/*      $OpenBSD: fgets.c,v 1.16 2016/09/21 04:38:56 guenther Exp $ */
/*-
 * Copyright (c) 1990, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Chris Torek.
 *
 * 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.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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 <errno.h>
#include <stdio.h>
#include <string.h>
#include "local.h"

/*
 * Read at most n-1 characters from the given file.
 * Stop when a newline has been read, or the count runs out.
 * Return first argument, or NULL if no characters were read.
 * Do not return NULL if n == 1.
 */
char *
fgets(char *buf, int n, FILE *fp)
{
        size_t len;
        char *s;
        unsigned char *p, *t;

        if (n <= 0) {           /* sanity check */
                errno = EINVAL;
                return (NULL);
        }

        FLOCKFILE(fp);
        _SET_ORIENTATION(fp, -1);
        s = buf;
        n--;                    /* leave space for NUL */
        while (n != 0) {
                /*
                 * If the buffer is empty, refill it.
                 */
                if (fp->_r <= 0) {
                        if (__srefill(fp)) {
                                /* EOF/error: stop with partial or no line */
                                if (s == buf) {
                                        FUNLOCKFILE(fp);
                                        return (NULL);
                                }
                                break;
                        }
                }
                len = fp->_r;
                p = fp->_p;

                /*
                 * Scan through at most n bytes of the current buffer,
                 * looking for '\n'.  If found, copy up to and including
                 * newline, and stop.  Otherwise, copy entire chunk
                 * and loop.
                 */
                if (len > n)
                        len = n;
                t = memchr(p, '\n', len);
                if (t != NULL) {
                        len = ++t - p;
                        fp->_r -= len;
                        fp->_p = t;
                        (void)memcpy(s, p, len);
                        s[len] = '\0';
                        FUNLOCKFILE(fp);
                        return (buf);
                }
                fp->_r -= len;
                fp->_p += len;
                (void)memcpy(s, p, len);
                s += len;
                n -= len;
        }
        *s = '\0';
        FUNLOCKFILE(fp);
        return (buf);
}
DEF_STRONG(fgets);