113 lines
3.8 KiB
C
113 lines
3.8 KiB
C
/* Close standard input, rewinding seekable stdin if necessary.
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Copyright (C) 2007, 2009-2022 Free Software Foundation, Inc.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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#include <config.h>
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#include "closein.h"
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#include <errno.h>
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#include <stdbool.h>
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#include <stdio.h>
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#include <unistd.h>
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#include "gettext.h"
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#define _(msgid) gettext (msgid)
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#include "close-stream.h"
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#include "closeout.h"
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#include "error.h"
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#include "exitfail.h"
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#include "freadahead.h"
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#include "quotearg.h"
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static const char *file_name;
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/* Set the file name to be reported in the event an error is detected
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on stdin by close_stdin. See also close_stdout_set_file_name, if
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an error is detected when closing stdout. */
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void
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close_stdin_set_file_name (const char *file)
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{
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file_name = file;
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}
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/* Close standard input, rewinding any unused input if stdin is
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seekable. On error, issue a diagnostic and _exit with status
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'exit_failure'. Then call close_stdout.
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Most programs can get by with close_stdout. close_stdin is only
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needed when a program wants to guarantee that partially read input
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from seekable stdin is not consumed, for any subsequent clients.
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For example, POSIX requires that these two commands behave alike:
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(sed -ne 1q; cat) < file
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tail -n +2 file
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Since close_stdin is commonly registered via 'atexit', POSIX
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and the C standard both say that it should not call 'exit',
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because the behavior is undefined if 'exit' is called more than
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once. So it calls '_exit' instead of 'exit'. If close_stdin
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is registered via atexit before other functions are registered,
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the other functions can act before this _exit is invoked.
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Applications that use close_stdout should flush any streams other
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than stdin, stdout, and stderr before exiting, since the call to
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_exit will bypass other buffer flushing. Applications should be
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flushing and closing other streams anyway, to check for I/O errors.
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Also, applications should not use tmpfile, since _exit can bypass
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the removal of these files.
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It's important to detect such failures and exit nonzero because many
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tools (most notably 'make' and other build-management systems) depend
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on being able to detect failure in other tools via their exit status. */
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void
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close_stdin (void)
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{
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bool fail = false;
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/* There is no need to flush stdin if we can determine quickly that stdin's
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input buffer is empty; in this case we know that if stdin is seekable,
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(fseeko (stdin, 0, SEEK_CUR), ftello (stdin))
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== lseek (0, 0, SEEK_CUR). */
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if (freadahead (stdin) > 0)
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{
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/* Only attempt flush if stdin is seekable, as fflush is entitled to
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fail on non-seekable streams. */
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if (fseeko (stdin, 0, SEEK_CUR) == 0 && fflush (stdin) != 0)
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fail = true;
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}
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if (close_stream (stdin) != 0)
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fail = true;
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if (fail)
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{
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/* Report failure, but defer exit until after closing stdout,
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since the failure report should still be flushed. */
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char const *close_error = _("error closing file");
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if (file_name)
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error (0, errno, "%s: %s", quotearg_colon (file_name),
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close_error);
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else
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error (0, errno, "%s", close_error);
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}
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close_stdout ();
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if (fail)
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_exit (exit_failure);
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}
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