/* Fmemopen implementation.

   Copyright (C) 2000-2018 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   Contributed by Hanno Mueller, kontakt@hanno.de, 2000.

   The GNU C Library is free software; you can redistribute it and/or

   modify it under the terms of the GNU Lesser General Public

   License as published by the Free Software Foundation; either

   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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

   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public

   License along with the GNU C Library; if not, see

   <http://www.gnu.org/licenses/>.  */

/*

 * fmemopen() - "my" version of a string stream

 * Hanno Mueller, kontakt@hanno.de

 *

 *

 * I needed fmemopen() for an application that I currently work on,

 * but couldn't find it in libio. The following snippet of code is an

 * attempt to implement what glibc's documentation describes.

 *

 *

 *

 * I already see some potential problems:

 *

 * - I never used the "original" fmemopen(). I am sure that "my"

 *   fmemopen() behaves differently than the original version.

 *

 * - The documentation doesn't say wether a string stream allows

 *   seeks. I checked the old fmemopen implementation in glibc's stdio

 *   directory, wasn't quite able to see what is going on in that

 *   source, but as far as I understand there was no seek there. For

 *   my application, I needed fseek() and ftell(), so it's here.

 *

 * - "append" mode and fseek(p, SEEK_END) have two different ideas

 *   about the "end" of the stream.

 *

 *   As described in the documentation, when opening the file in

 *   "append" mode, the position pointer will be set to the first null

 *   character of the string buffer (yet the buffer may already

 *   contain more data). For fseek(), the last byte of the buffer is

 *   used as the end of the stream.

 *

 * - It is unclear to me what the documentation tries to say when it

 *   explains what happens when you use fmemopen with a NULL

 *   buffer.

 *

 *   Quote: "fmemopen [then] allocates an array SIZE bytes long. This

 *   is really only useful if you are going to write things to the

 *   buffer and then read them back in again."

 *

 *   What does that mean if the original fmemopen() did not allow

 *   seeking? How do you read what you just wrote without seeking back

 *   to the beginning of the stream?

 *

 * - I think there should be a second version of fmemopen() that does

 *   not add null characters for each write. (At least in my

 *   application, I am not actually using strings but binary data and

 *   so I don't need the stream to add null characters on its own.)

 */

#include "libioP.h"

#if SHLIB_COMPAT (libc, GLIBC_2_2, GLIBC_2_22)

#include <errno.h>

#include <stdio.h>

#include <stdlib.h>

#include <stdint.h>

#include <string.h>

#include <sys/types.h>

typedef struct fmemopen_cookie_struct fmemopen_cookie_t;

struct fmemopen_cookie_struct

{

  char *buffer;

  int mybuffer;

  int binmode;

  size_t size;

  off64_t pos;

  size_t maxpos;

};

static ssize_t

fmemopen_read (void *cookie, char *b, size_t s)

{

  fmemopen_cookie_t *c;

  c = (fmemopen_cookie_t *) cookie;

  if (c->pos + s > c->size)

    {

      if ((size_t) c->pos == c->size)

	return 0;

      s = c->size - c->pos;

    }

  memcpy (b, &(c->buffer[c->pos]), s);

  c->pos += s;

  if ((size_t) c->pos > c->maxpos)

    c->maxpos = c->pos;

  return s;

}

static ssize_t

fmemopen_write (void *cookie, const char *b, size_t s)

{

  fmemopen_cookie_t *c;

  int addnullc;

  c = (fmemopen_cookie_t *) cookie;

  addnullc = c->binmode == 0 && (s == 0 || b[s - 1] != '\0');

  if (c->pos + s + addnullc > c->size)

    {

      if ((size_t) (c->pos + addnullc) >= c->size)

	{

	  __set_errno (ENOSPC);

	  return 0;

	}

      s = c->size - c->pos - addnullc;

    }

  memcpy (&(c->buffer[c->pos]), b, s);

  c->pos += s;

  if ((size_t) c->pos > c->maxpos)

    {

      c->maxpos = c->pos;

      if (addnullc)

	c->buffer[c->maxpos] = '\0';

    }

  return s;

}

static int

fmemopen_seek (void *cookie, off64_t *p, int w)

{

  off64_t np;

  fmemopen_cookie_t *c;

  c = (fmemopen_cookie_t *) cookie;

  switch (w)

    {

    case SEEK_SET:

      np = *p;

      break;

    case SEEK_CUR:

      np = c->pos + *p;

      break;

    case SEEK_END:

      np = (c->binmode ? c->size : c->maxpos) - *p;

      break;

    default:

      return -1;

    }

  if (np < 0 || (size_t) np > c->size)

    return -1;

  *p = c->pos = np;

  return 0;

}

static int

fmemopen_close (void *cookie)

{

  fmemopen_cookie_t *c;

  c = (fmemopen_cookie_t *) cookie;

  if (c->mybuffer)

    free (c->buffer);

  free (c);

  return 0;

}

FILE *

__old_fmemopen (void *buf, size_t len, const char *mode)

{

  cookie_io_functions_t iof;

  fmemopen_cookie_t *c;

  FILE *result;

  if (__glibc_unlikely (len == 0))

    {

    einval:

      __set_errno (EINVAL);

      return NULL;

    }

  c = (fmemopen_cookie_t *) malloc (sizeof (fmemopen_cookie_t));

  if (c == NULL)

    return NULL;

  c->mybuffer = (buf == NULL);

  if (c->mybuffer)

    {

      c->buffer = (char *) malloc (len);

      if (c->buffer == NULL)

	{

	  free (c);

	  return NULL;

	}

      c->buffer[0] = '\0';

      c->maxpos = 0;

    }

  else

    {

      if (__glibc_unlikely ((uintptr_t) len > -(uintptr_t) buf))

	{

	  free (c);

	  goto einval;

	}

      c->buffer = buf;

      if (mode[0] == 'w')

	c->buffer[0] = '\0';

      c->maxpos = strnlen (c->buffer, len);

    }

  c->size = len;

  if (mode[0] == 'a')

    c->pos = c->maxpos;

  else

    c->pos = 0;

  c->binmode = mode[0] != '\0' && mode[1] == 'b';

  iof.read = fmemopen_read;

  iof.write = fmemopen_write;

  iof.seek = fmemopen_seek;

  iof.close = fmemopen_close;

  result = _IO_fopencookie (c, mode, iof);

  if (__glibc_unlikely (result == NULL))

    {

      if (c->mybuffer)

	free (c->buffer);

      free (c);

    }

  return result;

}

compat_symbol (libc, __old_fmemopen, fmemopen, GLIBC_2_2);

#endif