1 /* $OpenBSD: fread.c,v 1.12 2014/05/01 16:40:36 deraadt Exp $ */
2 /*-
3 * Copyright (c) 1990, 1993
4 * The Regents of the University of California. All rights reserved.
5 *
6 * This code is derived from software contributed to Berkeley by
7 * Chris Torek.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 * 3. Neither the name of the University nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34 #include <stdio.h>
35 #include <string.h>
36 #include <stdint.h>
37 #include <errno.h>
38 #include <sys/param.h>
39 #include "local.h"
40
41 #define MUL_NO_OVERFLOW (1UL << (sizeof(size_t) * 4))
42
43 size_t
fread(void * buf,size_t size,size_t count,FILE * fp)44 fread(void *buf, size_t size, size_t count, FILE *fp)
45 {
46 /*
47 * Extension: Catch integer overflow.
48 */
49 if ((size >= MUL_NO_OVERFLOW || count >= MUL_NO_OVERFLOW) &&
50 size > 0 && SIZE_MAX / size < count) {
51 errno = EOVERFLOW;
52 fp->_flags |= __SERR;
53 return (0);
54 }
55
56 const size_t desired_total = count * size;
57 size_t total = desired_total;
58
59 /*
60 * ANSI and SUSv2 require a return value of 0 if size or count are 0.
61 */
62 if (total == 0) {
63 return (0);
64 }
65
66 FLOCKFILE(fp);
67 _SET_ORIENTATION(fp, -1);
68
69 // TODO: how can this ever happen?!
70 if (fp->_r < 0)
71 fp->_r = 0;
72
73 /*
74 * Ensure _bf._size is valid.
75 */
76 if (fp->_bf._base == NULL) {
77 __smakebuf(fp);
78 }
79
80 char* dst = buf;
81
82 while (total > 0) {
83 /*
84 * Copy data out of the buffer.
85 */
86 size_t buffered_bytes = MIN((size_t) fp->_r, total);
87 memcpy(dst, fp->_p, buffered_bytes);
88 fp->_p += buffered_bytes;
89 fp->_r -= buffered_bytes;
90 dst += buffered_bytes;
91 total -= buffered_bytes;
92
93 /*
94 * Are we done?
95 */
96 if (total == 0) {
97 goto out;
98 }
99
100 /*
101 * Do we have so much more to read that we should
102 * avoid copying it through the buffer?
103 */
104 if (total > (size_t) fp->_bf._size) {
105 /*
106 * Make sure that fseek doesn't think it can
107 * reuse the buffer since we are going to read
108 * directly from the file descriptor.
109 */
110 fp->_flags |= __SMOD;
111 break;
112 }
113
114 /*
115 * Less than a buffer to go, so refill the buffer and
116 * go around the loop again.
117 */
118 if (__srefill(fp)) {
119 goto out;
120 }
121 }
122
123 /*
124 * Read directly into the caller's buffer.
125 */
126 while (total > 0) {
127 ssize_t bytes_read = (*fp->_read)(fp->_cookie, dst, total);
128 if (bytes_read <= 0) {
129 fp->_flags |= (bytes_read == 0) ? __SEOF : __SERR;
130 break;
131 }
132 dst += bytes_read;
133 total -= bytes_read;
134 }
135
136 out:
137 FUNLOCKFILE(fp);
138 return ((desired_total - total) / size);
139 }
140