/* 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

 * SPDX-License-Identifier: GPL-2.0-or-later

 */

#include "config.h"

#include "mp2t.h"

#include <sys/types.h>

#ifdef HAVE_UNISTD_H

#include <unistd.h>

#endif

#include "wtap_module.h"

#include <wsutil/buffer.h>

#include <wsutil/pint.h>

#include "file_wrappers.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 {

    uint64_t bitrate;

    uint32_t start_offset;

    /* length of header data (e.g., TP_extra_header in BDAV m2ts files) before

     * each packet) */

    uint8_t header_len;

    /* length of trailing data (e.g. FEC) that's appended after each packet */

    uint8_t trailer_len;

} mp2t_filetype_t;

static int mp2t_file_type_subtype = -1;

void register_mp2t(void);

static bool

mp2t_read_packet(wtap *wth, FILE_T fh, int64_t offset, wtap_rec *rec, int *err,

                 char **err_info)

{

    mp2t_filetype_t *mp2t;

    uint64_t tmp;

    mp2t = (mp2t_filetype_t*) wth->priv;

    /*

     * MP2T_SIZE will always be less than WTAP_MAX_PACKET_SIZE_STANDARD, so

     * we don't have to worry about the packet being too big.

     */

    if (!wtap_read_bytes_or_eof_buffer(fh, &rec->data, MP2T_SIZE, err, err_info))

        return false;

    wtap_setup_packet_rec(rec, wth->file_encap);

    rec->block = wtap_block_create(WTAP_BLOCK_PACKET);

    /* XXX - relative, not absolute, time stamps */

    rec->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 = ((uint64_t)(offset - mp2t->start_offset) * 8); /* offset, in bits */

    rec->ts.secs = (time_t)(tmp / mp2t->bitrate);

    rec->ts.nsecs = (int)((tmp % mp2t->bitrate) * 1000000000 / mp2t->bitrate);

    rec->rec_header.packet_header.caplen = MP2T_SIZE;

    rec->rec_header.packet_header.len = MP2T_SIZE;

    return true;

}

static bool

mp2t_read(wtap *wth, wtap_rec *rec, int *err,

        char **err_info, int64_t *data_offset)

{

    mp2t_filetype_t *mp2t;

    mp2t = (mp2t_filetype_t*) wth->priv;

    /* if there's a header, skip it and go to the start of the packet */

    /* XXX - Eventually we might want to process the header (and trailer?) in

     * packet-mp2t.c, in which case we would read it in mp2t_read_packet and

     * include header_len in the packet_header lengths. We'd probably want

     * pseudo-header information to indicate it to packet-mp2t.c

     */

    if (mp2t->header_len!=0) {

        if (!wtap_read_bytes_or_eof(wth->fh, NULL, mp2t->header_len, err, err_info)) {

            return false;

        }

    }

    *data_offset = file_tell(wth->fh);

    if (!mp2t_read_packet(wth, wth->fh, *data_offset, rec, 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 (!wtap_read_bytes(wth->fh, NULL, mp2t->trailer_len, err, err_info)) {

            return false;

        }

    }

    return true;

}

static bool

mp2t_seek_read(wtap *wth, int64_t seek_off, wtap_rec *rec,

        int *err, char **err_info)

{

    if (-1 == file_seek(wth->random_fh, seek_off, SEEK_SET, err)) {

        return false;

    }

    if (!mp2t_read_packet(wth, wth->random_fh, seek_off, rec, err, err_info)) {

        if (*err == 0)

            *err = WTAP_ERR_SHORT_READ;

        return false;

    }

    return true;

}

static uint64_t

mp2t_read_pcr(uint8_t *buffer)

{

    uint64_t base;

    uint64_t ext;

    base = pntohu40(buffer);

    base >>= 7;

    ext = pntohu16(&buffer[4]);

    ext &= 0x01ff;

    return (base * 300 + ext);

}

static bool

mp2t_find_next_pcr(wtap *wth, uint8_t trailer_len,

        int *err, char **err_info, uint32_t *idx, uint64_t *pcr, uint16_t *pid)

{

    uint8_t buffer[MP2T_SIZE+TRAILER_LEN_MAX];

    bool found;

    uint8_t afc;

    unsigned 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 & pntohu16(&buffer[1]);

        found = true;

    }

    return found;

}

static wtap_open_return_val

mp2t_bits_per_second(wtap *wth, uint32_t first, uint8_t trailer_len,

        uint64_t *bitrate, int *err, char **err_info)

{

    uint32_t pn1, pn2;

    uint64_t pcr1, pcr2;

    uint16_t pid1, pid2;

    uint32_t idx;

    uint64_t 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 uint64_t

       otherwise, the multiplication would use uint32_t and could

       overflow before the result is assigned to the uint64_t bits_passed */

    bits_passed = (uint64_t)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, char **err_info)

{

    uint8_t buffer[MP2T_SIZE+TRAILER_LEN_MAX];

    uint8_t trailer_len = 0;

    uint8_t header_len = 0;

    unsigned sync_steps = 0;

    unsigned i;

    uint32_t first = 0;

    mp2t_filetype_t *mp2t;

    wtap_open_return_val status;

    uint64_t 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) {

                /* check for header with spurious sync byte in header */

                if (first < trailer_len) {

                    first += 1;

                    trailer_len -= 1;

                    if (-1 == file_seek(wth->fh, first, SEEK_SET, err)) {

                        return WTAP_OPEN_ERROR;

                    }

                    /* Shouldn't fail, we just read this */

                    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 < trailer_len; i++) {

                        if (MP2T_SYNC_BYTE == buffer[i]) {

                            first += i;

                            trailer_len -= i;

                            goto found;

                        }

                    }

                }

                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 the packet didn't start on a sync byte, the "trailer" might

     * be a header. At least BDAV M2TS does this with a four byte header. */

    header_len = MIN(first, trailer_len);

    first -= header_len;

    trailer_len -= header_len;

    if (-1 == file_seek(wth->fh, first, SEEK_SET, err)) {

        return WTAP_OPEN_ERROR;

    }

    wth->file_type_subtype = mp2t_file_type_subtype;

    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 = g_new(mp2t_filetype_t, 1);

    wth->priv = mp2t;

    mp2t->start_offset = first;

    mp2t->trailer_len = trailer_len;

    mp2t->header_len = header_len;

    mp2t->bitrate = bitrate;

    return WTAP_OPEN_MINE;

}

static int mp2t_dump_can_write_encap(int encap)

{

    /* Per-packet encapsulations aren't supported. */

    if (encap == WTAP_ENCAP_PER_PACKET) {

        return WTAP_ERR_ENCAP_PER_PACKET_UNSUPPORTED;

    }

    /* This is the only encapsulation type we write. */

    if (encap != WTAP_ENCAP_MPEG_2_TS) {

        return WTAP_ERR_UNWRITABLE_ENCAP;

    }

    return 0;

}

/* Write a record for a packet to a dump file.

   Returns true on success, false on failure. */

static bool mp2t_dump(wtap_dumper *wdh, const wtap_rec *rec,

    int *err, char **err_info _U_)

{

    /* We can only write packet records. */

    if (rec->rec_type != REC_TYPE_PACKET) {

        *err = WTAP_ERR_UNWRITABLE_REC_TYPE;

        *err_info = wtap_unwritable_rec_type_err_string(rec);

        return false;

    }

    /*

     * Make sure this packet doesn't have a link-layer type that

     * differs from the one for the file.

     */

    if (wdh->file_encap != rec->rec_header.packet_header.pkt_encap) {

        *err = WTAP_ERR_ENCAP_PER_PACKET_UNSUPPORTED;

        return false;

    }

    /* A MPEG-2 Transport Stream is just the packet bytes, with no header.

     * The sync byte is supposed to identify where packets start.

     * Note this drops existing headers and trailers currently, since we

     * don't include them in the record.

     */

    if (!wtap_dump_file_write(wdh, ws_buffer_start_ptr(&rec->data), rec->rec_header.packet_header.caplen, err)) {

        return false;

    }

    return true;

}

/* Returns true on success, false on failure; sets "*err" to an error code on

   failure */

static bool mp2t_dump_open(wtap_dumper *wdh, int *err _U_, char **err_info _U_)

{

    /* There is no header, so we just always return true. */

    wdh->subtype_write = mp2t_dump;

    return true;

}

static const struct supported_block_type mp2t_blocks_supported[] = {

    /*

     * We support packet blocks, with no comments or other options.

     */

    { WTAP_BLOCK_PACKET, MULTIPLE_BLOCKS_SUPPORTED, NO_OPTIONS_SUPPORTED }

};

static const struct file_type_subtype_info mp2t_info = {

    "MPEG2 transport stream", "mp2t", "mp2t", "ts;m2ts;mpg",

    false, BLOCKS_SUPPORTED(mp2t_blocks_supported),

    mp2t_dump_can_write_encap, mp2t_dump_open, NULL

};

void register_mp2t(void)

{

    mp2t_file_type_subtype = wtap_register_file_type_subtype(&mp2t_info);

    /*

     * Register name for backwards compatibility with the

     * wtap_filetypes table in Lua.

     */

    wtap_register_backwards_compatibility_lua_name("MPEG_2_TS",

                                                   mp2t_file_type_subtype);

}

/*

 * Editor modelines  -  https://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:

 */