/* ber.c
 *
 * Basic Encoding Rules (BER) file reading
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */

#include "config.h"

#include <errno.h>

#include "wtap-int.h"
#include "file_wrappers.h"
#include <wsutil/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 int ber_file_type_subtype = -1;

void register_ber(void);

static gboolean ber_full_file_read(wtap *wth, wtap_rec *rec, Buffer *buf,
                                   int *err, gchar **err_info,
                                   gint64 *data_offset)
{
  if (!wtap_full_file_read(wth, rec, buf, err, err_info, data_offset))
    return FALSE;

  /* Pass the file name. */
  rec->rec_header.packet_header.pseudo_header.ber.pathname = wth->pathname;
  return TRUE;
}

static gboolean ber_full_file_seek_read(wtap *wth, gint64 seek_off,
                                        wtap_rec *rec, Buffer *buf,
                                        int *err, gchar **err_info)
{
  if (!wtap_full_file_seek_read(wth, seek_off, rec, buf, err, err_info))
    return FALSE;

  /* Pass the file name. */
  rec->rec_header.packet_header.pseudo_header.ber.pathname = wth->pathname;
  return TRUE;
}

wtap_open_return_val ber_open(wtap *wth, int *err, gchar **err_info)
{
#define BER_BYTES_TO_CHECK 8
  guint8 bytes[BER_BYTES_TO_CHECK];
  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;

  if (!wtap_read_bytes(wth->fh, &bytes, BER_BYTES_TO_CHECK, err, err_info)) {
    if (*err != WTAP_ERR_SHORT_READ)
      return WTAP_OPEN_ERROR;
    return WTAP_OPEN_NOT_MINE;
  }

  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/APPLICATION less than 32 (arbitrary) */
  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_class == BER_CLASS_APP)) && (ber_tag < 32)))))
    return WTAP_OPEN_NOT_MINE;

  /* 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 WTAP_OPEN_NOT_MINE; /* 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 WTAP_OPEN_ERROR;

  wth->file_type_subtype = ber_file_type_subtype;
  wth->file_encap = WTAP_ENCAP_BER;
  wth->snapshot_length = 0;

  wth->subtype_read = ber_full_file_read;
  wth->subtype_seek_read = ber_full_file_seek_read;
  wth->file_tsprec = WTAP_TSPREC_SEC;

  return WTAP_OPEN_MINE;
}

static const struct supported_block_type ber_blocks_supported[] = {
  /*
   * These are file formats that we dissect, so we provide only one
   * "packet" with the file's contents, and don't support any
   * options.
   */
  { WTAP_BLOCK_PACKET, ONE_BLOCK_SUPPORTED, NO_OPTIONS_SUPPORTED }
};

static const struct file_type_subtype_info ber_info = {
  "ASN.1 Basic Encoding Rules", "ber", NULL, NULL,
  FALSE, BLOCKS_SUPPORTED(ber_blocks_supported),
  NULL, NULL, NULL
};

void register_ber(void)
{
  ber_file_type_subtype = wtap_register_file_type_subtype(&ber_info);

  /*
   * Register name for backwards compatibility with the
   * wtap_filetypes table in Lua.
   */
  wtap_register_backwards_compatibility_lua_name("BER", ber_file_type_subtype);
}

/*
 * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
 *
 * Local Variables:
 * c-basic-offset: 2
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 * End:
 *
 * vi: set shiftwidth=2 tabstop=8 expandtab:
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 */