Nitro with `bun` preset can't connect to WebSocket during development

Environment

Operating System: Linux
Node Version: v20.12.2
Nuxt Version: 3.13.1
CLI Version: 3.13.1
Nitro Version: 2.9.7
Package Manager: bun@1.1.27
Builder: -
User Config: compatibilityDate, devtools, nitro
Runtime Modules: -
Build Modules: -

Reproduction

https://github.com/Anoesj/nitro-bun-websocket-issue

[!NOTE]
I could not create a reproduction in Stackblitz/CodeSandbox, as I couldn't figure out how to use Bun there. Therefore, I created a repo instead. Make sure to read the README for reproduction steps.

Describe the bug

I'm trying to get WebSockets to work in a Nuxt application. I've turned on nitro.experimental.websocket in nuxt.config.ts and I'm using the bun Nitro preset.

During development (bun --bun run dev), the WebSocket's onopen event never fires, suggesting the connection can't be fully established, but doesn't "fail" either.

After building the app and previewing it (bun --bun run build && bun --bun run preview), the WebSocket does work.

When using the node-server Nitro preset instead, the WebSocket does not work in both development mode and after building and previewing the app.

When switching to node by omitting the --bun flag (so: bun run dev / bun run build && bun run preview), the WebSocket does work in both development mode and after building and preview the app, for both Nitro preset bun and node-server.

So all in all:	Runtime	Mode	Nitro preset
Bun	Dev	`bun`	❌
Bun	Build + preview	`bun`	✅
Bun	Dev	`node-server`	❌
Bun	Build + preview	`node-server`	❌
Node	Dev	`bun`	✅
Node	Build + preview	`bun`	✅
Node	Dev	`node-server`	✅
Node	Build + preview	`node-server`	✅

Additional context

Bun revision: 1.1.27+267afa293 Platform: Linux 6.8.0-40-generic x86_64 x86_64.

If this is a Nuxt issue, feel free to transfer the issue to the Nuxt repository.

Logs

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unjs / nitro