wiretap/mp2t.c

   1 /* mp2t.c
   2  *
   3  * ISO/IEC 13818-1 MPEG2-TS file format decoder for the Wiretap library.
   4  * Written by Weston Schmidt <weston_schmidt@alumni.purdue.edu>
   5  * Copyright 2012 Weston Schmidt
   6  *
   7  * $Id$
   8  *
   9  * Wiretap Library
  10  * This program is free software; you can redistribute it and/or
  11  * modify it under the terms of the GNU General Public License
  12  * as published by the Free Software Foundation; either version 2
  13  * of the License, or (at your option) any later version.
  14  *
  15  * This program is distributed in the hope that it will be useful,
  16  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  17  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18  * GNU General Public License for more details.
  19  *
  20  * You should have received a copy of the GNU General Public License
  21  * along with this program; if not, write to the Free Software
  22  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  23  */
  24
  25 #include "config.h"
  26
  27 #ifdef HAVE_SYS_TYPES_H
  28 #include <sys/types.h>
  29 #endif
  30
  31 #ifdef HAVE_UNISTD_H
  32 #include <unistd.h>
  33 #endif
  34
  35 #include "mp2t.h"
  36
  37 #include "wtap-int.h"
  38 #include "buffer.h"
  39 #include "file_wrappers.h"
  40 #include <errno.h>
  41 #include <stdlib.h>
  42 #include <string.h>
  43 #include <time.h>
  44
  45 #define MP2T_SYNC_BYTE      0x47
  46 #define MP2T_SIZE           188
  47 #define MP2T_QAM256_BITRATE 38810700    /* bits per second */
  48 #define MP2T_QAM64_BITRATE  26970350    /* bits per second */
  49
  50 /* we try to detect trailing data up to 40 bytes after each packet */
  51 #define TRAILER_LEN_MAX 40
  52
  53 /* number of consecutive packets we must read to decide that a file
  54    is actually an mpeg2 ts */
  55 #define SYNC_STEPS   10
  56
  57
  58 typedef struct {
  59     int start_offset;
  60     /* length of trailing data (e.g. FEC) that's appended after each packet */
  61     guint8  trailer_len;
  62 } mp2t_filetype_t;
  63
  64 static gboolean
  65 mp2t_read_packet(mp2t_filetype_t *mp2t, FILE_T fh, gint64 offset,
  66                  struct wtap_pkthdr *phdr, Buffer *buf, int *err,
  67                  gchar **err_info)
  68 {
  69     guint64 tmp;
  70     int bytes_read;
  71
  72     buffer_assure_space(buf, MP2T_SIZE);
  73     errno = WTAP_ERR_CANT_READ;
  74     bytes_read = file_read(buffer_start_ptr(buf), MP2T_SIZE, fh);
  75     if (MP2T_SIZE != bytes_read) {
  76         *err = file_error(fh, err_info);
  77         /* bytes_read==0 is end of file, not a short read */
  78         if (bytes_read>0 && *err == 0) {
  79             *err = WTAP_ERR_SHORT_READ;
  80         }
  81         return FALSE;
  82     }
  83
  84     /* XXX - relative, not absolute, time stamps */
  85     phdr->presence_flags = WTAP_HAS_TS;
  86
  87     /*
  88      * Every packet in an MPEG2-TS stream is has a fixed size of
  89      * MP2T_SIZE plus the number of trailer bytes.
  90      *
  91      * The bitrate is constant, so the time offset, from the beginning
  92      * of the stream, of a given packet is the packet offset, in bits,
  93      * divided by the bitrate.
  94      *
  95      * It would be really cool to be able to configure the bitrate...
  96      */
  97     tmp = ((guint64)(offset - mp2t->start_offset) * 8); /* offset, in bits */
  98     phdr->ts.secs = (time_t)(tmp / MP2T_QAM256_BITRATE);
  99     phdr->ts.nsecs = (int)((tmp % MP2T_QAM256_BITRATE) * 1000000000 / MP2T_QAM256_BITRATE);
 100
 101     phdr->caplen = MP2T_SIZE;
 102     phdr->len = MP2T_SIZE;
 103
 104     return TRUE;
 105 }
 106
 107 static gboolean
 108 mp2t_read(wtap *wth, int *err, gchar **err_info, gint64 *data_offset)
 109 {
 110     mp2t_filetype_t *mp2t;
 111
 112     mp2t = (mp2t_filetype_t*) wth->priv;
 113
 114     *data_offset = file_tell(wth->fh);
 115
 116     if (!mp2t_read_packet(mp2t, wth->fh, *data_offset, &wth->phdr,
 117                           wth->frame_buffer, err, err_info)) {
 118         return FALSE;
 119     }
 120
 121     /* if there's a trailer, skip it and go to the start of the next packet */
 122     if (mp2t->trailer_len!=0) {
 123         if (-1 == file_seek(wth->fh, mp2t->trailer_len, SEEK_CUR, err)) {
 124             return FALSE;
 125         }
 126     }
 127
 128     return TRUE;
 129 }
 130
 131 static gboolean
 132 mp2t_seek_read(wtap *wth, gint64 seek_off, struct wtap_pkthdr *phdr,
 133         Buffer *buf, int length _U_, int *err, gchar **err_info)
 134 {
 135     mp2t_filetype_t *mp2t;
 136
 137     if (-1 == file_seek(wth->random_fh, seek_off, SEEK_SET, err)) {
 138         return FALSE;
 139     }
 140
 141     mp2t = (mp2t_filetype_t*) wth->priv;
 142
 143     if (!mp2t_read_packet(mp2t, wth->random_fh, seek_off, phdr, buf,
 144                           err, err_info)) {
 145         if (*err == 0)
 146             *err = WTAP_ERR_SHORT_READ;
 147         return FALSE;
 148     }
 149     return TRUE;
 150 }
 151
 152 int
 153 mp2t_open(wtap *wth, int *err, gchar **err_info)
 154 {
 155     int bytes_read;
 156     guint8 buffer[MP2T_SIZE+TRAILER_LEN_MAX];
 157     guint8 trailer_len = 0;
 158     guint sync_steps = 0;
 159     int i;
 160     int first;
 161     mp2t_filetype_t *mp2t;
 162
 163
 164     errno = WTAP_ERR_CANT_READ;
 165     bytes_read = file_read(buffer, MP2T_SIZE, wth->fh);
 166
 167     if (MP2T_SIZE != bytes_read) {
 168         *err = file_error(wth->fh, err_info);
 169         if (*err != 0 && *err != WTAP_ERR_SHORT_READ)
 170             return -1;
 171         return 0;
 172     }
 173
 174     first = -1;
 175     for (i = 0; i < MP2T_SIZE; i++) {
 176         if (MP2T_SYNC_BYTE == buffer[i]) {
 177             first = i;
 178             break;
 179         }
 180     }
 181     if (-1 == first) {
 182         return 0; /* wrong file type - not an mpeg2 ts file */
 183     }
 184
 185     if (-1 == file_seek(wth->fh, first, SEEK_SET, err)) {
 186         return -1;
 187     }
 188     /* read some packets and make sure they all start with a sync byte */
 189     do {
 190        bytes_read = file_read(buffer, MP2T_SIZE+trailer_len, wth->fh);
 191        if (bytes_read < 0) {
 192           *err = file_error(wth->fh, err_info);
 193           return -1;  /* read error */
 194        }
 195        if (bytes_read < MP2T_SIZE+trailer_len) {
 196           if(sync_steps<2) return 0; /* wrong file type - not an mpeg2 ts file */
 197           break;  /* end of file, that's ok if we're still in sync */
 198        }
 199        if (buffer[0] == MP2T_SYNC_BYTE) {
 200                sync_steps++;
 201        }
 202        else {
 203            /* no sync byte found, check if trailing data is appended
 204               and we have to increase the packet size */
 205
 206            /* if we've already detected a trailer field, we must remain in sync
 207               another mismatch means we have no mpeg2 ts file */
 208            if (trailer_len>0)
 209                return 0;
 210
 211            /* check if a trailer is appended to the packet */
 212            for (i=0; i<TRAILER_LEN_MAX; i++) {
 213                if (buffer[i] == MP2T_SYNC_BYTE) {
 214                    trailer_len = i;
 215                    if (-1 == file_seek(wth->fh, first, SEEK_SET, err)) {
 216                        return -1;
 217                    }
 218                    sync_steps = 0;
 219                    break;
 220                }
 221            }
 222            /* no sync byte found in the vicinity, this is no mpeg2 ts file */
 223            if (i==TRAILER_LEN_MAX)
 224                return 0;
 225        }
 226     } while (sync_steps < SYNC_STEPS);
 227
 228     if (-1 == file_seek(wth->fh, first, SEEK_SET, err)) {
 229         return -1;
 230     }
 231
 232     wth->file_type_subtype = WTAP_FILE_TYPE_SUBTYPE_MPEG_2_TS;
 233     wth->file_encap = WTAP_ENCAP_MPEG_2_TS;
 234     wth->tsprecision = WTAP_FILE_TSPREC_NSEC;
 235     wth->subtype_read = mp2t_read;
 236     wth->subtype_seek_read = mp2t_seek_read;
 237     wth->snapshot_length = 0;
 238
 239     mp2t = (mp2t_filetype_t*) g_malloc(sizeof(mp2t_filetype_t));
 240     if (NULL == mp2t) {
 241         return -1;
 242     }
 243
 244     wth->priv = mp2t;
 245     mp2t->start_offset = first;
 246     mp2t->trailer_len = trailer_len;
 247
 248     return 1;
 249 }