1 /* Detect write error on a stream.
2 Copyright (C) 2003-2006, 2008-2023 Free Software Foundation, Inc.
3 Written by Bruno Haible <bruno@clisp.org>, 2003.
4
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
9
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
14
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <https://www.gnu.org/licenses/>. */
17
18 #include <config.h>
19
20 /* Specification. */
21 #include "fwriteerror.h"
22
23 #include <errno.h>
24
25 static int
26 do_fwriteerror (FILE *fp, bool ignore_ebadf)
27 {
28 /* State to allow multiple calls to fwriteerror (stdout). */
29 static bool stdout_closed = false;
30
31 if (fp == stdout)
32 {
33 if (stdout_closed)
34 return 0;
35
36 /* If we are closing stdout, don't attempt to do it later again. */
37 stdout_closed = true;
38 }
39
40 /* This function returns an error indication if there was a previous failure
41 or if fclose failed, with two exceptions:
42 - Ignore an fclose failure if there was no previous error, no data
43 remains to be flushed, and fclose failed with EBADF. That can
44 happen when a program like cp is invoked like this 'cp a b >&-'
45 (i.e., with standard output closed) and doesn't generate any
46 output (hence no previous error and nothing to be flushed).
47 - Ignore an fclose failure due to EPIPE. That can happen when a
48 program blocks or ignores SIGPIPE, and the output pipe or socket
49 has no readers now. The EPIPE tells us that we should stop writing
50 to this output. That's what we are doing anyway here.
51
52 Need to
53 1. test the error indicator of the stream,
54 2. flush the buffers both in userland and in the kernel, through fclose,
55 testing for error again. */
56
57 /* Clear errno, so that on non-POSIX systems the caller doesn't see a
58 wrong value of errno when we return -1. */
59 errno = 0;
60
61 if (ferror (fp))
62 {
63 if (fflush (fp))
64 goto close_preserving_errno; /* errno is set here */
65 /* The stream had an error earlier, but its errno was lost. If the
66 error was not temporary, we can get the same errno by writing and
67 flushing one more byte. We can do so because at this point the
68 stream's contents is garbage anyway. */
69 if (fputc ('\0', fp) == EOF)
70 goto close_preserving_errno; /* errno is set here */
71 if (fflush (fp))
72 goto close_preserving_errno; /* errno is set here */
73 /* Give up on errno. */
74 errno = 0;
75 goto close_preserving_errno;
76 }
77
78 if (ignore_ebadf)
79 {
80 /* We need an explicit fflush to tell whether some output was already
81 done on FP. */
82 if (fflush (fp))
83 goto close_preserving_errno; /* errno is set here */
84 if (fclose (fp) && errno != EBADF)
85 goto got_errno; /* errno is set here */
86 }
87 else
88 {
89 if (fclose (fp))
90 goto got_errno; /* errno is set here */
91 }
92
93 return 0;
94
95 close_preserving_errno:
96 /* There's an error. Nevertheless call fclose(fp), for consistency
97 with the other cases. */
98 {
99 int saved_errno = errno;
100 fclose (fp);
101 errno = saved_errno;
102 }
103 got_errno:
104 /* There's an error. Ignore EPIPE. */
105 if (errno == EPIPE)
106 return 0;
107 else
108 return -1;
109 }
110
111 int
112 fwriteerror (FILE *fp)
113 {
114 return do_fwriteerror (fp, false);
115 }
116
117 int
118 fwriteerror_no_ebadf (FILE *fp)
119 {
120 return do_fwriteerror (fp, true);
121 }
122
123
124 #if TEST
125
126 /* Name of a file on which writing fails. On systems without /dev/full,
127 you can choose a filename on a full file system. */
128 #define UNWRITABLE_FILE "/dev/full"
129
130 int
131 main ()
132 {
133 static int sizes[] =
134 {
135 511, 512, 513,
136 1023, 1024, 1025,
137 2047, 2048, 2049,
138 4095, 4096, 4097,
139 8191, 8192, 8193
140 };
141 static char dummy[8193];
142 unsigned int i, j;
143
144 for (i = 0; i < sizeof (sizes) / sizeof (sizes[0]); i++)
145 {
146 size_t size = sizes[i];
147
148 for (j = 0; j < 2; j++)
149 {
150 /* Run a test depending on i and j:
151 Write size bytes and then calls fflush if j==1. */
152 FILE *stream = fopen (UNWRITABLE_FILE, "w");
153
154 if (stream == NULL)
155 {
156 fprintf (stderr, "Test %u:%u: could not open file\n", i, j);
157 continue;
158 }
159
160 fwrite (dummy, 347, 1, stream);
161 fwrite (dummy, size - 347, 1, stream);
162 if (j)
163 fflush (stream);
164
165 if (fwriteerror (stream) == -1)
166 {
167 if (errno != ENOSPC)
168 fprintf (stderr, "Test %u:%u: fwriteerror ok, errno = %d\n",
169 i, j, errno);
170 }
171 else
172 fprintf (stderr, "Test %u:%u: fwriteerror found no error!\n",
173 i, j);
174 }
175 }
176
177 return 0;
178 }
179
180 #endif