lib/closein.c

   1 /* Close standard input, rewinding seekable stdin if necessary.
   2
   3    Copyright (C) 2007, 2009-2024 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 "closein.h"
  21
  22 #include <errno.h>
  23 #include <stdio.h>
  24 #include <unistd.h>
  25
  26 #include "gettext.h"
  27 #define _(msgid) gettext (msgid)
  28
  29 #include "close-stream.h"
  30 #include "closeout.h"
  31 #include <error.h>
  32 #include "exitfail.h"
  33 #include "freadahead.h"
  34 #include "quotearg.h"
  35
  36 static const char *file_name;
  37
  38 /* Set the file name to be reported in the event an error is detected
  39    on stdin by close_stdin.  See also close_stdout_set_file_name, if
  40    an error is detected when closing stdout.  */
  41 void
  42 close_stdin_set_file_name (const char *file)
  43 {
  44   file_name = file;
  45 }
  46
  47 /* Close standard input, rewinding any unused input if stdin is
  48    seekable.  On error, issue a diagnostic and _exit with status
  49    'exit_failure'.  Then call close_stdout.
  50
  51    Most programs can get by with close_stdout.  close_stdin is only
  52    needed when a program wants to guarantee that partially read input
  53    from seekable stdin is not consumed, for any subsequent clients.
  54    For example, POSIX requires that these two commands behave alike:
  55
  56      (sed -ne 1q; cat) < file
  57      tail -n +2 file
  58
  59    Since close_stdin is commonly registered via 'atexit', POSIX
  60    and the C standard both say that it should not call 'exit',
  61    because the behavior is undefined if 'exit' is called more than
  62    once.  So it calls '_exit' instead of 'exit'.  If close_stdin
  63    is registered via atexit before other functions are registered,
  64    the other functions can act before this _exit is invoked.
  65
  66    Applications that use close_stdout should flush any streams other
  67    than stdin, stdout, and stderr before exiting, since the call to
  68    _exit will bypass other buffer flushing.  Applications should be
  69    flushing and closing other streams anyway, to check for I/O errors.
  70    Also, applications should not use tmpfile, since _exit can bypass
  71    the removal of these files.
  72
  73    It's important to detect such failures and exit nonzero because many
  74    tools (most notably 'make' and other build-management systems) depend
  75    on being able to detect failure in other tools via their exit status.  */
  76
  77 void
  78 close_stdin (void)
  79 {
  80   bool fail = false;
  81
  82   /* There is no need to flush stdin if we can determine quickly that stdin's
  83      input buffer is empty; in this case we know that if stdin is seekable,
  84      (fseeko (stdin, 0, SEEK_CUR), ftello (stdin))
  85      == lseek (0, 0, SEEK_CUR).  */
  86   if (freadahead (stdin) > 0)
  87     {
  88       /* Only attempt flush if stdin is seekable, as fflush is entitled to
  89          fail on non-seekable streams.  */
  90       if (fseeko (stdin, 0, SEEK_CUR) == 0 && fflush (stdin) != 0)
  91         fail = true;
  92     }
  93   if (close_stream (stdin) != 0)
  94     fail = true;
  95   if (fail)
  96     {
  97       /* Report failure, but defer exit until after closing stdout,
  98          since the failure report should still be flushed.  */
  99       char const *close_error = _("error closing file");
 100       if (file_name)
 101         error (0, errno, "%s: %s", quotearg_colon (file_name),
 102                close_error);
 103       else
 104         error (0, errno, "%s", close_error);
 105     }
 106
 107   close_stdout ();
 108
 109   if (fail)
 110     _exit (exit_failure);
 111 }