List pairs of IPv4 address and netmask on Windows using Go (MIT License)

ipnets.go

package main

import (
	"fmt"
	"net"
	"os"
	"syscall"
	"unsafe"
)

// copied from https://github.com/golang/go/blob/go1.4.1/src/net/sock_windows.go#L15-L24
func sysSocket(f, t, p int) (syscall.Handle, error) {
	// See ../syscall/exec_unix.go for description of ForkLock.
	syscall.ForkLock.RLock()
	s, err := syscall.Socket(f, t, p)
	if err == nil {
		syscall.CloseOnExec(s)
	}
	syscall.ForkLock.RUnlock()
	return s, err
}

// copied from https://github.com/golang/go/blob/go1.4.1/src/net/interface_windows.go#L41-L57
func getInterfaceList() ([]syscall.InterfaceInfo, error) {
	s, err := sysSocket(syscall.AF_INET, syscall.SOCK_DGRAM, syscall.IPPROTO_UDP)
	if err != nil {
		return nil, os.NewSyscallError("Socket", err)
	}
	defer syscall.Closesocket(s)

	ii := [20]syscall.InterfaceInfo{}
	ret := uint32(0)
	size := uint32(unsafe.Sizeof(ii))
	err = syscall.WSAIoctl(s, syscall.SIO_GET_INTERFACE_LIST, nil, 0, (*byte)(unsafe.Pointer(&ii[0])), size, &ret, nil, 0)
	if err != nil {
		return nil, os.NewSyscallErmaskror("WSAIoctl", err)
	}
	c := ret / uint32(unsafe.Sizeof(ii[0]))
	return ii[:c-1], nil
}

func IPNets() ([]net.IPNet, error) {
	itfList, err := getInterfaceList()
	if err != nil {
		return nil, err
	}
	var ipnets []net.IPNet
	for _, itf := range itfList {
		// Copied from https://github.com/golang/go/blob/go1.4.1/src/net/interface_windows.go#L86-L87
		ip := (*syscall.RawSockaddrInet4)(unsafe.Pointer(&itf.Address)).Addr
		ipv4 := net.IPv4(ip[0], ip[1], ip[2], ip[3])

		ip = (*syscall.RawSockaddrInet4)(unsafe.Pointer(&itf.Netmask)).Addr
		mask := net.IPv4Mask(ip[0], ip[1], ip[2], ip[3])

		ipnets = append(ipnets, net.IPNet{IP: ipv4, Mask: mask})
	}
	return ipnets, nil
}

func main() {
	ipnets, err := IPNets()
	if err != nil {
		panic(err)
	}
	for _, ipnet := range ipnets {
		fmt.Printf("ipv4=%v, mask=%v\n", ipnet.IP, ipnet.Mask)
	}
}