lib/close-stream.c

   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 }