/* Detect write error on a stream.

   Copyright (C) 2003-2006, 2008-2025 Free Software Foundation, Inc.

   Written by Bruno Haible <bruno@clisp.org>, 2003.

   This program is free software: you can redistribute it and/or modify

   it under the terms of the GNU General Public License as published by

   the Free Software Foundation, either version 3 of the License, or

   (at your option) any later version.

   This program is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

#include <config.h>

/* Specification.  */

#include "fwriteerror.h"

#include <errno.h>

static int

do_fwriteerror (FILE *fp, bool ignore_ebadf)

{

  /* State to allow multiple calls to fwriteerror (stdout).  */

  static bool stdout_closed = false;

  if (fp == stdout)

    {

      if (stdout_closed)

        return 0;

      /* If we are closing stdout, don't attempt to do it later again.  */

      stdout_closed = true;

    }

  /* This function returns an error indication if there was a previous failure

     or if fclose failed, with two exceptions:

       - Ignore an fclose failure if there was no previous error, no data

         remains to be flushed, and fclose failed with EBADF.  That can

         happen when a program like cp is invoked like this 'cp a b >&-'

         (i.e., with standard output closed) and doesn't generate any

         output (hence no previous error and nothing to be flushed).

       - Ignore an fclose failure due to EPIPE.  That can happen when a

         program blocks or ignores SIGPIPE, and the output pipe or socket

         has no readers now.  The EPIPE tells us that we should stop writing

         to this output.  That's what we are doing anyway here.

     Need to

     1. test the error indicator of the stream,

     2. flush the buffers both in userland and in the kernel, through fclose,

        testing for error again.  */

  /* Clear errno, so that on non-POSIX systems the caller doesn't see a

     wrong value of errno when we return -1.  */

  errno = 0;

  if (ferror (fp))

    {

      if (fflush (fp))

        goto close_preserving_errno; /* errno is set here */

      /* The stream had an error earlier, but its errno was lost.  If the

         error was not temporary, we can get the same errno by writing and

         flushing one more byte.  We can do so because at this point the

         stream's contents is garbage anyway.  */

      if (fputc ('\0', fp) == EOF)

        goto close_preserving_errno; /* errno is set here */

      if (fflush (fp))

        goto close_preserving_errno; /* errno is set here */

      /* Give up on errno.  */

      errno = 0;

      goto close_preserving_errno;

    }

  if (ignore_ebadf)

    {

      /* We need an explicit fflush to tell whether some output was already

         done on FP.  */

      if (fflush (fp))

        goto close_preserving_errno; /* errno is set here */

      if (fclose (fp) && errno != EBADF)

        goto got_errno; /* errno is set here */

    }

  else

    {

      if (fclose (fp))

        goto got_errno; /* errno is set here */

    }

  return 0;

 close_preserving_errno:

  /* There's an error.  Nevertheless call fclose(fp), for consistency

     with the other cases.  */

  {

    int saved_errno = errno;

    fclose (fp);

    errno = saved_errno;

  }

 got_errno:

  /* There's an error.  Ignore EPIPE.  */

  if (errno == EPIPE)

    return 0;

  else

    return -1;

}

int

fwriteerror (FILE *fp)

{

  return do_fwriteerror (fp, false);

}

int

fwriteerror_no_ebadf (FILE *fp)

{

  return do_fwriteerror (fp, true);

}

#if TEST

/* Name of a file on which writing fails.  On systems without /dev/full,

   you can choose a filename on a full file system.  */

#define UNWRITABLE_FILE "/dev/full"

int

main ()

{

  static int sizes[] =

    {

       511,  512,  513,

      1023, 1024, 1025,

      2047, 2048, 2049,

      4095, 4096, 4097,

      8191, 8192, 8193

    };

  static char dummy[8193];

  unsigned int i, j;

  for (i = 0; i < sizeof (sizes) / sizeof (sizes[0]); i++)

    {

      size_t size = sizes[i];

      for (j = 0; j < 2; j++)

        {

          /* Run a test depending on i and j:

             Write size bytes and then calls fflush if j==1.  */

          FILE *stream = fopen (UNWRITABLE_FILE, "w");

          if (stream == NULL)

            {

              fprintf (stderr, "Test %u:%u: could not open file\n", i, j);

              continue;

            }

          fwrite (dummy, 347, 1, stream);

          fwrite (dummy, size - 347, 1, stream);

          if (j)

            fflush (stream);

          if (fwriteerror (stream) == -1)

            {

              if (errno != ENOSPC)

                fprintf (stderr, "Test %u:%u: fwriteerror ok, errno = %d\n",

                         i, j, errno);

            }

          else

            fprintf (stderr, "Test %u:%u: fwriteerror found no error!\n",

                     i, j);

        }

    }

  return 0;

}

#endif