Node.js HTTP Proxy TTFB Timeout (Keep-Alive Safe)

Problem

When implementing HTTP proxy/reverse-proxy code with TTFB (time-to-first-byte) timeouts, socket-based timeout logic fails on keep-alive connections. The first request works fine, but subsequent requests on reused sockets hang forever even though the upstream is dead.

Context / Trigger Conditions

• First HTTP request through proxy succeeds
• Second request (on same keep-alive connection) hangs indefinitely
• Upstream is a tunnel (cloudflared, ngrok) or service that can go offline
• Using socket.setTimeout() or proxyReq.on('socket', ...) for timeout logic
• Timeout callback never fires for reused connections
• Half-open TCP connections (remote closed, local doesn't know)

Root Cause