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package gateway
import (
"bytes"
"io/ioutil"
"net"
"os/exec"
)
func discoverGatewayUsingIp() (ip net.IP, err error) {
routeCmd := exec.Command("ip", "route", "show")
stdOut, err := routeCmd.StdoutPipe()
if err != nil {
return
}
if err = routeCmd.Start(); err != nil {
return
}
output, err := ioutil.ReadAll(stdOut)
if err != nil {
return
}
// Linux 'ip route show' format looks like this:
// default via 192.168.178.1 dev wlp3s0 metric 303
// 192.168.178.0/24 dev wlp3s0 proto kernel scope link src 192.168.178.76 metric 303
outputLines := bytes.Split(output, []byte("\n"))
for _, line := range outputLines {
if bytes.Contains(line, []byte("default")) {
ipFields := bytes.Fields(line)
ip = net.ParseIP(string(ipFields[2]))
break
}
}
err = routeCmd.Wait()
return
}
func discoverGatewayUsingRoute() (ip net.IP, err error) {
routeCmd := exec.Command("route", "-n")
stdOut, err := routeCmd.StdoutPipe()
if err != nil {
return
}
if err = routeCmd.Start(); err != nil {
return
}
output, err := ioutil.ReadAll(stdOut)
if err != nil {
return
}
// Linux route out format is always like this:
// Kernel IP routing table
// Destination Gateway Genmask Flags Metric Ref Use Iface
// 0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth0
outputLines := bytes.Split(output, []byte("\n"))
for _, line := range outputLines {
if bytes.Contains(line, []byte("0.0.0.0")) {
ipFields := bytes.Fields(line)
ip = net.ParseIP(string(ipFields[1]))
break
}
}
err = routeCmd.Wait()
return
}
func DiscoverGateway() (ip net.IP, err error) {
ip, err = discoverGatewayUsingRoute()
if err != nil {
ip, err = discoverGatewayUsingIp()
}
return
}