const msg = new TextEncoder().encode('data: hello\r\n\r\n')

Deno.serve((_) => {
  let timerId: number | undefined

  const body = new ReadableStream({
    start(controller) {
      timerId = setInterval(() => {
        controller.enqueue(msg)
      }, 1000)
    },
    cancel() {
      if (typeof timerId === 'number') {
        clearInterval(timerId)
      }
    },
  })

  return new Response(body, {
    headers: {
      'Content-Type': 'text/event-stream',
    },
  })
})