netio.go

func echo(wq *waiter.Queue, ep tcpip.Endpoint) {
	defer ep.Close()

	// Create wait queue entry that notifies a channel.
	waitEntry, notifyCh := waiter.NewChannelEntry(nil)

	wq.EventRegister(&waitEntry, waiter.EventIn)
	defer wq.EventUnregister(&waitEntry)

	for {
		v, _, err := ep.Read(nil)
		if err != nil {
			if err == tcpip.ErrWouldBlock {
				<-notifyCh
				continue
			}

			return
		}

		ep.Write(tcpip.SlicePayload(v), tcpip.WriteOptions{})
	}
}

https://sourcegraph.com/github.com/google/netstack@55fcc16/-/blob/tcpip/sample/tun_tcp_echo/main.go#L53:30