Function createNetNS

tailnet/test/integration/network.go:614–645

createNetNS creates a new network namespace with the given name. The returned file is a file descriptor to the network namespace. Note: all cleanup is handled for you, you do not need to call Close on the returned file.

(t *testing.T, name string)

// Note: all cleanup is handled for you, you do not need to call Close on the
// returned file.
func createNetNS(t *testing.T, name string) *os.File {
	// We use ip-netns here because it handles the process of creating a
	// disowned netns for us.
	// The only way to create a network namespace is by calling unshare(2) or
	// clone(2) with the CLONE_NEWNET flag, and as soon as the last process in a
	// network namespace exits, the namespace is destroyed.
	// However, if you create a bind mount of /proc/$PID/ns/net to a file, it
	// will keep the namespace alive until the mount is removed.
	// ip-netns does this for us. Without it, we would have to fork anyways.
	// Later, we will use nsenter to enter this network namespace.
	_, err := exec.Command("ip", "netns", "add", name).Output()
	require.NoError(t, wrapExitErr(err), "create network namespace via ip-netns")
	t.Cleanup(func() {
		_, _ = exec.Command("ip", "netns", "delete", name).Output()
	})

	// Open /run/netns/$name to get a file descriptor to the network namespace.
	netnsPath := fmt.Sprintf("/run/netns/%s", name)
	file, err := os.OpenFile(netnsPath, os.O_RDONLY, 0)
	require.NoError(t, err, "open network namespace file")
	t.Cleanup(func() {
		_ = file.Close()
	})

	// Exec "ip link set lo up" in the namespace to bring up loopback
	// networking.
	//nolint:gosec
	_, err = exec.Command("ip", "-netns", name, "link", "set", "lo", "up").Output()
	require.NoError(t, wrapExitErr(err), "bring up loopback interface in network namespace")

	return file
}

// createBridge creates a bridge in the given network namespace. The bridge is
// automatically brought up.