add strlcpy/strlcat, safe and sensible string copy/append

1 files changed, 140 insertions, 0 deletions

diff --git a/src/lib/libc/string/strlcpy.3 b/src/lib/libc/string/strlcpy.3
new file mode 100644
index 0000000000..e1ff016aaf
--- /dev/null
+++ b/src/lib/libc/string/strlcpy.3
@@ -0,0 +1,140 @@
+.\" $OpenBSD: strlcpy.3,v 1.1 1998/07/01 01:29:45 millert Exp $
+.\"
+.\" Copyright (c) 1998 Todd C. Miller <Todd.Miller@courtesan.com>
+.\" All rights reserved.
+.\"
+.\" 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. The name of the author may not be used to endorse or promote products
+.\"    derived from this software without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED ``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 AUTHOR 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.
+.\"
+.Dd June 22, 1998
+.Dt STRLCPY 3
+.Os
+.Sh NAME
+.Nm strlcpy,
+.Nm strlcat
+.Nd size-bounded string copying and concatenation
+.Sh SYNOPSIS
+.Fd #include <string.h>
+.Ft char *
+.Fn strlcpy "char *dst" "const char *src" "size_t size"
+.Ft char *
+.Fn strlcat "char *dst" "const char *src" "size_t size"
+.Sh DESCRIPTION
+The
+.Fn strlcpy
+and
+.Fn strlcat
+functions copy and concatenate strings respectively.  They are designed
+to be safer, more consistent, and less error prone replacements for
+.Xr strncpy 3
+and
+.Xr strncat 3 .
+Unlike those functions,
+.Fn strlcpy
+and
+.Fn strlcat
+take the full size of the buffer (not just the length) and guarantee to
+NUL-terminate the result (as long as
+.Fa size
+is larger than 0).  Note that you should include a byte for the NUL in
+.Fa size .
+.Pp
+The
+.Fn strlcpy
+function copies up to
+.Fa size
+- 1 characters from the NUL-terminated string
+.Fa src
+to
+.Fa dst ,
+NUL-terminating the result.
+.Pp
+The
+.Fn strlcat
+function appends the NUL-terminated string
+.Fa src
+to the end of
+.Fa dst .
+It will append at most
+.Fa size
+- strlen(dst) - 1 bytes, NUL-terminating the result.
+.Sh RETURN VALUES
+The
+.Fn strlcpy
+and
+.Fn strlcat
+functions return the total length of the string they tried to
+create.  For
+.Fn strlcpy
+that means the length of
+.Fa src .
+For
+.Fn strlcat
+that means the initial length of
+.Fa dst
+plus
+the length of
+.Fa src .
+While this may seem somewhat confusing it was done to make
+truncation detection simple.
+.Sh EXAMPLES
+The following code fragment illustrates the simple case:
+.Bd -literal -offset indent
+char *s, *p, buf[BUFSIZ];
+
+.Li ...
+
+(void)strlcpy(buf, s, sizeof(buf));
+(void)strlcat(buf, p, sizeof(buf));
+.Ed
+.Pp
+To detect truncation, perhaps while building a pathname, something
+like the following might be used:
+.Bd -literal -offset indent
+char *dir, *file, pname[MAXPATHNAMELEN];
+
+.Li ...
+
+if (strlcpy(pname, dir, sizeof(pname)) >= sizeof(pname))
+        goto toolong;
+if (strlcat(pname, file, sizeof(pname)) >= sizeof(pname))
+        goto toolong;
+.Ed
+.Pp
+Since we know how many characters we copied the first time, we can
+speed things up a bit by using a copy instead on an append:
+.Bd -literal -offset indent
+char *dir, *file, pname[MAXPATHNAMELEN];
+size_t n;
+
+.Li ...
+
+n = strlcpy(pname, dir, sizeof(pname));
+if (n >= sizeof(pname))
+        goto toolong;
+if (strlcpy(pname + n, file, sizeof(pname)) >= sizeof(pname) - n)
+        goto toolong;
+.Ed
+.Sh SEE ALSO
+.Xr snprintf 3 ,
+.Xr strncpy 3 ,
+.Xr strncat 3