netlink.go

package lldpd

import (
	"net"
	"syscall"

	"github.com/jsimonetti/rtnetlink"
	"github.com/mdlayher/netlink"
	"github.com/pkg/errors"
	"golang.org/x/sys/unix"
)

type nlListener struct {
	Messages chan *linkMessage
	list     map[uint32]struct{}
	log      Logger
}

// NewNLListener listens on rtnetlink for addition and removal
// of interfaces and inform users on the Messages channel.
func NewNLListener(log Logger) *nlListener {
	l := &nlListener{
		Messages: make(chan *linkMessage, 64),
		list:     make(map[uint32]struct{}),
		log:      log,
	}
	return l
}

// Start will start the listener
func (l *nlListener) Start() {
	go func() {
		err := l.Listen()
		if err != nil {
			l.log.Error("msg", "could not listen", "error", err)
		}
	}()
}

// Listen will start the listener loop
func (l *nlListener) Listen() error {
	nl, err := rtnetlink.Dial(&netlink.Config{Groups: unix.RTNLGRP_LINK})
	if err != nil {
		errors.Wrap(err, "could not dial rtnetlink")
	}

	//send request for current list of interfaces
	req := &rtnetlink.LinkMessage{}
	nl.Send(req, unix.RTM_GETLINK, netlink.Request|netlink.Dump)

	for {
		msgs, omsgs, err := nl.Receive()
		if err != nil {
			return errors.Wrap(err, "netlink receive error")
		}

		for i, msg := range msgs {
			if m, ok := msg.(*rtnetlink.LinkMessage); ok {
				if m.Type != syscall.ARPHRD_ETHER {
					// skip non-ethernet
					continue
				}

				if m.Family != syscall.AF_UNSPEC {
					// skip non-generic
					continue
				}

				if omsgs[i].Header.Type == unix.RTM_NEWLINK {
					if _, ok := l.list[m.Index]; !ok {

						link, _ := net.InterfaceByIndex(int(m.Index))
						l.Messages <- &linkMessage{
							ifi: link,
							op:  IF_ADD,
						}

						l.list[m.Index] = struct{}{}
						l.log.Info("msg", "netlink reports new interface", "ifname", m.Attributes.Name, "ifindex", m.Index)
					}
					continue
				}
				if omsgs[i].Header.Type == unix.RTM_DELLINK {
					if _, ok := l.list[m.Index]; ok {

						l.Messages <- &linkMessage{
							ifi: &net.Interface{
								Index: int(m.Index),
								Name:  m.Attributes.Name,
							},
							op: IF_DEL,
						}

						delete(l.list, m.Index)
						l.log.Info("msg", "netlink reports deleted interface", "ifname", m.Attributes.Name, "ifindex", m.Index)
					}
					continue
				}
			}
		}
	}
}

type linkOp uint8

const (
	IF_ADD linkOp = 1
	IF_DEL linkOp = 2
)

type linkMessage struct {
	ifi *net.Interface
	op  linkOp
}

func (l linkOp) String() string {
	switch l {
	case IF_ADD:
		return "ADD"
	case IF_DEL:
		return "DEL"
	default:
		return "UNKNOWN"
	}
}