unsafe2_setopt.go

package main

import (
	"net"
	"unsafe"
	"syscall"
)

func main() {
	conn, err := net.Dial("tcp", "www.taobao.com:80")
	if err != nil {
		panic(err)
	}

	if tcpConn, ok := conn.(*net.TCPConn); ok {
		fdAddr := *(**int)(unsafe.Pointer(tcpConn))
		sysfd := *(*int)(unsafe.Pointer(uintptr(unsafe.Pointer(fdAddr)) + 16))
		println("fd: ", sysfd)

		const tcpUserTimeout = 0x12
		syscall.SetsockoptInt(sysfd, syscall.IPPROTO_TCP, tcpUserTimeout, 1000)
	}
}