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      1 /*	$NetBSD: fgets.c,v 1.28 2012/03/15 18:22:30 christos Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 1990, 1993
      5  *	The Regents of the University of California.  All rights reserved.
      6  *
      7  * This code is derived from software contributed to Berkeley by
      8  * Chris Torek.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  * 3. Neither the name of the University nor the names of its contributors
     19  *    may be used to endorse or promote products derived from this software
     20  *    without specific prior written permission.
     21  *
     22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     32  * SUCH DAMAGE.
     33  */
     34 
     35 #include <sys/cdefs.h>
     36 #if defined(LIBC_SCCS) && !defined(lint)
     37 #if 0
     38 static char sccsid[] = "@(#)fgets.c	8.2 (Berkeley) 12/22/93";
     39 #else
     40 __RCSID("$NetBSD: fgets.c,v 1.28 2012/03/15 18:22:30 christos Exp $");
     41 #endif
     42 #endif /* LIBC_SCCS and not lint */
     43 
     44 #include <assert.h>
     45 #include <stdio.h>
     46 #include <errno.h>
     47 #include <string.h>
     48 #include "reentrant.h"
     49 #include "local.h"
     50 #ifdef _FORTIFY_SOURCE
     51 #undef fgets
     52 #endif
     53 
     54 /*
     55  * Read at most n-1 characters from the given file.
     56  * Stop when a newline has been read, or the count runs out.
     57  * Return first argument, or NULL if no characters were read.
     58  */
     59 char *
     60 fgets(char *buf, int n, FILE *fp)
     61 {
     62 	int len;
     63 	char *s;
     64 	unsigned char *p, *t;
     65 
     66 	_DIAGASSERT(buf != NULL);
     67 	_DIAGASSERT(fp != NULL);
     68 
     69 	FLOCKFILE(fp);
     70 	_SET_ORIENTATION(fp, -1);
     71 	s = buf;
     72 	n--;			/* leave space for NUL */
     73 	do {
     74 		/*
     75 		 * If the buffer is empty, refill it.
     76 		 */
     77 		if (fp->_r <= 0) {
     78 			if (__srefill(fp)) {
     79 				/* EOF/error: stop with partial or no line */
     80 				if (s == buf) {
     81 					FUNLOCKFILE(fp);
     82 					return (NULL);
     83 				}
     84 				break;
     85 			}
     86 		}
     87 		len = fp->_r;
     88 		p = fp->_p;
     89 
     90 		/*
     91 		 * Scan through at most n bytes of the current buffer,
     92 		 * looking for '\n'.  If found, copy up to and including
     93 		 * newline, and stop.  Otherwise, copy entire chunk
     94 		 * and loop.
     95 		 */
     96 		if (len > n) {
     97 			if (n < 0) {
     98 				/*
     99 				 * Caller's length <= 0
    100 				 * We can't write into the buffer, so cannot
    101 				 * return a string, so must return NULL.
    102 				 * Set errno and __SERR so it is consistent.
    103 				 * TOG gives no indication of what to do here!
    104 				 */
    105 				errno = EINVAL;
    106 				fp->_flags |= __SERR;
    107 				FUNLOCKFILE(fp);
    108 				return NULL;
    109 			}
    110 			len = n;
    111 		}
    112 		t = memchr(p, '\n', (size_t)len);
    113 		if (t != NULL) {
    114 			len = (int)(++t - p);
    115 			fp->_r -= len;
    116 			fp->_p = t;
    117 			(void)memcpy(s, p, (size_t)len);
    118 			s[len] = 0;
    119 			FUNLOCKFILE(fp);
    120 			return buf;
    121 		}
    122 		fp->_r -= len;
    123 		fp->_p += len;
    124 		(void)memcpy(s, p, (size_t)len);
    125 		s += len;
    126 		n -= len;
    127 	} while (n != 0);
    128 	*s = 0;
    129 	FUNLOCKFILE(fp);
    130 	return buf;
    131 }
    132