Uncaught WebSocketError: WebSocket was not cleanly closed.