1 | /* Close a stream, with nicer error checking than fclose's. |
2 | |
3 | Copyright (C) 1998-2002, 2004, 2006-2019 Free Software Foundation, Inc. |
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 | #include "close-stream.h" |
21 | |
22 | #include <errno.h> |
23 | #include <stdbool.h> |
24 | |
25 | #include "fpending.h" |
26 | |
27 | #if USE_UNLOCKED_IO |
28 | # include "unlocked-io.h" |
29 | #endif |
30 | |
31 | /* Close STREAM. Return 0 if successful, EOF (setting errno) |
32 | otherwise. A failure might set errno to 0 if the error number |
33 | cannot be determined. |
34 | |
35 | A failure with errno set to EPIPE may or may not indicate an error |
36 | situation worth signaling to the user. See the documentation of the |
37 | close_stdout_set_ignore_EPIPE function for details. |
38 | |
39 | If a program writes *anything* to STREAM, that program should close |
40 | STREAM and make sure that it succeeds before exiting. Otherwise, |
41 | suppose that you go to the extreme of checking the return status |
42 | of every function that does an explicit write to STREAM. The last |
43 | printf can succeed in writing to the internal stream buffer, and yet |
44 | the fclose(STREAM) could still fail (due e.g., to a disk full error) |
45 | when it tries to write out that buffered data. Thus, you would be |
46 | left with an incomplete output file and the offending program would |
47 | exit successfully. Even calling fflush is not always sufficient, |
48 | since some file systems (NFS and CODA) buffer written/flushed data |
49 | until an actual close call. |
50 | |
51 | Besides, it's wasteful to check the return value from every call |
52 | that writes to STREAM -- just let the internal stream state record |
53 | the failure. That's what the ferror test is checking below. */ |
54 | |
55 | int |
56 | close_stream (FILE *stream) |
57 | { |
58 | const bool some_pending = (__fpending (stream) != 0); |
59 | const bool prev_fail = (ferror (stream) != 0); |
60 | const bool fclose_fail = (fclose (stream) != 0); |
61 | |
62 | /* Return an error indication if there was a previous failure or if |
63 | fclose failed, with one exception: ignore an fclose failure if |
64 | there was no previous error, no data remains to be flushed, and |
65 | fclose failed with EBADF. That can happen when a program like cp |
66 | is invoked like this 'cp a b >&-' (i.e., with standard output |
67 | closed) and doesn't generate any output (hence no previous error |
68 | and nothing to be flushed). */ |
69 | |
70 | if (prev_fail || (fclose_fail && (some_pending || errno != EBADF))) |
71 | { |
72 | if (! fclose_fail) |
73 | errno = 0; |
74 | return EOF; |
75 | } |
76 | |
77 | return 0; |
78 | } |
79 | |