mp2t.c

/* mp2t.c
 *
 * ISO/IEC 13818-1 MPEG2-TS file format decoder for the Wiretap library.
 * Written by Weston Schmidt <weston_schmidt@alumni.purdue.edu>
 * Copyright 2012 Weston Schmidt
 *
 * Wiretap Library
 * 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"

#ifdef HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif

#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#include "mp2t.h"

#include "wtap-int.h"
#include <wsutil/buffer.h>
#include "file_wrappers.h"
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#define MP2T_SYNC_BYTE      0x47
#define MP2T_SIZE           188
#define MP2T_QAM256_BITRATE 38810700    /* bits per second */
#define MP2T_QAM64_BITRATE  26970350    /* bits per second */

/* we try to detect trailing data up to 40 bytes after each packet */
#define TRAILER_LEN_MAX 40

/* number of consecutive packets we must read to decide that a file
   is actually an mpeg2 ts */
#define SYNC_STEPS   10


typedef struct {
    int start_offset;
    /* length of trailing data (e.g. FEC) that's appended after each packet */
    guint8  trailer_len;
} mp2t_filetype_t;

static gboolean
mp2t_read_packet(mp2t_filetype_t *mp2t, FILE_T fh, gint64 offset,
                 struct wtap_pkthdr *phdr, Buffer *buf, int *err,
                 gchar **err_info)
{
    guint64 tmp;

    ws_buffer_assure_space(buf, MP2T_SIZE);
    if (!wtap_read_bytes_or_eof(fh, ws_buffer_start_ptr(buf), MP2T_SIZE, err, err_info))
        return FALSE;

    phdr->rec_type = REC_TYPE_PACKET;

    /* XXX - relative, not absolute, time stamps */
    phdr->presence_flags = WTAP_HAS_TS;

    /*
     * Every packet in an MPEG2-TS stream is has a fixed size of
     * MP2T_SIZE plus the number of trailer bytes.
     *
     * The bitrate is constant, so the time offset, from the beginning
     * of the stream, of a given packet is the packet offset, in bits,
     * divided by the bitrate.
     *
     * It would be really cool to be able to configure the bitrate...
     */
    tmp = ((guint64)(offset - mp2t->start_offset) * 8);	/* offset, in bits */
    phdr->ts.secs = (time_t)(tmp / MP2T_QAM256_BITRATE);
    phdr->ts.nsecs = (int)((tmp % MP2T_QAM256_BITRATE) * 1000000000 / MP2T_QAM256_BITRATE);

    phdr->caplen = MP2T_SIZE;
    phdr->len = MP2T_SIZE;

    return TRUE;
}

static gboolean
mp2t_read(wtap *wth, int *err, gchar **err_info, gint64 *data_offset)
{
    mp2t_filetype_t *mp2t;

    mp2t = (mp2t_filetype_t*) wth->priv;

    *data_offset = file_tell(wth->fh);

    if (!mp2t_read_packet(mp2t, wth->fh, *data_offset, &wth->phdr,
                          wth->frame_buffer, err, err_info)) {
        return FALSE;
    }

    /* if there's a trailer, skip it and go to the start of the next packet */
    if (mp2t->trailer_len!=0) {
        if (-1 == file_seek(wth->fh, mp2t->trailer_len, SEEK_CUR, err)) {
            return FALSE;
        }
    }

    return TRUE;
}

static gboolean
mp2t_seek_read(wtap *wth, gint64 seek_off, struct wtap_pkthdr *phdr,
        Buffer *buf, int *err, gchar **err_info)
{
    mp2t_filetype_t *mp2t;

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

    mp2t = (mp2t_filetype_t*) wth->priv;

    if (!mp2t_read_packet(mp2t, wth->random_fh, seek_off, phdr, buf,
                          err, err_info)) {
        if (*err == 0)
            *err = WTAP_ERR_SHORT_READ;
        return FALSE;
    }
    return TRUE;
}

wtap_open_return_val
mp2t_open(wtap *wth, int *err, gchar **err_info)
{
    guint8 buffer[MP2T_SIZE+TRAILER_LEN_MAX];
    guint8 trailer_len = 0;
    guint sync_steps = 0;
    int i;
    int first;
    mp2t_filetype_t *mp2t;


    if (!wtap_read_bytes(wth->fh, buffer, MP2T_SIZE, err, err_info)) {
        if (*err != WTAP_ERR_SHORT_READ)
            return WTAP_OPEN_ERROR;
        return WTAP_OPEN_NOT_MINE;
    }

    first = -1;
    for (i = 0; i < MP2T_SIZE; i++) {
        if (MP2T_SYNC_BYTE == buffer[i]) {
            first = i;
            break;
        }
    }
    if (-1 == first) {
        return WTAP_OPEN_NOT_MINE; /* wrong file type - not an mpeg2 ts file */
    }

    if (-1 == file_seek(wth->fh, first, SEEK_SET, err)) {
        return WTAP_OPEN_ERROR;
    }
    /* read some packets and make sure they all start with a sync byte */
    do {
       if (!wtap_read_bytes(wth->fh, buffer, MP2T_SIZE+trailer_len, err, err_info)) {
          if (*err != WTAP_ERR_SHORT_READ)
            return WTAP_OPEN_ERROR;  /* read error */
          if(sync_steps<2) return WTAP_OPEN_NOT_MINE; /* wrong file type - not an mpeg2 ts file */
          break;  /* end of file, that's ok if we're still in sync */
       }
       if (buffer[0] == MP2T_SYNC_BYTE) {
               sync_steps++;
       }
       else {
           /* no sync byte found, check if trailing data is appended
              and we have to increase the packet size */

           /* if we've already detected a trailer field, we must remain in sync
              another mismatch means we have no mpeg2 ts file */
           if (trailer_len>0)
               return WTAP_OPEN_NOT_MINE;

           /* check if a trailer is appended to the packet */
           for (i=0; i<TRAILER_LEN_MAX; i++) {
               if (buffer[i] == MP2T_SYNC_BYTE) {
                   trailer_len = i;
                   if (-1 == file_seek(wth->fh, first, SEEK_SET, err)) {
                       return WTAP_OPEN_ERROR;
                   }
                   sync_steps = 0;
                   break;
               }
           }
           /* no sync byte found in the vicinity, this is no mpeg2 ts file */
           if (i==TRAILER_LEN_MAX)
               return WTAP_OPEN_NOT_MINE;
       }
    } while (sync_steps < SYNC_STEPS);

    if (-1 == file_seek(wth->fh, first, SEEK_SET, err)) {
        return WTAP_OPEN_ERROR;
    }

    wth->file_type_subtype = WTAP_FILE_TYPE_SUBTYPE_MPEG_2_TS;
    wth->file_encap = WTAP_ENCAP_MPEG_2_TS;
    wth->file_tsprec = WTAP_TSPREC_NSEC;
    wth->subtype_read = mp2t_read;
    wth->subtype_seek_read = mp2t_seek_read;
    wth->snapshot_length = 0;

    mp2t = (mp2t_filetype_t*) g_malloc(sizeof(mp2t_filetype_t));

    wth->priv = mp2t;
    mp2t->start_offset = first;
    mp2t->trailer_len = trailer_len;

    return WTAP_OPEN_MINE;
}