/** Sockets can close while an asynchronous handler still owns a pending write.
 * Stop admission before calling this; do not release store ownership until both
 * the listener and every admitted handler have finished. */
export async function trackResponse(handler, req, res) {
  const finished = new Promise(resolve => {
    const done = () => { res.off('finish', done); res.off('close', done); resolve() }
    res.once('finish', done); res.once('close', done)
  })
  await handler(req, res)
  await finished
}

export async function drainRequests(server, activeHandlers) {
  const listenerClosed = new Promise(resolve => server.close(resolve))
  await Promise.all([...activeHandlers])
  // Browser TLS preconnect sockets have no admitted request to finish and can
  // otherwise hold server.close until the browser's idle timeout.
  server.closeAllConnections()
  await listenerClosed
}