fwrite() should also return 0 if either size or nmemb are 0.

Adapted from FreeBSD.  OK deraadt@

3 files changed, 22 insertions, 8 deletions

diff --git a/lib/libc/stdio/fread.3 b/lib/libc/stdio/fread.3
index 972d7b2e996..754636f8d01 100644
--- a/lib/libc/stdio/fread.3
+++ b/lib/libc/stdio/fread.3
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: fread.3,v 1.4 2007/05/31 19:19:31 jmc Exp $
+.\"	$OpenBSD: fread.3,v 1.5 2009/07/12 18:45:21 millert Exp $
 .\"
 .\" Copyright (c) 1990, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -31,7 +31,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: May 31 2007 $
+.Dd $Mdocdate: July 12 2009 $
 .Dt FREAD 3
 .Os
 .Sh NAME
@@ -74,6 +74,16 @@ and
 advance the file position indicator for the stream
 by the number of bytes read or written.
 They return the number of objects read or written.
+If
+.Fa size
+or
+.Fa nmemb
+is 0,
+.Fn fread
+and
+.Fn fwrite
+return 0 with no change made to the
+.Fa stream .
 If an error occurs, or the end-of-file is reached,
 the return value is a short object count (or zero).
 .Pp
diff --git a/lib/libc/stdio/fread.c b/lib/libc/stdio/fread.c
index 62906216d8b..c7389e76ed6 100644
--- a/lib/libc/stdio/fread.c
+++ b/lib/libc/stdio/fread.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: fread.c,v 1.6 2005/08/08 08:05:36 espie Exp $ */
+/*	$OpenBSD: fread.c,v 1.7 2009/07/12 18:45:21 millert Exp $ */
 /*-
  * Copyright (c) 1990, 1993
  *	The Regents of the University of California.  All rights reserved.
@@ -44,9 +44,7 @@ fread(void *buf, size_t size, size_t count, FILE *fp)
 	size_t total;
 
 	/*
-	 * The ANSI standard requires a return value of 0 for a count
-	 * or a size of 0.  Peculiarily, it imposes no such requirements
-	 * on fwrite; it only requires fread to be broken.
+	 * ANSI and SUSv2 require a return value of 0 if size or count are 0.
 	 */
 	if ((resid = count * size) == 0)
 		return (0);
diff --git a/lib/libc/stdio/fwrite.c b/lib/libc/stdio/fwrite.c
index 8a508dcdba7..a60f9e0807a 100644
--- a/lib/libc/stdio/fwrite.c
+++ b/lib/libc/stdio/fwrite.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: fwrite.c,v 1.5 2005/08/08 08:05:36 espie Exp $ */
+/*	$OpenBSD: fwrite.c,v 1.6 2009/07/12 18:45:21 millert Exp $ */
 /*-
  * Copyright (c) 1990, 1993
  *	The Regents of the University of California.  All rights reserved.
@@ -46,8 +46,14 @@ fwrite(const void *buf, size_t size, size_t count, FILE *fp)
 	struct __suio uio;
 	struct __siov iov;
 
+	/*
+	 * ANSI and SUSv2 require a return value of 0 if size or count are 0.
+	 */
+	if ((n = count * size) == 0)
+		return (0);
+
 	iov.iov_base = (void *)buf;
-	uio.uio_resid = iov.iov_len = n = count * size;
+	uio.uio_resid = iov.iov_len = n;
 	uio.uio_iov = &iov;
 	uio.uio_iovcnt = 1;