libpcap get MAC from AF_LINK sockaddr_dl (OSX) - c

I am trying to obtain the MAC addresses of all of my interface on OSX using C. The common ways to obtain it Linux dont work on BSD - from everything I have seen, you must obtain the interfaces and look for the ones that are of type AF_LINK. My problem is that the LLADDR(sockaddr_dl) gives me a whole bunch of data (which includes my MAC) and I dont know what format the data is in. For example; the following code will output:
Device: en1
link sdl_alen: 101 mac:
31:f8:1e:df:d6:22:1d:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:b0:06:10:00:01:00:00:00:c0:02:10:00:01:00:00:00:00:00:00:00:00:00:00:00:40
:03:10:00:01:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:03:00:6c:6f:30:00:00:00:00:00:00:00:00:00:00:00:00:00:70:03:10:00:01:00:00:00:e0:
02:10:00:01:00:00:
My MAC is bolded. It seems that this is the format all of the time, but I would be a lot more comfortable if I could cast LLADDR(sockaddr_dl) to something. In the net/if_dl.h, LLADDR is defied as:
#define LLADDR(s) ((caddr_t)((s)->sdl_data + (s)->sdl_nlen))
which, as far as I can tell, is saying that the results are of type (void *) - no help.
Other posts like:
Having a problem figuring out how to get Ethernet interface info on Mac OS X using ioctl/SIOCGIFADDR/SIOCGIFCONF?
seem to think they have it figured out, but if you look through the code, you can see it will not work due to sdl_alen not being 6.
int main() {
pcap_if_t *alldevs;
pcap_if_t *d;
pcap_addr_t *alladdrs;
pcap_addr_t *a;
struct sockaddr_dl* link;
char eb[PCAP_ERRBUF_SIZE];
char *addr_buf[40];
if (pcap_findalldevs(&alldevs, eb) == -1) {
printf("no devs found\n");
return(-1);
}
for (d = alldevs; d != NULL; d = d->next) {
printf("Device: %s\n", d->name);
alladdrs = d->addresses;
for (a = alladdrs; a != NULL; a = a->next) {
if(a->addr->sa_family == AF_LINK && a->addr->sa_data != NULL){
// MAC ADDRESS
//struct sockaddr_dl *sdl = (struct sockaddr_dl *) a->addr->sa_data;
link = (struct sockaddr_dl*)a->addr->sa_data;
char mac[link->sdl_alen];
caddr_t macaddr = LLADDR(link);
memcpy(mac, LLADDR(link), link->sdl_alen);
printf("link sdl_alen: %i\n", link->sdl_alen);
int i;
printf("mac: ");
for(i = 0; i<link->sdl_alen; i++){
printf("%02x:", (unsigned char)mac[i]);
}
printf("\n");
}
}
}
}

The problem is that you are casting the sockaddr->sa_data to sockaddr_dl instead of casting the sockaddr itself to sockaddr_dl. Keep in mind that sockaddr_dl is an OS X/BSD thing, so #ifdef that part for portability.
Don't do:
link = (struct sockaddr_dl*)a->addr->sa_data;
Do:
link = (struct sockaddr_dl*)a->addr;
Then you will get the correct sdl_alen and things will work with out any hacks. And if you want to really easily get the name of addresses that may be either AF_INET, AF_INET6, or AF_LINK use getnameinfo():
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <net/if_dl.h>
int get_sock_len(struct sockaddr *sa)
{
switch (sa->sa_family) {
case AF_INET:
return sizeof(struct sockaddr_in);
case AF_INET6:
return sizeof(struct sockaddr_in6);
case AF_LINK:
return sizeof(struct sockaddr_dl);
default:
return -1;
}
}
int get_numeric_address(struct sockaddr *sa, char *outbuf, size_t buflen) {
socklen_t len;
if ((len = get_sock_len(sa)) < 0) {
return -1;
}
if (getnameinfo(sa, len, outbuf, buflen, NULL, 0, NI_NUMERICHOST)) {
return -1;
}
return 0;
}
...
char buf[NI_MAXHOST];
if (!get_numeric_address(sa, buf, sizeof(buf))) { /* For some struct sockaddr *sa */
printf("address: %s\n", buf);
} else {
printf("doh!\n");
}

Here is what I ended up doing:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <sys/sockio.h>
#include <net/if.h>
#include <errno.h>
#include <net/if_dl.h>
#include <pcap.h>
#include "mac.h"
int main() {
printf("en1: %s\n", lookupDeviceMac("vnic0"));
}
unsigned char *lookupDeviceMac(char *dev){
pcap_if_t *alldevs;
pcap_if_t *d;
pcap_addr_t *alladdrs;
pcap_addr_t *a;
struct sockaddr_dl* link;
char eb[PCAP_ERRBUF_SIZE];
char *ret = malloc(6);
if (pcap_findalldevs(&alldevs, eb) == -1) {
printf("%s\n", eb);
return(ret);
}
for (d = alldevs; d != NULL; d = d->next) {
if(strcmp(d->name, dev) == 0){
printf("Device: %s\n", d->name);
alladdrs = d->addresses;
for (a = alladdrs; a != NULL; a = a->next) {
if(a->addr->sa_family == AF_LINK && a->addr->sa_data != NULL){
// MAC ADDRESS
//struct sockaddr_dl *sdl = (struct sockaddr_dl *) a->addr->sa_data;
link = (struct sockaddr_dl*)a->addr->sa_data;
char mac[link->sdl_alen];
caddr_t macaddr = LLADDR(link);
memcpy(mac, LLADDR(link), link->sdl_alen);
if(link->sdl_alen == 6){
// Seen in some sample code
sprintf(ret, "%02x:%02x:%02x:%02x:%02x:%02x",(unsigned char)mac[0],
(unsigned char)mac[1],
(unsigned char)mac[2],
(unsigned char)mac[3],
(unsigned char)mac[4],
(unsigned char)mac[5]);
} else if(link->sdl_alen > 6) {
// This is what happens in OSX 10.6.5
sprintf(ret, "%02x:%02x:%02x:%02x:%02x:%02x",(unsigned char)mac[1],
(unsigned char)mac[2],
(unsigned char)mac[3],
(unsigned char)mac[4],
(unsigned char)mac[5],
(unsigned char)mac[6]);
}
return(ret);
}
}
}
}
}

I was trying to see all devices reported by pcap_findalldevs and ended up here looking for information on interpreting AF_LINK addresses on MAC OS.
I'm used to seeing the struct sockaddr standing in for a interface family and being immediately cast to the appropriate type and not writing code to access *sa_data*.
For what I wanted it was sufficient to use link_ntoa to convert the address to a human readable form.
#import <Foundation/Foundation.h>
#include <pcap.h>
#include <netinet/in.h>
#include <net/if_dl.h>
int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
pcap_if_t* allDevs = NULL;
char errbuff[PCAP_ERRBUF_SIZE];
if (pcap_findalldevs(&allDevs, errbuff) <0) {
NSLog(#"Failed with error '%s'", errbuff);
}
else {
for (pcap_if_t* device = allDevs; device != NULL; device = device->next) {
for (pcap_addr_t* address = device->addresses; address != NULL; address = address->next) {
struct sockaddr* sa_addr = address->addr;
if (sa_addr->sa_family == AF_LINK) {
struct sockaddr_dl* link_addr = (struct sockaddr_dl*) sa_addr;
char* linkAddress = link_ntoa(link_addr);
NSLog(#"ntoa %s", linkAddress);
}
}
}
}
pcap_freealldevs(allDevs);
[pool drain];
return 0;
}
Running on my machine I get the following devices with AF_LINK entries.
2011-08-14 02:22:43.024 HomePlugToolHelper[12473:903] ntoa en0:0.16.cb.xx.x.xx
2011-08-14 02:22:43.027 HomePlugToolHelper[12473:903] ntoa fw0:0.16.cb.xx.xx.xx.xx.xx
2011-08-14 02:22:43.028 HomePlugToolHelper[12473:903] ntoa en1:0.16.cb.x.xx.xx
2011-08-14 02:22:43.028 HomePlugToolHelper[12473:903] ntoa lo0

Related

String concatenation maintaining destination length

I have a basic server-client program that I'm writing in C and I am stuck with an issue regarding strings and concatenation.
Basically I have some strings (in the example below just 2) that I have to put into a buffer which size is determined by:
total # of registered people * 33
Both the strings in the example have a length which is much less than the length of the buffer. I want to obtain something like this after the concatenation:
[0] [32]
people_list=Mark Amy\0;
where Mark(which is inserted secondly) is right at the start of the buffer (people_list) and Amy is 32 characters away from the start of Mark (I hope I've made myself clear).
This is because the client code was given to me and I cannot modify it. The client code takes the buffer and reads the first element, then jumps of 32 chars and reads again.
The output I get from the printf of the client is this:
connected to server
Registered people:
Mark
while I'd like this:
connected to server
Registered people:
Mark
Amy
The communication is implemented through sockets, which I have already checked, but if you wish to suggest some changes I would appreciate that.
Server code:
#include <stdio.h>
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <errno.h>
#define LENGTH 32
struct person {
char name[LENGTH+1];
struct person *next;
struct person *prev;
};
struct person *p_head = NULL;
void addPerson(char* name_p){
struct person *new = (struct person*) malloc(sizeof(struct person));
strcpy(new->name, name_p);
new->name[LENGTH]='\0';
new->next=p_head;
new->prev=NULL;
p_head=new;
}
int main(){
int fd_ser;
int fd_c;
int N=100;
char buf[N];
int times=0;
char* path="tmp/sock";
struct sockaddr_un sa;
unlink(path);
sa.sun_family=AF_UNIX;
strncpy(sa.sun_path,(char*) path, sizeof(sa.sun_path));
if((fd_ser=socket(AF_UNIX,SOCK_STREAM,0))<0){ //socket
perror((const char*) (size_t) errno);
exit(EXIT_FAILURE);
}
if ( bind(fd_ser,(struct sockaddr *)&sa, sizeof(sa))<0){
perror("bind\n");
}
listen(fd_ser,10); //listen
struct sockaddr_un addr;
int addr_size= sizeof(struct sockaddr_un);
fd_c=0;
while( (fd_c=accept(fd_ser,(struct sockaddr*) &addr, (socklen_t*)&addr_size))<0){
printf("waiting for connections...\n");
sleep(2);
}
//initialize list of people
char* Amy="Amy";
char* Mark="Mark";
addPerson(Amy);
addPerson(Mark);
//now concat the name strings in a buffer to be sent to the client
char* people_list;
unsigned int list_len;
int value;
struct person* ptr=(struct person*) malloc(sizeof(struct person));
ptr=p_head;
int offset=0;
int i=0;
while(ptr!=NULL){
i++;
people_list=realloc(people_list,i*LENGTH); //every single name has to be LENGTH characters
strcpy(&people_list[offset],ptr->name);
ptr=ptr->next;
offset=offset+LENGTH;
}
people_list[i*LENGTH]='\0';
list_len=(i*LENGTH)+1;
value=write(fd_c, &(list_len), sizeof(unsigned int));
if(value==-1){
perror("write length");
return -1;
}
int toWrite=list_len;
char *toRead=people_list;
while(toWrite>0){
value=write(fd_c, toRead, toWrite);
if(value==-1){
perror("write data");
return -1;
}
toWrite=toWrite-value;
toRead=toRead+value;
if(toRead<=people_list + list_len) break;
}
close(fd_c);
close(fd_ser);
return 0;
}
Client code:
#include <stdio.h>
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <assert.h>
#include <errno.h>
#define MAX_LENGTH 2048
#define LENGTH 32
int main(){
int fd_cli;
char* path="tmp/sock";
struct sockaddr_un sa;
sa.sun_family=AF_UNIX;
strncpy(sa.sun_path,(char*) path, sizeof(sa.sun_path));
if( (fd_cli = socket(AF_UNIX, SOCK_STREAM, 0))==-1){
perror((const char*) (size_t) errno);
return -1;
}
while( (connect(fd_cli,(struct sockaddr*)&sa, sizeof(struct sockaddr_un))) == -1 ) {
if ( errno == ENOENT ) { sleep(1); }
else perror("connect:");
errno=0;
sleep(1);
}
printf("connected to server\n");
int value;
unsigned int len_data;
value=read(fd_cli,&(len_data),sizeof(unsigned int));
if(value==-1){
perror("read length");
return -1;
}
char* buffer=malloc(len_data*sizeof(char));
int toRead=len_data;
char *toWrite=buffer;
while(toRead>0){
value=read(fd_cli, toWrite, toRead);
if(value==-1){
perror("read buffer");
return -1;
}
toRead=toRead-value;
toWrite=toWrite+value;
if(toWrite<=buffer + len_data) break;
}
int people_n = len_data / (LENGTH+1);
assert(people_n > 0); //proceeds only if there is at least one person registered
printf("Registered people:\n");
for(int i=0,p=0;i<people_n; ++i, p+=(LENGTH+1)) {
printf(" %s\n", &buffer[p]);
}
close(fd_cli);
return 0;
}
I really hope I've explained the problem clearly! Thank you for your help!
It's printing only the first user (Mark) because of this line:
int people_n = len_data / (LENGTH+1);
In this example, len_data = 65, LENGTH = 32. So when you are adding 1 to LENGTH, it will return 1 (65/33 = 1.96 => you get 1). Then it only prints the first user.
Consider using Valgrind. It will help you checking the use of the memory.

Issues printing a MAC address

A MAC address is parsed into an array of bytes (macaddr). The bytes are
printed with printf() one after another. The bytes are supposed to look as
pairs of hexadecimal characters. But some of them are padded with f
characters.
For example, for macaddr[3] it prints 'ffffffcc' rather than 'cc', i.e.
4 bytes instead of single byte. The rest of the array items are printed
correctly (macaddr[0] = 00, macaddr[1] = AA, macaddr[2] = BB,
etc.)
What's the problem?
Please help me to figure out what's wrong with the program.
#include <stdio.h>
#include <net/if.h> // struct ifconf
#include <errno.h>
#include <libnet.h>
#include <pcap.h>
#include <stdlib.h>
#include <unistd.h>
int getmacaddr() ;
int main(int argc, char *argv[])
{
getmacaddr();
}
int getmacaddr()
{
struct ifconf ifc;
struct ifreq *ifr;
int sfd;
int i;
int devnums;
char macaddr[ETHER_ADDR_LEN];
ifc.ifc_req = NULL;
sfd = socket(AF_INET,SOCK_DGRAM,0);
if(sfd == -1)
{
perror("socket : ");
return -1;
}
// get ifc.ifc_len
if(ioctl(sfd,SIOCGIFCONF,&ifc) == -1)
{
perror("ioctl - SIOCGIFCONF : ");
return -1;
}
devnums = ifc.ifc_len / sizeof(struct ifreq);
// malloc ifc.ifc_buf and get IFCONF list
ifc.ifc_buf = malloc(ifc.ifc_len);
memset(ifc.ifc_buf,0x0,ifc.ifc_len);
if(ioctl(sfd,SIOCGIFCONF,&ifc) == -1)
{
perror("ioctl - SIOCGIFCONF : ");
return -1;
}
for(i = 0; i < devnums; i++,ifc.ifc_req++)
{
// idfy dev
if( strcmp(ifc.ifc_req->ifr_ifrn.ifrn_name,"lo") && ifc.ifc_req->ifr_ifrn.ifrn_name != 0)
{
ifr = ifc.ifc_req;
// IP address
struct sockaddr_in *a = (struct sockaddr_in *) &ifr->ifr_addr;
printf("%s",inet_ntoa(a->sin_addr));
printf("\n");
//get IFHWADDR
if(ioctl(sfd,SIOCGIFHWADDR,ifr) == -1)
{
perror("ioctl - SIOCGIFHWADDR : ");
return -1;
}
}
}
memcpy(macaddr,ifr->ifr_hwaddr.sa_data,sizeof(macaddr));
for(i = 0; i < ETHER_ADDR_LEN; i++)
{
printf("%02x ",macaddr[i]);
}
printf("\n");
close(sfd);
// free(ifc.ifc_buf); <- ?? error
return 0;
}
EDIT
I've replaced the following line:
printf("%02x ",macaddr[i]);
with
printf("%02x ", (macaddr[i] & 0xff));
Try this:
printf("%02x ", (unsigned char)macaddr[i] & 0xff);
We specify the minimum field width in the format string. So to make sure that the value will look exactly as a single byte, you can leave only the first 16 bits by applying a bit mask.

Polling interface names via SIOCGIFCONF in Linux

I'm attempting to poll networking device names. I've pieced this together from various snippets,
http://unixhelp.ed.ac.uk/CGI/man-cgi?netdevice+7
http://lists.apple.com/archives/Unix-porting/2002/Apr/msg00134.html
http://ubuntuforums.org/showthread.php?t=1421487
But my output is just gibberish.
#include <stdio.h>
#include <stdlib.h>
#include <net/route.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#define BUFLEN 1024
#define SEQ 9999
int main (int argc, const char* argv[])
{
// File descriptor for socket
int socketfd;
struct ifconf conf;
struct ifreq req[10];
struct ifreq *ifr;
printf("Opening socket...");
socketfd = socket(AF_ROUTE, SOCK_RAW, 0);
if (socketfd >= 0) {
printf(" OK\n");
conf.ifc_len = sizeof(req);
conf.ifc_buf = (__caddr_t) req;
ioctl(socketfd,SIOCGIFCONF,&conf);
printf("Discovering interfaces...\n");
int i;
for (i=0; i<conf.ifc_len/sizeof(req[0]); i++) {
ifr = &conf.ifc_req[i];
printf("%d. %s\n", i+1, req[i].ifr_name);
}
}
else {
printf("Failed!\n");
}
return 0;
}
Output:
Opening socket... OK
Discovering interfaces...
?u???}??Gh???
2. p?9}?
3.
4. v?=?n??u?`?y??]g?<?~?v??
5.
6.
7.
8. ?v?T?
9. ?|?mw??j??v??h??|??v?T00~??v?$?|??|?#
10. T00~??v?$?|??|?#
I tried outputting each char of the ifr_name array one-by-one to see if they were null terminated but that didn't change much. Each iteration of my program outputs something different so this leads me to think I'm referencing something wrong. Can someone provide me some insight as to what I may be doing wrong?
Here's some code I put together for Mac OS X:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <arpa/inet.h>
#include <netinet/in.h>
/* This is defined on Mac OS X */
#ifndef _SIZEOF_ADDR_IFREQ
#define _SIZEOF_ADDR_IFREQ sizeof
#endif
int main (int argc, const char* argv[])
{
// File descriptor for socket
int socketfd;
struct ifconf conf;
char data[4096];
struct ifreq *ifr;
char addrbuf[1024];
int i;
printf("Opening socket...");
socketfd = socket(AF_INET, SOCK_DGRAM, 0);
if (socketfd >= 0) {
printf(" OK\n");
conf.ifc_len = sizeof(data);
conf.ifc_buf = (caddr_t) data;
if (ioctl(socketfd,SIOCGIFCONF,&conf) < 0) {
perror("ioctl");
}
printf("Discovering interfaces...\n");
i = 0;
ifr = (struct ifreq*)data;
while ((char*)ifr < data+conf.ifc_len) {
switch (ifr->ifr_addr.sa_family) {
case AF_INET:
++i;
printf("%d. %s : %s\n", i, ifr->ifr_name, inet_ntop(ifr->ifr_addr.sa_family, &((struct sockaddr_in*)&ifr->ifr_addr)->sin_addr, addrbuf, sizeof(addrbuf)));
break;
#if 0
case AF_INET6:
++i;
printf("%d. %s : %s\n", i, ifr->ifr_name, inet_ntop(ifr->ifr_addr.sa_family, &((struct sockaddr_in6*)&ifr->ifr_addr)->sin6_addr, addrbuf, sizeof(addrbuf)));
break;
#endif
}
ifr = (struct ifreq*)((char*)ifr +_SIZEOF_ADDR_IFREQ(*ifr));
}
close(socketfd);
}
else {
printf(" Failed!\n");
}
return 0;
}
Poll as in you want to be notified if an interface is added or removed? Or polled as in you just want to find out the interface names once from the system? If the latter, take a look at getifaddrs().
Please see http://git.netfilter.org/cgi-bin/gitweb.cgi?p=libmnl.git;a=blob;f=examples/rtnl/rtnl-link-dump.c;hb=HEAD on how to get the list of interfaces on Linux. AF_ROUTE is some BSD thing and the use of ioctl is discouraged on Linux for its apparent limitations (such as to convey multiple addresses on a single interface).

How to get MAC address of your machine using a C program?

I am working on Ubuntu. How can I get MAC address of my machine or an interface say eth0 using C program.
Much nicer than all this socket or shell madness is simply using sysfs for this:
the file /sys/class/net/eth0/address carries your mac adress as simple string you can read with fopen()/fscanf()/fclose(). Nothing easier than that.
And if you want to support other network interfaces than eth0 (and you probably want), then simply use opendir()/readdir()/closedir() on /sys/class/net/.
You need to iterate over all the available interfaces on your machine, and use ioctl with SIOCGIFHWADDR flag to get the mac address. The mac address will be obtained as a 6-octet binary array. You also want to skip the loopback interface.
#include <sys/ioctl.h>
#include <net/if.h>
#include <unistd.h>
#include <netinet/in.h>
#include <string.h>
int main()
{
struct ifreq ifr;
struct ifconf ifc;
char buf[1024];
int success = 0;
int sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP);
if (sock == -1) { /* handle error*/ };
ifc.ifc_len = sizeof(buf);
ifc.ifc_buf = buf;
if (ioctl(sock, SIOCGIFCONF, &ifc) == -1) { /* handle error */ }
struct ifreq* it = ifc.ifc_req;
const struct ifreq* const end = it + (ifc.ifc_len / sizeof(struct ifreq));
for (; it != end; ++it) {
strcpy(ifr.ifr_name, it->ifr_name);
if (ioctl(sock, SIOCGIFFLAGS, &ifr) == 0) {
if (! (ifr.ifr_flags & IFF_LOOPBACK)) { // don't count loopback
if (ioctl(sock, SIOCGIFHWADDR, &ifr) == 0) {
success = 1;
break;
}
}
}
else { /* handle error */ }
}
unsigned char mac_address[6];
if (success) memcpy(mac_address, ifr.ifr_hwaddr.sa_data, 6);
}
You want to take a look at the getifaddrs(3) manual page. There is an example in C in the manpage itself that you can use. You want to get the address with the type AF_LINK.
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <linux/if.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
int main()
{
struct ifreq s;
int fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);
strcpy(s.ifr_name, "eth0");
if (0 == ioctl(fd, SIOCGIFHWADDR, &s)) {
int i;
for (i = 0; i < 6; ++i)
printf(" %02x", (unsigned char) s.ifr_addr.sa_data[i]);
puts("\n");
return 0;
}
return 1;
}
Using getifaddrs you can get MAC address from the family AF_PACKET.
In order to display the MAC address to each interface, you can proceed like this:
#include <stdio.h>
#include <ifaddrs.h>
#include <netpacket/packet.h>
int main (int argc, const char * argv[])
{
struct ifaddrs *ifaddr=NULL;
struct ifaddrs *ifa = NULL;
int i = 0;
if (getifaddrs(&ifaddr) == -1)
{
perror("getifaddrs");
}
else
{
for ( ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next)
{
if ( (ifa->ifa_addr) && (ifa->ifa_addr->sa_family == AF_PACKET) )
{
struct sockaddr_ll *s = (struct sockaddr_ll*)ifa->ifa_addr;
printf("%-8s ", ifa->ifa_name);
for (i=0; i <s->sll_halen; i++)
{
printf("%02x%c", (s->sll_addr[i]), (i+1!=s->sll_halen)?':':'\n');
}
}
}
freeifaddrs(ifaddr);
}
return 0;
}
Ideone
I have just write one and test it on gentoo in virtualbox.
// get_mac.c
#include <stdio.h> //printf
#include <string.h> //strncpy
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h> //ifreq
#include <unistd.h> //close
int main()
{
int fd;
struct ifreq ifr;
char *iface = "enp0s3";
unsigned char *mac = NULL;
memset(&ifr, 0, sizeof(ifr));
fd = socket(AF_INET, SOCK_DGRAM, 0);
ifr.ifr_addr.sa_family = AF_INET;
strncpy(ifr.ifr_name , iface , IFNAMSIZ-1);
if (0 == ioctl(fd, SIOCGIFHWADDR, &ifr)) {
mac = (unsigned char *)ifr.ifr_hwaddr.sa_data;
//display mac address
printf("Mac : %.2X:%.2X:%.2X:%.2X:%.2X:%.2X\n" , mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
}
close(fd);
return 0;
}
Assuming that c++ code (c++11) is okay as well and the interface is known.
#include <cstdint>
#include <fstream>
#include <streambuf>
#include <regex>
using namespace std;
uint64_t getIFMAC(const string &ifname) {
ifstream iface("/sys/class/net/" + ifname + "/address");
string str((istreambuf_iterator<char>(iface)), istreambuf_iterator<char>());
if (str.length() > 0) {
string hex = regex_replace(str, std::regex(":"), "");
return stoull(hex, 0, 16);
} else {
return 0;
}
}
int main()
{
string iface = "eth0";
printf("%s: mac=%016llX\n", iface.c_str(), getIFMAC(iface));
}
On Linux, use the service of "Network Manager" over the DBus.
There is also good'ol shell program which can be invoke and the result grabbed (use an exec function under C):
$ /sbin/ifconfig | grep HWaddr
A very portable way is to parse the output of this command.
ifconfig | awk '$0 ~ /HWaddr/ { print $5 }'
Provided ifconfig can be run as the current user (usually can) and awk is installed (it often is). This will give you the mac address of the machine.
Expanding on the answer given by #user175104 ...
std::vector<std::string> GetAllFiles(const std::string& folder, bool recursive = false)
{
// uses opendir, readdir, and struct dirent.
// left as an exercise to the reader, as it isn't the point of this OP and answer.
}
bool ReadFileContents(const std::string& folder, const std::string& fname, std::string& contents)
{
// uses ifstream to read entire contents
// left as an exercise to the reader, as it isn't the point of this OP and answer.
}
std::vector<std::string> GetAllMacAddresses()
{
std::vector<std::string> macs;
std::string address;
// from: https://stackoverflow.com/questions/9034575/c-c-linux-mac-address-of-all-interfaces
// ... just read /sys/class/net/eth0/address
// NOTE: there may be more than one: /sys/class/net/*/address
// (1) so walk /sys/class/net/* to find the names to read the address of.
std::vector<std::string> nets = GetAllFiles("/sys/class/net/", false);
for (auto it = nets.begin(); it != nets.end(); ++it)
{
// we don't care about the local loopback interface
if (0 == strcmp((*it).substr(-3).c_str(), "/lo"))
continue;
address.clear();
if (ReadFileContents(*it, "address", address))
{
if (!address.empty())
{
macs.push_back(address);
}
}
}
return macs;
}
netlink socket is possible
man netlink(7) netlink(3) rtnetlink(7) rtnetlink(3)
#include <assert.h>
#include <stdio.h>
#include <linux/if.h>
#include <linux/rtnetlink.h>
#include <unistd.h>
#define SZ 8192
int main(){
// Send
typedef struct {
struct nlmsghdr nh;
struct ifinfomsg ifi;
} Req_getlink;
assert(NLMSG_LENGTH(sizeof(struct ifinfomsg))==sizeof(Req_getlink));
int fd=-1;
fd=socket(AF_NETLINK,SOCK_RAW,NETLINK_ROUTE);
assert(0==bind(fd,(struct sockaddr*)(&(struct sockaddr_nl){
.nl_family=AF_NETLINK,
.nl_pad=0,
.nl_pid=getpid(),
.nl_groups=0
}),sizeof(struct sockaddr_nl)));
assert(sizeof(Req_getlink)==send(fd,&(Req_getlink){
.nh={
.nlmsg_len=NLMSG_LENGTH(sizeof(struct ifinfomsg)),
.nlmsg_type=RTM_GETLINK,
.nlmsg_flags=NLM_F_REQUEST|NLM_F_ROOT,
.nlmsg_seq=0,
.nlmsg_pid=0
},
.ifi={
.ifi_family=AF_UNSPEC,
// .ifi_family=AF_INET,
.ifi_type=0,
.ifi_index=0,
.ifi_flags=0,
.ifi_change=0,
}
},sizeof(Req_getlink),0));
// Receive
char recvbuf[SZ]={};
int len=0;
for(char *p=recvbuf;;){
const int seglen=recv(fd,p,sizeof(recvbuf)-len,0);
assert(seglen>=1);
len += seglen;
if(((struct nlmsghdr*)p)->nlmsg_type==NLMSG_DONE||((struct nlmsghdr*)p)->nlmsg_type==NLMSG_ERROR)
break;
p += seglen;
}
struct nlmsghdr *nh=(struct nlmsghdr*)recvbuf;
for(;NLMSG_OK(nh,len);nh=NLMSG_NEXT(nh,len)){
if(nh->nlmsg_type==NLMSG_DONE)
break;
struct ifinfomsg *ifm=(struct ifinfomsg*)NLMSG_DATA(nh);
printf("#%d ",ifm->ifi_index);
#ifdef _NET_IF_H
#pragma GCC error "include <linux/if.h> instead of <net/if.h>"
#endif
// Part 3 rtattr
struct rtattr *rta=IFLA_RTA(ifm); // /usr/include/linux/if_link.h
int rtl=RTM_PAYLOAD(nh);
for(;RTA_OK(rta,rtl);rta=RTA_NEXT(rta,rtl))switch(rta->rta_type){
case IFLA_IFNAME:printf("%s ",(const char*)RTA_DATA(rta));break;
case IFLA_ADDRESS:
printf("hwaddr ");
for(int i=0;i<5;++i)
printf("%02X:",*((unsigned char*)RTA_DATA(rta)+i));
printf("%02X ",*((unsigned char*)RTA_DATA(rta)+5));
break;
case IFLA_BROADCAST:
printf("bcast ");
for(int i=0;i<5;++i)
printf("%02X:",*((unsigned char*)RTA_DATA(rta)+i));
printf("%02X ",*((unsigned char*)RTA_DATA(rta)+5));
break;
case IFLA_PERM_ADDRESS:
printf("perm ");
for(int i=0;i<5;++i)
printf("%02X:",*((unsigned char*)RTA_DATA(rta)+i));
printf("%02X ",*((unsigned char*)RTA_DATA(rta)+5));
break;
}
printf("\n");
}
close(fd);
fd=-1;
return 0;
}
Example
#1 lo hwaddr 00:00:00:00:00:00 bcast 00:00:00:00:00:00
#2 eth0 hwaddr 57:da:52:45:5b:1a bcast ff:ff:ff:ff:ff:ff perm 57:da:52:45:5b:1a
#3 wlan0 hwaddr 3c:7f:46:47:58:c2 bcast ff:ff:ff:ff:ff:ff perm 3c:7f:46:47:58:c2
This is a Bash line that prints all available mac addresses, except the loopback:
for x in `ls /sys/class/net |grep -v lo`; do cat /sys/class/net/$x/address; done
Can be executed from a C program.

How do I output my host’s IP addresses from a C program?

I need to display all the IP addresses from my local computer, using the C language. How can this be done?
#include <stdio.h>
#include <stropts.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <linux/netdevice.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <unistd.h>
int print_addresses(const int domain)
{
int s;
struct ifconf ifconf;
struct ifreq ifr[50];
int ifs;
int i;
s = socket(domain, SOCK_STREAM, 0);
if (s < 0) {
perror("socket");
return 0;
}
ifconf.ifc_buf = (char *) ifr;
ifconf.ifc_len = sizeof ifr;
if (ioctl(s, SIOCGIFCONF, &ifconf) == -1) {
perror("ioctl");
return 0;
}
ifs = ifconf.ifc_len / sizeof(ifr[0]);
printf("interfaces = %d:\n", ifs);
for (i = 0; i < ifs; i++) {
char ip[INET_ADDRSTRLEN];
struct sockaddr_in *s_in = (struct sockaddr_in *) &ifr[i].ifr_addr;
if (!inet_ntop(domain, &s_in->sin_addr, ip, sizeof(ip))) {
perror("inet_ntop");
return 0;
}
printf("%s - %s\n", ifr[i].ifr_name, ip);
}
close(s);
return 1;
}
int main(int argc, char *argv[])
{
int domains[] = { AF_INET, AF_INET6 };
int i;
for (i = 0; i < sizeof(domains) / sizeof(domains[0]); i++)
if (!print_addresses(domains[i]))
return 1;
return 0;
}
Your question might be imprecise but I am not sure why everyone is breaking your chops.
I think you are asking the basics in which case you probably want is getifaddrs. The man page has a little example program.
You can also get similar info using the SIOCGIFCONF option with ioctl(). There is some sample code on here and the web.
If you search around for these and similar terms you will find this question has been asked in various forms before. You have to dig around a bit.
Also note, these will not give you the public facing IP of your network if you are behind NAT.
Another way to do it in C. I do have to say though.... there are so many ways to do it from the shell, what's the point?
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <errno.h>
#include <ifaddrs.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
void show_address_info( struct ifaddrs *ifa ){
struct sockaddr_in *s4;
struct sockaddr_in6 *s6;
/* ipv6 addresses have to fit in this buffer */
char buf[64];
if (AF_INET == ifa->ifa_addr->sa_family){
s4 = (struct sockaddr_in *)(ifa->ifa_addr);
if (NULL == inet_ntop(ifa->ifa_addr->sa_family, (void *)&(s4->sin_addr), buf, sizeof(buf))){
printf("%s: inet_ntop failed!\n", ifa->ifa_name);
} else {
printf("IPv4 addr %s: %s\n", ifa->ifa_name, buf);
}
}
else if (AF_INET6 == ifa->ifa_addr->sa_family) {
s6 = (struct sockaddr_in6 *)(ifa->ifa_addr);
if (NULL == inet_ntop(ifa->ifa_addr->sa_family, (void *)&(s6->sin6_addr), buf, sizeof(buf))) {
printf("%s: inet_ntop failed!\n", ifa->ifa_name);
} else {
printf("IPv6 addr %s: %s\n", ifa->ifa_name, buf);
}
}
}
int main(int argc, char **argv){
struct ifaddrs *myaddrs, *ifa;
int status;
status = getifaddrs(&myaddrs);
if (status != 0){
perror("getifaddrs failed!");
exit(1);
}
for (ifa = myaddrs; ifa != NULL; ifa = ifa->ifa_next){
if (NULL == ifa->ifa_addr){
continue;
}
if ((ifa->ifa_flags & IFF_UP) == 0) {
continue;
}
show_address_info(ifa);
}
freeifaddrs(myaddrs);
return 0;
}
How about you simply cheat and look at the source of /sbin/ifconfig/ ? Nothing wrong with standing on the shoulders of other giants...
Not a complete solution yet, but take a look in /proc/net!
dev lists the available interface devices by name,
route lists some routes, as does ipv6_route,
arp lists devices in the actual routing table (does not include localhost).
Not as high-tech as the other solution, but it can be done with simple file reading. Linux specific, though.
You need POSIX function getaddrinfo() - it returns linked list of all IP addresses.
See man getaddrinfo for details and examples.
$ sudo ifconfig | grep 'inet addr' | cut -d':' -f2 | cut -d' ' -f1
213.xx.xxx.xx
192.168.xx.x
127.0.0.1
And you can put that into popen():
/* not tested */
ph = popen("sudo ifconfig | grep 'inet addr' | cut -d':' -f2 | cut -d' ' -f1", "r");
while (fgets(buf, sizeof buf, ph)) {
/* ip address, in nul-terminated string format, is in `buf` */
}
pclose(ph);
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
/*
* Who sez?
* http://blog.stackoverflow.com/2010/01/stack-overflow-where-we-hate-fun/
*/
int main(int argc, char *argv[])
{
int status;
const char * const cmd = /* die from END is too chatty */
"/sbin/ifconfig -a | \
perl -lne \
'print $1 if /inet6? addr:\\s*(\\S+)/; \
END { $. > 0 or \
warn(\"no output from ifconfig\\n\"), \
exit 1; }'";
status = system(cmd);
if (status < 0) {
perror("system");
return 1;
}
else if (status != 0) {
const char *extra;
status = WEXITSTATUS(status);
extra = status == 127 ? " (is /bin/sh ok?)" : "";
fprintf(stderr, "%s: command failed with status %d%s\n",
argv[0], status, extra);
}
return 0;
}

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