* decompress.c: Fix bugs with large buffers and weird inputs.

[bpt/emacs.git] / src / decompress.c

/* Interface to zlib.
   Copyright (C) 2013 Free Software Foundation, Inc.

This file is part of GNU Emacs.

GNU Emacs 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 3 of the License, or
(at your option) any later version.

GNU Emacs 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 GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */

#include <config.h>

#ifdef HAVE_ZLIB

#include <zlib.h>

#include "lisp.h"
#include "character.h"
#include "buffer.h"

\f
struct decompress_unwind_data
{
  ptrdiff_t old_point, start;
  z_stream *stream;
};

static void
unwind_decompress (void *ddata)
{
  struct decompress_unwind_data *data = ddata;
  inflateEnd (data->stream);

  /* Delete any uncompressed data already inserted and restore point.  */
  if (data->start)
    {
      del_range (data->start, PT);
      SET_PT (data->old_point);
    }
}

DEFUN ("decompress-gzipped-region", Fdecompress_gzipped_region,
       Sdecompress_gzipped_region,
       2, 2, 0,
       doc: /* Decompress a gzip-compressed region.
Replace the text in the region by the decompressed data.
On failure, return nil and leave the data in place.
This function can be called only in unibyte buffers.  */)
  (Lisp_Object start, Lisp_Object end)
{
  ptrdiff_t istart, iend, pos_byte;
  z_stream stream;
  int inflate_status;
  struct decompress_unwind_data unwind_data;
  ptrdiff_t count = SPECPDL_INDEX ();

  validate_region (&start, &end);

  if (! NILP (BVAR (current_buffer, enable_multibyte_characters)))
    error ("This function can be called only in unibyte buffers");

  /* This is a unibyte buffer, so character positions and bytes are
     the same.  */
  istart = XINT (start);
  iend = XINT (end);
  move_gap_both (iend, iend);

  stream.zalloc = Z_NULL;
  stream.zfree = Z_NULL;
  stream.opaque = Z_NULL;
  stream.avail_in = 0;
  stream.next_in = Z_NULL;

  /* This magic number apparently means "this is gzip".  */
  if (inflateInit2 (&stream, 16 + MAX_WBITS) != Z_OK)
    return Qnil;

  unwind_data.start = iend;
  unwind_data.stream = &stream;
  unwind_data.old_point = PT;

  record_unwind_protect_ptr (unwind_decompress, &unwind_data);

  /* Insert the decompressed data at the end of the compressed data.  */
  SET_PT (iend);

  pos_byte = istart;

  /* Keep calling 'inflate' until it reports an error or end-of-input.  */
  do
    {
      /* Maximum number of bytes that one 'inflate' call should read and write.
	 zlib requires that these values not exceed UINT_MAX.
	 Do not make avail_out too large, as that might unduly delay C-g.  */
      ptrdiff_t avail_in = min (iend - pos_byte, UINT_MAX);
      ptrdiff_t avail_out = min (1 << 14, UINT_MAX);

      ptrdiff_t decompressed;

      if (GAP_SIZE < avail_out)
	make_gap (avail_out - GAP_SIZE);
      stream.next_in = BYTE_POS_ADDR (pos_byte);
      stream.avail_in = avail_in;
      stream.next_out = GPT_ADDR;
      stream.avail_out = avail_out;
      inflate_status = inflate (&stream, Z_NO_FLUSH);
      pos_byte += avail_in - stream.avail_in;
      decompressed = avail_out - stream.avail_out;
      insert_from_gap (decompressed, decompressed, 0);
      QUIT;
    }
  while (inflate_status == Z_OK);

  if (inflate_status != Z_STREAM_END)
    return unbind_to (count, Qnil);

  unwind_data.start = 0;

  /* Delete the compressed data.  */
  del_range (istart, iend);

  return unbind_to (count, Qt);
}

\f
/***********************************************************************
			    Initialization
 ***********************************************************************/
void
syms_of_decompress (void)
{
  defsubr (&Sdecompress_gzipped_region);
}

#endif /* HAVE_ZLIB */