1  /* Close standard input, rewinding seekable stdin if necessary.
       2  
       3     Copyright (C) 2007, 2009-2022 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 <stdbool.h>
      24  #include <stdio.h>
      25  #include <unistd.h>
      26  
      27  #include "gettext.h"
      28  #define _(msgid) gettext (msgid)
      29  
      30  #include "close-stream.h"
      31  #include "closeout.h"
      32  #include "error.h"
      33  #include "exitfail.h"
      34  #include "freadahead.h"
      35  #include "quotearg.h"
      36  
      37  static const char *file_name;
      38  
      39  /* Set the file name to be reported in the event an error is detected
      40     on stdin by close_stdin.  See also close_stdout_set_file_name, if
      41     an error is detected when closing stdout.  */
      42  void
      43  close_stdin_set_file_name (const char *file)
      44  {
      45    file_name = file;
      46  }
      47  
      48  /* Close standard input, rewinding any unused input if stdin is
      49     seekable.  On error, issue a diagnostic and _exit with status
      50     'exit_failure'.  Then call close_stdout.
      51  
      52     Most programs can get by with close_stdout.  close_stdin is only
      53     needed when a program wants to guarantee that partially read input
      54     from seekable stdin is not consumed, for any subsequent clients.
      55     For example, POSIX requires that these two commands behave alike:
      56  
      57       (sed -ne 1q; cat) < file
      58       tail -n +2 file
      59  
      60     Since close_stdin is commonly registered via 'atexit', POSIX
      61     and the C standard both say that it should not call 'exit',
      62     because the behavior is undefined if 'exit' is called more than
      63     once.  So it calls '_exit' instead of 'exit'.  If close_stdin
      64     is registered via atexit before other functions are registered,
      65     the other functions can act before this _exit is invoked.
      66  
      67     Applications that use close_stdout should flush any streams other
      68     than stdin, stdout, and stderr before exiting, since the call to
      69     _exit will bypass other buffer flushing.  Applications should be
      70     flushing and closing other streams anyway, to check for I/O errors.
      71     Also, applications should not use tmpfile, since _exit can bypass
      72     the removal of these files.
      73  
      74     It's important to detect such failures and exit nonzero because many
      75     tools (most notably 'make' and other build-management systems) depend
      76     on being able to detect failure in other tools via their exit status.  */
      77  
      78  void
      79  close_stdin (void)
      80  {
      81    bool fail = false;
      82  
      83    /* There is no need to flush stdin if we can determine quickly that stdin's
      84       input buffer is empty; in this case we know that if stdin is seekable,
      85       (fseeko (stdin, 0, SEEK_CUR), ftello (stdin))
      86       == lseek (0, 0, SEEK_CUR).  */
      87    if (freadahead (stdin) > 0)
      88      {
      89        /* Only attempt flush if stdin is seekable, as fflush is entitled to
      90           fail on non-seekable streams.  */
      91        if (fseeko (stdin, 0, SEEK_CUR) == 0 && fflush (stdin) != 0)
      92          fail = true;
      93      }
      94    if (close_stream (stdin) != 0)
      95      fail = true;
      96    if (fail)
      97      {
      98        /* Report failure, but defer exit until after closing stdout,
      99           since the failure report should still be flushed.  */
     100        char const *close_error = _("error closing file");
     101        if (file_name)
     102          error (0, errno, "%s: %s", quotearg_colon (file_name),
     103                 close_error);
     104        else
     105          error (0, errno, "%s", close_error);
     106      }
     107  
     108    close_stdout ();
     109  
     110    if (fail)
     111      _exit (exit_failure);
     112  }