Fixes#23474
## Summary
When `request.cookies.set()` is called before `server.upgrade()`, the
cookies are now properly included in the WebSocket upgrade response
headers.
## Problem
Previously, cookies set on the request via `req.cookies.set()` were only
written for regular HTTP responses but were ignored during WebSocket
upgrades. Users had to manually pass cookies via the `headers` option:
```js
server.upgrade(req, {
headers: {
"Set-Cookie": `SessionId=${sessionId}`,
},
});
```
## Solution
Modified `src/bun.js/api/server.zig` to check for and write cookies to
the WebSocket upgrade response after the "101 Switching Protocols"
status is set but before the actual upgrade is performed.
The fix handles both cases:
- When `upgrade()` is called without custom headers
- When `upgrade()` is called with custom headers
## Testing
Added comprehensive regression tests in
`test/regression/issue/23474.test.ts` that:
- Verify cookies are set in the upgrade response without custom headers
- Verify cookies are set in the upgrade response with custom headers
- Use `Promise.withResolvers()` for efficient async handling (no
arbitrary timeouts)
Tests confirmed:
- ❌ Fail with system bun v1.2.23 (without fix)
- ✅ Pass with debug build v1.3.0 (with fix)
## Manual verification
```bash
curl -i -H "Connection: Upgrade" -H "Upgrade: websocket" \
-H "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==" \
-H "Sec-WebSocket-Version: 13" \
http://localhost:3000/ws
```
Response now includes:
```
HTTP/1.1 101 Switching Protocols
Set-Cookie: test=123; Path=/; SameSite=Lax
Upgrade: websocket
Connection: Upgrade
...
```
---------
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
