nexmon – Rev 1
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/* 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_QAM64_BITRATE 26970350 /* bits per second */
#define MP2T_PCR_CLOCK 27000000 /* cycles per second - 27MHz */
/* 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 {
guint32 start_offset;
guint64 bitrate;
/* 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;
/*
* MP2T_SIZE will always be less than WTAP_MAX_PACKET_SIZE, so
* we don't have to worry about the packet being too big.
*/
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.
*
* We assume that the bits in the transport stream are supplied at
* a constant rate; is that guaranteed by all media that use
* MPEG2-TS? If 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, in
* case our attempt to guess it from the PCRs of one of the programs
* doesn't get the right answer.
*/
tmp = ((guint64)(offset - mp2t->start_offset) * 8); /* offset, in bits */
phdr->ts.secs = (time_t)(tmp / mp2t->bitrate);
phdr->ts.nsecs = (int)((tmp % mp2t->bitrate) * 1000000000 / mp2t->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;
}
static guint64
mp2t_read_pcr(guint8 *buffer)
{
guint64 base;
guint64 ext;
base = pntoh40(buffer);
base >>= 7;
ext = pntoh16(&buffer[4]);
ext &= 0x01ff;
return (base * 300 + ext);
}
static gboolean
mp2t_find_next_pcr(wtap *wth, guint8 trailer_len,
int *err, gchar **err_info, guint32 *idx, guint64 *pcr, guint16 *pid)
{
guint8 buffer[MP2T_SIZE+TRAILER_LEN_MAX];
gboolean found;
guint8 afc;
guint timeout = 0;
found = FALSE;
while (FALSE == found && timeout++ < SYNC_STEPS * SYNC_STEPS) {
(*idx)++;
if (!wtap_read_bytes_or_eof(
wth->fh, buffer, MP2T_SIZE+trailer_len, err, err_info)) {
/* Read error, short read, or EOF */
return FALSE;
}
if (MP2T_SYNC_BYTE != buffer[0]) {
continue;
}
/* Read out the AFC value. */
afc = 3 & (buffer[3] >> 4);
if (afc < 2) {
continue;
}
/* Check the length. */
if (buffer[4] < 7) {
continue;
}
/* Check that there is the PCR flag. */
if (0x10 != (0x10 & buffer[5])) {
continue;
}
/* We have a PCR value! */
*pcr = mp2t_read_pcr(&buffer[6]);
*pid = 0x01ff & pntoh16(&buffer[1]);
found = TRUE;
}
return found;
}
static wtap_open_return_val
mp2t_bits_per_second(wtap *wth, guint32 first, guint8 trailer_len,
guint64 *bitrate, int *err, gchar **err_info)
{
guint32 pn1, pn2;
guint64 pcr1, pcr2;
guint16 pid1, pid2;
guint32 idx;
guint64 pcr_delta, bits_passed;
/* Find the first PCR + PID.
* Then find another PCR in that PID.
* Take the difference and that's our bitrate.
* All the different PCRs in different PIDs 'should' be the same.
*
* XXX - is this assuming that the time stamps in the PCRs correspond
* to the time scale of the underlying transport stream?
*/
idx = first;
if (!mp2t_find_next_pcr(wth, trailer_len, err, err_info, &idx, &pcr1, &pid1)) {
/* Read error, short read, or EOF */
if (*err == WTAP_ERR_SHORT_READ)
return WTAP_OPEN_NOT_MINE; /* not a full frame */
if (*err != 0)
return WTAP_OPEN_ERROR;
/* We don't have any PCRs, so we can't guess the bit rate.
* Default to something reasonable.
*/
*bitrate = MP2T_QAM64_BITRATE;
return WTAP_OPEN_MINE;
}
pn1 = idx;
pn2 = pn1;
while (pn1 == pn2) {
if (!mp2t_find_next_pcr(wth, trailer_len, err, err_info, &idx, &pcr2, &pid2)) {
/* Read error, short read, or EOF */
if (*err == WTAP_ERR_SHORT_READ)
return WTAP_OPEN_NOT_MINE; /* not a full frame */
if (*err != 0)
return WTAP_OPEN_ERROR;
/* We don't have two PCRs for the same PID, so we can't guess
* the bit rate.
* Default to something reasonable.
*/
*bitrate = MP2T_QAM64_BITRATE;
return WTAP_OPEN_MINE;
}
if (pid1 == pid2) {
pn2 = idx;
}
}
if (pcr2 <= pcr1) {
/* The PCRs for that PID didn't go forward; treat that as an
* indication that this isn't an MPEG-2 TS.
*/
return WTAP_OPEN_NOT_MINE;
}
pcr_delta = pcr2 - pcr1;
/* cast one of the factors to guint64
otherwise, the multiplication would use guint32 and could
overflow before the result is assigned to the guint64 bits_passed */
bits_passed = (guint64)MP2T_SIZE * (pn2 - pn1) * 8;
*bitrate = ((MP2T_PCR_CLOCK * bits_passed) / pcr_delta);
if (*bitrate == 0) {
/* pcr_delta < MP2T_PCR_CLOCK * bits_passed (pn2 != pn1,
* as that's the test for the loop above, so bits_passed
* is non-zero).
*
* That will produce a fractional bitrate, which turns
* into zero, causing a zero divide later.
*
* XXX - should we report this as "not ours"? A bitrate
* of less than 1 bit per second is not very useful for any
* form of audio/video, so presumably that's unlikely to
* be an MP2T file.
*/
return WTAP_OPEN_ERROR;
}
return WTAP_OPEN_MINE;
}
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;
guint i;
guint32 first = 0;
mp2t_filetype_t *mp2t;
wtap_open_return_val status;
guint64 bitrate;
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;
}
for (i = 0; i < MP2T_SIZE; i++) {
if (MP2T_SYNC_BYTE == buffer[i]) {
first = i;
goto found;
}
}
/*
* No sync bytes found, so not an MPEG-2 Transport Stream file.
*/
return WTAP_OPEN_NOT_MINE; /* wrong file type - not an mpeg2 ts file */
found:
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;
}
/* Ensure there is a valid bitrate */
status = mp2t_bits_per_second(wth, first, trailer_len,
&bitrate, err, err_info);
if (status != WTAP_OPEN_MINE) {
return status;
}
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;
mp2t->bitrate = bitrate;
return WTAP_OPEN_MINE;
}
/*
* Editor modelines - http://www.wireshark.org/tools/modelines.html
*
* Local variables:
* c-basic-offset: 4
* tab-width: 8
* indent-tabs-mode: nil
* End:
*
* vi: set shiftwidth=4 tabstop=8 expandtab:
* :indentSize=4:tabSize=8:noTabs=true:
*/