Add a new libc function, strnstr(3), which allows one to limit the

number of characters that are searched.  This is especially useful
with file operations and non-NUL terminated strings.

Silence from:	-audit, -hackers
MFC after:	5 days

3 files changed, 122 insertions, 11 deletions

diff --git a/lib/libc/string/Makefile.inc b/lib/libc/string/Makefile.inc
index 9c9f369..dcd2dfd 100644
--- a/lib/libc/string/Makefile.inc
+++ b/lib/libc/string/Makefile.inc
@@ -10,6 +10,7 @@ MISRCS+=bcmp.c bcopy.c bzero.c ffs.c index.c memccpy.c memchr.c memcmp.c \
 	memcpy.c memmove.c memset.c rindex.c strcasecmp.c strcat.c strchr.c \
 	strcmp.c strcoll.c strcpy.c strcspn.c strdup.c strerror.c \
 	strlcat.c strlcpy.c strlen.c strmode.c strncat.c strncmp.c strncpy.c \
+	strnstr.c \
 	strpbrk.c strrchr.c strsep.c strsignal.c strspn.c strstr.c strtok.c \
 	strxfrm.c swab.c wcscat.c wcschr.c wcscmp.c wcscpy.c wcscspn.c \
 	wcslcat.c wcslcpy.c wcslen.c wcsncat.c wcsncmp.c wcsncpy.c wcspbrk.c \
@@ -36,6 +37,7 @@ MLINKS+=strcpy.3 strncpy.3
 MLINKS+=strerror.3 perror.3 strerror.3 sys_errlist.3 strerror.3 sys_nerr.3
 MLINKS+=strlcpy.3 strlcat.3
 MLINKS+=strtok.3 strtok_r.3
+MLINKS+=strstr.3 strnstr.3
 MLINKS+=wmemchr.3 wmemcmp.3 wmemchr.3 wmemcpy.3 \
 	wmemchr.3 wmemmove.3 wmemchr.3 wmemset.3 \
 	wmemchr.3 wcscat.3 wmemchr.3 wcschr.3 \
diff --git a/lib/libc/string/strnstr.c b/lib/libc/string/strnstr.c
new file mode 100644
index 0000000..98c0103
--- /dev/null
+++ b/lib/libc/string/strnstr.c
@@ -0,0 +1,70 @@
+/*-
+ * Copyright (c) 2001 Mike Barcroft <mike@FreeBSD.org>
+ * Copyright (c) 1990, 1993
+ *	The Regents of the University of California.  All rights reserved.
+ *
+ * This code is derived from software contributed to Berkeley by
+ * Chris Torek.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ *    must display the following acknowledgement:
+ *	This product includes software developed by the University of
+ *	California, Berkeley and its contributors.
+ * 4. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__RCSID("@(#)strstr.c	8.1 (Berkeley) 6/4/93");
+__FBSDID("$FreeBSD$");
+
+#include <string.h>
+
+/*
+ * Find the first occurrence of find in s, where the search is limited to the
+ * first slen characters of s.
+ */
+char *
+strnstr(s, find, slen)
+	const char *s;
+	const char *find;
+	size_t slen;
+{
+	char c, sc;
+	size_t len;
+
+	if ((c = *find++) != '\0') {
+		len = strlen(find);
+		do {
+			do {
+				if ((sc = *s++) == '\0' || slen-- < 1)
+					return (NULL);
+			} while (sc != c);
+			if (len > slen)
+				return (NULL);
+		} while (strncmp(s, find, len) != 0);
+		s--;
+	}
+	return ((char *)s);
+}
diff --git a/lib/libc/string/strstr.3 b/lib/libc/string/strstr.3
index 0cea427..b4af3de 100644
--- a/lib/libc/string/strstr.3
+++ b/lib/libc/string/strstr.3
@@ -1,3 +1,4 @@
+.\" Copyright (c) 2001 Mike Barcroft <mike@FreeBSD.org>
 .\" Copyright (c) 1990, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
 .\"
@@ -40,7 +41,7 @@
 .Dt STRSTR 3
 .Os
 .Sh NAME
-.Nm strstr
+.Nm strstr , strnstr
 .Nd locate a substring in a string
 .Sh LIBRARY
 .Lb libc
@@ -48,6 +49,8 @@
 .In string.h
 .Ft char *
 .Fn strstr "const char *big" "const char *little"
+.Ft char *
+.Fn strnstr "const char *big" "const char *little" "size_t len"
 .Sh DESCRIPTION
 The
 .Fn strstr
@@ -56,22 +59,58 @@ locates the first occurrence of the null-terminated string
 .Fa little
 in the null-terminated string
 .Fa big .
+.Pp
+The
+.Fn strnstr
+function
+locates the first occurrence of the null-terminated string
+.Fa little
+in the string
+.Fa big ,
+where only the first number of characters, identified by
+.Fa len ,
+are searched.
+.Sh RETURN VALUES
 If
 .Fa little
-is the empty string,
-.Fn strstr
-returns
-.Fa big ;
+is an empty string,
+.Fa big
+is returned;
 if
 .Fa little
 occurs nowhere in
 .Fa big ,
-.Fn strstr
-returns NULL;
-otherwise
-.Fn strstr
-returns a pointer to the first character of the first occurrence of
-.Fa little .
+NULL is returned;
+otherwise a pointer to the first character of the first occurrence of
+.Fa little
+is returned.
+.Sh EXAMPLES
+The following sets the pointer
+.Va ptr
+to the
+.Dq Li Bar Baz
+portion of
+.Va largestring :
+.Bd -literal -offset indent
+const char *largestring = "Foo Bar Baz";
+const char *smallstring = "Bar";
+char *ptr;
+
+ptr = strstr(largestring, smallstring);
+.Ed
+.Pp
+The following sets the pointer
+.Va ptr
+to NULL, because only the first 4 characters of 
+.Va largestring
+are searched:
+.Bd -literal -offset indent
+const char *largestring = "Foo Bar Baz";
+const char *smallstring = "Bar";
+char *ptr;
+
+ptr = strnstr(largestring, smallstring, 4);
+.Ed
 .Sh SEE ALSO
 .Xr memchr 3 ,
 .Xr strchr 3 ,