SetsockoptInt IP_TRANSPARENT for net.Listener in golang

net.Listener.SetsockoptInt.IP_TRANSPARENT.for.Linux.go

package main

import (
	"fmt"
	"net"
	"os"
	"os/signal"
	"reflect"
	"syscall"
)

func rFieldByNames(i interface{}, fields...string) (field reflect.Value) {
	v := reflect.Indirect(reflect.ValueOf(i))
	for _, n := range fields {
		field = reflect.Indirect(v.FieldByName(n))
		v = field
	}
	return
}

func main() {
	l, err := net.Listen("tcp", ":40404")
	if err != nil {
		panic(err)
	}

	/*
		Method 1:
		from https://github.com/naoina/kuune.org/blob/master/content/text/get-fd-from-net-tcplistener-of-golang.md
		May not be compatible, but there will be no problems.
	*/
	fd := int(rFieldByNames(l, "fd", "pfd", "Sysfd").Int())
	if err = syscall.SetsockoptInt(fd, syscall.SOL_IP, syscall.IP_TRANSPARENT, 1); err != nil {
		syscall.Close(fd)
		fmt.Printf("syscall.SetsockoptInt err: %s", err)
		return
	}

	/*
		Method 2 (Not recommended):
		from https://github.com/LiamHaworth/go-tproxy/blob/master/tproxy_tcp.go
		There is a problem here, that is, the program will hung when it exits,
		because the program is blocked by the Accept function.
	 */
	//lt := l.(*net.TCPListener)
	//fh, err := lt.File()
	//if err != nil {
	//	fmt.Printf("get TCPListener file err: %s", err)
	//	return
	//}
	//fd := int(fh.Fd())
	//if err = syscall.SetsockoptInt(fd, syscall.SOL_IP, syscall.IP_TRANSPARENT, 1); err != nil {
	//	syscall.Close(fd)
	//	fmt.Printf("syscall.SetsockoptInt err: %s", err)
	//	return
	//}
	//fh.Close()

	go func() {
		for {
			c, err := l.Accept()
			if err == nil {
				c.Write([]byte("accept & close"))
				c.Close()
			} else {
				fmt.Println(err)
				break
			}
		}
	}()

	sigs := make(chan os.Signal, 1)
	done := make(chan bool)
	signal.Notify(sigs, os.Interrupt, syscall.SIGHUP, syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT)
	go func() {
		for range sigs {
			fmt.Println("stopping...")
			l.Close()
			done <- true
		}
	}()
	<-done
}