lib/closein.c

   1 /* Close standard input, rewinding seekable stdin if necessary.
   2
   3    Copyright (C) 2007, 2009-2019 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 "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 }