/* ber.c
 *
 * Basic Encoding Rules (BER) file reading
 *
 * $Id: ber.c 46803 2012-12-27 12:19:25Z guy $
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include "config.h"

#include <errno.h>

#ifdef HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif

#include "wtap-int.h"
#include "file_wrappers.h"
#include "buffer.h"
#include "ber.h"


#define BER_CLASS_UNI	0
#define BER_CLASS_APP	1
#define BER_CLASS_CON	2

#define BER_UNI_TAG_SEQ	16	/* SEQUENCE, SEQUENCE OF */
#define BER_UNI_TAG_SET	17	/* SET, SET OF */

static void ber_set_pkthdr(struct wtap_pkthdr *phdr, int packet_size)
{
  phdr->presence_flags = 0; /* yes, we have no bananas^Wtime stamp */

  phdr->caplen = packet_size;
  phdr->len = packet_size;

  phdr->ts.secs = 0;
  phdr->ts.nsecs = 0;
}

static gboolean ber_read(wtap *wth, int *err, gchar **err_info, gint64 *data_offset)
{
  gint64 offset;
  guint8 *buf;
  gint64 file_size;
  int packet_size;

  *err = 0;

  offset = file_tell(wth->fh);

  /* there is only ever one packet */
  if (offset != 0)
    return FALSE;

  *data_offset = offset;

  if ((file_size = wtap_file_size(wth, err)) == -1)
    return FALSE;

  if (file_size > WTAP_MAX_PACKET_SIZE) {
    /*
     * Probably a corrupt capture file; don't blow up trying
     * to allocate space for an immensely-large packet.
     */
    *err = WTAP_ERR_BAD_FILE;
    *err_info = g_strdup_printf("ber: File has %" G_GINT64_MODIFIER "d-byte packet, bigger than maximum of %u",
				file_size, WTAP_MAX_PACKET_SIZE);
    return FALSE;
  }
  packet_size = (int)file_size;

  buffer_assure_space(wth->frame_buffer, packet_size);
  buf = buffer_start_ptr(wth->frame_buffer);

  ber_set_pkthdr(&wth->phdr, packet_size);

  wtap_file_read_expected_bytes(buf, packet_size, wth->fh, err, err_info);

  return TRUE;
}

static gboolean ber_seek_read(wtap *wth, gint64 seek_off, struct wtap_pkthdr *phdr _U_,
			      guint8 *pd, int length, int *err, gchar **err_info)
{
  int packet_size = length;

  /* there is only one packet */
  if(seek_off > 0) {
    *err = 0;
    return FALSE;
  }

  if (file_seek(wth->random_fh, seek_off, SEEK_SET, err) == -1)
    return FALSE;

  ber_set_pkthdr(phdr, packet_size);

  wtap_file_read_expected_bytes(pd, packet_size, wth->random_fh, err, err_info);

  return TRUE;
}

int ber_open(wtap *wth, int *err, gchar **err_info)
{
#define BER_BYTES_TO_CHECK 8
  guint8 bytes[BER_BYTES_TO_CHECK];
  int bytes_read;
  guint8 ber_id;
  gint8 ber_class;
  gint8 ber_tag;
  gboolean ber_pc;
  guint8 oct, nlb = 0;
  int len = 0;
  gint64 file_size;
  int offset = 0, i;

  bytes_read = file_read(&bytes, BER_BYTES_TO_CHECK, wth->fh);
  if (bytes_read != BER_BYTES_TO_CHECK) {
    *err = file_error(wth->fh, err_info);
    if (*err != 0 && *err != WTAP_ERR_SHORT_READ)
      return -1;
    return 0;
  }

  ber_id = bytes[offset++];

  ber_class = (ber_id>>6) & 0x03;
  ber_pc = (ber_id>>5) & 0x01;
  ber_tag = ber_id & 0x1F;

  /* it must be constructed and either a SET or a SEQUENCE */
  /* or a CONTEXT less than 32 (arbitrary) */
  /* XXX: do we also want to allow APPLICATION */
  if(!(ber_pc &&
       (((ber_class == BER_CLASS_UNI) && ((ber_tag == BER_UNI_TAG_SET) || (ber_tag == BER_UNI_TAG_SEQ))) ||
	((ber_class == BER_CLASS_CON) && (ber_tag < 32)))))
    return 0;

  /* now check the length */
  oct = bytes[offset++];

  if(oct != 0x80) {
    /* not indefinite length encoded */

    if(!(oct & 0x80))
      /* length fits into a single byte */
      len = oct;
    else {
      nlb = oct & 0x7F; /* number of length bytes */

      if((nlb > 0) && (nlb <= (BER_BYTES_TO_CHECK - 2))) {
	/* not indefinite length and we have read enough bytes to compute the length */
	i = nlb;
	while(i--) {
	  oct = bytes[offset++];
	  len = (len<<8) + oct;
	}
      }
    }

    len += (2 + nlb); /* add back Tag and Length bytes */
    file_size = wtap_file_size(wth, err);

    if(len != file_size) {
      return 0; /* not ASN.1 */
    }
  } else {
    /* Indefinite length encoded - assume it is BER */
  }

  /* seek back to the start of the file  */
  if (file_seek(wth->fh, 0, SEEK_SET, err) == -1)
    return -1;

  wth->file_type = WTAP_FILE_BER;
  wth->file_encap = WTAP_ENCAP_BER;
  wth->snapshot_length = 0;

  wth->subtype_read = ber_read;
  wth->subtype_seek_read = ber_seek_read;
  wth->tsprecision = WTAP_FILE_TSPREC_SEC;

  return 1;
}
