Line | Count | Source (jump to first uncovered line) |
1 | | /* fflush.c -- allow flushing input streams |
2 | | Copyright (C) 2007-2025 Free Software Foundation, Inc. |
3 | | |
4 | | This file is free software: you can redistribute it and/or modify |
5 | | it under the terms of the GNU Lesser General Public License as |
6 | | published by the Free Software Foundation; either version 2.1 of the |
7 | | License, or (at your option) any later version. |
8 | | |
9 | | This file is distributed in the hope that it will be useful, |
10 | | but WITHOUT ANY WARRANTY; without even the implied warranty of |
11 | | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
12 | | GNU Lesser General Public License for more details. |
13 | | |
14 | | You should have received a copy of the GNU Lesser General Public License |
15 | | along with this program. If not, see <https://www.gnu.org/licenses/>. */ |
16 | | |
17 | | /* Written by Eric Blake. */ |
18 | | |
19 | | #include <config.h> |
20 | | |
21 | | /* Specification. */ |
22 | | #include <stdio.h> |
23 | | |
24 | | #include <errno.h> |
25 | | #include <unistd.h> |
26 | | |
27 | | #include "freading.h" |
28 | | |
29 | | #include "stdio-impl.h" |
30 | | |
31 | | #undef fflush |
32 | | |
33 | | |
34 | | #if defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 |
35 | | /* GNU libc, BeOS, Haiku, Linux libc5 */ |
36 | | |
37 | | /* Clear the stream's ungetc buffer, preserving the value of ftello (fp). */ |
38 | | static void |
39 | | clear_ungetc_buffer_preserving_position (FILE *fp) |
40 | 0 | { |
41 | 0 | if (fp->_flags & _IO_IN_BACKUP) |
42 | | /* _IO_free_backup_area is a bit complicated. Simply call fseek. */ |
43 | 0 | fseeko (fp, 0, SEEK_CUR); |
44 | 0 | } |
45 | | |
46 | | #else |
47 | | |
48 | | /* Clear the stream's ungetc buffer. May modify the value of ftello (fp). */ |
49 | | static void |
50 | | clear_ungetc_buffer (FILE *fp) |
51 | | { |
52 | | # if defined __sferror || defined __DragonFly__ || defined __ANDROID__ |
53 | | /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */ |
54 | | if (HASUB (fp)) |
55 | | { |
56 | | fp_->_p += fp_->_r; |
57 | | fp_->_r = 0; |
58 | | } |
59 | | # elif defined __EMX__ /* emx+gcc */ |
60 | | if (fp->_ungetc_count > 0) |
61 | | { |
62 | | fp->_ungetc_count = 0; |
63 | | fp->_rcount = - fp->_rcount; |
64 | | } |
65 | | # elif defined _IOERR /* Minix, AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, UnixWare, mingw, MSVC, NonStop Kernel, OpenVMS */ |
66 | | /* Nothing to do. */ |
67 | | # else /* other implementations */ |
68 | | fseeko (fp, 0, SEEK_CUR); |
69 | | # endif |
70 | | } |
71 | | |
72 | | #endif |
73 | | |
74 | | #if ! (defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1) |
75 | | /* GNU libc, BeOS, Haiku, Linux libc5 */ |
76 | | |
77 | | # if (defined __sferror || defined __DragonFly__ || defined __ANDROID__) && defined __SNPT |
78 | | /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */ |
79 | | |
80 | | static int |
81 | | disable_seek_optimization (FILE *fp) |
82 | | { |
83 | | int saved_flags = fp_->_flags & (__SOPT | __SNPT); |
84 | | fp_->_flags = (fp_->_flags & ~__SOPT) | __SNPT; |
85 | | return saved_flags; |
86 | | } |
87 | | |
88 | | static void |
89 | | restore_seek_optimization (FILE *fp, int saved_flags) |
90 | | { |
91 | | fp_->_flags = (fp_->_flags & ~(__SOPT | __SNPT)) | saved_flags; |
92 | | } |
93 | | |
94 | | # else |
95 | | |
96 | | static void |
97 | | update_fpos_cache (_GL_ATTRIBUTE_MAYBE_UNUSED FILE *fp, |
98 | | _GL_ATTRIBUTE_MAYBE_UNUSED off_t pos) |
99 | | { |
100 | | # if defined __sferror || defined __DragonFly__ || defined __ANDROID__ |
101 | | /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */ |
102 | | # if defined __CYGWIN__ || defined __ANDROID__ |
103 | | /* fp_->_offset is typed as an integer. */ |
104 | | fp_->_offset = pos; |
105 | | # else |
106 | | /* fp_->_offset is an fpos_t. */ |
107 | | /* Use a union, since on NetBSD, the compilation flags determine |
108 | | whether fpos_t is typedef'd to off_t or a struct containing a |
109 | | single off_t member. */ |
110 | | union |
111 | | { |
112 | | fpos_t f; |
113 | | off_t o; |
114 | | } u; |
115 | | u.o = pos; |
116 | | fp_->_offset = u.f; |
117 | | # endif |
118 | | fp_->_flags |= __SOFF; |
119 | | # endif |
120 | | } |
121 | | # endif |
122 | | #endif |
123 | | |
124 | | /* Flush all pending data on STREAM according to POSIX rules. Both |
125 | | output and seekable input streams are supported. */ |
126 | | int |
127 | | rpl_fflush (FILE *stream) |
128 | 0 | { |
129 | | /* When stream is NULL, POSIX and C99 only require flushing of "output |
130 | | streams and update streams in which the most recent operation was not |
131 | | input", and all implementations do this. |
132 | | |
133 | | When stream is "an output stream or an update stream in which the most |
134 | | recent operation was not input", POSIX and C99 requires that fflush |
135 | | writes out any buffered data, and all implementations do this. |
136 | | |
137 | | When stream is, however, an input stream or an update stream in |
138 | | which the most recent operation was input, C99 specifies nothing, |
139 | | and POSIX only specifies behavior if the stream is seekable. |
140 | | mingw, in particular, drops the input buffer, leaving the file |
141 | | descriptor positioned at the end of the input buffer. I.e. ftell |
142 | | (stream) is lost. We don't want to call the implementation's |
143 | | fflush in this case. |
144 | | |
145 | | We test ! freading (stream) here, rather than fwriting (stream), because |
146 | | what we need to know is whether the stream holds a "read buffer", and on |
147 | | mingw this is indicated by _IOREAD, regardless of _IOWRT. */ |
148 | 0 | if (stream == NULL || ! freading (stream)) |
149 | 0 | return fflush (stream); |
150 | | |
151 | 0 | #if defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 |
152 | | /* GNU libc, BeOS, Haiku, Linux libc5 */ |
153 | | |
154 | 0 | clear_ungetc_buffer_preserving_position (stream); |
155 | |
|
156 | 0 | return fflush (stream); |
157 | |
|
158 | | #else |
159 | | { |
160 | | /* What POSIX says: |
161 | | 1) About the file-position indicator (-> fseeko, ftello): |
162 | | The file position indicator is incremented by fgetc() and decremented |
163 | | by ungetc(): |
164 | | <https://pubs.opengroup.org/onlinepubs/9699919799/functions/fgetc.html> |
165 | | "... the fgetc() function shall ... advance the associated file |
166 | | position indicator for the stream ..." |
167 | | <https://pubs.opengroup.org/onlinepubs/9699919799/functions/ungetc.html> |
168 | | "The file-position indicator is decremented by each successful |
169 | | call to ungetc()..." |
170 | | 2) fflush discards bytes pushed back by ungetc: |
171 | | <https://pubs.opengroup.org/onlinepubs/9699919799/functions/fflush.html> |
172 | | "...any characters pushed back onto the stream by ungetc() |
173 | | or ungetwc() that have not subsequently been read from the |
174 | | stream shall be discarded..." |
175 | | This implies implicitly: fflush does not change the file position |
176 | | indicator. |
177 | | 3) Effects on the file descriptor, if the file descriptor is capable of |
178 | | seeking: |
179 | | <https://pubs.opengroup.org/onlinepubs/9699919799/functions/fflush.html> |
180 | | "...the file offset of the underlying open file description shall |
181 | | be set to the file position of the stream..." */ |
182 | | |
183 | | /* POSIX does not specify fflush behavior for non-seekable input |
184 | | streams. Some implementations purge unread data, some return |
185 | | EBADF, some do nothing. */ |
186 | | off_t pos = ftello (stream); |
187 | | if (pos == -1) |
188 | | { |
189 | | errno = EBADF; |
190 | | return EOF; |
191 | | } |
192 | | |
193 | | /* Clear the ungetc buffer. */ |
194 | | clear_ungetc_buffer (stream); |
195 | | |
196 | | /* To get here, we must be flushing a seekable input stream, so the |
197 | | semantics of fpurge are now appropriate to clear the buffer. To |
198 | | avoid losing data, the lseek is also necessary. */ |
199 | | { |
200 | | int result = fpurge (stream); |
201 | | if (result != 0) |
202 | | return result; |
203 | | } |
204 | | |
205 | | # if (defined __sferror || defined __DragonFly__ || defined __ANDROID__) && defined __SNPT |
206 | | /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */ |
207 | | |
208 | | { |
209 | | /* Disable seek optimization for the next fseeko call. This tells the |
210 | | following fseeko call to seek to the desired position directly, rather |
211 | | than to seek to a block-aligned boundary. */ |
212 | | int saved_flags = disable_seek_optimization (stream); |
213 | | int result = fseeko (stream, pos, SEEK_SET); |
214 | | |
215 | | restore_seek_optimization (stream, saved_flags); |
216 | | return result; |
217 | | } |
218 | | |
219 | | # else |
220 | | |
221 | | pos = lseek (fileno (stream), pos, SEEK_SET); |
222 | | if (pos == -1) |
223 | | return EOF; |
224 | | /* After a successful lseek, update the file descriptor's position cache |
225 | | in the stream. */ |
226 | | update_fpos_cache (stream, pos); |
227 | | |
228 | | return 0; |
229 | | |
230 | | # endif |
231 | | } |
232 | | #endif |
233 | 0 | } |