helpers_linux.go

package subnet

import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"net"
	"os"
	"strconv"
	"strings"
)

//SetInterfaceStatus brings up or down a network interface.
func SetInterfaceStatus(iName string, up bool, debug bool) error {
	statusString := "down"
	if up {
		statusString = "up"
	}
	sargs := fmt.Sprintf("link set dev %s %s mtu %d qlen %d", iName, statusString, devMtuSize, devTxQueLen)
	args := strings.Split(sargs, " ")
	return commandExec("ip", args, debug)
}

//SetDevIP sets the local IP address of a network interface.
func SetDevIP(iName string, localAddr net.IP, addr *net.IPNet, debug bool) error {
	sargs := fmt.Sprintf("%s %s netmask %s", iName, localAddr.String(), net.IP(addr.Mask).String())
	args := strings.Split(sargs, " ")
	return commandExec("ifconfig", args, debug)
}

// SetDefaultGateway sets the systems gateway to the IP / device specified.
func SetDefaultGateway(gw, iName string, debug bool) error {
	sargs := fmt.Sprintf("add default gw %s dev %s", gw, iName)
	args := strings.Split(sargs, " ")
	return commandExec("route", args, debug)
}

// AddRoute routes all traffic for addr via interface iName.
func AddRoute(addr, viaAddr net.IP, iName string, debug bool) error {
	sargs := fmt.Sprintf("add %s gw %s dev %s", addr.String(), viaAddr.String(), iName)
	args := strings.Split(sargs, " ")
	return commandExec("route", args, debug)
}

// DelRoute deletes the route in the system routing table to a specific destination.
func DelRoute(addr, viaAddr net.IP, iName string, debug bool) error {
	sargs := fmt.Sprintf("del %s gw %s dev %s", addr.String(), viaAddr.String(), iName)
	args := strings.Split(sargs, " ")
	return commandExec("route", args, debug)
}

// GetNetGateway return net gateway (default route) and nic.
// Credit: https://github.com/bigeagle/gohop/blob/master/hop/iface.go
func GetNetGateway() (gw, dev string, err error) {
	file, err := os.Open("/proc/net/route")
	if err != nil {
		return "", "", err
	}

	defer file.Close()
	rd := bufio.NewReader(file)

	s2byte := func(s string) byte {
		b, _ := strconv.ParseUint(s, 16, 8)
		return byte(b)
	}

	for {
		line, isPrefix, err := rd.ReadLine()

		if err != nil {
			return "", "", err
		}
		if isPrefix {
			return "", "", errors.New("Parse error: Line too long")
		}
		buf := bytes.NewBuffer(line)
		scanner := bufio.NewScanner(buf)
		scanner.Split(bufio.ScanWords)
		tokens := make([]string, 0, 8)

		for scanner.Scan() {
			tokens = append(tokens, scanner.Text())
		}

		iface := tokens[0]
		dest := tokens[1]
		gw := tokens[2]
		mask := tokens[7]

		if bytes.Equal([]byte(dest), []byte("00000000")) &&
			bytes.Equal([]byte(mask), []byte("00000000")) {
			a := s2byte(gw[6:8])
			b := s2byte(gw[4:6])
			c := s2byte(gw[2:4])
			d := s2byte(gw[0:2])

			ip := net.IPv4(a, b, c, d)

			return ip.String(), iface, nil
		}

	}
}