setns.go

package main

import (
	"fmt"
	"io"
	"net/http"
	"os"
	"syscall"

	"github.com/opencontainers/runc/libcontainer/system"
)

func doNetns(nsPath string) error {
	ns, err := os.Open(nsPath)
	if err != nil {
		return err
	}
	return system.Setns(ns.Fd(), syscall.CLONE_NEWNET)
}

func doGet(port string) {
	response, err := http.Get("http://localhost:" + port)
	if err != nil {
		fmt.Fprintf(os.Stderr, "%s\n", err)
	} else {
		defer response.Body.Close()
		_, err := io.Copy(os.Stderr, response.Body)
		if err != nil {
			fmt.Fprintf(os.Stderr, "%s\n", err)
		}
	}
}

func main() {
	doNetns(os.Args[1])
	doGet(os.Args[2])
}