1  /* Close a stream, with nicer error checking than fclose's.
       2  
       3     Copyright (C) 1998-2002, 2004, 2006-2022 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 "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  }