Orthogonal approach to read()/write() that handles EINTR and counts > 2^31

[gnulib.git] / lib / safe-write.c

diff --git a/lib/safe-write.c b/lib/safe-write.c
new file mode 100644 (file)
index 0000000..5596203
--- /dev/null
+++ b/lib/safe-write.c
@@ -0,0 +1,83 @@
+/* An interface to write() that retries after interrupts.
+   Copyright (C) 1993, 1994, 1998, 2002 Free Software Foundation, Inc.
+
+   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 "safe-write.h"
+
+/* Get ssize_t.  */
+#include <sys/types.h>
+#if HAVE_UNISTD_H
+# include <unistd.h>
+#endif
+
+#include <errno.h>
+#ifndef errno
+extern int errno;
+#endif
+
+#include <limits.h>
+
+/* We don't pass an nbytes count > SSIZE_MAX to write() - POSIX says the
+   effect would be implementation-defined.  Also we don't pass an nbytes
+   count > INT_MAX but <= SSIZE_MAX to write() - this triggers a bug in
+   Tru64 5.1.  */
+#define MAX_BYTES_TO_READ INT_MAX
+
+/* Write up to COUNT bytes at BUF to descriptor FD, retrying if interrupted.
+   Return the actual number of bytes written, zero for EOF, or (size_t) -1
+   for an error.  */
+size_t
+safe_write (int fd, const void *buf, size_t count)
+{
+  size_t total_written = 0;
+
+  if (count > 0)
+    {
+      const char *ptr = (const char *) buf;
+      do
+       {
+         size_t nbytes_to_write = count;
+         ssize_t result;
+
+         /* Limit the number of bytes to write in one round, to avoid running
+            into unspecified behaviour.  But keep the file pointer block
+            aligned when doing so.  */
+         if (nbytes_to_write > MAX_BYTES_TO_READ)
+           nbytes_to_write = MAX_BYTES_TO_READ & ~8191;
+
+         result = write (fd, ptr, nbytes_to_write);
+         if (result < 0)
+           {
+#ifdef EINTR
+             if (errno == EINTR)
+               continue;
+#endif
+             return result;
+           }
+         total_written += result;
+         ptr += result;
+         count -= result;
+       }
+      while (count > 0);
+    }
+
+  return total_written;
+}