i have the following simple code to capture all the arp packet sent to my device but it doesn't print anything
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <net/ethernet.h>
int main(){
int sock;
char recvbuf[2048];
if((sock=socket(PF_PACKET,SOCK_DGRAM,htons(ETH_P_ARP)))==-1){
perror("socket error");
return -1;
}
for(;;){
if(recvfrom(sock,recvbuf,sizeof(recvbuf),0,NULL,NULL)==-1){
perror("recvfrom error");
}
struct ether_header *e;
e=(struct ether_header *)recvbuf;
printf("arp from :%s\n",e->ether_shost);
}
}
the output is like:
arp from :
arp from :
arp from :
arp from :
arp from :
CodePudding user response:
A string, to be printed with %s
, is a sequence of characters terminated with the special null-terminator character '\0'
.
The data in e->ether_shost
is a series of six bytes, not characters, not null-terminated, and you need to print them one by one as small integers (usually in hexadecimal notation):
printf("hhx:hhx:hhx:hhx:hhx:hhx\n",
e->ether_shost[0], e->ether_shost[1], e->ether_shost[2],
e->ether_shost[3], e->ether_shost[4], e->ether_shost[5]);
For an explanation of the format used, see e.g. this printf
reference.