Sample Go application to check connectivity binding to a device, useful for VRF

vrf.go

package main

import (
	"context"
	"flag"
	"fmt"
	"log"
	"net"
	"syscall"
)

func main() {
	s := flag.Bool("server", false, "server")
	address := flag.String("address", "127.0.0.1:80", "address")
	vrfName := flag.String("vrf", "", "vrf")
	flag.Parse()
	if *s {
		listen(*address, *vrfName)
	} else {
		dial(*address, *vrfName)
	}
}

func listen(address, vrfName string) {
	lc := net.ListenConfig{Control: controlOnConnSetup(vrfName)}

	ln, err := lc.Listen(context.Background(), "tcp", address)
	if err != nil {
		log.Fatal(err)
	}

	ln.Accept()
	fmt.Println("Accepted")
	ln.Close()
}

func dial(address, vrfName string) {
	d := net.Dialer{Control: controlOnConnSetup(vrfName)}
	conn, err := d.Dial("tcp", address)
	if err != nil {
		log.Fatal(err)
	}
	conn.Close()
}

func controlOnConnSetup(vrfName string) func(network string, address string, c syscall.RawConn) error {
	return func(network string, address string, c syscall.RawConn) error {
		if vrfName == "" {
			return nil
		}
		var operr error
		fn := func(fd uintptr) {
			operr = syscall.SetsockoptString(int(fd), syscall.SOL_SOCKET, syscall.SO_BINDTODEVICE, vrfName)
		}
		if err := c.Control(fn); err != nil {
			return err
		}
		if operr != nil {
			return operr
		}
		return nil
	}
}