snapnet.c

一个学习SNMP项目：tmoerlan.

/* $Id: snapnet.c,v 1.2 2003/09/17 11:26:10 tmoerlan Exp $ */

#include <sys/types.h>
#include <netinet/in_systm.h>
#include <netinet/in.h>
#include <netinet/ip.h>
//#include <linux/ip.h>
#include <sys/socket.h>
#include "io.h"
#include "packet.h"
#include "snap.h"
#include "d_printf.h"

#define MAX_MTU 3924
/*
#define iphdr ip
#define protocol ip_p
#define ihl ip_hl
*/

struct iphdr
  {
#if __BYTE_ORDER == __LITTLE_ENDIAN
    unsigned int ihl:4;
    unsigned int version:4;
#elif __BYTE_ORDER == __BIG_ENDIAN
    unsigned int version:4;
    unsigned int ihl:4;
#else
# error	"Please fix <bits/endian.h>"
#endif
    u_int8_t tos;
    u_int16_t tot_len;
    u_int16_t id;
    u_int16_t frag_off;
    u_int8_t ttl;
    u_int8_t protocol;
    u_int16_t check;
    u_int32_t saddr;
    u_int32_t daddr;
    /*The options start here. */
  };


char pbuf[3 * MAX_MTU];

int snap_recv_pkt(int sock, packet_t **p) {

  struct iphdr *iph;
  int len;

  if ((len = recvfrom(sock, pbuf, sizeof(pbuf), 0, NULL, NULL)) < 0) {
    perror("recvfrom");
    *p = NULL;
    return -1;
  }

  iph = (struct iphdr *)pbuf;
	/* verify it's a SNAP packet */
	if ((iph->protocol != IPPROTO_SNAP) || (iph->ihl < 6)) {
		return -1;
	}

  *p = unmarshal_packet(pbuf, len, sizeof(pbuf));
  if (*p == NULL) {
    return -1;
  } else {
    return 0;
  }
}