libc/stdio: Allow fopen/freopen modes in any order (except initial r/w/a).

Austin Group issue #411 requires 'e' to be accepted before and after 'x',
and encourages accepting the characters in any order, except the initial
'r', 'w' or 'a'.

Given that glibc accepts the characters after r/w/a in any order and that
diagnosing this problem may be hard, change our libc to behave that way as
well.

1 files changed, 28 insertions, 27 deletions

diff --git a/lib/libc/stdio/flags.c b/lib/libc/stdio/flags.c
index 1878c2f..b7552a4 100644
--- a/lib/libc/stdio/flags.c
+++ b/lib/libc/stdio/flags.c
@@ -51,7 +51,7 @@ __FBSDID("$FreeBSD$");
 int
 __sflags(const char *mode, int *optr)
 {
-	int ret, m, o;
+	int ret, m, o, known;
 
 	switch (*mode++) {
 
@@ -78,34 +78,35 @@ __sflags(const char *mode, int *optr)
 		return (0);
 	}
 
-	/* 'b' (binary) is ignored */
-	if (*mode == 'b')
-		mode++;
-
-	/* [rwa][b]\+ means read and write */
-	if (*mode == '+') {
-		mode++;
-		ret = __SRW;
-		m = O_RDWR;
-	}
-
-	/* 'b' (binary) can appear here, too -- and is ignored again */
-	if (*mode == 'b')
-		mode++;
-
-	/* 'x' means exclusive (fail if the file exists) */
-	if (*mode == 'x') {
-		mode++;
-		if (m == O_RDONLY) {
-			errno = EINVAL;
-			return (0);
+	do {
+		known = 1;
+		switch (*mode++) {
+		case 'b':
+			/* 'b' (binary) is ignored */
+			break;
+		case '+':
+			/* [rwa][b]\+ means read and write */
+			ret = __SRW;
+			m = O_RDWR;
+			break;
+		case 'x':
+			/* 'x' means exclusive (fail if the file exists) */
+			o |= O_EXCL;
+			break;
+		case 'e':
+			/* set close-on-exec */
+			o |= O_CLOEXEC;
+			break;
+		default:
+			known = 0;
+			break;
 		}
-		o |= O_EXCL;
-	}
+	} while (known);
 
-	/* set close-on-exec */
-	if (*mode == 'e')
-		o |= O_CLOEXEC;
+	if ((o & O_EXCL) != 0 && m == O_RDONLY) {
+		errno = EINVAL;
+		return (0);
+	}
 
 	*optr = m | o;
 	return (ret);