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275 lines
6.0 KiB
C
275 lines
6.0 KiB
C
/* Fmemopen implementation.
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Copyright (C) 2000-2019 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Hanno Mueller, kontakt@hanno.de, 2000.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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/*
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* fmemopen() - "my" version of a string stream
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* Hanno Mueller, kontakt@hanno.de
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*
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*
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* I needed fmemopen() for an application that I currently work on,
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* but couldn't find it in libio. The following snippet of code is an
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* attempt to implement what glibc's documentation describes.
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*
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*
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*
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* I already see some potential problems:
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*
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* - I never used the "original" fmemopen(). I am sure that "my"
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* fmemopen() behaves differently than the original version.
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*
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* - The documentation doesn't say wether a string stream allows
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* seeks. I checked the old fmemopen implementation in glibc's stdio
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* directory, wasn't quite able to see what is going on in that
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* source, but as far as I understand there was no seek there. For
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* my application, I needed fseek() and ftell(), so it's here.
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*
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* - "append" mode and fseek(p, SEEK_END) have two different ideas
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* about the "end" of the stream.
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*
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* As described in the documentation, when opening the file in
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* "append" mode, the position pointer will be set to the first null
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* character of the string buffer (yet the buffer may already
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* contain more data). For fseek(), the last byte of the buffer is
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* used as the end of the stream.
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*
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* - It is unclear to me what the documentation tries to say when it
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* explains what happens when you use fmemopen with a NULL
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* buffer.
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*
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* Quote: "fmemopen [then] allocates an array SIZE bytes long. This
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* is really only useful if you are going to write things to the
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* buffer and then read them back in again."
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*
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* What does that mean if the original fmemopen() did not allow
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* seeking? How do you read what you just wrote without seeking back
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* to the beginning of the stream?
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*
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* - I think there should be a second version of fmemopen() that does
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* not add null characters for each write. (At least in my
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* application, I am not actually using strings but binary data and
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* so I don't need the stream to add null characters on its own.)
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*/
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#include "libioP.h"
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#if SHLIB_COMPAT (libc, GLIBC_2_2, GLIBC_2_22)
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#include <errno.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <stdint.h>
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#include <string.h>
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#include <sys/types.h>
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typedef struct fmemopen_cookie_struct fmemopen_cookie_t;
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struct fmemopen_cookie_struct
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{
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char *buffer;
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int mybuffer;
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int binmode;
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size_t size;
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off64_t pos;
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size_t maxpos;
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};
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static ssize_t
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fmemopen_read (void *cookie, char *b, size_t s)
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{
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fmemopen_cookie_t *c;
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c = (fmemopen_cookie_t *) cookie;
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if (c->pos + s > c->size)
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{
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if ((size_t) c->pos == c->size)
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return 0;
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s = c->size - c->pos;
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}
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memcpy (b, &(c->buffer[c->pos]), s);
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c->pos += s;
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if ((size_t) c->pos > c->maxpos)
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c->maxpos = c->pos;
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return s;
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}
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static ssize_t
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fmemopen_write (void *cookie, const char *b, size_t s)
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{
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fmemopen_cookie_t *c;
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int addnullc;
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c = (fmemopen_cookie_t *) cookie;
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addnullc = c->binmode == 0 && (s == 0 || b[s - 1] != '\0');
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if (c->pos + s + addnullc > c->size)
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{
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if ((size_t) (c->pos + addnullc) >= c->size)
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{
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__set_errno (ENOSPC);
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return 0;
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}
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s = c->size - c->pos - addnullc;
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}
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memcpy (&(c->buffer[c->pos]), b, s);
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c->pos += s;
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if ((size_t) c->pos > c->maxpos)
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{
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c->maxpos = c->pos;
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if (addnullc)
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c->buffer[c->maxpos] = '\0';
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}
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return s;
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}
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static int
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fmemopen_seek (void *cookie, off64_t *p, int w)
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{
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off64_t np;
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fmemopen_cookie_t *c;
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c = (fmemopen_cookie_t *) cookie;
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switch (w)
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{
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case SEEK_SET:
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np = *p;
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break;
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case SEEK_CUR:
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np = c->pos + *p;
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break;
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case SEEK_END:
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np = (c->binmode ? c->size : c->maxpos) - *p;
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break;
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default:
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return -1;
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}
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if (np < 0 || (size_t) np > c->size)
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return -1;
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*p = c->pos = np;
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return 0;
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}
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static int
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fmemopen_close (void *cookie)
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{
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fmemopen_cookie_t *c;
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c = (fmemopen_cookie_t *) cookie;
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if (c->mybuffer)
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free (c->buffer);
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free (c);
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return 0;
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}
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FILE *
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__old_fmemopen (void *buf, size_t len, const char *mode)
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{
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cookie_io_functions_t iof;
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fmemopen_cookie_t *c;
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FILE *result;
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if (__glibc_unlikely (len == 0))
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{
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einval:
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__set_errno (EINVAL);
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return NULL;
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}
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c = (fmemopen_cookie_t *) malloc (sizeof (fmemopen_cookie_t));
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if (c == NULL)
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return NULL;
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c->mybuffer = (buf == NULL);
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if (c->mybuffer)
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{
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c->buffer = (char *) malloc (len);
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if (c->buffer == NULL)
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{
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free (c);
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return NULL;
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}
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c->buffer[0] = '\0';
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c->maxpos = 0;
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}
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else
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{
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if (__glibc_unlikely ((uintptr_t) len > -(uintptr_t) buf))
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{
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free (c);
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goto einval;
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}
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c->buffer = buf;
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if (mode[0] == 'w')
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c->buffer[0] = '\0';
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c->maxpos = strnlen (c->buffer, len);
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}
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c->size = len;
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if (mode[0] == 'a')
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c->pos = c->maxpos;
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else
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c->pos = 0;
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c->binmode = mode[0] != '\0' && mode[1] == 'b';
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iof.read = fmemopen_read;
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iof.write = fmemopen_write;
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iof.seek = fmemopen_seek;
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iof.close = fmemopen_close;
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result = _IO_fopencookie (c, mode, iof);
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if (__glibc_unlikely (result == NULL))
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{
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if (c->mybuffer)
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free (c->buffer);
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free (c);
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}
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return result;
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}
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compat_symbol (libc, __old_fmemopen, fmemopen, GLIBC_2_2);
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#endif
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