MFC discussed with: jilles, -developers

MFC r266971:

  - Return NULL and set errno to EINVAL if size is 0 (as required by POSIX).
  Update the manpage to reflect this change.
  - Always set the current position to the first null-byte when opening in append
  mode. This makes the implementation compatible with glibc's. Update the test
  suite.

  Reported by:	pho
  Approved by:	cognet

2 files changed, 18 insertions, 8 deletions

diff --git a/lib/libc/stdio/fmemopen.c b/lib/libc/stdio/fmemopen.c
index 581a91e..ebd3596 100644
--- a/lib/libc/stdio/fmemopen.c
+++ b/lib/libc/stdio/fmemopen.c
@@ -57,6 +57,14 @@ fmemopen(void * __restrict buf, size_t size, const char * __restrict mode)
 	int flags, rc;
 
 	/*
+	 * POSIX says we shall return EINVAL if size is 0.
+	 */
+	if (size == 0) {
+		errno = EINVAL;
+		return (NULL);
+	}
+
+	/*
 	 * Retrieve the flags as used by open(2) from the mode argument, and
 	 * validate them.
 	 */
@@ -119,14 +127,7 @@ fmemopen(void * __restrict buf, size_t size, const char * __restrict mode)
 	 */
 	switch (mode[0]) {
 	case 'a':
-		if (ck->bin) {
-			/*
-			 * This isn't useful, since the buffer isn't allowed
-			 * to grow.
-			 */
-			ck->off = ck->len = size;
-		} else
-			ck->off = ck->len = strnlen(ck->buf, ck->size);
+		ck->off = ck->len = strnlen(ck->buf, ck->size);
 		break;
 	case 'r':
 		ck->len = size;
diff --git a/lib/libc/stdio/fopen.3 b/lib/libc/stdio/fopen.3
index f11f4e0..b39cb5a 100644
--- a/lib/libc/stdio/fopen.3
+++ b/lib/libc/stdio/fopen.3
@@ -302,6 +302,15 @@ for any of the errors specified for the routines
 .Xr fclose 3
 and
 .Xr fflush 3 .
+.Pp
+The
+.Fn fmemopen
+function
+may also fail and set
+.Va errno
+if the
+.Fa size
+argument is 0.
 .Sh SEE ALSO
 .Xr open 2 ,
 .Xr fclose 3 ,