/*-
 * Copyright (c) 2017 Taylor R. Campbell
 * 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. 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 THE 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 THE 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.
 */

#define	_POSIX_C_SOURCE	200809L

#include "read_block.h"

#include <assert.h>
#include <stdint.h>
#include <unistd.h>

#include "attribute.h"

/*
 * read_block(fd, buf, len)
 *
 *	Read up to len bytes of data from fd into buf.  Short read only
 *	on EOF.  Return -1 and set errno on failure; otherwise return
 *	number of bytes read.
 */
ssize_t
read_block(int fd, void *buf, size_t len)
{
	char *p = buf;
	size_t n = len;
	const char *const end attr_diagused = p + n;
	ssize_t nread = 0;

	while (0 < n && (nread = read(fd, p, n)) != 0) {
		if (nread == -1)
			return -1;
		p += (n < (size_t)nread? n : (size_t)nread); /* paranoia */
		n -= (n < (size_t)nread? n : (size_t)nread); /* paranoia */
		assert(p + n == end);
	}

	assert(n == 0 || nread == 0); /* complete read or EOF */
	return len - n;
}