xref: /freebsd/lib/libc/stdio/fmemopen.c (revision 646b68f04d021f978a3ded82442d5387e610e2a5)

/*-
Copyright (C) 2013 Pietro Cerutti <gahr@FreeBSD.org>

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.
*/

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include "local.h"

struct fmemopen_cookie
{
	char	*buf;	/* pointer to the memory region */
	char	 own;	/* did we allocate the buffer ourselves? */
	char     bin;   /* is this a binary buffer? */
	size_t	 size;	/* buffer length in bytes */
	size_t	 len;	/* data length in bytes */
	size_t	 off;	/* current offset into the buffer */
};

static int	fmemopen_read  (void *cookie, char *buf, int nbytes);
static int	fmemopen_write (void *cookie, const char *buf, int nbytes);
static fpos_t	fmemopen_seek  (void *cookie, fpos_t offset, int whence);
static int	fmemopen_close (void *cookie);

FILE *
fmemopen (void * __restrict buf, size_t size, const char * __restrict mode)
{
	struct fmemopen_cookie *ck;
	FILE *f;
	int flags, rc;

	/*
	 * Retrieve the flags as used by open(2) from the mode argument, and
	 * validate them.
	 * */
	rc = __sflags (mode, &flags);
	if (rc == 0) {
		errno = EINVAL;
		return (NULL);
	}

	/*
	 * There's no point in requiring an automatically allocated buffer
	 * in write-only mode.
	 */
	if (!(flags & O_RDWR) && buf == NULL) {
		errno = EINVAL;
		return (NULL);
	}

	/* Allocate a cookie. */
	ck = malloc (sizeof (struct fmemopen_cookie));
	if (ck == NULL) {
		return (NULL);
	}

	ck->off  = 0;
	ck->size = size;

	/* Check whether we have to allocate the buffer ourselves. */
	ck->own = ((ck->buf = buf) == NULL);
	if (ck->own) {
		ck->buf = malloc (size);
		if (ck->buf == NULL) {
			free (ck);
			return (NULL);
		}
	}

	/*
	 * POSIX distinguishes between w+ and r+, in that w+ is supposed to
	 * truncate the buffer.
	 */
	if (ck->own || mode[0] == 'w') {
		ck->buf[0] = '\0';
	}

	/* Check for binary mode. */
	ck->bin = strchr(mode, 'b') != NULL;

	/*
	 * The size of the current buffer contents is set depending on the
	 * mode:
	 *
	 * for append (text-mode), the position of the first NULL byte, or the
	 * size of the buffer if none is found
	 *
	 * for append (binary-mode), the size of the buffer
	 *
	 * for read, the size of the buffer
	 *
	 * for write, 0
	 */
	switch (mode[0]) {
	case 'a':
		if (ck->bin) {
			/*
			 * This isn't useful, since the buffer isn't
			 * allowed to grow.
			 */
			ck->off = ck->len = size;
		} else
			ck->off = ck->len = strnlen(ck->buf, ck->size);
		break;
	case 'r':
		ck->len = size;
		break;
	case 'w':
		ck->len = 0;
		break;
	}

	/* Actuall wrapper. */
	f = funopen ((void *)ck,
	    flags & O_WRONLY ? NULL : fmemopen_read,
	    flags & O_RDONLY ? NULL : fmemopen_write,
	    fmemopen_seek, fmemopen_close);

	if (f == NULL) {
		if (ck->own)
			free (ck->buf);
		free (ck);
		return (NULL);
	}

	/*
	 * Turn off buffering, so a write past the end of the buffer
	 * correctly returns a short object count.
	 */
	setvbuf (f, (char *) NULL, _IONBF, 0);

	return (f);
}

static int
fmemopen_read (void *cookie, char *buf, int nbytes)
{
	struct fmemopen_cookie *ck = cookie;

	if (nbytes > ck->len - ck->off)
		nbytes = ck->len - ck->off;

	if (nbytes == 0)
		return (0);

	memcpy (buf, ck->buf + ck->off, nbytes);

	ck->off += nbytes;

	return (nbytes);
}

static int
fmemopen_write (void *cookie, const char *buf, int nbytes)
{
	struct fmemopen_cookie *ck = cookie;

	if (nbytes > ck->size - ck->off)
		nbytes = ck->size - ck->off;

	if (nbytes == 0)
		return (0);

	memcpy (ck->buf + ck->off, buf, nbytes);

	ck->off += nbytes;

	if (ck->off > ck->len)
		ck->len = ck->off;

	/*
	 * We append a NULL byte if all these conditions are met:
	 * - the buffer is not binary
	 * - the buffer is not full
	 * - the data just written doesn't already end with a NULL byte
	 */
	if (!ck->bin && ck->off < ck->size && ck->buf[ck->off - 1] != '\0')
		ck->buf[ck->off] = '\0';

	return (nbytes);
}

static fpos_t
fmemopen_seek (void *cookie, fpos_t offset, int whence)
{
	struct fmemopen_cookie *ck = cookie;


	switch (whence) {
	case SEEK_SET:
		if (offset > ck->size) {
			errno = EINVAL;
			return (-1);
		}
		ck->off = offset;
		break;

	case SEEK_CUR:
		if (ck->off + offset > ck->size) {
			errno = EINVAL;
			return (-1);
		}
		ck->off += offset;
		break;

	case SEEK_END:
		if (offset > 0 || -offset > ck->len) {
			errno = EINVAL;
			return (-1);
		}
		ck->off = ck->len + offset;
		break;

	default:
		errno = EINVAL;
		return (-1);
	}

	return (ck->off);
}

static int
fmemopen_close (void *cookie)
{
	struct fmemopen_cookie *ck = cookie;

	if (ck->own)
		free (ck->buf);

	free (ck);

	return (0);
}