xref: /freebsd/lib/libc/stdio/fgets.c (revision 9bc300465e48e19d794d88d0c158a2adb92c7197)
1 /*-
2  * SPDX-License-Identifier: BSD-3-Clause
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 "namespace.h"
36 #include <errno.h>
37 #include <stdio.h>
38 #include <string.h>
39 #include "un-namespace.h"
40 #include "local.h"
41 #include "libc_private.h"
42 
43 #undef fgets	/* _FORTIFY_SOURCE */
44 
45 /*
46  * Read at most n-1 characters from the given file.
47  * Stop when a newline has been read, or the count runs out.
48  * Return first argument, or NULL if no characters were read.
49  */
50 char *
51 fgets(char * __restrict buf, int n, FILE * __restrict fp)
52 {
53 	size_t len;
54 	char *s, *ret;
55 	unsigned char *p, *t;
56 
57 	FLOCKFILE_CANCELSAFE(fp);
58 	ORIENT(fp, -1);
59 
60 	if (n <= 0) {		/* sanity check */
61 		fp->_flags |= __SERR;
62 		errno = EINVAL;
63 		ret = NULL;
64 		goto end;
65 	}
66 
67 	s = buf;
68 	n--;			/* leave space for NUL */
69 	while (n != 0) {
70 		/*
71 		 * If the buffer is empty, refill it.
72 		 */
73 		if ((len = fp->_r) <= 0) {
74 			if (__srefill(fp)) {
75 				/* EOF/error: stop with partial or no line */
76 				if (!__sfeof(fp) || s == buf) {
77 					ret = NULL;
78 					goto end;
79 				}
80 				break;
81 			}
82 			len = fp->_r;
83 		}
84 		p = fp->_p;
85 
86 		/*
87 		 * Scan through at most n bytes of the current buffer,
88 		 * looking for '\n'.  If found, copy up to and including
89 		 * newline, and stop.  Otherwise, copy entire chunk
90 		 * and loop.
91 		 */
92 		if (len > n)
93 			len = n;
94 		t = memchr((void *)p, '\n', len);
95 		if (t != NULL) {
96 			len = ++t - p;
97 			fp->_r -= len;
98 			fp->_p = t;
99 			(void)memcpy((void *)s, (void *)p, len);
100 			s[len] = 0;
101 			ret = buf;
102 			goto end;
103 		}
104 		fp->_r -= len;
105 		fp->_p += len;
106 		(void)memcpy((void *)s, (void *)p, len);
107 		s += len;
108 		n -= len;
109 	}
110 	*s = 0;
111 	ret = buf;
112 end:
113 	FUNLOCKFILE_CANCELSAFE();
114 	return (ret);
115 }
116