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Since xrealloc dies on failure it is safe to directly assign to the
original pointer.  Theo agrees, and so does the rest of the tree
(ssh, etc. all do this already).

Saves a bunch of variables and assignments.

OK niallo@

/*	$OpenBSD: buf.c,v 1.13 2007/05/29 00:19:10 ray Exp $	*/
/*
 * Copyright (c) 2003 Jean-Francois Brousseau <jfb@openbsd.org>
 * All rights reserved.
 *
 * 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. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED ``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
 * THE AUTHOR 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/queue.h>
#include <sys/stat.h>

#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <stdarg.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

#include "buf.h"
#include "xmalloc.h"
#include "worklist.h"

#define BUF_INCR	128

struct rcs_buf {
	u_int	cb_flags;

	/* buffer handle, buffer size, and data length */
	u_char	*cb_buf;
	size_t	 cb_size;
	size_t	 cb_len;
};

#define SIZE_LEFT(b)	(b->cb_size - b->cb_len)

static void	rcs_buf_grow(BUF *, size_t);

/*
 * rcs_buf_alloc()
 *
 * Create a new buffer structure and return a pointer to it.  This structure
 * uses dynamically-allocated memory and must be freed with rcs_buf_free(),
 * once the buffer is no longer needed.
 */
BUF *
rcs_buf_alloc(size_t len, u_int flags)
{
	BUF *b;

	b = xmalloc(sizeof(*b));
	/* Postpone creation of zero-sized buffers */
	if (len > 0)
		b->cb_buf = xcalloc(1, len);
	else
		b->cb_buf = NULL;

	b->cb_flags = flags;
	b->cb_size = len;
	b->cb_len = 0;

	return (b);
}

/*
 * rcs_buf_load()
 *
 * Open the file specified by <path> and load all of its contents into a
 * buffer.
 * Returns the loaded buffer on success or NULL on failure.
 * Sets errno on error.
 */
BUF *
rcs_buf_load(const char *path, u_int flags)
{
	int fd;
	ssize_t ret;
	size_t len;
	u_char *bp;
	struct stat st;
	BUF *buf;

	buf = NULL;

	if ((fd = open(path, O_RDONLY, 0600)) == -1)
		goto out;

	if (fstat(fd, &st) == -1)
		goto out;

	if (st.st_size > SIZE_MAX) {
		errno = EFBIG;
		goto out;
	}
	buf = rcs_buf_alloc(st.st_size, flags);
	for (bp = buf->cb_buf; ; bp += (size_t)ret) {
		len = SIZE_LEFT(buf);
		ret = read(fd, bp, len);
		if (ret == -1) {
			int saved_errno;

			saved_errno = errno;
			rcs_buf_free(buf);
			buf = NULL;
			errno = saved_errno;
			goto out;
		} else if (ret == 0)
			break;

		buf->cb_len += (size_t)ret;
	}

out:
	if (fd != -1) {
		int saved_errno;

		/* We may want to preserve errno here. */
		saved_errno = errno;
		(void)close(fd);
		errno = saved_errno;
	}

	return (buf);
}

/*
 * rcs_buf_free()
 *
 * Free the buffer <b> and all associated data.
 */
void
rcs_buf_free(BUF *b)
{
	if (b->cb_buf != NULL)
		xfree(b->cb_buf);
	xfree(b);
}

/*
 * rcs_buf_release()
 *
 * Free the buffer <b>'s structural information but do not free the contents
 * of the buffer.  Instead, they are returned and should be freed later using
 * free().
 */
void *
rcs_buf_release(BUF *b)
{
	void *tmp;

	tmp = b->cb_buf;
	xfree(b);
	return (tmp);
}

/*
 * rcs_buf_get()
 */
u_char *
rcs_buf_get(BUF *b)
{
	return (b->cb_buf);
}

/*
 * rcs_buf_empty()
 *
 * Empty the contents of the buffer <b> and reset pointers.
 */
void
rcs_buf_empty(BUF *b)
{
	memset(b->cb_buf, 0, b->cb_size);
	b->cb_len = 0;
}

/*
 * rcs_buf_putc()
 *
 * Append a single character <c> to the end of the buffer <b>.
 */
void
rcs_buf_putc(BUF *b, int c)
{
	u_char *bp;

	bp = b->cb_buf + b->cb_len;
	if (bp == (b->cb_buf + b->cb_size)) {
		/* extend */
		if (b->cb_flags & BUF_AUTOEXT)
			rcs_buf_grow(b, (size_t)BUF_INCR);
		else
			errx(1, "rcs_buf_putc failed");

		/* the buffer might have been moved */
		bp = b->cb_buf + b->cb_len;
	}
	*bp = (u_char)c;
	b->cb_len++;
}

/*
 * rcs_buf_getc()
 *
 * Return u_char at buffer position <pos>.
 *
 */
u_char
rcs_buf_getc(BUF *b, size_t pos)
{
	return (b->cb_buf[pos]);
}

/*
 * rcs_buf_append()
 *
 * Append <len> bytes of data pointed to by <data> to the buffer <b>.  If the
 * buffer is too small to accept all data, it will attempt to append as much
 * data as possible, or if the BUF_AUTOEXT flag is set for the buffer, it
 * will get resized to an appropriate size to accept all data.
 * Returns the number of bytes successfully appended to the buffer.
 */
size_t
rcs_buf_append(BUF *b, const void *data, size_t len)
{
	size_t left, rlen;
	u_char *bp, *bep;

	bp = b->cb_buf + b->cb_len;
	bep = b->cb_buf + b->cb_size;
	left = bep - bp;
	rlen = len;

	if (left < len) {
		if (b->cb_flags & BUF_AUTOEXT) {
			rcs_buf_grow(b, len - left);
			bp = b->cb_buf + b->cb_len;
		} else
			rlen = bep - bp;
	}

	memcpy(bp, data, rlen);
	b->cb_len += rlen;

	return (rlen);
}

/*
 * rcs_buf_fappend()
 *
 */
size_t
rcs_buf_fappend(BUF *b, const char *fmt, ...)
{
	size_t ret;
	int n;
	char *str;
	va_list vap;

	va_start(vap, fmt);
	n = vasprintf(&str, fmt, vap);
	va_end(vap);

	if (n == -1)
		errx(1, "rcs_buf_fappend: failed to format data");

	ret = rcs_buf_append(b, str, n);
	xfree(str);
	return (ret);
}

/*
 * rcs_buf_len()
 *
 * Returns the size of the buffer that is being used.
 */
size_t
rcs_buf_len(BUF *b)
{
	return (b->cb_len);
}

/*
 * rcs_buf_write_fd()
 *
 * Write the contents of the buffer <b> to the specified <fd>
 */
int
rcs_buf_write_fd(BUF *b, int fd)
{
	u_char *bp;
	size_t len;
	ssize_t ret;

	len = b->cb_len;
	bp = b->cb_buf;

	do {
		ret = write(fd, bp, len);
		if (ret == -1) {
			if (errno == EINTR || errno == EAGAIN)
				continue;
			return (-1);
		}

		len -= (size_t)ret;
		bp += (size_t)ret;
	} while (len > 0);

	return (0);
}

/*
 * rcs_buf_write()
 *
 * Write the contents of the buffer <b> to the file whose path is given in
 * <path>.  If the file does not exist, it is created with mode <mode>.
 */
int
rcs_buf_write(BUF *b, const char *path, mode_t mode)
{
	int fd;
 open:
	if ((fd = open(path, O_WRONLY|O_CREAT|O_TRUNC, mode)) == -1) {
		if (errno == EACCES && unlink(path) != -1)
			goto open;
		else
			err(1, "%s", path);
	}

	if (rcs_buf_write_fd(b, fd) == -1) {
		(void)unlink(path);
		errx(1, "rcs_buf_write: rcs_buf_write_fd: `%s'", path);
	}

	if (fchmod(fd, mode) < 0)
		warn("permissions not set on file %s", path);

	(void)close(fd);

	return (0);
}

/*
 * rcs_buf_write_stmp()
 *
 * Write the contents of the buffer <b> to a temporary file whose path is
 * specified using <template> (see mkstemp.3). NB. This function will modify
 * <template>, as per mkstemp
 */
void
rcs_buf_write_stmp(BUF *b, char *template)
{
	int fd;

	if ((fd = mkstemp(template)) == -1)
		err(1, "%s", template);

	rcs_worklist_add(template, &rcs_temp_files);

	if (rcs_buf_write_fd(b, fd) == -1) {
		(void)unlink(template);
		errx(1, "rcs_buf_write_stmp: rcs_buf_write_fd: `%s'", template);
	}

	(void)close(fd);
}

/*
 * rcs_buf_grow()
 *
 * Grow the buffer <b> by <len> bytes.  The contents are unchanged by this
 * operation regardless of the result.
 */
static void
rcs_buf_grow(BUF *b, size_t len)
{
	b->cb_buf = xrealloc(b->cb_buf, 1, b->cb_size + len);
	b->cb_size += len;
}