open_pcap.c

mgcp协议源代码。支持多种编码：g711

/**************************************************************************** 
**
** File: open_pcap.c
**
** Author: Mike Borella
**
** Comments: Set up pcap to sniff the packets we want.  Most of these 
** commands are listed in the pcap(3) man page.
**
*****************************************************************************/

#include <stdio.h>
#include <pcap.h>
#include "config.h"
#include "open_pcap.h"
#include "error.h"

#define SNAPLEN      1514
#define PROMISC      1
#define READ_TIMEOUT 500


extern struct arg_t *my_args;
extern int datalink;

/*----------------------------------------------------------------------------
 *
 * pcap_open()
 *
 *----------------------------------------------------------------------------
 */

void open_pcap(void)
{
  extern char *pcap_cmd;
  extern pcap_t *pd;
  bpf_u_int32 localnet, netmask;
  struct bpf_program fcode;
  char errorbuf[PCAP_ERRBUF_SIZE];

  /*
   * Look up the device and get a handle to it
   */

  char* verboseWarning = "You do not have permission to access %s.\nNormally, only root has such access.  Please log on as root and try again.\nIf you do not have root access, you may ask your system administrator to change\nthe device permissions such that you can run this program as a normal user,\nor to install sudo and let everyone to run ipgrab as root, without a password.\nSorry for the hassle.  Cheers.\n\n";

  if (my_args->i == NULL) 
  {
      my_args->i = pcap_lookupdev(errorbuf);
      if (my_args->i == NULL) 
      {
	  fprintf (stderr, verboseWarning, my_args->i);
	  GWF_error_fatal("open_pcap: pcap_lookupdev() failed for %s: %s", 
			  my_args->i, errorbuf);
      }
  }
  
  /*
   * Get a file descriptor to the device
   */

  pd = pcap_open_live(my_args->i, SNAPLEN, PROMISC, READ_TIMEOUT, errorbuf);
  if (pd == NULL)
  {
      fprintf (stderr, verboseWarning, my_args->i);
      GWF_error_fatal("open_pcap: pcap_open_live() failed for %s: %s", 
		      my_args->i, errorbuf);
  }

  /*
   * Determine local net and netmask
   */

  if (pcap_lookupnet(my_args->i, &localnet, &netmask, errorbuf) < 0)
    GWF_error_fatal("open_pcap: pcap_lookupnet() failed for %s: %s", 
		    my_args->i, errorbuf);
  
  /*
   * Compile command line filter spec info fcode FSM
   */

  if (pcap_compile(pd, &fcode, pcap_cmd, 0, netmask) < 0)
    GWF_error_fatal("pcap_compile: %s", pcap_geterr(pd));

  /*
   * Set the pcap filter with our fcode FSM.  That should do it...
   */

  if (pcap_setfilter(pd, &fcode) < 0)
    GWF_error_fatal("pcap_setfilter: %s", pcap_geterr(pd));

  /*
   * Get the data link type 
   */

  datalink = pcap_datalink(pd);
  if (datalink < 0) 
    GWF_error_fatal("pcap_datalink: %s", pcap_geterr(pd));

}