Send ping-pong messages in Turbopack HMR to detect broken connections

[Joffref]

Goals

1. Improve reliability of the Turbopack HMR WebSocket connection, especially in unstable network environments.
2. Allow detection of broken or stale connections caused by proxies, VPNs, or sleep mode.
3. Enable clients to reconnect or reload when a connection is no longer valid.

Non-Goals

1. Make this a default option (could be opt-in via config for now).
2. Replace existing HMR mechanisms or protocols.
3. Introduce a full WebSocket management layer.

Background

Note: This feature is particularly relevant when running a remote development environment.

Turbopack's HMR currently relies on a persistent WebSocket connection. However, in practice, these connections can silently break due to proxies, VPNs, or other network conditions. Without a keep-alive mechanism (such as ping/pong), the client may not detect the disconnection, resulting in a stale development session where HMR silently stops working.

Other development tools—such as Vite, Parcel, and Webpack Dev Server—use periodic heartbeat messages to monitor connection health and automatically trigger reconnections when needed.

Proposal

Introduce an optional ping/pong heartbeat in Turbopack’s HMR server and client. This would involve:

• The client sending a ping every N seconds.
• The server responding with a pong.

If the client doesn't receive a pong in a timeout window, it assumes the connection is broken and attempts to reconnect or reload the page.