forked from hashicorp/envconsul
/
default_route.go
54 lines (49 loc) · 1.15 KB
/
default_route.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
package util
import (
"bufio"
"fmt"
"io"
"net"
"os"
"runtime"
)
// DefaultRoute will read /proc/net/route and look for an IPv4 default
// gateway. IPv6 gateways will not be found. It will then return the gateway as
// an IP.
func DefaultRoute() (ip net.IP, err error) {
if runtime.GOOS != "linux" {
return ip, fmt.Errorf("not attempting to determine default gateway on non-linux OS")
}
file, err := os.Open("/proc/net/route")
if err != nil {
return
}
defer file.Close()
return scanRouteFile(file)
}
func scanRouteFile(input io.Reader) (ip net.IP, err error) {
scanner := bufio.NewScanner(input)
defaultRoute := net.IPv4(0, 0, 0, 0)
for scanner.Scan() {
var iface string
var destBytes, gatewayBytes []byte
conversions, _ := fmt.Sscanf(scanner.Text(), "%s %x %x", &iface, &destBytes, &gatewayBytes)
if conversions == 3 {
dest := net.IP(destBytes)
if dest.Equal(defaultRoute) {
ip = net.IP(reverseBytes(gatewayBytes))
}
}
}
err = scanner.Err()
return
}
func reverseBytes(slice []byte) []byte {
result := make([]byte, len(slice), cap(slice))
i := len(slice) - 1
for _, b := range slice {
result[i] = b
i--
}
return result
}