comparison src/libid3tag-0.15.1b/tag.c @ 85:545efbb81310

Import initial set of sources

+/*
+ * 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(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;
+}