xref: /freebsd/lib/libc/stdio/fgetln.c (revision dad64f0e)
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 #if defined(LIBC_SCCS) && !defined(lint)
36 static char sccsid[] = "@(#)fgetln.c	8.2 (Berkeley) 1/2/94";
37 #endif /* LIBC_SCCS and not lint */
38 #include <sys/cdefs.h>
39 __FBSDID("$FreeBSD$");
40 
41 #include "namespace.h"
42 #include <errno.h>
43 #include <limits.h>
44 #include <stdio.h>
45 #include <stdlib.h>
46 #include <string.h>
47 #include "un-namespace.h"
48 #include "libc_private.h"
49 #include "local.h"
50 
51 /*
52  * Expand the line buffer.  Return -1 on error.
53  */
54 int
55 __slbexpand(FILE *fp, size_t newsize)
56 {
57 	void *p;
58 
59 	if (fp->_lb._size >= newsize)
60 		return (0);
61 	if (newsize > INT_MAX) {
62 		errno = ENOMEM;
63 		return (-1);
64 	}
65 	if ((p = realloc(fp->_lb._base, newsize)) == NULL)
66 		return (-1);
67 	fp->_lb._base = p;
68 	fp->_lb._size = newsize;
69 	return (0);
70 }
71 
72 /*
73  * Get an input line.  The returned pointer often (but not always)
74  * points into a stdio buffer.  Fgetln does not alter the text of
75  * the returned line (which is thus not a C string because it will
76  * not necessarily end with '\0'), but does allow callers to modify
77  * it if they wish.  Thus, we set __SMOD in case the caller does.
78  */
79 char *
80 fgetln(FILE *fp, size_t *lenp)
81 {
82 	unsigned char *p;
83 	char *ret;
84 	size_t len;
85 	size_t off;
86 
87 	FLOCKFILE_CANCELSAFE(fp);
88 	ORIENT(fp, -1);
89 	/* make sure there is input */
90 	if (fp->_r <= 0 && __srefill(fp)) {
91 		*lenp = 0;
92 		ret = NULL;
93 		goto end;
94 	}
95 
96 	/* look for a newline in the input */
97 	if ((p = memchr((void *)fp->_p, '\n', (size_t)fp->_r)) != NULL) {
98 		/*
99 		 * Found one.  Flag buffer as modified to keep fseek from
100 		 * `optimising' a backward seek, in case the user stomps on
101 		 * the text.
102 		 */
103 		p++;		/* advance over it */
104 		ret = (char *)fp->_p;
105 		*lenp = len = p - fp->_p;
106 		fp->_flags |= __SMOD;
107 		fp->_r -= len;
108 		fp->_p = p;
109 		goto end;
110 	}
111 
112 	/*
113 	 * We have to copy the current buffered data to the line buffer.
114 	 * As a bonus, though, we can leave off the __SMOD.
115 	 *
116 	 * OPTIMISTIC is length that we (optimistically) expect will
117 	 * accommodate the `rest' of the string, on each trip through the
118 	 * loop below.
119 	 */
120 #define OPTIMISTIC 80
121 
122 	for (len = fp->_r, off = 0;; len += fp->_r) {
123 		size_t diff;
124 
125 		/*
126 		 * Make sure there is room for more bytes.  Copy data from
127 		 * file buffer to line buffer, refill file and look for
128 		 * newline.  The loop stops only when we find a newline.
129 		 */
130 		if (__slbexpand(fp, len + OPTIMISTIC))
131 			goto error;
132 		(void)memcpy((void *)(fp->_lb._base + off), (void *)fp->_p,
133 		    len - off);
134 		off = len;
135 		if (__srefill(fp)) {
136 			if (__sfeof(fp))
137 				break;
138 			goto error;
139 		}
140 		if ((p = memchr((void *)fp->_p, '\n', (size_t)fp->_r)) == NULL)
141 			continue;
142 
143 		/* got it: finish up the line (like code above) */
144 		p++;
145 		diff = p - fp->_p;
146 		len += diff;
147 		if (__slbexpand(fp, len))
148 			goto error;
149 		(void)memcpy((void *)(fp->_lb._base + off), (void *)fp->_p,
150 		    diff);
151 		fp->_r -= diff;
152 		fp->_p = p;
153 		break;
154 	}
155 	*lenp = len;
156 	ret = (char *)fp->_lb._base;
157 end:
158 	FUNLOCKFILE_CANCELSAFE();
159 	return (ret);
160 
161 error:
162 	*lenp = 0;		/* ??? */
163 	fp->_flags |= __SERR;
164 	ret = NULL;
165 	goto end;
166 }
167