tag.c

/*
 * libid3tag - ID3 tag manipulation library
 * Copyright (C) 2000-2004 Underbit Technologies, Inc.
 *
 * 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * $Id: tag.c,v 1.20 2004/02/17 02:04:10 rob Exp $
 */
 
# ifdef HAVE_CONFIG_H
#  include "config.h"
# endif
 
# include "global.h"
 
# include <string.h>
# include <stdlib.h>
 
# ifdef HAVE_ASSERT_H
#  include <assert.h>
# endif
 
# include "id3tag.h"
# include "tag.h"
# include "frame.h"
# include "compat.h"
# include "parse.h"
# include "render.h"
# include "latin1.h"
# include "ucs4.h"
# include "genre.h"
# include "crc.h"
# include "field.h"
# include "util.h"
 
/*
 * NAME:    tag->new()
 * DESCRIPTION: allocate and return a new, empty tag
 */
struct id3_tag *id3_tag_new(void)
{
  struct id3_tag *tag;
 
  tag = malloc(sizeof(*tag));
  if (tag) {
    tag->refcount      = 0;
    tag->version       = ID3_TAG_VERSION;
    tag->flags         = 0;
    tag->extendedflags = 0;
    tag->restrictions  = 0;
    tag->options       = /* ID3_TAG_OPTION_UNSYNCHRONISATION | */
                         ID3_TAG_OPTION_COMPRESSION | ID3_TAG_OPTION_CRC;
    tag->nframes       = 0;
    tag->frames        = 0;
    tag->paddedsize    = 0;
  }
 
  return tag;
}
 
/*
 * NAME:    tag->delete()
 * DESCRIPTION: destroy a tag and deallocate all associated memory
 */
void id3_tag_delete(struct id3_tag *tag)
{
  assert(tag);
 
  if (tag->refcount == 0) {
    id3_tag_clearframes(tag);
 
    if (tag->frames)
      free(tag->frames);
 
    free(tag);
  }
}
 
/*
 * NAME:    tag->addref()
 * DESCRIPTION: add an external reference to a tag
 */
void id3_tag_addref(struct id3_tag *tag)
{
  assert(tag);
 
  ++tag->refcount;
}
 
/*
 * NAME:    tag->delref()
 * DESCRIPTION: remove an external reference to a tag
 */
void id3_tag_delref(struct id3_tag *tag)
{
  assert(tag && tag->refcount > 0);
 
  --tag->refcount;
}
 
/*
 * NAME:    tag->version()
 * DESCRIPTION: return the tag's original ID3 version number
 */
unsigned int id3_tag_version(struct id3_tag const *tag)
{
  assert(tag);
 
  return tag->version;
}
 
/*
 * NAME:    tag->options()
 * DESCRIPTION: get or set tag options
 */
int id3_tag_options(struct id3_tag *tag, int mask, int values)
{
  assert(tag);
 
  if (mask)
    tag->options = (tag->options & ~mask) | (values & mask);
 
  return tag->options;
}
 
/*
 * NAME:    tag->setlength()
 * DESCRIPTION: set the minimum rendered tag size
 */
void id3_tag_setlength(struct id3_tag *tag, id3_length_t length)
{
  assert(tag);
 
  tag->paddedsize = length;
}
 
/*
 * NAME:    tag->clearframes()
 * DESCRIPTION: detach and delete all frames associated with a tag
 */
void id3_tag_clearframes(struct id3_tag *tag)
{
  unsigned int i;
 
  assert(tag);
 
  for (i = 0; i < tag->nframes; ++i) {
    id3_frame_delref(tag->frames[i]);
    id3_frame_delete(tag->frames[i]);
  }
 
  tag->nframes = 0;
}
 
/*
 * NAME:    tag->attachframe()
 * DESCRIPTION: attach a frame to a tag
 */
int id3_tag_attachframe(struct id3_tag *tag, struct id3_frame *frame)
{
  struct id3_frame **frames;
 
  assert(tag && frame);
 
  frames = realloc(tag->frames, (tag->nframes + 1) * sizeof(*frames));
  if (frames == 0)
    return -1;
 
  tag->frames = frames;
  tag->frames[tag->nframes++] = frame;
 
  id3_frame_addref(frame);
 
  return 0;
}
 
/*
 * NAME:    tag->detachframe()
 * DESCRIPTION: detach (but don't delete) a frame from a tag
 */
int id3_tag_detachframe(struct id3_tag *tag, struct id3_frame *frame)
{
  unsigned int i;
 
  assert(tag && frame);
 
  for (i = 0; i < tag->nframes; ++i) {
    if (tag->frames[i] == frame)
      break;
  }
 
  if (i == tag->nframes)
    return -1;
 
  --tag->nframes;
  while (i++ < tag->nframes)
    tag->frames[i - 1] = tag->frames[i];
 
  id3_frame_delref(frame);
 
  return 0;
}
 
/*
 * NAME:    tag->findframe()
 * DESCRIPTION: find in a tag the nth (0-based) frame with the given frame ID
 */
struct id3_frame *id3_tag_findframe(struct id3_tag const *tag,
                    char const *id, unsigned int index)
{
  unsigned int len, i;
 
  assert(tag);
 
  if (id == 0 || *id == 0)
    return (index < tag->nframes) ? tag->frames[index] : 0;
 
  len = strlen(id);
 
  if (len == 4) {
    struct id3_compat const *compat;
 
    compat = id3_compat_lookup(id, len);
    if (compat && compat->equiv && !compat->translate) {
      id  = compat->equiv;
      len = strlen(id);
    }
  }
 
  for (i = 0; i < tag->nframes; ++i) {
    if (strncmp(tag->frames[i]->id, id, len) == 0 && index-- == 0)
      return tag->frames[i];
  }
 
  return 0;
}
 
enum tagtype {
  TAGTYPE_NONE = 0,
  TAGTYPE_ID3V1,
  TAGTYPE_ID3V2,
  TAGTYPE_ID3V2_FOOTER
};
 
static
enum tagtype tagtype(id3_byte_t const *data, id3_length_t length)
{
  if (length >= 3 &&
      data[0] == 'T' && data[1] == 'A' && data[2] == 'G')
    return TAGTYPE_ID3V1;
 
  if (length >= 10 &&
      ((data[0] == 'I' && data[1] == 'D' && data[2] == '3') ||
       (data[0] == '3' && data[1] == 'D' && data[2] == 'I')) &&
      data[3] < 0xff && data[4] < 0xff &&
      data[6] < 0x80 && data[7] < 0x80 && data[8] < 0x80 && data[9] < 0x80)
    return data[0] == 'I' ? TAGTYPE_ID3V2 : TAGTYPE_ID3V2_FOOTER;
 
  return TAGTYPE_NONE;
}
 
static
void parse_header(id3_byte_t const **ptr,
          unsigned int *version, int *flags, id3_length_t *size)
{
  *ptr += 3;
 
  *version = id3_parse_uint(ptr, 2);
  *flags   = id3_parse_uint(ptr, 1);
  *size    = id3_parse_syncsafe(ptr, 4);
}
 
/*
 * NAME:    tag->query()
 * DESCRIPTION: if a tag begins at the given location, return its size
 */
signed long id3_tag_query(id3_byte_t const *data, id3_length_t length)
{
  unsigned int version;
  int flags;
  id3_length_t size;
 
  assert(data);
 
  switch (tagtype(data, length)) {
  case TAGTYPE_ID3V1:
    return 128;
 
  case TAGTYPE_ID3V2:
    parse_header(&data, &version, &flags, &size);
 
    if (flags & ID3_TAG_FLAG_FOOTERPRESENT)
      size += 10;
 
    return 10 + size;
 
  case TAGTYPE_ID3V2_FOOTER:
    parse_header(&data, &version, &flags, &size);
    return -size - 10;
 
  case TAGTYPE_NONE:
    break;
  }
 
  return 0;
}
 
static
void trim(char *str)
{
  char *ptr;
 
  ptr = str + strlen(str);
  while (ptr > str && ptr[-1] == ' ')
    --ptr;
 
  *ptr = 0;
}
 
static
int v1_attachstr(struct id3_tag *tag, char const *id,
         char *text, unsigned long number)
{
  struct id3_frame *frame;
  id3_ucs4_t ucs4[31];
 
  if (text) {
    trim(text);
    if (*text == 0)
      return 0;
  }
 
  frame = id3_frame_new(id);
  if (frame == 0)
    return -1;
 
  if (id3_field_settextencoding(&frame->fields[0],
                ID3_FIELD_TEXTENCODING_ISO_8859_1) == -1)
    goto fail;
 
  if (text)
    id3_latin1_decode((const id3_latin1_t *)text, ucs4);
  else
    id3_ucs4_putnumber(ucs4, number);
 
  if (strcmp(id, ID3_FRAME_COMMENT) == 0) {
    if (id3_field_setlanguage(&frame->fields[1], "XXX") == -1 ||
    id3_field_setstring(&frame->fields[2], id3_ucs4_empty) == -1 ||
    id3_field_setfullstring(&frame->fields[3], ucs4) == -1)
      goto fail;
  }
  else {
    id3_ucs4_t *ptr = ucs4;
 
    if (id3_field_setstrings(&frame->fields[1], 1, &ptr) == -1)
      goto fail;
  }
 
  if (id3_tag_attachframe(tag, frame) == -1)
    goto fail;
 
  return 0;
 
 fail:
  id3_frame_delete(frame);
  return -1;
}
 
static
struct id3_tag *v1_parse(id3_byte_t const *data)
{
  struct id3_tag *tag;
 
  tag = id3_tag_new();
  if (tag) {
    char title[31], artist[31], album[31], year[5], comment[31];
    unsigned int genre, track;
 
    tag->version = 0x0100;
 
    tag->options |=  ID3_TAG_OPTION_ID3V1;
    tag->options &= ~ID3_TAG_OPTION_COMPRESSION;
 
    tag->restrictions =
      ID3_TAG_RESTRICTION_TEXTENCODING_LATIN1_UTF8 |
      ID3_TAG_RESTRICTION_TEXTSIZE_30_CHARS;
 
    title[30] = artist[30] = album[30] = year[4] = comment[30] = 0;
 
    memcpy(title,   &data[3],  30);
    memcpy(artist,  &data[33], 30);
    memcpy(album,   &data[63], 30);
    memcpy(year,    &data[93],  4);
    memcpy(comment, &data[97], 30);
 
    genre = data[127];
 
    track = 0;
    if (comment[28] == 0 && comment[29] != 0) {
      track = comment[29];
      tag->version = 0x0101;
    }
 
    /* populate tag frames */
 
    if (v1_attachstr(tag, ID3_FRAME_TITLE,  title,  0) == -1 ||
    v1_attachstr(tag, ID3_FRAME_ARTIST, artist, 0) == -1 ||
    v1_attachstr(tag, ID3_FRAME_ALBUM,  album,  0) == -1 ||
    v1_attachstr(tag, ID3_FRAME_YEAR,   year,   0) == -1 ||
    (track        && v1_attachstr(tag, ID3_FRAME_TRACK, 0, track) == -1) ||
    (genre < 0xff && v1_attachstr(tag, ID3_FRAME_GENRE, 0, genre) == -1) ||
    v1_attachstr(tag, ID3_FRAME_COMMENT, comment, 0) == -1) {
      id3_tag_delete(tag);
      tag = 0;
    }
  }
 
  return tag;
}
 
static
struct id3_tag *v2_parse(id3_byte_t const *ptr)
{
  struct id3_tag *tag;
  id3_byte_t *mem = 0;
 
  tag = id3_tag_new();
  if (tag) {
    id3_byte_t const *end;
    id3_length_t size;
 
    parse_header(&ptr, &tag->version, &tag->flags, &size);
 
    tag->paddedsize = 10 + size;
 
    if ((tag->flags & ID3_TAG_FLAG_UNSYNCHRONISATION) &&
    ID3_TAG_VERSION_MAJOR(tag->version) < 4) {
      mem = malloc(size);
      if (mem == 0)
    goto fail;
 
      memcpy(mem, ptr, size);
 
      size = id3_util_deunsynchronise(mem, size);
      ptr  = mem;
    }
 
    end = ptr + size;
 
    if (tag->flags & ID3_TAG_FLAG_EXTENDEDHEADER) {
      switch (ID3_TAG_VERSION_MAJOR(tag->version)) {
      case 2:
    goto fail;
 
      case 3:
    {
      id3_byte_t const *ehptr, *ehend;
      id3_length_t ehsize;
 
      enum {
        EH_FLAG_CRC = 0x8000  /* CRC data present */
      };
 
      if (end - ptr < 4)
        goto fail;
 
      ehsize = id3_parse_uint(&ptr, 4);
 
      if (ehsize > end - ptr)
        goto fail;
 
      ehptr = ptr;
      ehend = ptr + ehsize;
 
      ptr = ehend;
 
      if (ehend - ehptr >= 6) {
        int ehflags;
        id3_length_t padsize;
 
        ehflags = id3_parse_uint(&ehptr, 2);
        padsize = id3_parse_uint(&ehptr, 4);
 
        if (padsize > end - ptr)
          goto fail;
 
        end -= padsize;
 
        if (ehflags & EH_FLAG_CRC) {
          unsigned long crc;
 
          if (ehend - ehptr < 4)
        goto fail;
 
          crc = id3_parse_uint(&ehptr, 4);
 
          if (crc != id3_crc_compute(ptr, end - ptr))
        goto fail;
 
          tag->extendedflags |= ID3_TAG_EXTENDEDFLAG_CRCDATAPRESENT;
        }
      }
    }
    break;
 
      case 4:
    {
      id3_byte_t const *ehptr, *ehend;
      id3_length_t ehsize;
      unsigned int bytes;
 
      if (end - ptr < 4)
        goto fail;
 
      ehptr  = ptr;
      ehsize = id3_parse_syncsafe(&ptr, 4);
 
      if (ehsize < 6 || ehsize > end - ehptr)
        goto fail;
 
      ehend = ehptr + ehsize;
 
      bytes = id3_parse_uint(&ptr, 1);
 
      if (bytes < 1 || bytes > ehend - ptr)
        goto fail;
 
      ehptr = ptr + bytes;
 
      /* verify extended header size */
      {
        id3_byte_t const *flagsptr = ptr, *dataptr = ehptr;
        unsigned int datalen;
        int ehflags;
 
        while (bytes--) {
          for (ehflags = id3_parse_uint(&flagsptr, 1); ehflags;
           ehflags = (ehflags << 1) & 0xff) {
        if (ehflags & 0x80) {
          if (dataptr == ehend)
            goto fail;
          datalen = id3_parse_uint(&dataptr, 1);
          if (datalen > 0x7f || datalen > ehend - dataptr)
            goto fail;
          dataptr += datalen;
        }
          }
        }
      }
 
      tag->extendedflags = id3_parse_uint(&ptr, 1);
 
      ptr = ehend;
 
      if (tag->extendedflags & ID3_TAG_EXTENDEDFLAG_TAGISANUPDATE) {
        bytes  = id3_parse_uint(&ehptr, 1);
        ehptr += bytes;
      }
 
      if (tag->extendedflags & ID3_TAG_EXTENDEDFLAG_CRCDATAPRESENT) {
        unsigned long crc;
 
        bytes = id3_parse_uint(&ehptr, 1);
        if (bytes < 5)
          goto fail;
 
        crc = id3_parse_syncsafe(&ehptr, 5);
        ehptr += bytes - 5;
 
        if (crc != id3_crc_compute(ptr, end - ptr))
          goto fail;
      }
 
      if (tag->extendedflags & ID3_TAG_EXTENDEDFLAG_TAGRESTRICTIONS) {
        bytes = id3_parse_uint(&ehptr, 1);
        if (bytes < 1)
          goto fail;
 
        tag->restrictions = id3_parse_uint(&ehptr, 1);
        ehptr += bytes - 1;
      }
    }
    break;
      }
    }
 
    /* frames */
 
    while (ptr < end) {
      struct id3_frame *frame;
 
      if (*ptr == 0)
    break;  /* padding */
 
      frame = id3_frame_parse(&ptr, end - ptr, tag->version);
      if (frame == 0 || id3_tag_attachframe(tag, frame) == -1)
    goto fail;
    }
 
    if (ID3_TAG_VERSION_MAJOR(tag->version) < 4 &&
    id3_compat_fixup(tag) == -1)
      goto fail;
  }
 
  if (0) {
  fail:
    id3_tag_delete(tag);
    tag = 0;
  }
 
  if (mem)
    free(mem);
 
  return tag;
}
 
/*
 * NAME:    tag->parse()
 * DESCRIPTION: parse a complete ID3 tag
 */
struct id3_tag *id3_tag_parse(id3_byte_t const *data, id3_length_t length)
{
  id3_byte_t const *ptr;
  unsigned int version;
  int flags;
  id3_length_t size;
 
  assert(data);
 
  switch (tagtype(data, length)) {
  case TAGTYPE_ID3V1:
    return (length < 128) ? 0 : v1_parse(data);
 
  case TAGTYPE_ID3V2:
    break;
 
  case TAGTYPE_ID3V2_FOOTER:
  case TAGTYPE_NONE:
    return 0;
  }
 
  /* ID3v2.x */
 
  ptr = data;
  parse_header(&ptr, &version, &flags, &size);
 
  switch (ID3_TAG_VERSION_MAJOR(version)) {
  case 4:
    if (flags & ID3_TAG_FLAG_FOOTERPRESENT)
      size += 10;
  case 2:
  case 3:
    return (length < 10 + size) ? 0 : v2_parse(data);
  }
 
  return 0;
}
 
static
void v1_renderstr(struct id3_tag const *tag, char const *frameid,
          id3_byte_t **buffer, id3_length_t length)
{
  struct id3_frame *frame;
  id3_ucs4_t const *string;
 
  frame = id3_tag_findframe(tag, frameid, 0);
  if (frame == 0)
    string = id3_ucs4_empty;
  else {
    if (strcmp(frameid, ID3_FRAME_COMMENT) == 0)
      string = id3_field_getfullstring(&frame->fields[3]);
    else
      string = id3_field_getstrings(&frame->fields[1], 0);
  }
 
  id3_render_paddedstring(buffer, string, length);
}
 
/*
 * NAME:    v1->render()
 * DESCRIPTION: render an ID3v1 (or ID3v1.1) tag
 */
static
id3_length_t v1_render(struct id3_tag const *tag, id3_byte_t *buffer)
{
  id3_byte_t data[128], *ptr;
  struct id3_frame *frame;
  unsigned int i;
  int genre = -1;
 
  ptr = data;
 
  id3_render_immediate(&ptr, "TAG", 3);
 
  v1_renderstr(tag, ID3_FRAME_TITLE,   &ptr, 30);
  v1_renderstr(tag, ID3_FRAME_ARTIST,  &ptr, 30);
  v1_renderstr(tag, ID3_FRAME_ALBUM,   &ptr, 30);
  v1_renderstr(tag, ID3_FRAME_YEAR,    &ptr,  4);
  v1_renderstr(tag, ID3_FRAME_COMMENT, &ptr, 30);
 
  /* ID3v1.1 track number */
 
  frame = id3_tag_findframe(tag, ID3_FRAME_TRACK, 0);
  if (frame) {
    unsigned int track;
 
    track = id3_ucs4_getnumber(id3_field_getstrings(&frame->fields[1], 0));
    if (track > 0 && track <= 0xff) {
      ptr[-2] = 0;
      ptr[-1] = track;
    }
  }
 
  /* ID3v1 genre number */
 
  frame = id3_tag_findframe(tag, ID3_FRAME_GENRE, 0);
  if (frame) {
    unsigned int nstrings;
 
    nstrings = id3_field_getnstrings(&frame->fields[1]);
 
    for (i = 0; i < nstrings; ++i) {
      genre = id3_genre_number(id3_field_getstrings(&frame->fields[1], i));
      if (genre != -1)
    break;
    }
 
    if (i == nstrings && nstrings > 0)
      genre = ID3_GENRE_OTHER;
  }
 
  id3_render_int(&ptr, genre, 1);
 
  /* make sure the tag is not empty */
 
  if (genre == -1) {
    for (i = 3; i < 127; ++i) {
      if (data[i] != ' ')
    break;
    }
 
    if (i == 127)
      return 0;
  }
 
  if (buffer)
    memcpy(buffer, data, 128);
 
  return 128;
}
 
/*
 * NAME:    tag->render()
 * DESCRIPTION: render a complete ID3 tag
 */
id3_length_t id3_tag_render(struct id3_tag const *tag, id3_byte_t *buffer)
{
  id3_length_t size = 0;
  id3_byte_t **ptr,
    *header_ptr = 0, *tagsize_ptr = 0, *crc_ptr = 0, *frames_ptr = 0;
  int flags, extendedflags;
  unsigned int i;
 
  assert(tag);
 
  if (tag->options & ID3_TAG_OPTION_ID3V1)
    return v1_render(tag, buffer);
 
  /* a tag must contain at least one (renderable) frame */
 
  for (i = 0; i < tag->nframes; ++i) {
    if (id3_frame_render(tag->frames[i], 0, 0) > 0)
      break;
  }
 
  if (i == tag->nframes)
    return 0;
 
  ptr = buffer ? &buffer : 0;
 
  /* get flags */
 
  flags         = tag->flags         & ID3_TAG_FLAG_KNOWNFLAGS;
  extendedflags = tag->extendedflags & ID3_TAG_EXTENDEDFLAG_KNOWNFLAGS;
 
  extendedflags &= ~ID3_TAG_EXTENDEDFLAG_CRCDATAPRESENT;
  if (tag->options & ID3_TAG_OPTION_CRC)
    extendedflags |= ID3_TAG_EXTENDEDFLAG_CRCDATAPRESENT;
 
  extendedflags &= ~ID3_TAG_EXTENDEDFLAG_TAGRESTRICTIONS;
  if (tag->restrictions)
    extendedflags |= ID3_TAG_EXTENDEDFLAG_TAGRESTRICTIONS;
 
  flags &= ~ID3_TAG_FLAG_UNSYNCHRONISATION;
  if (tag->options & ID3_TAG_OPTION_UNSYNCHRONISATION)
    flags |= ID3_TAG_FLAG_UNSYNCHRONISATION;
 
  flags &= ~ID3_TAG_FLAG_EXTENDEDHEADER;
  if (extendedflags)
    flags |= ID3_TAG_FLAG_EXTENDEDHEADER;
 
  flags &= ~ID3_TAG_FLAG_FOOTERPRESENT;
  if (tag->options & ID3_TAG_OPTION_APPENDEDTAG)
    flags |= ID3_TAG_FLAG_FOOTERPRESENT;
 
  /* header */
 
  if (ptr)
    header_ptr = *ptr;
 
  size += id3_render_immediate(ptr, "ID3", 3);
  size += id3_render_int(ptr, ID3_TAG_VERSION, 2);
  size += id3_render_int(ptr, flags, 1);
 
  if (ptr)
    tagsize_ptr = *ptr;
 
  size += id3_render_syncsafe(ptr, 0, 4);
 
  /* extended header */
 
  if (flags & ID3_TAG_FLAG_EXTENDEDHEADER) {
    id3_length_t ehsize = 0;
    id3_byte_t *ehsize_ptr = 0;
 
    if (ptr)
      ehsize_ptr = *ptr;
 
    ehsize += id3_render_syncsafe(ptr, 0, 4);
    ehsize += id3_render_int(ptr, 1, 1);
    ehsize += id3_render_int(ptr, extendedflags, 1);
 
    if (extendedflags & ID3_TAG_EXTENDEDFLAG_TAGISANUPDATE)
      ehsize += id3_render_int(ptr, 0, 1);
 
    if (extendedflags & ID3_TAG_EXTENDEDFLAG_CRCDATAPRESENT) {
      ehsize += id3_render_int(ptr, 5, 1);
 
      if (ptr)
    crc_ptr = *ptr;
 
      ehsize += id3_render_syncsafe(ptr, 0, 5);
    }
 
    if (extendedflags & ID3_TAG_EXTENDEDFLAG_TAGRESTRICTIONS) {
      ehsize += id3_render_int(ptr, 1, 1);
      ehsize += id3_render_int(ptr, tag->restrictions, 1);
    }
 
    if (ehsize_ptr)
      id3_render_syncsafe(&ehsize_ptr, ehsize, 4);
 
    size += ehsize;
  }
 
  /* frames */
 
  if (ptr)
    frames_ptr = *ptr;
 
  for (i = 0; i < tag->nframes; ++i)
    size += id3_frame_render(tag->frames[i], ptr, tag->options);
 
  /* padding */
 
  if (!(flags & ID3_TAG_FLAG_FOOTERPRESENT)) {
    if (size < tag->paddedsize)
      size += id3_render_padding(ptr, 0, tag->paddedsize - size);
    else if (tag->options & ID3_TAG_OPTION_UNSYNCHRONISATION) {
      if (ptr == 0)
    size += 1;
      else {
    if ((*ptr)[-1] == 0xff)
      size += id3_render_padding(ptr, 0, 1);
      }
    }
  }
 
  /* patch tag size and CRC */
 
  if (tagsize_ptr)
    id3_render_syncsafe(&tagsize_ptr, size - 10, 4);
 
  if (crc_ptr) {
    id3_render_syncsafe(&crc_ptr,
            id3_crc_compute(frames_ptr, *ptr - frames_ptr), 5);
  }
 
  /* footer */
 
  if (flags & ID3_TAG_FLAG_FOOTERPRESENT) {
    size += id3_render_immediate(ptr, "3DI", 3);
    size += id3_render_binary(ptr, header_ptr + 3, 7);
  }
 
  return size;
}