main.go

package main

import (
	"fmt"
	"net"
	"os"
	"runtime"

	"github.com/vishvananda/netlink"
	"github.com/vishvananda/netns"
)

var (
	nsName = "go-ns"
	brName = "br1"
	veth1  = "172.18.0.20/16"
	veth0  = "172.18.0.10/16"
	b      = "172.18.0.1/16"
)

func main() {
	la := netlink.NewLinkAttrs()
	la.Name = brName
	br := &netlink.Bridge{LinkAttrs: la}
	if err := netlink.LinkAdd(br); err != nil {
		fmt.Printf("unable to add bridge %s: %v\n", la.Name, err)
		os.Exit(1)
	}
	addr, err := netlink.ParseAddr(b)
	if err != nil {
		fmt.Printf("unable to parse addr: %v", err)
		os.Exit(1)
	}

	if err := netlink.AddrAdd(br, addr); err != nil {
		fmt.Printf("unable to add address: %v\n", err)
		os.Exit(1)
	}

	if err := netlink.LinkSetUp(br); err != nil {
		fmt.Printf("unable to set link up: %v\n", err)
		os.Exit(1)
	}

	attr := netlink.NewLinkAttrs()
	attr.Name = "veth0"
	veth := &netlink.Veth{
		PeerName:  "veth1",
		LinkAttrs: attr,
	}
	if err := netlink.LinkAdd(veth); err != nil {
		fmt.Printf("unable to add link: %v\n", err)
		os.Exit(1)
	}

	addr, err = netlink.ParseAddr(veth0)
	if err != nil {
		fmt.Printf("unable to parse addr: %v", err)
		os.Exit(1)
	}

	if err := netlink.AddrAdd(veth, addr); err != nil {
		fmt.Printf("unable to add address: %v\n", err)
		os.Exit(1)
	}

	if err := netlink.LinkSetUp(veth); err != nil {
		fmt.Printf("unable to set link up: %v", err)
		os.Exit(1)
	}

	if err := netlink.LinkSetMaster(veth, br); err != nil {
		fmt.Printf("unable to link veth to bridge: %v\n", err)
		os.Exit(1)
	}

	// Lock the OS Thread so we don't accidentally switch namespaces
	runtime.LockOSThread()
	defer runtime.UnlockOSThread()

	// Save the current network namespace
	origins, err := netns.Get()
	if err != nil {
		fmt.Printf("unable to get current network namespace: %v", err)
		os.Exit(1)
	}
	defer origins.Close()

	// Create a new network namespace
	ns, err := netns.NewNamed(nsName)
	if err != nil {
		fmt.Printf("unable to create named namespace %s: %v\n", nsName, err)
		os.Exit(1)
	}
	defer ns.Close()

	if err := netns.Set(origins); err != nil {
		fmt.Printf("unable to set namespace: %v\n", err)
		os.Exit(1)
	}

	peer, err := netlink.LinkByName("veth1")
	if err != nil {
		fmt.Printf("unable to get link by name: %v", err)
		os.Exit(1)
	}

	if err := netlink.LinkSetNsFd(peer, int(ns)); err != nil {
		fmt.Printf("unable to set link into a new ns: %v\n", err)
		os.Exit(1)
	}

	if err := netns.Set(ns); err != nil {
		fmt.Printf("unable to set namespace: %v\n", err)
		os.Exit(1)
	}

	addr, err = netlink.ParseAddr(veth1)
	if err != nil {
		fmt.Printf("unable to parse addr: %v", err)
		os.Exit(1)
	}

	if err := netlink.AddrAdd(peer, addr); err != nil {
		fmt.Printf("unable to add address: %v\n", err)
		os.Exit(1)
	}

	if err := netlink.LinkSetUp(peer); err != nil {
		fmt.Printf("unable to set link up: %v", err)
		os.Exit(1)
	}

	// TODO: handle error
	gtw, _, _ := net.ParseCIDR("172.18.0.1/32")
	_, dst, _ := net.ParseCIDR("0.0.0.0/0")

	if err := netlink.RouteAdd(&netlink.Route{
		Scope:     netlink.SCOPE_UNIVERSE,
		Dst:       dst,
		LinkIndex: peer.Attrs().Index,
		Gw:        gtw,
	}); err != nil {
		fmt.Printf("unable to add default route: %v\n", err)
		os.Exit(1)
	}
}