Read arp table using cgo on macos

arp-macos.go

package main

import (
	"fmt"
	"time"
)

/*

// Ideas and much code from:
// https://opensource.apple.com/source/network_cmds/network_cmds-457/arp.tproj/arp.c

//#include <net/route.h>

//#include <net/if_arp.h>
//#include <net/ethernet.h>

//#include <sys/sysctl.h>
//#include <sys/socket.h>


#include <sys/param.h>
#include <sys/file.h>
#include <sys/socket.h>
#include <sys/sockio.h>
#include <sys/sysctl.h>
#include <sys/ioctl.h>
#include <sys/time.h>

#include <net/if.h>
#include <net/if_dl.h>
#include <net/if_types.h>
#include <net/route.h>

#include <netinet/in.h>
#include <netinet/if_ether.h>

#include <arpa/inet.h>

#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <netdb.h>
#include <nlist.h>
#include <paths.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>

#ifndef SA_SIZE
#define SA_SIZE(sa)                                             \
    (  (!(sa) || ((struct sockaddr *)(sa))->sa_len == 0) ?      \
        sizeof(uint32_t)            :                               \
        1 + ( (((struct sockaddr *)(sa))->sa_len - 1) | (sizeof(uint32_t) - 1) ) )
#endif

typedef void (action_fn)(struct sockaddr_dl *sdl,
	struct sockaddr_inarp *s_in, struct rt_msghdr *rtm);

extern void pushARPEntry(char *, char *, char*);

static int arp_search(in_addr_t addr, action_fn *action)
{
	int mib[6];
	size_t needed;
	char *lim, *buf, *newbuf, *next;
	struct rt_msghdr *rtm;
	struct sockaddr_inarp *sin2;
	struct sockaddr_dl *sdl;
	char ifname[IF_NAMESIZE];
	int st, found_entry = 0;

	// This is the mib entry for the "route info" for all protocols - it does not seem to have
	// any text equivalent. (I tried to use Go's syscall.Sysctl() directly with no luck - all
	// the possible name variations I could think of fail to be found.)
	mib[0] = CTL_NET;
	mib[1] = PF_ROUTE;
	mib[2] = 0;
	mib[3] = AF_INET;
	mib[4] = NET_RT_FLAGS;
	mib[5] = RTF_LLINFO;
	if (sysctl(mib, 6, NULL, &needed, NULL, 0) < 0)
		err(1, "route-sysctl-estimate");
	if (needed == 0)	// empty table
		return 0;
	buf = NULL;
	for (;;) {
		newbuf = realloc(buf, needed);
		if (newbuf == NULL) {
			if (buf != NULL)
				free(buf);
			errx(1, "could not reallocate memory");
		}
		buf = newbuf;
		st = sysctl(mib, 6, buf, &needed, NULL, 0);
		if (st == 0 || errno != ENOMEM)
			break;
		needed += needed / 8;
	}
	if (st == -1)
		err(1, "actual retrieval of routing table");
	lim = buf + needed;
	for (next = buf; next < lim; next += rtm->rtm_msglen) {
		rtm = (struct rt_msghdr *)next;
		sin2 = (struct sockaddr_inarp *)(rtm + 1);
		sdl = (struct sockaddr_dl *)((char *)sin2 + SA_SIZE(sin2));
		//if (rifname && if_indextoname(sdl->sdl_index, ifname) &&
		//    strcmp(ifname, rifname))
		//	continue;
		if (addr) {
			if (addr != sin2->sin_addr.s_addr)
				continue;
			found_entry = 1;
		}
		(*action)(sdl, sin2, rtm);
	}
	free(buf);
	return (found_entry);
}

static char *arp_print_lladdr(struct sockaddr_dl *sdl)
{
	static char buf[256];
        char *cp;
        int n, bufsize = sizeof (buf), p = 0;

	bzero(buf, sizeof (buf));
        cp = (char *)LLADDR(sdl);
        if ((n = sdl->sdl_alen) > 0) {
                while (--n >= 0)
                        p += snprintf(buf + p, bufsize - p, "%02x%s",
			    *cp++ & 0xff, n > 0 ? ":" : "");
        }
	return (buf);
}

static void arp_push_entry(struct sockaddr_dl *sdl, struct sockaddr_inarp *addr, struct rt_msghdr *rtm) {

	static char ifname[IF_NAMESIZE];

	char *ipaddr = inet_ntoa(addr->sin_addr);

	char *macaddr = (char *)"";

	if (sdl->sdl_alen) {
		macaddr = arp_print_lladdr(sdl);
	}

	int useifname = 0;

	useifname = if_indextoname(sdl->sdl_index, ifname) != NULL;

	pushARPEntry(
		ipaddr,
		macaddr,
		useifname ? ifname : "");
}

static void full_arp_search() {
	arp_search(0, arp_push_entry);
}

*/
import "C"

type ARPEntry struct {
	IPAddress  string
	MACAddress string
	IFName     string
}

var ARPTable []ARPEntry

//export pushARPEntry
func pushARPEntry(ipaddr *C.char, macaddr *C.char, ifname *C.char) {
	ARPTable = append(ARPTable, ARPEntry{
		IPAddress:  C.GoString(ipaddr),
		MACAddress: C.GoString(macaddr),
		IFName:     C.GoString(ifname),
	})
}

func main() {

	start := time.Now()
	ARPTable = nil
	C.full_arp_search()

	fmt.Printf("%#v (%v)\n", ARPTable, time.Since(start))

}