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1/* $OpenBSD: freopen.c,v 1.21 2025/08/08 15:58:53 yasuoka 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 <sys/types.h>
35#include <sys/stat.h>
36#include <fcntl.h>
37#include <errno.h>
38#include <limits.h>
39#include <unistd.h>
40#include <stdio.h>
41#include <stdlib.h>
42#include "local.h"
43
44/*
45 * Re-direct an existing, open (probably) file to some other file.
46 * ANSI is written such that the original file gets closed if at
47 * all possible, no matter what.
48 */
49FILE *
50freopen(const char *file, const char *mode, FILE *fp)
51{
52 int f;
53 int flags, isopen, oflags, sverrno, wantfd;
54
55 if ((flags = __sflags(mode, &oflags)) == 0) {
56 (void) fclose(fp);
57 return (NULL);
58 }
59
60 if (!__sdidinit)
61 __sinit();
62
63 FLOCKFILE(fp);
64
65 /*
66 * There are actually programs that depend on being able to "freopen"
67 * descriptors that weren't originally open. Keep this from breaking.
68 * Remember whether the stream was open to begin with, and which file
69 * descriptor (if any) was associated with it. If it was attached to
70 * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
71 * should work. This is unnecessary if it was not a Unix file.
72 */
73 if (fp->_flags == 0) {
74 fp->_flags = __SEOF; /* hold on to it */
75 isopen = 0;
76 wantfd = -1;
77 } else {
78 /* flush the stream; POSIX, not ANSI, requires this. */
79 (void) __sflush(fp);
80 /* if close is NULL, closing is a no-op, hence pointless */
81 isopen = fp->_close != NULL;
82 if ((wantfd = fp->_file) < 0 && isopen) {
83 (void) (*fp->_close)(fp->_cookie);
84 isopen = 0;
85 }
86 }
87
88 /* Get a new descriptor to refer to the new file. */
89 f = open(file, oflags, DEFFILEMODE);
90 if (f == -1 && isopen) {
91 /* If out of fd's close the old one and try again. */
92 if (errno == ENFILE || errno == EMFILE) {
93 (void) (*fp->_close)(fp->_cookie);
94 isopen = 0;
95 f = open(file, oflags, DEFFILEMODE);
96 }
97 }
98 sverrno = errno;
99
100 /*
101 * Finish closing fp. Even if the open succeeded above, we cannot
102 * keep fp->_base: it may be the wrong size. This loses the effect
103 * of any setbuffer calls, but stdio has always done this before.
104 */
105 if (isopen && f != wantfd)
106 (void) (*fp->_close)(fp->_cookie);
107 if (fp->_flags & __SMBF)
108 free((char *)fp->_bf._base);
109 fp->_w = 0;
110 fp->_r = 0;
111 fp->_p = NULL;
112 fp->_bf._base = NULL;
113 fp->_bf._size = 0;
114 fp->_lbfsize = 0;
115 if (HASUB(fp))
116 FREEUB(fp);
117 _UB(fp)._size = 0;
118 fp->_ungetwc_inbuf = 0;
119 if (HASLB(fp))
120 FREELB(fp);
121 fp->_lb._size = 0;
122
123 if (f == -1) { /* did not get it after all */
124 fp->_flags = 0; /* set it free */
125 FUNLOCKFILE(fp);
126 errno = sverrno; /* restore in case _close clobbered */
127 return (NULL);
128 }
129
130 /*
131 * If reopening something that was open before on a real file, try
132 * to maintain the descriptor. Various C library routines (perror)
133 * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
134 */
135 if (wantfd >= 0 && f != wantfd) {
136 if (dup3(f, wantfd, oflags & O_CLOEXEC) >= 0) {
137 (void) close(f);
138 f = wantfd;
139 }
140 }
141
142 fp->_flags = flags;
143 fp->_file = f;
144 fp->_cookie = fp;
145 fp->_read = __sread;
146 fp->_write = __swrite;
147 fp->_seek = __sseek;
148 fp->_close = __sclose;
149
150 /*
151 * When opening in append mode, even though we use O_APPEND,
152 * we need to seek to the end so that ftell() gets the right
153 * answer. If the user then alters the seek pointer, or
154 * the file extends, this will fail, but there is not much
155 * we can do about this. (We could set __SAPP and check in
156 * fseek and ftell.)
157 */
158 if (oflags & O_APPEND)
159 (void) __sseek(fp, 0, SEEK_END);
160 FUNLOCKFILE(fp);
161 return (fp);
162}
163DEF_STRONG(freopen);