package main

import (
	"log"
	"net"
	"syscall"
	"time"

	"golang.org/x/sys/windows"
)

func newOverlapped() (*windows.Overlapped, error) {
	var ov windows.Overlapped
	h, err := windows.CreateEvent(nil, 0, 1, nil)
	if h == 0 {
		return nil, err
	}
	ov.HEvent = h
	return &ov, nil
}

func readClosed(conn net.Conn) bool {
	var readClosed bool
	f := func(fd uintptr) bool {
		one := make([]byte, 1024)
		var n uint32
		ov, err := newOverlapped()
		if err != nil {
			return false
		}
		defer windows.CloseHandle(ov.HEvent)

		err = windows.ReadFile(windows.Handle(fd), one, &n, ov)
		if err != nil && err == syscall.ERROR_IO_PENDING {
			if err = windows.GetOverlappedResult(windows.Handle(fd), ov, &n, true); err != nil {
				return false
			}
		}

		if err != nil && err != syscall.EAGAIN || err == nil && n == 0 {
			readClosed = true
		}

		return true
	}

	conn.SetReadDeadline(time.Time{})

	var rawConn syscall.RawConn
	var err error
	switch v := conn.(type) {
	case *net.TCPConn:
		rawConn, err = v.SyscallConn()
		if err != nil {
			log.Fatal(err)
		}
	default:
		return false
	}

	// half closed
	if err := rawConn.Read(f); err != nil {
		return true
	}

	return readClosed
}

func main() {
	conn, err := net.Dial("tcp", "localhost:8888")
	if err != nil {
		log.Fatal(err)
	}
	println(readClosed(conn))
}