How to get all addresses and masks from local interfaces in go? - networking

Question

How can I get all addresses and masks from local interfaces in golang?
I need the actual network mask configured along with every IP address.
This code does not show the network masks in Windows 7:
package main
import (
"fmt"
"log"
"net"
)
func localAddresses() {
ifaces, err := net.Interfaces()
if err != nil {
log.Print(fmt.Errorf("localAddresses: %v\n", err.Error()))
return
}
for _, i := range ifaces {
addrs, err := i.Addrs()
if err != nil {
log.Print(fmt.Errorf("localAddresses: %v\n", err.Error()))
continue
}
for _, a := range addrs {
log.Printf("%v %v\n", i.Name, a)
}
}
}
func main() {
localAddresses()
}
UPDATE: This issue has been fixed in Go: https://github.com/golang/go/issues/5395

Answer 1

There are multiply types of addresses that a net.Interface might have. The Addr is just an interface which may contain a net.IPAddr. But with a type assertion or type switch you can access the actual address type:
package main
import (
"fmt"
"net"
)
func localAddresses() {
ifaces, err := net.Interfaces()
if err != nil {
fmt.Print(fmt.Errorf("localAddresses: %+v\n", err.Error()))
return
}
for _, i := range ifaces {
addrs, err := i.Addrs()
if err != nil {
fmt.Print(fmt.Errorf("localAddresses: %+v\n", err.Error()))
continue
}
for _, a := range addrs {
switch v := a.(type) {
case *net.IPAddr:
fmt.Printf("%v : %s (%s)\n", i.Name, v, v.IP.DefaultMask())
}
}
}
}
func main() {
localAddresses()
}
Edit
Unfortunately the net package doesn't return the Mask of the address. So, you will have to do the low level syscalls that the net package does. The code below is an example, but parsing of the ip and the mask still needs to be done:
package main
import (
"fmt"
"net"
"os"
"syscall"
"unsafe"
)
func getAdapterList() (*syscall.IpAdapterInfo, error) {
b := make([]byte, 1000)
l := uint32(len(b))
a := (*syscall.IpAdapterInfo)(unsafe.Pointer(&b[0]))
// TODO(mikio): GetAdaptersInfo returns IP_ADAPTER_INFO that
// contains IPv4 address list only. We should use another API
// for fetching IPv6 stuff from the kernel.
err := syscall.GetAdaptersInfo(a, &l)
if err == syscall.ERROR_BUFFER_OVERFLOW {
b = make([]byte, l)
a = (*syscall.IpAdapterInfo)(unsafe.Pointer(&b[0]))
err = syscall.GetAdaptersInfo(a, &l)
}
if err != nil {
return nil, os.NewSyscallError("GetAdaptersInfo", err)
}
return a, nil
}
func localAddresses() error {
ifaces, err := net.Interfaces()
if err != nil {
return err
}
aList, err := getAdapterList()
if err != nil {
return err
}
for _, ifi := range ifaces {
for ai := aList; ai != nil; ai = ai.Next {
index := ai.Index
if ifi.Index == int(index) {
ipl := &ai.IpAddressList
for ; ipl != nil; ipl = ipl.Next {
fmt.Printf("%s: %s (%s)\n", ifi.Name, ipl.IpAddress, ipl.IpMask)
}
}
}
}
return err
}
func main() {
err := localAddresses()
if err != nil {
panic(err)
}
}
Some code shamelessly borrowed from interface_windows.go. Even comments are left intact

Answer 2

I'm modifying #ANisus answer and get all interfaces & masks (tested on Windows 10 & WSL in it (Microsoft Ubuntu 16.04.5 LTS):
package main
import (
"fmt"
"net"
)
func localAddresses() {
ifaces, err := net.Interfaces()
if err != nil {
fmt.Print(fmt.Errorf("localAddresses: %+v\n", err.Error()))
return
}
for _, i := range ifaces {
addrs, err := i.Addrs()
if err != nil {
fmt.Print(fmt.Errorf("localAddresses: %+v\n", err.Error()))
continue
}
for _, a := range addrs {
switch v := a.(type) {
case *net.IPAddr:
fmt.Printf("%v : %s (%s)\n", i.Name, v, v.IP.DefaultMask())
case *net.IPNet:
fmt.Printf("%v : %s [%v/%v]\n", i.Name, v, v.IP, v.Mask)
}
}
}
}
func main() {
localAddresses()
}

Answer 3

This should give you the ipnet you're looking for.
ip, ipnet, err := net.ParseCIDR(a.String())

Answer 4

I know this post for Windows 7, but if you use Mac OS X hope this could help you.
Just Call GetNetMask("en0")
func GetNetMask(deviceName string) string {
switch runtime.GOOS {
case "darwin":
cmd := exec.Command("ipconfig", "getoption", deviceName, "subnet_mask")
out, err := cmd.CombinedOutput()
if err != nil {
return ""
}
nm := strings.Replace(string(out), "\n", "", -1)
log.Println("netmask=", nm, " OS=", runtime.GOOS)
return nm
default:
return ""
}
return ""
}