New module 'fwriteerror'.

1 files changed, 122 insertions, 0 deletions

diff --git a/lib/fwriteerror.c b/lib/fwriteerror.c
new file mode 100644
index 0000000000..364db86093
--- /dev/null
+++ b/lib/fwriteerror.c
@@ -0,0 +1,122 @@
+/* Detect write error on a stream.
+   Copyright (C) 2003 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 2, 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, write to the Free Software Foundation,
+   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
+
+#if HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+/* Specification.  */
+#include "fwriteerror.h"
+
+#include <errno.h>
+
+int
+fwriteerror (FILE *fp)
+{
+  /* Need to
+     1. test the error indicator of the stream,
+     2. flush the buffers (what fclose() would do), testing for error again.
+     We can equally well swap these steps; this leads to smaller code.  */
+
+  /* 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 (fflush (fp))
+    return -1; /* errno is set here */
+
+  if (ferror (fp))
+    {
+      /* 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)
+	return -1; /* errno is set here */
+      if (fflush (fp))
+	return -1; /* errno is set here */
+      /* Give up on errno.  */
+      errno = 0;
+      return -1;
+    }
+
+  return 0;
+}
+
+
+#if TEST
+
+/* Name of a file on which writing fails.  On systems without /dev/full,
+   you can choose a filename on a full filesystem.  */
+#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);
+
+	  if (fclose (stream))
+	    fprintf (stderr, "Test %u:%u: fclose failed, errno = %d\n",
+		     i, j, errno);
+	}
+    }
+
+  return 0;
+}
+
+#endif