mpv/libmpdemux/ebml.c

/*
 * native ebml reader for the Matroska demuxer
 * Written by Aurelien Jacobs <aurel@gnuage.org>
 * Based on the one written by Ronald Bultje for gstreamer
 * Licence: GPL
 */

#include "config.h"
#ifdef HAVE_MATROSKA

#include <stdlib.h>

#include "stream.h"
#include "ebml.h"
#include "bswap.h"


/*
 * Read: the element content data ID.
 * Return: the ID.
 */
uint32_t
ebml_read_id (stream_t *s, int *length)
{
  int i, len_mask = 0x80;
  uint32_t id;

  for (i=0, id=stream_read_char (s); i<4 && !(id & len_mask); i++)
    len_mask >>= 1;
  if (i >= 4)
    return EBML_ID_INVALID;
  if (length)
    *length = i + 1;
  while (i--)
    id = (id << 8) | stream_read_char (s);
  return id;
}

/*
 * Read a variable length unsigned int.
 */
uint64_t
ebml_read_vlen_uint (uint8_t *buffer, int *length)
{
  int i, j, num_ffs = 0, len_mask = 0x80;
  uint64_t num;

  for (i=0, num=*buffer++; i<8 && !(num & len_mask); i++)
    len_mask >>= 1;
  if (i >= 8)
    return EBML_UINT_INVALID;
  j = i+1;
  if (length)
    *length = j;
  if ((int)(num &= (len_mask - 1)) == len_mask - 1)
    num_ffs++;
  while (i--)
    {
      num = (num << 8) | *buffer++;
      if ((num & 0xFF) == 0xFF)
        num_ffs++;
    }
  if (j == num_ffs)
    return EBML_UINT_INVALID;
  return num;
}

/*
 * Read a variable length signed int.
 */
int64_t
ebml_read_vlen_int (uint8_t *buffer, int *length)
{
  uint64_t unum;
  int l;

  /* read as unsigned number first */
  unum = ebml_read_vlen_uint (buffer, &l);
  if (unum == EBML_UINT_INVALID)
    return EBML_INT_INVALID;
  if (length)
    *length = l;

  return unum - ((1 << ((7 * l) - 1)) - 1);
}

/*
 * Read: element content length.
 */
uint64_t
ebml_read_length (stream_t *s, int *length)
{
  int i, j, num_ffs = 0, len_mask = 0x80;
  uint64_t len;

  for (i=0, len=stream_read_char (s); i<8 && !(len & len_mask); i++)
    len_mask >>= 1;
  if (i >= 8)
    return EBML_UINT_INVALID;
  j = i+1;
  if (length)
    *length = j;
  if ((int)(len &= (len_mask - 1)) == len_mask - 1)
    num_ffs++;
  while (i--)
    {
      len = (len << 8) | stream_read_char (s);
      if ((len & 0xFF) == 0xFF)
        num_ffs++;
    }
  if (j == num_ffs)
    return EBML_UINT_INVALID;
  return len;
}

/*
 * Read the next element as an unsigned int.
 */
uint64_t
ebml_read_uint (stream_t *s, uint64_t *length)
{
  uint64_t len, value = 0;
  int l;

  len = ebml_read_length (s, &l);
  if (len == EBML_UINT_INVALID || len < 1 || len > 8)
    return EBML_UINT_INVALID;
  if (length)
    *length = len + l;

  while (len--)
    value = (value << 8) | stream_read_char (s);

  return value;
}

/*
 * Read the next element as a signed int.
 */
int64_t
ebml_read_int (stream_t *s, uint64_t *length)
{
  int64_t value = 0;
  uint64_t len;
  int l;

  len = ebml_read_length (s, &l);
  if (len == EBML_UINT_INVALID || len < 1 || len > 8)
    return EBML_INT_INVALID;
  if (length)
    *length = len + l;

  len--;
  l = stream_read_char (s);
  if (l & 0x80)
    value = -1;
  value = (value << 8) | l;
  while (len--)
    value = (value << 8) | stream_read_char (s);

  return value;
}

/*
 * Read the next element as a float.
 */
long double
ebml_read_float (stream_t *s, uint64_t *length)
{
  long double value;
  uint64_t len;
  int l;

  len = ebml_read_length (s, &l);
  switch (len)
    {
    case 4:
      {
        union {uint32_t i; float f;} u;
        u.i = stream_read_dword (s);
        value = u.f;
        break;
      }

    case 8:
      {
        union {uint64_t i; double d;} u;
        u.i = stream_read_qword (s);
        value = u.d;
        break;
      }

    case 10:
      {
        union {uint8_t data[10]; long double ld;} u;
        if (stream_read (s, u.data, 10) != 10)
          return EBML_FLOAT_INVALID;
        value = be2me_ldbl(u.ld);
        break;
      }

    default:
      return EBML_FLOAT_INVALID;
    }

  if (length)
    *length = len + l;

  return value;
}

/*
 * Read the next element as an ASCII string.
 */
char *
ebml_read_ascii (stream_t *s, uint64_t *length)
{
  uint64_t len;
  char *str;
  int l;

  len = ebml_read_length (s, &l);
  if (len == EBML_UINT_INVALID)
    return NULL;
  if (length)
    *length = len + l;

  str = (char *) malloc (len+1);
  if (stream_read(s, str, len) != (int) len)
    {
      free (str);
      return NULL;
    }
  str[len] = '\0';

  return str;
}

/*
 * Read the next element as a UTF-8 string.
 */
char *
ebml_read_utf8 (stream_t *s, uint64_t *length)
{
  return ebml_read_ascii (s, length);
}

/*
 * Skip the next element.
 */
int
ebml_read_skip (stream_t *s, uint64_t *length)
{
  uint64_t len;
  int l;

  len = ebml_read_length (s, &l);
  if (len == EBML_UINT_INVALID)
    return 1;
  if (length)
    *length = len + l;

  stream_skip(s, len);

  return 0;
}

/*
 * Read the next element, but only the header. The contents
 * are supposed to be sub-elements which can be read separately.
 */
uint32_t
ebml_read_master (stream_t *s, uint64_t *length)
{
  uint64_t len;
  uint32_t id;

  id = ebml_read_id (s, NULL);
  if (id == EBML_ID_INVALID)
    return id;

  len = ebml_read_length (s, NULL);
  if (len == EBML_UINT_INVALID)
    return EBML_ID_INVALID;
  if (length)
    *length = len;

  return id;
}


/*
 * Read an EBML header.
 */
char *
ebml_read_header (stream_t *s, int *version)
{
  uint64_t length, l, num;
  uint32_t id;
  char *str = NULL;

  if (ebml_read_master (s, &length) != EBML_ID_HEADER)
    return 0;

  if (version)
    *version = 1;

  while (length > 0)
    {
      id = ebml_read_id (s, NULL);
      if (id == EBML_ID_INVALID)
        return NULL;
      length -= 2;

      switch (id)
        {
          /* is our read version uptodate? */
        case EBML_ID_EBMLREADVERSION:
          num = ebml_read_uint (s, &l);
          if (num != EBML_VERSION)
            return NULL;
          break;

          /* we only handle 8 byte lengths at max */
        case EBML_ID_EBMLMAXSIZELENGTH:
          num = ebml_read_uint (s, &l);
          if (num != sizeof (uint64_t))
            return NULL;
          break;

          /* we handle 4 byte IDs at max */
        case EBML_ID_EBMLMAXIDLENGTH:
          num = ebml_read_uint (s, &l);
          if (num != sizeof (uint32_t))
            return NULL;
          break;

        case EBML_ID_DOCTYPE:
          str = ebml_read_ascii (s, &l);
          if (str == NULL)
            return NULL;
          break;

        case EBML_ID_DOCTYPEREADVERSION:
          num = ebml_read_uint (s, &l);
          if (num == EBML_UINT_INVALID)
            return NULL;
          if (version)
            *version = num;
          break;

          /* we ignore these two, they don't tell us anything we care about */
        case EBML_ID_VOID:
        case EBML_ID_EBMLVERSION:
        case EBML_ID_DOCTYPEVERSION:
        default:
          if (ebml_read_skip (s, &l))
            return NULL;
          break;
        }
      length -= l;
    }

  return str;
}

#endif /* HAVE_MATROSKA */