sh: Rework code to remove '\0' from shell input.

This fixes bugs where '\0' was not removed correctly and speeds up the
parser.

bin/sh/input.c

@@ -195,8 +195,7 @@ preadfd(void)
 int
 preadbuffer(void)
 {
-	char *p, *q;
-	int more;
+	char *p, *q, *r, *end;
 	char savec;
 
 	while (parsefile->strpush) {
@@ -224,34 +223,31 @@ preadbuffer(void)
 		}
 	}
 
-	q = p = parsefile->buf + (parsenextc - parsefile->buf);
-
-	/* delete nul characters */
-	for (more = 1; more;) {
-		switch (*p) {
-		case '\0':
-			p++;	/* Skip nul */
-			goto check;
-
-		case '\n':
-			parsenleft = q - parsenextc;
-			more = 0; /* Stop processing here */
-			break;
-
-		default:
-			break;
-		}
-
-		*q++ = *p++;
-check:
-		if (--parselleft <= 0) {
-			parsenleft = q - parsenextc - 1;
-			if (parsenleft < 0)
-				goto again;
-			*q = '\0';
-			more = 0;
+	p = parsefile->buf + (parsenextc - parsefile->buf);
+	end = p + parselleft;
+	*end = '\0';
+	q = strchrnul(p, '\n');
+	if (q != end && *q == '\0') {
+		/* delete nul characters */
+		for (r = q; q != end; q++) {
+			if (*q != '\0')
+				*r++ = *q;
 		}
+		parselleft -= end - r;
+		if (parselleft == 0)
+			goto again;
+		end = p + parselleft;
+		*end = '\0';
+		q = strchrnul(p, '\n');
 	}
+	if (q == end) {
+		parsenleft = parselleft;
+		parselleft = 0;
+	} else /* *q == '\n' */ {
+		parsenleft = q - parsenextc + 1;
+		parselleft -= parsenleft;
+	}
+	parsenleft--;
 
 	savec = *q;
 	*q = '\0';

bin/sh/tests/parser/Makefile

@@ -73,6 +73,7 @@ FILES+=		line-cont10.0
 FILES+=		line-cont11.0
 FILES+=		no-space1.0
 FILES+=		no-space2.0
+FILES+=		nul1.0
 FILES+=		only-redir1.0
 FILES+=		only-redir2.0
 FILES+=		only-redir3.0

bin/sh/tests/parser/nul1.0

@@ -0,0 +1,12 @@
+# $FreeBSD$
+# Although POSIX does not specify the effect of NUL bytes in scripts,
+# we ignore them.
+
+{
+	printf 'v=%03000d\0%02000d' 7 2
+	dd if=/dev/zero bs=1000 count=1 status=none
+	printf '1 w=%03000d%02000d1\0\n' 7 2
+	printf '\0l\0v\0=\0$\0{\0#\0v\0}\n'
+	printf '\0l\0w\0=\0\0$\0{\0#\0w}\0\0\0\n'
+	printf '[ "$lv.$lw.$v" = "5001.5001.$w" ]\n'
+} | ${SH}