help with programming pcap on Snow Leopard

[Andy Huang <andy.y.huang () gmail com>]

Hi,

I am new to pcap, I am trying to write a simple packet sniffer on MAC OS X
10.6.2 (Snow Leopard), here is the code I got from the net, I have an
AirPort (Wifi) connection, but the code that runs with SUDO was unable to
capture any packet. any advice is greatly appreciated.

#include <pcap.h>
#include <string.h>
#include <stdlib.h>

#define MAXBYTES2CAPTURE 2048


/* processPacket(): Callback function called by pcap_loop() everytime a
packet */
/* arrives to the network card. This function prints the captured raw data
in  */
/*
hexadecimal.
*/
void processPacket(u_char *arg, const struct pcap_pkthdr* pkthdr, const
u_char * packet){

 int i=0, *counter = (int *)arg;

 printf("Packet Count: %d\n", ++(*counter));
 printf("Received Packet Size: %d\n", pkthdr->len);
 printf("Payload:\n");
 for (i=0; i<pkthdr->len; i++){

    if ( isprint(packet[i]) ) /* If it is a printable character, print it */
        printf("%c ", packet[i]);
    else
        printf(". ");

     if( (i%16 == 0 && i!=0) || i==pkthdr->len-1 )
        printf("\n");
  }
 return;
}



/* main(): Main function. Opens network interface and calls pcap_loop() */
int main(int argc, char *argv[] ){

 int i=0, count=0;
 pcap_t *descr = NULL;
 char errbuf[PCAP_ERRBUF_SIZE], *device=NULL;
 memset(errbuf,0,PCAP_ERRBUF_SIZE);

 if( argc > 1){  /* If user supplied interface name, use it. */
    device = argv[1];
 }
 else{  /* Get the name of the first device suitable for capture */

    if ( (device = pcap_lookupdev(errbuf)) == NULL){
        fprintf(stderr, "ERROR: %s\n", errbuf);
        exit(1);
    }
 }

 printf("Opening device %s\n", device);

 if ( (descr = pcap_open_live(device, MAXBYTES2CAPTURE, 0,  512, errbuf)) ==
NULL){
    fprintf(stderr, "ERROR: %s\n", errbuf);
    exit(1);
 }

 /* Loop forever & call processPacket() for every received packet*/
 if ( pcap_loop(descr, -1, processPacket, (u_char *)&count) == -1){
    fprintf(stderr, "ERROR: %s\n", pcap_geterr(descr) );
    exit(1);
 }

pcap_close(descr);

return 0;

}
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