glibc/libio/fmemopen.c

244 lines
5.5 KiB
C

/* Fmemopen implementation.
Copyright (C) 2000, 2002 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, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
/*
* 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.
*
* No, it isn't really tested yet. :-)
*
*
*
* 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 <errno.h>
#include <libio.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include "libioP.h"
typedef struct fmemopen_cookie_struct fmemopen_cookie_t;
struct fmemopen_cookie_struct
{
char *buffer;
int mybuffer;
size_t size;
_IO_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 = 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 -1;
}
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, _IO_off64_t *p, int w)
{
_IO_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->size - *p;
break;
default:
return -1;
}
if (np < 0 || (size_t) np > c->size)
return -1;
c->pos = np;
return np;
}
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 *
fmemopen (void *buf, size_t len, const char *mode)
{
cookie_io_functions_t iof;
fmemopen_cookie_t *c;
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';
}
else
c->buffer = buf;
c->size = len;
if (mode[0] == 'w')
c->buffer[0] = '\0';
c->maxpos = strlen (c->buffer);
if (mode[0] == 'a')
c->pos = c->maxpos;
else
c->pos = 0;
iof.read = fmemopen_read;
iof.write = fmemopen_write;
iof.seek = fmemopen_seek;
iof.close = fmemopen_close;
return _IO_fopencookie (c, mode, iof);
}