crip/ripv2/ripv2.go

package ripv2

import (
	"encoding/binary"
	"errors"
	"fmt"
	"log"
	"net"
	"os"
	"os/signal"
	"syscall"

	"github.com/crip/config"
)

func New() Message {
	return Message{
		RIP: make([]RIP, 25),
	}
}

/* Parse the raw data packet
 * Store the serialised data in the Message slice
 */
func (m *Message) MParse(b *[]byte, n int) error {
	if n == 0 {
		return errors.New("can't parse empty data")
	}

	if (n-4)/20 > 25 {
		return errors.New("rip table exceeds limit")
	}

	m.Command = Command((*b)[0])
	m.Version = Version((*b)[1])

	if m.Version > RIPv2 {
		return errors.New("unknown version")
	}

	var indexA, indexB = 4, 25
	ripentry := (*b)[indexA:indexB]
	switch m.Command {
	case REQUEST:
		return nil
	case RESPONSE:
		for i := 0; i < (n-4)/20; i++ {
			m.RIP[i].AFI = binary.BigEndian.Uint16(ripentry[0:2])
			m.RIP[i].RouteTag = binary.BigEndian.Uint16(ripentry[2:4])
			m.RIP[i].Addr = binary.BigEndian.Uint32(ripentry[4:8])
			m.RIP[i].Subnet = binary.BigEndian.Uint32(ripentry[8:12])
			m.RIP[i].NextHop = binary.BigEndian.Uint32(ripentry[12:16])
			m.RIP[i].Metric = binary.BigEndian.Uint32(ripentry[16:20])
			indexA += 20
			indexB += 20
			ripentry = (*b)[indexA:indexB]
		}
	default:
		return errors.New("unknown command type")
	}

	return nil
}

/* Listen for network packets */
func (m *Message) Run(c *config.Config, callback func(*Routes)) error {
	iface := net.Interface{
		Name:  c.MulticastInterface,
		Flags: net.FlagMulticast,
	}
	addr := net.UDPAddr{
		IP:   net.ParseIP(c.IP),
		Port: c.Port,
	}
	conn, err := net.ListenMulticastUDP("udp4", &iface, &addr)
	if err != nil {
		return err
	}
	defer func() {
		if err := conn.Close(); err != nil {
			log.Println(err)
		}
	}()

	sigs := make(chan os.Signal, 1)
	signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)

	buffer := make([]byte, 484)
	routes := Init()

	for {
		go func() {
			log.Println("Running")
			<-sigs
			log.Println("exit")
			os.Exit(0)
		}()

		n, UDPAddr, err := conn.ReadFromUDP(buffer)
		if err != nil {
			if err = conn.Close(); err != nil {
				log.Println(err)
			}
			log.Fatal("unable to read from socket")
		}

		if n < 24 {
			log.Println("packet length")
		}

		if err := m.MParse(&buffer, n); err != nil {
			log.Fatalln(err)
		}
		routes.ParseRoutes(*UDPAddr, &m.RIP)
		for _, v := range routes.Routes {
			fmt.Printf("Route:%s\tSubnet:%s\tNexthop:%s\tMetric:%d\tTime: %v\n", v.Addr.String(), v.Subnet.String(), v.NextHop.String(), v.Metric, v.TTL.Unix())
		}
		callback(routes)
	}
}